ACQUIRED COLOUR VISION DEFECTS IN OPTIC NERVE DISORDERS- A COMPARISON BETWEEN ISHIHARA S TEST AND ROTH 28-HUE TEST DR. TEENA MARIET MENDONCA

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1 ACQUIRED COLOUR VISION DEFECTS IN OPTIC NERVE DISORDERS- A COMPARISON BETWEEN ISHIHARA S TEST AND ROTH 28-HUE TEST By DR. TEENA MARIET MENDONCA Dissertation Submitted to the Rajiv Gandhi University of Health Sciences, Karnataka, Bangalore In partial fulfillment Of the requirements for the degree of Master of Surgery In OPHTHALMOLOGY Under the guidance of DR. ANDREW KENNETH VASNAIK M.S. PROFESSOR, DEPARTMENT OF OPHTHALMOLOGY ST. JOHN S MEDICAL COLLEGE BANGALORE i

2 DECLARATION BY THE CANDIDATE I hereby declare that this dissertation/thesis entitled ACQUIRED COLOUR VISION DEFECTS IN OPTIC NERVE DISORDERS- A COMPARISON BETWEEN ISHIHARA S TEST AND ROTH 28-HUE TEST is a bonafide and genuine research work carried out by me under the guidance of Dr. ANDREW KENNETH VASNAIK, Professor, Department of Ophthalmology, St. John s Medical College, Bangalore. Date Bangalore Dr.Teena Mariet Mendonca Department of Ophthalmology St. Johns Medical College Hospital, Bangalore ii

3 CERTIFICATE BY THE GUIDE This is to certify that the dissertation entitled ACQUIRED COLOUR VISION DEFECTS IN OPTIC NERVE DISORDERS- A COMPARISON BETWEEN ISHIHARA S TEST AND ROTH 28-HUE TEST is a bonafide research work done by Dr. Teena Mariet Mendonca in partial fulfillment of the requirement for the degree of M.S. Ophthalmology. Date: Place: Bangalore Dr. Andrew Kenneth Vasnaik M.S. Professor, Department of Ophthalmology, St. John s Medical College Bangalore iii

4 ENDORSEMENT BY THE HOD, HEAD OF THE INSTITUTION This is to certify that the dissertation entitled ACQUIRED COLOUR VISION DEFECTS IN OPTIC NERVE DISORDERS- A COMPARISON BETWEEN ISHIHARA S TEST AND ROTH 28-HUE TEST is a bonafide research work done by Dr. Teena Mariet Mendonca under the guidance of Dr. Andrew Kenneth Vasnaik, Professor, Department of Ophthalmology, St. John s Medical College, Bangalore. Seal & Signature of the HOD Seal & Signature of the Principal Dr. Reji Koshy Thomas M.S. Professor and Head, Department of Ophthalmology, St. John s Medical College Dr. Prem Pais M.D. DEAN, St. John s Medical College Date: Place: Bangalore Date: Place: Bangalore iv

5 COPYRIGHT Declaration by the Candidate I hereby declare that the Rajiv Gandhi University of Health Sciences, Karnataka shall have the rights to preserve, use and disseminate this dissertation / thesis in print or electronic format for academic / research purpose. Date: Dr. Teena Mariet Mendonca Place: Bangalore Rajiv Gandhi University of Health Sciences, Karnataka v

6 ACKNOWLEDGEMENT I thank God Almighty for his grace and blessings in all my academic pursuits. I am deeply indebted to many people for guiding and helping me in my endeavor to make this dissertation a reality. I sincerely thank my guide, Dr. Andrew Kenneth Vasnaik, Professor, Department of Ophthalmology, St. John s Medical College Hospital, who outlined the study and under whose overall supervision this study was carried out. I take this opportunity to express my gratitude and respect to my teacher Dr. Suneetha N, Professor, Department of Ophthalmology, for her untiring guidance at every stage of this work. I thank her whole heartedly for all the support and inspiration she has given me. I am grateful to her for her expert opinion, advice in statistical analysis and guidance at every point of the study. I thank Dr. Mary Joseph, Dr. Usha Vasu, Dr. Nibedita Acharya and Dr. Bhargavi Pawar for helping in various aspects of the study, for all the valuable suggestions and support. My sincere gratitude to the faculty of Ophthalmology Department, Dr. Reji Koshy Thomas, Dr. Manjoo C.S, Dr. Colin Nazareth, Dr. Mary Varghese, Dr. Sunu Mathew, Dr. Yamini Priya, Dr. Kiran Kumar, Dr Soumya, Dr Sadiq, and Dr. Sangeetha who have encouraged me at every stage in the conduct of this study. Sincere thanks are also due to my seniors, Dr. Sripathi Kamath, Dr. Sharon D Souza, Dr. Mohsina, Dr. Anitha, Dr. Raghavendra and to my colleagues Dr. Deepti S. Joshi, Dr. Ranjani, Dr. Caroline, Dr. Jerry, Dr. Shweta and Dr. Joel whose valuable help, cooperation and support made this study possible. The help extended to me by the staff of the Department of Ophthalmology has been remarkable. I would sincerely like to thank all the patients who took part in the study. I am very thankful to my parents and sister who have encouraged me at every stage of my dissertation work. Date: Dr. Teena Mariet Mendonca Place: Bangalore vi

7 LIST OF ABBREVIATIONS USED BCVA Best corrected visual acuity B-Y Blue yellow C V Colour vision D- 15 Farnsworth D- 15 test FM 100 Hue test Farnsworth Munsell 100 Hue test GES Global error score HRR plates Hardy,Rand, Rittler Plates IIH Idiopathic Intracranial hypertension IOP Intra ocular pressure OPD Out Patient Department RAPD Relative Afferent Pupillary Defect R-G Red-Green vii

8 ABSTRACT Background and objectives: Colour vision defects associated with ocular diseases have been reported since 17 th century. Acquired colour vision defects are due to varied etio pathogenesis including toxic, vascular, inflammatory, neoplastic, demyelinating and degenerative disorders of the optic nerve, retinal disorders and diseases of the visual cortex. Colour vision tests that were originally intended for the study of congenital dyschromatopsias produce confusing results when applied to patients with acquired diseases. Ishihara test plates primarily designed for detecting congenital dyschromatopsias, are widely used to detect acquired colour vision defects because of their convenience, apparent simplicity of administration and availability. This study was done to compare the results of Ishihara s test and Roth 28 hue test in identifying and quantification of colour vision abnormalities in Optic Nerve disorders and to establish patterns of colour vision defects in acquired optic Nerve disorders. Materials and methods: Inclusion criteria: Patients with various optic nerve disorders attending the OPD of St. Johns Medical College Hospital, Bangalore from September 2010 to August 2012 Exclusion criteria: Children < 10 years, Elderly patients >65 years, Visual Acuity <6/18, Macular disorders, Pseudophakia, Congenital colour blindness, Media opacities like >grade 2 Nuclear Sclerosis Study design- Prospective, cross sectional, comparative study viii

9 71 patients of various optic neuropathies were included in the study. Comprehensive ophthalmic examination including Visual acuity assessment using standard ETDRS chart, slit lamp examination, Fundus examination, and IOP measurement were done. Colour vision was tested mono-ocularly with Ishihara s test (38 plates) and Roth 28 Hue test. Statistical analysis: Descriptive statistics, Pearson s correlation test and Kruskal- Wallis test were done using SPSS version 16.0 Results: The study included 139 eyes of 71 patients with various Optic Neuropathies. The mean age was 36 years with age range being 11 to 64 years. The causes of optic neuropathies included, Papilledema (34%), optic neuritis (15%), optic atrophy (14.3 %) Glaucomatous optic neuropathy (13%), and Tobacco-Alcohol amblyopia (7%). Two patients had Traumatic optic neuropathy and one patient had non-arteritic ischaemic optic neuropathy. On comparing Ishihara and Roth test, there was statistically significant correlation between two tests (P<0.001). On comparing BCVA with both the test results, statistically significant correlation was found. (Ishihara: p=0.001, Roth: p<0.001). Blue yellow defects were found in 34% of optic neuritis patients and 80% of papilledema patients had normal colour vision. Conclusion: Even though Ishihara s test was designed to screen congenital colour vision defects, our study shows that it can be still used to detect colour vision abnormalities in acquired colour vision defects such as optic neuropathies because the results are comparable to arrangement test such as Roth test. Visual acuity plays a key role while evaluating colour vision abnormalities. Our study shows that visual acuity correlates well with results of both the tests. Ishihara test showed a tendency to pick up severe colour vision loss while Roth test showed different pattern abnormalities. ix

10 We also found that, in contrary to common clinical knowledge, optic neuropathies do not always result in red-green colour vision loss. Majority of the patients with optic neuritis showed blue yellow defect in our study, and resolved cases of optic neuritis showed normal colour vision. Thus, in conclusion we believe that Ishihara s test can still be used as an important clinical tool for evaluation of colour vision. Key words: Acquired colour vision defects, Ishihara s test, Roth 28 hue test x

11 TABLE OF CONTENTS Page No. 1. Introduction 1 2. Aims and Objectives 4 3. Review of Literature 5 4. Materials and Methods Results Discussion Conclusion Summary Bibliography Annexure 73 xi

12 LIST OF TABLES Table Title no 1 Differences between congenital and acquired colour vision defects Page no 14 2 Verriest s classification of acquired colour vision anomalies 3 Roth 28 Hue Test (Qualitative) Vs Ishihara test-cross tabulation Correlation of Ishihara s test results and Global error score on Roth 28-hue test Comparison of BCVA with Ishihara test 50 6 Comparison of BCVA with Roth 28 hue test 51 7 Comparison of Presence of RAPD with Roth test results 53 8 Comparison of Presence of RAPD with Ishihara test results 53 xii

13 LIST OF FIGURES Figure Title Page no no 1 Spectral sensitivity curves for three classes of cones 11 2 Results of Farnsworth- Munsell colour vision testing 27 3 Ishihara s test plates 34 4 Roth 28 Hue test 34 5 Age distribution of cases 39 6 Gender distribution 40 7 Incidence of comorbidities 41 8 Causes of optic nerve dysfunction 42 9 Systemic diagnosis Roth 28 Hue test results Ishihara test results Correlation between GES and Ishihara test Visual acuity Comparison of BCVA with Ishihara test 50 xiii

14 15 Comparison of BCVA with Roth 28 hue test Patterns of colour vision defects in Optic neuritis Patterns of colour vision defects in Papilledema Patterns of colour vision defects in Optic Atrophy 56 xiv

15 1. INTRODUCTION Colour vision is the ability to discriminate a light stimulus as a function of its wavelength. Various sensory and cognitive processes combine to result in the sense of colour. The co-operative physical effects of light and objects and physiological reaction of the eye to light and psychological context of colour perception together produce picture perceptions of our surrounding. 1 Information about colour is transformed from the stimulus through the initial stages of the human visual system. The biological basis of colour vision can be divided into two stages: the first is the light-sensitive cone photoreceptor cells in the retina and the second is the neural components that process information about wavelength gathered by the photoreceptors. The classic colour matching experiment shows that the normal human visual system is trichromatic: only three dimensions of spectral variation are coded by the visual system. After the initial encoding of light by the cones, further processing occurs. Colour vision defects associated with ocular disease have been reported since 17 th century. Kollner in 1912 wrote that, Patients with retinal diseases develop blue - yellow discrimination loss, where as optic nerve disorders cause red-green discrimination loss. Exceptions to Kollner s Rule include glaucoma and some retinal diseases such as central cone degeneration which may result in red-green defects. In some cases, there might be nonspecific chromatic loss. 2 Acquired colour vision defects are due to varied etiopathogenesis including toxic, vascular, inflammatory, neoplastic, demyelinating and degenerative disorders of optic nerve, retinal diseases and diseases of visual cortex. The damage caused by these 1

16 disorders is very nonselective, and the patterns of defect in hue discrimination are entirely different from those caused by congenital abnormalities of photo pigment composition. As a result of this, colour vision tests that were originally intended for the study of congenital dyschromatopsia produce confusing results when applied to patients with acquired diseases. 3 Ishihara test plates are widely used to detect colour vision defects because of their convenience and apparent simplicity of administration. 4 The major disadvantages of Ishihara test plates are that, they do not contain designs for defects for tritan defects, and that patients require good visual acuity to resolve the test. Consequently Ishihara test is not appropriate for the assessment of majority of acquired anomalies, which are associated with tritan type of defects. 2 Arrangement tests such as Farnsworth Munsell 100 Hue test (FM 100 Hue Test), Roth 28 hue test can be used to estimate both nature and extent of defective colour vision. Error score in Roth 28 hue is comparable to that of 100 hue test and Roth 28 hue test is shorter and simpler to administer. It is an alternative to FM100 hue testing in a situation that needs to assess colour discrimination quantitatively and quickly. 5 As colour vision defects can be quantified using Roth 28 hue test, it helps in follow up of patients. This study was done to compare the results of Ishihara s test and Roth 28 hue test in identifying and quantification of colour vision abnormalities in Optic Nerve disorders and to establish patterns of colour vision defects in acquired optic Nerve disorders. These two tests have been in use for so many years, there is no study done so far comparing them in acquired colour vision defects. 2

17 2. OBJECTIVES OF THE STUDY Primary Objective: To compare Ishihara s test and Roth 28 hue test in detecting colour vision defects in various optic nerve disorders. Secondary Objective: To determine the patterns of colour vision defects in various optic nerve disorders 3

18 3. REVIEW OF LITERATURE Light and colour Optical radiation is a part of electromagnetic spectrum consists of non ionising radiation of wavelength ranging from 200nm up to 10000nm.This is further divided into clusters or wavebands each consisting of radiations which elicit similar biologic reactions. Light is visible radiation and visible spectrum extends from about 370nm at violet end to 723nm at red end. Visible light appears white to human eye but it is actually composed of individual segments of coloured light corresponding to specific wavelengths. White light such as sunlight can be split into its component colours by passing it through a suitable prism or diffraction grating. The effect produced is spectrum of colors. 6 Colour sense This is the faculty that allows us to distinguish between different colours as excited by the light of different wavelengths. The appreciation of colours is function of cones and therefore occurs only in photopic vision that is with lights of moderate to high intensity and some degree of light adaptation by the retina. In very low intensities of illumination, the dark adapted eye sees no colour and all objects are seen in shades of grey differing in brightness. Colour is a perceptual phenomenon, not just a physical property of an object. Many factors determine the colour perceived: The spectral composition of light reflected from object as well as from surroundings is important. Sensation of colour is subjective. Individuals are taught names for their colour sensations and subsequently use the names whenever the same sensation is produced. The visual system is designed to achieve object colour constancy that is colour of an object does not 4

19 change much when wavelength and intensity of illumination are altered. The explanation for object colour constancy is that, colour depends primarily on brightness of an object at various wavelengths, relative to other objects in field of view. Wavelength discrimination Colour is not a property that is present in external objects but is rather an internal construct of the individual, dependent on the wavelength composition of light entering the eye and on the structure of the eye and nervous system. 7 The normal observer is able to detect a difference between two spectral lights that differ by as little as 1nm in wavelength in the regions of 490nm (blue-green) and 585nm (yellow). In other regions it is necessary to have a greater wavelength, but only in violet and red a difference of >4nm is necessary. Optical factors affecting colour The lens Lens absorbs shorter wavelengths. In young people absorption is only significant for wavelengths <450nm, but in older people absorption can be up to 550 to 600nm.Wavelength absorbed is primarily blue and wavelengths passed are red and green. Hence lens appears yellow. Macular pigment Macula has a carotenoid pigment called Xanthophyll in an area up to 5 degrees from fovea which absorbs blue light. 5

20 Chromatic aberration The lens is not corrected for chromatic aberration. Blue wavelengths are focussed closer to lens than red because shorter wavelengths are bent more by the lens. Styles-Crawford effect Cones are more sensitive to light entering radially than tangentially. Light entering near the edge of pupil is less effective than light entering at the center of pupil. Photochemistry of colour vision The cone pigments consist of 11-Cis Retinal and Opsin.11-Cis Retinal is similar to that of Rhodopsin and Opsin is known as Photopsin.The green sensitive and red sensitive cone pigments are very similar in structure, their Opsins show 96% homology of amino acid sequence; whereas, each of these pigments have only 43% homology with Opsin of blue sensitive cones. All the three cone pigments have 41% homology with Rod pigment Rhodopsin. Theories of colour vision The first theories of colour vision were based on logical interference rather than on experimental evidence. Trichromatic theory Thomas Young (1801) proposed that eye perceives colours in terms of three primary colour stimuli; they are red green and blue. The theory postulates the existence of three types of cones, each containing different photo pigments, maximally sensitive to specific wavelength of light. Humans with normal colour vision have three populations of cone photoreceptors that are classed according to their relative spectral 6

21 sensitivities as short ( nm), medium ( nm) and long ( nm) wavelength sensitive cones, and abbreviated S, M and L respectively. Three pigments are Erythropsin, Chloropsin and Cyanopsin respectively. Helmholtz (1852) proposed the theory of difference between additive colour mixing and subtractive colour mixing. Additive colour mixing This theory describes creation of range of colours by the mixing of light from two or more coloured light sources. It is known as additive because each source adds light of selected wavelengths to the mixture. Subtractive colour mixing Describes creation of range of colours by mixing two or more colours that absorb light of selected wavelength from incident illumination usually white light. The biological basis of colour vision can be divided into two components: the first is the light-sensitive cone photoreceptor cells in the retina and the second is the neural components that process information about wavelength gathered by the photoreceptors. Red green colour vision is mediated by neural circuitry that compares the quantal catches of Land M cones; blue yellow colour vision is mediated by circuitry that compares the summed quantal catches of L and M cones with the quantal catch of S cones. People with normal colour vision can distinguish more than million colours, but people who are colour blind see many fewer colours. 7

22 Opponent process theory The other principal 19 th Century theory of colour vision was the opponent colour theory, first put forth by Ewald Hering. The Trichromatic theory by itself was not adequate to explain how mixtures of lights of different colours could produce lights of yet another colour, or even appear to be colourless. Certain pairs of colours, such as red and green or yellow and blue, seem to be mutually exclusive. 8 Mixing such coloured lights together do not yield composite sensations (such as reddish-green or bluish-yellow), but rather result in entirely different colour sensations (yellow and white respectively). Hering proposed that colour vision was mediated by opponentcolour processes that would account for the dual exclusivity of certain colour sensations. Although it was at first thought that the trichromatic and opponent colour theories were mutually exclusive, a unification of the two became possible when it was found, by 20th Century physiological experiments, that photoreception is a trichromatic process, while subsequent neural processing of visual information takes place according to an opponent-colour coding scheme. 9 The colour opponent process states that colour vision is trichromatic at the level of photoreceptors but colour opponency is explained by subsequent neural processing. The human visual system interprets information about colour by processing signals from cones and rods in an antagonistic manner. The three types of cones (L for long, M for medium and S for short) have some overlap in the wavelengths of light to which they respond, so it is more efficient for the visual system to record differences between the responses of cones, rather than each type of cone's individual response. The opponent colour theory suggests that there are three opponent channels: red versus green, blue versus yellow, and black versus white (the latter type is achromatic and detects light-dark variation, or luminance). Responses to one colour of an 8

23 opponent channel are antagonistic to those to the other colour. That is, opposite opponent colours are never perceived together there is no "greenish red" or "yellowish blue". While the trichromatic theory defines the way the retina of the eye allows the visual system to detect colour with three types of cones, the opponent process theory accounts for mechanisms that receive and process information from cones. Besides the cones, which detect light entering the eye, the biological basis of the opponent theory involves two other types of cells: bipolar cells, and ganglion cells. Information from the cones is passed to the bipolar cells in the retina, which may be the cells in the opponent process that transform the information from cones. The information is then passed to ganglion cells, of which there are two major classes: Magnocellular or large-cell layers and Parvocellular or small-cell layers. Parvocellular cells, or P cells, handle the majority of information about colour, and fall into two groups: one that processes information about differences between firing of L and M cones, and one that processes differences between S cones and a combined signal from both L and M cones. The first subtypes of cells are responsible for processing red green differences, and the second process blue yellow differences. 9

24 The physiological basis of colour vision Normal human colour vision is trichromatic, which means that any colour can be reproduced by a mixture of three judiciously chosen primary colours. The different classes of cones respond to light over a large range of wavelengths, and as a result they have overlapping sensitivity curves (Figure 1). Each cone can only signal the rate at which light is absorbed and cannot alone convey information about wavelength (the so-called Principle of Univariance ).The visual system derives trichromatic colour vision by comparing the responses of the three different classes of cone. Such comparisons are thought to be made initially at the level of tertiary neurons: midget ganglion cells appear to be specialised for comparing red- and green-cone responses, whereas at least four distinct ganglion cell types appear to be specialised for comparing blue-cone responses to those of the red and green cones. Within the central retina, midget cells are thought to draw inputs into the centre of their receptive fields from single cones; there is still controversy as to whether the surround is normally drawn in a precise manner from cones of a different class or indiscriminately from adjacent cones. The receptive fields of ganglion cells conveying blue-cone signals are larger than those of the midget cells and thus support an inferior level of spatial resolution. The dichotomy between the red/green- and blue-cone systems is respected in the lateral geniculate nucleus (LGN); the midget ganglion cells transmit signals to the Parvocellular layers of the LGN, whereas the ganglion cells sub serving the blue cones transmit to a neuro chemically distinct Koniocellular pathway. The Koniocellular layers in turn project to the lower echelons of layers 3 and 4A of the primary visual cortex, whereas the parvocellular layers project to layer 4Cb. 10

25 Figure 1 Spectral sensitivity curves for the three classes of Cones. Relative sensitivity is plotted against wavelength. The blue cones (inverted triangles) have a peak sensitivity at about 419nm, the green cones (upright triangles) have a peak sensitivity at about 531nm and the red cones (circles) have a peak sensitivity at about 558nm. While the different types of cone have distinct sensitivities, there is a great degree of overlap. 11

26 Congenital colour blindness Congenital colour vision deficiency results from genetic mutations that affect the expression of the full complement of normal cone photoreceptors. They are generally classified by severity (anomalous trichromacy, dichromacy, and monochromacy) and may be further classified by the type of cones affected. 10 Congenital colour vision deficiency is a common functional disorder of vision affecting 2-8% of males and 0.4 % of females in Caucasian societies. 11 Tritanopia, in which the short wavelength sensitive photopigment is absent, shows Autosomal Dominant inheritance and its prevalence lies between 1 in and 1 in Tritanomaly, in which short wavelength sensitive photo pigment is abnormal, has a prevalence of approximately 1 in Anomalous trichomatism (prevalence 5-6%): Mechanism to perceive all three primary colours is present but defective for one or two of them. Protanomaly: Defective appreciation of red colour Deuteranomaly: Defective appreciation of green colour Tritanomaly: Defective appreciation of blue colour Dichromatism (prevalence 2%): In this condition, mechanism to perceive one of the three primary colours is completely absent. Protanopia(1%):Complete red colour defect Deuteranopia(1%):Complete green colour defect Tritanopia(0.005%):complete blue colour defect 12

27 Achromatopsia (prevalence 0.003%) Cone monochromatism: It is characterised ability to perceive only one primary colour. There are normal rods and only S cones which are sensitive to blue light and absent L and M cones. Rod monochromatism: It is inherited as Autosomal Recessive trait. It is characterised by total colour blindness, day blindness, nystagmus and normal fundus. Acquired colour vision defects In addition to the congenital disorders of colour vision, acquired abnormalities of colour vision are known since 17 th century. They result from alterations in the anatomical structure of the eye, the visual pathway and the cortical receiving areas. Table 1 delineates the differences between congenital and acquired defects. Köllner in 1912 wrote an acute description of the progressive nature of colour vision loss secondary to ocular disease, dividing defects into blue-yellow and progressive redgreen blindness. 15 This classification has become known as Köllner s rule, which states that patients with retinal disease develop blue-yellow discrimination loss, whereas optic nerve disease causes red-green discrimination loss. Exceptions to Köllner s rule 16, 17 include some optic nerve diseases, notably glaucoma, which is primarily associated with blue-yellow defects, and also some retinal disorders such as central cone degeneration which may result in red-green defects. Indeed, in some cases, there might be a non-specific chromatic loss. 2 13

28 Unlike congenital defects, acquired colour vision anomalies are evenly distributed between males and females. 18, 19 A summary of characteristic differences between congenital and acquired defects is given in Table 1. Table 1: Differences between congenital and acquired colour vision defects Congenital colour vision defects Acquired colour vision defects Present at birth Type and severity of defect is stable throughout life Onset after birth Type and severity of defect may fluctuate Type of defect can be classified precisely Both eyes are equally affected Type of defect may not be easy to classify. Combined or non-specific deficiencies frequently occur Monocular differences in the type and severity of the defect often occur and visual fields are normal Visual acuity is unaffected (except in monochromatism) Visual acuity is often reduced and visual field defects often occur Predominantly protan or deutan Predominantly tritan-like Higher prevalence in males equal prevalence in males and females 14

29 Classification of acquired colour vision deficiency Acquired dyschromatopsias are more complex and variable in nature. Damage to retina or optic nerve may be the result of trauma, inflammatory disease, intoxication, metabolic disorder, degeneration, inherited dystrophy, vascular and neoplastic diseases. The pathogenesis and clinical presentation of acquired dyschromatopsias are entirely different from congenital disorders. Of the many attempts to classify acquired colour vision deficiencies, Verriest s classification published in 1963 is the most widely used. It is based on extensive empirical observations of the nature of colour vision disturbances found in acquired disease. Three major types of acquired dyschromatopsias called type 1, 2 and 3 are included. Type 1 and 2 are associated with a major axis of defective hue discrimination in red-green region of Farnsworth- Munsell diagram, much like protan and deutan defect. While type 3 is associated with confusion between blue and yellow (Tritan like). 9 15

30 Table 2: Verriest s classification of acquired colour vision anomalies 20 Name Alternative names Colour discrimination defect Visual acuity Type I Acquired R-G, protan-like Type II Acquired R-G, deutan-like Type III Acquired B-Y, tritan-like Mild to severe confusion of R-G hues, little or no loss of B-Y CD Mild to severe confusion of R-G hues with a concomitant mild loss of B-Y CD Mild to moderate confusion of B-Y hues with a lesser impairment of R-G CD Moderate to severe reduction Moderate to severe reduction May be normal or moderately reduced R-G = red-green, B-Y = blue-yellow, CD = colour discrimination Type I Acquired Red-Green Deficits There is progressive deterioration of Red-green chromatic discrimination with loss of visual acuity. The photopic luminosity function (curve) becomes more and more scotopic. In advanced stages, there is total colour blindness that resembles congenital achromatopsia. This condition is associated with retinal diseases, especially those involving photoreceptors of the posterior pole (macular cones are destroyed). Type II Acquired Red-Green Deficits There is a red-green discrimination loss which is moderate or severe with a concomitant Blue-yellow loss which is mild. The apparent saturation of colours is 16

31 decreased and in advanced cases, the 500 nm region of the spectrum looks grey to the patient. In late stages, there is eccentric fixation with nearly complete achromatopsia. Seen in: Optic neuritis Retrobulbar neuritis Optic atrophies Toxic optic neuropathies Optic nerve or chiasm tumours Type III Acquired Blue-Yellow Deficits This is the most frequent acquired deficit. There is a mild to moderate blue-yellow sensitivity loss. In early stages there is a blue deficit. However in the later stages the disease proceeds to dichromacy with a neutral zone (that appears grey) around 500 nm. Seen in: nuclear cataract glaucomatous optic neuropathy chorioretinal inflammation vascular disorders chorioretinal degeneration papilledema autosomal dominant optic atrophy senile macular degeneration 17

32 Optic nerve Diseases It was reported by Kollner and has since been confirmed by other investigators that diseases of the optic nerve tend to produce an acquired type II, red/green type of colour vision defect. Optic atrophy will frequently result in an acquired defect of red/green discrimination no matter what the source of damage to the optic nerve. Compression of the nerve by a tumour, damage by inflammatory disease or toxins, and demyelinating diseases can all produce the same result. Just as the etiology of damage to the nerve is nonspecific, the location along the course of the optic nerve is equally indiscriminate. The axons may be damaged in the anterior optic nerve or in the orbital or intracranial course of the nerve, all resulting in the same acquired colour vision defect. Acquired dyschromatopsias of Optic nerve diseases causing type 1 and type 2 21, 22 defects Retrobulbar neuritis Toxic optic neuropathy Leber s Optic neuropathy Compressive optic neuropathy(optic nerve and chiasm) Traumatic optic neuropathy Type 3 defects 23 Dominantly inherited optic neuropathy Glaucoma and ocular hypertension Chronic papilloedema Anterior ischaemic optic neuropathy 18

33 The acquired red/green colour deficiency associated with optic neuropathies is most pronounced in an eye in which the papillo-macular bundle has been disturbed, producing a central scotoma with reduced acuity. Diseases that preferentially damage this part of the visual field include acute retro bulbar optic neuritis, tobacco-alcohol amblyopia, and Leber s optic atrophy. 9 However, not all optic nerve diseases result in red/green dyschromatopsias. As a general rule, if acuity is spared by the insult to the nerve, a type III blue/yellow defect may predominate. 24 Traumatic optic atrophy followed by peripheral damage to the visual field have been reported in association with a type III defect. 25 Non selective colour vision defects such as equal defect in red-green and blue yellow colour systems have also been found Schneck M E et al in a study involving 438 patients of optic neuritis demonstrated mixed red green (29.6%) and blue yellow (40.8%) defects and blue yellow defect was more common in acute phase and red green defect (42.1%) at 6 months. The results from this study provide no evidence to support Kollner's rule stating that red-green defects are selectively associated with optic neuritis Retinal diseases Acquired dyschromatopsias that are the result of retinal diseases most commonly produce a type III or tritan-like defect in colour vision. The retinal diseases that can produce type III defects include toxic, inflammatory, vascular, and degenerative or dystrophic processes. The tritan-like rule for the dyschromatopsias of retinal disease is not an absolute one, however. In fact, many diseases which result in a type III (tritanlike) defect early in their course have been shown to develop subsequently into type I or II disorders. Type III defects are present in retinal diseases at times when central 19

34 visual acuity remains relatively well preserved. Retinal diseases that produce type I defects are usually photoreceptor degenerations. Type I defects are characterized by impairment of red-green discrimination in patients with central scotomas and markedly reduced visual acuity caused by central fovea1 and perifoveal retinal lesions. Primary cone dystrophies are the best example of this type of acquired dyschromatopsia. Such defects often start as type III, progressing to type I and ultimately deteriorating into complete achromatopsia. Stargardts disease is considered to be the most typical of the type I defects, and may undergo a progression from an initial type III defect associated with a loss of sensitivity at the blue end of the spectrum to type 1 defect Acquired dyschromatopsias of retinal disease-type 1 defects Retinal detachment(macula on) Toxic retinal neuropathy(chloroquine toxicity) Retinal and choroidal inflammatory diseases Peripheral chorioretinal dystrophies Diabetic retinopathy Cystoid macular edema Central serous retinopathy Retinal vein occlusion Juvenile retinoschisis Type 2 and 3 defects Juvenile macular degeneration Cone dystrophy 20

35 Glaucoma Glaucoma is perhaps the most common optic neuropathy, producing death of optic nerve fibers and loss of the ganglion cell layer of the retina. The most common disturbances of the visual field in this disease are paracentral scotomas and reduction in visual sensitivity in the Bjerrum region (along with preserved visual acuity). Far the most common acquired dyschromatopsia associated with glaucoma is a type III defect. In terms of the spatial distribution of visual field defects, glaucoma is a disease that results in a pattern of disturbance that is similar to that found in some purely retinal disorders, such as Retinitis Pigmentosa. In both cases a type III acquired dyschromatopsia is produced. Prevalence estimates for the different types of colour vision defect in POAG have 33, 34 been obtained using a variety of non-computerised tests. Based on these reports typical prevalence are 20 40% for normal colour discrimination, 30 50% blue-yellow defects, 5% for red-green defects, and 20 30% for a general loss of chromatic discrimination. 35 Several possible explanations have been suggested for this predominance of blueyellow (tritan-like) defects in POAG, including: Short wavelength cones or their neuronal connections are less able to resist the effects of raised IOP 36 There is selective damage to blue-yellow sensitive ganglion cells or their axons. Blue-yellow ganglion cells have larger receptive fields, are larger than red-green cells, and have a unique morphology and connectivity to second order neurons, which may make blue-yellow ganglion cells more susceptible to IOP related damage 37 21

36 The relative scarcity of ganglion cells which code blue-yellow signals, and the relatively little overlap between adjacent receptive fields of these ganglion cells. 38,39 As a consequence, although only a few ganglion cells may cease to function, there is preferential impairment of the blue-yellow discrimination threshold compared with red-green, even if the proportion of damaged fibres is the same for both types. 40 Differentiation between age related and glaucomatous changes in colour vision was established when a group of patients with POAG was compared with a control group, matched for age and lens density. There were significantly more F-M 100 hue error scores in the glaucoma group, demonstrating that their colour vision loss is partly caused by the disease process, and cannot be explained solely on the basis of changes in age and lens density. 2 The Pathophysiological Basis for the Acquired Dyschromatopsias Verriest mentioned three general hypotheses to account for acquired colour vision defects. For type I defects (seen chiefly by Verriest in juvenile macular degeneration) he postulated a general destruction of macular cones with a selective preponderance of damage to red-sensitive cones. Type II defects, found primarily in diseases of the optic nerve, could be attributed to a (possibly) greater susceptibility of those ganglion cell axons that transmit red/green opponent information. The most common acquired defects are the blue/yellow or type III (found in 58% of the eyes with a clearly distinguishable axis of acquired hue discrimination defect), and are most often due to diseases of the retina and/or choroid

37 The second of Verriest s hypotheses noted above (that of greater susceptibility of neurons encoding colour contrast information) has been entertained by several investigators to explain the hue discrimination defects found in diseases of the optic nerve (predominantly type II defects). In retrobulbar optic neuritis, there is a preponderance of damage to red green discrimination with apparent relative preservation of luminance contrast detection. The third of the hypotheses mentioned by Verriest concerns the lower sensitivity of the blue cone system. It proposes that diffuse damage to the retina is more likely to be detected as a defect in blue discrimination (hence a type III defect), since this is the colour vision mechanism with the lowest physiologic reserve. 43 Tests for colour vision For routine clinical use, simpler tests have been developed that can be rapidly administered and easily interpreted. The most common clinical tests are plate tests, which provide a basic screening method for detecting congenital colour defects. More demanding than these are arrangement tests, which provide a quantitative analysis of colour vision. The most complicated clinical tool is the Anomaloscope, which is required for accurate diagnosis of congenital colour vision defects. For all types of tests, proper testing conditions are crucial. No single test is ideal, and for colour vision evaluation a battery of tests is recommended. 23

38 The Nagel Anomaloscope The colour matching tests that are used as gold standard to detect protan and deutan defects are based on Rayleigh equation: Red+green=yellow. 11 The Nagel anomaloscope is considered as the gold standard to detect protan and duetan defects. It depends on the Rayleigh equation where normals may match pure yellow (589 nm) with a mixture of pure red (670 nm and green (545 nm). Anomalous observers require more red in the mixture (protanomaly) or more green (deuteranomaly). Dichromats (protanopes or deuteranopes) will accept a wide range of red green mixtures to match yellow because they are matching brightness, not colour. Advantages: Test has a long and hallowed history that is well respected. Disadvantages: Expensive instrument that requires an experienced examiner s skills. Validity: Validation measures of other colour vision tests are based on this instrument. Calibration: Requires spectroscope to calibrate. 43 Lantern Tests Lantern tests were conceived as occupational tests to evaluate railway personnel and airline pilots and their ability to discriminate navigational aids and signals. Their value lies in their ability to simulate the work place. They do not specifically screen for colour defects. The expectation is that colour defectives will not do as well as normals. Even though lantern tests have been used for close to one hundred years, their validation and the availability of information on their reliability is almost nonexistent. 24

39 Eldridge-Green Lantern (1891) This test device consists of seven coloured glass filters, seven modifying glass filters and seven apertures. The colour filters simulate signal lights. The modifying filters simulate foggy, rainy, smoky and other meteorological conditions. The apertures simulate changes in distance. Larger aperture sizes may be used in ambient illumination while small apertures require dark adaptation. The test is complicated by the hundreds of possible combinations of filters and apertures. Arrangement Tests Arrangement tests were introduced 60 years ago as a way of grading the colour abilities of observers with normal colour vision, and they have also been used to provide a quantitative evaluation of colour abilities in colour-defective observers. In an arrangement test, the observer is presented with a randomly arranged set of coloured samples and is asked to arrange them in sequence. The number of errors provides a measure of overall chromatic discrimination, and analysis of the pattern of the errors determines whether there is a red-green, blue, or indeterminate defect. Four different arrangement tests are used in clinical colour vision testing: Farnsworth- Munsell 100-hue test, Farnsworth Dichotomous Panel D-15 test, Lanthony Desaturated Panel D-15, and Roth 28 hue test. Farnsworth - Munsell 100 hue test: It is a test of colour discrimination and colour confusion designed by the late commander Dean Farnsworth in The l00-hue test consists of a series of 85 coloured caps (15 colours in the original test design have since been eliminated). The colours of the caps correspond to a circle of hues in the CIE chromaticity diagram, as 25

40 shown in Figure 2. The 85 caps are divided into four groups, stored in boxes, and the patient is required to arrange them in linear sequence between pairs of reference caps which are placed at the ends of each box. The order of the caps produced by the subject is then plotted on a circular (polar) diagram. This is arranged so that the correct ordering of caps will produce a circle of points close to the center of the diagram, while incorrect placement (transpositional errors) in the ordering of caps will cause points to be plotted farther away from the center of the diagram. Characteristic patterns are produced by confusions between similar hues in patients with congenital colour vision defects. For such patients, errors in ordering of the caps are usually confined to restricted zones which are located at directly opposite positions from one another in the colour circle. While the l00-hue test provides a straightforward way of characterizing hue discrimination defects in patients with dyschromatopsias, it is inconvenient and time-consuming test. The results are rather tedious to record, and even with the use of instruments that allow automation of the recording and diagramming process, the administration time of the test remains a definite drawback to its use. 9 26

41 Figure 2: Results of Farnsworth- Munsell colour vision testing The performance on F-M 100 hue test varies as a function of age. Younger children make significantly more misplacement errors. The performance of older adults also deteriorates with age. 44 one of the great merits of the 100-Hue test is that those elements suitable for detecting small variations in colour discrimination are also suitable for detecting colour confusion. As the coloured caps were chosen to cover the entire colour circle it happens that in some areas certain consecutive caps follow the confusion lines of all known dichromats. In addition to detecting classical types of dichromats, Verriest (1964) has shown that the 100-Hue can detect the so-called 27

42 scotopic type of confusion characteristic of many subjects with acquired colour defects. The validity and reliability of the test for detecting the three well-known congenital types of dichromat are high and correlate well with similar findings on the Pickford anomaloscope and with data obtained from the Konig-Helmholtz colorimeter and also with results obtained from dichotomous tests such as the Ishihara. 45 The Farnsworth D-15 (Dichotomous) Panel Test The D- 15 panel is rather like a subset of the l00 hue test. It consists of a series of 15 colour caps placed in a single box with a single reference sample at one end. The patient s arrangement of the colour caps is plotted on a circular diagram. Whereas the 100-hue test records transpositional errors between adjacent caps (adjacent hues), the D-15 test records confusions of nonadjacent hues located across the hue circle from one another. Translocational errors in the ordering of the caps produce lines which crisscross the hue circle from one side to the other, highlighting axes of isochromatic hue confusion. The colour differences between caps are greater than those of the 100- hue test. Protan, deutan and tritan-like defects produce characteristic patterns on the D-15 chart. 28

43 The Roth 28 hue test The Roth 28 hue test, first described in 1966, is a subset of FM 100 hue test because it uses every third colour cap from FM 100 hue test. This test falls between D-15 and 100 hue tests. Since D-15 test does not furnish sufficient information about mildly affected anomalous trichromats, and 100 hue tests is too time consuming, this test is desirable. The 28 hue test studies characteristic axes of dyschromatopsia similar to FM100 hue test and it is most comprehensive colour vision test. 6 The 28 hue test is constructed by selecting every third cap from 100 hue test. The colour caps therefore consist of 1, 4, 7, 10.79, 82 of 100 hue test. Their colour intervals are larger than those of 100 hue test. The design and scoring of this test closely resembles that of D-15 test. By presenting more colour caps to patient the 28 hue test allows greater expression of colour confusion. (Figure 4) Error score in Roth 28 hue is comparable to that of 100 hue test as Roth 28 hue test is shorter and simpler to administer. It is an alternative to FM100 hue testing in a situation that needs to assess colour discrimination quantitatively and quickly. 5 As colour vision defects can be quantified using Roth 28 hue test, it helps in follow up of patients. Pre test considerations: The test is intended to be administered on a black background to prevent surroundings from affecting colour perceptions by patient. Illumination should be approximately 6700Kelvin at 25 foot Candles or greater Children over 5 years can perform the test 29

44 The test should be conducted at working distance of 50 cm The test is not affected by mild to moderate colour vision loss Testing procedure: Examiner selects reference cap and places it in the box. The patient is then instructed to select colour disc which most closely matches reference cap and to place it in the box next to reference cap. Patient then continues select next closest colour disc and to place each in sequence in the box. Patient is permitted to alter the sequence prior to completion. At the completion if the test examiner slides the lid to secure the test discs. Scoring: Scoring for each case is accomplished by reading the colour chip numbers on reverse side of the case and recording the sequence selected by the patient.it is diagrammed on score sheet by connecting the dots in order selected by patient. If the lines remain outside the circle then patient is regarded as normal.if the lines cross repeatedly the patient has colour vision defect. Type of colour vision defect is determined by comparing these cross over lines to see if they are parallel to protan,deutan,tritan or tetartan lines. Confusions occurring regularly in a certain direction across the score sheet reveal the type of defect. Calculation of error scores: For each of 28 caps difference of the cap number from numbers of the adjacent caps is calculated (value x).values x and 84(= (82-1) +3)-x will be then compared and lower will be chosen as distance. The shortest distance is then calculated which is taken as corrected x. Values of distance on both sides will be 30

45 added then value 6 (corresponding to error free handling of the test) is subtracted and resulting value is stored as local error score sum of which is taken as global error score. 10 Plate Tests Plate tests have been used for more than a century to separate colour-defective from colour-normal observers. The most common plate tests are pseudoisochromatic plates, in which symbols (numbers, letters, or geometric figures) composed of coloured dots are presented on a background of coloured dots. The colours are chosen so that the symbol and background colours are distinct for those with normal colour vision but are more similar (pseudo-isochromatic) for colour-defective persons. Pseudoisochromatic means apparently or falsely equal colours. That is colours are trickily chosen to fall within colour diagram zones where defective observers are most likely to be identified. In some cases, the colour-defective person is unable to see any pattern whereas colour-normal persons readily identify the figures. At other times, two different figures are seen, one by colour-normal persons and another by colourdefective persons (achromats may not be able to see even the defective figure).they are based either on theoretical properties of a colour vision system or on statistical data about confusion colours from known colour defectives. The most common use of plate tests is to identify persons with congenital colour defects. Pseudoisochromatic plates (for example, HRR plates, Ishihara test, Dvorine test and City university colour vision test) provide efficient screening of congenital red-green defects. Plate tests have the advantages of being relatively inexpensive, easily available, simple to use, and appropriate with children and persons who are illiterate. They are only suitable for screening purposes, however, because they neither provide a quantitative 31

46 evaluation of colour vision nor distinguish the type and severity of the colour vision defect. Plate tests are designed to distinguish congenital colour-defective from colournormal observers, but they do not evaluate the wide range of abilities and aptitudes of observers. When used improperly (nonstandard illumination, binocular viewing, coloured lenses), their efficiency can diminish dramatically. Ishihara plates The Ishihara Colour Blindness test named after a Japanese Professor at the University of Tokyo Dr. Shinobu Ishihara (1917), is the most well known tool to test for red-green colour blindness. A collection of 38 plates filled with coloured dots build the base of this test. The dots are coloured in different shades of a colour and a number or a line is hidden inside with different shades of another colour (Figure 3). The small test consists of 24 different plates (or cards) and the large test of 38. The plates follow a setup of four different test designs: 1. Transformation plates anomalous colour observers give different responses to colour normal observers. [Plates 2-7] 2. Disappearing digit (Vanishing) plates only the normal observer is meant to recognize the coloured pattern. [Plates 9-13] 3. Hidden digit plates only the anomalous observer should see the pattern. [Plates 14-15] 4. Qualitative plates intended to classify protan from deutan and mild from severe anomalous colour perception. [Plates 16-23] The plates are designed to be appreciated correctly in a room which is adequately lit by natural day light. The plates are held at 75cm. The numerals which are seen on 32

47 plates are stated, and each answer should be given without more than 3 seconds delay. Analysis of results can be done by standard guidelines given in instruction manual. Ishihara test is effective in detecting congenital colour vision defects but it has great limitations in classifying the defects and estimating severity of them. 46 Because Ishihara test is apparently simple to administer and it is relatively quicker test it is used widely as screening test for colour vision abnormalities. According to Hardy L G et al Ishihara test is rough screening method for red green defect. It is a gross test, fails to classify type of colour vision defect and cannot be used to give satisfactory evaluation of extent and degree of defect. 4 33

48 Figure 3: Ishihara plates Figure 4: Roth 28 Hue test 34

49 4. MATERIALS AND METHODS Study design- This was a prospective, cross sectional, comparative study Source of data - Patients with various optic nerve disorders attending OPD of St. John s Medical College Hospital, Bangalore from September 2010 to August Sample size-71 cases Inclusion Criteria- Optic neuritis Optic atrophy Traumatic optic neuropathy Drug induced optic neuropathy Ischemic Optic Neuropathy Established cases of glaucoma- CDR >0.6 with visual field loss Exclusion Criteria- children <10 years Elderly patients >65 years and whose dexterity is poor, disabling them from performing the test Visual Acuity <6/18 Macular disorders Pseudophakia Congenital colour blindness Media opacities, like >grade 2 Nuclear Sclerosis 35

50 Method of collection of data: Patients with various optic nerve disorders attending OPD of St. John s Hospital Bangalore were included in the study after taking informed consent. A detailed history including demographics, ocular disease, past medical illness, drug history and personal history was taken. Ophthalmological examination included: Best corrected visual acuity assessed using illuminated ETDRS Chart and scored with Log MAR Scale, near vision with Times New Roman chart, contrast sensitivity with Pelli Robson chart, slit-lamp examination, applanation tonometry, refraction, fundus examination with direct, indirect ophthalmoscope and 90 D lens. Colour vision was tested (monocularly) with Ishihara test plates and Roth 28 hue test with near vision correction. Ishihara test was administered as follows-the patients were made to read the plates in Natural daylight. The plates were held 75 cm from the subject and tilted so that the plane of the paper is at right angles to the line of vision. The numerals which are seen on plates 1-25 are stated and each answer should be given without more than three seconds delay. If the subject is unable to read the numerals, plates were used and the winding lines between two x s were traced. Each tracing should be completed within 10 seconds. Out of plates 1-21 if >17 plates are read normally, the colour vision was regarded as normal. If <13 plates were, colour vision was grouped as severe colour vision defect. If 14 to 16 plates were read, colour vision was grouped as moderate colour vision defect. Classification of colour vision defect was done according to the standard guidelines provided by Dr.Shinobu Ishihara in instruction manual. 36

51 Roth 28 Hue test was conducted as follows-test was conducted on a black background under day light at a distance of 50 cm. The cap number 82 is the reference cap and it is the starting and end point of the test.the patients were instructed to arrange the remaining 27 caps, by selecting a cap closest in colour to the previously arranged cap and placing them in a circular sequence, without any time limit. Scoring for each case was accomplished by reading colour cap numbers on the reverse side of the case and the score sheet was plotted. Scoring method: For each of 28 caps difference of the cap number from numbers of the adjacent caps was calculated (value x).values x and 84(= (82-1) +3)-x was then compared and lower will be chosen as distance. The shortest distance was then calculated which is taken as corrected x. Values of distance on both sides was added then value 6 (corresponding to error free handling of the test) was subtracted and resulting value is stored as local error score sum of which was taken as global error score. 10 Qualitative interpretation of the test was done by plotting the score sheet. If the lines remain outside the circle then the patient is termed to be normal. The type of defect is determined by comparing the crossover lines to see if they are parallel to protan, deutan and tritan colour confusion axes. In case of multiple crossover lines which are not parallel to any colour confusion axes was regarded as nonspecific colour vision defect. 37

52 Statistical Analysis: The data was analysed as follows: first the descriptive statistics were computed which included median and inter-quartile distance for quantitative variables, and category frequency counts with percentages for qualitative variables. Inferential statistics were done next as follows: Chi-square test was done to study the correlation between two qualitative variables. The Kruskal-Wallis test was done to study the correlation between quantitative variables and qualitative variables having more than two groups. (BCVA was not normally distributed, hence nonparametric test was done). Statistical significance was considered when p was <0.05. All tests were done using SPSS version

53 5. RESULTS In our study titled Acquired Colour Vision Defects In Optic Nerve Disorders-A Comparison between Ishihara s Test and Roth 28-Hue Test 139 eyes of 71 patients with various optic nerve disorders who presented to the Department of Ophthalmology were included. Age distribution of Patients The age range of study patients was from 11 years to 64 years with a mean (±SD) of 36.51(±14.79). Figure 5: Age distribution of Patients 35 Age distribution No of cases < >61 Age group in years 39

54 Gender distribution of patients The study included 35/ /71(49.30%) males and 35/71(50.70%) females. Figure 6: Gender distribution of patients Gender distribution of cases Males Females 50.70% 49.30% 40

55 Incidence of comorbidities: Diabetes Mellitus was found in 9% of the patients and hypertensionn was found in 11% of the patients. One patient had Sarcoidosis with systemic vasculitiss and two patients were diagnosed to have Systemic Lupus Erythematosis. Figure 7: Incidence of comorbidities Comorbidities Nil DM Sarcoidosis SLE Hypertension 3% 1% 11% 9% 76% 41

56 Causes of optic nerve dysfunction Figure 8: Optic nerve dysfunction Causes of optic nerve dysfunction Other causes 5% TON 2% Normal 9% Optic Neuritis 15% NAION 1% Glaucoma 13% Papilloedema 34% Tobacco alcohol amblyopia 7% Optic atrophy 14% The various causes for optic nerve dysfunction found in our study are as follows: Most common was papilledema, which was found in 47/139, eyes and optic neuritis which was found in 21/139 eyes. Other causes were Optic atrophy 20/139 eyes, Glaucomatous optic neuropathy 18/139 eyes, Tobacco-Alcohol amblyopia10/139 eyes. Two patients had Traumatic optic neuropathy and one patient had non arteritic ischaemic optic neuropathy. Other causes of disc edema were Grade 4 hypertensive retinopathy(1 patient), Diabetic papillopathy (1 patient),disc edema due to orbital pseudotumour (2 patients) and disc edema due to orbital neoplasm(orbital lymphoma- 1 patient). 42

57 Systemic diagnosis Figure 9: Systemic diagnosis Systemic Diagnosis Pitutary adenoma 11% Others 18% Normal 36% Systemic vasculitis 1% CVT 13% IIH 16% Demyelinating disease 5% No systemic disease was found in 27/71 patients. Papilledema due to cerebral venous thrombosis (CVT) was found in 10 patients and Idiopathic Intracranial Hypertension (IIH) was found in 12 patients. Intracranial infections such as pyogenic meningitis were found in one patient and rickettsial meningitis was found in one patient. Intracranial mass lesions causing optic neuropathy such as pitutary adenoma was found in 8 patients, one patient had pineal gland tumour and one patient had craniopharyngioma. Optic neuritis due to demyelinating disease was found in 4 patients. 43

58 Roth 28 hue test results Figure 10: Roth 28 hue test results Roth 28 Hue test Non specific 13% Protan 1% Duetan 4% Tritan 16% Normal 66% On Roth 28 hue test 91/139 eyes were found to have normal colour vision. Two eyes had Protan, 6eyes had Duetan and 22 eyes had tritan defects. Eighteen eyes had diffuse nonspecific chromatic loss. 44

59 Ishihara test results Figure 11: Ishihara test results Ishihara test 91 No of Cases No plates <13 plates plates >17 plates Ishihara test results Normal colour vision (>17 plates) was found in 91 eyes; 16 eyes had moderate colour vision defect (14-16 plates); 15 eyes had severe colour vision defect (<13 plates): 17 eyes were not able to read any of the plates. 45

60 Comparison between Roth 28 Hue Test (Qualitative Analysis) and Ishihara test Table 3 Roth 28 Hue Test(Qualitative) Vs Ishihara test-cross tabulation Ishihara Pearson- Chi square value Severe CV defect Moderate CV defect Normal C V Total Roth Nonspecific P<0.001 Patterns Normal Total On comparing colour vision defects determined by Roth 28 Hue test and Ishihara test, 74 eyes showed normal colour vision by both the tests. There was statistically significant correlation (p<0.001) between the two tests. On Ishihara s test 91 eyes showed normal colour vision. Of these on Roth testing, only 74 eyes showed normal colour vision and 17 eyes had abnormal colour vision; 9 had severe colour vision defect and 8 eyes showed colour pattern defects. On the other hand, 91/139 eyes showed normal colour vision by Roth test, again only 74 eyes showed normal colour vision by Ishihara s test. Remaining 14 eyes showed severe colour vision defect and 3 showed moderate defects by Ishihara s test. 46

61 Severe colour vision defect was detected in 32 eyes by Ishihara s test. Of these 32 eyes only 4 eyes were detected to have nonspecific colour vision defect(severe) by Roth test; 14/32 had normal colour vision and 14/32 showed a pattern abnormality. (Table 3) Roth test showed a tendency towards detecting more pattern abnormalities, with 30/139 showing different colour patterns. Ishihara Vs Roth 28 hue Quantitative analysis Global error score determined by Roth 28 Hue test was compared with Ishihara test results using Kruskal-Wallis test. Increasing values of Global error score was associated with severe colour vision defect by Ishihara test and this correlation was statistically significant (p<0.001). In the presence of severe colour vision defect by Ishihara test, the median (interquartile distance) Global error score was 282 (680), while with moderate colour vision defect by Ishihara test the Global error score was 264 (582), for normal colour vision by Ishihara test GES was 0 (120) Table 4: Correlation of colour vision using Ishihara s test and Global error score on Roth 28-hue test. Roth 28 Hue test-global Error Score Median Inter quartile distance Ishihara Test Severe CV defect Moderate CV defect Pearson-Chi square Value normal P<

62 Figure 12: Correlation of colour vision using Ishihara s test and Global error score on Roth 28-hue test. Box plot depicting global error score and correlation with Ishihara test results. Bars depict 10 th and 90 th percentile of Global error score. The top and bottom of the boxes represent 25 th and 75 th percentile and line segment inside the box represents median. Global Error Score Severe Moderate Normal 48

63 Visual Acuity Figure 13: Visual acuity BCVA No of cases Log MAR BCVA Best corrected visual acuity was taken in all the groups and recorded according to Log MAR chart. Visual acuity of Log MAR 0(6/6 Snellen s) was found in 83 eyes. 22 eyes had visual acuity of 0.2(6/9). Comparison of BCVA with Ishihara test Best corrected visual acuity was compared to Ishihara test results using Kruskal- Wallis test. Statistically significant correlation (p=0.001) was found between BCVA and severity of colour vision defects. Severe colour vision defect by Ishihara test was associated with the poorest BCVA, with median (interquartile distance) BCVA of 0.20 (0.05), while moderate colour vision defect by Ishihara test had a median BCVA of 0.10 (0.03) and normal colour vision by Ishihara test had a median BCVA of zero (0.20) 49

64 Table 5: Comparison of BCVA with Ishihara test BCVA (log MAR) Median Inter quartile distance Ishihara Test Severe CV defect Moderate CV defect Normal Pearson-Chi square Value P=0.001 Figure 14: Comparison of BCVA with Ishihara test BCVA Severe Moderate Normal 50

65 Percentile Box Plot depicting correlation between BCVA and Ishihara test results. Bars depict 10 th and 90 th percentile of BCVA. The top and bottom of the boxes represent 25 th and 75 th percentile and line segment inside the box represents median. Comparison of BCVA with Roth 28 hue test Best corrected visual acuity was compared to Roth test results using Kruskal -Wallis test. Severe colour vision defect by Roth test associated with the least median (interquartile distance) Log MAR BCVA of 0.20(0.30), moderate colour vision defect with median Logmar BCVA of 0.20 (0.50) and normal colour vision by Roth test with a median Logmar BCVA of 0(0.20). (Table 4 & Figure 11) Table 6: Comparison of BCVA with Roth 28 hue test BCVA (log MAR) Median Inter quartile distance Roth Test nonspecific patterns normal Pearson-Chi square Value P=

66 Figure 15: Comparison of BCVA with Roth 28 hue test BCVA Non specific Patterns Normal Percentile Box Plot depicting correlation between BCVA and Roth test results. Bars depict 10 th and 90 th percentile of BCVA. The top and bottom of the boxes represent 25 th and 75 th percentile and line segment inside the box represents median. 52