LENS
Correlate the structure of the lens with its functions. Define cataract and describe its epidemiology Classify cataract on the basis of morphology, aetiology and maturity of cataract. Diagnose a case of cataract; describe the complications of cataract in children and adults. Describe the surgical procedures for the treatment of age-related cataract and enlist the complications of cataract surgery.
It is a highly organized transparent spheroid structure that has evolved to perform refraction of the light entering in the eye. It does not posses nerve, blood vessels or connective tissue.
Biconvex Lens Diameter varies from 8.8 to 9.2 (9mm) Lens grow in size continuously throughout life. Its weight is about 60 mgm at the birth and up-to 250 mgm by 80 years of age. Antero-posterior thickness changes with accommodation. Thickness is 4.75 5 mm (4.5mm) (un-accommodated) in adults. Circumference is known as equator
Lens is suspended in eye by Zonules which are inserted on anterior surface of equatorial lens capsule and attached to ciliary body(pars Plicata- Ciliary Processes). Zonular fibres are series of fibrillin rich fibre.
Histologically lens consists of three major components: 1. Capsule is a thick collagenese basement membrane which is transparent, elastic acellular envelop, thick at anterior pre-equatorial region (21 micron ), thinnest at the posterior pole (4 micron ). Anterior pole is approximately 14 micron thick.
2. Lens Epithelium It is a single layer of cells lining the anterior capsule and extends to the equatorial lens bow. Zone of epithelial cells: a. Central cells do not actively divide, they divide under pathological conditions only. b. Pre-equatorial germinal zone : cells rarely divide.
C. Germinal zone: constitute of the stem cell population. The newly formed cells from germinal zone are forced into transitional zone where they elongate and differentiate to form mass of the lens. The lens capsule regulate the transport of metabolite, nutrients and electrolytes to the lens fibers.
3. Lens substance: It constitute the main mass of the lens. It is divided intoa. Nucleus b. Cortex Nucleus: consists of (i) Embryonic nucleus (it contains primary lens fibres that are formed in lens vesicle)
(ii) Fetal nucleus: it contains embryonic nucleus and all fibres added to the lens before birth (iii) Infantile nucleus: it contains embryonic, fetal nucleus together with all the fibres added up-to the age of 4 years. (iv) Adult nucleus: composed of all fibres added before sexual maturation The nucleus consists of densely compacted lens fibres and higher refractive index than cortex.
LENS Anatomy Cortex Capsule 3 Adult Nu 4 - Infantile Nu 5 Foetal Nu 6 Embryonic Nu. 6 5 3 4 25 September 2014 11
It is located peripherally and is composed of secondary fibres formed continuously after sexual maturation. It is further divided into: Deep cortex Intermediate cortex Superficial cortex
Lens fibres contain high concentrations of crystalline. Crystalline represent the major protein of the lens (constitute 90% of total protein content of lens). Crystalline has the following constituents: Alpha Beta and, Gamma
The lens serves two major functions: Focusing of visible light rays on the fovea Accomodation Preventing damage from ultraviolet radiation by reaching the retina
Lens function and transparency is dependant on the supply of appropriate nutrient to its various structures. Metabolic needs of a adult lens is met by the aqueous and vitreous. There is continuous transport of ions into and out of the lens.
The transparency is dependent on highly organized structure of lens, dense packing of crystalline. Avascularity, absence of pigments and optimal hydration. By act of accommodation it changes focusing power. Accommodation occurs by increasing the curvature of anterior surface thereby changing refractive power of lens. Light transmission and elasticity of lens decreases with age.
Any opacity in the lens or its capsule, whether developmental or acquired is called cataract. Developmental opacities are usually partial and stationary, whereas acquired opacities are progressive. They progress until the entire lens is involved, but exceptions are well known in both types.
Classification based on Etiology Classification based on Morphology Classification based on Maturity Classification based on the Age of onset
Developmental Acquired
Hereditary Intrauterine causes o Rubella o Toxoplasmosis o CMV o Steroids
1. Age related (senile) 2. Secondary cataract (Chronic Uveitis, ACG) 3. Cataract associated with ocular diseases 4. Cataract associated with systemic diseases (pre-senile) (Diabetes, galactosemia etc) 5. Traumatic Cataract 6. Drug induced cataract (Steroids and others)
Capsular (Ant and Post) Subcapsular (Ant and Post) Nuclear Cortical
Immature Mature Hypermature Morgagnian
Congenital Infantile Juvenile Presenile Senile
Senility Sunlight (specially UV A and UV-B component) Severe Diarrheal dehydration Vitamin A,C, E deficiency Diabetes Smoking Corticosteroids Genetic
Caused by degeneration and opacification of existing lens fibres, formation of aberrant fibres or deposition of other material in their place. Factors causing disturbance of critical intra and extra-cellular equilibrium of water and electrolyte or deranges the colloid system within the fibres tends to bring about opacification.
Fibrous metaplasia of fibres (in complicated cataract) Epithelial cell necrosis (Glaucomflecken) Deposition of abnormal products of metabolism, drugs or metals.
Biochemical Processes o Hydration o Denaturation of Lens Proteins o Sclerosis
The Changes in the Epithelial Cells and the Capsule Changes in the Lenticular Fibres Sclerosis
1. Blurring of vision 2. Frequent change of glasses due to rapid change in refractive index of the lens 3. Painless, progressive gradual diminution of vision due to reduction in transparency of the lens 4. Second sight or myopic shift in case of nuclear cataract causing index myopia, improving near vision.
5. Loss or marked diminution of vision in bright sunlight or bright light beam in central posterior subcapsular cataract. 6. Monocular diplopia or polyopia in presence of cortical spoke opacities 7. Glare in posterior subcapsular cortical cataract due to increased scattering of light
8. Colored haloes around the light as seen in cortical cataract due to irregular refractive index in different parts of the lens. 9. Color shift, reds are accentuated 10. Visual field loss, generalized reduction in sensitivity due to loss of transparency
Appearance of Black Spots Reduction of Visual Fields Uni ocular Polyopia Lenticular Myopia Changes in Colour values
Chronic open angle glaucoma Macular degeneration Optic atrophy Corneal dystrophy Retinopathy associated with systemic disorders (hypertension or diabetes)
Visual Acuity Direct Distant Ophthalmoscopy (Fundal Glow) Light Reflex Slit Lamp Examination
Medical Surgical
Refraction Dark Glasses
Indications Visual Improvement Medical Indications Cosmetic Indications
Couching Intracapsular Cataract Extraction (ICCE) Extracapsular Cataract Extraction (ECCE) Phacoemulsification
Surgical Techniques Complications Management of complications
Usually unknown Maternal (and infantile) malnutrition Maternal Viral (rubella) infection Placental Haemorrhage causing deficient oxygenation Hypocalcaemia Chromosomal abnormality (Down syndrome) Metabolic disorders (galactosaemia) Dr Sanjay Shrivastava 25 September 2014 41
Informant usually parents History of white spot in pupillary area Child is usually brought with history of diminution of vision / does not recognize objects and parents Unsteady eyes Deviation of eye Associated symptoms of systemic disease, if present Dr Sanjay Shrivastava 25 September 2014 42
Diminished vision (at times it is difficult to establish in very young children) Lenticular opacity Nystagmus Deviation of eye, usually convergent squint There may be other ocular and systemic abnormalities in cases of rubella nuclear cataract Dr Sanjay Shrivastava 25 September 2014 43
I. Investigations: 1. Detailed history 2. Detailed clinical examination- visual status, intra-ocular tension, fundus examination, B scan ultrasonography to exclude posterior segment abnormality like growth/ retinoblastoma, A scan to determine axial length of the eye, retinoscopy and cover test to exclude squint. Dr Sanjay Shrivastava 25 September 2014 44
3. Laboratory investigations: A. Blood Test Blood glucose, calcium and phosphorus RBC transferase and Galactokinase levels TORCH test Hepatitis B virus Dr Sanjay Shrivastava 25 September 2014 45
B. Urine analysis: For reducing substance for galactosaemia For amino acids (to exclude Lowe syndrome in suspected cases) Dr Sanjay Shrivastava 25 September 2014 46
B. Treatment 1. Timing of surgery a. Bilateral Dense cataract by 6 weeks b. Bilateral partial if vision is not significantly affected, surgery may be delayed up to the age of 2 years or up to puberty Dr Sanjay Shrivastava 25 September 2014 47
c. Uniocular dense cataract- urgent surgery within days d. Partial Uniocular cataract- if vision is not significantly affected, surgery may be delayed up to the age of 2 years or up to puberty Dr Sanjay Shrivastava 25 September 2014 48
* Uniocular cataract if vision is affected then early surgery, preferably within first six weeks of birth with immediate fitting of contact lens. * Fixation develops between 2-4 months of age, therefore any cataract interfering with vision should be dealt before this age, and the earliest possible time is preferred * Medical/ Paediatric fitness for anaesthesia should be obtained. Dr Sanjay Shrivastava 25 September 2014 49
3. Operative procedure a. Aspiration and irrigation (ECCE) b. Lensectomy (Pars plana or anterior route) c. Aspiration and irrigation (ECCE) with primary posterior capsulotomy with partial anterior vitrectomy Dr Sanjay Shrivastava 25 September 2014 50
4. Post-operative visual rehabilitation: a. Posterior Chamber IOL (PMMA or acrylic polymer foldable lens) in patients who are more than two years in age, Uniocular cataract where contact lens fitting is not possible/ practical. b. Contact lens after surgery for uniocular cataract at very young age. Dr Sanjay Shrivastava 25 September 2014 51
c. Aphakic Spect- In bilateral cataract operated cases below the age of two years. These cases are implanted posterior chamber IOL as secondary procedure at later age. d. Occlusion therapy for treatment of amblyopia / prevention of amblyopia. Dr Sanjay Shrivastava 25 September 2014 52
Posterior capsular opacification Secondary membrane formation Proliferation of lens epithelium (Sommerring ring) Glaucoma Retinal detachment Dr Sanjay Shrivastava 25 September 2014 53
Aquired (Trauma, Large eye ball, High Myopia) Hereditary o Marfans Syndrome o Homocystinuria o Weil Marchesani Syndrome
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