Colour vision discrimination and. Colour contrast sensitivity in cataract and pseudophakia. Björn Friström and Björn L. Lundh

Transcription

1 Colour contrast sensitivity in cataract and pseudophakia Björn Friström and Björn L. Lundh Department of Ophthalmology, University of Linköping, Linköping, Sweden ABSTRACT. Purpose: To study the influence of cataract on peripheral and central colour contrast sensitivity. Methods: Peripheral and central colour contrast sensitivity was measured with a computer graphics system along the protan, deutan and tritan axes. Included were 30 patients with cataract divided into three sub-groups: cortical cataract, nuclear sclerosis and posterior subcapsular cataract. Colour contrast was measured before and after cataract operation. Results: There were significant differences in peripheral colour contrast thresholds comparing the preoperative and postoperative results. This difference existed even in patients (nω19) with a pre-operative visual acuity Ø0.5 (mean 0.6). The tritan axis was the one most affected by cataract. There was no significant difference between cataract sub-groups. Also, the central colour contrast sensitivity was affected by cataract. Again, the tritan axis was the most affected one. There was no significant difference between the cataract sub-groups. We also found large and significant differences in central colour contrast thresholds between normal subjects and postoperative values from the cataract group in all colour axes. The colour contrast sensitivity was poorer in pseudophakes than in normals. There was a difference between the three groups of different IOL material used (PMMA, acrylic and silicone). The difference was significant in the protan axis, the acrylic group having the best colour contrast sensitivity. Conclusion: Peripheral colour contrast sensitivity was affected by cataract, even when only moderately developed. This finding is of importance and should be considered when the method is used to study other eye diseases e.g. glaucoma. Central colour contrast sensitivity was also affected by cataract. The pseudophakes were found to have poorer colour contrast sensitivity than normals. The material in the IOL seemed to be of importance for colour contrast. Key words: colour contrast colour axes cataract IOL. Acta Ophthalmol. Scand. 2000: 78: Copyright c Acta Ophthalmol Scand ISSN Colour vision discrimination and contrast sensitivity deteriorate progressively with advancing age (Derefeldt et al. 1979; Roy et al. 1991). This decline in normal sensitivity with age has been explained by optical factors, e.g. senile miosis and increased density of the optical media, or by neural factors (Pinckers 1980; Elliot et al. 1990; Spear 1993; van den Berg & Ijspeert 1995; Fiorentini et al. 1996). Age related diseases, such as cataract (Rouhiainen et al. 1996) and glaucoma (Drance et al. 1981), also affect colour vision and contrast sensitivity. Evaluation of visual fields from glaucoma patients also having cataract is frequently performed in the clinic and presents a significant problem (Guthauser & Flammer 1988; Heuer et al. 1988; Wood et al. 1989; Buldenz et al. 1993; Stewart et al. 1995; Smith et al. 1997). Detecting visual field deterioration due to the glaucomatous process, distinct from the influence of cataract (or even natural ageing), is of the utmost importance in glaucoma management (Bengtsson et al. 1997; Martin 1997), as is early diagnosis of the glaucoma disease. Arden and co-workers developed a test for colour contrast sensitivity. With a computer and colour monitor system peripheral contrast sensitivity (extramacular field) or central (macular) contrast sensitivity may be examined (Arden et al. 1988a, 1988b). This test directly measures colour contrast sensitivity, which is the chromatic equivalent of spatial luminance contrast sensitivity. Luminance contrast is defined as a modulation ratio: (L max ªL min )/(L max πl min ) and luminance contrast sensitivity is the inverse of the threshold value; sensitivityω1/threshold. There is no agreement regarding definition of colour contrast. The criterion used here are those adopted by Arden and co-workers to perform this test. They used a system described by Silberstein and MacAdam (1945) to specify all colours that could be confused with a chosen colour. The loci of colours that could be confused fall within an ellipse, which can be specified by describing its major and minor axes. Arden and coworkers chose a locus in the CIE (Commission Internationale de l Eclairage) colour triangle where the two axes approximately correspond to the protan and tritan colour confusion lines. By specifying colour contrast sensitivity along protan, deutan and tritan colour axes, they could specify the properties of colour vision (Gündüz et al. 1988). The coloured gratings are low in spatial frequency so that aberrations in the eye do not affect discrimination. There are three classes of cones in retina with different spectral sensitivities (Daw & Hart 1987). The program uses the standard relative spectral sensitivity functions in calculating the outputs required for equiluminous colours of varying chromaticity. With a heterochromatic brightness matching test it is possible to adjust for each patient s relative spectral sensitivity. In this 506

2 way, isoluminant colour contrast thresholds can be obtained from patients with a normal or yellowed lens. The peripheral colour contrast sensitivity test is superior to perimetry in glaucoma screening according to Yu et al. (1991). Friström (1997), using the same test and a similar design, also found a large difference in peripheral colour contrast thresholds between normals and glaucoma patients. There was, however, no appropriate cutoff point to separate the two groups. Before the test can be adapted to glaucoma screening, influence of early stages of common diseases has to be clarified. For example, low-grade diabetes type II retinopathy has been found to affect contrast sensitivity (Friström 1998). The purpose of this study was to evaluate the influence of cataract on peripheral and central colour contrast sensitivity. Methods Test system and procedures Peripheral and central colour contrast sensitivity was measured with the system previously described by Arden et al. (1988a, 1988b) and Yu et al. (1991). The colours were displayed on a Nec Multi Sync 6 FG monitor with a dot pitch of 0.28 mm driven by a computer (Intel DX processor) containing a graphics card (TSL 206 with 24-bit palette) and a software graphics program. At the resolution we used, pixels, the card has a refresh rate of 90 Hz. All colours were specified in terms of the Commission Internationale d Eclairage XYZ stimulus values and could be varied along a protan, deutan or tritan colour confusion line. Calibration of the system was performed before every test period using an internal auto-calibration program (with a photocell attached to the monitor screen). The patients were positioned in a chin rest with one eye patched. The cornea of the tested eye was at a distance of 52 cm from the monitor screen for the peripheral test and at a distance of 100 cm for the central test. During the peripheral test, the patients were instructed to look at the fixation point at the centre of the screen and a closed circuit television camera was placed below the monitor to check the fixation. The patients own distance correction spectacles were used for the central test. No glass correction was used for the peripheral test unless the refractive error of the tested eye was outside the range π2 D- ª4D. If this range was exceeded, we corrected according to the error, but did not add any correction for the 52 cm distance. Initially, the relative spectral sensitivity of each patient was obtained by a heterochromatic flicker brightness match performed by the patient. The colour test system automatically adjusts its output according to the individual variations in order to produce equiluminous colours during the following test procedures. For the central test, a letter was presented in the centre of the screen. One of nine specific letters of standard optotype was displayed, subtending a visual angle of 3æ. During the peripheral test, a colour contrasting annulus concentric with the fixation spot was shown to the patient. The annulus had a radius of 12.5æ in the extramacular field and a width of 1æ of arc. During the test, a sector of the annulus, 45æ in size, was removed in either the upper right, the upper left, the lower left or the lower right quadrant. The patient was asked to identify this quadrant while still fixating the central fixation point. The letter or the annulus appeared on the screen for 200 ms every second and was a mixture of the two colours of which the background was composed. When the colour contrast was 0%, the letter or the annulus had the same hue as the background, and when the colour contrast was 100%, the difference to the background was at its maximum along that colour axis. The threshold was determined by a modified binary search scheme (Arden et al. 1991) which made the test relatively quick to perform. Patients Colour contrast thresholds were obtained from 30 patients before and after cataract extraction. Patients with diabetes were excluded, as were patients with other known eye diseases. Patients with soft Table 1. Demographic and clinical characteristics (Means SD). V.A. V.A. Number Age M/F pre-op. post-op. Total Cat Group / Cortical / Nuclear sclerosis / Subcaps/nuclear sclerosis / Normal subjects /19 Visual acuity M/FΩMale/Female, V.A.ΩVisual acuity. drusen were also excluded, since it has been shown that soft drusen affects colour contrast (Frennesson et al. 1995). Patients with very mild macular pigmentary changes were not excluded, however. Patients with postoperative visual acuity 0.7 were excluded. Our aim was to recruit 10 patients to each of three cataract groups: 1. Cortical cataract, 2. Nuclear sclerosis, 3. Posterior subcapsular cataract. However, the majority of subjects in the third group were also found to have a certain degree of nuclear sclerosis. The demographic and clinical characteristics of the patients can be seen in Table 1. Clinical examinations including visual acuity, tonometry, biomicroscopy of the fundus, slit-lamp examination, slit-lamp photography of the lens and colour contrast sensitivity test were performed preoperatively. Most patients selected, had a moderately reduced visual acuity. The lowest preoperative visual acuity to be included was 0.1. One to four months after surgery, the patients were re-examined with the same tests but were not slit-lamp photographed. Surgery was performed with the phacoemulsification technique and all eyes had a posterior chamber lens implanted. The IOL material was silicone (nω6), acrylic (nω7) or PMMA (nω17). The choice of IOL was not dictated by the study design, but left to the decision of the cataract surgeon for each patient. To evaluate the heterochromatic flicker brightness match test in patients with clinically significant cataract, we recruited five other cataract patients. For these five patients, two central colour contrast sensitivity tests were performed. The first one was carried through after completing the initial calibrating heterochromatic flicker brightness match test by the patient, and the second one after calibration by the assistant. The assistant was a female of 31 years of age, with no eye disease and normal colour vision (Standard Pseudoisochromatic Plates: SPP1 and SPP2, Igaku-Shoin, Tokyo). 507

3 Normal contrast threshold reference values for the method were obtained earlier at the department. The study was approved by the Ethics Committee of the Medical Faculty of Linköping University. The patients were included only after informed consent was obtained. Student s t-test of paired data (twotailed) was used for evaluation of differences before and after cataract operation within groups. ANOVA followed by Scheffé s F-test for multiple comparison was used for evaluation of differences between groups (significance level 5%). Results Peripheral colour contrast thresholds The results are presented in Table 2. There are large and highly significant dif- ferences in all colour axes in the pooled cataract group. There are also significant differences in colour contrast thresholds before and after cataract operation in all cataract sub-groups and all axes except the protan and deutan axes in the nuclear sclerosis group. The largest difference was obtained in the tritan axis in the subcaps/ nuclear sclerosis group (43.9 percentage units, p ). Although rather large differences between cataract groups were obtained, there was no significance in the ANOVA analysis. 19 patients, found in all three sub-groups, had a preoperative visual acuity Ø0.5. Mean visual acuity for the group was 0.6. Even in this group, all colour axes were found to be significantly affected. Again, the largest difference was found in the tritan axis (mean diff percentage units, p ). Comparing colour axes in the pooled cataract group, the largest difference preoperatively postoperatively was obtained in the tritan axis. ANOVA analysis showed significant differences between the protan and tritan axes (mean diff percentage units, pω0.0001) and between the deutan and the tritan axes (mean diff percentage units, p ). Central colour contrast thresholds The results are presented in Table 3. There were large and significant differences in all colour axes in the pooled cataract group. There were also significant differences in colour contrast thresholds before and after cataract operation in all cataract sub-groups. The largest differences were obtained in the nuclear sclerosis group (diff percentage units, p ) and the subcaps/nuclear sclerosis group (diff percentage units, p ), again in the tritan axis. There Table 2. Peripheral colour contrast thresholds SD (%) before and after cataract surgery. Protan axis Deutan axis Tritan axis Preop Postop Preop Postop Preop Postop Total group, cat group (nω30) Diff: 12.4 (p ) Diff: 11.8 (pω0.0003) Diff: 33.4 (p ) Cortical cat (nω10) Diff: 12.1 (pω0.0085) Diff: 17.8 (pω0.0012) Diff: 22.7 (p ) Nuclear sclerosis (nω9) Diff: 7.3 (pω0.069) Diff: 2.4 (pω0.54) Diff: 32.4 (pω0.01) Subcaps nucl. scl. Diff: 16.9 (pω0.0094) Diff: 14.0 (pω0.035) Diff: 43.9 (p ) (nω11) Cat. VØ0.5 (nω19) Diff: 9.3 (pω0.0003) Diff: 7.8 (pω0.04) Diff: 29.4 (p ) Cat.Ωcataract. VΩvisual acuity. DiffΩdifference between preoperative and postoperative values. Statistical evaluation: Student s t-test of paired data. Table 3. Central colour contrast thresholds SD (%) before and after cataract surgery and in normal subjects with no surgery. Protan axis Deutan axis Tritan axis Preop Postop Preop Postop Preop Postop Total group, cat Group (nω30) Diff: 10.2 (pω0.0004) Diff: 9.6 (p ) Diff: 41.0 (p ) Cortical cat (nω8) Diff: 10.8 (pω0.003) Diff: 8.8 (pω0.012) Diff: 36.3 (pω0.0003) Nuclear-sclerosis (nω9) Diff: 3.8 (pω0.036) Diff: 5.8 (pω0.016) Diff: 43.0 (p ) Subcaps Nucl.scl. (nω11) Diff: 15.1 (pω0.026) Diff: 13.4 (pω0.013) Diff: 42.9 (p ) Normals (nω27) CatΩcataract, DiffΩdifference between preoperative and postoperative values. Statistical evaluation: Student s t-test of paired data. 508

4 Table 4. Central colour contrast thresholds SD (%) from patients in the pooled cataract group after cataract surgery and grouped after the material in the intraocular lens. Protan axis Deutan axis Tritan axis PMMA (nω17) Acrylic (nω7) Silicone (nω6) Difference in protan axis: PMMA-AcrylicΩ9.2 (pω0.026), Silicone-AcrylicΩ13.5 (pω0.007) Statistical evaluation: ANOVA Scheffé. Table 5. Peripheral and central colour contrast tresholds SD (%) for the protan, deutan and tritan colour axes obtained after the heterochromatic flicker brightness match was performed by the patient or by the assistant. Peripheral contrast Flicker by patient Flicker by assistant Central contrast Flicker by patient Flicker by assistant Protan (nω5) Diff: 2.6 (NS) Diff: 10.3 (NS) Deutan (nω5) Diff: 1.8 (NS) Diff: 6.0 (NS) Tritan (nω5) Diff: 5.9 (NS) Diff: 0.4 (NS) NSΩnot significant (Student s t-test paired data). Mean ageω72.4, Mean visual acuityω0.44. was no significant difference between cataract sub-groups in the ANOVA analysis. There were large differences between colour axes. ANOVA analysis showed significant differences between the protan and the tritan axes (mean diff percentage units, p ) and between the deutan and the tritan axes (mean diff percentage units, p ). Also, there were large differences between normal subjects and postoperative values from the pooled cataract group in all colour axes. In the protan axis, the difference was 9.7 percentage units, p , in the deutan axis 10.5 percentage units, pω and in the tritan axis 6.0 percentage units, pω In the pooled cataract group, 18 patients had a postoperative visual acuity of 1.0. The means for this group were for the protan axis 13.2, for the deutan axis 13.3 and for the tritan axis 14.7 percentage units. When comparing the normal subjects and these 18 patients, there were still significant differences in all axes. For the protan axis, the difference was 7.0 (p ), for the deutan axis 6.5 (p ) and for the tritan axis 4.1 (pω0.0065) percentage units. Table 4 shows the postoperative central colour contrast thresholds from all patients divided into three groups according to the material in the IOL used in each patient. The acrylic group had the lowest colour contrast thresholds in all colour axes. In the protan axis, the difference was significant when comparing the acrylic group and the PMMA group (9.2 percentage units, pω0.026) and also when comparing the acrylic group and the silicone group (13.5 percentage units, pω0.007). Heterochromatic flicker brightness match Table 5 shows peripheral and central colour contrast thresholds obtained after the heterochromatic flicker brightness match had been performed by the patient or by the assistant. The test was performed on five patients with cataract with a mean age 72.4 years and a mean visual acuity There was no significant difference in colour contrast when the heterochromatic flicker brightness match was performed by the assistant or by the patients. Discussion The most important effect of cataract on the optical system of the eye is light scattering. Forward light scattering (light scattered towards the retina) accounts for reduced contrast sensitivity, reduced visual acuity and glare. There are mainly three morphological types of senile cataract: cortical, nuclear, and posterior subcapsular, although mixtures are common. Different types of early cataract have been shown to influence contrast sensitivity at different spatial frequencies. Cortical opacities reduced contrast sensitivity at high spatial frequencies and posterior subcapsular opacities at low and medium spatial frequencies (Rouhainen et al. 1996). Moss et al. (1995) found that a posterior subcapsular cataract affected the blue-on-yellow automated perimetry most, while the white-on-white was more sensitive to anterior cortical cataract. This difference could be explained on the basis of pupil size. At the high bowl luminance used for the blue-on-yellow stimulus, the pupil will constrict and this may well have a greater effect on the posterior subcapsular cataract. At lower background luminances, a larger pupil will invite peripheral opacities to produce maximal effect. In our study, we found no significant differences in central or peripheral colour contrast sensitivity between the different types of cataract. The tritan axis was the most affected one in both the central and peripheral colour contrast test, and this difference is significant when comparing the tritan axis with the protan and deutan axes. This result was expected, as the cataractous lens cuts out the shorter wavelengths, acting like a yellow filter. There were large and significant differences for all colour axes for both peripheral and central colour contrast in the pooled cataract group when comparing the preoperative and postoperative results. These differences also existed when studying the 19 patients with visual acuity Ø0.5 separately (Table 2). The system used to measure colour contrast assesses each patient s relative spectral sensitivity with the heterochromatic flicker brightness match test. This means that the apparatus automatically adjusts its output to inter-individual variations manifested in this match, and isoluminant colour contrast can be obtained for those patients who have a yellowed lens (Arden et al. 1988b). More advanced cataracts will produce a further decrease in retinal illumination and the adjustment from the match test is probably of limited value for this group of patients. In a small group of patients with cataract (nω5) and mean visual acuity 0.44, we found small and non-significant differences in colour contrast obtained after the heterochromatic flicker brightness match test was performed by the patient or by the assistant. These facts are of importance if 509

5 the peripheral colour contrast test is used in glaucoma screening. Such screening will not only detect the glaucomas but also indicate abnormality in patients with cataract. Not only the mature cataracts will be detected but also those with moderate influence on visual acuity. Jay et al. (1982) examined colour perception in pseudophakia with the Farnsworth-Munnsell 100-hue test and found that IOL patients had significantly poorer scores compared to normals. Using the same test, Harper et al. (1988) and Mäntyjärvi et al. (1997) found no difference between normals and pseudophakes. Instead, in anomaloscope testing, Mäntyjärvi et al. (1997) found a better blue colour sensitivity in the IOL eyes than in normal phakic eyes. In our study, central colour contrast sensitivity was poorer in pseudophakic patients than in normal subjects. The difference was significant for all colour axes, but was least pronounced in the tritan axis. This is in agreement with the results from Knowles et al. (1996). The reason for the reduced colour contrast sensitivity in pseudophakes is not clear. Photochemical retinal damage from the operating microscope (Jampol et al. 1985) or increased short-wavelength light transmission through the intraocular lens (Werner & Hardenberg 1983) has been suggested. These theories seem less plausible today. The operating microscope we used has a UV blocking filter, and for all IOL lenses used, the manufacturers claim that there is effective absorption of the ultraviolet light. Another possibility is postoperative cystoid macular oedema. No clinical macular oedema was found at the postoperative examination in any of the patients included in our study, but a high incidence of low grade macular oedema can be found (62.5%) when performing fluorescein angiography (Menchini et al. 1993). Mäntyjärvi & Tuppurainen (1997) found that luminance contrast sensitivity was significantly worse in pseudophakes than in normal eyes. They also found a significant difference between the PMMA lens and the silicone lens in 10 patients with a silicone IOL in one eye and a PMMA in the other. The contrast sensitivity was slightly better in the eyes with silicone IOL. In our study, we found significant differences in colour contrast sensitivity between groups with different types of IOL. This suggests that the material used in the IOL (or possibly the design?) could influence the colour contrast sensitivity. This will be investigated further in a larger study. Acknowledgements The present investigation was supported by the Research Foundation of Östergötland County Council and by the Swedish Medical Research Council (Project K99-73X A). References Arden GB, Gündüz K & Perry S (1988a): Color vision testing with a computer graphics system: preliminary results. Doc Ophthalmologica 69: Arden GB, Gündüz K & Perry S (1988b): Color vision testing with a computer graphics system. Clin Vision Sci 2: Arden GB, Berninger T, Hogg CR & Perry S (1991): A survey of color discrimination in German ophthalmologists. Ophthalmology 98: Bengtsson B, Lindgren A, Heijl A, Lindgren G, Åsman P& Patella M (1997): Perimetric probability maps to separate change caused by glaucoma from that caused by cataract. Acta Ophthalmol Scand 75: van den Berg TJTP & Ijspeert JK (1995): Light scattering in donor lenses. Vision Res 35: Budenz DL, Feuer WJ & Andersson DR (1993): The effect of simulated cataract on the glaucomatous visual field. Ophthalmology 100: Daw NW & Hart WM (1987): Adler s Physiology of the eye, 8th edn., edited by Moses RA and Hart WM, Mosby, St Louis. Derefeldt G, Lennerstrand G & Lundh B (1979): Age variations in normal human contrast sensitivity. Acta Ophthalmol (Copenh) 57: Drance SM, Lakowski R, Schulzer M & Douglas GR (1981): Acquired color vision changes in glaucoma. Arch Ophthalmol 99: Elliot D, Withaker D & Mac Veigh D (1990): Neural contribution to spatiotemporal contrast sensitivity decline in healthy ageing eyes. Vision Res 30: Fiorentini A, Porciatti V, Morrone MC & Burr DC (1996): Visual ageing: unspecific decline of the responses to luminance and colour. Vision Res 36: Frennesson C, Nilsson UL & Nilsson SEG (1995): Colour contrast sensitivity in patients with soft drusen, an early stage of ARM. Doc Ophthalmol 90: Friström B (1997): Peripheral colour contrast thresholds in ocular hypertension and glaucoma. Acta Ophthalmol Scand 75: Friström B (1998): Peripheral and central colour contrast sensitivity in diabetes. Acta Ophthalmol Scand 76: Gündüz K, Arden GB, Perry S, Weinstein GW & Hitchings RA (1988): Color vision defects in ocular hypertension and glaucoma quantification with a computer-driven color television system. Arch Ophthalmol 106: Guthauser U, Flammer J (1988): Quantifying visual field damage caused by cataract. Am J Ophthalmol 106: Harper RA, Kirkness CM & Jay B (1988): Colour discrimination in Pseudophakia. Eye 2: Heuer DK, Anderson DR, Knighton RW, Feuer WJ & Gressel MG (1988): The influence of simulated light scattering on automated perimetric threshold measurements. Arch Ophthalmol 106: Jampol LM, Kraff C, Sanders DR, Alexander K & Lieberman H (1985): Near-UV radiation from the operating microscope and pseudophakic cystoid macular edema. Arch Ophthalmol 103: Jay JL, Gautam VB & Allan D (1982): Colour perception in pseudophakia. Br J Ophthalmol 66: Knowles PJ, Tregear SJ, Ripley LG & Casswell AG (1996): Colour vision in diabetic and normal pseudophakes is worse than expected. Eye 10: Martin L (1997): Cataract and high-pass resolution perimetry. Acta Ophthalmol Scand 75: Menchini U, Bandello F, Brancato R, Camesasca FI & Galdini M (1993): Cystoid macular oedema after extracapsular cataract extraction and intraocular lens implantation in diabetic patients without retinopathy. Br J Ophthalmol 77: Moss ID, Wild JM & Whitaker DJ (1995): The influence of age-related cataract on blue-onyellow perimetry. Invest Ophthalmol Vis Sci 36: Mäntyjärvi M, Syrjäkoski J, Tuppurainen K & Honkonen V (1997): Colour vision through intraocular lens. Acta Ophthalmol Scand 75: Mäntyjärvi M & Tuppurainen K (1997): Contrast sensitivity in patients with silicone intraocular lenses. Ophthalmologica 211: Pinckers A (1980): Color vision and age. Ophthalmologica 181: Rouhiainen P, Rouhiainen H & Salonen JT (1996): Contrast sensitivity in different types of early lens opacities. Acta Ophthalmol Scand 74: Roy MS, Podgor MJ, Collier B & Gunkel RD (1991): Color vision and age in a normal North American population. Graefe s Arch Clin Exp Ophthalmol 229: Silberstein L & MacAdam DL (1945): The distribution of color matchings around a color center. J Opt Soc Am 35: Smith SD, Katz J & Quigley HA (1997): Effect of cataract extraction on the results of automated perimetry in glaucoma. Arch Ophthalmol 115: Spear PD (1993): Neural bases of visual defi- 510

6 cits during ageing. Vision Res 33: Stewart WC, Rogers GM, Crinkley CMC & Carlson AN (1995): Effect of cataract extraction on automated fields in chronic open-angle glaucoma. Arch Ophthalmol 113: Werner JS & Hardenbergh FE (1983): Spectral sensitivity of the pseudophakic eye. Arch Ophthalmol 101: Wood JM, Wild JM, Smerdon DL & Crews SJ (1989): Alterations in the shape of the automated perimetric profile arising from cataract. Graefe s Arch Clin Exp Ophthalmol 227: Yu TC, Falcao-Reis F, Spieleers W& Arden GB (1991): Peripheral color contrast, a new screening test for preglaucomatous visual loss. Invest Ophthalmol Vis Sci 32: Received on December 13th, Accepted on March 26th, Corresponding author: Björn Friström, MD Department of Ophthalmology University of Linköping S Linköping, Sweden Tel: π Fax: π