Red-green Defects Research Articles

A study of nonglaucomatous optic neuropathies in a teaching hospital in Western Maharashtra

Background: Nonglaucomatous optic neuropathy (NGON) is defined as clinical evidence of optic nerve impairment without glaucomatous field/disc changes. Etiology is diverse and elusive in many patients. Causes of NGON include traumatic, compressive, inflammatory, demyelinating, toxic, nutritional, hereditary, vascular, infiltrative, and idiopathic. NGON disorders can be misdiagnosed as glaucoma and can be preventable or life-threatening. In some, fellow eye involvement is common. This can lead to inadequate management and influence prognosis which can be prevented by multispecialty approach. Physicians and ophthalmologists must be vigilant against threatening NGON forms. It is essential to track burden as most literature focused on particular NGON subtype. Aim: The aim was to study the clinical presentation of NGON in a teaching hospital. Setting and Design: This was a prospective, hospital-based, cross-sectional, observational study. Materials and Methods: A total of 86 eyes of 61 NGON patients were studied from January 2021 to June 2022 in a tertiary care hospital. Detailed history and comprehensive ophthalmic examination were performed in ambulatory patients. Nonambulatory patients were examined using torchlight. Ancillary investigations were performed, to confirm the clinical diagnosis wherever applicable. Statistical Analysis: Microsoft Excel was used for statistical analysis. Results: The mean age of study patients was 44.87 ± 16.05 years with a male: female ratio of 2.8:1. Unilateral eye involvement was seen in 36 (59.02%). Best-corrected visual acuity = 3/60–1/60 was noted in 41 (47.67%) patients. Red-green defect and contrast sensitivity were reduced by 59.30% and 66.28%, respectively. Relative afferent pupillary defect (RAPD) was noted in 52.46% of patients with Grade 5 RAPD in 40.63%. The most common visually evoked potential type and visual field defect noted were axonal and central scotoma (n = 31 [36.05%] and n = 26 [30.23%]), respectively. Traumatic optic neuropathy was diagnosed in 15 (24.59%) followed by inflammatory optic neuritis in 11 (18.04%) patients. Conclusion: Diagnosing cause of NGON in clinical practice is challenging, but emerging burden cannot be neglected. Knowledge of various NGON types helps narrow differential diagnoses and execute efficient, targeted workup. Timely recognition alters visual, neurological prognosis and saves the lives of patients sometimes.

The Impact of Colour Vision Defect on Consumer’s Fruits Selection Process while Purchasing from Retail Fruit Shops in Bangladesh

Color Vision Defect affects about one in twelve males and two hundred women worldwide, according to research. CVD has a big impact in almost every marketing and branding circumstance, especially when product color is the key. This study began with a Red-Green CVD test of 522 Dhaka residents. Since few research have measured color blindness in Bangladesh, this study can be used as one of the Bangladesh color vision deficiency baseline results. The important factor of this study is whether this result is comparable to Bangladesh’s earlier result and whether Bangladesh has a lower/higher CVD prevalence than other nations. The most common CVD is Red-Green Colour Vision Defect. Green fruits turn yellow and red when maturing and CVD patients have trouble distinguishing neighboring colours like Red, Green, Brown, etc. After examining baskets of green and ripe yellow, red, and partly reddish fruits, this study evaluated the findings. This study found out that people with color vision defects had trouble choosing fruits from baskets. Furthermore, the study tested hypotheses to determine severity of Red-Green CVD and found out it to be less than expected probably due to coping mechanism, experience etc. in Red-Green CVD subjects.

Optical Coherence Tomography Angiography Parameters of the Retina in SARS-CoV-2 Recovered Subjects.

This study aims to evaluate retinochoroidal optical coherence tomography angiography (OCTA) parameters in patients recovered from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This studywas an observational study that included 80 subjects being discharged after having negative reports on the reverse transcription-polymerase chain reaction (RT-PCR) test for SARS-CoV-2 to evaluate OCTA parameters of the retina. The subjects underwent an ophthalmic evaluation that included best-corrected visual acuity (BCVA), intraocular pressure (IOP), color vision (CV), contrast sensitivity (CS), and optical coherence tomography (OCT) parameters. OCTA was done for all patients and was evaluated for foveal avascular zone (FAZ) area, perimeter, and circularity index, and vessel density (VD) in superficial capillary plexus (SCP), deep capillary plexus (DCP), outer retina (OR), outer retina chorio-capillaries (ORCC), chorio-capillaries (CC), and choroid (C) using 3 x 3 mm scans. The OCTA parameters were compared with normative data of the Indian population for various parameters in question. The subjects included 54/80 (67.5%) males and 26/80 (32.5%) females having a mean age of 52.40 ± 15.71 (18-60) years. The systemic evaluation revealed 38.75% of subjects had hypertension, 30% had diabetes, 20% had kidney disease, 5% had tuberculosis, and 3.75% had coronary artery disease.The mean distance BCVA was logarithm of the minimum angle of resolution (LogMAR) (1.17 ± 0.22), mean IOP was 17.0 ± 4.0 mmHg, mean CS was 2.13 ± 0.36, 50.62% of subjects had normal CV on Farnsworth test while 47% had tritanopia, and none of the subjects had red-green CV defect on Ishihara plates. The OCT scan was normal in 90% of eyes while the posterior vitreous detachment was seen in 4% of eyes, broad vitreomacular adhesion in 2.5% of eyes, and the globally adherent epiretinal membrane was seen in 2.5% of eyes. The mean central macular thickness (CMT) measured 245.14 ± 28.41 micrometers. The mean FAZ area measured 0.37 ± 0.15 mm2, the perimeter was 3.28 ± 1.08 mm, and the circularity index measured 0.41 ± 0.10. The average VD in SCP measured 16.06 ± 12.29, in DCPmeasured 9.11 ± 8.75, in ORmeasured 6.38 ± 7.37, in ORCC measured 42.53 ± 12.46, in CCmeasured 25.83 ± 16.31, and in C measured 25.52 ± 17.49. The VD in coronavirus disease 2019 (COVID-19) subjects was significantly lesser than that in the healthy Indian population in all layers except ORCC. The SARS-CoV-2 recovered subjects have a reduced VD in retinochoroidal layersfrom COVID-19, an underlying systemic disease, or both. The CS values fall within normal limits. Several subjects show tritanopia on the Farnsworth test but no red-green CV defect on Ishihara plates.

A model for assessing the efficacy of colour vision aids.

Optical filter aids are marketed which claim to improve colour discrimination in red-green colour vision defectives. An earlier model has been revised and used to assess 9 currently available aids. Spectral reflectances (400-700 nm) for 80 colours equally spaced in hue angle at four equally spaced saturations were synthesised from chromatically adjacent Munsell colours. Aid induced chromaticity changes for Protanomals and Deuteranomals were calculated. Five aids enhanced red-green discrimination significantly for Protanomals and six for Deuteranomals and one aid reduced it significantly for both defectives. Five aids enhanced blue-yellow discrimination in Protanomals and Deuteranomals for whom it is not needed.

Evaluation of the Third edition of the City University Colour Vision Test.

The 3rd edition of the City University Colour Vision Test (CUT) was originally based on the Farnsworth-Munsell D-15 test (D15). The first part of the test is for detecting a defect, and the second part is used to diagnose the type and severity of the defect. This study evaluates the CUT 3rd edition relative to the Ishihara and the D15 colour vision tests. Fifty nine colour vision normal subjects and 60subjects with a congenital red-green colour vision defect were recruited. Subjects were tested with the Ishihara and CUT tests. Subjects who failed the Ishihara also performed the D15 test. The agreement between the Ishihara and CUT screening plates was marginally higher when using the CUT failure criterion of >1 error compared with using >2 errors. If the diagnostic plates were included with the screening plates in determining the pass/fail outcomes, the agreement between the Ishihara and CUT was high, with a first-order agreement coefficient (AC1) of 0.90. The AC1 coefficient agreement between the D15 and CUT diagnostic plates in terms of pass/fail was 0.81 when using the D15 failure criteria of >1 or >0 crossing. The level of agreement between the 3rd edition of the CUT and D15 was lower than the 2nd edition of the CUT. The primary reason for the lower agreement of the 3rd edition of the CUT was that it had a lower specificity relative to the D15 compared to the 2nd edition. Although the CUT predictive value for failing the D15 is over 90%, the predictive value for passing shows that 19%-25% of patients who pass the 3rd edition of the CUT test will fail the D15. The 3rd edition tends to misclassify protans as deutans or cannot classify the type of defect relative to the D15 and Ishihara.

Cerebral visual impairment‐related vision problems in primary school children: a cross‐sectional survey

To estimate how many children in mainstream primary schools have cerebral visual impairment (CVI)-related vision problems and to investigate whether some indicators might be useful as red flags, if they were associated with increased risk for these problems. We conducted a survey of primary school children aged 5 to 11years, using whether they were getting extra educational help and/or teacher- and parent-reported behaviour questionnaires to identify children at risk for CVI. These and a random 5% sample were assessed for CVI-related vision problems. We compared the usefulness of potential red flags using likelihood ratios. We received questionnaires on 2298 mainstream-educated children and examined 248 children (152 [61%] males, 96 females [39%]; mean age 8y 1mo, SD 20mo, range 5y 6mo-11y 8mo). We identified 78 out of 248 children (31.5% of those examined, 3.4% of the total sample), who had at least one CVI-related vision problem. The majority (88%) were identified by one or more red flag but none were strongly predictive. Fewer than one in five children with any CVI-related vision problem had reduced visual acuity. Children with CVI-related vision problems were more prevalent than has been appreciated. Assessment of at-risk children may be useful so that opportunities to improve outcomes for children with CVI-related vision problems are not missed.

The burden of color vision defect in Nepal – an iceberg phenomenon

Background: Color vision tests are routinely performed and are mandatory in most part of the world. However, in Nepal and many other developing countries, color vision may often be overlooked. We evaluated a possible burden of color vision in a group of patients who were specifically evaluated for a color vision defects. This study evalutes the awareness of color vision defect among the patients evaluated and highlights the importance of the color vision evaluation.
 Methods: A sequential group of 73 people from August to September 2017 specifically evalu­ated for color vision defect for recruitment of government employment were evaluated. Ishi­harapseudo-isochromatic plates and Farnsworth-Munsell Dichotomous D-15 test were used for screening. Mean and Standard deviation were used for descriptive analysis of the data.
 Results: Fifty-seven were male and sixteen were female. The mean age was 23 years (SD ± 3.7). On evaluation of the color vision defect, 9 (12.3%) were found to have total color vision defect (achromatopsia), 3 (4%)-red-green defect and 1(1%) with blue red defect. None of the patients had undergone color vision test at eye hospital previously. There were 4 patients who were registered drivers who had color vision defect.
 Conclusions: Color vision is an important part of the vision. It should not be ignored.All of the patients evaluated were found to be unware of their condition. Early detection of color vision defects in individuals, if possible, at school level can help them to determine their careers and future endeavors at early stage.

THE BURDEN OF COLOR VISION DEFECT IN NEPAL – AN ICEBERG PHENOMENON

Background: Color vision tests are routinely performed and are mandatory in most part of the world. However, in Nepal and many other developing countries, color vision may often be overlooked. We evaluated a possible burden of color vision in a group of patients who were specifically evaluated for a color vision defects. This study evalutes the awareness of color vision defect among the patients evaluated and highlights the importance of the color vision evaluation.
 Methods: A sequential group of 73 people from August to September 2017 specifically evalu­ated for color vision defect for recruitment of government employment were evaluated. Ishi­harapseudo-isochromatic plates and Farnsworth-Munsell Dichotomous D-15 test were used for screening. Mean and Standard deviation were used for descriptive analysis of the data.
 Results: Fifty-seven were male and sixteen were female. The mean age was 23 years (SD ± 3.7). On evaluation of the color vision defect, 9 (12.3%) were found to have total color vision defect (achromatopsia), 3 (4%)-red-green defect and 1(1%) with blue red defect. None of the patients had undergone color vision test at eye hospital previously. There were 4 patients who were registered drivers who had color vision defect.
 Conclusions: Color vision is an important part of the vision. It should not be ignored.All of the patients evaluated were found to be unware of their condition. Early detection of color vision defects in individuals, if possible, at school level can help them to determine their careers and future endeavors at early stage.

Genetic Testing as a New Standard for Clinical Diagnosis of Color Vision Deficiencies.

PurposeThe genetics underlying inherited color vision deficiencies is well understood: causative mutations change the copy number or sequence of the long (L), middle (M), or short (S) wavelength sensitive cone opsin genes. This study evaluated the potential of opsin gene analyses for use in clinical diagnosis of color vision defects.MethodsWe tested 1872 human subjects using direct sequencing of opsin genes and a novel genetic assay that characterizes single nucleotide polymorphisms (SNPs) using the MassArray system. Of the subjects, 1074 also were given standard psychophysical color vision tests for a direct comparison with current clinical methods.ResultsProtan and deutan deficiencies were classified correctly in all subjects identified by MassArray as having red–green defects. Estimates of defect severity based on SNPs that control photopigment spectral tuning correlated with estimates derived from Nagel anomaloscopy.ConclusionsThe MassArray assay provides genetic information that can be useful in the diagnosis of inherited color vision deficiency including presence versus absence, type, and severity, and it provides information to patients about the underlying pathobiology of their disease.Translational RelevanceThe MassArray assay provides a method that directly analyzes the molecular substrates of color vision that could be used in combination with, or as an alternative to current clinical diagnosis of color defects.

Defects of colour vision: A review of congenital and acquired colour vision deficiencies

Colour vision deficiencies (CVDs) can be categorised as being congenital or acquired. Some CVDs are already present at birth, as inherited conditions that are the result of changes at the photo-pigment level and are non-pathological, incurable and do not change over time. Examples are red-green defects which are inherited as an X-linked recessive trait. Acquired CVD develops secondary to ocular and systemic conditions or as a side effect of certain medications or sometimes toxic effects of chemicals, and trauma and ageing can also be important in some CVDs.

Comparison of Panel D-15 Tests in a Large Older Population

To determine the frequency and type of color vision defects in a large group of randomly selected older people using two versions of the D-15 and to examine the agreement between the two tests. The Adams desaturated D-15 test was administered under Illuminant C (MacBeth lamp, ∼ 100 lux) to a group of 865 individuals aged 58 to 102 years (mean, 75.2 ± 9.1 years). No exclusion criteria, other than the reported presence of a congenital color defect, were applied. Testing was binocular with habitual near correction. If any error was made on this test, the Farnsworth D-15 was administered under identical conditions. On both tests, a color confusion score of 30 or higher was considered failing, and for those failing the test, color defect type (blue-yellow, red-green, or nonselective) was determined using the method of Vingrys and King-Smith (1988). The majority (60.8%) of the people tested passed both tests. For the sample as a whole, the failure rates of the Adams desaturated D-15 and the Farnsworth D-15 were 36.2% and 20.76%, respectively. As expected, for both tests, failure rate increased markedly with age. Among those who failed both tests, 17.5% of the population, the proportion of specific agreement for red-green and blue-yellow defects was high, 88%. The vast majority of those failing either or both tests had blue-yellow defects, in agreement with previous studies. Blue-yellow defects were quite common among the aged, becoming increasingly prevalent with increasing age. More people failed the Adams desaturated D-15 than the Farnsworth D-15, but among those who failed, the proportion of blue-yellow defects was similar for the two tests, approximately 75%. The agreement between the two tests in identifying acquired red-green and blue-yellow errors was high.

Trichromatic and Dichromatic Relative Sensitivity to Green Light in a Mild Hypoxic Environment

Several studies have reported that individuals with normal color vision have a relative decrease in sensitivity to green light in hypoxic environments approximating altitudes above 4000 m. Because there is little available information describing the effects of mild hypoxic environments (less than 4000 m) in subjects with deficient color-vision, we examined the effect of mild hypoxia on the relative sensitivity to green light for color-normal and color-deficient subjects. Relative sensitivity to the green light was measured using the Medmont C-100 at ground and 3780 m in an altitude chamber. There were 30 subjects, 13 with normal color vision and 17 with a congenital red-green defect, who participated in the study. The relative sensitivity to the green light was determined from the average of four settings measured during the 4.5-h trial. Color-normals and anomalous trichromats showed a small decrease in the relative sensitivity to the green light at 3780 m compared to ground. In contrast to the trichromatic results, the relative sensitivity of the dichromats to the green light did not differ between 3780 m and ground. Our results show that a decrease in the relative sensitivity to green light can occur in hypoxic environments that are equivalent to altitudes greater than 3700 m in individuals with trichromatic but not dichromatic color vision. Although the change in sensitivity was significant, it was small and unlikely to have any operational impact.

S.P.62 Ocular characteristics of Duchenne Muscular Dystrophy

<h2>Abstract</h2> Electroretinogram (ERG) abnormalities have been described in Duchenne Muscular Dystrophy (DMD). Short isoforms of dystrophin are highly expressed in retina. We sought to expand the retinal phenotypes associated with different DMD genotypes. We studied the ocular characteristics of 16 DMD boys, mean age 9.5years (range 4–15years), glucocorticosteroid (GC) treated, with a range of genotypes: six had mutations at the 5′ end of the gene involving exons 3–13, predicted to affect the full length dystrophin Dp427, seven patients exons 44–57, affecting Dp427 and Dp260, and three patients at the 3′ end, in exon 70, affecting expression of Dp427, Dp260 and Dp71. Visual acuity, colour vision, intra-ocular pressure measures (IOP) and full field ganzfeld flash ISCEV Electroretinograms (ERGs) were assessed. Patients had normal visual acuity, one boy had a red-green colour vision defect, and two had raised IOP due to steroid use. ‘Negative' scotopic ERGs with reduced a:b-wave amplitude ratios were recorded in all patients with mutations involving exons 44–57, one patient with a 8–13 deletion and two patients with the 3′ mutation involving exon 70. The scotopic oscillatory potential (OP2) was reduced in all boys with mutations of exons 44–57, and in one with 8–13. The photopic OP2 was reduced in patients with deletions upstream of exon 30, but preserved in those patients in whom scotopic OP2 was attenuated. Photopic ERG a:b-wave amplitude ratios were reduced across the cohort, including those with 5′ mutations in whom scotopic a:b ratios had been normal. These data show a strong association of mutations downstream of exon 30, the promoter region for Dp260, with abnormal scotopic ERGs. In contrast photopic ERG abnormalities were widespread across all genotypes which may relate to the greater proportion of Dp427, compared with other isoforms, at the synapse of cones to cone on-bipolar cells. Our clinical evaluation also reminds us to monitor IOP during GC treatment.

Rayleigh Equation Anomaloscope from Commercially Available LEDs

Most precise classification of CVD (color vision deficits) can be provided by using anomaloscope. Today anomaloscopes are available, which can evaluate red-green (Rayleigh) and blue-green (Moreland) color defects. DOI: http://dx.doi.org/10.5755/j01.ms.18.2.1928

Color-deficient cone mosaics associated with Xq28 opsin mutations: A stop codon versus gene deletions

Our understanding of the etiology of red–green color vision defects is evolving. While missense mutations within the long- (L-) and middle-wavelength sensitive (M-) photopigments and gross rearrangements within the L/M-opsin gene array are commonly associated with red–green defects, recent work using adaptive optics retinal imaging has shown that different genotypes can have distinct consequences for the cone mosaic. Here we examined the cone mosaic in red–green color deficient individuals with multiple X-chromosome opsin genes that encode L opsin, as well as individuals with a single X-chromosome opsin gene that encodes L opsin and a single patient with a novel premature termination codon in his M-opsin gene and a normal L-opsin gene. We observed no difference in cone density between normal trichomats and multiple or single-gene deutans. In addition, we demonstrate different phenotypic effects of a nonsense mutation versus the previously described deleterious polymorphism, (LIAVA), both of which differ from multiple and single-gene deutans. Our results help refine the relationship between opsin genotype and cone photoreceptor mosaic phenotype.

Quantitative assessment of commercial filter ‘aids’ for red‐green colour defectives

The claims made for 43 commercial filter 'aids', that they improve the colour discrimination of red-green colour defectives, are assessed for protanomaly and deuteranomaly by changes in the colour spacing of traffic signals (European Standard EN 1836:2005) and of the Farnsworth D15 test. Spectral transmittances of the 'aids' are measured and tristimulus values with and without 'aids' are computed using cone fundamentals and the spectral power distributions of either the D15 chips illuminated by CIE Illuminant C or of traffic signals. Chromaticities (l,s) are presented in cone excitation diagrams for protanomaly and deuteranomaly in terms of the relative excitation of their long (L), medium (M) and short (S) wavelength-sensitive cones. After correcting for non-uniform colour spacing in these diagrams, standard deviations parallel to the l and s axes are computed and enhancement factors E(l) and E(s) are derived as the ratio of 'aided' to 'unaided' standard deviations. Values of E(l) for traffic signals with most 'aids' are <1 and many do not meet the European signal detection standard. A few 'aids' have expansive E(l) factors but with inadequate utility: the largest being 1.2 for traffic signals and 1.3 for the D15 colours. Analyses, replicated for 19 'aids' from one manufacturer using 658 Munsell colours inside the D15 locus, yield E(l) factors within 1% of those found for the 16 D15 colours.

Red-Green Color Vision Impairment in Duchenne Muscular Dystrophy

The present study evaluated the color vision of 44 patients with Duchenne muscular dystrophy (DMD) (mean age 14.8 years; SD 4.9) who were submitted to a battery of four different color tests: Cambridge Colour Test (CCT), Neitz Anomaloscope, Ishihara, and American Optical Hardy-Rand-Rittler (AO H-R-R). Patients were divided into two groups according to the region of deletion in the dystrophin gene: upstream of exon 30 (n=12) and downstream of exon 30 (n=32). The control group was composed of 70 age-matched healthy male subjects with no ophthalmological complaints. Of the patients with DMD, 47% (21/44) had a red-green color vision defect in the CCT, confirmed by the Neitz Anomaloscope with statistical agreement (P<.001). The Ishihara and the AO H-R-R had a lower capacity to detect color defects--5% and 7%, respectively, with no statistical similarity between the results of these two tests nor between CCT and Anomaloscope results (P>.05). Of the patients with deletion downstream of exon 30, 66% had a red-green color defect. No color defect was found in the patients with deletion upstream of exon 30. A negative correlation between the color thresholds and age was found for the controls and patients with DMD, suggesting a nonprogressive color defect. The percentage (66%) of patients with a red-green defect was significantly higher than the expected <10% for the normal male population (P<.001). In contrast, patients with DMD with deletion upstream of exon 30 had normal color vision. This color defect might be partially explained by a retina impairment related to dystrophin isoform Dp260.

Tilted disc syndrome and colour vision

To study colour vision in patients with tilted disc syndrome. Colour vision was examined using Boström-Kugelberg (B-K) plates, Farnsworth-Munsell 100-hue test (FM-100) and Farnsworth panel D-15 and Lanthony desaturated panel tests. A total of 35 eyes of 21 patients were examined. Seventeen eyes (49%) of 11 patients were found to have a colour vision defect in at least one eye. The severity of the colour vision defect differed between eyes for six of eight patients with bilateral tilted discs. In two of these patients, colour vision was normal in one eye. Seven patients had a unilateral tilted disc and three of these individuals had a colour vision defect in the affected eye. Of all eyes with a colour vision defect, a red-green defect was found in four eyes (24%), a blue defect in one eye (6%), and a mixed defect in 12 eyes (70%). Colour vision defects were not related to visual acuity or to severity of visual field defects. This is the first report of colour vision defects in tilted disc syndrome. In the differential diagnosis of tilted disc syndrome, chiasmal lesions and glaucoma, the examination of colour vision may add valuable information. Further, it is recommended that young people with tilted disc syndrome undergo an examination of colour vision so that they can be given appropriate career guidance.

Looking for the dichromatic version of a colour vision model

Different hypotheses on the sensitivity of photoreceptors and post-receptoral mechanisms were introduced in different colour vision models to derive acceptable dichromatic versions. Models with one (Ingling and T'sou, Guth et al, Boynton) and two linear opponent stages (DeValois and DeValois) and with two non-linear opponent stages (ATD95) were used. The L- and M-cone sensitivities of red–green defectives were either set to zero (cone-loss hypothesis) or replaced by that of a different cone-type (cone-replacement hypothesis), whereas for tritanopes the S-cone sensitivity was always assumed to be zero. The opponent mechanisms were either left unchanged or nulled in one or in all the opponent stages. The dichromatic models obtained have been evaluated according to their performance in three tests: computation of the spectral sensitivity of the dichromatic perceptual mechanisms, prediction of the colour loci describing dichromatic appearance and prediction of the gamut of colours that dichromats perceive as normal subjects do.

Color vision.

Many visual disorders produce acquired color vision defects. Color vision theory emphasizes several stages of visual processing: prereceptoral filters (lens, macular pigment, pupil), cone photopigments (L-, M-, and S-cones), and postreceptoral processes (red-green, S-cone, and luminance channels). Congenital color defects, which affect 8% to 10% of males and 0.4% to 0.5% of females, result from alterations in the photopigment absorption spectra or the absence of one or more photopigments. The most common defects are color vision deficiencies (protan and deutan defects), which are milder than the rarer achromatopsias (complete loss of color vision). Acquired color vision defects can be attributed to a number of different causes: alteration of prereceptoral filters, reduced cone photopigment optical density, greater loss of one cone type than the others, and disruption of postreceptoral processes. Acquired color vision defects have been divided into three classes: type 1, red-green defect with scotopization; type 2, red-green defect without scotopization; and type 3, blue defects (with or without pseudoprotanomaly). Blue defects are usually type 3 acquired defects because congenital tritan defects have an incidence of one in several tens of thousands. Red-green defects can be acquired or congenital, and ruling out acquired defects can require a battery of tests (plates and arrangement tests, anomaloscopy, perhaps genetic analysis). Color vision tests must be administered carefully (with a standard illuminant and protocol), and pupillary miosis or high lens density should be noted and their possible effects considered when interpreting test results. Plate tests provide a simple screening method but do not provide a diagnosis. Arrangement tests and anomaloscope testing take more time and make greater demands on the tester, but they provide a more thorough evaluation. When standard protocols are followed and results are interpreted in terms of prereceptoral filters, photopigment optical density, cone loss, and disruption of postreceptoral processes, a battery of color vision tests can be useful in the differential diagnosis, after progression of the disease, and for evaluating the effectiveness of treatment.