Cone structure and retinal sensitivity assessment in patients with red-green colour vision deficiency using multimodal imaging.

To assess alterations in cone morphology, retinal sublayer thicknesses and vessel densities (VDs) in eyes with non-pathological high myopia (HM) and their correlation with retinal sensitivity (RS). This prospective study included 43 patients with non-pathological HM and 38 age-matched healthy volunteers. Participants underwent detailed ophthalmic evaluations. Cone morphology was assessed using adaptive optics scanning laser ophthalmoscopy. The thicknesses of the myoid and ellipsoid zone (MEZ), photoreceptors outer segment (OS), central macula and choroid were measured by optical coherence tomography (OCT). Retinal VDs of the superficial and deep capillary plexus (DCP) were evaluated by OCT angiography, and RS was assessed through microperimetry. Group comparisons were conducted, and correlations among these parameters were explored. The HM group showed significantly reduced cone density and regularity, increased cone dispersion and spacing at 3° eccentricity across four quadrants (all p<0.001) and decreased VDs (all p<0.01), except for foveal VDs in both capillary plexuses and parafoveal VD in DCP (all p>0.05). Additionally, MEZ, OS, central macula and choroid were thinner in HM (all p<0.001). Multivariate regression indicated that higher cone density correlated with shorter axial length (p=0.013) and higher DCP whole VD (p=0.009). Better RS was related to higher cone density (p=0.026), thicker MEZ (p<0.001), thicker choroid (p=0.044) and higher DCP whole VD (p=0.009). Our findings demonstrate that impaired DCP perfusion independently predicts cone loss in non-pathological HM, independent of axial elongation. RS impairment is associated with cone loss, MEZ thinning and DCP hypoperfusion, indicating synergistic microvascular and structural damage in HM-related vision impairment.

To investigate the influence of color vision on myopia development by testing refraction error and axial length of the eye for high school students with and without color vision deficiency (CVD). A school-based cross-sectional, cluster sample study was conducted to test the color vision and refractive error of 16,539 high school students. Students were screened for CVD using a pseudoisochromatic plate. CVD was confirmed in students failing the test using a Farnsworth-Munsell 100-Hue Test which also served to classify the subtype (protan or deutan). Three classmates of each CVD subject, matched in five myopia risk factors, were chosen to form the normal color vision (CN) control group. Ophthalmic examinations were performed to determine refractive status and axial length. Of the students, 309 were found to have red-green CVD and 927 were selected as the CN control group. The prevalence of myopia in the CVD group (45.6%) was significantly lower than that of the CN group (65.8%; P<0.001). The CVD group was also less myopic in refraction (P<0.001) than CN, and protan subjects had shorter axial lengths than those in the control group (P=0.007). Color vision deficiencies appear to influence the development of myopia. The observed lower incidence of myopia in people with CVD may be linked to the reduced functionality of the L/M chromatic mechanism.

Dear Sir, As members of the state's medical board, the authors wish to share some of the difficulties encountered while testing candidates for color vision deficiency (CVD). Though many methods for color vision testing are available, there is no consensus on the ideal method, with different countries using different tests. In India, the Ishihara charts are the most widely used, with additional use of Edridge-Green lantern in civil services and Martin lantern in armed forces.[1,2] The Ishihara test is quick and easy and is an excellent screening tool to detect those with red-green CVD. However, it has a limited ability to classify CVD and determine its severity. Organizations that require the correct recognition of colored signals (principally transport groups such as the Civil Aviation Authority, Railways, Maritime, and Naval and Air force) depend on a standard lantern test which imitates actual signal systems simulating the workplace. Lanterns do not specifically screen for color defects. It is surprising that even now, the general design of lanterns has not changed very much since their creation in 1891. With the exception of the Farnsworth lantern used in the USA, there are scarce studies on the validation and reliability of lanterns. The panel tests, including the Farnsworth Panel D-15 and Farnsworth–Munsell 100-hue tests, are much more accurate in classifying color deficiency. Farnsworth Panel D-15 Test is considerably quicker and more convenient test for routine clinical use. Though not very sensitive, its speed and accuracy make it useful. The relative insensitivity can also be an asset in judging the practical significance of mild degrees of color deficiency. For example, individuals who fail the Ishihara plates but pass the D-15 panel will probably not have color discrimination problems under most circumstances and in most jobs.[3] Nagels anomaloscopes is considered the gold standard for color vision testing in clinical research, however, it is an expensive instrument requiring an experienced examiner's skills. Color vision is graded into higher and lower grade depending on the size of the aperture in the Edridge-Green lantern (1.3 mm vs. 13 mm),[1] with the technical services category of Indian civil services, which includes police services requiring higher grade of color vision. The United States police service no longer implements a color vision standard though monochromats are barred.[4] Those who fail initial color vision screening by pseudoisochromatic plates should be further evaluated by anamaloscope or D-15 test to include anomalous trichromats who are the most numerous among the CVD persons. In an ongoing study, 500 candidates who appeared in the divisional medical board were studied. Ishihara chart was used for initial screening of all candidates with further use of Edridge-Green lantern for candidates found to have CVD and selected for jobs requiring high grade of color vision. Sixty candidates (13%) were found to have CVD; 39 of those were selected for jobs requiring accurate color perception. None of the candidates found to have CVD on testing by Ishihara chart could pass the lantern test. Only 21 candidates found to have CVD were previously aware of their deficiency. Since color judgment is an integral part of work in various occupations, a screening test to establish color vision should be undertaken while giving career's advice. An early diagnosis of CVD might allow for early modifications in educational and other activities. Furthermore, there is a need to supplement the existing color vision tests for various services in India, with more objective, diagnostic tests such as the D-15, maintaining standard illumination. Use of color enhancing appliances (X-chrome and chromagen contact lenses) should be ruled out. Computer-based programs are needed so that easily reproducible and acceptable methods of testing are developed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.

Assessment of photoreceptor recovery and visual function utilizing adaptive optics and microperimetry in patients with surgically closed macular holes.

Longitudinal assessment of cone structure and lesion remodeling in laser-induced retinopathy.

To study pathologic changes in the photoreceptors in eyes with idiopathic macular telangiectasia (MacTel) type 2 using adaptive optics scanning laser ophthalmoscopy (AO-SLO). Thirteen eyes with nonproliferative MacTel type 2 and 10 normal eyes underwent a full ophthalmologic examination, spectral-domain optical coherence tomography (SD-OCT), and imaging with an original prototype AO-SLO system. All eyes with MacTel type 2 were examined with fluorescein angiography (FA), fundus autofluorescence (FAF), confocal blue reflectance (CBR), and fundus-monitoring microperimetry (MP). All eyes with MacTel type 2 had ring-like dark areas and/or small patchy regions on AO-SLO images; significantly lower cone density than that of normal eyes in each hemisphere at 0.5 mm from the foveal center; an area with parafoveal reflectance in CBR that was larger than the hyperfluorescence area in FA, the area of increased FAF, the dark areas on AO-SLO, and the area of decreased retinal sensitivity on MP. Dark areas on AO-SLO roughly corresponded to the leakage area in FA, but dark areas were also seen in areas without FA leakage in 11 eyes, including an eye with the earliest clinical signs of MacTel. Visual acuity and retinal sensitivity correlated with mean cone density 0.5 mm from the center of the fovea. In eyes with MacTel type 2, AO-SLO revealed unique dark regions in the cone mosaic and decreased cone density that was associated with decreased vision, even in areas with normal vasculature, which suggests that this feature represents early neuronal changes involved in the pathogenesis of MacTel type 2.

Morphologic and Functional Assessment of Photoreceptors in Laser-Induced Retinopathy Using Adaptive Optics Scanning Laser Ophthalmoscopy and Microperimetry

Purpose: To assess the Medmont C100 test as a colour vision screening tool. Methods: One hundred and seventeen young male adults were screened with the Medmont C100, Ishihara plates, and the screening mode of the Oculus Anomaloscope tests. All subjects were tested under constant room illumination, namely that of a day light fluorescent lamp at 200 lux. Inclusion criteria were visual acuities (VA) of 20/20 or better with or without correction and absence of known ocular pathologies.Aided and unaided visual acuities were measured with the Snellen VA chart. Results: Five out of the117 subjects, were found to have red-green colour vision deficiency (CVD) with Ishihara and anomaloscope tests indicating a 4.7% CVD prevalence, while the Medmont C100 test yielded 33 cases of red-green deficiency indicating CVD prevalence of 28%. With the Ishihara test, all five subjects were identified as deutans, while the anomaloscope revealed three as deutans and two as protans, and the Medmont C100 test identified all 33 cases as protans. Conclusion: The Medmont C100 test yielded significantly higher prevalence of protan CVD compared with the Ishihara platesand Anomaloscope tests. These findings suggest that caution should be taken when using Medmont C100 test for colour vision screening as it tends togive more false positive results with bias for protans. (S Afr Optom 2011 70(1) 14-20)

Purpose: To assess the Medmont C100 test as a colour vision screening tool. Methods: One hundred and seventeen young male adults were screened with the Medmont C100, Ishihara plates, and the screening mode of the Oculus Anomaloscope tests. All subjects were tested under constant room illumination, namely that of a day light fluorescent lamp at 200 lux. Inclusion criteria were visual acuities (VA) of 20/20 or better with or without correction and absence of known ocular pathologies. Aided and unaided visual acuities were measured with the Snellen VA chart. Results: Five out of the 117 subjects, were found to have red-green colour vision deficiency (CVD) with Ishihara and anomaloscope tests indicating a 4.7% CVD prevalence, while the Medmont C100 test yielded 33 cases ofred-green deficiency indicating CVD prevalence of 28%. With the Ishihara test, all five subjects were identified as deutans, while the anomaloscope revealed three as deutans and two as pro-tans, and the Medmont C100 test identified all 33 cases as protans. Conclusion: The Medmont C100 test yielded significantly higher prevalence of protan CVD compared with the Ishihara platesand Anomaloscope tests. These findings suggest that caution should be taken when using Medmont C100 test for colour vision screening as it tends to give more false positive results with bias for pro-tans. (S Afr Optom 2011 70(1) 14-20)

We have used the Farnsworth-Munsell 100-hue (FM 100) test and Mollon-Reffin (MR) test to evaluate the colour vision of 93 subjects, 30.4 ± 9.7 years old, who had red-green congenital colour vision deficiencies. All subjects lived in Belém (State of Pará, Brazil) and were selected by the State of Pará Traffic Department. Selection criteria comprised the absence of visual dysfunctions other than Daltonism and no history of systemic diseases that could impair the visual system performance. Results from colour vision deficient were compared with those from 127 normal trichromats, 29.3 ± 10.3 years old. For the MR test, measurements were taken around five points of the CIE 1976 colour space, along 20 directions irradiating from each point, in order to determine with high-resolution the corresponding colour discrimination ellipses (MacAdam ellipses). Three parameters were used to compare results obtained from different subjects: diameter of circle with same ellipse area, ratio between ellipse’s long and short axes, and ellipse long axis angle. For the FM 100 test, the parameters were: logarithm of the total number of mistakes and positions of mistakes in the FM diagram. Data were also simultaneously analysed in two or three dimensions as well as by using multidimensional cluster analysis. For the MR test, Mollon-Reffin Ellipse #3 (u’ = 0.225, v’ = 0.415) discriminated more efficiently than the other four ellipses between protans and deutans once it provided larger angular difference in the colour space between protan and deutan confusion lines. The MR test was more sensitive than the FM 100 test. It separated individuals by dysfunctional groups with greater precision, provided a more sophisticated quantitative analysis, and its use is appropriate for a more refined evaluation of different phenotypes of red-green colour vision deficiencies.

The purpose of this study was to report a case of acute zonal occult outer retinopathy (AZOOR) with spontaneous remission that was followed up using adaptive optics scanning laser ophthalmoscopy (AO-SLO). The right eye of a 31-year old myopic man diagnosed with AZOOR was followed up. The patient underwent a full ophthalmologic examination, spectral-domain optical coherence tomography (SD-OCT), multifocal electroretinography (mfERG) and imaging with prototype AO-SLO systems (Canon Inc) at the first visit, 1 month after, and 2 months after. Images focused on the photoreceptor layer were recorded in the area, and a montage of AO-SLO images was created. The patient presented with acute onset of a blind spot and photopsia in his right eye. On AO-SLO, focal dark areas could be observed on the right eye but not on the left eye at the first examination (cone density 8,589/mm(2), mosaic regularity of cone photoreceptors 38.5 %, cone spacing 0.567). The dark areas on AO-SLO corresponded to areas of disrupted inner segments and outer segments (IS/OS) line or ellipsoid of the IS and abnormal area in mfERG. After 1 and 2 months, his symptoms tended to disappear gradually without any treatment. IS/OS line and mfERG could be nearly normalized. Furthermore, normal cone mosaic could be observed in areas where some focal dark spots could be observed at the first examination (cone density 10,112/mm(2), mosaic regularity of cone photoreceptors 39.9 %, cone spacing 0.606). AO-SLO is a useful tool of diagnosis and follow-up of AZOOR. This study might suggest reversible cone damage could occur in some cases of AZOOR with spontaneous remission.

Color Vision Deficiences in Two Cases of Digoxin Toxicity

Occupational exposure to petroleum-derived organic solvents has been associated with acquired colour vision impairment. Evidence from low- and middle-income settings remains limited. To examine the association between occupational exposure to benzene/gasoline and red-green colour vision deficiency among petrol station workers in Khartoum State, Sudan. An analytical case-control study was conducted (February May 2022) at 19 petrol stations. Adult male participants were classified as cases (red-green colour vision deficiency) or controls (normal colour vision) using Ishihara plates (1999 edition). Exposure status (occupational petrol station work) and covariates were obtained via structured interviews. Visual acuity was assessed using the Landolt C Snellen chart. Odds ratios (ORs) with 95% confidence intervals (CIs) were estimated; multivariable logistic regression was used to adjust for age, smoking status, and work duration. A total of 176 participants (88 cases, 88 controls) were included. Occupational exposure was more frequent among cases than controls (64.8% vs. 47.7%). Exposure was associated with higher odds of red-green colour vision deficiency (adjusted OR ≈ 2.0; 95% CI 1.09–3.66; p = 0.02). Visual acuity was largely normal in both groups. Smoking was common but was not independently associated with colour vision deficiency after adjustment (p > 0.05). Occupational exposure at petrol stations was associated with red-green colour vision deficiency. Given the cross-sectional nature of exposure assessment and use of a screening tool for colour vision, findings should be interpreted as associative. Enhanced occupational health surveillance and eye safety practices are warranted.

Retinitis pigmentosa (RP), the most common inherited retinal disease, is characterized by progressive photoreceptor degeneration. It remains unknown to what extent surviving photoreceptors transduce light and support vision in RP. To address this, we correlated structure and functional measures using adaptive optics scanning laser ophthalmoscopy (AOSLO), adaptive optics microperimetry, and adaptive optics optical coherence tomography (AO-OCT)-based optoretinograms (ORGs). Four patients with RP were imaged with AOSLO across the visual field covering the transition zone (TZ) of normal to diseased retina. Cone density was estimated in discrete regions spanning the TZ. Visual sensitivity was assessed by measuring increment thresholds for a 3-arcmin stimulus targeted via active eye tracking in AOSLO. ORGs were measured at the same locations using AO-OCT to assess the cones' functional response to a 528 ± 20-nm stimulus. Individual cone outer segment (COS) lengths were measured from AO-OCT in each subject. Cone density was significantly reduced in patients with RP. Density reduction correlated with TZ location in 3 patients with RP, while a fourth had patches of reduced density throughout the retina. ORG amplitude was reduced in regions of normal and reduced cone density in all patients with RP. ORG response and COS length were positively correlated in controls but not in patients with RP. Despite deficits in cone density and ORG, visual sensitivity remained comparable to controls in three of four patients with RP. ORG-based measures of retinal dysfunction may precede deficits in cone structure and visual sensitivity. ORG is a sensitive measure of RP disease status and has significant potential to provide insight into disease progression and treatment efficacy.

Cone mosaic in eyes with varied axial length using adaptive optics scanning laser ophthalmoscopy.