Specificity of the chromatic noise influence on the luminance contrast discrimination to the color vision phenotype

Many studies have examined how color and luminance information are processed in the visual system. It has been observed that chromatic noise masked luminance discrimination in trichromats and that luminance thresholds increased as a function of noise saturation. Here, we aimed to compare chromatic noise inhibition on the luminance thresholds of trichromats and subjects with severe deutan or protan losses. Twenty-two age-matched subjects were evaluated, 12 trichromats and 10 with congenital color vision impairment: 5 protanopes/protanomalous, and 5 deuteranopes/deuteranomalous. We used a mosaic of circles containing chromatic noise consisting of 8 chromaticities around protan, deutan, and tritan confusion lines. A subset of the circles differed in the remaining circles by the luminance arising from a C-shaped central target. All the participants were tested in 4 chromatic noise saturation conditions (0.04, 0.02, 0.01, 0.005 u′v′ units) and 1 condition without chromatic noise. We observed that trichromats had an increasing luminance threshold as a function of chromatic noise saturation under all chromatic noise conditions. The subjects with color vision deficiencies displayed no changes in the luminance threshold across the different chromatic noise saturations when the noise was composed of chromaticities close to their color confusion lines (protan and deutan chromatic noise). However, for tritan chromatic noise, they were found to have similar results to the trichromats. The use of chromatic noise masking on luminance threshold estimates could help to simultaneously examine the processing of luminance and color information. A comparison between luminance contrast discrimination obtained from no chromatic and high-saturated chromatic noise conditions could be initially undertaken in this double-duty test.

Dichromacy: Color Vision Impairment and Consanguinity in Heterogenous Population of Pakistan

Background and Objectives: Dichromacy, an X-linked recessive disorder is identified worldwide, more in males than females. In European Caucasians, its incidence is 8% in males and 0.5% in females. In India, it is 8.73% in males and 1.69% in females, and in Iran, it is 8.18% in males and 0.43% in females. Population based epidemiological data about dichromacy in different ethnic groups in Pakistan is not available. The aim of this study was to find out the population prevalence of inherited red-green dichromacy in a heterogenous population of the district of Chiniot, Punjab, Pakistan, and to determine the impact of consanguinity and ethnicity. Methods: In this cross-sectional study, boys and girls of the higher secondary schools were examined in the three tehsils of district Chiniot. Pseudoisochromatic Ishihara Test has been employed for detection of dichromacy in the study population. The sample size was calculated statistically as 260, which was expanded to 705 and divided by population density of the three tehsils. Results: Screening of 359 males and 346 females revealed 19 (5.29%) dichromat males and only 2 (0.58%) females. The study population belonged to 23 castes / isonym groups. The consanguinity found in the district of Chiniot is 84.82% and in the dichromat families, it is 85.71%, of which 52.37% are first cousin. Interpretation & Conclusion: The study has shown that the incidence of dichromacy could be reduced through genetic counseling

Color Vision Impairment Differentiates Alzheimer Dementia From Dementia With Lewy Bodies

Objective: Dementia with Lewy bodies (DLB) is frequently misdiagnosed for Alzheimer dementia (AD), especially in its earlier stages. We characterized color vision impairment (CVI) in patients with DLB versus patients with AD to determine its usefulness in improving accuracy of early diagnosis. Methods: We retrospectively reviewed charts of patients with AD, DLB, and patients with mild cognitive impairment suspected to be in the prodromal phase of DLB (pro-DLB) or prodromal phase of AD (pro-AD). All patients underwent an online 15-hue color vision arrangement test. Results: Fifty-two patients were included in this study with a median age of 77 years, of which 44% were female. No significant differences in gender, age, or Montreal Cognitive Assessment existed among patients with AD (n = 15), pro-AD (n = 5), pro-DLB (n = 8), and DLB (n = 24). Of the 52 patients, 4 (2 AD, 1 DLB, and 1 pro-AD) had CVI history from a young age and were excluded from final analyses. New-onset CVI prevalence differed significantly based on diagnosis: patients with pro-AD (20%), patients with AD (15%), patients with pro-DLB (38%), and patients with DLB (78%, P < .001). In a stepwise multivariate logistic regression analysis to determine factors associated with CVI, “diagnosis type” as a binary variable (DLB or pro-DLB vs AD or pro-AD) was the only variable retained in the model (odds ratio = 9.8 [95% CI: 2.3-42.1], P < .001). Conclusions: Color vision impairment in patients with DLB showed a prevalence similar to the core features of DLB (∼80%) and can be supportive to a diagnosis of DLB versus AD. Pending prospective confirmation of our findings, simple online color vision testing could be incorporated into multivariate diagnostic tools to possibly improve accuracy of early diagnosis of DLB.