Dyschromatopsia and contrast sensitivity changes in COVID-19 patients

To evaluate the alterations in the psycho-physical tests, contrast sensitivity (CS) and hue discrimination (total estimation score, TES) in COVID-19 patients.

A prospective case-control study was undertaken in 2021-22 to look at CS and TES among COVID-19 patients and RT-PCR negative normal subjects by a mobile app "smart optometry" and X-Rite's free online version of Farnsworth-Munsell 100 hue test. Strict visual acuity (minimum of 6/9 equivalent on Snellen) and other clinical parameters were used as exclusion criteria to filter potentially confounding pre-receptoral co-morbid conditions. The effect of mismatch in recruiting age and sex matched controls during the pandemic were analyzed by multivariate linear regression.

One-way ANOVA ruled out any influence of gender on CS and TES; however, there was significant difference in the TES on Mann Whitney U test (TES- 2.95 +/- 3.8 for cases; 0.30 +/- 1.1 for controls; p <0.001) and it persisted after accounting for age. Six controls with breakthrough infections had a significant deterioration in TES (Mean scores -3.0; 95% CI = -5.89 to -0.11; p = 0.04) on paired t test. Qualitative analysis showed that S-cone mediated deficiencies outnumber those affecting M-L cone mediated deficiencies. Among 53 subjects exhibiting three sensory features, anosmia, loss of taste and dyschromatopsia, nine (16.98%) had all features concurrently.

The study demonstrates that COVID-19 infection leads to altered TES representing dyschromatopsia -an ocular counterpart of anosmia, with little difference on CS.