ABSTRACT
Post-COVID-19, recorded were various ophthalmological symptoms and visual impairment. We hypothesised that colour vision may be affected too. We assessed colour discrimination using the Farnsworth-Munsell 100 Hue test (FM-100) in individuals, who have had COVID-19 (N=77; 18–68 years). Total error score (TES) indicated superior colour discrimination in 34 observers. The Vingrys–King-Smith C-index (severity) exceeded the normal cutoff measure in 44 observers. In participants (N=35) with average TES, the Vingrys–King-Smith analysis revealed subtle colour deficiencies – either a mild tritan defect (‘blue’ or blue-yellow) or moderate defect with a diffuse error pattern. A minor sub-sample (N=6) manifested poor discrimination or colour vision loss (N=2), with a tritan or diffuse error pattern. √TES negatively correlated with the recovery time lapse. Partial error scores (√PES) indicated prevailing B–Y errors, regardless of the elapsed post-illness period. Overall, the results indicate that about half of those who have recovered from COVID-19 reveal predominantly mild Type III acquired colour discrimination loss, characteristic of retinal disorders and vascular disease. Conceivably, coronavirus infection caused hypoperfusion (reduced vascular supply) at the retinal and/or post-retinal stages of the visual system having affected neural mechanisms of colour discrimination. The mild impairment appears to be reversible with a favourite prognosis.