Colour discrimination in post-COVID-19 observers assessed by the Farnsworth-Munsell 100-Hue test

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.

Impact of Prolonged Screening and COVID-19 Infection on Acquired Colour Vision Deficiencies Assessed by the Farnsworth–Munsell 100 Hue Test

“…It is worth noting and emphasising the novelty of the study conducted as it is the first to comprehensively analyse whether excessive screen usage can be related to the increase in acquired colour vision deficiencies. Furthermore, in line with the only pre-published study on the relationship between colour vision and COVID-19 [13], it can be affirmed that COVID-19 infection is not related to the acquisition and development of defects in colour vision. This conclusion is of great significance because if there had been a relationship, the colour vision of the global population could have been affected.…”

“…Additionally, the effects of COVID-19 infection on colour vision have not been a primary focus of research. While most studies on ocular manifestations of COVID-19 [12] do not address colour discrimination, Paramei et al [13] noted a potential short-term effect on colour vision, which was transient and reversible.…”