Abstract
Daily experience shows that colour of a very distant object cannot be accurately determined. It is assumed that visual acuity (VA) loss is one of the factors at play in this case. The effects of reduced VA as a result of refractive error or optical defocus on colour vision have not been examined. Such study willdictate the need or otherwise for optical correction before assessment of colour vision. The purpose of this study therefore, was to investigate the effects of optical defocus on colour vision in individuals with normal colour vision. Twenty nine young adult subjects (11 male and 18 females) were included in this study. Their ages ranged from 11 to 29 years with a mean of 22.1 ± 3.4 years. All subjects had VA of 6/6 or better and normal colour vision. The colour vision was evaluated with the Farnsworth panel D-15 (desaturated). Each subject was optically defocused to VA of 6/24, 6/60 and 1/60(6/360) at 6 meters respectively and colour vision was assessed at each reduced VA. At VA of 6/24, colour vision was not affected in all subjects. When the VA was reduced to 6/60, however, 15 (51%) of the subjects failed the colour vision test. When the VA was further reduced to 1/60 by optical defocus, 24 (83%) of the subjects failed the colour vision test. It was concluded that optical defocus and reduced VA can adversely affect colour vision test findings. While VA reduction to 6/24 may not affect the colour vision results, VA of 6/60 can. It is therefore, recommended that in clinical colour vision testing and colour vision screening, VA should first be assessed andcompensated, especially if uncorrected VA is 6/24 or worse.
Highlights
Colour is an extremely important component of the information that we gather with our eyes and most of us use it so automatically that we fail to appreciate how important it is in our daily activities
This study shows that optical defocus influences colour vision, the visual acuity (VA) at which this would occur was found to be worse than 6/24
Large uncorrected refractive errors resulting in decreased VA worse than 6/24 can affect colour vision findings
Summary
Colour is an extremely important component of the information that we gather with our eyes and most of us use it so automatically that we fail to appreciate how important it is in our daily activities. It serves as a non-linguistic code that gives us instant information about the world around us[1]. There are two types of photoreceptors, namely rods and cones. Rods mediate vision at low light levels and serve vision only under conditions such as at night; in contrast,cone photoreceptors mediate vision under light levels[1]. A minimal requirement for colour discrimination is the presence of at least two kinds of cone pigments (dichromats), but normal colour vision requires the presence of all the three trichomats[3]
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