2010 BC Guide in Determining Fitness to Drive

Impaired colour visionIndividuals with impaired colour vision (colour blindness) lack a perceptual sensitivity to someor all colours. These impairments are usually congenital and in general, individuals learn tocompensate for the inability to distinguish colours when driving. Therefore, colour visionimpairments are not routinely considered by OSMV as a matter of driver fitness.Impaired contrast sensitivityVisual contrast sensitivity refers to the ability to perceive differences between an object and itsbackground. Depending on the cause, a loss of contrast sensitivity may or may not be associatedwith a corresponding loss of visual acuity. Declines in contrast sensitivity are associated withnormal aging, and can also result from conditions such as cataracts, age-related maculardegeneration, glaucoma, and diabetic retinopathy.Dark adaptation and glare recoveryDark adaptation refers to the process in which the visual system adjusts to a change from a welllitenvironment to a dark environment. Glare recovery refers to the process in which the eyesrecover visual sensitivity following exposure to a source of glare, such as oncoming headlightswhen driving at night.Prolonged dark adaptation is associated with normal aging and results in decreased visual acuityat night. It may also be the result of a medical condition, and where severe, may be referred to as‘night blindness’. Night blindness may be caused by a number of medical conditions includingretinitis pigmentosa, vitamin A deficiency, diabetes, cataracts or macular degeneration.As with dark adaptation, individuals require a longer time to recover from glare as they age. Inaddition, medical conditions associated with prolonged glare recovery include cataracts andcorneal edema. Individuals may also experience prolonged glare recovery following laserassisted in situ keratomileusis (LASIK) or panretinal laser photocoagulation (PRP) surgery.A number of illnesses can affect glare recovery time, with prolonged recovery times reported inindividuals with diabetes, vascular disease, and hypertension. Retinal conditions withdemonstrated relationships to prolonged glare recovery include age-related maculopathy, ‘cured’retinal detachment, and central serous retinopathy.Hemianopia and quadrantanopiaHemianopia, vision loss in one half of the visual field, or quadrantanopia, vision loss in onequarter of the visual field, can occur as a result of stroke, trauma, or a tumour. They are notusually caused by a problem with the eye itself. Examples of hemianopia and quadrantanopiaare provided below. The shaded areas represent vision field loss.254