2010 BC Guide in Determining Fitness to Drive

NystagmusNystagmus is an involuntary, rapid, rhythmic movement of the eyeball. The movements may behorizontal, vertical, rotary, or mixed. Nystagmus which occurs before 6 months of age is calledcongenital or early onset, whereas that occurring after 6 months is labelled acquired nystagmus.Early onset nystagmus may be inherited, or the result of eye or visual pathway defects. In manycases, the cause is unknown. Causes of acquired nystagmus are many and it may be a symptomof another condition such as stroke, multiple sclerosis, or even a blow to the head.Many individuals with nystagmus have significant impairments in their vision, with some havinglow vision or legal blindness.Medical conditions causing vision impairmentCataractsA cataract is an opacification or clouding of the crystalline lens of the eye, which blocks lightfrom reaching the retina. Cataracts may be due to a variety of causes. Some are congenital, butfew occur during the early years of life. The majority of cataracts are the result of the agingprocess. The presence of a cataract can interfere with visual functioning by decreasing acuity,contrast sensitivity, and visual field.Diabetic retinopathyDiabetic retinopathy is the most common eye disease in those with diabetes and results insignificant impairments in vision (blurred vision, vision loss) and is a leading cause of blindnessin adults. It is caused by changes in the blood vessels of the retina (microvascular retinalchanges) as a result of the disease.There are two types of diabetic retinopathy: background (non-proliferative) and proliferative.Background retinopathy reflects early changes in the retina and often is asymptomatic.However, it may result in decreased visual acuity. Background diabetic retinopathy can progressinto a more advanced or proliferative stage.Proliferative retinopathy is the result of retinal hypoxia (lack of oxygen to the retina) and carriesa much graver prognosis. The lack of oxygen to the retina results in a proliferation of newvessels in the retina or on the optic disc (neovascularization). Without treatment, the new vesselscan leak blood into the centre of the eye, resulting in blurred vision. Fluid (exudate) also canleak into the centre of the macula (that part of the eye where sharp, straight-ahead vision occurs),a condition called macular edema. The leakage causes swelling of the macula resulting inblurred vision. Macular edema can occur at any stage of diabetic retinopathy, but is more likelyto occur as the disease progresses. Research indicates that approximately half of those withproliferative retinopathy also have macular edema.256