Section 2: Vision

2.5 Diabetic Retinopathy

According to recent statistics (Vision Problems in the U.S., 2000), 10 to 14 million people in the United States have diabetes. Nearly 40 percent, or 4 to 6 million, have diabetic retinopathy, which is the most common type of diabetic eye disease (National Eye Institute [NEI], 2000),and one of the leading causes of blindness in the United States (Richter, 1987). The incidence of diabetic retinopathy has increased with the increase in the long-term survival of diabetics (Richter, 1987). The prevalence increases with age and disease duration, with women affected more often than men (NEI, 2000).

There are two types of diabetic retinopathy: background and proliferative. Characteristic features of background retinopathy include micoraneurysms, venous dilation, exudates, hemorrhages, and retinal edema (Richter, 1987). Background retinopathy is often asymptomatic, but may result in decreased visual acuity. Proliferative retinopathy is the result of retinal hypoxia and carries a much graver prognosis (Richter, 1987). Proliferative retinopathy is characterized by a proliferation of new vessels in the retina or on the optic disc (neovascularization). Hemorrhage, retinal breaks, and retinal detachment can occur in the network of fragile vessels, resulting in vision loss and blindness.

Frequent eye examinations (every 6 to 12 months for diabetics) are an important step in the early detection and prevention of diabetic retinopathy. Laser surgery is the current treatment of choice for diabetic retinopathy. In proliferative retinopathy, the risk of severe vision loss has been reduced by 60 percent with the use of laser surgery (NEI, 2000). Vasectomy, evacuation of hemorrhagic or fibrous tissue in the vitreous, may be the treatment of choice in individuals with advanced proliferative retinopathy or retinal detachment.

Diabetic Retinopathy and Driving Literature Review

The overwhelming majority of the literature on diabetic retinopathy and driving is concerned with the effects of panretinal photocoagulation (PRP) for proliferative diabetic retinopathy on visual fields. PRP reduces the risk of severe visual loss in proliferative diabetic retinopathy (The Diabetic Retinopathy Research Group, 1978). However, the procedure is associated with visual field loss and reductions in peripheral vision (Sieberth, Alexandrides, and Feng, 1987; Zaluski, Marcil, Lamer, and Lambert, 1986).

Buckley, Jenkins, and Benjamin (1992) studied the effects of PRP in 30 diabetic patients following full PRP. Fifteen of the patients failed the Humphrey binocular visual field test (a visual field less than 120 degrees along the horizontal with 20 degrees above and below the horizontal level). Patients who failed were more likely to be hypertensive and to have undergone treatment with a xenon laser. No differences were noted between those who passed and those who failed on a number of factors including age, sex, diabetic age, and number and size of burns. Hulbert and Vernon (1992) assessed the visual fields of 21 diabetics following PRP. In that investigation, 89 percent of the patients treated with laser alone met the United Kingdom Driver and Vehicle Licensing Agency (DVLA) visual field requirements. Similar to the findings reported by Buckley et al., treatment with xenon laser was associated with a higher risk of failure of DVLA requirements. However, unlike Buckley, et al., Hulbert and Vernon found that total burn area also was associated with a higher rate of failure. In a significantly larger sample, Mackie, Webb, Hutchinson, et al. (1995) evaluated 100 diabetic patients following bilateral PRP for proliferative diabetic retinopathy. Thirty percent of their patients failed to reach the DVLA standards following treatment. Finally, Pearson, Tanner, Keightley, and Casswell (1998) report the results of PRP in diabetic patients. 42 percent of uniocular fields from treated eyes and 12 percent of binocular fields from those having bilateral PRP failed the United Kingdom’s licensing requirements. In this investigation, Type II diabetes was associated with a significant increase in risk of failure. The large variation in failure rates across studies is likely due to variations in sample size and differences in the interpretations of minimum field requirements. For example, Pearson, Keightley, and Casswell (1998) reported on evaluations of visual field defects in 60 diabetic patients following PRP from the chairman of the Visual Standards Sub-Committee of the Royal College and separate evaluations from four consulting ophthalmologist. Significant discrepancies existed for both binocular and uniocular fields. In order to reduce the variability in assessments, guidelines are provided. In addition, Hulbert and Vernon (1992) provide guidelines for laser treatment in diabetic retinopathy aimed at preserving the driving visual field.