Risk factors associated with contrast sensitivity loss in diabetic patients

Psychophysical tests in patients with diabetes mellitus reveal deficits of central vision before the development of overt retinopathy. We evaluated the contrast sensitivity thresholds in 30 patients with type II diabetes mellitus and without retinopathy, taking into account the crystalline lens density. Risk factors for contrast sensitivity deficits were investigated.

Contrast sensitivity was compared in 30 aretinopathic diabetic patients and age-matched controls. Contrast thresholds were determined for stationary gratings at three spatial frequencies (6, 15, and 27 cycles/deg) and for mesopic (5 cd/m2) and low photopic (85 cd/m2) vision. Lens density was measured using a IntraOptics opacity lensmeter.

Significant contrast sensitivity losses at all three spatial frequencies were observed in low photopic and mesopic vision in diabetic patients. The optical density of the lens in the diabetic group did not differ from that in the controls. Contrast sensitivity deficits were positively correlated with patient's age, systolic blood pressure and nephropathy at all three spatial frequencies. No relationship between cardiovascular autonomic neuropathy and contrast sensitivity defects was observed.

These data suggest that contrast sensitivity deficits in diabetic patients without retinopathy are not solely explained by a diabetes-induced increases in lens optical density. Abnormalities of the retina or its neural connections occurring before the onset of clinically detectable retinopathy may be involved. Risk factors for these deficits are advanced age, high systolic blood pressure, and nephropathy.