TABLE 2

Possible mechanisms of vision impairment in diabetes

Cellular defectsClinical featuresEffects on visual function
Increased vascular permeability, capillary nonperfusionSymptoms: decreased central acuity; signs: retinal thickening, cystoid macular edema, lipid exudatesLight scattering within retina blurs image; cysts compress neurons; loss of glutamate; glutamine cycling between glial cells and neurons; increased susceptibility of neurons to plasma-derived toxic factors; possible ischemia of neurons
Primary neuronal impairmentSymptoms: decreased night and color vision; signs: nerve fiber layer defects, retinal depression sign, normal-appearing retinaReduced contrast sensitivity, dark adaptation, color vision, ERG responses
  • ERG, electroretinogram.