This study followed the tenants of the Declaration of Helsinki and institutional review board approval was obtained at the University of Illinois at Chicago. The experiments were undertaken with the understanding and written consent of each subject. Thirty-four subjects diagnosed with type 2 DM were recruited from the Retina and General Eye Clinics of the University of Illinois at Chicago, Department of Ophthalmology and Visual Sciences. Each subject was examined by a retina specialist and medical histories were obtained from their records. The stage of NPDR was graded clinically according to the Early Treatment of Diabetic Retinopathy Study (ETDRS) scale
4 and the subjects were classified as diabetic with no apparent DR (NDR;
N = 17) or diabetic with mild NPDR (MDR;
N = 17) based on fundus examination. Subjects classified as MDR had minimal retinal vascular abnormalities including microaneurysms, hard exudates, and cotton-wool spots (equivalent to ETDRS
4 level 35 or less). No subject had other ocular or systemic diseases known to affect the retina. Exclusion criteria included sickle cell disease, retinal vascular occlusions, age-related macular degeneration, glaucoma, and high myopia (more than 6 diopters). Lens status was graded by slit lamp examination using a clinical scale that ranged from clear to 4+. Subjects with more than mild (2+) nuclear sclerotic, posterior subcapsular, or cortical lens opacities were excluded. Most NDR subjects (
N = 10) had clear lenses or trace nuclear sclerotic cataract; one NDR subject had a 2+ nuclear sclerotic cataract. Likewise, MDR subjects ranged from clear/trace (
N = 6) to 2+ nuclear sclerotic cataract (
N = 2). None of the subjects had a history of diabetic macular edema. Subject characteristics including age, sex, best-corrected visual acuity, estimated diabetes duration, and HbA1c percentage are provided in the
Table. Visual acuity for the NDR group was slightly (0.07 log MAR), but significantly, better than that of the MDR group (t = 2.66,
P = 0.01). The duration of diabetes was significantly shorter for the NDR group compared to the MDR group (t = 3.49,
P = 0.002). There was no significant difference in HbA1c between the NDR and MDR groups (t = 1.13,
P = 0.27).