Is neuronal dysfunction an early sign of diabetic retinopathy? Microperimetry and Spectral Domain Optical Coherence Tomography (SD-OCT) Study in individuals with diabetes, but no diabetic retinopathy

Purpose To elucidate changes in the neurosensory retina in the macular area, using spectral domain OCT and correlate with functional loss on fundus-related microperimetry, in patients with diabetes and no diabetic retinopathy compared with age-matched healthy volunteers. Methods This was a prospective study enroling 39 patients in each group. All patients underwent comprehensive dilated eye examination. The foveal thickness and the photoreceptor layer thickness at the foveal centre were measured using spectral domain OCT, and the mean retinal sensitivity of central 20 degrees was measured using microperimetry. Results The mean age of the patients with diabetes was 50.92 +/- 4.75 years, and of controls, 49.87 +/- 5.50 years. SD-OCT measured photoreceptor layer thickness (PLT) to be 61.62 +/- 4.48 mu m in cases, and 68.79 +/- 7.84 mu m in controls (P < 0.0001); foveal thickness (FT) was 168.64 +/- 16.46 mu m in cases and 177.74 +/- 14.58 mu m in controls (P = 0.012). The mean retinal sensitivity (MRS) of the central 20 degrees, measured on microperimetry was 15.74 +/- 3.74 db in cases and 17.70 +/- 1.5 db in controls (P < 0.003). In cases compared with controls (aged under 50 years) statistically significant differences were noted in all the three outcome variables: FT, P = 0.030; PLT, P = 0.015; and MRS, P = 0.020. The duration of diabetes influenced only the PLT (P = 0.017). Statistical analysis was performed with Student's t-test and chi(2) test. Conclusion Neuronal damage was observed in those eyes that did not have clinical evidence of diabetic retinopathy. Eye (2009) 23, 1824-1830; doi:10.1038/eye.2009.184; published online 24 July 2009