L/M and S-cone ERGs in Subjects with No or Early Diabetic Retinopathy

Abstract

Abstract: : Purpose: To examine the function of the L/M and S-cone retinal pathways in those with no or early diabetic retinopathy using ERG techniques that selectively stimulate the L/M and S-cones and compare these findings with results from a clinical color vision test. Methods: 53 subjects with Type 1 or 2 diabetes with either no (NDR) (n=31) or early background retinopathy (BDR) (n=22) aged 16-70 years and 42 age-matched control subjects were recruited. Monocular ERGs were recorded using a miniature Ganzfeld LED stimulator. The silent substitution S-cone ERG was elicited by a constant luminance 650nm background over which 535nm and 450nm stimuli balanced at 33Hz to be equiluminant for the M-cone were presented in square wave form at 4.16Hz. The L/M-cone ERG response was recorded to a constant 450nm background over which a 650nm stimulus was presented for 200ms at 1.8Hz. Color vision was assessed monocularly with the desaturated D15. Results: The S-cone ERG was normal in those with NDR. The S-cone a- and b-wave latency was significantly increased in those with BDR compared with the controls; the b-wave latency was also significantly increased compared with the NDR group. The L/M-cone ERG a-wave latency was significantly increased in both the NDR and BDR groups (see table below). The total error score was only significantly higher in those with BDR. One Type 1 subject with BDR had a protan-like defect; the remaining defects were anarchic. * indicates p<0.05 compared with controls ^# indicates p<0.05 compared with NDR Conclusions: The results indicate that retinal function, seen in the increased L/M-cone ERG a-wave latency, is abnormal even in those with NDR, but that this is not associated with a significant change in color vision. Progression from NDR to BDR is associated with S-cone ERG abnormalities and the development of a non-specific color vision defect.  

Keywords: electroretinography: clinical • color vision • diabetic retinopathy