[Electroretinogram before and after panretinal photocoagulation in diabetic retinopathy]

Visual acuity and visual fields with the Goldmann perimeter were measured, and electroretinograms (ERGs) were recorded in 25 eyes of 16 patients with pre-proliferative diabetic retinopathy who underwent panretinal photocoagulation (PRP) before PRP and one, three, and six months after PRP. ERGs were recorded with the use of a corneal contact lens electrode. With Ganzfeld stimulation, stimulating flashes were given from the dimmest flash to the maximum 2.0 J white flash, using neutral density filters. Visual acuity was significantly decreased more than two lines and visual field defects by isopter I/4 were found one month after PRP. ERGs showed a significant prolongation of a-and b-wave peak latency and a significant reduction of wave amplitude in both waves. From the analysis of the b-wave amplitude-stimulus intensity function, using the Naka-Rushton equation, the sensitivity parameter (K) was increased one month after PRP in comparison to before PRP. Namely, threshold sensitivity was attenuated. The sensitivity recovered three months after PRP. By examining two factors (i.e., the maximum amplitude of the b-wave and the sensitivity parameter (K)), within the range of the Naka-Rushton equation, this result showed that PRP reduced the sensitivity of the retina quantitatively.