Purpose: To compare the sensitivity of the photopic negative response (PhNR) from the shortwave (S)-sensitive and the long (L)- and medium (M)-wave-sensitive cone electroretinograms (ERGs), with the pattern electroretinogram (PERG) in the early stages of primary open-angle glaucoma (POAG).
Methods: Eighteen patients under treatment for diagnosed POAG and 19 normal control subjects were investigated. S-cone ERGs were elicited using adaptation to 650-nm light to suppress L-cone activity, and substitution between 450 nm and 535 nm to silence M-cone response at luminances higher than rod saturation. PhNRs from the L&M-cone pathways were elicited by a 200-msec pulse of red light (650 nm) on a continuous blue (450 nm) background. PERGs were recorded in accordance with the International Society for Clinical Electrophysiology of Vision (ISCEV) standard.
Results: Each method showed a statistically significant difference in the two groups. The S-cone PhNR was the most sensitive test and provided the most statistically significant results, with the largest area enclosed by the receiver operating characteristic (ROC) curve.
Conclusions: The findings indicate that all three types of ERG may be useful in glaucoma investigation. The L- and M-cone PhNRs may have a role in monitoring established glaucoma. The previously reported high sensitivity of the PERG was confirmed. Extensive diffuse damage to S-cone bipolar and bistratified ganglion cells appears to occur at a very early stage in POAG, owing to a pressure-related mechanism, and the S-cone PhNR was the most sensitive test. It may in future have an important role in diagnosis and monitoring of early glaucoma. Further investigation of this possibility is recommended.