Responses of Postreceptoral Pathways Elicited by L- and M-Cone Isolating ON- and OFF-Electroretinograms in Glaucoma Patients

PURPOSE: To compare the electroretinographical (ERG) responses elicited by L- and M-cone isolating ON- and OFF-sawtooth stimuli in normal subjects and glaucoma patients. METHODS: Twenty-one normal subjects and 44 primary open-angle glaucoma patients participated in the study. L- and M-cone isolating (18% cone contrast; 284 cd/m(2)) rapid ON- and rapid OFF-sawtooth (4 Hz) stimuli with two stimulus sizes (full-field (FF) and central 70° diameter) were generated using the triple silent substitution technique. ON- and OFF-response asymmetries were studied by adding the two (to obtain L-add and M-add responses). The initial positive (P) and subsequent late negative (LN) components of the L-add and M-add ERGs were compared between the subject groups and correlated with retinal nerve fiber layer thickness (RNFLT) and pattern ERG responses. RESULTS: The responses to L-ON and to M-OFF stimuli and vice versa resembled each other particularly with 70° stimuli. The P(L-add) amplitudes were not significantly different between the normal subjects and glaucoma patients, whereas the LN(L-add) amplitude was significantly (P < 0.01) smaller in the glaucoma patients. Both P(M-add) and LN(M-add) were not significantly different between the subject groups. The PERG amplitude with 0.8° check sizes and the 0.8°/16° amplitude ratio (PERG ratio) were significantly (P < 0.05) different between the subject groups. The 70° LN(L-add) amplitude and the 0.8° PERG amplitude were significantly correlated with RNFLT. CONCLUSIONS: The ERGs to 70° cone isolating sawtooth stimuli reflect cone opponency. The cone opponent ERG responses were not significantly different between glaucoma patients and normal subjects. Luminance driven L-add responses were significantly different, indicating that central luminance signals are mainly affected in glaucoma.