Abstract
Purpose :
To compare the electroretinographical (ERG) responses elicited by L- and M-cone isolating incremental (On) and decremental (Off) sawtooth stimuli in normal subjects and glaucoma patients.
Methods :
Twenty-one normal subjects and 44 primary open angle glaucoma patients participated in the present study. L- and M-cone isolating rapid On- and Off-sawtooth (4Hz) stimuli were generated using the triple silent substitution technique. The cone contrast was 18% with a mean luminance of 284 cd/m2. ERGs were recorded with Full-Field (FF) and 70 deg diameter stimuli. The On- and Off-ERG responses were summed (called Ladd and Madd) to study the response asymmetries to increments and decrements. The steady state pattern ERG (PERG) was also recorded in a subpopulation of each group with 0.8 and 16 deg black and white checkerboard stimuli at the rate of 15 reversals/s. The initial positive (P) and subsequent late negative (LN) ERG components of Ladd and Madd were compared between the subject groups and correlated with retinal nerve fiber layer thickness (RNFLT) and PERG.
Results :
The responses to L-On stimuli resembled those to M-Off stimuli and vice versa particularly with 70° stimuli. The PLadd amplitudes were not significantly different between the two suject groups. However, the PLadd with 70 deg stimuli was significantly (P < 0.01) smaller compared to those of FF stimuli. The amplitudes of the LNLadd in FF were similar in the two subject groups, whereas, for the 70 deg stimuli, the LNLadd amplitude was significantly (P < 0.01) smaller in the glaucoma patients. Both PMadd and LNMadd were not significantly different between the subject groups. The PERG amplitude in response to 0.8 deg check sizes and the ratio of the amplitude of responses to 0.8 deg over that to 16 deg checks (PERG Ratio) were significantly (P < 0.05) different between the subject groups. The LNLadd amplitude with 70 deg diameter stimuli and the PERG amplitude with 0.8 deg checks were significantly correlated with the retinal nerve fiber layer thickness.
Conclusions :
The responses to cone isolating sawtooth stimuli elicited ERGs that strongly reflect (parvocellularly based) cone opponency. Compared to (magnocellular) luminance based responses (PERG), the cone opponent ERG responses have little diagnostic value, indicating that the magnocellular system is functionally more affected by glaucoma.
This is a 2021 ARVO Annual Meeting abstract.