The scotopic electroretinogram of macaque after retinal ganglion cell loss from experimental glaucoma.

This study describes the dark-adapted electroretinograms (ERGs) of macaque monkeys with severe visual field defects and substantial retinal ganglion cell loss as a consequence of long-standing ocular hypertension. Monocular experimental glaucoma was produced by argon laser trabeculoplasty, and visual fields were assessed with behavioral static perimetry. Electroretinographic responses to brief ganzfeld flashes under fully dark-adapted conditions were recorded using DTL fiber electrodes in anesthetized animals. The authors quantified retinal layer thickness and cell loss in 1-micron radial sections and inspected optic nervous under the light microscope. At the lowest intensities, a sensitive negative component of the scotopic ERG, which normally peaks approximately 200 msec after stimulus onset, was present in the control eyes but was reduced greatly or was virtually absent in the experimental eyes of monkeys with severe visual field loss. A previously unreported sensitive positive component of the scotopic ERG remained in both eyes. In the control eyes, the positive component gave rise to a sharp peak approximately 120 msec after stimulus onset, but in the experimental eyes, because of the absence of the more delayed sensitive negative potential, it was sustained, lasting as long as 700 msec. Scotopic a- and b-waves and oscillatory potentials in the experimental eyes were not consistently different from control eyes. Ganglion cell and optic nerve loss in the experimental eyes was substantial, and there was little other obvious retinal damage. A sensitive negative component is reduced or absent from the dark-adapted ERGs of macaque monkeys with severe visual field defects and substantial retinal ganglion cell loss as a consequence of long-standing ocular hypertension.