Comparison of ganglion cell loss and cone loss in experimental glaucoma

To compare the loss of ganglion cells to cone loss in the macular area of monkey eyes with experimental glaucoma.

Experimental glaucoma was induced in eyes of three cynomolgus monkeys by argon laser applications to the trabecular meshwork. The average duration +/- S.D. of glaucoma in the experimental animals was 3.8 +/- 0.5 months. Glaucomatous damage was estimated, before the animals were killed, by evaluating stereoscopic photographs of the optic disk and red-free photographs of the nerve fiber layer. Ganglion cell nucleoli and cone pedicles were counted by using light microscopy from slides containing strips of retinal tissue. Cell density was then calculated by using the modified Abercrombie formula. Percent loss of ganglion cells and cones was determined from three eyes of three monkeys in 300-micron segments that were 900 to 1,200 microns superior and inferior to the foveal center.

Cone loss was not found at 4.5 to 6 degrees eccentricity above and below the fovea, whether damage was mild or severe. The average loss +/- S.D. of ganglion cells was 81.1% +/- 10.7%, whereas the average cone loss was only 3.5% +/- 6.4%.

Marked parafoveal cone loss was not found in experimental glaucoma in which extensive damage to ganglion cells occurred.