Retinal ganglion cell death in experimental glaucoma

Aims-To determine whether parasol retinal ganglion cells (magnocellular pat hway) are selectively lost in the primate model of glaucoma. Methods-Ocular hypertension was induced in one eye of six Macaca fascicular is monkeys for 6-14 weeks. The retinal ganglion cells in these eyes were la belled retrogradely with the tracer horseradish peroxidase (HRP) implanted into the optic nerve and subsequently examined in retinal whole mount prepa rations. The degree of retinal ganglion cell loss was estimated from Nissl stained tissue by comparison with the contralateral untreated control eye. Results-In the three glaucomatous retinas with the best labelling 1282 cell s could be classified, of which 182 were parasol cells and 1100 were midget cells. Linear regression analysis did not demonstrate a significant reduct ion in the proportion of parasol to midget cells with increasing cell loss (regression slope 0.023, 95%, CI -0.7 to 0.11). Compared with the control e ye the cell soma of the remaining retinal ganglion cells in glaucomatous ey es were reduced in size by 20% for parasol cells (p=0.003) and by 16% for m idget cells (p<0.001). Conclusion-The results of this study do not support the hypothesis that sel ective loss of parasol retinal ganglion cells occurs in experimental glauco ma. In addition, the change in cell soma size distributions following ocula r hypertension suggests that both parasol and midget retinal ganglion cells undergo shrinkage before cell death.