Expansion of visual receptive fields in experimental glaucoma

Abstract

Glaucoma is a major cause of blindness and is characterized by death of retinal ganglion cells. In a rat model of glaucoma in which intraocular pressure is raised by cautery of episcleral veins, the somata and dendritic arbors of surviving retinal ganglion cells expand. To assess physiological consequences of this change, we have measured visual receptive-field size in a primary retinal target, the superior colliculus. Using multiunit recording, receptive-field sizes were measured for glaucomatous eyes and compared to both those measured for contralateral control eyes and to homolateral eyes of unoperated animals. Episcleral vein occlusion increased intraocular pressure. This was accompanied by a significant increase in receptive-field size across the superior colliculus. The expansion of receptive fields was proportional to both degree and duration of the increase of intraocular pressure. We suggest that this increase in the size of receptive fields of glaucomatous eyes may be related to the increase in the size of dendritic arbors of the surviving ganglion cells in retina.

Adaptive Changes in the Retina and Central Visual Areas in Glaucoma

“…In primates glaucoma RGC death leads to changes in the lateral geniculate nucleus (LGN) and visual area 1 where cell loss and the shrinkage of lateral geniculate nucleus was noted (23). Similar changes have been shown in the death of specific cell types in the LGN (22,24,28). In spite of massive literature that has emerged in the past decade regarding glaucoma, we are still uncertain regarding the initiation of RGC death.…”

“…Recent evidence from mouse and rat studies showed that the optic axonal terminal synapses degenerate from the distal to proximal direction and precede the degeneration and death of RGCs (33)(34)(35). We theorize that the larger visual receptive fields in the superior colliculus of rats with elevated IOP may be the consequence of expanding terminals of the intact axons into spaces vacated by dying retinal axon terminals (22). Within 6-8 weeks of induced glaucoma, electrophysiological mapping showed no significant changes in receptive field sizes when recorded in the superior colliculus.…”

“…Within 6-8 weeks of induced glaucoma, electrophysiological mapping showed no significant changes in receptive field sizes when recorded in the superior colliculus. Dramatic changes were not observed until 4-10 months following IOP elevation (22). Visual receptive fields measured in the contralateral superior colliculus fall in the range of 15 to 20° ( Figure 1A) in normal animals.…”

“…This increase in soma size can be attributed as a precursor to their death. Another possibility is derived from developmental studies on the retina that points to the fact that increase in [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] in glaucomatous eye that are almost doubled in size when compared to normal. In these topographic mapping there was no overlap of receptive fields in the normal eye mapping, however, experimental glaucomatous eye showed numerous overlapping receptive fields.…”

Microbead models in glaucoma

“…No bead models have been used for invasive electrophysiological assessment of retinal ganglion cells and the only published study is based on an episcleral cautery model (King et al, 2006). It is likely that the majority of microbead models result in some obscuration of the visual axis.…”