Effect of short-term intraocular pressure increase on cat retinal ganglion cell activity.

By means of microelectrode recordings receptive field properties and flicker responses of cat retinal ganglion cells were studied during elevated intraocular pressure (IOP). At moderate IOP elevation (perfusion pressure, PP, approx. 50 mm Hg), a slight increase in the maintained activity and the neuronal activation obtained from the receptive field (RF)-center or RF-periphery occurred in some of the neurons. At critical perfusion pressure (PP 30-10 mm Hg), the RF-periphery mechanisms were less sensitive to ischemia than the RF-center mechanisms. The spontaneous activity was completely suppressed at an average PP of 36.6 +/- 9.0 mm Hg, the flicker-evoked responses at 17.7 +/- 9.6 mm Hg. At critical perfusion pressures, the stimulus-response latency increased by 20 ms at stimulation frequencies of 10-20 Hz. The critical flicker frequency was already slightly reduced at a PP of 50 mm Hg and decreased further with a further decrease in PP. The threshold values of the intensity function shifted to higher luminance levels when PP was reduced to less than 40 mm Hg, but the slope remained constant. A close interneuronal correlation was found in simultaneous recordings of pairs of ganglion cells during different levels of increased IOP. This finding indicates that the interneuronal response variability to IOP increase appearing in successively recorded neurons was predominantly caused by experimental factors. The main impairment in retinal neuronal function during increased IOP seems to occur proximal to the receptors but distal to the retinal ganglion cell somata.