Flash and pattern electroretinograms during and after acute intraocular pressure elevation in cats.

Retinal functionality during short-term intraocular pressure (IOP) elevation and simultaneous systemic blood pressure (BP) variations was evaluated in the cat by recording the electroretinogram in response to both homogenous flickering light (FERG) and contrast reversing gratings (PERG). The mean arterial blood pressure (BPm) was pharmacologically adjusted to different levels and a large range of IOP values was tested. Results indicate that both FERG and PERG responses are impaired when the eye perfusion pressure (PP = BPm - IOP) is reduced and they disappear at a critical PP value of about 20 mm Hg, irrespective of the absolute value of the IOP. In addition, when the critical perfusion pressure is maintained for periods longer than 5 min, the recovery of the PERG response, when present, is always delayed compared to the full recovery of the FERG response. These findings support the hypothesis that vascular factors, ie, the impairment of the retinal blood supply, may be responsible for the disappearance of the retinal electrical activity during short-term IOP elevation. Furthermore, the retinal ganglion cells, presumably the main source of the PERG response, appear less likely to recover from the acute ischemic episode.