Visual evoked potentials were recorded in six normal subjects and in three patients with primary open-angle glaucoma, while intraocular pressure was artificially elevated in stepwise increases. The resulting perfusion-pressure amplitude curves in our controls showed a kink, which can be interpreted as a sign of vascular autoregulation. No kink was observed in the curves of our glaucoma patients, which we interpret as indicating a lack of vascular autoregulation in primary open-angle glaucoma.

SUMMARY Twenty eyes of 10 healthy subjects, 11 eyes of seven patients with low tension glaucoma, and three eyes of three patients with ischaemic optic neuropathy were investigated. Visual evoked responses were recorded under stepwise artificially increased intraocular pressures. The results of the visual evoked response recording (pressure compliance test) allow a clear distinction to be made between healthy subjects, patients with low tension glaucoma, and patients with ischaemic optic neuropathy. In the groups investigated a lack of autoregulation of the optic nerve head circulation was found in patients with low tension glaucoma only. Patients with anterior ischaemic optic neuropathy showed the same pressure compliance behaviour as healthy subjects. The methods used here seem to provide a practicable clinical tool in the differential diagnosis of low tension glaucoma.

Healthy subjects show, in a special pressure compliance test of the optic nerve head, signs of autoregulation of optic nerve head circulation. In this test visual evoked response (VER) amplitudes were recorded during stepwise increased intraocular pressures. In the resulting VER amplitude/pressure curves glaucoma patients did not show the sign of autoregulation of optic nerve head circulation which is seen in healthy subjects. It is known that topically applied timolol maleate may affect optic nerve head circulation. Therefore the pressure compliance test was performed in 20 healthy eyes before and after 3 days of topically applied timolol maleate 0.5%. The aim of the study was to test the effect of topically applied timolol on optic nerve head autoregulation. In addition we determined the ocular perfusion pressures, heart rate and mean arterial blood pressure. While the ocular perfusion pressures show a slight, but statistically not significant, decrease under timolol, the systemic parameters and the autoregulation behavior did not change.

In a planned, randomized, double blind study ocular perfusion pressures were measured before and after a 3-day regimen of 2% carteolol hydrochloride or 0.5% timolol maleate. A pressure tolerance test was also carried out. The results of this test revealed the critical pressure: it is the artificially increased intraocular pressure at which the visual function (monitored by visually evoked cortical potentials) is reduced to 20% of its initial value. The ocular prefusion pressures are affected by both drugs. They are more clearly reduced by carteolol than by timolol. The critical pressure is affected by both drugs too. After application of carteolol, the critical pressure is clearly lower than after application of timolol. The difference is statistically significant (p < 0.05).

The analysis of corneal topography has recently become popular, mainly as a consequence of the rapid development of refractive surgery techniques. To date, computer-assisted evaluation of photokeratoscope pictures has been the most popular method used to assess corneal topography. The processing system described previously by other authors requires hand-digitizing of the photokeratoscope pictures and therefore the constant presence of an operator for a considerable amount of time. We have introduced the use of a video camera to digitize the photokeratoscope images, making the processing automatic and quicker. Moreover, precision glass spheres have been used to calibrate the system in order to minimize the intrinsic errors even further. The data obtained from the computerized analysis are presented in three different ways. Besides having the numerical values in diopters, corneal maps with various shades of grey are used, together with the quantitative, three-dimensional representation of corneal astigmatism. An automated system for the analysis of corneal topography was tested for both experimental models and clinical conditions. It was easy to use and showed high precision (less than 1% error when processing photographs of precision glass spheres).