Intraocular pressure responses to systemic autonomic stimulation.

The intraocular pressure (IOP) responses to two standard tests of autonomic nerve function were studied in 15 healthy subjects, mean age 33 years (range: 20-64). Both tests are based on cardiovascular reflexes: (1) The rise in diastolic blood pressure provoked by sustained isometric muscle contraction, a response mediated by the sympathetic nervous system and (2) The heart-rate responses to the Valsalva manoeuvre, a response mediated by the parasympathetic nervous system. During sustained isometric exercise, the mean IOP decreased significantly from baseline values of 12.60 mmHg (SEM 0.55) to 11.26 mmHg (SEM 0.32, p less than 0.05) while mean diastolic blood pressure increased by 20.80 mmHg (range: +12 to +53 mmHg). However there was no direct correlation between them (r = -0.05). Post exercise the mean IOP remained significantly lower than baseline values for five minutes (p less than 0.01). During the Valsalva manoeuvre, there was a significant increase in IOP of 7.20 mmHg from a baseline of 12.80 mmHg (SEM 0.45) to 20.00 mmHg (SEM 0.78, p less than 0.001); during the recovery period, mean IOP was significantly lower than baseline values at 12.13 mmHg (SEM 0.39, p less than 0.05). The mean Valsalva ratio was normal at 1.68 (range: 1.2-2.6). The possible mechanisms involved in these responses are discussed.