The amplitude of the intraocular pressure pulse and pulsatile ocular blood flow (POBF) were correlated with the axial length and refraction of 68 eyes of healthy subjects. Measurements were obtained with subjects in the sitting position using an ophthalmic A-scan and a pneumotonometer linked to a Langham ocular blood-flow system. The amplitude of the ocular pulse and the magnitude of POBF were found to decrease with increasing axial length (r = -0.61, P less than 0.001 and r = -0.74, P less than 0.001, respectively). A similar close relationship was found between the ocular pulse amplitude and POBF and the refractive state of the eye (r = 0.63, P less than 0.001 and r = 0.7, P less than 0.001, respectively). The reasons for the association are discussed and the importance of the observations in the construction of studies in which ocular pulse amplitude or POBF are to be measured in different groups of subjects is emphasised.

The pulsatile ocular blood flow (POBF)

Urinary excretion of orally administered lactulose and 51 chromium labelled ethylenediamine tetra-acetate (5lCr-EDTA) was measured in 12 healthy adult subjects and in six patients with ileostomies to assess intestinal permeability. In normal subjects, 24 hour urinary recovery of 51Cr-EDTA was significantly greater than that of lactulose (mean (SEM) 2*27 (0-15) v 0*50 (0.08)% oral dose; p<0001), but in ileostomy patients recovery of the two markers was the same. In normal subjects, therefore, the difference between the two markers may arise from bacterial breakdown of lactulose but not of 51Cr-EDTA in the distal bowel, urinary excretion of lactulose representing small intestinal permeation and that of 51Cr-EDTA representing both small and large intestinal permeation. The markers were then given simultaneously to nine patients receiving non-steroidal antiinflammatory drugs (NSAIDs) for rheumatoid arthritis and osteoarthritis. The 24 hour urinary recovery of 5ICr-EDTA in the patients was significantly greater than normal (4-64 (1-20) v 2-27 (0.15)% oral dose; p<0-01), but that of lactulose was not significantly affected. Moreover, the increase in 51Cr-EDTA recovery was most noticeable in the later urine collections. Both of these findings suggest that NSAIDs may increase colonic permeability.

Using pneumotonometry combined with a Langham ocular blood-flow system, measurements of pulsatile ocular blood flow (POBF) were performed in eight ocular normotensive patients with implanted cardiac pacemakers, with the subjects assuming both the erect and the supine postures. Sequential measurements of POBF were made at pre-set values of heart rate over the physiological range between 60 and 120 beats/min at intervals of 10 beats/min. With patients in the supine position, measurements of cardiac output and stroke volume indices were also recorded by impedance cardiography. The mean pulse amplitude of the intraocular pressure (the ocular pulse) decreased as heart rate increased, and this change was statistically significant in both postures according to repeated-measures analysis of variance (erect: f = 18.7, P less than 0.0001; supine: f = 18.8, P less than 0.0001). As measured in supine patients following an increase in heart rate, the pulse amplitude decreased in parallel with a decline in stroke volume index (f = 18.8, P less than 0.0001). Up to a level of 90 beats/min, the mean POBF increased with heart rate, but it declined above this rate in both erect and supine postures. At all heart rates, intraocular pressure was higher when subjects were supine than when they stood erect (f = 4.3, P less than 0.001). At lower heart rates of 70 and 80 beats/min, ocular pulse volume and POBF were significantly lower in supine patients than in erect subjects (70 beats/min: t = 3.89, P less than 0.01 vs; t = 3.87, P less than 0.01; 80 beats/min: t = 2.85, P less than 0.05 vs; t = 2.87, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Measurements of pulsatile ocular blood flow (POBF) have been recorded in a group of healthy, ocular normotensive volunteers and ocular hypertensive patients recruited from outpatients. Use ofa pneumotonometric probe linked to a Langham ocular blood flow system enabled readings of intraocular pressure and its variation with heart rate (ocular pulse) to be taken in erect and supine positions. Pulsatile ocular blood flow was calculated from these values by means of the pressure-volume relationship previously described for living human eyes. Assumption of the supine posture was accompanied by a significant rise in intraocular pressure; in normal eyes (mean, with SEM) (3-1 (0-4) mmHg, p<0-0001) and to a greater extent in ocular hypertensive eyes (4-7 (0.6) mmHg, p<0-0001). The POBF did not differ significantly between normotensive and ocular hypertensive groups in either the erect or supine postures. In both groups, however, assumption of the supine posture was accompanied by a significant fail in POBF (normals: -121 (21) tl/min, p<0-0001; ocular hypertensives: -75 (16) pl/min, p<00002). These reductions in POBF represent decrements of 27-5 (3.0)% and 17-1 (3-8)% respectively. Pulsatile ocular blood flow is reduced in the supine posture, and this may result in tissue hypoxia in subjects at risk of developing glaucoma. A companion paper describes the measurement of POBF in a group of patients with chronic open angle glaucoma treated with topical timolol 0*25%.