Provocative test combining water drinking and homatropine eye drops: Applanation versus tonography

Abstract

In twenty subjects (ten open-angle glaucoma suspects, two cases of open-angle glaucoma, and eight first-degree relatives of patients with open-angle glaucoma), the rise in applanation tension after water drinking (20 ml./kg. body-weight) combined with gutt. Homatropine 2 per cent. was significantly greater after 45 than after I5 min. (ooi < P < 0-02). The maximum rise occurred at or betweeln 30 and 45 min. after the provocation. A high maximum applanation reading tended to occur significantly later than a low maximum (0.01 < P <0.05). Another twenty subjects (fourteen open-angle glaucoma suspects, five first-degree relatives of patients with open-angle glaucoma, and one patient with "unilateral" openangle glaucoma) each had a water-drinking homatropine applanation test and a waterdrinking homatropine tonography test in random order on one eye. The effects of the provocation were measured by a second applanation or tonography reading 45 min. after the provocation. The applanation test was considered marginally better than the tonography test because the rise in applanation tension in the former was slightly more significant than the rise in outflow resistance, and the scatter of the rise in applanation tension was noticeably smaller than the scatter of the rise in outflow resistance. It is therefore planned to compare the effects of a water-drinking homatropine applanation test on normal subjects and patients with open-angle glaucoma. The older the patient the higher the rise in applanation tension in response to water drinking plus homatropine (significant at 0.01 < P < 0.05). The rise in applanation tension in the water-drinking homatropine tonography test, i.e. when a 4-min. tonography had been done after the initial applanation tension (before provocation), tended to be higher if the axial length was short (significant correlation P < 0.01), probably because the squeezing-out effect of the initial tonography magnified a tendency for the effect of provocation to be dependent on the surface area of the corneo-scleral envelope.