[The threshold of pupil-blocking force].

The purpose of this study was to quantitate the dynamic changes which take place in the anterior eye segment during the prone position test. The pupil-blocking force was measured before and after the prone position test (PTT) by a method of image analysis using a computer. The changes in the magnitude of pupillary block were evaluated. The mechanics of this provocation seems to be both pupillary block and direct lens block angle-closure. Pupil-blocking force standardizes the assessment of the eyes with relative pupil-block. The present results provide valuable information in the analysis of the mechanism of primary angle-closure glaucoma and also contribute to the determination of a real value for the threshold of the pupil-blocking force (approximately 0.1 or greater), followed by a clinically significant elevation of intraocular pressure.