Ultrasound biomicroscopic morphometry of the anterior eye segment before and after one drop of pilocarpine

To measure anterior eye-segment morphometric data using ultrasound biomicroscopy. This is a new high-frequency, high-resolution ultrasound method enabling the visualisation of the anterior segment of the living eye with magnification similar to a light microscope. Thirteen morphometric parameters of the anterior eye segment were measured before and after the application of one drop of pilocarpine in 10 eyes of 5 persons, using a Zeiss-Humphrey Ultrasound Biomicroscope at a frequency of 50 MHz. In each session, 3 morphometric parameters in the central images (corneal thickness, anterior chamber depth, pupillary diameter) were measured 4 times, and 10 parameters in the radial images (scleral thickness, angle-opening distance, trabecular-iris angle, trabecular-ciliary process distance [TCPD], iris thickness, 1, 2 and 3, iris-ciliary process distance, iris-lens contact distance [ILCD], iris elevation) were measured on the 3, 6 and 9 o'clock meridians three times each. Statistically significant changes were noted in the following parameters: pupillary diameter, iris thickness 1 and 2, and TCPD were decreased, while ILCD was increased after pilocarpine. Wide chamber angles showed a tendency to become narrower and narrow ones to become wider after pilocarpine. One drop of pilocarpine caused significant changes in the anterior eye segment morphology. Not only the pupillary diameter decreased but iris thickness and trabecular-ciliary process distance were also decreased simultaneously. At the same time the contact surface between the lens and iris increased significantly. Ultrasound biomicroscopy gives new morphometric image information about the anterior eye segment which is not available using conventional gonioscopy or ophthalmic echography.