Observation of physiological change in the human ciliary body using an ultrasound biomicroscope during accommodation]

PURPOSE: To evaluate changes in the ciliary body during accommodation using an ultrasound biomicroscope (UBM). SUBJECTS AND METHODS: Eleven healthy persons, aged from 24 to 33 years, served as subjects. They were asked to lie in the supine position and to fixate a target placed on the ceiling 2 m above with the left eye. A concave lens with the power of -6 to -8 diopters was then placed before the fixating left eye. The thickness of the ciliary body in the right eye was measured by UBM in the nonaccommodative and accommodative states. FINDINGS: The anterior chamber in the right eye became significantly shallow during accommodation. The thickness of the ciliary body significantly increased during accommodation at 0.5 mm and 1.0 mm posterior to the scleral spur. It significantly decreased at 2.0 mm, 2.5 mm and 3.0 mm posterior to the scleral spur. CONCLUSION: During induced accommodation in the left eye, the anterior portion of the ciliary body in the right eye increased and the posterior portion decreased in thickness. The findings imply that the circular ciliary muscles are mainly involved in accommodation and not the longitudinal muscles.