Comparison of a noninvasive measurement of optic nervehead mechanical compliance with an invasive method.

We have postulated that abnormal mechanical support of the optic nervehead at the level of the lamina cribrosa could be the precursor of glaucomatous damage. Recent studies have shown deformations of the lamina cribrosa to be among the earliest changes in glaucoma. To evaluate the support of the nervehead, we have developed a noninvasive optical method to measure the optic nervehead compliance, namely, the displacement of the optic nervehead induced by an artificial increase in intraocular pressure. To test the validity of the method, we have compared noninvasive measurements obtained in post-mortem enucleated human eyes with those recorded using an invasive technique. Both methods had a reproducibility better than 6 microns and induced no damage capable of interfering with the results. The displacements measured by both methods were similar, thus indicating that our optical method is capable of measuring bulk motion of the optic nervehead. Our results were identical with those obtained by other authors using a third method. The data obtained also established the normal range of optic nervehead displacements induced by a range of intraocular pressure increments.