Optic Disc Surface Compliance Testing Using Confocal Scanning Laser Tomography in the Normal Monkey Eye

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Abstract
To determine the effect of acute, experimentally increased intraocular pressure on deformation of the surface of the optic nerve head (optic nerve head surface compliance testing) in normal monkey eyes using confocal scanning laser tomography. A total of 156 compliance tests were performed on 48 normal eyes of 30 monkeys in three separate studies. Compliance testing involved obtaining confocal scanning laser tomographic images using a 10° and/or 15° and/or 20° scan angle at various times after intraocular pressure was raised from 10 to 30 or 45 mm Hg. At each point, six images were analyzed to provide a value for a parameter, called mean position of the disc, which was used to express the amount of deformation the surface of the optic nerve head had undergone at that point. Statistical analysis (ANOVA) was performed to evaluate differences in the amounts of deformation in individual eyes at different intraocular pressures and at different compliance testing sessions (studies 1 and 2) and in the two eyes of individual monkeys under the same conditions (study 3). The majority of eyes showed posterior deformation of the surface of the optic nerve head ranging from 15 to 86 μm as early as 10 minutes after intraocular pressure was increased from 10 to 30 mm Hg. When pressure was increased from 30 to 45 mm Hg in a subset of these eyes, most showed additional deformation. Of the 12 eyes for which both 15° and 20° images were obtained at the same compliance test, 7 showed larger amounts of deformation in the 20° images. Of the 18 monkeys tested in both eyes, 12 showed some differences and 4 showed substantial differences between the two eyes. In the normal monkey eye, the surface of the optic nerve head deforms rapidly (in as few as 10 minutes) in response to increased intraocular pressure. The amount of deformation varies between subjects and even within the two eyes of individual monkeys. Increasing the scan angle from 15° to 20° frequently increases the amount of deformation detected, suggesting that the peripapillary sclera and the optic nerve head may be involved in the deformation in some eyes.