Abstract
Abstract: :
Purpose: To characterize microscopic changes in the lamina cribrosa in vivo in a primate model of experimental glaucoma using newly developed technology for improved imaging: an adaptive optics scanning laser ophthalmoscope (AOSLO). Methods: Both eyes of three rhesus monkeys that had undergone monocular laser treatment in the right eye to produce ocular hypertension and the right eye of a normal control monkey were imaged. The stage of glaucoma for each treated eye was assessed behaviorally by standard clinical perimetry. At the time of imaging, two of the three monkeys were at a moderate stage (MD < –8 dB) and the third had advanced stage glaucoma (MD = –28 dB). To determine whether there were associated changes in the structure of the lamina cribrosa the monkeys were anesthetized and the lamina cribrosa in each eye was imaged using the AOSLO. Off–line analysis entailed registration of the 15 best video frames to obtain a single image. Morphological parameters of the pores in lamina cribrosa [area, major axis length, elongation (major axis/minor axis)] and nearest neighbor distances were measured. Results: Pore areas (in units of pixels) showed substantial intra and inter subject variability in the four normal eyes (mean ± SD for the eyes was: 339±205; 419±261; 233±131; 140±82). Pore area was significantly greater (t–Test, p<0.05) and more variable in all three glaucomatous eyes compared to their normal fellow eyes [1) OD 493±489 OS 233±131, 2) OD 1076±1051 OS 419±261, 3) OD 719±593 OS 140±82]. In the eye that was at an advanced stage of glaucoma elongation of the pores was also evident. Nearest neighbor distances were greater in the glaucomatous eye than the fellow eye in all three pairs but statistical significance (p<0.05) was achieved in two pairs only. Conclusions: AOSLO has the potential to provide high resolution, non–invasive visualization of lamina cribrosa changes during glaucoma. The presence of moderate glaucomatous damage is reflected by a mean enlargement and increased variability in the sizes of the lamina pores. The results suggest that AOSLO imaging can provide clinical documentation of structural alterations of lamina cribrosa during progression of glaucomatous changes.
Keywords: lamina cribrosa • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • optic disc