QUANTITATIVE-ANALYSIS OF THE LAMINA-CRIBROSA IN-VIVO USING A SCANNINGLASER OPTHALMOSCOPE

Purpose. Structural changes in the lamina cribrosa have been implicate d in the pathogenesis of glaucomatous optic nerve atrophy. The purpose of this study was to develop a method for morphometric analysis of th e lamina cribrosa pores in vivo, using a scanning laser ophthalmoscope . Methods. A prototype Zeiss confocal laser scanning ophthalmoscope wa s used to acquire images of the lamina cribrosa. The images were digit ised and aligned to compensate for eye movements. Thirty-two consecuti ve images were averaged to reduce noise. The images were processed to adjust for luminance gradients prior to segmentation and analysis. Det ails of the image processing are described. Results. The end result of processing the images was a binary (black and white) image that can b e used for automated computer assisted measurements. The pores of the lamina cribrosa are well represented and retain their overall shape in the binary image, as judged by superimposing the binary image on the unprocessed image. We also established the repeatability, reproducibil ity and intercession variability of this technique. Repeated images of the internal lamina cribrosa of 10 patients were acquired, by two obs ervers in two separate visits, and the images were processed before au tomated computer measurements. The parameters evaluated were number of pores, area covered by the pores and area covered by the visible lami na cribrosa. The coefficient of variation for number of pores, pore ar ea and lamina area was 6.9%, 2.1% and 4.3% for observer A and 5.5%, 2. 1% and 5.8% for observer B. Pearson product moment correlation coeffic ient between the two observers was 0.94, 0.99 and 0.97 for the above p arameters respectively. There was no significant difference between th e measurements on visit 1 and 2 for both observers. Conclusions. The t echnique described allows, for the first time, in vivo morphometry of the internal lamine cribrosa surface. This method has good reproducibi lity, suggesting future clinical applications.