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Lisa A. Ostrin, Li-Fang Hung, Earl L. Smith, III, Christine F. Wildsoet; Lamina Cribrosa Geometry and Axial Length in Normal Rhesus Monkeys. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3469.
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Myopes have a 2-3 times higher risk of developing glaucoma. The lamina cribrosa, which has been implicated as a site of neural damage in glaucoma, has previously been shown to undergo biomechanical changes with increased intra-ocular pressure. This study begins to address the question of whether structural changes in the lamina cribrosa explain why myopes are more susceptible to glaucomatous damage, by examining the relationship between axial length and refraction with lamina cribrosa gross morphology in the context of experimental myopia.
En face scanning electron microscopy (SEM) images of the lamina cribrosa (LC) were obtained from 21 enucleated eyes of 11 rhesus monkeys (aged 128±38 days) that been part of experimental myopia studies. In vivo axial lengths, measured with an IOLMaster, and refractions (spherical equivalent, SE) were available for these eyes. To visualize the lamina cribrosa pores, optic nerve head (ONH) tissue was washed in 10% NaOH to remove cellular and neural components after fixation with gluteraldehyde. Scleral canal dimensions (area, Feret’s diameter and circumference) for all eyes, as well as LC pore geometry for a subset of 10 eyes (304±60 pores per eye), were analyzed with Adobe Photoshop and ImageJ. Summary statistics and results of correlation analyses are reported.
For the 21 eyes, mean axial length was 16.25±0.68 mm (range: 15.11-18.58 mm) and SE was -4.16±3.92 D (range: -7.63 to +11.44 D). Scleral canal area was 0.821±0.149 mm2 (range: 0.6-1.16 mm2) and was positively correlated with axial length, i.e. longer eyes tended to have larger scleral canals, as were scleral canal perimeter and diameter (r2=0.48, 0.41 and 0.44 respectively). Lamina cribrosa pores ranged in size from 0.83 to 1505.14 µm2 (mean: 268±214 µm2). However, pore size and axial length were not correlated (r2=0.001).
In these eyes, some of which were part of lens- and diffuser-induced myopia experiments, scleral canal size, but not lamina cribrosa pore size, was correlated with axial length and SE. This study provides the basis for further investigations into the effects of myopia on lamina cribrosa, including the influence of duration and degree of myopia.
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