Quantitative regional structure of the normal human lamina cribrosa. A racial comparison.

We digitized magnified photographs of cross-sections of the laminae cribrosae of 16 normal subjects 50 or more years of age. The sample included 7 blacks and 9 age-matched whites. Connective tissue area as a proportion of the lamina cribrosa area was significantly less and pores were significantly larger in the superior and inferior than in the nasal and temporal quadrants of the lamina cribrosa. These differences were more pronounced for peripheral as compared with central regions of the lamina cribrosa. Less connective tissue support for nerve fibers in the superior and inferior quadrants of the optic nerve head could contribute to their greater susceptibility to glaucoma damage by allowing greater distortion of these regions at elevated intraocular pressures. The least connective tissue support was present in the inferoperipheral region of the lamina cribrosa, which may be related to the greater frequency of superior visual field defects in glaucoma. Blacks had larger total lamina cribrosa area, indicating a larger optic nerve head, and also a greater number of laminar pores than whites. However, the connective tissue proportion and pore size distribution in the laminae cribrosae of blacks were almost identical to those of whites. We found no evidence suggesting that the greater susceptibility of blacks to glaucoma damage is due to less connective tissue support for nerve fibers passing through their laminae cribrosae than in whites.