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Editors Selection IGR 9-4

Basic research: Architecture ONH

Comment by Ross Ethier on:

20090 3-D histomorphometry of the normal and early glaucomatous monkey optic nerve head: lamina cribrosa and peripapillary scleral position and thickness, Yang H; Downs JC; Girkin C et al., Investigative Ophthalmology and Visual Science, 2007; 48: 4597-4607

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Yang et al. (1244) have used sophis-ticated image processing and computerized reconstruction techniques to carefully examine a long-standing question: what happens to the architecture of the optic-nerve head in early glaucoma? This is the second of a series of articles in which optic-nerve tissues from paired eyes in monkeys with experimentally-induced unilateral ocular hypertension were morphometrically analyzed and compared. It is not trivial to quantify the complex geometry of optic-nerve head tissues in three dimensions, and the authors introduce a number of important concepts that enable this to be done and will form the basis of further such studies. Although the number of animals studied is small (n = 3), the results are striking: the lamina cribrosa showed clear signs of thickening, even when accounting for the inter-individual variations in lamina thickness in control eyes. Moreover, the lamina and the peripapillary sclera were posteriorly displaced in the experimental glaucoma eyes when compared to their fellow controls.

The lamina cribrosa and peripapillary sclera actively remodel in response to elevated IOP, and that this remodelling begins relatively early in the disease process

These results were observed early in the disease process ‐ two eyes showed changes after only three weeks of detectable change in nerve topography. It is important to understand that the observed changes in optic-nerve head archi-tecture were not due to the direct effects of pressure in the early glaucoma eyes, since both experimental and control eyes were fixed at the same IOP of 10 mmHg. The data strongly suggest that the lamina cribrosa and peripapillary sclera actively remodel in response to elevated IOP, and that this remodelling begins relatively early in the disease process. This reinforces the concept that the connective tissues of the optic nerve are mechanically important structures that respond actively to IOP. The next challenges are to understand the nature of this biomechanical response, and to determine how these important data in monkeys translate to the human disease.

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