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Editors Selection IGR 15-2

Anatomical Structures: IOP-induced laminar changes in POAG and APAC

Comment by Ian Sigal on:

55960 Changes in the lamina and prelamina after intraocular pressure reduction in patients with primary open-angle glaucoma and acute primary angle-closure, Park HY; Shin HY; Jung KI et al., Investigative Ophthalmology and Visual Science, 2014; 55: 233-239

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Deformations of the optic nerve head (ONH), particularly the lamina cribrosa, in response to IOP elevation are likely to be a major factor on retinal ganglion cell axon insult and thus play a role in the development and progression of glaucoma. Park et al. acquired and analyzed SD-OCT images from 20 patients with primary open-angle glaucoma (POAG) who underwent glaucoma surgery and 17 patients with acute primary angle-closure (APAC) who underwent laser peripheral iridoplasty. Eyes were imaged before and one month after the IOP-reducing intervention, and the anterior prelaminar and laminar surfaces delineated manually on several B-scans. The positions of these surfaces relative to Bruch's membrane opening and their changes with IOP treatment were analyzed.

The most important result was that for similar IOP reductions APAC patients showed significantly more pronounced anterior movement of the laminar and prelaminar tissues and thickening of the prelaminar tissues than POAG patients. The effects of the IOP reduction on POAG eyes confirm previous findings [1], but the comparison with APAC eyes is novel to the study by Park et al. The results are interesting because if the changes in prelaminar and laminar tissues due to the IOP-reduction treatment are taken as a measure of 'relief' from the insult to the axons due to the elevated IOP, then the smaller changes in POAG eyes could suggest that these eyes benefit less from IOP-lowering treatment than APAC eyes. The actual 'relief' to the axons may be the result of a complex interaction between the level of IOP, tissue anatomy, biomechanical properties (e.g., stiffness) and astrocyte sensitivity among other factors, and not directly captured by lamina or prelaminar displacement. Also, the results show that after a couple of days exposure to elevated IOP (2.5 ± 1.3 days in APAC eyes), there are still significant differences in morphology and sensitivity to IOP reduction with eyes that lived under chronic IOP elevation (at least 78 ± 21 days in POAG eyes). However, as a cross-sectional study, the results cannot tell if the characteristics of the POAG eyes are the result of the chronic IOP elevation, or if they were an existing risk factor.

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