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Jonathan Pieter Vande Geest, Jianhua Tong, Forest Danford, Avinash Ayyalasomayajula, Urs Utzinger, ; Quantification of the pressure dependent anterior microstructure of the lamina cribrosa using multiphoton microscopy. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4248.
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It is postulated that pressure-induced structural changes of the lamina cribrosa (LC) result in blockage of axonal transport and may therefore be a major contributor to the development of Primary Open Angle Glaucoma (POAG). Despite extensive structural characterization using multiple imaging modalities, two-photon microscopy of the LC from the intraocular side of the eye (anterior), in particular, combined with pressure-inflation has not been yet investigated.
Four pig eyes were acquired one hour post-mortem from the University of Arizona Meat Science Laboratory. The eye was halved at the equator and a gentle microdissection procedure was performed to remove the choroid, retina, and prelaminar tissue from the optic nerve head. The posterior pole was then mounted into a novel micro-optomechanical device designed for anterior LC imaging. All image data was quantified as maximum intensity projections. The sample was pre-conditioned by cycling between 5 mmHg and 45 mmHg ten times at a rate of 1 mL/min with a ten second hold at each state. Four different intraocular pressure (IOP) levels were investigated: 5, 15, 30, 45mmHg. In order to mitigate any viscoelastic effects, the pressure was held constant at the desired level for 30 minutes prior to imaging.
The mean major and minor axes of the LC measured 3.31 ± 0.24 mm and 1.88 ± 0.10 mm, respectively. The mean porosity, defined as the ratio of fluid volume to total volume, was quantified as 71.3 ± 1.2. The mean depth from the rim of the optic disc to the central vasculature was 148.1 ± 25.6 μm at 5 mmHg. No significant differences were found in the major and minor axes, and porosity of the LC at all pressure levels (p > 0.05). However, the depth significantly increased with changes in IOP, particularly from 15 mmHg to 30 mmHg (p = 0.023) and from 30 mmHg to 45 mmHg (p = 0.012).
The approach used herein is capable of quantifying the macroscopic and microscopic changes in the LC as a function of intraocular pressure on the same sample. This approach will be used to investigate IOP-induced structural changes of anterior human LC and assess its role in the development of POAG.
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