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Christian M. Hammer, Christoph Braunsmann, Johannes Rheinländer, Tilman Schäffer, Friedrich E. Kruse, Ursula Schlötzer-Schrehardt; Evaluation Of Lamina Cribrosa And Peripapillary Sclera Stiffness in Pseudoexfoliation and Normal Eyes By Atomic Force Microscopy. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4813.
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© ARVO (1962-2015); The Authors (2016-present)
In previous studies, the lamina cribrosa (LC) of pseudoexfoliation (PEX) eyes was shown to exhibit conspicuous elastotic alterations, which were proposed to account for biomechanical changes of the LC, rendering the optic nerve head (ONH) vulnerable to intraocular pressure. In this pilot study, we evaluated the suitability of atomic force microscopy (AFM) for the comparative analysis of biomechanical properties of LC and peripapillary sclera (ppSC) in eyes with and without PEX syndrome.
Frontal cryosections of 5 µm thickness were prepared from the ONH of age-matched eyes with (n=3) and without (n=3) PEX syndrome at the level of the LC. Unfixed sections were dried, frozen, and reconstituted in phosphate buffered saline immediately before AFM. For each section, three regions of interest (ROI) measuring 90x90 µm² and containing at least one LC-beam were selected manually for AFM force mapping. One additional ROI was placed on the ppSC surrounding the LC in each specimen. The AFM used was endowed with a NanoWorld sphere-cantilever (spring constant k=4.5 N/m, tip radius R= 0.98 µm). The force curves were generated with a maximum indentation force of 50 nN, resulting in an indentation depth of approximately 500-1000 nm.
The LC- and ppSC-derived values were expressed as Young’s modulus and summarized as medians for every force map. The LC-related medians averaged on 8.0 kPa (±0.6) for PEX eyes as opposed to 13.4 kPa (±1.5) for normal age-matched eyes, indicating a marked reduction in Young’s modulus by 40% in PEX specimens. The respective ppSC-related values were 80.0 kPa (±21.2) for PEX and 124.5 kPa (±37.5) for control eyes, reflecting a similar PEX-associated decrease in Young’s modulus by 35%.
These data provide evidence for AFM as a suitable technology for direct biomechanical analyses of ONH connective tissues, encouraging further large-scale analyses. The marked decrease in stiffness and increased deformability of LC and ppSC tissue in PEX eyes may reflect an inherent tissue weakness and increased vulnerability for glaucomatous optic nerve damage.
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