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Nripun Sredar, Kevin M Ivers, Hope M Queener, George Zouridakis, Jason Porter; Examining in vivo changes in predominant lamina cribrosa beam orientation in experimental glaucoma using an automated approach. Invest. Ophthalmol. Vis. Sci. 2014;55(13):898. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The lamina cribrosa is suggested to be the initial site of damage to retinal ganglion cell axons in glaucoma. We sought to characterize changes in predominant anterior lamina cribrosa surface (ALCS) beam orientation in vivo during the progression of experimental glaucoma (EG).
We analyzed adaptive optics scanning laser ophthalmoscope (AOSLO) montages of ALCS beams previously acquired in fellow eyes of 4 rhesus monkeys at multiple time-points before and after induction of unilateral experimental glaucoma. AOSLO montages were pre-processed to minimize variations in illumination using a homomorphic filter and contrast-enhanced using a contrast limiting adaptive histogram equalization technique. The predominant orientations of laminar beams throughout a montage were estimated at different overlapping local regions of interest using principal component analysis (PCA). Differences in predominant beam orientation were calculated at corresponding locations over time in control and EG eyes.
The PCA-based method was validated using synthetic data (images of known orientation with different levels of blur and noise) and yielded estimates with small errors in local orientation (0.2 ± 0.2°). The mean difference in local laminar beam orientation across 4 control eyes each assessed at 3 different time-points was low (7.6 ± 1.1°). The mean difference in local beam orientation in EG eyes before the first significant change in beam orientation was 9.3 ± 3.4°. The first time point with a significant change in local beam orientation (mean difference across EG eyes = 38.5 ± 14.7°) coincided with the time of first significant change in manually marked ALCS pore geometry previously reported in these EG eyes. We observed that local predominant beam orientations were mainly radial at baseline, but appeared mainly circumferential at later stages of EG.
The PCA-based method operates directly on in vivo grayscale images without the need for binary segmentation, can accurately find local predominant orientation (as indicated by the low errors in synthetic images), and is repeatable (as observed by the low mean differences in control eyes over time). The PCA-based technique can be used to accurately and objectively detect in vivo changes in predominant laminar beam orientation in early EG and track longitudinal changes during disease progression.
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