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Deepa Kasaragod, Sujin Hoshi, Shinichi Fukuda, Simone Beheregaray, Tetsuro Oshika, Yoshiaki Yasuno; A Study of Short Term and Long Term Effects of IOP on Scleral Ultrastructure Using Polarization Sensitive Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4261.
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Recent studies have shown the association of scleral birefringence with scleral biomechanical properties. This has profound implications with respect to the early diagnosis of glaucoma based on the ultrastructural and biomechanical changes in sclera using polarization sensitive optical coherence tomography (PS-OCT). Here, we study the association of IOP with scleral birefringence based on its short term and long-term effects in the reorganization and orientation of collagen fibers in sclera.
Twenty eyes of subjects with neovascular age related macular degeneration receiving intravitreal anti-vascular endothelial growth factor (VEGF) therapy were measured. Scleral birefringence was obtained using custom-made prototype PS-OCT system before and after the injection of anti-VEGF. The PS-OCT volumes were obtained from region superior to cornea over scanning range 3 x 3mm over 512 A-scans x 128 B-scans. The PS-OCT volume was analyzed by a newly developed algorithm based on Bayesian statistics and quantitative scleral birefringence was obtained. Scleral birefringence of each measurement was characterized by mean, mode and standard deviation of the distribution of birefringence in a region of interest. IOP before and after the anti-VEGF therapy was measured using Goldmann’s applanation tonometer.
Significant elevation of IOP was obtained after the anti-VEGF therapy (paired t-test, p < 0.0001). Statistically significant negative correlation was found between the mean as well as standard deviation of scleral birefringence and IOP measured before anti-VEGF therapy (Pearson’s correlation, r = -0.47, p = 0.036 for mean, r =-0.47, p= 0.037 for standard deviation) (Figure 1). However, no significant correlation was found between the mode of scleral birefringence and IOP measured before anti-VEGF therapy. Interestingly, no significant correlation was found between any of the parameters of scleral birefringence and IOP after anti-VEGF therapy (Figure 2).
The results would suggest that the negative correlation of IOP with scleral birefringence is a result of the long term effect of IOP to the scleral ultrastructure including collagen. The short term alteration of IOP by anti-VEGF injection would have only non-significant effect to the scleral ultrastructure.
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