Quantification of change in axonal birefringence following surgical reduction in intraocular pressure.
BACKGROUND AND OBJECTIVE: the purpose of this study was to examine the hypothesis that retinal nerve fiber layer (RNFL) birefringence increases following surgical reduction of intraocular pressure (IOP). PATIENTS AND METHODS: twenty-six glaucomatous eyes requiring trabeculectomy or drainage implant were enrolled. Optical coherence tomography (OCT), scanning laser polarimetry (SLP), and IOP measurements were performed preoperatively and 3 months postoperatively. The OCT and SLP images were aligned using a new algorithm that aligns the vessels in an OCT image to those in the corresponding SLP reflectance image. The SLP retardance values at the location of the OCT scan circle were then extracted using the OCT scan circle position inferred by the algorithm. Sixty-four corresponding RNFL segments were extracted from SLP and OCT to calculate RNFL birefringence. A significant birefringence change was defined as 1.96 times the weighted test-retest standard deviation in four contiguous segments. RESULTS: preoperative IOP (19.3 ± 6.1 mm Hg) was significantly (P < .001) lower than postoperative IOP (10.4 ± 3.7 mm Hg). Average birefringence magnitude did not change (P = .19) postoperatively. Localized birefringence magnitude increased significantly in 6 (23%) eyes and decreased significantly in 7 (27%) eyes. CONCLUSION: in this cohort, variable changes in localized birefringence were observed following surgical reduction of IOP.
Sehi, M; Grewal, DS; Zhu, H; Feuer, WJ; Greenfield, DS
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