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Shinichi Fukuda, Simone Beheregaray, Deepa Kasaragod, Kotaro Ishii, Yoshiaki Yasuno, Tetsuro Oshika; Evaluation of Bleb Birefringence after Glaucoma Surgery using Anterior Segment Polarization-Sensitive Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2014;55(13):943.
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Anterior segment optical coherence tomography (OCT) can offer important morphological information regarding the bleb function after trabeculectomy and Ex-Press Tube Shunt. However, evaluation of tissue property such as fibrosis of blebs is difficult with the conventional OCT. Polarization-sensitive OCT (PS-OCT), which is a variant of functional extensions of OCT, can improve the image contrast of OCT by measuring birefringence of biological fibrous tissues. We evaluated the birefringence of trabeculectomy and Ex-Press tube shunt blebs using anterior segment PS-OCT.
Thirty eight eyes of 30 patients with glaucoma were included. There were 18 men and 12 women, with mean age of 72.4 ± 8.5 years. Of 38 eyes, 17 (44.7%) had primary open-angle glaucoma, 7 (18.4%) had primary angle-closure glaucoma, 13 (34.2%) had pseudoexfoliation glaucoma, and 1 (2.6%) had secondary glaucoma. A custom-made three-dimensional anterior segment PS-OCT built by Computational Optics Group, University of Tsukuba was utilized in this study. The system is also based on a swept-source OCT technology, and the light source was a 30,000 Hz wavelength sweeping laser which sweeps over 110 nm across a center wavelength of 1.3 μm. Blebs were scanned with a horizontal-fast raster pattern on scanning ranges of 12 × 12 mm2, including 512 horizontal × 128 vertical A-lines.
The intraocular pressure (IOP) was higher than 21mmHg in 3 eyes (7.9%), lower or equal to 21mmHg with eye drops in 24 eyes (63.1%), and lower or equal to 21mmHg without eye drops in 11 eyes (28.9 %). In the high IOP group that we consider as non-functioning blebs, the area above the sclera flap displayed abnormal birefringence. According to the general anatomy of a bleb, the tissue above a normal bleb should be conjunctiva and Tenon’s capsule that should not possess birefringence. Hence the phase retardation image in high IOP group indicates abnormal birefringence. On the other hand, phase retardation image of the bleb in the low IOP without eye drops group that we consider as a functioning bleb showed no abnormal birefringence inside of bleb.
It was suggested that PS-OCT is a useful tool for the detailed evaluation of blebs after trabeculectomy and Ex-Press tube shunt surgery by giving information about birefringence and fibrotic changes of the bleb tissues.
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