Author: Dr Tetsuro Oshika

Optical coherent tomography (OCT) technologies are evolving. We have been working on two new generations of anterior segment OCT (AS-OCT). First project is Topcon Triton, which is OCT angiography (OCTA) focusing on microvasculatures of the anterior ocular segment. We apply a novel motion correction algorithm which improves OCTA image quality by stitching repeated OCT volume scans or aligning intra– and inter-B-frames. And then, OCTA images are generated by a ratio method which analyzes four consecutive OCT B-scan images to evaluate intensity changes. Furthermore, a special viewer program was utilized to visualize microvasculatures in en-face and cross-sectional views of OCTA data along with corresponding structural OCT images. AS-OCTA was used to assess corneal neovascularization and vascular changes in filtering bleb after trabeculectomy. Highly detailed vasculature in the sclera were observed both in normal eye and the eyes with corneal neovascularization. It was possible to elucidate neovascularization especially in the area of corneal neovascularization in detail using projection and en-face OCTA images. We were able to assess surgical outcomes and wound healing reaction of a filtering bleb after trabeculectomy with combination of en-face images and cross sectional images.

Second project is polarization sensitive (PS)-OCT. The polarization state of light changes when passing through abnormal fibrotic tissue (e.g., in the scar). PS-OCT uses these polarization state changes to measure the depth-resolved polarization properties of tissues. PS-OCT obtains two types of birefringence data, referred to as (1) phase retardation data and (2) local birefringence data.PS-OCT can also obtain intensity images simultaneously, which perfectly co-register with the phase retardation and local birefringence images. Phase retardation images provide the accumulated polarization effect along the depth. Local birefringence is a truly depth-resolved polarization quantity. We applied this technology to assess filtering blebs after glaucoma surgery and eyes with keratoconus including its early stages.