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Transscleral OCT to image anterior segment shows potential
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LUBECK, Germany — Transscleral infrared optical coherence tomographic imaging shows “significant potential” as a noninvasive diagnostic tool for the anterior chamber, according to Hans Hoerauf, MD, and colleagues.
Currently, options for in vivo imaging of the anterior chamber are limited. Ultrasound biomicroscopy is useful, but it requires an immersion technique and a trained examiner. Dr. Hoerauf and colleagues investigated the possibility of using a slit-lamp-mounted noncontact optical coherence tomographer (OCT) to image the anterior chamber.
In a pilot study, they used a modified OCT system to perform noncontact, two-dimensional, cross-sectional imaging of the structures of the anterior segment in a group of healthy volunteers. The prototype was equipped with a superluminescence diode with an infrared wavelength of 1310 nm. (Existing OCT systems, which use a wavelength of 830 nm, achieve only limited penetration of the sclera.)
Measurements of the eye were performed perpendicular to the sclera over the pars plana, the ciliary body and the chamber angle region or perpendicular to the surface of the iris.
Complete visualization of the anterior chamber angle was possible with the infrared OCT system. Peripheral cornea appeared hyporeflective. Scanning with the incident beam perpendicular to the scleral surface resulted in a maximized reflection in the OCT image. Off-axis, the reflectivity decreased. Posterior to the trabecular meshwork, a hyporeflective area could be reproducibly demonstrated, corresponding to the longitudinal part of the ciliary muscle, Dr. Hoerauf said.
Directing the incident OCT beam through the iris resulted in complete shadowing of retroiridal structures caused by a combination of both the high backscattering and absorption properties of the iris pigment epithelium, he added.
“In contrast to the existing systems, complete transscleral visualization of the chamber angle and the ciliary body could be achieved,” Dr. Hoerauf wrote in the June issue of Archives of Ophthalmology. “The aim of further studies should be an increase of scleral transmission, which may be achieved by pressure to the scleral surface, or the use of glycerin, which may increase the transparency of the sclera.”