OCT can play a role in corneal, anterior segment procedures

Ophthalmologists are familiar with the use of optical coherence tomography (OCT) for the back of the eye. Now, there also is a role for OCT in anterior segment corneal procedures and complications, reported Ronald Smith, MD, of the United States at the World Ophthalmology Congress on Wednesday.

Dr. Smith said that at the Doheny Eye Institute at the University of Southern California, where he is chairman, studies are being conducted looking at the use of corneal and anterior segment OCT for the disorders of the cornea and anterior segment.

Dr. Smith pointed out the advantages of OCT, including its high resolution, its non-contact to the eye, and its wider field possible. OCT has been used to determine corneal thickness, to determine ablation depth, and to understand the thickness of the flap and stromal bed.

OCT has a scanning pattern of 8 radial lines and provides a 3-D reconstruction of the cornea for some cases. OCT also provides the average and the smallest thickness of the cornea at each quadrant. It's repeatable at less than 2 microns and it works well with ultrasound OCT. Dr. Smith added that OCT is useful in confirming the various disorders of ectasia of the cornea.

Dr. Smith presented several case studies where OCT images were used to help diagnose various cornea disorders. Cases included a post-op, day 1 LASIK case, in which the flaps were distinguishable by the OCT characteristics.

Another case involved keratectasia in which the patient had LASIK nine years ago with two enhancements. Dr. Smith said the question was, "What's the next step in the management of the case?" The OCT showed a thin inner layer, indicating an ectatic type of complication. The OCT finding determined that another excimer laser procedure was out of the question.

"(OCT) is a way to determine if there is ectasia present in this post-operative case," Dr. Smith said. "That means we would not advise an enhancement. We advised Intacs or a contact lens."

OCT is also useful to determine exactly the parameters inside the cornea when Intacs are inserted. OCT can determine the recess-to-recess anterior chamber width. A recent study showed that standard deviation using OCT for the anterior chamber width was very small compared to the standard deviation using the usual techniques for determining anterior segments widths.

Dr. Smith then cited the work of Jonathan Song, MD at Doheny. Dr. Song is interested in deep lamellar endothelial keratoplasty (DLEK). Dr. Song is using OCT technology to study the positioning of the inner layer of the endothelium and stroma in patients who have had DLEK and Descemet stripping endothelial keratoplasty (DSEK). Dr. Song feels that this imaging approach may give the clarity that physicians need to determine exactly what is being done in patients who have had this type of corneal surgery.