Optical Coherence Tomography Gives New Insight Into Choroid

Optical coherence tomography (OCT) has revolutionized many aspects of ophthalmology, and the Ophthalmic Imaging Center at Cleveland Clinic’s Cole Eye Institute continues to push the envelope on its uses.

OCT has been used for several years to image the retina and the vitreoretinal interface, but not to evaluate the choroid, as it was widely believed that OCT could not obtain quality choroidal images, says Peter K. Kaiser, MD, Director of the Ophthalmic Imaging Center.

“However, it turns out that the reason we weren’t imaging the choroid had to do with how we focused the OCT device. If we focus the device more into the choroid than the retina, essentially pushing the focus further into the eye, we can actually image the choroid with current OCT scanners,” says Dr. Kaiser.

This technique was first described by Richard F. Spaide, MD, of New York, who termed it enhanced depth imaging.

“There are various names for this technique, but what it really allows is evaluating the choroid, and in some cases, you can image the sclera and orbital fat,” Dr. Kaiser says.

This is important because some diseases affect the choroid in different ways, and having better information aids in diagnosis and care, he notes.

Diagnosing Central Serous Chorioretinopathy

One of the earliest applications Dr. Kaiser and his colleagues have found is that the choroid is thickened in patients with central serous chorioretinopathy. In those patients, an enhanced imaging OCT scan is a much easier way to make a diagnosis than with fluorescein or indocyanine green angiography.

“When you are able to see the choroid is thickened in both eyes, you know your diagnosis is central serous. We previously had no way to differentiate it from other masquerade syndromes such as age-related macular degeneration (AMD),” he says.

This is particularly true in older patients who have subretinal pigment epithelial fluid, in whom the condition can be misdiagnosed as exudative AMD.

“I have seen numerous patients who have been receiving anti-VEGF injections at an outside ophthalmologist’s office and they come to me for a second opinion. We do enhanced depth imaging and are able to tell them they have central serous chorioretinopathy and don’t need any injections, and in fact they have a much better visual prognosis,” he says.

Automated Software

In the past, Dr. Kaiser notes, ophthalmologists had to do manual measurements to determine choroidal thickness, which is tedious. The Ophthalmic Imaging Center has developed automated analysis software that allows physicians to look at choroidal thickness, area and volume across the OCT scan.

Dr. Kaiser and his colleagues have made several other interesting observations about the choroid in their work. For example, patients who are extremely myopic have a very thin choroid. Patients with age-related choroidal atrophy have features that are not typical of macular degeneration but are still losing vision. “It is a different mechanism than macular degeneration,” he says.

Enhanced depth OCT also is useful in managing uveitis. “With treatment, you can actually see the choroidal thickness go back toward normal in many uveitic disorders,” Dr. Kaiser says.

He and his colleagues also are using enhanced depth imaging to examine retinal degeneration and ocular tumors.

“This is a field in its infancy. In the past, we couldn’t really image the choroid, so we didn’t really pay attention to it. Now that we can image it, we are looking at it in more detail,” he says.

The Ophthalmic Imaging Center is using different-wavelength OCT systems that have different penetration than the currently available commercial spectral domain OCT devices to obtain an even better view of the choroid.

“As we do more and more scans, we learn more and more about this area,” Dr. Kaiser says.