Anterior segment coherence tomography systems vary in scanning width, depth, and resolution. The data generated are useful for diagnostic and surgical planning purposes. Angiography is being developed as a new application.
Anterior segment optical coherence tomography (AS-OCT) has utility for a number of different applications.
David Huang, MD, PhD, described features of the available systems and reviewed some uses for AS-OCT. Dr. Huang is Peterson Professor of Ophthalmology and professor of Biomedical Engineering, Oregon Health and Science University, Portland, OR.
Clinicians can now choose from a number of commercially available AS-OCT systems. The units include devices developed for retinal imaging that have been additionally adapted for corneal imaging and instruments that are dedicated for anterior segment imaging.
The two types of devices differ in wavelength. The combination retinal/corneal imaging devices are all 840 nm wavelength spectral-domain systems and have a benefit of higher axial resolution (3 to 9 μm). In contrast, the dedicated AS-OCT devices are 1,310 nm swept-source systems that give better penetration but at the cost of lower resolution of approximately 10 μm.
“With the 840 nm systems, it is possible to delineate the corneal epithelium and endothelium, Bowman’s layer, and the LASIK flap interface,” Dr. Huang said. “It is more difficult to see these thin structures at the 1,310 nm wavelength, but the reduced scattering loss at the longer wavelength allows more consistent visualization of deeper structures such as the scleral spur, angle recess, and even the ciliary body.”
The dedicated AS-OCT platforms also scan deeper (10-11 mm versus 2-6 mm).
“With their greater depth, the dedicated systems can image the entire anterior segment from the cornea to the lens,” Dr. Huang explained. “Unfortunately, the dedicated AS-OCT systems are only marketed outside the United States at the current time.”