Optical Coherence Tomography (OCT) of the Anterior Eye Segment
DESCRIPTIONOptical coherence tomography (OCT) is a high resolution method of imaging the ocular structures. OCT for the anterior eye segment is being evaluated as a rapid and non-invasive diagnostic and screening tool for the detection of angle closure glaucoma.
The classification of glaucoma (primary open-angle or angle-closure) relies heavily upon knowledge of the anterior segment anatomy, particularly that of the anterior chamber angle. Angle-closure glaucoma is characterized by obstruction of aqueous fluid drainage through the trabecular meshwork (the primary fluid egress site) from the eye's anterior chamber. The width of the angle is one factor affecting the drainage of aqueous humor. A wide unobstructed iridocorneal angle allows sufficient drainage of aqueous humor, whereas a narrow angle may impede the drainage system and leave the patient susceptible to angle-closure glaucoma. The treatment for this condition is a peripheral iridotomy (laser) or peripheral iridectomy (surgery).
Slit lamp biomicroscopy is used to evaluate the anterior chamber, however, the chamber angle can only be examined with specialized lenses, the most common of these being the gonioscopic mirror. In this procedure a gonio lens is applied to the surface of the cornea under topical anesthesia and the image magnified with the slit lamp. Gonioscopy is the standard method for clinically assessing the anterior chamber angle. Other techniques for imaging the anterior eye segment include ultrasonography and optical coherence tomography.
Ultrasonography uses high frequency mechanical pulses (10 to 20 MHz) to build up a picture of the front of the eye. An ultrasound scan along the optical axis assesses corneal thickness, anterior chamber depth, lens thickness and axial length. Ultrasound scanning across the eye creates a two-dimensional image of the ocular structures. It has a resolution of 100 microns, but only moderately high intra-observer and low inter-observer reproducibility. Ultrasound biomicroscopy (about 50 MHz) has a resolution of 30 to 50 microns. As with gonioscopy, this technique requires placement of a probe under topical anesthesia.
Optical coherence tomography (OCT) is a non-invasive method that creates an image of light reflected from the ocular structures. In this technique a reflected light beam interacts with a reference light beam. The coherent (positive) interference between the two beams (reflected and reference) is measured by an interferometer, allowing construction of an image of the ocular structures. This method allows cross-sectional imaging at a resolution of 6 to 25 microns. The Stratus OCT™ (Carl Zeiss Meditec), which utilizes a 0.8 micron wavelength light source, was designed for evaluating the optic nerve head, retinal nerve fiber layer and retinal thickness. The Zeiss Visante OCT™ uses a 1.3 micron wavelength light source and is designed specifically for imaging the anterior eye segment. Light of this wavelength penetrates the sclera, allowing high-resolution cross-sectional imaging of the anterior chamber angle and ciliary body. The light is, however, typically blocked by pigment, preventing exploration behind the iris. Ultra high resolution OCT can achieve a spatial resolution of 1.3 microns, allowing imaging and measurement of corneal layers.
The Visante OCT received marketing clearance through the U.S. Food and Drug Administration (FDA) 510(k) process in 2005, listing the Stratus OCT and Orbscan™ II as predicate devices. The 510(k) summary describes the Visante OCT as “a non-contact, high resolution tomographic and biomicroscopic device indicated for the in vivo imaging and measurement of ocular structures in the anterior segment, such as corneal and LASIK flap thickness.”
The AC Cornea OCT from Canada is not cleared for marketing in the United States.
An early application of OCT technology was the evaluation of the cornea before and after refractive surgery. Since this is a non-invasive procedure that can be conducted by a technician, it has been proposed that this device may provide a rapid diagnostic and screening tool for the detection of angle closure in glaucoma. Also being investigated is the possibility that the 0.8 micron wavelength Stratus OCT, which is already available in a number of eye departments, may provide sufficient detail for routine clinical assessment of the anterior chamber angle in glaucoma patients. Add-on lens are also available for imaging the anterior segment with OCT devices designed for posterior segment imaging.
See the Ophthalmologic Techniques of Evaluating Glaucoma for other ophthalmologic techniques of evaluating glaucoma.
POLICYScanning computerized ophthalmic (e.g., OCT) imaging of the anterior eye segment is considered investigational.
POLICY EXCEPTIONSFederal Employee Program (FEP) may dictate that all FDA-approved devices, drugs or biologics may not be considered investigational and thus these devices may be assessed only on the basis of their medical necessity.
POLICY GUIDELINESInvestigative service is defined as the use of any treatment procedure, facility, equipment, drug, device, or supply not yet recognized by certifying boards and/or approving or licensing agencies or published peer review criteria as standard, effective medical practice for the treatment of the condition being treated and as such therefore is not considered medically necessary.
The coverage guidelines outlined in the Medical Policy Manual should not be used in lieu of the Member's specific benefit plan language.
POLICY HISTORY1/11/2008: Policy added
3/27/2008: Reviewed and approved by the Medical Policy Advisory Committee (MPAC)
04/22/2010: Policy description updated. Policy statement unchanged. Added FEP verbiage to the Policy Exceptions section.
03/07/2011: Added new CPT code 92132 to the Code Reference section.
05/07/2012: Policy title changed from "Anterior Eye Segment Optical Imaging" to "Optical Coherence Tomography (OCT) of the Anterior Eye Segment" to be consistent with the scope of the policy. Policy statement unchanged. Removed deleted CPT code 0187T from the Code Reference section.
04/17/2013: Policy reviewed; no changes.
03/18/2014: Policy reviewed; no changes.
SOURCE(S)Blue Cross & Blue Shield Association Policy # 9.03.18
CODE REFERENCEThis may not be a comprehensive list of procedure codes applicable to this policy.