SL-OCT: Anterior Chamber Imaging Technology at the Slit Lamp
Slit-lamp–adapted optical coherence tomography (SL-OCT; Heidelberg Engineering, Heidelberg, Germany), which began as an experimental prototype 10 years ago, has now become a valuable clinical tool for evaluating the anterior segment.
The SL-OCT was created to improve anterior segment imaging by combining noncontact, high-resolution technology with the ease of use of a conventional clinical slit lamp. The scanning technology and image acquisition of the commercial version have been dramatically increased from those of the initial prototype, providing a complete image of the anterior segment in less than 1 second without contact to the eye (Figure 1). This system offers clinicians an elevated level of functionality with automated analysis of the entire anterior segment, including the cornea, angles, and anterior chamber.
The SL-OCT is mounted on a standard slit lamp, so its basic operation is intuitive and easy for clinicians. The design also provides a work-flow benefit; the slit-lamp examination is conducted as normal, and the OCT may be switched on and used as needed.
ADVANTAGES OF OCT
Compared with ultrasound technology, OCT imaging has numerous advantages. Most significantly, the OCT scan is noncontact. Additionally, the images are of a higher resolution and acquired more quickly than with ultrasound. Unlike some optical diagnostic instruments, which have problems with optical artifacts, suffer distortion due to oblique illumination and scanning, or require complicated mathematical corrections, the SL-OCT's cross-sectional images are produced perpendicularly to the eye and are virtually free of distortions, allowing more valid data to be retrieved.
Patients tolerate the SL-OCT examination well with no negative reactions. In several clinical circumstances, the OCT images can be helpful in explaining the disease process to the patient. We have found this to be valuable, as patients with a deeper understanding of their disease seem to comply better with treatment regimens.
SL-OCT is helpful in any clinical situation in which a precise cross-sectional image of the anterior segment of the eye is required. Furthermore, the device allows storage and retrieval, objective quantification, and printing of digital images of the anterior segment.
APPLICATIONS
The most important clinical applications of the technology are currently in corneal and refractive surgery and in glaucoma screening.
In refractive surgery, applications for the device's precise cross-sectional imaging of the cornea and anterior chamber include corneal thickness measurement, flap visualization and determination of the residual stromal thickness in LASIK. In phakic IOL implantation, the SL-OCT's ability to measure anterior chamber depth and width are valuable for surgical planning. In our experience, use of SL-OCT in these applications improves clinical practice.1-3
In cornea and external disease, clinical applications for this technology include imaging of corneal disorders. The depth of corneal scarring can be determined before phototherapeutic keratectomy or corneal transplant surgery, particularly lamellar transplant procedures. Recently, we have used the SL-OCT to assess the results of the newer lamellar corneal procedures such as Descemet's stripping automated endothelial keratoplasty, (DSAEK; Figure 2). As in corneas that have undergone LASIK, the lamellar graft after DSAEK can be visualized and measured, which is extremely helpful to further refine these new surgical techniques.
In the field of glaucoma, the digital gonioscopy feature provided by the SL-OCT can be used to determine the condition of the anterior chamber angles without placing a gonioscopy lens on the eye.4 This allows objective screening for narrow and occludable angles with high sensitivity and specificity (Figure 3). It also allows quantitative assessment of the angles after filtering surgery or iridotomy. In some circumstances, SL-OCT imaging can even replace gonioscopy, which is a tremendous advantage for both patient and clinician.
CONCLUSION
This technology is more cost-effective than other systems. The OCT is mounted on the slit lamp, making its use more efficient in the daily flow of patients through the clinic. The ease of use and reasonable cost of the SL-OCT will make it increasingly popular among ophthalmologists.
Christopher Wirbelauer, MD, is an Attending Physician at the Klinik für Augenheilkunde, Vivantes Klinikum Neukölln, Berlin. Dr. Wirbelauer states that he has no financial interest in the products or companies mentioned. Dr. Wirbelauer may be reached at +49-30-13014-3131; christopher.wirbelauer@vivantes.de.
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