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Inside Eyetube.net | May 2011

Fourier-Domain OCT for the Anterior Segment

Fourier-domain optical coherence tomography (FD-OCT) has allowed anterior segment surgeons to perform quantitative biomicroscopy. With this diagnostic tool, surgeons can measure anatomic features present in the anterior segment. Additionally, this imaging technology is useful in diagnosing corneal pathologies. FD-OCT has also become an invaluable tool for assessing clinical situations in which therapeutic decisions have to be made, such as those discussed here. In my practice, I routinely use the Cirrus (Carl Zeiss Meditec, Jena, Germany), the 3D OCT-2000 (Topcon Corp., Tokyo), and the RTVue (Optovue Inc., Fremont, California) to image the cornea and anterior segment. I use the RTVue for most corneal diagnostic purposes.

Anterior stromal corneal scars. These are frequently found after nummular keratitis or foreign body impact. With FD-OCT, we can measure the depth of the stromal trough to decide the best treatment option: phototherapeutic keratectomy (PTK) or anterior lamellar keratoplasty. If laser is done, the way to perform PTK—transepithelial or not—the depth of the ablation, and calculation of the refractive compensation can be determined. If lamellar keratoplasty is performed, the depth of the cut can be tailored to the corneal pathology.

Anterior stromal surface status. Stromal surface irregularities are normally not visible on corneal topography (Placido disc and Scheimpflug) due to epithelial compensation. FD-OCT can measure beyond the epithelium, revealing the reason for bad visual quality. Post-PRK haze is a good example of a condition for which this technology is useful for determining the proper depth of a corrective PTK ablation.

Post-LASIK flap and glaucoma assessment. FD-OCT can be used to examine the LASIK flap interface for fluid accumulation. This can be valuable in glaucoma assessment in post-LASIK eyes. I have seen eyes with mid to high intraocular pressure (IOP) values with optic disc progressive cupping, where liquid in the LASIK flap interface was probably misleading the IOP measurement. FD-OCT is more sensitive than biomicroscopy in identifying epithelium in the flap interface and the extension of the membrane.

Intrastromal corneal implants. Ring segments and refractive inlays are clearly imaged and measured with FDOCT to assess their position within the cornea.

Anterior chamber angle. The anterior chamber angle can be measured and studied with high precision with FDOCT. It has been interesting to address the effect of peripheral argon iridoplasty on the angle anatomy and correlate this with IOP level.

Phakic IOL implantation. For both anterior and posterior chamber phakic IOLs, FD-OCT allows surgeons to determine the exact distance between the lens and any anatomic structure, which can be relevant to the safety of the implantation.

FD-OCT is here to stay, having become an indispensable diagnostic procedure in most protocols, and providing useful and relevant information in most clinical situations.

Jaime Aramberri, MD, practices at the Begitek Ophthalmology Clinic, San Sebastian, Spain, and the Okular Ophthalmology Clinic, Vitoria, Spain. Dr. Aramberri states that he has no financial interest in the products or companies mentioned in this article. He may be reached at e-mail: jaimearamberri@telefonica.net.