The long-term goal of this project is to utilize newly available very high-speed optical coherence tomography (OCT) technology to guide surgical treatments of anterior eye diseases. Measuring aberrations in the optical surfaces of the cornea requires great precision. OCT is well known for its exquisite spatial resolution; but until recently it has not had sufficient speed to overcome the inherent biological motion of the eye and capture the shape of the cornea. The development of Fourier-domain (FD) OCT technology has made the requisite speed possible.
The specific aims are:
1. To develop a very high-speed anterior segment OCT instrument. An FD-OCT system capable of 26,000 axial scans/second and 5 micrometer resolution has been tested. Preliminary data show that it is able to map corneal thickness with a precision of 1 micrometer root-mean-square and to measure corneal power with a precision of 0.2 diopters. Motion correction algorithms will be developed to further improve the precision. The system will be used for corneal mapping, including pachymetry, epithelial thickness, LASIK flap, post-LASIK stromal bed thickness, anterior/posterior topography, corneal power, and astigmatism.
2. To develop OCT-guided corneal laser surgery for the treatment of irregular and opacified corneas. Although wavefront sensing and Placido-ring topography have been used to guide laser corneal surgeries, these methods are often unable to make valid measurements of irregular corneas. Our preliminary results showed that OCT can reliably measure the diseased corneas that are most in need of surgical remedy. Corneal thickness or topography maps obtained by the OCT system will be used to program the depth of femtosecond laser corneal dissection and excimer laser ablation. OCT-guided femtosecond laser lamellar keratoplasty and excimer laser phototherapeutic keratectomy (PTK) will be tested in rabbit studies. Patients with corneal scar, ectasia, dystrophy, or irregular astigmatism following corneal surgery will be scanned, and laser surgery will be simulated by computer to evaluate the visual outcome. The simulation will take into account measurement variability, laser delivery error, healing effects, and visual optics. These tests will prepare for future human trials.
3. To develop an OCT-based intraocular lens (IOL) power formula. IOL power selection is difficult in patients who have had previous laser vision correction, often resulting in significant near- or far-sightedness after the cataract surgery. Laser ablation alters the natural relationship between the front and back corneal surfaces, causing error in conventional keratometry and IOL calculation. This increasingly common problem could be solved by measuring both anterior and posterior corneal powers with OCT. The OCT-based IOL formula will be tested in a clinical trial.
4. To develop OCT for measuring tear film thickness and tear meniscus, measuring anterior chamber (AC) cell grading in uveitis, measuring AC angle and visualizing trabecular meshwork; and to demonstrate applications of OCT in other corneal and anterior segment conditions, including keratoconus, corneal opacities, acanthamoeba keratitis, post-LASIK corneal changes, other lamellar corneal surgeries, iris masses and other uveal or scleral pathologies.