Applications of Ultrahigh-speed Long-range
Wide-field OCT in Anterior Eye Diseases
NIH R01 EY028755 - PI: Dr. David Huang
Optical coherence tomography (OCT) is uniquely able to achieve micron depth resolution while imaging a large 3-dimensional (3D) volume. This enables 3D imaging and precise measurements in the anterior segment of the eye, including the cornea, conjunctiva, sclera, anterior chamber, iris, and crystalline lens. Anterior segment OCT is already widely used in ophthalmology. But a number of high-impact applications were held back by limited speed, range, penetration, and disease-specific algorithms. Therefore the specific aims are to:
(1) Develop ultrahigh performance OCT for anterior eye. A novel vertical-cavity surface-emitting laser (VCSEL) will be used to develop an OCT prototype with ultrahigh-speed, wide-field, long-range, and high-penetration. The high speed and penetration will allow blood vessel imaging (angiography) in iris tumors. The wide field and long range will enable accurate whole anterior-segment biometry from the apex of the cornea to the posterior surface of the crystalline lens, which will take intraocular lens (IOL) formulas and custom scleral contact lens design to a new level of accuracy.
(2) Develop OCT angiography (OCTA) of iris tumors. Distinguishing between benign and malignant tumors, including deadly melanomas, is crucial for planning treatments that minimize damage to sensitive eye tissues and reduce the risk of metastasis. Increased vascularity marks malignant transformation in tumors. The proposed ultrahigh performance OCT prototype will enable OCTA in tumors with sufficient penetration to characterize both tumor vasculature and volume. Novel software algorithms will be used to suppress motion, projection, and shadow artifacts, segment tissue boundaries, and calculate quantitative vascular density and tortuosity measurements. The technology could be useful in the evaluation of tumor angiogenesis elsewhere.
(3) Improve OCT-based IOL power formula. Previously we developed an OCT-based IOL formula that improved cataract surgery refractive outcome in post-myopic LASIK eyes. We now propose to further improve the OCT-based IOL formula so that it could improve refractive outcome in all cataract surgeries, and be used to select toric as well non-toric IOL. The long-range OCT can accurately measure the crystalline lens equatorial position to improve the prediction of IOL position, which is a crucial variable that currently limits the accuracy of IOL formulas. High-speed OCT together with ray-tracing will enable more accurate net corneal power and astigmatism measurements, especially in post-radial keratotomy and post-hyperopic LASIK eyes.
(4) Improve scleral lens fitting with wide-field OCT. Scleral contact lens vaults over the cornea and offers an important nonsurgical option to restore comfort and vision to patients with irregular corneal shape or ocular surface inflammation. The primary limitation of scleral lens is the difficult trial-and-error fitting process. We will use wide-field OCT corneoscleral topography to improve the selection of the initial trial lens and design advanced radially asymmetric scleral lenses that are highly customized to the subject ocular surface.
OCT-aided Differential Diagnosis and Treatment
of Irregular Corneas
NIH R01 EY029023 - PI: Dr. Yan Li
To see well, the cornea must maintain near perfect clarity and shape. Several disease processes can distort corneal shape and degrade vision. These include ectasia/keratoconus (stromal thinning and bulging), primary epithelial deformation (contact lens-related warpage, dry eye, epithelial basement membrane dystrophy), and stromal changes (scar, stromal dystrophy, surgery). Some of these conditions can appear similar on standard anterior topography and yet require very different treatments. Therefore a goal of this project is to use OCT, a 3-dimensional imaging technology with micrometer-level resolution, to differentiate between different types of corneal shape irregularities. The unique ability of OCT to measure epithelial thickness and posterior topography will be used to develop new metrics for staging and monitoring of ectasia and primary epithelial deformation. We will also improve the treatment of corneal stromal irregularities by combining OCT planning and topography-guided excimer laser ablation, which has only recently become available in the U.S. Our overall goal is to improve the early detection, differential diagnosis, staging, monitoring, and treatment of irregular corneas by using advanced optical imaging and laser technologies to achieve the following Specific Aims:
(1) Develop an OCT-based system to classify and evaluate corneal shape irregularities. Standard corneal topography only measures the anterior corneal surface and cannot by itself differentiate between different causes of irregularities. In a cross-sectional clinical study, we will develop mathematical analyses of OCT maps of corneal anterior and posterior topography, epithelium, and pachymetry to improve the early detection, classification, and staging of irregularities including ectasia, epithelial deformations, and stromal changes.
(2) Develop OCT metrics for more sensitive detection of keratoconus progression. Standard anterior topographic parameters such as maximum keratometry have poor reproducibility and poor detection sensitivity in early disease. Our preliminary results show that OCT epithelial and posterior topographic measurements are more sensitive to early keratoconus and have better repeatability. This could enable more timely identification of patients who need collagen crosslinking to stabilize the cornea. Early detection of progression will be tested in a longitudinal study of patients with subclinical keratoconus.
(3) Develop OCT-and-topography guided phototherapeutic keratectomy (PTK) for irregular corneas. We have demonstrated that transepithelial PTK with OCT planning can significantly improve vision for patients with scarred or irregular corneas. We propose to further improve operative results using the newly available topography-guided excimer laser, which has been approved for laser-assisted in situ keratomileusis (LASIK) in normal eyes but has not yet been tested in PTK. We plan to conduct a clinical trial of OCT-and-topography guided PTK for patients with corneal scars, stromal dystrophies, and other irregularities.
PROJECT NARRATIVE
Different conditions that affect corneal shape and vision require different treatments: collagen crosslinking for keratoconus, contact lens abstention for warpage, medical/physical treatments for dry eye, and laser for stromal opacity/irregularities. This project aims to develop optical coherence tomography (OCT), a micrometer-level precision 3-dimensional imaging technology, to detect, differentiate, stage, and monitor different types of corneal shape irregularities. Furthermore, the treatment of stromal opacity and irregularities will be improved by using both OCT and topography to precisely guide excimer laser ablation and restore a smooth corneal surface.