Imaging After Cornea Surgery

Abstract

The cornea is an avascular tissue in the anterior portion of the globe that consists of six layers, including the epithelium, basement membrane, Bowman’s layer, stroma, Descemet’s membrane, and endothelium. The cornea measures approximately 400 μm in thickness centrally and features an intrinsic convex outward curvature, which provides light refraction. Corneal opacification is the second most common cause of blindness worldwide. In fact, according to the World Health Organization, glaucoma, age-related macular degeneration, and diabetic retinopathy are less common causes. Corneal opacification can result from postinfectious corneal scars, trauma, cicatrizing disorders (e.g., trachoma), nutritional deficiencies (e.g., vitamin A deficiency), and inherited disorders. Treatment options for corneal opacification include corneal transplantation, either penetrating (full-thickness) or lamellar (partial-thickness), or a corneal prosthetic device (keratoprosthesis). Cross-sectional imaging after keratoplasty is obtained when the cornea is opaque – from edema and graft failure or rejection, for example – and direct visualization of the anterior chamber and the fundus is not possible. Ultrasound biomicroscopy (UBM) is used to assess the anterior chamber and the drainage angle of the eye and B-scan ultrasound to evaluate the status of the vitreous and retina. Occasionally diagnostic imaging is performed to evaluate for postoperative complications. Otherwise, normal post-keratoplasty changes observed on CT or MRI can be incidental findings on diagnostic imaging performed for unrelated reasons. Imaging with CT or MRI is done after keratoprosthesis implantation to evaluate rare orbital complications of the procedure or to assess for tooth resorption in the case of the osteo-odonto-keratoprosthesis (OOKP). Corneal surgery can also be performed for correcting refractive errors of the eye, such as myopia, hyperopia, astigmatism, and presbyopia, usually with the goal of eliminating the need for glasses or contact lenses. This field is known as orthokeratology and encompasses numerous types of procedures. Laser-assisted in situ keratomileusis (LASIK) is the most widely performed method of refractive surgery. Other corneal refractive surgical procedures include laser thermal keratoplasty (LTK) and intrastromal corneal ring segments (Intacs). Complications after refractive cornea surgeries are generally diagnosed clinically; anterior segment optical coherence tomography (OCT) can serve as an adjunctive to diagnosis and planning for possible further interventions.