Browse the corpus

Keratoconus (KC) is one of the most common corneal ectasia, characterized by progressive, non-inflammatory changes in corneal stromal collagen and manifests as the protrusion and alteration of the central and paracentral cornea. The pathology usually progresses in the first three decades of life and, if not managed on time, can result in a drop in visual acuity. The management of keratoconus is governed by many factors such as age, stage of keratoconus, schiempflug imaging characteristics, and visual acuity. The various management options include spectacles, contact lenses, corneal collagen cross-linking (CXL)with riboflavin, Intacs, penetrating keratoplasty, and deep anterior lamellar keratoplasty. CXL is a technique of strengthening the corneal tissue by using riboflavin and ultraviolet-A light to halt the progression of progressive keratoconus. In CXL, riboflavin act as a photosensitizing agent, and UVA improves the formation of intra and interfibrillar covalent bonds by oxidative photosensitization. This activity describes the collagen cross-linking procedure's role in managing keratoconus. It highlights a number of clinical factors that should be considered in patients who undergo collagen cross-linking. Objectives: Describe the common clinical and topographic features of keratoconus. Summarize the mechanism of action of collagen crosslinking. Outline the indications for the collagen crosslinking procedure. Review potential outcomes of the procedure in the available literature. Access free multiple choice questions on this topic.

Keratoconus (KC) is one of the most prevalent corneal ectatic disorders characterized by progressive, non-inflammatory changes in stromal collagen structure and usually results in protrusion and alteration of the central and paracentral cornea.[1] The etiology of this condition remains unknown; however, several ocular and systemic associations exist, like Leber congenital amaurosis, atopy, Down syndrome, and the connective tissue disorders of Ehlers-Danlos and Marfan syndromes. Presentation is typically in the second or third decade of life with features of progressive myopia and astigmatism. The initial presentation is unilateral; however, both eyes eventually become involved.[2] On examination, several eponymous clinical signs may increase the suspicion for KC. Munson’s sign is a V shape bulging of the lower eyelid on downgaze. A slit-lamp examination may reveal Vogt striae: fine, vertical, stromal stress lines, and a Fleischer ring: a ring-like configuration of epithelial iron deposits. Distant direct ophthalmoscopy reveals a characteristic “oil-droplet” reflex, and retinoscopy can demonstrate a characteristic scissoring reflex. Placido-disc topography, Scheimpflug imaging, and optical coherence tomography allow for detecting subtle changes in corneal topography, tomography, and epithelium changes associated with KC. A well-known classification system is an Amsler-Krumeich system which uses the patient’s refractive error, central keratometry readings, central corneal thickness, and the presence or absence of scarring. Notably, the Amsler-Krumeich system does not utilize corneal topographic values. Various topographic indices have been proposed for diagnosing preclinical KC (forme fruste keratoconus) and clinical KC. Rabinowitz suggests the following topographical characteristics of KC: increased areas of keratometric readings surrounded by areas of reduced corneal power, inferior-superior symmetry, and skewed radial axes.[3] The newer Scheimpflug imaging-based Pentacam system (Oculus GmbH, Wetzlar, Germany) utilizes the Belin/Ambrósio Enhanced Ectasia Display (BAD) to screen for KC using maximal keratometry, anterior and posterior elevation, and tomographic thickness data.[4]

Placido-disc topography, Scheimpflug imaging, and optical coherence tomography allow for detecting subtle changes in corneal topography, tomography, and epithelium changes associated with KC. A well-known classification system is an Amsler-Krumeich system which uses the patient’s refractive error, central keratometry readings, central corneal thickness, and the presence or absence of scarring. Notably, the Amsler-Krumeich system does not utilize corneal topographic values. Various topographic indices have been proposed for diagnosing preclinical KC (forme fruste keratoconus) and clinical KC. Rabinowitz suggests the following topographical characteristics of KC: increased areas of keratometric readings surrounded by areas of reduced corneal power, inferior-superior symmetry, and skewed radial axes.[3] The newer Scheimpflug imaging-based Pentacam system (Oculus GmbH, Wetzlar, Germany) utilizes the Belin/Ambrósio Enhanced Ectasia Display (BAD) to screen for KC using maximal keratometry, anterior and posterior elevation, and tomographic thickness data.[4] Treatment of early keratoconus involves prescribing spectacles to improve vision, but as the disease progresses, rigid gas-permeable contact lenses are required. In a small but significant proportion of patients, disease progression may require eventual corneal transplantation. Several new therapeutic options have emerged, including refractive, optical, and lamellar surgery, which slow the progression of the disease and/or delay more intensive treatment. Collagen cross­linking (CXL) with ultraviolet A (UV-A) light and riboflavin (vitamin B2) is a relatively new treatment that reportedly slows the advancement of the disease in its early stages.[5] CXL was introduced to clinical practice in the late 1990s and has since completely modified conservative management of progressive corneal ectasia. CXL utilizes riboflavin as a photosensitizer, which, when exposed to longer wavelength UV-A, induces chemical reactions in the corneal stroma and ultimately results in the formation of covalent bonds between the collagen molecules. This collagen crosslinking increases the tensile strength and rigidity of the cornea, preventing further thinning and ectasia.[5]

Common complications related to this include temporary corneal haze (10 to 90%), delayed epithelial closure, sterile infiltrates, and central stromal scars. The literature describes postoperative microbial keratitis from bacterial, herpetic, protozoal, and fungal sources.[34] The stromal haze is usually temporary and appears to be likely due to increased edema and keratocyte activation and occurs three to six months post-operatively.[34][35] Rarer but more serious side effects include corneal melts and endothelial failure. Treatment failure is also a noted complication, defined as the progression of the condition with an increase in Kmax values of 1.0 D over the pre-operative value or greater than a 10% decrease in pachymetry readings six months post-operatively; this may occur in up to 10% of patients.[1]

An interprofessional team approach involving subspecialty-trained physicians and ophthalmic-trained nurses providing patient support and follow-up care will lead to the best outcomes. With early detection of keratoconus by healthcare members, corneal crosslinking is an effective way of slowing down and potentially halting progression.[39] [Level 3]

Nursing, allied health staff, and interprofessional team help monitor these patients after the surgery for BCL removal, intraocular pressure check, regular medication use, Schiempflug imaging visit, and to document any progression with the change of spectacles or contact lenses.[40]