Health Problem: Keratoconus is the most common corneal degenerative disorder, with prevalence estimates varying from 760 to 3300 cases per 100,000 people. In keratoconus, collagen fibers within the cornea weaken and no longer maintain the normal round shape of the cornea. Consequently, the cornea bulges outward, steepens, and develops a progressive conical shape. This abnormal shape prevents light entering the eye from focusing directly on the retina, resulting in irregular astigmatism and progressive myopia or visual loss. Keratoconus is generally detected by the second decade and is a predominantly bilateral form of corneal degeneration.

Technology Description: Corneal cross-linking (CXL) uses a combination of riboflavin (vitamin B2) eye drops, absorbed throughout the cornea stroma, with ultraviolet A (UVA) radiation to trigger a photochemical reaction that changes the cross-links between and within collagen fibers in the corneal stroma. This is believed to strengthen and increase the biomechanical stiffness of the corneal stroma, thereby flattening the steepened cornea into a more normal shape so that vision improves. Different approaches to remove or penetrate the corneal epithelium and different UVA light intensities have given rise to a variety of CXL approaches. Conventional CXL (C-CXL) involves removing the epithelium, after which riboflavin drops are applied to the cornea and the UVA irradiation is performed, typically for 30 minutes at an intensity of 3 milliwatts per square centimeter (mW/cm2).

Controversy: CXL may provide a treatment option for patients with progressive keratoconus, but the procedure may carry risks for complications. In addition, it is still unclear as to whether CXL actually yields improvements in measures of visual acuity, corneal topography and thickness, refractive parameters, and quality of life. Furthermore, additional, better-quality studies are required to define the patient population that is most likely to respond to CXL.

Key Questions:

  • Do CXL treatments improve measures of corneal topography, visual acuity, and refraction in patients with progressive keratoconus?
  • Is CXL safe?
  • What is the comparative effectiveness of C-CXL and alternative CXL procedures?
  • Have definitive patient selection criteria been established for CXL for the treatment of progressive keratoconus?

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