Corneal ectasia is the progressive steepening and thinning of the cornea that can occur naturally or be induced surgically. A patient with corneal ectasia will often experience an increase in ocular aberrations and decreased best corrected visual acuity (BCVA). Due to these aberrations and loss of BCVA, these patients report varying degrees of visual symptoms including glare, halo, multiple images, and ghosting. A patient with corneal ectasia may need to wear gas permeable or other specialty contact lenses to obtain their best visual acuity due to the corneal irregularity. Often glasses are not able to fully correct a patient with corneal ectasia.

Various forms of ectasia exist including keratoconus, pellucid marginal degeneration, wound ectasia after penetrating keratoplasty (PK), and keratoglobus. The reported incidence and prevalence rates reported for keratoconus tend to vary widely from an incidence as high as 1 in 400, to a long-term study in the United States reporting 54.5 per 100,000.¹,² It has been generally considered to occur equally in men and women; however, more recent studies have shown an increased risk of development of keratoconus in men, African-Americans, and Latinos and lower risk in women, Asian-Americans, and people with diabetes.¹ Keratoconus can begin before puberty and may continue to progress even after the age of 40. The weakening and degradation of the corneal collagen results in the progressive thinning and steepening observed in eyes with keratoconus.³

Corneal ectasia can also occur after laser-assisted keratomileusis (LASIK), small incision lenticule extraction, and photorefractive keratectomy. Risk factors for corneal ectasia include high preoperative myopia, thin residual stromal bed, high total percentage of tissue altered, and forme fruste keratoconus on preoperative topography.⁴ Corneal ectasia can develop in a normal appearing cornea preoperatively.⁵ Similar to keratoconus, in corneal ectasia following corneal refractive surgery, there is a suspected weakening and degradation of the corneal collagen resulting in biomechanical instability of the cornea in the residual stromal bed.⁶,⁷

In April 2016, the Food and Drug Administration (FDA)-approved corneal crosslinking for progressive keratoconus and corneal ectasia following refractive surgery. Corneal cross-linking is performed to slow or halt the progression of keratoconus and corneal ectasia by increasing the biomechanical rigidity of the cornea. It is thought to achieve this by replicating the age-related cross-linking that occurs in the cornea naturally with time.⁸ The procedure is performed using ultraviolet-A (UV-A) light
and topical riboflavin as a photosensitizing agent to result in local photopolymerization.⁹ Different from other corneal ectasia surgical treatments (intrastromal corneal ring segments and PK), this procedure can be performed in earlier stages of disease progression to prevent further vision loss from progressive corneal ectasia.