Progressive Corneal Ectasia Resulting from LASIK Surgery

Progressive Corneal Ectasia Resulting from LASIK Surgery

Introduction

Corneal ectasia is a potentially serious problem when it arises spontaneously and it is among the most dreaded of potential side effects of corneal refractive surgery such as LASIK. Today, the greatest ongoing challenge faced by refractive surgeons is identifying patients who are at risk of developing ectasia after LASIK. Corneal ectasia after LASIK is among the more serious complications with visual morbidity that in some cases requires corneal transplantation. Ectasia is also called iatrogenic Keratoconus or secondary Keratoconus because it is basically a surgically induced version of the naturally occurring disease Keratoconus.

What is ectasia?

Ectasia is a bulging of the cornea. Ectasia is a very serious long-term complication of LASIK. In other words, progressive thinning and steepening of the cornea may occur after laser in situ keratomileusis (LASIK). This condition commonly referred to as post-LASIK ectasia.

What causes ectasia and which surgery is it associated with?

It has been suggested that the two main causes of post-LASIK ectasia are:

1- Preexisting corneal pathology (keratoconus or forme fruste keratoconus): It accounts for more than 30% of cases of post-LASIK ectasia.

2- Mechanical instability: Mechanical instability is produced by the weakening of the residual stromal bed induced by flap creation and laser ablation. The reduction of the mechanical stability of the cornea results from the thinning of the stromal bed to such a point that it is unable to withstand the eye’s IOP (Intraocular pressure). Eyes with a residual stromal thickness of 250 microns or less account for 56% of cases of post LASIK ectasia and those with a residual stromal thickness of 300 microns or less account for 77% of cases.

What is the progression and the potential results to the patient?

Corneal ectasia is considered as a gradually progressive (worsening) condition and refractive characteristics of corneal ectasia after LASIK include moderate residual myopia and increased astigmatism with reduced best spectacle-corrected visual acuity. Corneal shape changes characteristic of ectasia after LASIK include increased corneal toricity, asymmetric inferior steepening, and change in total corneal thickness greater than the intended change from ablation alone. Another one of the most distinctive postoperative changes occurring with severe corneal ectasia after LASIK is distortion of anterior corneal shape.

It must be noted that young age, changing refractive error with astigmatism, eye rubbing, thin cornea, and abnormal topography are some of the features that may identify patients with very early stage or Forme Fruste Keratoconus - a term used to describe patients that are more likely to progress to Keratoconus. Refractive Surgery in these patients has the potential to speed up the progression of their condition.

How is ectasia diagnosed?

Various findings suggest that corneal topography could be more predictive of ectasia than many of the criteria used by currently available risk calculators.

How can corneal ectasia be treated?

The treatment of corneal ectasia can be performed in a doctor’s office. Usually, only one cornea is treated at one sitting. The treatment is performed under topical anesthesia (using freezing eye drops). The surgeon removes the surface layer of the cornea (epithelium) and the eye is treated with application of photosensitizing Ribo?avin eye drops for 30 minutes. The eye is then exposed to UVA light from a distance of about 5 cm for 30 minutes. The total treatment lasts about an hour per eye. After the treatment, antibiotic eye drops are then applied; a bandage contact lens will be inserted that will be removed by the surgeon during a follow-up visit. Protective eyewear, such as sunglasses should be worn for a few days until complete healing takes place. On average, the epithelium of the eye regrows between 4 days to 1 week at which time the surgeon will remove the bandage contact lens.

How can corneal ectasia be prevented?

Of the various postoperative complications associated with LASIK surgery, ectasia appears to be the easiest to avoid with proper preoperative screening. Careful and preoperative assessment of the cornea, in particular, can greatly reduce the risk of ectasia. Similarly, experts strongly suggest against offering corneal ablative procedures to patients with corneal topography suggestive of keratoconus or forme frusta keratoconus. Another recommendation is testing contact lens-wearing patients after several weeks without using their lenses to eliminate the possibility of lens-induced corneal warpage.

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