Cross-Linking

Corneal collagen cross-linking is a technique which uses UV light and a photosensitizer to strengthen chemical bonds in the cornea. The goal of the treatment is to halt progressive and irregular changes in corneal shape known as ectasia. These changes are typically marked by corneal thinning and an increase in the anterior and/or posterior curvatures of the cornea, and often lead to high levels of myopia and astigmatism. The most common form of ectasia is keratoconus.

Indications

The primary purpose of crosslinking is to halt the progression of ectasia. Likewise, the best candidate for this therapy is an individual with keratoconus or post-refractive surgery ectasia who has documented progression of the disease. There currently are no definitive criteria for progression, but parameters to consider are change in refraction (including astigmatism), uncorrected visual acuity, best corrected visual acuity, and corneal shape (topography and tomography).

Contraindications

  • Corneal thickness of less than 400 microns is a contraindication to the standard treatment protocol
  • Prior herpectic infection is a contraindication because it may result in viral reactivation
  • Concurrent infection
  • Severe corneal scarring or opacification
  • History of poor epithelial wound healing
  • Severe ocular surface disease (ex. dry eye)
  • Autoimmune disorders

Surgical Technique

The primary goal of the first stage of therapy is to allow riboflavin (vitamin B2) to diffuse into the cornea. While there are several variations on the techniques used to accomplish this, all entail either removing or weakening the epithelial barrier of the cornea. In all instances the patient is first given anesthetic drops. A speculum is placed in the eye that is going to be treated to keep the eye lids open. After disrupting the epithelium, drops of Riboflavin hypertonic solution are given at intervals of 2 minutes for 30 minutes, or until riboflavin can been seen in the anterior chamber of the eye by use of the blue filter on slit lamp examination.

After adequate riboflavin absorption, the corneal thickness is checked. If found below 400 microns, Riboflavin Hypotonic Solution to be applied at 2 minute intervals, until the corneal thickness reaches 400 microns. Then patient is positioned with the UV light (typically 365-370um) at a small distance (1-5cm) from the corneal apex for 30 minutes. During these 30 minutes, Riboflavin Hypertonic Solution to be instilled at 2 minute intervals.

Following irradiation, antibiotic drops and steroid drops are instilled are and a bandage contact lens is placed. The patient is given eye drops post operatively for a few days.

The bandage contact lens will be removed 3 days after procedure. An eye shield is applied to the eye for the first 24 hours. Patient is to wear sunglasses for the first 5 days whilst at home.

Advise to Patient:

 

  • Do not rub the eye for 2 weeks
  • Put the drops in a timely manner
  • Wash hands before putting in the drops
  • Can watch TV or use the computer
  • Can have a shower and pat dry face
  • No make up for 1 week
  • No driving until eyesight is stabilized
  • No swimming for 2 weeks

Advise to Patient:

  • Corneal haze
  • Slight incidence that cross linking does not work
  • Infection