Photochemical corneal collagen cross‑linkage using riboflavin and ultraviolet A for keratoconus and keratectasia

The corneal collagen cross‑linkage (CXL) procedures are normally done as outpatient procedures using topical anaesthesia, and typically take 60 to 90 minutes.

In epithelium‑off CXL, the epithelium is first abraded with a blunt spatula to allow penetration of riboflavin into the corneal tissue. Riboflavin eye drops are applied to the corneal surface before the procedure and intermittently during the procedure. The corneal surface is exposed to ultraviolet A (UVA) radiation: precise timings and treatment protocols vary. Postoperatively, topical antibiotics and anti-inflammatory drops are normally prescribed, with topical steroids if necessary. In some cases, a bandage contact lens may also be used for a few days. The procedure is done on 1 eye at a time and may also be repeated if needed.

In epithelium‑on (transepithelial) CXL, the corneal epithelial surface is left intact (or may be partially disrupted) and a longer riboflavin loading time is needed.

Sometimes the procedure is used in combination with other interventions such as intracorneal ring segment (ICRS) implantation, photorefractive keratectomy (PRK) or phakic intraocular lens (PIOL) implantation to improve visual acuity. These combination procedures are referred to as 'CXL‑plus'.

The mechanism of action of the CXL procedures is not fully understood: they may increase the number of 'anchors' that bond collagen fibres together and strengthen the cornea. This is expected to stop the progression of the disease but the duration of benefit is uncertain.