Epithelium-on Cross-linking Versus Observation of Fellow Eyes of Patients With Unilateral Clinically Evident Keratoconus

Keratoconus (KC) is a bilateral asymmetric progressive corneal degenerative disease associated with corneal thinning and protrusion with resultant irregular astigmatism and visual loss.

Although several studies showed that epithelium-off corneal cross-linking (epi-off CXL) is more effective in preventing KC progression compared with epithelium-on corneal cross-linking (epi-on CXL), the removal of corneal epithelium in epi-off CXL might be associated with a number of serious complications such as persistent epithelial defects and sight-threatening infectious keratitis. Additionally, recent systematic reviews and meta-analysis concluded that epi-on CXL is as effective as epi-off CXL in terms of visual and topographic stability of keratoconus, but has the advantage of being much safer avoiding the complications of epithelial removal.

The management of the better eye, of young patients with unilateral clinically evident KC, is controversial. Some ophthalmologists prefer to cross-link the better eye, while others prefer to conservatively follow it up, in order to avoid complications of epithelial removal in epi-off CXL.

Inclusion criteria

Patients aged 12 to 30 years presented with forme fruste (FFKC) or subclinical KC, based on the following criteria:

• Normal slit lamp examination
• Normal topography in FFKC and suspicious topography in subclinical KC with asymmetric bow-tie or inferior steeping (inferior-superior value less than 1.40 D in the anterior sagittal curvature map in pentacam)
• Clinical and topographic features of KC in the other eye.

Exclusion criteria

• Corrected distance visual acuity (CDVA) worse than 0.1 logMAR
• Corneal thickness at the thinnest location less than 400 μm
• Severe ocular allergy (active catarrhal keratoconjunctivitis)
• Other corneal or ocular diseases
• Systemic diseases such as diabetes mellitus and autoimmune diseases