Corneal crosslinking in pellucid marginal degeneration
Reviewed by Su Young

Fourteen studies were included in this first review examining the use of corneal-crosslinking (CXL) to treat pellucid marginal degeneration (PMD). PMD is a bilateral, non-inflammatory corneal thinning disorder characterised by inferior peripheral corneal thinning 1-3mm from the limbus in the 4 to 8 o’clock position. Compared to other corneal thinning conditions like keratoconus, corneal steepening in PMD occurs more inferiorly and closer to the limbus. Progression of PMD is important because keratoplasty in PMD is associated with significant comorbidity (e.g. decentered grafts closer to limbus confer a greater risk of vascularisation, suture erosion and rejection). All of the studies included additional treatments that were used with CXL: photorefractive keratectomy (PRK), phototherapeutic keratectomy (PTK) and intrastromal corneal ring segment (ICRS). CXL was shown to halt disease progression and stabilise / improve vision in all studies. Four studies included follow-up duration >1 year. Combined CXL and laser vision correction demonstrated a greater improvement in uncorrected distance visual acuity (UDVA) vs. CXL alone. In the studies, CXL was performed immediately after surface ablation, theoretically combining benefits of both treatments. None of the studies reported any complications, however rare but serious potential complications can occur and should be noted. The authors concluded that CXL seems to be safe and effective in the management of PMD, but existing literature is limited, with short-term follow-up and the retrospective nature of most studies. There is a lack of evidence supporting efficacy and stability of CXL in PMD, and well-controlled prospective studies with long-term follow-up are necessary.

Corneal cross-linking: an effective treatment option for pellucid marginal degeneration.
Yong J, Hatch KM.
SEMINARS IN OPHTHALMOLOGY
2019;34(7-8):512-7.