Progressive Corneal Thinning And Flattening Post Collagen Cross Linking With Dresden Protocol - Visual And Topographic Outcomes

To evaluate the visual, tomographic and epithelial thickness changes in keratoconus eyes that developed excessive flattening and thinning after corneal collagen cross-linking (CXL) with the Dresden protocol.

Study conducted at Cornea department of a tertiary eye hospital in a metropolitan city.

A retrospective observational study including 11 eyes of 8 patients with keratoconus who had undergone standard epithelium-off CXL ranging from1.5 years to 12 years ago. Inclusion criteria were ≥4 D reduction in  keratometry  and ≥100 µm thinning at the thinnest point compared to baseline.Clinical data included visual acuity, history of eyerubbing/ allergy,  keratometry, pachymetry, and anterior segment imaging. Scheimpflug tomography (Pentacam) and swept-source OCT (ANTERION®) assessed corneal and epithelial changes.The 11 included eyes had mild to severe keratoconus. Included eyes had undergone isotonic and hypotonic collagen cross linking depending on the thickness.

Mean follow-up was 6.95 years (range: 1.5–12 years). Mean age at CXL was 17 years. 55% patients reported habitual eye rubbing.Best-corrected visual acuity similarly improved by ≥2 lines in 4 eyes (36.4%), while 6 eyes (54.5%) demonstrated ≥1-line gain. One eye underwent optical keratoplasty following post-CXL hydrops.The magnitude of flattening was classified as mild (4 D), moderate (4-8D), severe (>8D).Maximum flattening > 8.3D was seen in 27% eyes. 45.45 % of eyes demonstrated pachymetric thinning > 200 micron with severe reduction of 290 micron in 1 eye. Epithelial mapping demonstrated hyperplasia overlying zones of maximal stromal flattening, suggesting compensatory remodelling.

Excessive corneal flattening and thinning represents an uncommon long-term response after Dresden protocol collagen cross linking. Patients require prolonged follow-up with serial tomography, to identify these changes. Simultaneously, identifying individuals who are at risk for this pronounced effect and educating them about control of risk factors such as allergic eye disease and eye rubbing habits is important. Collagen cross linking, even though is a time tested modality of treatment in progressive keratoconus, should not be the end of care. Over decades our understanding of the sequelae of this procedure is still improving and therefore longterm followup of these patients is essential.