Central versus paracentral cone location and outcomes of accelerated cross-linking in keratoconus patients

Purpose: To compare outcomes 1 year after accelerated cross-linking (CXL) between keratoconus eyes with central cones to those with paracentral cones. Methods: In this post hoc analysis of data from a prospective multicentre study, consecutive progressive keratoconus eyes treated with accelerated CXL were included. Preoperative and 1 year post CXL manifest refraction, corneal cylinder, maximal keratometry (Kmax), central corneal thickness and coma were assessed. Central and paracentral cones were defined as cones within the central 3 mm and those between 3 and 5 mm, respectively. Eyes with apical scarring and peripheral cones (>5 mm) were excluded. The primary outcome measures were changes in best spectacle-corrected visual acuity (BSCVA) and Kmax. Results: Overall, 314 eyes (n = 314) with a mean age of 27.5 ± 7.7 years were included. At baseline, the central cone group was younger (p < 0.001), had lower corneal astigmatism (p = 0.03) and coma (p = 0.02). At 1 year post CXL, after adjusting for baseline characteristics (age, BSCVA, corneal astigmatism, Kmax and coma), the central cone group showed a greater reduction in myopia (mean difference 1.27 ± 0.60D, p = 0.04) and more improvement in BSCVA (mean difference 0.08 ± 0.02 logMAR, p < 0.001) compared to the paracentral group. There was no significant difference in progression rates between the central and paracentral groups (ΔKmax > 2D, 6.7% vs. 6.5%, respectively, p = 0.83). Conclusions: This large-scale study of keratoconus eyes 1 year after accelerated CXL indicates that compared to those with paracentral cones, central cones have on average almost one additional line improvement in BCSVA and 1.27 D more reduction in myopia.