OPD scan III accuracy: Topographic and aberrometric indices after accelerated corneal cross-linking

To determine topographic and aberrometric changes after accelerated cross-linking (ACXL; 18 mW/cm² for 5 min) as measured with OPD Scan III (Nidek Inc., Tokyo, Japan) and their repeatability in patients with mild and moderate keratoconus (KCN).

In this prospective study, 25 eyes with mild KCN [Ksteep = 47.24 ± 3.11 diopter (D)] and 20 moderate cases (Ksteep = 52.86 ± 4.39 D) were examined under mesopic conditions (20 lux) twice, 30-45 min apart, at baseline and 6 and 12 months afterwards. Extracted indices were Ksteep, Kflat, ocular and corneal irregularity, ocular and corneal total higher order aberrations (HOAs), coma, trefoil, and spherical aberration (SA). Repeatability index (RI) and intraclass correlation coefficients (ICCs) were determined.

In mild cases, Ksteep and corneal irregularity had lower RI, but Kflat and ocular irregularity had higher RI (all P > 0.050) at 1 year. The RI for ocular total HOAs, coma, and SA decreased and showed no significant change for trefoil (all P > 0.050). Moderate cases showed non-significant increases in RI for Ksteep, Kflat, ocular and corneal irregularity (all P > 0.050), and all aberrometry indices, and significant increases in RI for ocular coma (P = 0.046) and corneal trefoil (P = 0.037). At 1 year, ICC was >0.75 for all indices except ocular and corneal trefoil (ICC = 0.613 and 0.390) in moderate cases.

At one year after ACXL, OPD Scan III showed acceptable repeatability in mild cases. In moderate cases, topographic indices had acceptable repeatability but poorer compared to the mild group. Overall, ocular HOAs showed better repeatability than corneal ones. These changes should be considered in the interpretation of measurements.