Diagnosis of Early Post-LASIK Ectasia With Mean Keratometry-Matched Controls

To identify topographic and wavefront aberration parameters that distinguish early post-LASIK (PL) ectasia (PLE) from stable PL corneas, keratoconus (KC), and normal eyes when matched for mean central keratometry.

This retrospective comparative study included 200 patients (n = 50 per group): early PLE, stable PL, early KC, and normal eyes, matched for mean central keratometry (∼41.0 D). Corneal topographic indices [index of surface variance (ISV), index of vertical asymmetry (IVA), index of height asymmetry (IHA), index of height decentration, central keratoconus index], keratometric parameters (flat K, steep K, K_max), pachymetry, higher-order aberrations (HOAs), coma, astigmatism, and a novel asymmetry-to-symmetry (A/S) aberration ratio.

PLE exhibited higher K_max (46.9 ± 3.1 D) compared with PL (45.2 ± 1.7 D; P <0.01), although lower than early-KC (48.2 ± 4.3 D). Pentacam indices showed elevated ISV (40.98 vs. 23.68), IVA (0.38 vs. 0.16), and IHA (10.22 vs. 6.41) in PLE versus PL (all P < 0.001). PLE eyes had higher anterior HOA RMS (∼3.5 μm) than PL (∼2.5 μm) and normal (∼1.1 μm), approaching early KC (∼5.1 μm). Asymmetric aberrations (coma, astigmatism, trefoil) were disproportionately increased in PLE, whereas symmetric aberrations (spherical aberration, defocus) remained comparable (P ≈ 0.9). The A/S ratio was higher in PLE (0.60 ± 0.44) versus PL (0.30 ± 0.16, P < 0.001). Receiver-operator-characteristics analysis identified IVA (area under the receiver-operator-characteristics curve 0.802), ISV (0.786), coma (0.771), HOA RMS (0.740), and A/S ratio (0.728) as useful discriminators of PLE. An A/S ratio >0.54 yielded 96% specificity for ectasia detection.

Early PLE shows distinctive disproportionate increases in asymmetric aberrations, quantified by the A/S ratio. In combination with ISV, IVA, and coma, this metric may facilitate early diagnosis of PLE, enabling timely intervention to prevent progression.