Corneal Topographic Index Changes Following Standard Corneal Collagen Cross-Linking In Progressive Keratoconus: A 6-Month Prospective Controlled Study

To evaluate the effect of standard epithelium-off corneal collagen cross-linking (CXL) on corneal topographic

indices including maximum keratometry (Kmax), simulated keratometry (simK), index of surface variance (ISV),

index of vertical asymmetry (IVA), keratoconus index (KI), and corneal astigmatism over a 6-month follow-up

period in progressive keratoconus patients.

Department of Ophthalmology, Recep Tayyip Erdogan University Training and Research Hospital, Rize, Turkey.

Prospective controlled study.

Sixty eyes of 60 patients with progressive keratoconus (Kmax increase ≥1.0 D over 6-12 months) underwent standard Dresden protocol CXL (epithelium-off, riboflavin 0.1%, UVA 370 nm, 3 mW/cm², 30 min); 60 healthy eyes served as controls. Corneal topography was performed preoperatively and at 1, 3, and 6 months postoperatively. Parameters included Kmax, Kmin, simK, corneal astigmatism, ISV, IVA, KI, CKI, and thinnest corneal thickness. Success was defined as stabilization (Kmax change ≤1.0 D) or improvement (Kmax decrease ≥0.5 D). Statistical analysis: repeated measures ANOVA and paired t-test (SPSS 23.0; p<0.05)

Mean Kmax decreased significantly from 52.4±4.8 D preoperatively to 51.6±4.5 D at 6 months (mean reduction

0.8±1.2 D; p=0.002). SimK decreased from 47.8±3.6 D to 47.2±3.4 D (p=0.014). ISV decreased from 68.2±24.1 to

63.5±22.8 (p=0.008) and IVA decreased from 0.82±0.31 to 0.74±0.28 (p=0.003). KI showed minimal change

(1.18±0.12 to 1.16±0.11; p=0.087). Corneal astigmatism decreased from 4.2±2.1 D to 3.8±1.9 D (p=0.023). At 6

months, topographic stabilization was achieved in 91.7% (55/60) of eyes, with improvement in 43.3% (26/60) and

progression in only 8.3% (5/60). In the progressing eyes, mean Kmax increase was 1.3±0.2 D. At 1 month,

transient Kmax increase was observed (53.1±5.0 D; p=0.041), normalizing by 3 months.

Standard CXL effectively stabilizes corneal topography in progressive keratoconus, with topographic stabilization

or improvement in over 90% of eyes at 6 months. Multiple topographic indices including ISV, IVA, and corneal

astigmatism show statistically significant improvement. Clinicians should be aware of transient topographic

worsening at 1 month, which does not predict treatment failure.