Progression of keratoconus by longitudinal assessment with corneal topography.

PURPOSE

To investigate the longitudinal changes in corneal topographic indices over time in patients with mild keratoconus (KC) and to determine predictive factors for the increase in corneal curvature.

METHODS

The authors retrospectively reviewed the data of 94 eyes of patients with mild KC who had undergone computerized videokeratography (Orbscan IIz; Bausch & Lomb Surgical, Rochester, NY) at least twice at an interval of ≥1 year. Patients with an increase of ≥1.50 diopters (D) in the central keratometry (K) were placed in the progression group, and the others were placed in the nonprogression group. In each group, the quantitative topographic parameters were compared and tested as predictive factors for KC progression. Additionally, corneal astigmatic changes were evaluated by means of vector analysis.

RESULTS

In total, 94 eyes of 85 patients were included. Twenty-five of 94 (26.5%) eyes showed progression of the central K ≥1.50 D; progression took 3.5 years on average. Median time to progression by Kaplan-Meier analysis was 12 years. Significant predictors for KC progression were as follows: highest point on the anterior elevation from the anterior best-fit sphere (BFS), ≥0.04 mm; irregularity index at 3 mm, ≥6.5 D; irregularity index at 5 mm, ≥6.0 D; thinnest pachymetry, <350 μm at baseline examination; yearly change rate of anterior BFS, ≥0.1 D/y; central K, ≥0.1 D/y; simulated K in maximum, ≥0.15 D/y; simulated K in minimum, ≥0.2 D/y; and anterior chamber depth, ≥0.0 mm/y. The dominant with-the-rule pattern of astigmatism at the baseline examination was changed to an oblique pattern of astigmatism at the last examination.

CONCLUSIONS

Mild KC tended to be progressive in approximately 25% of patients, and progression lasted 3.5 years on average. Longitudinal changes in the corneal topography quantitative indices can be used as predictors of KC progression.