Corneal volume, pachymetry, and correlation of anterior and posterior corneal shape in subclinical and different stages of clinical keratoconus

Purpose: To evaluate the corneal volume, pachymetry, and correlation of anterior and posterior corneal shape in subclinical and clinical keratoconus.

Setting: Vissum Corporation, Alicante, Spain.

Methods: Eyes were placed into 1 of 4 groups as follows: keratoconus 2 (grade II), keratoconus 1 (grade I), subclinical (subclinical keratoconus), and control (normal eyes). All eyes had an ophthalmologic examination including corneal evaluation (curvature, elevation, asphericity, pachymetry, corneal volume) by rotating Scheimpflug imaging (Pentacam). The posterior-anterior corneal power ratio was also calculated.

Results: Seventy-one eyes (51 patients; aged 16 to 64 years) were evaluated. Astigmatism and keratometry of both corneal surfaces were statistically significantly higher in the keratoconus 1 and 2 groups (P<or=.02). Posterior astigmatism was statistically significantly higher in the subclinical group than in the control group (P = .01). A strong correlation (r>or=-0.81) was found between anterior and posterior curvature in the normal and subclinical groups; the correlation was weaker in clinical keratoconus cases (r<or=-0.56). The correlation in astigmatism between the anterior and posterior surface was good in all keratoconus groups (r>or=0.81). The posterior-anterior corneal power ratio was significantly higher in the keratoconus 2 group than in the other groups (P<or=.01). Pachymetric readings were progressively lower in eyes with subclinical, early, or moderate keratoconus (P<.01). The corneal volume was statistically significantly lower in the keratoconus 2 group than in the other groups (P = .04).

Conclusion: The correlation between anterior and posterior corneal curvature was lower in keratoconus, although the correlation between anterior and posterior astigmatism was maintained.