Corneal biomechanical properties in normal, post-laser in situ keratomileusis, and keratoconic eyes
Accepted 15 April 2007.
Purpose
To compare the biomechanical properties of normal, post-laser in situ keratomileusis (LASIK), and keratoconic corneas evaluated by corneal hysteresis and the corneal resistance factor measured with the Reichert Ocular Response Analyzer (ORA).
Settings
Instituto Oftalmológico de Alicante, Vissum, Alicante, Spain.
Methods
Two hundred fifty eyes were divided into 3 groups: normal (control group), post-LASIK, and keratoconus. The corneal biomechanical properties were measured with the ORA, which uses a dynamic bidirectional applanation process. The main outcome measures were intraocular pressure, corneal hysteresis, and the corneal resistance factor.
Results
The control group had 165 eyes; the LASIK group, 65 eyes; and the keratoconus group, 21 eyes. In the control group, the mean corneal hysteresis value was 10.8 mm Hg ± 1.5 (SD) and the mean corneal resistance factor, 11.0 ± 1.6 mm Hg. The corneal hysteresis value was lower in older eyes, and the difference between the youngest age group (9 to 14 years) and oldest age group (60 to 80 years) was statistically significant (P = .01, t test). One month after LASIK, corneal hysteresis and the corneal resistance factor decreased significantly, from 10.44 to 9.3 mm Hg and from 10.07 to 8.13 mm Hg, respectively. In the keratoconus group, the mean corneal hysteresis was 7.5 ± 1.2 mm Hg and the mean corneal resistance factor, 6.2 ± 1.9 mm Hg. There were statistically significant differences in both biomechanical parameters between keratoconic eyes and post-LASIK eyes (P<.001, t test).
Conclusions
The corneal hysteresis and corneal resistance factor values were significantly lower in keratoconic eyes than in post-LASIK eyes. Future work is needed to determine whether these differences are useful in detecting keratoconus when other diagnostic tests are equivocal.
From the Department of Refractive Surgery (Ortiz, Piñero, Shabayek, Alio), Instituto Oftalmológico de Alicante, Vissum, and Division of Ophthalmology (Alio), Miguel Hernández University, Medical School, Alicante, and the Department of Ophthalmology (Arnalich-Montiel), Hospital Universitario Ramón y Cajal, Madrid, Spain
Corresponding author: Dolores Ortiz, PhD, Research and Investigation Department, Instituto Oftalmológico Alicante, Vissum Corp., Avenida Denia s/n, Edificio Vissum, 03016 Alicante, Spain.
No author has a financial or proprietary interest in any material or method mentioned.
Supported in part by a grant of the Spanish Ministry of Health, Instituto Carlos III, Red Temática de Investigación en Oftalmologia, Subproyecto de Cirugia Refractiva y Calidad Visual (C03/13).
ABSTRACT