Corneal biomechanical properties in normal, post-laser in situ keratomileusis, and keratoconic eyes.
OBJECTIVE
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).


METHODS
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.
Ortiz
Dolores
D
Department of Refractive Surgery, Instituto Oftalmológico de Alicante, Vissum, Miguel Hernández University, Medical School, Alicante, Spain. rdioa@vissum.com
Piñero
David
D
Shabayek
Mohamed H
MH
Arnalich-Montiel
Francisco
F
Alió
Jorge L
JL
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D002648:Child; D003315:Cornea / Q000502:physiology* / Q000601:surgery; D004547:Elastic Tissue / Q000502:physiology; D005260:Female; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology; D007640:Keratoconus / Q000503:physiopathology* / Q000601:surgery; D020731:Keratomileusis, Laser In Situ; D008297:Male; D008875:Middle Aged; D011184:Postoperative Period; D011446:Prospective Studies