To compare corneal biomechanical parameters and two measures of intraocular pressure
(IOP) in eyes before and after excimer laser refractive surgery, with the Ocular Response
Analyser (ORA).
Eighty normal eyes of 41 patients undergoing excimer laser refractive surgery in Birmingham,
U.K. were recruited into three groups: Laser Assisted-Epithelial Keratomileusis (LASEK)
(Myopes), Laser Assisted in Situ Keratomileusis (LASIK) (myopes) and LASIK (hyperopes).
The preop and 3 months postop Goldmann correlated IOP (IOPg), corneal compensated
IOP (IOPcc), corneal hysteresis (CH), and corneal resistance factor (CRF) were measured
by the ORA. Central corneal thickness (CCT) was measured using ultrasonic pachymeter.
The differences of the changes in IOPg, IOPcc, CH, CRF and CCT between the three groups
were estimated. A General Linear Model was selected to investigate the influence of
gender, age, initial conditions (CH, CRF, CCT, IOPcc and IOPg) and changes in CCT
on the measured IOP.
The differences between the mean IOPg, CH and CRF after refractive surgery were statistically
significant for all three groups. The hyperopic LASIK group had a significantly smaller
change compared to the other groups (which had no statistical significance). The preop
IOPg, preop CH and gender were significant predictors of the changes in measured pressure
and biomechanical parameters after surgery in the myopic groups only.
CH and CRF were found to decrease after both myopic and hyperopic refractive surgery.
CH and CRF measurement may prove important tools to clarify the role of corneal biomechanics
for refractive surgery.