Correlation between corneal biomechanical measurements and ablation depth in customised photorefractive keratectomy

Mirzaei Mohammad

Purpose: To evaluate correlation between corneal biomechanical measurements and ablation depth in myopia and myopic- astigmatism after customised photorefractive keratectomy.

Setting: Laser Refractive center, Alavi Eye Hospital, Department of ophthalmology, Medical Science University of Tabriz – IRAN.

Methods: In 96 eyes with myopia and myopic astigmatism the Ocular Response Analyzer (ORA) was used to measure corneal histeresis (CH), corneal resistance factor (CRF), Goldman-correlated intraocular pressure (IOPg), and corneal-compensated IOP (IOPcc) before and 3 months after custom PRK.

Preoperative manifest refraction spherical equivalent (MRSE), central corneal thickness (C.C.T) and ablation depth (AD) were recorded. The changes of parameters after PRK were calculated and correlation between attempted correction of MRSE and AD, and correlation between the AD and the changes in CH, CRF,IOPg andIOPcc were examined. Statistical analysis was performed using SPSS15 software and a P-value less than 0.05 was considered significant.

Results: Preoperative mean attempted correction of MRSE, C.C.T and mean AD were -4.13±1.98D, 544±34µ and 74.81±31 µ respectively.
The preoperative mean CH and CRF (10.00±1.36mm Hg and 10.20±1.51mm Hg respectively) were significantly higher than postoperative values (7.55±1.81mm Hg and 6.74±1.72mm Hg respectively) (P<0.001).

The higher attempted correction of MRSE was correlated with higher AD (R_S=0.87 P<0.001), higher ΔCH (R_S=0.41 P<0.001), and higher ΔCRF(R_S=0.66 P<0.001).

Conclusion: Changes in CH and CRF after custom PRK suggest alteration in corneal biomechanics correlating with attempted correction , and CRF was more affected than CH.