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N. Gupta, K. L. Fry, P. S. Hersh; Ora Measurements After PRK and LASIK. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5331.
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© ARVO (1962-2015); The Authors (2016-present)
To analyze corneal biomechanics following LASIK and PRK.
A retrospective chart review was carried out on 113 eyes that underwent LASIK and 121 eyes that underwent PRK for the treatment of myopia or myopia with astigmatism. Pre- and postoperative data at three months following surgery was assessed including: UCVA, BSCVA, MRSE, and predictability. The Ocular Response Analyzer (Reichert Inc.) was used to gather biomechanical data, including corneal hysteresis (CH) and corneal resistance factor (CRF).
Mean preoperative MRSE for LASIK and PRK eyes was -4.34D (ranging -0.68 to -8.35) and -6.64D (ranging -0.58 to -13.15) respectively. Three months postoperatively, mean predictability was 0.00D (SD 0.58) for LASIK eyes and -0.21D (SD 0.81) for PRK eyes.Mean CH showed a statistically significant decrease following LASIK and PRK in all eyes (p<0.01). Mean CH decreased from 10.77mmHg (SD 1.50) to 8.92mmHg (SD 1.21) for LASIK eyes and from 10.41mmHG (SD 1.95) to 7.56mmHg (SD 1.48) for PRK eyes. Mean CRF also showed a statistically significant decrease after surgery (p<0.01 for LASIK and PRK eyes). Mean CRF decreased from 10.5mmHG (SD 1.82) to 7.3mmHg (SD 1.48) for LASIK eyes and from 10.09mmHg (SD 2.09) to 6.1mmHg (SD 1.88) for PRK eyes. Comparison of mean change in CH showed that PRK induced a statistically significant greater change in CH compared to LASIK eyes (p<0.01). Mean change in CH for LASIK eyes was 17.8% compared to 26.5% for PRK eyes. Comparison of change in CRF for LASIK and PRK was 30.5% and 39.8% respectively which failed to reach significance. No association between preoperative CH or CRF and predictability was found.
Refractive surgery induces significant changes in the biomechanical properties of the cornea with a decrease in CH and CRF values. The clinical implications, if any, remain to be clarified.
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