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G.–Y. Yoon, S. MacRae; Corneal thickness required to correct higher order aberrations in customized laser refractive surgery . Invest. Ophthalmol. Vis. Sci. 2004;45(13):222.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To estimate the amount of additional corneal thickness that needs to be ablated to correct higher order aberrations and to understand the difference in total ablation volume between myopic and hyperopic customized correction. Methods: An ablation thickness profile to correct various higher order aberrations in addition to defocus and astigmatism was calculated based on the eye’s aberration and the refractive index of the cornea. This thickness profile was used to calculate the maximum ablation thickness and volume of the total ablation with and without higher order aberration correction. Aberrations were measured using a Shack–Hartmann wavefront sensor in a pre–LASIK population of 208 myopic (–3.55Dsph, –1.01Dcyl) and 36 hyperopic eyes (2.70Dsph, –0.88Dcyl). The average higher order rms (3rd – 5th order) in myopic and hyperopic groups was 0.41±0.16µm and 0.48±0.18µm, respectively, for a 6mm pupil. Calculations were performed for a 6 mm optical zone with no transition zone. Results: In both myopic and hyperopic groups, the maximum ablation thickness when correcting higher order aberrations was on average, 2.5µm larger than without higher order correction. Total ablation volume was significantly increased when correcting higher order aberrations through 4th order compared to when correcting only 2nd order aberrations. The increase in ablation volume for myopic and hyperopic customized corrections through 4th order was 0.097 (13% increase) and 0.046 (10% increase) mm3, respectively. In both groups, there was no significant difference between correcting through 4th order or through 5th order. Conclusions: Correcting higher order aberrations does not cause a significant increase in the maximum ablation thickness compared to conventional refractive surgery. However, total ablation volume is significantly increased when correcting higher order aberrations. This additional increase in volume of total ablation thickness for myopic customized corrections is approximately twice as large as that for hyperopic customized corrections, mainly due to increases caused by trefoil and coma.
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