Abstract
Purpose: :
To determine the induction of spherical aberration (SA) after high myopic LASIK using different ablation profiles by comparing two-dimensional SA curves (RAWS plot).
Methods: :
This was a retrospective analysis of SA induction in 29 high myopic eyes (SEQ -7 to -9.5 D) after LASIK with the Hansatome microkeratome (Bausch & Lomb) and MEL80 (Carl Zeiss Meditec). Three different ablation profiles were used: the MEL80 Munnerlyn profile (TSA, 5 eyes), the MEL80 aspheric profile (ASA, 14 eyes), and a proprietary non-linear aspheric ablation profile (NLA, 10 eyes). A 6-mm optical zone was used for all eyes. SA was measured before and at least 3 months after surgery using the WASCA (AMO). We previously published a single parameter metric to represent raw spherical aberration (RAWS) to functionally describe the cumulative spherical aberration for an eye over a range of physiological pupil sizes. To derive the RAWS parameter, spherical aberration is plotted over pupil analysis zones from 4500 to 6000 µm (4.5 to 6.5mm). The RAWS parameter (unit = µm2) is then equal to the area under the plot. The pupil size at which SA induction reached 0.4 µm was calculated, referred to as the Zone in which Aberrations were Not Increased Significantly (ZANIS).
Results: :
Mean SEQ treated was -7.65±1.04 D for TSA, -7.82±0.56 for ASA, and -8.01±0.97 for NLA ablation profiles. SA induction exponentially increased for larger analysis zones for all three profiles. At the 6-mm analysis zone, mean SA induction was 0.56±0.14 µm for TSA, 0.48±0.10 µm for ASA, and 0.27±0.20 µm for NLA ablation profiles. The RAWS parameter was 439±107 µm2 for TSA, 358±118 µm2 for ASA, and 156±162 µm2 for NLA. ZANIS was 5.63-mm for TSA, 5.82-mm for ASA, and 6.32-mm for NLA ablation profiles. The average scotopic pupil size in our entire patient population (10,351 eyes) is 5.67 mm, with only 26% larger than 6.32 mm.
Conclusions: :
The NLA ablation profile proved more effective in rendering a low spherical aberration induction within the average scotopic pupil. These findings may explain why previous studies have found no correlation between night vision disturbances and pupil sizes below and above 6-mm after high myopic LASIK.
Keywords: refractive surgery: LASIK • aberrations