Flap-induced aberrations for the LASIK refractive surgery

Abstract

 

Purpose

 

Corneal flap creation during the LASIK surgery induces changes in refraction and high-order aberrations, which have to be taken into account for more precise treatment planning. The flap-induced aberration, do not depend on the ablation magnitude, but may be different for different surgeons, different tools, of different sites. We propose to estimate the flap-induced aberrations and use these estimates to adjust the treatment target accordingly.

 

Methods

 

Flap-induced aberrations may be measured directly, when the flap is placed back with no ablation performed. It can also be estimated statistically. For instance, the trend line of induced spherical aberration, SA vs. pre-operative spherical equivalent, SE typically crosses the axis SE=0 at some non-zero level, . This value quantifies the change in SA when no ablation is performed, just the flap is created. Also the flap-induced aberrations may also be derived from a flap-creation model, which takes into account site-specific parameters. The value of may depend on multiple factors, including the difference for the flap creation with mechanical microkeratome vs. femto-second laser [3,4], individual surgeon’s techniques, operating environment, etc.

 

Results

 

Statistics of flap-induced SA calculated with data from controlled clinical studies shows significant differences between different operating sites (Fig. 1) Flap-induced aberrations may be taken into account during the treatment planning, when treatment target adjustment is applied to compensate for these aberrations. The adjustments may be derived statistically for each site, surgeon, or tool (see Fig. 2). The site-specific SA0 can be readjusted such that the adjusted scatter plot will become more compact with increased correlation and R2 values (compare Fig.2 B and C). This allows a better fit for the nomogram adjustment as well as more precise modeling of the cornea healing.

 

Conclusions

 

Flap-induced aberrations for LASIK treatments may substantially contribute to the surgery outcome. The magnitude of aberrations is different for different surgeons, sites, or tools, an should be estimated for each surgeon individually. Data for different surgeons may be combined for subsequent analysis and adjustments.

 

 

 

Fig. 2. Induced SA vs. pre-op SE trend lines for two surgeons (A), regression for measured SA data (B), and regression for the data adjusted by the surgeon-specific .

 

Keywords: 683 refractive surgery: LASIK