gms | German Medical Science

SMILE surgery for moderate and high myopia is, compared with our experience with microkeratome-based LASIK and femtosecond laser-based LASIK, more accurate and precise.

During the last 5 years, more than 4,000 SMILE surgeries have been performed at the Department of Ophthalmology, Aarhus University Hospital. The first, close to 2,000 surgeries have been systematically quality assessed and data analysed for potential predictors for the outcome [1], [2].

Although the prediction error in SMILE appears almost independent of the attempted correction, there seems to be a small, but significant increasing under-correction with increasing refractive correction attempt. A small, but significant influence of increasing age, gender and corneal curvature corresponded to the previous study. A small, but significant effect of which eye was operated was, however, noted. Right eyes were 0.1 dioptres under- corrected compared with left eyes. The influence of the predictors was, however, very small, and except for the attempted correction, we do not suggest that these findings are used for nomogram adjustment. For attempted correction, it may be considered to decrease the attempted correction by 0.25 for low corrections (−1 to −2 dioptres) and to increase the attempted correction by 0.25 dioptres for high corrections (−8 and above).

Ninety-five percent of the variation in the SE prediction error could not be explained in the present study. The total standard deviation on the prediction error was 0.50 dioptres, corresponding to a variance of 0.25 dioptres. Considering that clinical refractions may be associated with a standard deviation of 0.4 dioptres, corresponding to a variance of 0.16 dioptres, and that empirical factors related to age, gender, eye, corneal power and treatment attempt explain 0.05 dioptres, only 0.04 dioptres of the variance need to be explained. This amounts to a standard deviation of 0.2 dioptres on the prediction error. Further optimisation of the femtosecond laser may be able to reduce the prediction error, but most remaining errors possibly are related to individual differences in the compensatory epithelial hyperplasia.

It seems reasonable to believe that the most important factor to improve the refractive predictability of the SMILE procedure is very standardised protocols for the preoperative refractive evaluation of patients, preferably by repeated measurements of clinical refraction before surgery is planned.