Autorefractometry is less accurate in LASIK eyes

It has been demonstrated that autorefractometry is less accurate in eyes that have undergone LASIK when compared with non-operated eyes, according to a recent study published in the American Journal of Ophthalmology.

Led by Thomas Kohnen et al., Department of Ophthalmology, Medical Centre of J.W. Goethe-University, Frankfurt, Germany, the researchers examined the factors influencing the reliability of autorefractometry before and after LASIK for myopia and myopic astigmatism.

The study group comprised a total of 250 consecutive eyes belonging to 132 patients with an average preoperative spherical equivalent of the subjective refraction (SR) of -6.59 D. All patient data was reviewed before LASIK and 1 month afterwards, including SR, objective automated reaction (AR) and visual acuity.

Additionally, subgroup analysis was performed with regards to preoperative myopia and excimer laser optical zone (OZ).

The mean post-LASIK spherical equivalent difference was +0.13±0.51 D in comparison with a preoperative difference in spherical equivalent of –0.30±0.58 D. The respective postoperative difference between spherical equivalents by optical zone size were as follows: for small OZ (5.0–5.5 mm) = –0.61 D; for OZ 5.6–6.0 mm = –0.36 D; and for 6.1–7.0 mm = –0.16 D. Further, the higher the preoperative myopia, the increasingly myopic the AR when compared with the SR.

Based on the results, the authors concluded that the reliability of automated refraction is lowered following LASIK and this is influenced by the excimer laser optical zone size and the preoperative myopia. Specifically, refraction was less accurate with a small OZ and high preoperative myopia.