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Impressum
Predictability of auto-refractometry after LASIK
Mirshahi A., Gerhardt D., Bühren J., Wellermann G., Kohnen T.
University Eye Clinic Frankfurt/Main
Automated refractometry (AR) is a useful tool for determination of subjective
refraction. However it seems to be less reliable after laser in situ keratomileusis
(LASIK) than preoperatively. Aim of this study was to evaluate the accuracy
of AR after LASIK considering different central laser treatment zones
(optical zone).
Methods: Results of 95 consecutive LASIK operations (57 patients,
mean age: 37 years, myopic and myopic astigmatism) were evaluated retrospectively.
The operation was performed using a scanning spot excimer laser (Technolas
C-LASIK 217) and HansatomeTM microkeratome. Four groups were evaluated:
a) optical zone between 5 - 5.5, b) 5.6 - 6, c) 6.1 - 6.5, d) 6.6 - 7
mm. Pre- and postoperative subjective and automated refraction data (Topcon
RM-A2300) were compared.
Results: The mean preoperative spherical equivalent (SE) of autorefractometry
was -6.76 D (±2.65), mean preoperative subjective refraction (SE)
was -6.9 D (±2.71), [rpre=0.99, rpost1=0.78, rpost12=0.7]. The
difference between the objective (AR) and subjective refraction was calculated
(SE, average): preoperatively all: 0.14 D (±0.41), 1 month postoperatively
-0.18 D (±0.58), 12 months postoperatively -0.35 D (±0.59).
Group results:
a) preop 0.18 (±0.6), post 1 mo -0.68 (±0.51), post 12 mo
-0.7 (±0.62),
b) preop 0.16 (±0.39), post 1 mo -0.26 (±0.51), post 12
mo -0.6 (±0.46),
c) preop 0.12 (±0.33), post 1 mo 0.07 (±0.53), post 12 mo
-0.2 (±0.49),
d) preop 0.08 (±0.32), post 1 mo 0.17 (±0.41), post 12 mo
0.32 (±0.4).
Conclusion: Generally auto-refractometry results after LASIK are
not as accurate as preoperatively. If the optical zone is lower than 6.1
mm the device underestimates the subjective refraction (more myopic values).
The smaller the optical zone, the higher it underestimates. In the case
when the optical zone is higher than 6.5 mm the autorefractomter overestimates
the true refraction (more hyperopic values).