[Quality assurance in biometry before cataract surgery: which patients have an increased risk of aberrance from target refraction?].

BACKGROUND: An important factor for patient satisfaction after cataract surgery is the achieval of the planned target refraction. The formulae which are used to calculate the necessary refractive power of the intraocular lens (IOL) to be implanted have been improved over time in order to deliver exact predictions even in those cases in which the measurements of an eye deviate greatly from the norm. We examined which of the routinely measured biometric values have an influence on reaching target refraction. PATIENTS AND METHODS: This retrospective investigation reports on a case series of 153 eyes of 146 patients within 6 months in which a cataract operation was performed. The average age at the time of operation was 73.5 years. Four measurements were taken preoperatively: refraction (Ref), axial length (AL), corneal refractive power (CR) and anterior chamber depth (ACD). Each of these measurements was examined regarding its influence on the refractive outcome. One of three end points was possible for each eye: achievement of target refraction within ± 0.5 dpt, aberrance from target refraction by more than + 0.5 dpt and aberrance from target refraction by more than - 0.5 dpt. A multivariate regression analysis was performed in which aberrance from target refraction was defined as the dependent variable and the four mentioned measurements were set as independent variables. RESULTS: Of the 153 eyes, in 91 eyes the target refraction was achieved within 0.5 dpt (group 1). In 37 eyes the aberrance from target refraction was more than - 0.5 dpt (group 2) and in 25 eyes it was more than + 0.5 dpt (group 3). The mean measurement values in groups 1, 2 and 3 were as follows: for preoperative refraction 0.0 dpt/0.5 dpt/0.625 dpt, for corneal refractive power 42.84 dpt/42.29 dpt/42.67 dpt, for axial length 23.41 mm/23.36 mm/23.73 mm and for anterior chamber depth 3.07 mm/3.00 mm/3.20 mm. No statistically significant relation between the respective measured values or a combination thereof and the refractive result could be demonstrated. CONCLUSIONS: The formulae for calculating IOL power available today are highly developed and integrate preoperative biometries in a non-linear way, so that there is little difference between measurements within the norm and outlying ones concerning their influence on the refractive result. When conducting quality assurance efforts, we recommend to direct attention to factors influencing anterior chamber depth.