Postoperative stability of refractive error after cataract surgery

Abstract

Aim. The goal of the present study is to determine how much time must pass after a cataract surgery with no complications to achieve a sufficiently stable refraction. Subjects and methods. We measured the postoperative refraction of 61 pseudophakic subjects (mean age: 74.32 ± 7.11 years) five times with an autorefractor. The subjects had undergone unilateral cataract surgery and the time intervals for the measurement went from one day to eight weeks after the operation. In order to obtain the spherical equiva- lent (SE) and the cylinder power, the difference from each measurement and the last measurement in the seventh or eighth week post-surgery was taken. The Friedman test for paired samples was used to see if there were any significant differences in spherical equivalent and cylinder power in the 5 measurements taken. In addition, two repeated measure- ments were taken on one eye of 16 phakic subjects with good ocular health pertaining to a similar age group to determine the measurement uncertainty of the autorefractor (± 1.96 SD for the measured value differences). Results. In the case of the spherical equivalent, we found no statistically significant difference between the individual re- peated test series. The cylinder power was significantly higher on the first day after the operation than during all subsequent appointments, but then showed no significant difference between all measurements taken during the examinations after the first day. The differences in the spherical equivalent between one measurement and the reference measurement (7 - 8 weeks after the surgery) resulted in 95 % confidence intervals (± 1.96 SD) of approximately ± 2.00 dioptres (D) on the first day post-surgery and lay between ± 1.20 D and ± 0.80 D in post-surgery weeks 1, 3 and 5. The corresponding con- fidence intervals for the cylinder power were ± 2.00 D on the first day post-surgery and lay between ± 1.27 D and ± 0.88 D in post-surgery weeks 1, 3 and 5. The statistical dispersion of the spherical equivalent and the cylinder power decreased slightly as the time from the surgery increased. We estimated a measurement uncertainty for automated refractometry performed on older phakic eyes of ± 0.80 D for the spherical equivalent and ± 1.16 D for the cylinder power. Conclusion. The refractive power of a pseudophakic eye can be determined with sufficient certainty after one to three weeks after undergoing cataract surgery without compli- cations. This means that optical aids to correct any residual refractive error or presbyopia can be prescribed earlier than before and, hence, the number of follow-up appointments required to measure a stable refraction can be reduced. Keywords Cataract, postoperative refraction, refraction measurement, repeated automated refractometry, Intraocular lenses (IOL)