Purpose:
To assess how refractive error predicts spectacle independence in post cataract surgery patients with monovision or multifocal lenses
Methods:
Patients undergoing bilateral cataract surgery were randomized to receive either diffractive multifocal IOLs (Tecnis ZM900) or monofocal IOLs (Akreos AO) with 1.0-1.5 D of monovision. Three months after surgery patients were interviewed about spectacle dependence and refracted. Refractions were converted into vector notation. Logistic regression was used to evaluate whether spectacle dependence for near and distance were related to overall refractive error, spherical error, signed spherical error, and astigmatic error. The eyes of each multifocal patient were labelled as being "better" or "worse" if they had the higher or lower total refractive error respectively. The eyes of each monovision patient were labelled as "near" or "distance".
Results:
212 patients were randomised, 187 attended at 3 months. 176 patients were analysable after allowing for intraoperative complications, post-op IOL exchanges and failure to progress to second eye surgery. Spectacle independence was 26% in the monovision arm and 74% in the multifocal arm (P<0.001). In the monovision arm the mean spherical equivalent in the distance and near eyes were +0.075 D and -0.92 D respectively. The mean astigmatism was -0.76 D. In the multifocal arm the mean spherical equivalent was -0.22 D and the mean astigmatism was -0.67 D. In multifocal patients for each dioptre of spherical error in the "worse" eye the odds of being spectacle independent decreased by 61.7% (P=0.06). In monovision patients for each dioptre that signed spherical error in the "near" eye increased, the odds of being spectacle independent decreased by 64% (P=0.003). Spherical error in the "better" multifocal or "distance" monovision eye had no influence on spectacle independence. Astigmatism had no influence on spectacle independence.
Conclusions:
Increasing myopia strongly predicts spectacle independence in monovision. Spherical error in the "worse" eye of multifocal patients may predict spectacle independence. Low levels of astigmatic error do not predict spectacle dependence in multifocal or monovision patients.
Clinical Trial:
http://www.isrctn.org ISRCTN 37400841
Keywords: presbyopia • intraocular lens • clinical (human) or epidemiologic studies: treatment/prevention assessment/controlled clinical trials