Spectacle correction of anisometropia following cataract surgery

INTRODUCTION Modern cataract surgery is one of the safest, most effective, and frequently executed surgical procedures in ophthalmology performed today [1, 2]. Around 300 000 cataract surgical procedures refunded by the National Health Fund (NFZ) are performed yearly in Poland starting from 2017 [3]. The vast majority of cataract operations produce excellent visual outcomes, which improve the quality of life of patients [4, 5]. It has to be noted that significant binocular vision impairments rarely present after cataract surgery [6], and most (72.7%) biometry prediction errors are within the ±0.5 D range. However, in specific postoperative conditions, problems with binocular vision caused by anisometropia may occur. One of them is refractive prediction error – “refractive surprise”, described as error higher than ±2.0 D, reported by Lundström et al. in 3555/282 811 cases [7]. Another problem affecting binocular vision is postoperative aphakia, and high refractive error in the non-operated eye [8]. Spectacles are the most common, non-invasive, optical correction of ametropia. Like any method they have advantages, disadvantages, and limitations of use. The intended refractive result of cataract surgery is usually the improvement of uncorrected distance visual acuity (implantation of monofocal intraocular lens [IOL] calculated for emmetropia). However, in selected clinical situations, IOL power is calculated for near (e.g. in myopic eyes). An IOL placement can imitate the physiological condition of phakia, but it does not entirely eliminate patients’ need to use spectacles or contact lenses. Residual refractive error and/ or insufficient refractive power for near vision often require a correction. Moreover, many patients endure anisometropia after cataract treatment. This condition produces the differential prismatic effect in spectacles (anisophoria) and unequal spectacle magnification (aniseikonia). These issues may cause patient distress and difficulties with everyday tasks. However, there is individual tolerance of anisophoria and aniseikonia. Patients not tolerating the mentioned effects will experience asthenopia symptoms and binocular vision problems. Due to limited vertical fusional reserve capacity, the vertical differential prism may cause not only asthenopia symptoms (vertical differential prism more than 1 PD [9]) but, in some cases, double vision. Due to ocular prism adaptation, tolerance of differential prism in a horizontal direction may be higher than 5 PD, as described by Henson and North [10].