A number of studies have reported the influence of astigmatism on visual function. Several studies have shown that retaining some of myopic astigmatism of against-the-rule would increases the depth of focus and increases near VA, without decreasing distance VA, in case the astigmatism cannot be corrected perfectly when cataract surgery for emmetropia is conducted [1] [8] [9] [10] [11] [12]. However, studies are increasing about adverse effects of astigmatism on visual function. Kamiya et al.[13] reported that uncorrected distant VA was better in eyes with less astigmatism. Wolffsohn et al. [14] reported that even if the uncorrected astigmatism is as small as 1D, it would significantly diminish the VA and affect the patient’s independence and quality of life. Wiggins and Daum [15] reported that patients with 0.50D of uncorrected cylinder complained of more eye fatigue and discomfort than well corrected patients when using a visual display terminal. Rosenfield et al. [16] suggested that small astigmatism should be corrected for comfort when working on a computer. Kazuhiro et al. [17] reported that visual function is affected by astigmatism even when conventional VA is good, irrespective of the axes of astigmatism. Singh et al. [1] recently investigated the relationship between uncorrected astigmatism and VA in pseudophakia. They reported that uncorrected myopic astigmatism of more than 1 D results in a large loss of distance VA, without additional benefit to near VA, and that uncorrected hyperopic astigmatism results in deterioration of both distance and near VAs. They also showed that myopic astigmatism decreased VA by 0.31 (logMAR) per diopter regardless of the direction of the astigmatism axis and 0.23 (logMAR) per diopter for hyperopic astigmatism in emmetropic pseudophakia. Hasegawa et al. [18] reported that astigmatic defocus deteriorates contrast sensitivity.
The current study showed significant differences between monofocal and toric IOLs, with distant UCVA of 0.55 logMAR with monofocal IOLs and 0.38 logMAR with toric IOLs, 2 months postoperatively.
Therefore, implantation of a toric IOL is strongly recommended for patients with both cataract and corneal astigmatism [19] [20]. However, myopic patients who determined to nearsighted target such as -3D have to wear spectacle as usual after surgery, so the remaining astigmatism can be corrected by spectacle. Therefore, toric IOL is not actively recommended in such cases. However, these patients do not always wear spectacle at home and they often take them off when taking a shower or reading a book. The uncorrected visual acuity can be quite important considering that times without spectacle is not short at home.
According to a study by Nael et al [21] on activity limitations due to decreased VA, 17.9% or those whose distance Snellen VA is better than 20/63–20/60 (0.3–0.5 log MAR) have limitations with regard to activities of daily living (ADL) [22] [23] [24] [25] [26] such as dressing, washing, toileting, and eating, whereas nearly twice as many (32.2%) of those who have VA worse than 20/63 (0.5 logMAR) have ADL limitations.
Myopia is a very common ophthalmologic disease, and its prevalence is increasing worldwide. Considering educational activities, continuous urbanization, and westernization, it is estimated that the prevalence of myopia will continue to increase [27] [28]. Myopic patients are increasingly undergoing cataract surgery; therefore, consultation on toric IOL with myopic target refraction is likely to increase. Based on the results of this study, we recommend toric IOL implantation in such patients to offer better quality of life after cataract surgery.
In conclusion, implantation of a toric IOL was superior to monofocal IOL in terms of UCVA in both near and distance for cataract patients with astigmatism even when target refraction power is determined to myopia. This may be meaningful for future clinical applications. To the best of our knowledge, this is the first study to quantify it.