The SI in this study at 31 months postoperatively was 1.08 ± 0.19, and there was no significant difference compared to that at 1 month postoperatively. The average SEs were − 0.60 ± 0.74 D at 1 month postoperatively and − 0.60 ± 0.86 D at the last follow-up, indicating the long-term safety and stability. A previous study has shown similar results of monovision FS-LASIK in the corresponding population at 1-year follow-up. 11 In this study, the SEs in 76.67% and 93.33% of the eyes were within ± 0.50 D and ± 1 D, respectively, compared with the target SE. Previous studies showed a corresponding figure of 99% within ± 0.50 D at 1-year follow-up.11 The minor difference may be explained by the higher preoperative SE in our result (–6.97 D vs. − 5.21 D) and the corresponding myopia progression. Another possible explanation may be an increase in corneal astigmatism and lens thickness. Therefore, in patients aged over 40 years with high myopia or ultrahigh myopia undergoing FS-LASIK, a minor decrease in UDVA, especially in nD-eyes, may occur during long-term follow-up. It is necessary to fully inform patients before surgery and to routinely perform long-term follow-up. This study is the first to report the clinical safety of FS-LASIK in patients with myopia combined with presbyopia in 2.5-year follow-up.
Monovision surgery using FS-LASIK provided good VA at a near-to-far distance in the long-term follow-up. In 80% of the subjects, the binocular VA was 20/20, it was 20/25 in 100% of all subjects at all distances, and the VA (logMAR) in 100% of the subjects was <–0.02. A 1-year follow-up study showed that the average binocular distance VA was 0 ± 0.18 logMAR, and 64% of the subjects achieved or exceeded 20/20 at all distances. 12 Monovision surgery using ICL implantation also showed good binocular VA at 43-month follow-up: the binocular VAs (logMAR) at 0.4 m, 0.8 m, and 5 m was < 0.04 ± 0.13. In 68.75% of the subjects, the binocular VA was 20/20 or better at all distances. 13 The subjective satisfaction rates of visual experience at near and far distances in this study were both 80%, which was similar to the results of previous studies (81.25% and 87.50%, respectively)12,13. The results show that monovision surgery using FS-LASIK provides long-term stable and good binocular VA at a near-to-far distance for people with myopia and presbyopia.
The average age of the subjects in this study was 49 years. During the follow-up, the average ADD progression rate was 0.26 ± 0.15 D/y. Previous studies on patients with an average age of 50 years who underwent monovision surgery using FS-LASIK showed that the ADD increased from 1.80 ± 0.60 D to 2.18 ± 0.69 D, with an average progression of 0.38 ± 0.60 D, in 3-month follow-up. 14 A 43-month follow-up study of monovision surgery using ICL implantation in patients with an average age of 43 years showed that the ADD increased from 0.69 ± 0.40 D preoperatively to 1.31 ± 0.58 D at 43 months postoperatively, and the progression rate was 0.17 D/y. 13 The short-term change in ADD after FS-LASIK may be related to increased accommodation due to the change from vision with frame spectacles to the naked eye after surgery. This study showed a higher rate of presbyopia progression in long-term observation, which may be related to the older age and preoperative ADD of the included patients. Studies on the ADD progress rate with detailed age groups of patients with myopia with presbyopia will help to answer this question.
At the last follow-up, there was no significant difference in high-order aberrations between the D-eyes and nD-eyes. The mean postoperative SA was 0.11 µm. A previous study suggested an increase of 0.10 µm in SA at 3 months after FS-LASIK in patients with high myopia. 15 In this study, the SA was 0.11 µm, which may be explained by the different age-related corneal changes in response to FS-LASIK.
This study is the first to use the novel qCSF test to evaluate patients with myopia and presbyopia after monovision surgery using FS-LASIK. The results showed significant differences in CS (1.5–12.0 cpd), AULCSF, and CSF acuity between D-eyes and nD-eyes at the last follow-up. In comparison of CS at different spatial frequencies, 1.5 ~ 3.0, 3.0 ~ 4.5, and > 4.5 log units indicate mild, moderate, and severe CS changes, respectively. 16 In this study, there was a minor but significant difference in CS between the D-eyes and nD-eyes, suggesting that monovision surgery using FS-LASIK has a slight effect on the CS of nD-eyes. It is worth noting that the qCSF tests in this study were performed without distance VA correction. Previous studies on CS in Chinese adults with ametropia showed that qCSF readings are not correlated with refraction error but have a certain negative correlation with age.17 Therefore, this study attempts to evaluate CS in a daily life situation after FS-LASIK for more clinical practice value by not correcting the distance refraction error. The results showed that the nD-eyes could see the displayed numbers in low to moderate spatial frequency; however, there was a certain difference between the D-eyes and nD-eyes, indicating a lower CS of nD-eyes at low to moderate spatial frequency in daily life.
This study has the following limitations. First, this was a single-center study with a relatively small sample size. Multicenter studies with larger subjects are required to provide high-quality clinical evidence; second, due to the upgrading of equipment, the comparison of aberration and qCSF was conducted between the D-eyes and nD-eyes at the last follow-up, and the preoperative results were not included.
In conclusion, FS-LASIK is safe and practical for the correction of myopes with presbyopia, with long-term efficacy at near and far distances. Compared with D-eyes, the CS in nD-eyes may be impaired at low and moderate spatial frequencies.