In the present study, we assessed the outcome afforded by the V4c ICL according to lighting conditions, and found that it improved optical quality under both bright and dark conditions, while achieving greater improvement in the dark in the S group. In a recent study, Miao et al measured optical quality at 1 and 3 months after V4c ICL implantation, using the same instrument as in our study, and found no significant difference between the two time points . However, they did not measure the optical parameters preoperatively, nor did they consider the effect of lighting. To the best of our knowledge, this is the first study to objectively assess optical quality in detail under different light conditions after this novel surgical procedure.
During the entire 3-month follow-up, optical quality showed significant improvement under both bright and dark conditions. There could be three explanations for these results. First, the ICL afforded better retinal magnification than spectacles . Kamiya et al previously reported 1.00 and 0.88-fold improvements in retinal magnification after phakic IOL implantation and use of spectacles, respectively, for correction of high myopia; furthermore, a shrinking image could reduce visual quality . Second, ICL implantation induces significantly higher contrast sensitivity and less spherical aberration [19-21], which could result in better optical quality. Third, single-vision spectacle lenses used to correct myopia could increase hyperopic defocus in the peripheral retina, which may also affect visual quality [22-24].
In the present study, the V4c ICL yielded similar outcomes under both bright and dark conditions, with the exception that the OSI was reduced more under dark than bright conditions; thus, the V4c ICL had stable and excellent performance under different lighting conditions, albeit with a better ability to reduce the extent of scattering in the dark. Due to a lack of relevant previous literature, we can only speculate regarding this increased performance. One possibility is that there is an impact of ring-shaped dysphotopsia, as reported by Eppig and co-workers  and Eom and co-workers  in 2015 and 2017, respectively, according to a special visual sequela induced by V4c implantation. Both studies suggested that dysphotopsia may be influenced by illumination intensity, and Eom and co-workers reported a subjective feeling in patients that dysphotopsia was more obvious under bright conditions, which may have resulted in less improvement . Furthermore, V4c implantation partially resolves the peripheral hyperopic defocus problem, whereby rod cells receive more signal stimulus, and this could also lead to greater improvement in optical quality. It could also be a sign of deeper problems and should be investigated accordingly.
As expected, we found that patients with super-high myopia experienced greater improvement in visual quality than the high myopia patients, which could be explained by the lower retinal magnification and more serious hyperopic defocus associated with thicker spectacles . Although the differences in MTF frequency, Strehl ratio, and PVAs between the two groups under bright conditions were not significant by 3 months postoperatively, there was a trend toward a better outcome in group S than in group H. The precise reasons of for convergence between the two groups at 3 months need to be studied further. In addition, because many previous studies have shown that ICL yields better outcomes in cases with large refractive errors , we propose that ICL implantation should be the first choice for super-high myopia patients.
A limitation in this study was that we did not collect long-term follow-up data. Also, because the OQAS only measure monocular optical quality at one time, further binocular visual function evaluations are needed. Although the OQAS objectively evaluates optical quality, it cannot measure retina function, yet high myopia patients often show retinal changes. During our follow-up, we also received some complaints from patients about their scotopia, so additional questionnaire measures are necessary to capture this. Overall, it remains unclear how these differences affect patients’ experience and daily activities.