Optical quality after posterior chamber Phakic implantation of an intraocular Lens with a central hole (V4c implantable Collamer Lens) under different lighting conditions

Consecutive patients requiring ICL implantation to correct high myopia were included in our study. The inclusion criteria were as follows: (1) high myopia with or without astigmatism (manifest SE, − 6.00 D or more); (2) stable refraction within 2 years; (3) a central corneal endothelial cell count > 2000 cells/mm2; (4) an absolute anterior chamber depth (ACD) > 2.8 mm (5) without other ocular or systemic diseases or anomalies (6) without previous or postoperative refractive surgery. Written informed consent was obtained from all participants. The Ethics Committee of Shanghai Ninth Peoples’ Hospital approved the work. All relevant tenets of the Declaration of Helsinki were followed throughout the study.

ICL V4c (Hole ICL™; STAAR Surgical) was used in all eyes included in this study. The ICL power calculation was performed by a modified vertex formula according to the manufacturer. All surgeries were operated following standard procedures [12]. Topical antibiotic agents were used for 3 days before surgery. After pupil dilating and topical anesthesia, ICL was inserted through a 3 mm clear corneal incision. Viscoelastics in the anterior chamber was completely washed out with balanced salt solution, then miotic agent was instilled. After surgery, steroidal (0.1% betamethasone, Rinderon; Shionogi, Osaka, Japan) and antibiotic (0.5% levofloxacin, Cravit; Santen, Osaka, Japan) medications were topically administered four times per day for 2 weeks, with the dose being reduced gradually.

The modulation transfer function (MTF) cutoff frequency, Strehl ratio, objective scattering index (OSI), and predicted visual acuities (PVAs, 100, 20, and 9%), under scotopic and photopic lighting conditions, were measured using the Optical Quality Analysis System™ (OQAS; Visiometrics, Terrassa, Spain) preoperatively and at 1 week, 1 month, and 3 months after surgery. First, scotopic measurements were performed in a dark room, with the addition of black covers on the instrument, to rule out any influence of light from the computer screen. Second, after turning on the room light source, and a light reflex was induced by shining a penlight (250 lm) into the contralateral eye, photopic measurements were performed. Pupil diameters under both lighting conditions were also measured, with the exception of the OSI (performed for a 4.0 mm pupil); all of the above measurements were performed under the corresponding pupil diameter. Since uncorrected refractive error can directly affect the optical outcome of the system, the manifest refractive errors were fully corrected during these measurements. The spherical error (up to − 8.00 D) was automatically corrected by the double-pass system, and the residual spherical error (over − 8.00 D) and cylindrical error were corrected with an external lens. All measurements were performed three times and the mean value was calculated and recorded. According to measure principle of OQAS, participates with lower OSI, higher MTF cutoff, higher Strehl ratio and higher PVAs tend to have better optical quality, and the determination of the fundamentals and definitions of the parameters have been described previously [13]. The logMAR (logarithm of the minimal angle of resolution) visual acuity and IOP were also measured at each time-point.

A total of 91 eyes (46 patients) were included. All surgeries were uneventful and no intraoperative complication was observed. Table 1 shows the preoperative and postoperative demographic data of the study population. All surgical procedures were uneventful, and no postoperative complication, such as cataract formation, pupillary block, pigment dispersion syndrome, or axis rotation, occurred during the 3-month observation period. No eye was lost during the 3-month follow-up.

Figure 1 shows the preoperative and postoperative optical quality. Under both light and dark conditions, all optical quality parameters achieved significant improvement at 3 months after implantation. To further analyze the optical quality data, we measured the changes (postoperative – preoperative, showed as ΔOSI, ΔMTF cutoff, ΔStrehl ratio and ΔPVAs) in each optical quality parameter for each timepoint. Table 2 compared the data obtained under bright and dark conditions. Overall, the V4c ICL performed similarly under both bright and dark conditions, except for the OSI, which showed a greater reduction under dark conditions (P = 0.02, 0.004, and 0.002 at 1 week, 1 month, and 3 months, respectively).

To determine how the V4c ICL affected the degree of myopia, we further divided the patients into super high myopia (group S, SE greater than − 10 D) and high myopia (group H, SE from − 6 D to − 10 D) groups, and measured changes in optical quality parameters in each group under both bright and dark conditions. There was no significant difference in population, sex, or age between the two groups. Except for the MTF cutoff frequency, Strehl ratio and PVAs at 3 months postoperatively under bright conditions, changes in all parameters in group S were significantly greater than those in group H at all time points, both under bright and dark conditions (Table 3 and Table 4).