Previous studies of eyes after corneal refractive laser surgery have focused primarily on monofocal IOLs [22,26−28] and bifocal IOLs [8−11]. In our study, we present this retrospective case series of trifocal IOL (AT LISA tri839MP) implantation in patients who underwent a previous corneal refractive laser surgery for myopia. The AT LISA tri839MP used in our study is a monolithic diffractive trifocal intraocular lens which is made of collapsible hydrophilic acrylate (25%) with a hydrophobic surface. Its optical zone has a diameter of 6.0 mm, a total diameter of 11.0 mm, and a four-turn intraocular lens with a zero angle. The intraocular lens combines a bifocal diffraction range from 4.34 to 6.00 mm, and a trifocal diffraction range (over 4.34 mm) on the front surface of the lens, which is achieved based on the asymmetrical light split, that is 30%, 20%, and 50% of the incoming light is split at near focus, intermediate focus, and distant focus respectively. It was developed to overcome the photic phenomena and the poor level of intermediate vision of traditional multifocal IOLs  and has already been demonstrated to have good outcomes of visual acuity at near, intermediate and far distance and high postoperative satisfaction . Patients were extensively counselled regarding the possible side effects of the treatment such as night glare, halos and decreased contrast sensitivity, even the possibility of deteriorated visual quality after a refractive corneal laser procedure. The final decision was made based on their wishes to restore vision and hence becoming independent of spectacles.
Intraocular lens implantation in eyes with previous corneal refractive laser surgery is full of challenges due to the difficulty in IOL power calculation [26,31,32]. To date, some reported IOL power calculation methods have been used for IOL implantation in eyes with previous corneal refractive laser surgery providing relatively accurate outcomes [27,33,34]. However, obvious hyperopia is often observed postoperatively [35,36]. For the lens power calculation in the present study, a multi-formula average method was applied which has been described and proven to be accurate in our previous study . Besides that, a modified aphakic refraction technique was used for the first operative eyes of patients who underwent bilateral implantation and the eyes with large difference (> 1.0 D) in the IOL calculated results from multi-formulas. Both these improvements were made based on the previous investigation and to pursuit accuracy in IOL power calculation.
In the refraction outcome, the mean postoperative SE was reduced to −0.56 D ± 0.49 while Chow’s study reported a −0.92 D ± 0.76 with a significant myopic shift . In addition, 48% of eyes were within ± 0.50 D of emmetropia and 91% within ± 1.0 D at postoperative 3 months in our study. All our cases were targeted for emmetropia, and the results were similar to Vrijman’s study with a lower percentage of eyes with ± 0.50 D. This is because most of the patients included were preoperatively high myopia with either less spherical equivalent (9 eyes, 43%, with < −6.00 D) or longer axial length (16 eyes, 76%, with > 26.00 mm). It is consistent with Vrijman’s finding that results were less predictable in eyes with myopia greater than 6.0 D .
The results of vision outcomes show a statically significant improvement after surgery. The mean postoperative CDVA and UDVA was 0.00 ± 0.05 and 0.10 ± 0.16 (logMAR), respectively. Both these two outcomes are significantly better than preoperative outcomes (Table 2, P < 0.001). The mean value of postoperative CDVA agrees with the result of Chang and colleagues (20/19, Snellen Vision) by converting into Snellen Vision . To accurately evaluate the visual outcomes of trifocal IOLs after previous corneal refractive surgery, the monocular UDVA, UIVA and UNVA were recorded at last follow up in our study, and the mean values (logMAR) were 0.02 ± 0.07, 0.10 ± 0.10 and 0.15 ± 0.11 respectively. However, among the few reports using multifocal IOL implantation, only Chang’s study recorded the same visual outcomes wherein the mean UIVA was 0.22 ± 0.15 (logMAR) as slightly higher than the value we observed.
As an important indicator for the vision over the entire range, defocus curve was also recorded in this study. In 2015, Jonker et. al. compared the defocus curves after trifocal IOL implantation with that after bifocal IOL implantation in cataract patients . In the comparison, the defocus curves of the trifocal IOL group showed a more continuous performance at the intermediate range under photopic and mesopic conditions. In the defocus curve of our study, the curve transited smoothly in the range between the peaks with defocus of 0.00 D and −3.00 D and reached the bottom as 0.14 logMAR at −2.50 D. Besides the defocus of 1.50 D (with a visual acuity of 0.34 logMAR), all visual acuities tested at other defocus diopters were better than 0.23 logMAR, maintaining a functional range of visual acuity. These results further demonstrate the good and wide range visual outcomes of trifocal IOL implantation after previous corneal refractive laser surgery for myopia.
In terms of the questionnaires survey, three patients (19%) reported halos and glare in postoperative 3 months, while no patient reported flare. Two of these three patients needed to use spectacles to read small print or a newspaper or book or to do some handwork. Looking back on the preoperative parameters of the two patients, both of their surgery eyes were with high myopia (preoperative spherical equivalents are −7.60 and −12.37 respectively). It seems that the capsule of high myopic patients is larger, and the stability of intraocular lenses is slightly worse compared to normal patients. The position and functional deviation of intraocular lens might lead to bad visual symptoms such as halos. In the other hand, the preoperative symptoms of halos or glare, and the status of the fellow untreated eye from patients who was performed unilateral surgery, might affect the postoperative visual outcomes and interfere with the clinical analysis of the efficiency of trifocal IOL implantation. Unfortunately, all the information had not been recorded preoperatively. Nevertheless, the total spectacles independence rate is 81% (thirteen patients), and those patients without halos or glare all have scores better than 3.67. Overall, the questionnaires survey showed good quality of life postoperatively in the current study.
The limitation of this study was the small sample size. Undoubtedly, a larger sample size would be more helpful to shed light onto the efficiency of trifocal IOL implantation after previous corneal refractive laser surgery for myopia. However, due to the uncertain side effects of mutifocal IOL implantation after previous corneal surgery, the number of patients who balanced the side effects by their demands for becoming independent of spectacles are rare.