The lens design prevents rigorous assessment of residual refractive error, increasing the difficulty of its surgical correction after implantation of MIOLs. In addition, problems related to the measurement of refractive error by automated devices, or the estimation of high-order aberrations with Hartmann-Shack aberrometers, should be taken into account if wavefront-guided surgery is desired.

LASER EXCIMER IN THE CORRECTION OF POSTOPERATIVE AMETROPIA

There are some reasons why excimer laser use in pseudophakic patients may have different results, compared to phakic patients with primary laser surgery. The fact that they are typically older (2-3 decades) may be associated with lower predictability and efficacy of laser ablation, increased risk of tear film changes17,18, and corneal aberrations19. Corneal incisions performed during cataract surgery may interfere with the creation of the corneal flap, increasing the risk of complications and negatively conditioning surgical outcomes20,21. Laser excimer kerato-refractive surgery should only be performed 3-6 months after IOL implantation surgery, due to the risk of complications associated with the integrity of the initial incision, subclinical corneal edema, refractive stability, and the stability of the IOL itself22. Despite the possible risks mentioned above, the use of this method in the correction of postoperative ametropia presents excellent results, with excellent safety and efficacy profiles10,22,23. For these reasons it is the most frequently used method, leaving the other surgical techniques, such as replacing the IOL or implanting a piggyback IOL, for situations of large ametropia where excimer laser techniques are contraindicated13,24.

Specifically regarding the use of kerato-refractive excimer laser in the correction of postoperative ametropia after implantation of MIOLs, there are still only a few published studies, most of them also with relatively small samples.

CRITERIA FOR EXCIMER LASER ENHANCEMENT SURGERY

There are currently no fully established and unanimously accepted criteria for performing excimer laser after the implementation of MIOLs.

Despite this, Muftuoglu et al25 established the following as indications:

• Better uncorrected visual acuity for far ≤ 20/25;
• Manifest spherical equivalent ± 0.75D;
• Patient dissatisfaction with initial visual result due to residual refractive error.

RESULTS

Data published in the literature show excellent refractive and visual results after this procedure: virtually all patients achieve a refraction of ± 1.00D, with over 90% with ± 0.50D; the best uncorrected distance visual acuity varies between 0.0-0.1 logMAR according to studies13,16,24,26-28.

INFLUENCE OF THE TYPE OF PRE-LASER AMETROPIA

The possible influence of the type of pre-laser ametropia on the obtained results, is still somewhat contradictory. While Muftuoglu et al24 and Schallhorn et al13 did not show statistically significant differences in the best uncorrected distance visual acuity, or post-laser spherical equivalent, between myopic or hyperopic patients, Piñero et al16 concluded that hyperopic eyes had less predictable results, attributing this to the difficulty in estimating the refractive error in patients with MIOLs.

LASIK vs PRK

Apart from the known particularities and differences between these two excimer laser techniques, in the particular case of postoperative ametropia correction after implantation of MIOLs, the results obtained are similar between them. There were no statistically significant differences regarding postoperative refraction and better uncorrected distance visual acuity13. Moreover, Schallhorn et al13 did not show any difference in postoperative dry eye symptoms between the two techniques. Nonetheless, LASIK is the preferred technique for conditioning faster and relatively painless recovery. The authors prefer PRK because, in their experience, it is a technique with less impact on the ocular surface and very well tolerated by this group of older patients, minimizing surgical risks. In his view, the reasons for this increased tolerance are due to intrinsic corneal changes (senile hypoesthesia) and the fact that most treatments are unilateral.

REFRACTIVE vs. DIFFRACTIVE MIOLs

Data on the comparison of results in patients with refractive or diffractive multifocal lenses are particularly scarce. Apparently, there are no differences regardless of the type of lens used16.

TORIC MIOLs

Schallhorn et al13 performed excimer laser after the implantation of 94 toric MIOLs (out of a total of 782 eyes) and did not find any significant difference in the post-laser cylindrical refraction among patients.

WAVEFRONT GUIDED EXCIMER LASER

The use of wavefront may also be advantageous in these circumstances, as it will theoretically induce fewer high-order aberrations, with greater refractive predictability, and improved contrast sensitivity29. However, the available studies show a greater inability of the wavefront sensor to perform its measurements on refractive MIOLs, with more high order aberrations, large differences between wavefront and manifest refraction, and loss of lines at the best uncorrected visual acuity, both for near and far28,30. Even with diffractive MIOLs, doubts arise as lens configuration can distort measurements31. Moreover, Jendritza et al27 showed that the use of wavefront did not bring any advantage over high order aberrations in the correction of residual refractive errors after implantation of MIOLs.

CONCLUSIONS

There is no doubt that the use of excimer laser in the correction of residual refractive errors after implantation of MIOLs presents excellent results, both refractive and visual. However, more studies, with more significant samples, are needed to answer the various doubts that remain on this topic.

In order to increase the satisfaction rate of patients with multifocal lenses, a rigorous preoperative assessment and selection of candidates is critical:

1. Patient education – explain risks and benefits of implanting this type of lens in order to fit the expectations created.
2. Identification, prevention and treatment of eye surface diseases.
3. Determination of final refractive target – should be ± 0.5D of the MIOL refractive target and minimize residual astigmatism.
4. Identification of ocular comorbidities (OCT, corneal topography) that contraindicate the implantation of MIOLs.

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