Corneal refractive surgery for presbyopia is on the rise. In the near future, more patients who have undergone presbyopia correction will be presenting for cataract surgery. We already know that these patients are demanding regarding refractive outcomes. For those who were truly satisfied with their outcomes after presbyopia surgery— those who did not use spectacle correction for daily activities before cataract formation—the only acceptable refractive result in pseudophakia will be perfect refraction and spectacle independence. A possible decrease of pseudoaccommodation in the pseudophakic state should be explained to these patients before surgery.
If presbyopia correction was not completely satisfying, these patients will expect cataract surgery to solve whatever visual problems remained after presbyopia-correcting surgery. For these reasons, we should increase our efforts in the quest for perfection and be cautious in providing informed consent regarding the visual and refractive results of cataract surgery.
APPROACHING SURGERY
Presby-LASIK has been performed in recent years with varying ablation profiles and centration techniques. Because we may not know the type of profile used in a given patient, problems can arise when these patients present for cataract surgery. The original corneal topographies are of little help, especially if presby- LASIK also corrected for basic refractive defects. For this reason, preoperative assessments of visual function and of corneal anatomy is crucial.
Corneal topography should be obtained with a Scheimpflug camera or a scanning slit machine (Figure 1), as Placido-based machines may not be accurate enough to detect subtle and localized changes in corneal curvature. Ocular aberrometry should follow, as it can help to identify lower- and higher-order aberrations at various pupil diameters. Using this technology, we may observe some changes in the magnitude of refractive cylinder and axis with different aperture diameters.
Pupil diameter under different lighting conditions must also be considered, as we can expect slight enlargement of small pupils and slight narrowing of wide pupils following cataract surgery.
ASSESSING REFRACTION AND CURVATURE
If cataract density allows it, a large part of the preoperative investigation should be dedicated to refraction. Eyes that have previously undergone presby-LASIK have an extended range of focus, a multifocal corneal surface over the pupil area, and presence of various degrees of regular and irregular astigmatism.
The issue of astigmatism is especially important. Corneal astigmatism can improve near vision function, and actually it may be the reason for the extended range of focus in the presby-LASIK (ie, multifocal) eye. However, I would caution that astigmatism recorded by autorefractors may differ from that recorded clinically, because coma can mimic astigmatism, as it does in eyes with keratoconus. If possible, a defocus curve should be obtained, starting from full optical correction, to better understand the actual refractive condition from the perspective of IOL power calculation.
PRESBY-LASIK, IOL POWER CALCULATION, and iol selection
IOL power calculation appears to be the core problem with cataract surgery in this population. Ideally, patients who were satisfied with their visual outcomes after presby-LASIK should be implanted with an IOL power that reproduces their refractive condition prior to cataract surgery. The IOL should also correct for any residual ametropia present after presby-LASIK.
The difficulty with IOL power calculation lies in keratometry (K) reading selection. In these eyes, manual and automated keratometers are probably not reliable, including those embedded into the IOLMaster (Carl Zeiss Meditec) and the Lenstar (Haag-Streit). Corneal topographers are often inaccurate near the pupil center, and even in that area the corneal curvature may vary by 2.00 to 3.00 D. My suggestion is to consider the corneal curvature nearest to the visual axis. Additionally, I always warn patients about possible postoperative deviations from the intended refraction.
As for IOL selection, the choice is easier. In my experience, a neutral-aspheric monofocal IOL that will leave the corneal aberrations unchanged is best. As presby-LASIK is based on corneal aberrations of lower and higher orders, the best option is to leave these aberrations unchanged when implanting the IOL. I would not consider spherical, hyperaspheric, toric, or multifocal IOLs here, as outcomes with these lenses in these eyes cannot be accurately anticipated. Therefore, my choice would be the Akreos MI60 IOL (Bausch + Lomb), a hydrophilic acrylic lens with neutral-aspheric optics that can be implanted through a sub–2-mm incision.
SURGICAL TIPS
Microincision cataract surgery (MICS) is mandatory in eyes with such complex corneal optics, as a minimally invasive technique has less chance of changing the eye’s corneal shape and aberrations. Additionally, eyes after presby- LASIK are probably good candidates for laser cataract surgery, due to the resulting regularity and centration of the capsulotomy. In the postoperative period, regular capsular bag contraction, good IOL centration, and absence of IOL optic tilt can be expected after laser surgery.
Refraction should be checked frequently after surgery, starting with the first postoperative week, and the final outcome should be evaluated only after capsular bag closure. In cases with large refractive deviation from the intended value, the IOL should be removed and exchanged. MICS lenses can be removed through a sub–3-mm incision, and surgery is relatively easy immediately after capsular bag sealing.
CONCLUSION
Patient counseling for cataract surgery after presby- LASIK can be derived from these considerations:
- The results of presby-LASIK may not be maintained after cataract surgery;
- IOL power calculation is difficult;
- Corneal optics will not improve with cataract surgery;
- Monofocal neutral-aspheric IOLs are mandatory; and
- IOL exchange may be required for the optimal result.
Despite proper patient counseling, I believe cataract surgery after presby-LASIK will reveal unexpected refractive problems and difficulties that cannot be anticipated at this moment. Will photopsia be an issue? What about glare? Will IOL material play a role? Many questions remain—still a further quest!
Roberto Bellucci, MD, is Chief of the Ophthalmic Unit, Hospital and University of Verona, Italy. Dr. Bellucci states that he is a consultant to Bausch + Lomb. He may be reached at e-mail: robbell@tin.it.
