Successful cataract and refractive surgery procedures share three key elements: (1) performing complicationfree surgery, (2) achieving the desired refractive target, and (3) properly managing patient expectations. It is difficult to adjust patient expectations postoperatively when a complication occurred during surgery or when the refractive outcome was off-target, thus requiring a secondary enhancement procedure. Nowadays, with the availability of advanced treatment planning software for laser-based treatments and IOL power computing devices such as the IOLMaster (Carl Zeiss Meditec) and the Lenstar (Haag-Streit), there are fewer acceptable excuses for botching an accurate refractive outcome.
With that said, refractive errors still do occur, and it is important to have a strategy in place for managing these cases postoperatively. In the previous pages, other authors contributing to this Cover Focus share their strategies for performing refractive enhancements after PRK, LASIK, and cataract surgery. Below I describe how I avoid their need after presbyopia-correcting procedures that I currently perform. I also provide surgical pearls for each strategy.
ACHIEVING THE CORRECT REFRACTIVE OUTCOME
Each presbyopia-correcting treatment has its own sweet spot in terms of refractive outcomes. That is, the range of vision best achieved with one treatment is generally not the same as that achieved with another. Manufacturers conduct studies to determine the optimal performance of their products and use these results to establish recommended target refractions. If the surgeon does not achieve the target, then the product should not be expected to work as designed.
Different presbyopia-correcting procedures can also require different target refractions, which are further discussed below. Surgeons cannot rely on simple subtraction, where the preoperative refraction minus the surgical treatment (ie, laser input or lens power) equals the postoperative refractive outcome. Today, it is recognized that many confounding factors come into play and can be the source of off-target refractive outcomes, including wound healing, surgically induced astigmatism due to wound size and surgical technique, regression, capsular bag contraction, and effective lens position. Despite these challenges and uncertainties, patients do not expect anything less than the best possible outcome.
I use a scoresheet (Excel spreadsheet) to evaluate my equipment and my surgical technique; this serves as an objective metric to strengthen or adjust my nomograms for various procedures. With each new product, piece of equipment, and surgical technique that is introduced into my practice, my personal refractive and visual outcomes are monitored by tabulating them in this spreadsheet. After the first five eyes, we observe results for 2 to 4 weeks and then adjust the targeting if needed. Then another 10 eyes are operated, observed, and the targeting adjusted again if needed. It is also at this point that I start taking note of visual performance for varying refractive outcomes.
CORNEA-BASED PRESBYOPIA SOLUTIONS
My practice offers Supracor LASIK, Intracor, and Kamra corneal inlay (AcuFocus, Inc.) implantation. The preoperative manifest spherical refraction of the patient plays a key role in selecting the type of treatment to be performed (Figure 1), assuming both eyes have similar refractions and the astigmatism is not significant (ie, 1.00 D or less).
If the spherical error is mildly hyperopic, between 0.50 and 1.00 D, we perform Intracor with the 520F femtosecond laser (Technolas Perfect Vision GmbH). If the spherical error is closer to plano, between 0.50 and -0.75 D, a Kamra corneal inlay is implanted in the nondominant eye. If the spherical error is mildly myopic, between -0.75 and -1.50 D, monovision LASIK is performed in the dominant eye, targeting plano, and the nondominant eye is left untreated. For patients more hyperopic than 1.00 D or more myopic than -1.50 D, we recommend Supracor LASIK using the 217P excimer laser (Technolas Perfect Vision GmbH).
Intracor. This femtosecond laser-based treatment for presbyopia creates five concentric rings around the visual axis to weaken the center of the cornea, thus creating a central area with a near addition. Because this treatment induces a mild myopic shift, the ideal candidate has mild hyperopia (ie, up to 1.00 D). In these cases, our target manifest refraction spherical equivalent (MRSE) is plano, and the estimated visual outcome in the treated eye is as follows: distance UCVA of 20/20, intermediate UCVA of 20/25, and near UCVA of J2. Treatment is initially performed in the nondominant eye; if the patient is not satisfied with the achieved binocular near UCVA, then we proceed with Intracor treatment in the second eye.
In these cases, we have found that centering the treatment between the pupil center and the Purkinje reflex produces the best outcomes. Additionally, aggressive massaging of the eye for 30 to 60 seconds immediately after the femtosecond laser application—while the bubbles are still visible—will increase intraocular pressure and help to separate the collagen fibers within the rings.
Kamra corneal inlay. As part of the global clinical trial of the Kamra, our patient recruitment is based on a preoperative MRSE of 0.50 to -0.75 D. We implant the inlay underneath a thick flap or pocket created at least 200 μm below the corneal surface. At commercial sites, patients with an MRSE beyond the manufacturer’s suggestion may receive the inlay in the nondominant eye after simultaneous LASIK with a refractive target of -0.75 D. Then the dominant eye undergoes LASIK with a refractive target of plano, thus achieving modified monovision. The likely visual outcome in the implanted eye is distance UCVA of 20/20, intermediate UCVA of 20/25, and near UCVA of J2.
The most crucial pearl with regard to implanting the inlay is meticulous centration. Check the inlay at the slit lamp after implantation; if it is off-center, lift the flap and recenter the inlay.
Monovision LASIK. Some presbyopic patients present preoperatively with an MRSE of -0.75 to -1.50 D, which is usually acceptable for near vision but not distance. We suggest treating the dominant eye with LASIK to target a plano MRSE and leaving the nondominant eye untreated. The likely visual outcome of the treated eye is distance UCVA of 20/20, intermediate UCVA of 20/40, and near UCVA of J8. Because of the slight myopia in the untreated eye, however, binocular outcomes can be as follows: distance UCVA of 20/25, intermediate UCVA of 20/25, and near UCVA of J2.
Our pearl in these cases is to put the patient on a monovision contact lens trial first to determine if he or she would be satisfied with the overall vision as well as with the visual imbalance.
Supracor LASIK. This new presbyopic LASIK algorithm creates a near vision add centrally, an aberration-neutral transition zone, and a distance correction zone peripherally. We currently use Supracor LASIK in hyperopic and myopic presbyopes, post-LASIK presbyopes, and pseudophakic presbyopes to treat refractive error and presbyopia simultaneously. Our target MRSE is -0.50 D, and the likely visual outcome is distance UCVA of 20/25, intermediate UCVA of 20/20, and near UCVA of J2.
Here our pearls include targeting a mildly myopic outcome, centering the treatment on the pupil, and first treating the nondominant eye to determine if near vision is adequate. If near vision is acceptable, the dominant eye can then be treated with standard LASIK; if near vision is not acceptable, however, we perform Supracor in the dominant eye.
LENS-BASED PRESBYOPIA SOLUTIONS
If the surgeon and patient agree to address presbyopia by replacing the crystalline lens, the choice of IOL is crucial. The options we offer these patients are the Crystalens AO (Bausch + Lomb), the AcrySof IQ Restor +3.0 D (Alcon Laboratories, Inc.), the AT LISA (Carl Zeiss Meditec), and the Tecnis Multifocal (Abbott Medical Optics, Inc.). As our experience grows with a specific IOL, we eventually develop a nomogram to customize the A-constant, increasing the predictability of refractive outcomes.
Crystalens AO. Using the SRK/T formula, our personalized A-constant for the Crystalens AO is 119.1; our MRSE target is -0.50 D. With this refractive outcome, the likely visual result is a distance UCVA of 20/25, intermediate UCVA of 20/20, and near UCVA of J3.
In these patients, we target a mildly myopic outcome to improve near vision. We find it helpful to end the case with a firm eyeball and with the Crystalens in a posteriorly vaulted position in the capsule. Timely Nd:YAG treatment (no earlier than 3 months after surgery) can be performed to release capsular tension.
AcrySof IQ Restor +3.0 D. With this IOL, our A-constant is 119.5 using the SRK/T formula and our MRSE target is 0.25 D. With this refractive outcome, the likely visual result is a distance UCVA of 20/25, intermediate UCVA of 20/40, and near UCVA of J1.
Our pearl with this lens is to target plano or a mildly hyperopic outcome and make a 5.0-mm capsulorrhexis so the rhexis edge overlaps the optic.
AT LISA. Again using the SRK/T formula, our A-constant is 117.9 and the target MRSE is plano. With this refractive outcome, the likely visual result is a distance UCVA of 20/25, intermediate UCVA of 20/40, and near UCVA of J1.
Here our pearls are to target plano, to make a 5.5-mm capsulorrhexis, and to insert the IOL directly into the capsular bag.
Tecnis Multifocal. Our A-constant is 119.3 for this lens using the SRK/T formula, and our MRSE target is 0.25 D. With this MRSE outcome, the likely visual result is a distance UCVA of 20/20, intermediate UCVA of 20/50, and near UCVA of J1 at close range.
Our pearl in these cases is to target plano or a mildly hyperopic outcome.
Presbyopia-correcting treatments provide an additional range of vision compared with monofocal strategies; however, there are trade-offs. Multifocal options, whether in the cornea or lens, provide patients with the most reliable reading ability, but the sacrifices of contrast vision, glare, and halos must be discussed extensively with the patient before surgery. Monofocal options such as accommodating lenses, monovision LASIK, and corneal inlays provide good quality of vision and improved range of vision, although they can fall short of patient expectations with regard to the delivery of near vision.
Today we can offer our presbyopic patients various corneal and lens-based options for treatment, and more options are on the horizon. Two crucial steps we should not overlook are, first, to talk to the patient as part of the preoperative counseling process, thus discovering their needs and wants; and, second, to recommend the presbyopic solution that most closely fits these expectations. Achieving good refractive outcomes is a significant key to success in presbyopia treatment and ranks as a close second to managing patient expectations. The strategy outlined above allows our practice to achieve good refractive outcomes, usually without need for a secondary enhancement procedure.
Robert Edward T. Ang, MD, is Senior Consultant at the Asian Eye Institute, Philippines. Dr. Ang states that he has financial interest in AcuFocus, Inc.; Allergan, Inc.; Bausch + Lomb; and Technolas Perfect Vision. He may be reached at e-mail: RTAng@asianeyeinstitute.com.