Article

Don’t fear the post-refractive cornea

When treating post-refractive cataract patients, manage expectations and stay current on techniques.

As post-refractive patients enter the cataract surgery population, they often desire visual freedom and embrace technology at a higher rate than most cataract surgery patients. Some surgeons can be intimidated by these patients’ high expectations and the increased complexity presented by post-refractive eyes.

Rather than shying away from difficult conversations or avoiding new technologies, surgeons should engage with these patients to customize their surgical goals. The keys to managing post-refractive cataract patients are expectation management and awareness of the best techniques and technologies.

ANATOMICAL SUCCESS ISN’T THE ONLY GOAL

Most of us have our basic cataract surgery speech rather standardized: risks, benefits, alternatives and potential complications. Then, we customize the message for that patient. For example, Flomax gives pupil risk. High myopes have higher retinal detachment risk. Pseudoexfoliation risks pupillary or zonular issues.

We customize the message because it’s wise to invest in our patients’ expectations. It helps patients make wiser decisions, and it also builds trust in the patient-doctor relationship. As the saying goes, if we discuss a potential issue preoperatively and it comes to fruition, we are geniuses; if we only discuss it postop, patients assume we caused it.

The above examples are classic internal, structural issues, and cataract surgery has traditionally been a structural surgery. It’s not anymore, however. Cataract surgery is a refractive surgery; this fact doesn’t stem from who the surgeon is or the available astigmatism or presbyopia-correcting options, but rather what our patients desire and expect. And our patients desire and expect great vision.

When patient expectations are high — and they are — we have a whole new set of discussion variables when patients prepare for surgery. Epithelial basement membrane dystrophy, which I peel and allow to heal before repeating measurements, can be a subtle outcome killer. Dry eye can wreck preop measurement quality and affect visual stability postoperatively. And then there’s prior refractive surgery.

POST-REFRACTIVE EXPECTATIONS ARE HIGH, ACCURACY LOWER …

Each of the above corneal findings can limit the accuracy of the surgery or require other management alongside the cataract surgery. Prior refractive surgery, however, not only decreases the postoperative accuracy, but it also is associated with increased expectations.

Most of these patients experienced many years of near visual perfection after their LASIK or PRK. We might be tempted to think, “Oh, it’s just like a prior low hyperope who saw everything clearly when younger.” But there’s a big difference: Surgery gave the post-refractive patients their best vision ever. And they want the same thing again.

Accurately predicting lens powers when targeting post-hyperopic LASIK and PRK and post-RK eyes remains very difficult, but post-myopic LASIK and PRK cataract results have improved greatly in the last several years with the addition of the Barrett True-K formula. Using this formula, about two-thirds of eyes can achieve a result within 0.5 D of the target, according to research from Abulafia A, et al, published in March 2016 in the Journal of Cataract and Refractive Surgery. Two-thirds is still short of the 85% to 90% virgin eyes can achieve with quality measurements and the Barrett Universal II or Hill-RBF formulas, but it still represents improvement over other post-LASIK formulas, according to the research from Abulafia A, et al.

One exciting new option in refractive cataract surgery is the Light Adjustable Lens from RxSight. A three-piece IOL, it is adjustable in power of up to 2D sphere and 2D cylinder post operatively in the United States, with a CE mark of 3D of cylinder in Europe. Our practice has begun commercial cases and are also in a post-LASIK and post-PRK clinical trial.

… BUT MANY CAN ADAPT WITH ENTHUSIASM

Despite the decreased refractive accuracy with most currently available IOL technologies, there are some positive characteristics of most post-refractive patients.

First, they tend to embrace surgical technology. Second, they have generally experienced neuroadaptation after their prior surgery, so the idea of introducing new optics within their visual systems is not new. Many of these patients, particularly those who can be candidates for presbyopia correcting IOLs, are happier after cataract surgery than the virgin cornea patients whose optics “should” be better.

The view through a LASIK flap of an extended-depth-of-focus lens in a patient’s eye.

ALL REFRACTIVE SURGERY IS NOT THE SAME

Before directing the patient discussion and presenting options, we must know the patient’s history. In medical school, we all learned the need to be specific and accurate. For example, merely describing a patient as hypothyroid was asking for trouble: is it primary, secondary or tertiary hypothyroidism? A patient labeled as “hypothyroid” could even have had the complete opposite condition if taking supplementary levothyroxine after thyroid ablation or surgery for hyperthyroidism.

While we don’t need complex hormone feedback schematics to understand refractive surgery as it pertains to cataract options, knowing the specific surgical history is important. Unfortunately, we cannot always get records from prior decades when these patients had refractive surgery. Patients might remember if it was PRK or LASIK, a distinction that doesn’t make a significant difference in my cataract planning process, but they often don’t recall their initial type of refractive error, which is more important to know.

When it’s obvious what type of correction they’ve had, it’s easy to select the appropriate Barrett True-K formula, which has the same name but performs different calculations whether the myopic, hyperopic or RK version of the formula is selected. RK scars are easy to spot on exam, and a patient with a 26-mm eye and flat cornea can generally be assumed to have had a myopic ablation in the past. In uncertain cases in which topography isn’t clear, using the Gullstrand ratio of anterior corneal curvature to posterior corneal curvature can be helpful, though measuring the posterior cornea is more difficult. A ratio of less than 83% is evidence of myopic correction through anterior flattening, and a ratio of above 83% is indicative of hyperopic correction. If the ratio is nearly 83%, it is likely that the patient may have just had astigmatic correction with minimal spherical equivalent change, and a traditional IOL formula may be very effective.

The optical differences between older, conventional LASIK and newer wavefront-optimized, wavefront-guided or topography-guided LASIK do not typically affect my cataract recommendations, unless I see significant irregularity or decentration on topography.

DISCUSS ACCURACY ISSUES WITH PATIENTS

The Haag-Streit Lenstar 900 and Zeiss IOLMaster 700 integrate the Barrett True-K formula for convenience — remember to ensure that you or your technician selects the appropriate type of prior surgery. I use the ASCRS website with more formulas so I can show patients the range of lens powers. Particularly for the post-hyperopic and post-RK patients with a large range, showing them the large range of IOL powers can help emphasize the reduced accuracy.

In fact, I never describe IOL power calculation; I describe IOL power estimation. The whole point of the previous refractive surgery was to change the ratio of corneal curvature to length of the eye, I tell patients, so it’s not surprising that we need unique lens power estimation formulas.

Even with intraoperative aberrometry and newer lens power estimation formulas, the projected IOL power should still make sense. If not, it should be double and triple checked. For example, if a patient was happy after previous LASIK or PRK, they were probably close to emmetropic. Since the typical human crystalline lens is about 20 D, any projected IOL power significantly higher or lower than 20 D in a patient who was happy after LASIK or PRK needs to be interpreted in light of the axial length and anterior chamber depth of the eye to see if it makes sense.

ON ADDRESSING ASTIGMATISM

Hitting the appropriate refractive target always includes minimizing astigmatism, and this can be a tricky situation. How do we separate the contributions of the posterior cornea and lens in light of an altered anterior curvature? If the refraction matches the topography, then great. If not, the Barrett True-K toric can be helpful.

I also recommend asking patients the quality of their vision immediately after their refractive surgery. If patients indicate the vision was never really great, then I’m a little more likely to think their post-refractive corneal shape did not fully correct their refractive astigmatism. Some surgeons trust intraoperative aberrometry more for the spherical than cylindrical measurements, though it may have some helpfulness. Post-operative IOL power adjustability may provide an advantage.

... AND PRESBYOPIA

Because post-refractive patients often pursue innovation and surgical means of improving quality of life through vision, many of these patients are the most interested in presbyopia correction. The old thinking that presbyopia-correcting IOLs are only suitable for virgin eyes has shifted as lens technology has improved.

For patients with a good ocular surface and a well centered ablation profile of prior LASIK or PRK, a J&J Vision Tecnis Symfony or Alcon ReStor ActiveFocus IOL is a very reasonable option. In particular, Kevin Waltz, OD, MD, et al., presented very favorable data using Symfony in post-myopic eyes at the 2017 AAO meeting. The data set for the talk, “Extended Depth of Focus IOL in Post-Myopic Refractive Surgery Patients,” even included RK eyes.

Despite slightly less advantageous optical corneas for these lenses, the patients’ ability to neuroadapt to the lenses and appreciate the depth of vision often leads to success.

POSTOPERATIVE CONCERNS

Post-refractive patients have a higher chance of healing with unexpected refractive error following cataract surgery. In addition to careful counseling and modern methods of IOL selection, surgeons need to be ready to complete the process with any necessary enhancement. In my experience, since some virgin eyes still heal with more than half a diopter of error from target, enhancement capabilities are an important part of a modern cataract practice to begin with.

For post-refractive patients, enhancements can be a little trickier. If the prospect of lifting an old LASIK flap is intimidating for a surgeon, then a PRK touch-up is a possibility for most. Only rarely will an in-the-bag IOL exchange be necessary for high degrees of refractive surprise, but these in-the-bag exchanges are rarely difficult when performed in the first three months. For surgeons not comfortable with corneal refractive surgery, it is common to make an agreement with a refractive surgeon to collaborate on cases needing post-operative enhancement.

CONCLUSION

As post-refractive patients begin to have cataract surgery, we should not be intimidated by the increased complexity of their cases. Instead, we can create a more rewarding experience for both these patients and ourselves by listening well and identifying the large number of these patients who may benefit from the same kind of personalized plan we would offer anyone else. OM

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