Optimizing the Crystalens HD in Refractive Cataract Surgery

Learn how this surgeon maximizes visual outcomes preoperatively, intraoperatively and postoperatively.

By Uday Devgan, MD, FACS

The ideal intraocular lens implant would be similar to the young, natural crystalline lens. It would provide sharp vision over a wide range of distances with great image quality and no dysphotopsias. Currently, there are no man-made body parts, whether IOLs, heart valves or artificial hips, that perform as well as the natural body part of a young, healthy patient. Nevertheless, we're getting closer to achieving such perfection every year, at least when it comes to IOLs.

The Crystalens HD is the only FDA-approved accommodating IOL that provides a substantial improvement in range of vision compared with traditional monofocal IOLs. Simply inserting an accommodating IOL at the time of cataract surgery isn't enough. To maximize visual results for patients, we need to achieve refractive accuracy, optimize the ocular surface and retina, and exceed patient expectations.

In this article, I'll discuss how to achieve the most accurate postoperative refractive results and use limbal relaxing incisions to reduce astigmatism. I'll also review IOL positioning and how to optimize the ocular surface and retina to obtain the best visual outcomes.

Increasing Refractive Accuracy

The difference between cataract surgery and refractive cataract surgery is having the ability to accurately control the postoperative refractive result, eliminating defocus and astigmatism. Delivering a desired post-op refractive result, usually plano, is important for the optimum performance of the Crystalens HD and for patient satisfaction.

The single most important modification you can make in practice to achieve accurate IOL calculations is to move away from applanation A-scan and incorporate immersion A-scan or, if possible, the IOL Master (Carl Zeiss Meditec, Dublin, Calif.). The IOL Master is a noncontact optical coherence biometric device that more accurately measures axial lengths through light. Although it's significantly more accurate than ultrasound A-scan, it doesn't work as well in eyes with severe cataracts, particularly posterior subcapsular and dense cataracts, which limit the view into the eye.

In my practice, I use the IOL Master for nearly all cataract patients, reserving A-scan ultrasound only for those in whom optical measurements aren't feasible, or in situations where I want to doublecheck the IOL Master's calculations. With these techniques, the percentage of patients achieving an accurate post-op refractive status (goal +/− 0.50D) has increased, but this is only for the spherical equivalent. To maximize the patient's visual results, you need to address corneal astigmatism to ensure it's approximately 0.50D or less in most cases.

When calculating the power of an IOL, it's critical to use a newer-generation theoretical formula (ie, Hoffer Q, SRK-T, Holladay 1 and 2, Haigis) and not a regression formula.¹ It's also important to track your results and then personalize the A-constant you use for your lens calculations. For patients who've undergone previous corneal refractive surgery, lens calculations are far more difficult to establish and require more detailed methods.

Address Astigmatism

Every incision made in the cornea has the potential to affect astigmatism. What's the effect of your incision in routine cataract surgery? For most surgeons, cutting a 2.5-mm to 3.0-mm self-sealing, corneal incision creates a flattening effect of approximately 0.25D to 0.50D at the axis of the incision.² If the patient has a small amount of preexisting corneal astigmatism at the site of your planned incision, your incision may be enough to reduce or eliminate the astigmatism. However, a considerable percentage of patients will have significant corneal astigmatism that requires specific treatment.³

Learning to use LRIs at the time of cataract surgery is an effective way to reduce preexisting corneal astigmatism and achieve post-op emmetropia. Topography is the most effective way to properly understand the extent of the corneal astigmatism, and it will make your LRI planning more accurate. Excellent nomograms and instructions are available from some of the pioneers of LRIs, such as Louis D. "Skip" Nichamin, MD,³ Doug D. Koch, MD,⁴ and Jim P. Gills, MD,⁵ among others. Practicing the technique of LRIs as well as honing your own nomogram will help you deliver consistent results (Figure 1).

Figure 1. To optimize the performance of the Crystalens HD, the eye must be left in focus with the astigmatism reduced to 0.50D or less. In this case, a limbal relaxing incision in the peripheral cornea neutralized with-the-rule astigmatism.

For more significant degrees of astigmatism (0.75D or higher), it's recommended you use LRIs. A key consideration when making the LRI is the additive effect of your clear corneal incision. If the patient has 1.00D of corneal astigmatism at 90° and you make a clear corneal incision at 180°, which causes 0.50D of flattening, the patient may need 1.50D of LRIs at the 90° meridian.

It's not always possible to deliver post-op emmetropia due to variations in lens calculations, labeling and positioning, and patient healing. In these patients, it's helpful to employ methods to address post-op refractive surprises. For small, spherical residual refractive errors, implanting a piggyback IOL into the ciliary sulcus is an easy option for most cataract surgeons.

Corneal refractive surgery can be a very accurate way to correct residual refractive errors. PRK and LASIK are very accurate methods for those who have access to an excimer laser. Modern methods of surface ablation provide excellent results for patients, and they're well within the scope of care of any general ophthalmologist. Surgeons without an excimer laser should consider teaming up with a local refractive surgeon who has one.

Positioning the IOL

Intraoperatively, clinicians should position the IOL so it's vaulted posteriorly to achieve an accurate IOL calculation, which is largely determined by an effective lens position. If the Crystalens HD is properly positioned, the post-op result will be more accurate than if it were shifted anteriorly, which could induce a myopic shift. It's believed that the best visual results and accommodative amplitude are achieved with this lens positioning. Note that if the anterior chamber deflates at the end of the case, simply reinflating it with balanced salt solution isn't enough. You must reposition the IOL to ensure the haptic footplates are at the capsular bag equator and the optic is vaulted posteriorly. To keep the IOL in this position, your incisions must be completely watertight at the end of the surgery.

Now that you've achieved your post-op goal of plano with minimal corneal astigmatism, the patient will recover sharp vision as long as his ocular surface and retina are healthy.

Optimize the Ocular Surface and Retina

The first refracting surface of the eye is the tear film, so it's important to optimize the ocular surface. This entails treating preoperative conditions, such as blepharitis, dry eye, tear film dysfunction and corneal irregularities. Dry eye is particularly common in cataract patients, so make sure you screen them carefully during the preoperative examination.

Lissamine green or rose bengal staining are vital and may be more effective in detecting dry eye than simply examining the tear lake and tear film break-up time. If the patient has any degree of dry eye syndrome, it's important to tell him about this before surgery, since surgical procedures can further exacerbate dry eye (Figure 2).

Figure 2. This patient has dry eye syndrome that was further exacerbated by cataract surgery and subsequent LASIK surgery for the treatment of residual refractive error. While this patient is plano with no astigmatism, her vision is suboptimal due to a compromised ocular surface. A strict treatment regimen restored her vision.

With a healthy ocular surface and accurate refractive results, light can sharply focus on the retina. Any irregularities of the macula, particularly cystoid macular edema (CME), also can lead to suboptimal vision after surgery. Preoperative screening using optical coherence tomography may be beneficial to weed out patients with macular pathology who wouldn't fully reap the benefits of an IOL like the Crystalens HD.

Eyes with epiretinal membranes are more prone to post-op CME, but even normal retinas are at risk, because of the inflammation created during routine cataract surgery. Research shows that the perioperative use of topical NSAIDs is important for the prevention and treatment of CME.⁶ For this reason, I recommend using a topical NSAID for all cataract patients. Dosing begins 3 days before surgery and then continues for 6 weeks following surgery. The NSAIDs not only help resolve inflammation, they're also effective at reducing pain and irritation, which increases patient comfort.

Exceed Patient Expectations

The goal for any refractive surgeon is to meet or exceed the expectations of patients. Making sure patients have a realistic expectation of the limits of refractive IOL surgery is important, because no surgery or lens implant is perfect. The Crystalens HD can provide the wide range of vision found in patients who are in their 40s but not the amazing level of accommodation seen in teenagers.

A 65-year-old patient doesn't expect a plastic surgeon to make her look 25 years old again; rather, she expects to look better. Similarly, we need to help our 65-year-old patients understand they won't be able to see as well as they did when they were 25, but we certainly can help them see better.

With anatomic and refractive accuracy, patients can recover a wide range of sharp vision without eyeglasses. I anticipate that in the years to come, our technology will progress further, and while we may never find the fountain of youth, we'll certainly be able to restore a larger degree of accommodation. OM

References

1. Hoffer KJ. The Hoffer Q formula: a comparison of theoretic and regression formulas. J Cataract Refract Surg. 1993;19:700–712.
2. Borasio E, Mehta JS, Maurino V. Torque and flattening effects of clear corneal temporal and on-axis incisions for phacoemulsification. J Cataract Refract Surg. 2006;32:2030–2038.
3. Nichamin LD. Nomogram for limbal relaxing incisions. J Cataract Refract Surg. 2006;32:1408; author reply.
4. Wang L, Misra M, Koch DD. Peripheral corneal relaxing incisions combined with cataract surgery. J Cataract Refract Surg. 2003;29:712–722.
5. Gills JP. Treating astigmatism at the time of cataract surgery. Curr Opin Ophthalmol. 2002;13:2–6.
6. O'Brien TP. Emerging guidelines for use of NSAID therapy to optimize cataract surgery patient care. Curr Med Res Opin. 2005;21:1131–1137.