emmetropia
Aiming for Emmetropia
Managing refractive error after multifocal implantation.
BY DAVID R. HARDTEN, M.D.

When discussing how to achieve emmetropia using lens-based surgery, it is imperative to consider that some patients may need postoperative enhancements. When using multifocal IOLs, the vision is most satisfactory when you hit the target right on because the residual sphere or residual cylinder can affect both the distance and the near acuity. Preoperative planning significantly helps improve the accuracy of targeting, but in some patients you may need to adjust that target postop based upon patient feedback. One important aspect of multifocal IOL implants is trying to achieve maximum visual acuity at various distances. This requires patients to tolerate some loss of contrast at each specific distance.

Improving Chances for Emmetropia

One important skill in improving emmetropia is to maximize the accuracy of axial-length measurement with either immersion ultrasound biometry or the IOL Master (Carl Zeiss Meditec, Inc., Dublin, Calif.). Another task that can improve accuracy is making certain that your keratometers are properly calibrated. Additionally, using one of the newest IOL calculation formulas, such as the Hoffer Q or Holladay II for short eyes, or SRK/T for long eyes, may be beneficial. These factors may be able to improve your ability to achieve good results with multifocal or premium IOLs.

I discuss multifocals with all patients considering IOL surgery but, as we know, not all patients are good candidates for multifocal implants. Patients have different needs. Some may desire mainly good distance vision in both eyes, some near in both eyes and others monovision. The presbyopic IOLs are really designed for patients interested in the concept of distance, intermediate and near vision with both eyes simultaneously.

Presbyopic Patients Who Have Myopic Results

What do you do if after a presbyopic IOL implantation, you end up with a patient who has a myopic result? Most often, these patients will comment that they still want both good distance and near vision. This leaves you to present them with two options: wear glasses or undergo an enhancement procedure.

Multiple options exist for enhancement procedures. Laser vision correction, which in my opinion is the most accurate, has the ability to correct both sphere and cylinder. Within laser vision correction you have multiple options, such as PRK or LASIK, and you can use a variety of different technologies such as custom or standard. In some patients, you may need to enhance one eye, in others, both eyes.

I typically reserve the option of enhancement (laser vision correction, IOL exchange or piggyback) until I have completed surgery on both eyes. This way, I can evaluate the results and the balance of the optics. This is important because, if by chance a patient ends up myopic in the first eye, you may be able to get close to emmetropia in the distance with the second eye, resulting in a happy patient. I usually tell patients they need to wait until both eyes have been done before I decide what to do with a myopic, hyperopic or astigmatic result.

If, after the presbyopic IOL surgery, the patient is on the hyperopic side, the same options are available. In general, if the patient is within 1.5 D or 2 D on the hyperopic side, I prefer laser vision correction. This is true whether I have implanted a multifocal, a premium aspheric IOL or a standard distance-only IOL.

If the patient needs a large correction, he or she still will be symptomatic at 6 months to a year postop. I tend to enhance very large corrections earlier. Often, patients who require small corrections will adapt over time. Most often, if there is 0.5 D of hyperopia and the patient is symptomatic, in time the patient will learn to adapt to the residual error.

I typically wait 6 months postop to do most corrections, because most of the enhancements will be for corrections for less than 1 D of spherical or astigmatic refractive error. I then open the capsule if there is any capsular fibrosis or haze, at around 4 or 5 months postop, before I do laser vision correction. This helps make certain that the symptoms from a hazy capsule do not contribute to the visual dissatisfaction.

For laser vision correction after multifocal IOL implantation in patients who have had previous limbal-relaxing incisions or astigmatic keratotomy, I prefer PRK. In patients with no relaxing incisions, an otherwise healthy epithelium and no anterior basement membrane dystrophy, LASIK offers a faster visual recovery.

Figure. A piggyback IOL is useful as a rescue procedure and can also provide an excellent refractive result.

Custom vs. Standard LASIK

Another question that needs to be answered is, do I use custom or standard LASIK? Custom LASIK offers a better result for astigmatic targeting with iris registration. It also offers potential opportunity to improve corneal higher-order aberrations. It is important that these patients have a pushed-plus manifest refraction that matches the wavefront. The wavefront capture after a multifocal IOL may show results that are surprising, and it may be more difficult to capture the wavefront because of the multifocal IOL or capsular opacity. You also have to consider the effects of capsular opacity; a small capsulorrhexis may not allow you to capture what can currently be treated in the United States with a 5 mm zone.

Standard LASIK may be all that is possible in some eyes, and it typically provides good results. You have to make sure that you are refracting patients carefully by pushing the plus, and by making sure that their UCVA makes sense with what you have for their refraction. It does not make sense for standard or for a custom ablation for a patient who is 20/40 uncorrected and has a refraction of -2.5 D.

Piggyback IOLs or IOL Exchanges

Piggyback IOLs (Figure) or IOL exchanges are useful as a rescue procedure, but I think you will find that these procedures will account for less than 5% of enhancements. If the patient has a high spherical result after the initial surgery, this may be the right choice. Select a lens that has a posterior vault and a three-piece design to maximize stability in the sulcus and minimize chafe on the iris.

IOL exchanges are even less common than piggyback IOLs, but may still be needed. One tip to keep in mind when performing an IOL exchange is that before you remove the first implant from the eye, put the second implant into the bag to protect the capsule while cutting and removing the other IOL.

In summary, if there is a need for enhancement, laser vision correction is the most accurate for sphere and cylinder, but you should be familiar with the techniques of IOL exchange or piggyback IOLs in order to have alternatives that will best suit each patient case.

David R. Hardten, M.D. is in active clinical practice at Minnesota Eye Consultants, where he also serves as director of research and fellowships, and is an adjunct associate professor of Ophthalmology at the University of Minnesota. He can be reached at phone 612-813-3632, fax 612-813-3658 or email drhardten@mneye.com.