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Conventional IOL presbyopia correction: six steps to success
Mixing IOL powers creates a smoothly blended range of uncorrected vision customized for each patient.
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 William F. Maloney |
We have been describing in recent columns the evolution of conventional IOL presbyopia correction during its 20-year history. This fourth and final column in this series is intended to serve as a blueprint for those ready to employ this approach.
The conventional IOL approach to presbyopia correction is unique in that the accommodative effect is not IOL dependent. The reading result is therefore not limited by a specific IOL technology with a fixed accommodative range. This versatility, derived from employing just the right amount of myopic defocus, is a unique advantage of the conventional IOL approach because it allows for a reading result tailored to each patient’s unique goals and needs.
Such varied results are only an advantage, however, when the requisite planning is carefully employed. This means more surgeon involvement well before the surgery begins, no matter which IOL you choose.
No automatic solution
Surgeons understandably seek to minimize the number of variables in this process because each introduces a potential for variable results. But despite what paid presenters would have you believe, there is no automatic solution, no universal foolproof formula to a successful presbyopia correction incorporated into one or another IOL. Each has strengths but also important weaknesses. How else to explain the current trend toward mixing two different accommodative implants in search of an IOL pairing capable of delivering the full range of reading results patients really want?
This trend toward mixing different “fixed” presbyopia IOLs spotlights the reality that we have repeatedly emphasized in this column — presbyopia correction is presently anything but automatic. It is as much art as science, and the surgeon is as much architect as technician. The surgeon as architect must shift some emphasis from doing to designing, for presbyopia correction succeeds or fails primarily in the planning.
Mixed powers
The essence of the conventional IOL approach is also to create a complementary IOL pairing. But here the mix is of different powers, not different technologies. The goal of this approach is to design a unique pair of IOLs that together provide a smoothly blended range of uncorrected vision without gaps. Built on a 20-year track record, selecting just the right power blend for each patient is a well-established process. Here is the blueprint outlining the six essential elements for designing each one-of-a-kind conventional IOL pairing for presbyopia correction.
Blueprint for conventional IOL presbyopia correction
1. Establish desired reading goal.
Using the focus zone chart (Figure), the patient selects his desired reading goal as either zone 1 full reading or zone 2 social reading with the understanding that zone 2 will require less distance compromise. It is crucial that the patient knows the specific activities that lie within each reading focus zone and the distance compromise accompanying each.
Our example patient has selected zone 1 reading with the understanding that zone 5 distance focus may be compromised enough to require glasses for those activities.
2. Select near IOL power.
Zone 1 requires a total of 3 D of accommodative effect and zone 2 requires 2 D. The pseudoaccommodation inherent in every conventional IOL reliably provides 1 D of that accommodative effect. Thus, the amount of supplemental myopic defocus in the reading eye that is required for zone 1 reading capability is 2 D while zone 2 requires just 1 D. Our patient’s biometry directed us to a target of –1.92 D for the near focus IOL. This is the primary element in this process from which all remaining variables derive.
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Image: Maloney WF |
3. Test for dominance and interocular defocus threshold.
Dominance and defocus tolerance testing have been previously described in this column in detail. Typically, the dominant eye is selected for distance. This convention is by no means essential, however, and may be reversed in the case of an avid reader.
The patient’s defocus tolerance threshold should be comfortably above the degree of myopic defocus employed. Our patient is right eye dominant and readily tolerates more than 2 D of interocular focus difference.
4. Select distance IOL power.
The distance IOL power is determined by the amount of interocular defocus tolerated. In this patient, we want to be comfortably below 2 D of interocular difference and preferably closer to the 1.5 D that is almost universally readily accepted. Our selected distance IOL points to a refractive target of –0.32 D, creating an interocular focus difference of 1.6 D, well below his tolerance threshold.
5. Establish expectations.
This IOL pairing of –1.92 D for the nondominant reading eye and –0.32 D for the dominant distance eye can be expected to focus zones 1, 2, 3 and 4 in a smoothly blended range of uncorrected vision. The patient is counseled that activities such as night driving that fall within zone 5 will require glasses, and he willingly accepts this anticipated compromise because, typical of most cataract patients, he does limited night driving and other zone 5 activities.
6. Exceed expectations.
As we saw in the last column (“Precise ‘presbyometry’ key to conventional IOL presbyopia correction,” January 2007), the anticipated compromise never materialized. The –0.32 D of myopic defocus resulted in such a small reduction in distance focus that this patient never needed to use glasses for his limited zone 5 activities. Typical of most cataract patients, the anticipated compromise never materialized.
For more information:
- William F. Maloney, MD, can be reached at 2023 West Vista Way, Suite A, Vista, CA 92083 U.S.A.; +1-760-941-1400; fax: +1-760-941-9643; e-mail: maloneyeye@yahoo.com. Dr. Maloney has no financial interest in any ophthalmic product and has no financial relationship with any ophthalmic company.
- Lens-based Refractive Surgery Column Mission Statement: To educate readers on all aspects of lens implant refractive surgery including presbyopia correction, refractive cataract surgery, refractive lens exchange and phakic IOLs.