Presbyopia success depends on comprehensive preop evaluation

Instruments are key to accurate, efficient preop assessment.

William F. Maloney

In the November 1, 2005 issue of Ocular Surgery News Europe/Asia-Pacific Edition, I wrote about the specific set of preop tests we have gradually come to use for presbyopia correction. I want to describe that process in greater detail now.

As expected, the number of questions on preop testing has increased markedly since the recent CMS ruling allowing private payment for these additional presbyopia services. For example, how do you measure for ocular dominance? What instrument do you use for pupillography? Will you explain that test for the defocus tolerance? Can you send me a copy of the focus zone chart and your informed consent? The number of questions such as these in the past month indicates to me that a significant number of surgeons have now decided to act on presbyopia correction.

It is reminiscent of a similar juncture 20 years ago when an excellent ECCE procedure was suddenly no longer good enough. As soon as the foldable IOL was introduced, the trickling transition to phacoemulsification became a torrent, and the number of phaco surgeons increased from 5% to 95%. Now we are once again about to be reminded that “nothing is more powerful than an idea whose time has come.”

In the last column (May 1, 2006 issue), I wrote about the cost of admission to phase 2 of the IOL revolution for surgeons who plan to perform presbyopia correction. I reminded younger colleagues that their phase 1 predecessors purchased expensive new technology and acquired significant new skills such as microscopic surgery and phaco en route to the goal of uncorrected distance vision using the IOL.

Today, phase 2 also requires new techniques and technology to achieve the new goal of presbyopia correction. Many of these new prerequisites are elements of this comprehensive preop evaluation.

Preop evaluation

Before the patient’s preop appointment, I have performed a complete examination and recommended cataract surgery or refractive lens exchange. The cataract patient has elected to have presbyopia-correcting cataract surgery. This additional evaluation is to determine the specific surgical approach and the particular IOL that will best meet the patient’s reading vision goals. The emphasis is on an individually tailored, personalized approach to presbyopia correction from the outset.

1. Questionnaire: Administered by staff (Figure 1)
Completed by the patient in the reception area, the questionnaire is designed to identify relevant elements of the patient’s lifestyle and vision status. Current spectacle use, reading and night driving habits are especially important. Cataract patients typically limit their night driving, which increases our options for near vision.

2. Ocular dominance testing: Administered by staff, surgeon
If any degree of myopic defocus is to be employed, these tests are vital. Much has been written about ocular dominance. The generally accepted guideline that myopic defocus should be calculated for the nondominant eye is not always the case. More important, it misses the point. We test thoroughly for ocular dominance not to identify the nondominant eye, but rather to assess the overall blur suppression capacity and thus the patient’s ability to accept myopic defocus.

The stronger the dominance, the greater the ability of that eye to suppress the blur of myopic defocus from the fellow eye. Dominance and suppression are two sides of the same coin.

We then perform these five tests.

Target alignment: Administered by surgeon. With correction in place, the patient targets an object at least 10 feet away. Holding an 8 × 10 inch card (available from an optical supply store) with a central hole 1 inch in diameter at full arms’ length, have the patient raise the card from below to align the target within the hole. Maintaining alignment, the card is drawn in to cover the dominant eye. Repeat with different distance targets three times.

Camera to eye: Administered by staff. It is important that a camera prop is used. The patient is asked to take a photo of an object. The dominant eye aligns the photo. Repeat with different distance targets three times.

Plus lens test: Administered by staff. With correction in a trial frame and a distance Snellen acuity chart, place a +1.5 D lens over each eye. Dominant eye is less blurred by the additional plus.

Alternating occlusion: Administered by staff. With correction in place using a distance Snellen acuity chart, alternately occlude both eyes. Focus in the dominant eye seems sharper.

Refractive variance: Administered by staff. With distance correction in a trial frame, the dominant eye accepts less plus added in 0.25 D increments at near than the nondominant eye. It is the degree of dominance that we are after with this series of tests. Repeatedly brisk, unequivocal responses indicate strong dominance and therefore a strong blur suppression mechanism. This means that a greater degree of myopic defocus will be tolerated, allowing several options for full zone 1 reading correction, if that is our goal. Since some degree of defocus is necessary with each type of presbyopia IOL, we rely heavily on this data.

3. Worth 4-dot fusion/suppression: Administered by surgeon
In addition to testing fusion, we also use this test to further assess dominance/suppression. The single white target dot is immediately and unequivocally seen in whichever color lens (red or green) covers the dominant eye in patients with strong dominance. It is a supporting indicator of the degree of myopic defocus we can employ.

4. Titmus stereopsis: Administered by surgeon
We have come to appreciate an important correlation between stereopsis and the interocular defocus threshold. Candidates with less than full stereopsis — the majority of cataract patients — consistently tolerate more defocus. Full stereopsis is an indication that this patient will likely tolerate less.

5. 3-D multifunction analysis: Administered by staff (Figure 2)
One of the two instruments we have found to expedite the presbyopia evaluation is the multifunctional 3DWave (Marco). It reliably captures the following data in a matter of seconds per eye.

Refraction. Refraction is accurate, in particular the cylinder and axis. It is compared to the manifest refraction obtained during the initial exam and the corneal topography. Any discrepancies must be reconciled before the final plan is in place.

Corneal topography. Undiagnosed corneal pathology is sometimes discovered, but this data is used primarily for astigmatic assessment. A refractive error of just 0.5 D can affect the presbyopia outcome. Therefore, we correct any existing astigmatism of 0.75 D or greater with peripheral astigmatic keratotomy.

Corneal wavefront analysis. The pattern of lower- and higher-order corneal aberrations is used in planning astigmatism correction, particularly in cases in which there is a discrepancy between the manifest refraction and corneal topography.

Lenticular wavefront analysis. Presbyopia correction using today’s lens implants requires full presbyopia, or nearly so. Candidates are therefore in the age range in which they have some lenticular changes. Isolating the aberrations of the crystalline lens may be an important element in determining and documenting whether a candidate for presbyopia correction is rightly categorized as a cataract or refractive lens exchange patient.

Accommodative wavefront analysis. It is increasingly evident that natural accommodation results from dynamic changes in both corneal and lenticular aberrations that occur with accommodative effort. This instrument captures these near wavefront patterns. This is a beta version of the software. As deformable presbyopic implants are introduced, these patterns may allow the same complementary aberrations seen in natural accommodation. Currently, these data are being evaluated to determine haptic orientation of the Crystalens (eyeonics) in an attempt to optimally align the “accommodative arching” property that has recently been proposed as its mechanism of action.

Pupillography. It is difficult to overemphasize the importance of pupillography in this process, especially for candidates who will be driving at night. This instrument measures photopic, mesopic and scotopic pupil diameter.

6. Interocular defocus threshold: Administered by staff
As we have already seen, myopic defocus is an indispensable tool in treating presbyopia. It is utilized in varying degrees to enhance the accommodative effect of each presbyopic IOL, most important for patients seeking full zone 1 reading.

Each patient must be able to easily suppress the blur from any defocus employed. This is measured as a function of the dominance/suppression capacity and the interocular difference tolerance threshold, determined as follows.

Trial frame with full distance correction.

Occlude the near eye. Add –0.25 D increments to fellow eye until blur is reported.

Occlude the distance eye. Add +0.25 D increments until blur is reported. Place this new refraction for both eyes in trial frame.

Note the interocular difference. It is usually at least 1 D.

Continue to add to this initial interocular difference by alternatively adding –0.25 D increments to the near eye and +0.25 D increments to the distance eye until the difference is not tolerated.

Note this greater interocular difference. It is usually 2 D or greater.

The patient’s interocular tolerance threshold lies between these two points, usually closer to the second higher value. However, if a candidate has weak dominance/suppression results or large scotopic pupils, we lean toward the initial value.

For final confirmation, measure the visual acuity for both distance and near with both eyes open and the trial frame in place. If acuity in the distance eye is at least 20/25 for distance and 20/50 at near, while the acuity in the near eye is at least 20/25 for reading and 20/50 for distance, that degree of interocular defocus will typically be comfortably below the symptom threshold. For cataract patients, use the best corrected visual acuity as the 20/20 baseline.

Except under full scotopic conditions such as back road night driving, most of our patients are asymptomatic with a surprising amount of defocus: 73% accept 2 D interocular defocus, 87% accept 1.5 D, and 100% accept 1 D.

7. Biometry: Administered by surgeon
Presbyopic IOL calculations must start at exact emmetropia. From there any defocus is calculated, and then the total accommodative effect can be correctly assessed.

Contact biometry does not pass this accuracy test. The noncontact immersion method does, but logistically it does not approach the Carl Zeiss Meditec IOLMaster. Despite some technical glitches, I consider this instrument essential because it is superb at its primary function – consistent, highly accurate biometry in about 1 minute per eye. Although an experienced technician can learn to use this instrument, I do this measurement myself for all presbyopia corrections. With the denser cataracts, accurate axial length measurements are possible but highly technique dependent. The keratometry and anterior chamber depth measurements vary beyond accepted tolerances among different technicians. Exact emmetropia is central to our success. As the surgeon, no one will do more than I to ensure the accuracy necessary to achieve our intended result.

8. Reading vision selection: Administered by surgeon
Since this session involves selection of a particular IOL for a patient, I begin with a review of all results, looking for data that might preclude use of a certain IOL.

We then turn to the focus zone chart to illustrate the range of possible visual outcomes (Figure 3). This is a valuable tool in the preop discussion because the inherent compromises are readily apparent.

Presbyopia correction is first and foremost about restoring reading vision, but the specific range of near vision most important to each candidate varies widely. The focus zone chart facilitates the reading selection by highlighting specific activities within each zone. I often use zone specific props such as a cell phone keypad and a variety of reading samples such as stock charts, sheet music, price tags and restaurant menus. Is the type of near vision most important to you found chiefly within zone 1 or zone 2? With the reading range selected, the possible corresponding intermediate and distance zones begin to fall into place.

Then we turn to IOL selection. Each presbyopic IOL has a given set of focus zones that it characteristically delivers. This fixed range of focus can usually be expanded with the appropriate use of either myopic or hyperopic defocus, which is the topic of our next column.

The ReStor (Alcon) typically delivers zones 1, 3, 4 and 5 but not 2 without hyperopic defocus. The Array (Advanced Medical Optics) and Crystalens deliver zones 3, 4, 5 and often, although not always, zone 2, but never zone 1 without myopic defocus. We are awaiting the new ReZoom (AMO) for this evaluation. A conventional IOL targeted for emmetropia typically delivers zones 3, 4, 5 and because of the property of pseudoaccommodation often at least part of zone 2. The blended vision approach employs varying degrees of myopic defocus in a specific complementary pair of conventional IOLs tailored to deliver whichever four contiguous focus zones the patient selects.

The particular IOL most likely to deliver the patient’s desired range of focus is then selected. The patient must demonstrate a solid understanding of the focus zones that will be within his uncorrected range and the remaining zones that will likely require some correction, at least for certain activities such as night driving. A copy of the focus zone chart indicating the patient’s selected focus range is signed and entered in the medical record.

9. Comprehensive interpretation: Administered by surgeon
All preop data is compiled in a presbyopia profile form that we have created for our EMR system. This is important documentation of the entire preop evaluation and helpful during this final interpretation in which each element is weighed in considering the specific refractive plan.

Spherical correction. IOL power is selected after consideration of any myopic or hyperopic defocus to be employed. The defocus plan is checked against the tolerance threshold and dominance/suppression data. IOL power calculation is compared using the SRK-T, Hoffer, Holladay and Haigis formulas. All are included in the IOLMaster calculation software.

Planning your success

Preparing for presbyopia correction is the art of weaving each of these preop elements into a unique surgical plan that reflects each patient’s individual profile. The number of variables in this preop equation and the degree of accuracy required make presbyopia correction seem to be a daunting challenge, and at first it is. But so was that dramatic transition from ECCE to phaco 20 years ago. Now, as then, it will prove to be well worth the effort.

Next month

Increase each IOL’s accommodative effect with just the right amount of myopic defocus.

For more information:

• William F. Maloney, MD, is head of Eye Surgery Associates of Vista, Calif., and a well-known teacher of cataract and lens-based refractive surgery techniques. He 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. In the interest of objectivity, Dr. Maloney has no financial interest in any ophthalmic product and has no financial relationship with any ophthalmic company.