Laying the Groundwork for Future Treatments
Accurately registering laser treatments to the iris is even more important for aspheric ablations than for monofocal ablations.
BY COLMAN R. KRAFF, MD
The FDA investigational team for the multifocal Advanced CustomVue ablation (Advanced Medical Optics, Inc., Santa Ana, CA) has recently concluded a small US investigational study of wavefront-guided aspheric ablations in hyperopic presbyopes.
The multifocal Advanced CustomVue ablation differs from a standard hyperopic correction in that a subtle ablation shape change is made to the patient’s wavefront map using variable spot scanning (VSS) technology (Advanced Medical Optics, Inc.). The treatment makes the curvature of the eye more aspheric to allow for near vision in the center of the cornea that blends into distance vision in the periphery.
In addition to expanding the patient’s range of vision with the curvature change, the Advanced CustomVue software creates a wavefront-guided correction that considers the individual’s specific higher-order aberrations. It further customizes the treatment by taking into account the patient’s pupil dynamics and size. For a patient with large pupils, increasing the central near zone to fully encompass the reading pupil will have the best results.
This treatment provides what I consider omnifocal vision for hyperopic presbyopes. It balances and optimizes the optics throughout the entire range of vision to provide a longer depth of focus and a wider depth of field. The result is that patients can see well at all distances, including near, far, and intermediate, under a variety of lighting conditions.
THE ROLE OF IR
The presbyopia study is among the first to incorporate Advanced CustomVue iris registration (IR) technology (Advanced Medical Optics, Inc.), which I believe is critical to successfully treating presbyopes.
My IR capture rate has improved to about 95% since IR was first introduced. My practice’s technicians have also gotten better at taking the WaveScan so that they now produce better quality images in which IR can more easily identify and match iris markers. Learning how to adjust lighting conditions as necessary is another important factor in successfully engaging IR at the laser.
IR ensures that the wavefront pattern ablated at the time of surgery corresponds precisely to the patient’s preoperative wavefront map. This is partly accomplished by compensating for any cyclotorsion that occurs between the measurement and treatment. For any patient, compensating for cyclotorsion should provide crisper vision through the better correction of cylinder and higher-order aberrations.
In aspheric presbyopic ablations, IR becomes even more important, because the treatment size and location are dependent upon the pupil’s size and centroid. The change in curvature that provides the near vision enhancement must be delivered directly over the center of the entrance pupil. The pupil centroid can shift as the pupil changes size. Without IR to identify and compensate for any shifts that occur, it is impossible to know whether the presbyopic treatment is accurately centered.
US STUDY RESULTS
In the investigational study, we treated 20 subjects with aspheric ablations in their nondominant eyes. We targeted the dominant eyes for emmetropia with a normal CustomVue hyperopic correction.
The patients in the study are an average of 46.7 years old (range, 41 to 57 years) and predominantly male (70%). In the aspheric eyes, the mean preoperative sphere was +1.50D (+0.25 to +2.50D), with minimal cylinder (mean, 0.30D; range, 0 to 1.00D). Thus far, 3-month follow-up is available on 16 subjects, 11 have reached the 6-month mark, and eight have reached 9 months.
Preoperatively, no patient had distance or intermediate UCVA of 20/20 or better. Six months postoperatively, 73% of the patients were seeing 20/20 at distance in their aspheric eye, and all saw at least 20/25 (Figure 1). Binocularly, 100% of patients had 20/20 distance UCVA. We saw similar results for intermediate UCVA.
The patients’ near vision improvements were dramatic as well. Preoperatively, only 5% of subjects could see J1 uncorrected. Postoperatively, 100% of patients saw J1 or better in their aspheric eye at 6 months (Figure 2), and this outcome held true when they were tested binocularly.
Patients were more satisfied with their UCVAs at both distance and near postoperatively than they had been with their BCVA before surgery.
W. Bruce Jackson, MD, and colleagues in Ottawa, Canada, have been involved in a larger-scale study of presbyopic ablations, with data on many patients now available out to 12 months. They are treating both eyes of the subjects, which we would expect to be more effective in reducing dependence on spectacles.
Dr. Jackson’s team has reported excellent visual acuity results. At 1 year, 100% of the subjects achieved a UCVA of both 20/25 or better for distance and J3 or better for near. Eighty-five percent were seeing at least 20/25 and J1 simultaneously.
The patients had high rates of satisfaction with night vision, which we have also seen in the US study and indicates that contrast sensitivity is not adversely affected. In fact, the Canadian data show that while the treatment somewhat reduces contrast sensitivity, patients experience improvement in this category throughout the postoperative period. At 12 months, contrast sensitivity is well within normal values for 50- to 75-year-olds.
The investigators also found that higher-order aberrations are stable following the treatment. Coma, for example, which many expected would increase, went up only slightly and then remained stable. Spherical aberration shifted from positive to negative, as would be expected from the creation of an aspheric, more prolate cornea. This effect also remained stable throughout the postoperative period.
One very interesting feature of the Canadian study is that the eyes treated after IR was introduced ended up a little closer to emmetropia and had slightly better near acuity than those treated without IR.
In the US study, I would expect to see even better results when we begin enrolling patients in a larger clinical trial and can treat both eyes with an aspheric correction as has been done in Canada. This approach should give patients an even broader, truly omnifocal range of vision.
To prepare for the addition of wavefront-guided presbyopic corrections, practitioners will need to become proficient with IR. The technology is something I prefer to use in all treatments, but it is absolutely essential to obtaining optimal results in presbyopic corrections.