Nearly all of the patient complaints of visual symptoms and the poor visual outcomes of any presbyopia treatment are the result of decentration due to centering treatment on the center of the pupil rather than on the visual axis.
It is not possible to capture the precise visual axis using current technology, Dr. Tamayo added, but centering treatment on the Purkinje image is a useful surrogate for the visual axis.
The procedure itself creates a multifocal cornea with different powers at different points along the surface of the cornea. The surgeon creates a peripheral knee on the cornea, which creates distinct areas of negative spherical aberration and a central area of positive spherical aberration. It is this combination of positive spherical aberrations with negative spherical aberrations that creates the increase in depth of focus and improves near vision.
Correcting presbyopia by altering the cornea is not a perfect solution.
Dr. Tamayo cautioned that normal aging processes mean that presbyopia will continue to progress over time. Laser correction needs to be repeated after about seven years for most patients. In addition, the correction can be tweaked or even reversed as needed for patients in whom the procedure is not successful.
Excimer laser device manufacturers have long recognized the potential for presbyLASIK procedures, he said.
One key advantage from the ophthalmologist’s perspective is that almost any current excimer laser device can be used to correct presbyopia with a simple software upgrade.
Dr. Tamayo presented a prospective study of excimer laser presbyopia treatment of 121 eyes in 66 patients who were followed for 38 to 66 months. The mean preoperative sphere was 0.180 +- 2.2 D (-5.0 to + 5 D) and the mean preop cylinder was -0.736 +- 0.97 (-6.5 to 0.0 D). Most of the patients, 57.9%, were hyperopic, 14% were myopic myopia and 10.7% were emmetropic. Within the study group, 86.8% received presbyLASIK, 13.2% presbyLASEK and 9.9% were being re-treated.
After surgery, 97.5% had 20/40 or better uncorrected distance binocular vision and 85.9% had 20/40 or better uncorrected monocular vision. With correction, 100% of patients had 20/25 or better distance binocular vision and 96.8% had 20/25 or better monocular vision.