Presbyopic laser vision correction: Analyzing PRK method at 1 year

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Results from follow-up to 1 year in 16 patients treated with PRK using a multifocal bi-aspheric ablation profile show good visual acuity outcomes and patient satisfaction.

Dr. Eskina

By Cheryl Guttman Krader; Reviewed by Erika N. Eskina, MD

Moscow-Photorefractive keratectomy (PRK) using a proprietary multifocal bi-aspheric ablation profile (PresbyMax, Schwind eye-tech solutions) and a micromonovision-based approach is a safe and effective treatment for ametropic presbyopes, according to outcomes of patients followed for up to 1 year, said Erika N. Eskina, MD.

“We chose to use PRK rather than LASIK because surface ablation greatly increases the possibilities of the method and expands the indications,” said Dr. Eskina, professor, Department of Ophthalmology, National Medical-Surgical Center, and medical director, laser surgery clinic, “SPHERE,” Moscow, Russia. “However, we recognize that some ophthalmologists still question the effectiveness and predictability of PRK.

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“Our initial experience has already suggested a modification to the refractive target that we believe will be beneficial, and further study with longer follow-up is still needed to show the safety and effectiveness of corneal presbyopia correction with the use of a surface ablation technique,” she said.

Visual acuities

Data collected in a cohort of 16 bilaterally treated patients showed good distance and near visual acuity associated with a high rate of spectacle independence. Contrast sensitivity was maintained within the normal range, no eyes lost more than 1 line of best-corrected visual acuity (BCVA), and patient satisfaction was high. There was a slight residual myopia in the dominant eye.

The treatments were planned using the manufacturer’s custom ablation manager software and performed with its 500-Hz excimer laser (Amaris). Targets included up to 0.75 D of anisometropia, a surgical add of 1.75 D to 2.25 D, and refractions of –0.13 D in the dominant (distance) eye and –0.875 D in the non-dominant (near) eye.

“The PresbyMax principle, introduced in 2009, is based on both eyes contributing equally to providing visual acuity at all distances by actively participating in the visual process,” Dr. Eskina said.

Beginning in 2012, the micromonovision approach forms slight anisometropia, which together with an additional amount of spherical aberration enlarges the add effect in binocular vision conditions. In addition the change in target refraction with micromonovision increases the distance uncorrected visual acuity (UCVA) of the dominant eye, Dr. Eskina explained.

Eligibility criteria for the treatment include age ≥40 years, sphere +5 to –6 D, astigmatism ≤2 D, photopic pupil size ≤3 mm, and scotopic/mesopic pupil size ≥4.50 mm. Patients with monocular vision, whose profession requires excellent visual acuity in different light conditions, and those with unrealistic expectations are excluded.

“Presbyopia correction with this procedure requires a careful preoperative exam with use of strict exclusion criteria and a detailed explanation to the patient concerning visual recovery,” Dr. Eskina said.

About the study group

The study group included 6 patients with myopia and 10 with hyperopia. Mean preoperative SE for those with myopia was –4.15 D in the eye treated for distance and –4.54 D in the near eye; corresponding values in the hyperopic group were +2.14 and +1.98 D, respectively. Patients had a mean near add of 1.95 D at 40 cm preoperatively and average pupil size of 2.86 mm in photopic conditions and 5.03 mm in scotopic conditions.

All patients were seen at 6 months, and at that visit, binocular near UCVA was 0.2 logRAD or better in all patients with hyperopia and 0.1 logRAD or better in all patients with myopia. At 12 months, those same near UCVA levels were reached by 6 (67%) of the patients with hyperopia and 3 (50%) of the patients with myopia.

Binocular distance UCVA was 0.1 logMAR or better in all patients with hyperopia at 6 and 12 months and 0.0 logMAR or better in all patients with myopia. At both 6 and 12 months all patients had binocular BCVA of 0.0 logMAR or better.

“The majority of hyperopes gained at least 3 lines in both binocular near and distance UCVA,” Dr. Eskina said. “Among the myopes, the majority gained at least 3 lines in distance UCVA and had almost no loss of lines in binocular near UCVA.”

However, while near vision improvement was achieved rapidly, recovery in distance acuity took up to 3 months in the patients with myopia and even longer in the patients with hyperopia.

Analyzing refractive outcomes

Analyses of refractive outcomes showed the postoperative anisometropic target of 0.75 D was achieved in both groups at 6 and 12 months, but there was a slight residual myopia in both eyes which became less within the observation period.

“Small residual myopia in the distance eye may decrease distance UCVA and influence the patient’s satisfaction level,” Dr. Eskina said. “In the future, we believe that slightly increasing the refractive target in the distance eye by about –0.25 D from the manifest value in the myopes and from the cycloplegic value in the hyperopes will be beneficial.”

Corneal wavefront aberrometry measurements obtained at 6 mm showed mean preoperative spherical aberration was similar at baseline in the myopic and hyperopic eyes, but there was an increase in spherical aberration in those with myopia, and consistent with the treatment plan, a shift to negative values in the those with hyperopia.

Erika N. Eskina, MD

E: eeskina@sfe.ru

This article was adapted from Dr. Eskina’s presentation at the 2014 meeting of the American Society of Cataract and Refractive Surgery. Dr. Eskina has no relevant financial interests to disclose.