PRK Enhancement Improves Visual Acuity, Refractive Outcomes

A nurse supervises an eye test at the diabetes clinic at St. Thomas’ Hospital in Central London. The Governmnet has launched the National Service framework for diabetes, which encourages diabetes sufferers to undertake eye tests and other check ups. 11/11/03: A contact lens which can be surgically fitted into the eye is to be made available to patients at private clinics across the UK, it was announced. The treatment involves implanting a thin lens between the eye’s natural lens and the iris to permanently correct sight problems such as severe long and short-sightedness. (Photo by Chris Young – PA Images/PA Images via Getty Images)
Study offers option for those with residual refractive error after primary PRK.

Photorefractive keratectomy (PRK) enhancement following primary PRK surgery is associated with both improved refractive outcomes and visual acuity, according to research published in Ophthalmology and Therapy. 

Researchers conducted a retrospective analysis of patients who underwent wavefront-optimized PRK enhancement following PRK refractive surgery at a single center to analyze their visual outcomes as well as the safety, efficacy, and predictability of the enhancement. PRK enhancement following PRK surgery is not currently approved by the US Food and Drug Administration (FDA). 

The primary reason for retreatment was dissatisfaction due to residual refractive error after primary PRK. Of the 2995 eyes that underwent primary PRK between 2014 and 2019, 188 required enhancement, with an enhancement rate of 6%. The cohort for the current study included 188 eyes from 141 patients who underwent PRK enhancement after primary PRK. Mean time between procedures was approximately 60 months. 

Within the cohort, 172 eyes had myopia, 9 had mixed astigmatism, and 7 had hyperopia. 

Between the treatment group and the control group — which consisted of patients who did not undergo PRK enhancement after primary PRK — researchers noted no significant difference in patient age, and women required PRK enhancement at a higher rate than men compared with the control group. No other measured factors — corrected distance visual acuity (CDVA), diopters of cylinder, pachymetry, and keratometry values — showed a statistically significant difference. 

Before enhancement, only 4% of eyes had an uncorrected distance visual acuity (UDVA) of 20/20 or better and 56% had a UDVA of 20/40 or better. Comparatively, 99% of eyes had a CDVA of 20/20 or better and 100% of eyes had a CVDA of 20/40 or better. In the 3 months following the enhancement, 85% and 99% of eyes had a UDVA of 20/20 or 20/40 or better, respectively; at 12 months, UDVA of 20/20 or 20/40 or better was noted in 75% and 99% of patients, respectively. Efficacy was 1.10 at 3-months and 1.27 at 12 months, which exceeds FDA target criteria. 

UDVA after enhancement was the same or better than the CDVA before the enhancement in 84% of eyes. At 12 months after enhancement, 75% of eyes had  UDVA equal to or better than DCVA before the enhancement. Retreatment CDVA at 12 months demonstrated a loss of 2 or more lines in less than 1% of eyes, with 1 patient developing a corneal ulcer in 1 eye. 

Safety indices were 0.89 and 0.96 and the 3- and 12-month visits, respectively; FDA primary safety target criteria include a less than 5% rate of eyes with the loss of 2 or more lines of CDVA. 

Average attempted refractive treatment for sphere was -0.91 D and +1.01 D; for cylinder, the average attempted refractive treatment was -0.59 D. At 3 months and 12 months, 88% and 98% and 86% and 98% of eyes were within ±0.50 D and ±1.00 D of the intended target, respectively. A linear regression analysis demonstrated a strong relationship between attempted and achieved SE, with R2 values of 0.8181 and 0.7943 at 3 and 12 months. 

At 3 months following the enhancement, 94% and 99% of eyes had astigmatism of, at most, 0.50 D and 1.00 D, respectively; this percentage was 90% and 100% of eyes at the 12-month follow-up. At 12 months, the angle of error arithmetic mean was approximately -2.2 ˚, with an absolute mean of 10.4 °. 

Study limitations include the loss of patients to follow-up, as well as the nonrandomized, retrospective nature of the study, the inclusion of primarily myopic, rather than hyperopic eyes, and the inclusion of patients with residual refractive error and those who were unsatisfied with primary PRK despite having UDVA of 20/20 or better at the time of the enhancement. 

“Our study establishes the effectiveness, predictability, and safety of PRK retreatments following primary PRA meeting or exceeding the FDA criteria,” the research concludes. “Given the lack of discussion of PRK after PRK outcomes in the recent literature, we hope our results provide a precedent that will allow fellow clinicians to confidently manage post-PRK refractive surgery patients requiring retreatments.”


Moshirfar M, Villareal A, Thomson AC, et al. PRK enhancement for residual refractive error after primary PRK: A retrospective study. Ophthalmol Ther. Published online January 30, 2021. doi:10.1007/s40123-021-00331-8