Photorefractive keratectomy for hyperopia: Long-term nonlinear and vector analysis of refractive outcome

Abstract Purpose To characterize the refractive changes after excimer laser photorefractive keratectomy for the correction of hyperopia over a follow-up up to 3 years and to assess refractive stability and changes in astigmatism. Design Noncomparative, nonrandomized, retrospective, interventional case series. Participants Thirty-eight hyperopic eyes of 28 patients (age range, 33–62 years) with refraction in the range +1.00 to +8.00 diopters (D). Mean attempted correction was +3.33 ± 0.98 D (range, +1.00 to +4.00 D). Data were compared to those from 216 eyes treated for myopia in the range −1.00 to −12.70 D. Intervention The hyperopic correction was made using an erodible mask inserted in the laser optical pathway to produce a circular ablation measuring 6.5 mm in diameter. An axicon was then used to create a blend transition zone from 6.5 mm up to 9.4 mm in diameter. Eyes were evaluated 3 to 11 times (5.5 ± 2.4) over a 3- to 34-month follow-up (16.8 ± 8.4 months). Main outcome measures Vector analysis of refractive error, applying a nonlinear statistical model fitting the spherical equivalent, and the sphere component data. The fit parameters were the long-term error at stabilization (e ∞ ), the amount of regression (e 0 ), being the difference of refractive errors immediately after surgery and at stabilization, and the time constant (T 12 ) giving the temporal scale length by which the overcorrection halves (regression half-life). Cylinder was analyzed by a linear regression. Results The initial overcorrection was much larger after hyperopic treatments than myopic ones (e 0 = −3.26 ± 0.35 D vs. +1.43 ± 0.35 D), and it takes typically four times longer to regress (T 12 = 3.30 ± 0.91 months). Refractive stabilization is reached after more than 1 year, with a satisfactory refractive result. The hyperopic treatment induces a mean astigmatism of 1.00 D, which remains constant throughout the follow-up, and tends to be aligned along the with-the-rule meridian. Conclusions The advantages of a reasonably well-designed algorithm to correct hyperopia (e ∞ = + 0.20 ± 0.23 D) are counterbalanced by the long time to refractive stabilization and by the induced astigmatism.