F. Carones et al., Photorefractive keratectomy for hyperopia - Long-term nonlinear and vectoranalysis of refractive outcome, OPHTHALMOL, 106(10), 1999, pp. 1976-1982
Purpose: To characterize the refractive changes after excimer laser photore
fractive 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 s
eries.
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 attem
pted correction was +3.33 +/- 0.98 D (range, +1.00 to +4.00 D). Data were c
ompared 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 inse
rted 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 zo
ne 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 nonl
inear statistical model fitting the spherical equivalent, and the sphere co
mponent data. The fit parameters were the long-term error at stabilization
(epsilon(infinity)), the amount of regression (epsilon(0)), being the diffe
rence of refractive errors immediately after surgery and at stabilization,
and the time constant (T-1/2) giving the temporal scale length by which the
overcorrection halves (regression half-life). Cylinder was analyzed by a l
inear regression.
Results: The initial overcorrection was much larger after hyperopic treatme
nts than myopic ones (epsilon(0) = -3.26 +/- 0.35 D vs. +1.43 +/- 0.35 D),
and it takes typically four times longer to regress (T-1/2 = 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 ast
igmatism of 1.00 D, which remains constant throughout the follow-up, and te
nds to be aligned along the with-the-rule meridian.
Conclusions: The advantages of a reasonably well-designed algorithm to corr
ect hyperopia (epsilon(infinity) = +0.20 +/- 0.23 D) are counterbalanced by
the long time to refractive stabilization and by the induced astigmatism.