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Laser corneal refractive surgery is based typically on an excimer laser to change corneal curvature and compensate for refractive errors of the eye.1 In the presence of hyperopic refractive error, the treatment goal is to increase the corneal power by decreasing corneal curvature (radii) without induction of aberrations and to keep this change stable over time.
Clinical results suggest that small optical zones may produce a less predictable correction due to greater and more variable regression.2 Smaller optical zones appear to yield lower quality of vision, possibly by induction of aberration in the peripheral ablation area and an increased effect of any decentration.3 When possible, larger optical zones (preferrably 5.5-mm zones) should be chosen.4 As laser technology has progressed, there has been a gradual increase in the diameters of the optical and ablation zones.
Stability is often described as no change in the patient's manifest refraction over time. According to the US Food and Drug Administration's (FDA) definition, this should be <1.00 diopter (D) over 12 months. The problem with hyperopic patients is that they are able to compensate a latent hyperopia, with this latency becoming manifest as the patients age. Therefore, latent hyperopia and regression should be clearly differentiated. Topography to measure the change in the refractive power was recommended as a reproducible and objective method in an earlier publication. 5 Using this method, changes between 3 and 12 months postoperatively and a period of up to 3 years after LASIK are analyzed. The time required to achieve corneal stability after LASIK needs to be further investigated. Consistent with Waring et al,6 our experience shows that the intended corneal curvature is achieved after 3 months and that only minor changes are to be expected after this time point. Our study is designed to describe an objective method to evaluate corneal stability after refractive surgery.
Postoperative topographic stability and refractive stability over time are compared based on analysis of the topographies at 3 months and at 1 and 3 years postoperatively and evaluation of the relative power changes. Based on the comparison of topographic stability and changes in refractive stability, true refractive regression can be distinguished from regression due to latent hyperopia changing to manifest hyperopia.
Patients and Methods
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