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L. Wang, B. L. Shoss, M. P. Weikert, D. D. Koch; Ocular Functional Optical Zone Changes Following Wavefront-Guided LASIK/PRK. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4212.
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Traditionally, the functional optical zone (FOZ) is analyzed based on corneal topography. Better optical quality of the anterior corneal surface may not optimize retinal image quality of the eye due to the effect of the internal optics. Furthermore, wavefront-guided ablation is based on ocular wavefront aberrations and may not produce uniform ablation on the cornea. Therefore, analysis of FOZ based on ocular optical quality of the eye is more appropriate. The purpose of this study was to investigate, based on retinal image quality, the size of the ocular FOZ before and after wavefront-guided myopic or hyperopic LASIK/PRK.
Consecutive cases that underwent wavefront-guided myopic or hyperopic laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) (CustomVue, Abbott Medical Optics [AMO], Santa Ana, CA) were reviewed. Subjects that had wavefront measurements with ≥ 6 mm pupil before and at least 3 months after LASIK or 6 months after PRK were included. Assuming full correction of 2nd order aberrations, using ZernikeTool program (AMO), we calculated polychromatic modulation transfer function (MTF) at 9 cyc/deg with Stiles-Crawford effect for 2-6 mm pupils. FOZ was defined as the zone over which the MTF at 9 cyc/deg was ≥ 0.18. This criterion is consistent with 0.0 LogMAR (Snellen equivalent 20/20) or better vision.
In 72 eyes that underwent myopic PRK, the amount of refractive correction was -3.71 ± 1.75 D (range -0.63 to -7.69 D); 99% of eyes (71/72) had FOZ ≥ 6 mm preoperatively, 65% of eyes (47/72) had FOZ ≥ 6 mm postoperatively; for the one eye with pre-op FOZ < 6 mm (5.8 mm), the post-op FOZ was 5.5 mm. In 30 eyes that underwent hyperopic LASIK/PRK, the refractive correction was 0.84 ± 0.57 D (range 0.35 to 1.76 D); 77% of eyes (23/30) had FOZ ≥ 6 mm preoperatively, 73% of eyes (22/30) had FOZ ≥ 6 mm postoperatively; for the 7 eyes with pre-op FOZ < 6 mm, 5 eyes had increased post-op FOZ to 6 mm or larger. In both groups, post-op FOZ decreased with increasing magnitude of 4th-order spherical aberration and higher-order aberrations (3rd-6th order) (all P<0.05).
Compared with pre-op FOZ, in eyes following wavefront-guided myopic PRK, FOZ decreased to a zone smaller than 6 mm in approximately 1/3 of eyes; in eyes with prior hyperopic LASIK/PRK, FOZ decreased in about 1/4 of eyes and increased in 5 of the 7 eyes that had pre-op FOZ < 6 mm. Wavefront aberrations play an important role in determining the size of ocular FOZ.
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