Differences in Image Quality after Three Laser Keratorefractive Procedures for Myopia

Abstract

SIGNIFICANCE: Psychophysical estimates of spatial and depth vision have been shown to be better after bilateral ReLEx small-incision lenticule extraction (SMILE) refractive surgery for myopia, relative to photorefractive keratectomy (PRK) and femtosecond laser-assisted in situ keratomileusis (FS-LASIK). The present study provides the optical basis for these findings using computational image quality analysis.PURPOSE: This study aimed to compare longitudinal changes in higher-order wavefront aberrations and image quality before and after bilateral PRK, FS-LASIK, and SMILE refractive procedures for correcting myopia.METHODS: Wavefront aberrations and image quality of both the eyes of 106 subjects (n = 40 for FS-LASIK and SMILE and n = 26 for PRK) were determined pre-operatively and at 1-week, 1-month, 3-month, and 6-month post-operative intervals using computational through-focus analysis for a 6-mm pupil diameter. Image quality was quantified in terms of its peak value and its interocular difference, residual defocus that was needed to achieve peak image quality (best focus), and the depth of focus. RESULTS:The increase in root mean squared deviations of higher-order aberrations post-operatively was lesser after SMILE (1-month visit median [25th to 75th interquartile range], 0.34 μm (0.28 to 0.39 μm]) than after PRK (0.80 μm [0.74 to 0.87 μm]) and FS-LASIK (0.74 μm [0.59 to 0.83 μm]; P ≤ .001), all relative to pre-operative values (0.20 μm [0.15 to 0.30 μm]). The peak image quality dropped and its interocular difference increased, best focus shifted myopically by 0.5 to 0.75 D, and depth of focus widened significantly after PRK and FS-LASIK surgeries, all relative to pre-operative values ( P < .001). All these changes were negligible but statistically significant in a minority of instances after SMILE surgery ( P ≥ .01).CONCLUSIONS: Although all three refractive surgeries correct myopia, the image quality and its similarity between eyes are better and closer to pre-operative values after SMILE, compared with FS-LASIK and PRK. These results can be explained from the underlying increase in higher-order wavefront aberrations experienced by the eye post-operatively.

The Value of Eccentric Infrared Photorefraction in Evaluating Keratoconus

“…Given that the photorefraction luminance profile reflects the underlying optics of the cornea, it is important to note that these results may not be unique to keratoconus. Similar results are expected to be found in other corneal dystrophies (e.g., pellucid marginal degeneration, granular, lattice, and macular dystrophies), 29 inflammatory conditions (e.g., herpes simplex keratitis), 24,28 autoimmune disorders (e.g., Steven-Johnson syndrome), 25 and corneal surgery (e.g., keratorefractive and keratoplasty procedures), 23,27 all of which result in an increased magnitude of the eye's irregular astigmatism and higher-order aberrations. The extent of nonlinearity in the photorefraction luminance profile is also expected to vary with the underlying magnitude of corneal distortions experienced in these conditions.…”

“…A characteristic feature of distorted corneas is an increase in the magnitude of higher-order wavefront aberrations 20,23–29 . For instance, the root mean square deviation of higher-order aberrations is approximately fivefold to sevenfold larger in keratoconus 20 and approximately threefold to fourfold larger after keratorefractive procedures, 27 both relative to controls with matched pupil sizes.…”

“…A characteristic feature of distorted corneas is an increase in the magnitude of higher-order wavefront aberrations. 20,[23][24][25][26][27][28][29] For instance, the root mean square deviation of higher-order aberrations is approximately fivefold to sevenfold larger in keratoconus 20 and approximately threefold to fourfold larger after keratorefractive procedures, 27 both relative to controls with matched pupil sizes. Optical modeling studies show that the addition of higher-order wavefront aberrations (e.g., spherical aberration) to defocus renders the photorefraction luminance gradient nonmonotonic and shifts this profile toward increasing hyperopia or myopia, depending on the sign of the wavefront aberration.…”

Clinical outcomes of stromal lenticule rotation to correct mixed astigmatism

“…Similar to other corneal refractive surgeries, corneal modification may influence the optical quality of the cornea, creating HOAs that will lead to distorted images. 20 Studies report that increased anterior corneal surface HOAs after photorefractive keratectomy, LASIK, and laser-assisted subepithelial keratectomy are mainly from increased spherical and coma aberrations. [21][22][23] A notable finding in our study was unchanged spherical aberration.…”