Abstract
Introduction: Contrast sensitivity function after laser ablation of the cornea in refractive surgery is an important tool for measuring quality of visual function. The effect of small incision lenticule extraction (SMILE) and femtosecond laser in situ keratomileusis (FS-LASIK) on visual function can be compared by measuring spatial contrast sensitivity.
 Purpose: This study was to compare contrast sensitivity function in patients undergoing refractive surgery for myopia at Tilganga Institute of Ophthalmology.
 Methods: In a retrospective study, 15 subjects who underwent refractive surgeries comprising 9 cases of SMILE and 6 cases of FS-LASIK at Tilganga Eye Hospital were enrolled in the study. A major assessment included best corrected monocular contrast sensitivity with functional vision analyzer at spatial frequencies of 1.5, 3, 6, 12, and 18 cycles/deg in photopic condition (85 cd/m2) before, 3 months, and 1 year after the surgery. The average functional acuity contrast test scores for each spatial frequency were recorded. Differences between preoperative and postoperative contrast sensitivity at each spatial frequency were analyzed through parametric paired Student’s t-test.
 Results: Contrast sensitivity of postoperative FS-LASIK and SMILE did not differ from preoperative values at a photopic level. However, at high spatial frequency (12 and 18 cycles/deg), contrast sensitivity function improved significantly (p < 0.05) in eyes after FS-LASIK. Eyes after SMILE surgery did not show any reduction in contrast sensitivity at all the spatial frequencies.
 Conclusion: Under photopic conditions, the contrast sensitivity function is unaffected by SMILE or FS-LASIK.
Highlights
Contrast sensitivity function after laser ablation of the cornea in refractive surgery is an important tool for measuring quality of visual function
All subjects were programmed for small incision lenticule extraction (SMILE) and LASIK procedure
The present study showed that both SMILE and FS-LASIK were predictable for the correction of myopia and myopic astigmatism and had better outcome of visual acuity
Summary
Contrast sensitivity function after laser ablation of the cornea in refractive surgery is an important tool for measuring quality of visual function. The effect of small incision lenticule extraction (SMILE) and femtosecond laser in situ keratomileusis (FS-LASIK) on visual function can be compared by measuring spatial contrast sensitivity. At high spatial frequency (12 and 18 cycles/deg), contrast sensitivity function improved significantly (p < 0.05) in eyes after FS-LASIK. The 1,053 nm wavelength of light used by the laser is not absorbed by optically transparent tissues It can be focused anywhere within the cornea where the energy can be raised to a threshold such that a plasma is generated.[14] The corneal flap is kept aside and the excimer laser is applied to reshape the surface of the cornea by removing anterior stromal tissue. At a wavelength of 193 nm, high-energy photons break organic molecular bonds of the superficial corneal tissue in a process called ablative photodecomposition.[16,17] Further improvement in lasers occurs with eye-tracking systems that allow precise corneal ablation during eye movement.[18]
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