Abstract
Objective: To evaluate the effect of an aspheric LASIK refractive enhancement performed by relifting the original flap on the higher order aberrations (HOA) of the eye and the relationship between central corneal thickness (CCT) and intra-ocular pressure (IOP). Methods: Consecutive case series of 30 eyes requiring refractive enhancement from 1804 uncomplicated primary LASIK procedures performed in 2012. Flap relift and wavefront optimized ablation (Wavelight Allegretto Eye Q 400 Hz excimer laser) were performed in all cases. Pre-and post-operative examination included Shack-Hartmann aberrometry for 3 mm and 5 mm pupil sizes, CCT and IOP. Postoperative results at 1 year were compared to baseline values. Results: Changes in average values of coma, spherical aberration (SA), trefoil, CCT and IOP were not significant. Linear regression revealed significant associations between change (y) in trefoil and pre-enhancement value of trefoil for 3 mm pupil (0.828x-0.045, r=0.722, p<0.001), coma and pre-enhancement value of coma for 5 mm pupil (y=0.281x-0.030, r=0.501, n=30, p=0.048), SA for 3 mm pupil compared with change in CT (y=0.0080-0.0009x, r=-0.378, p=0.0392), and SA for 5 mm pupil compared with change in CCT (y=0.0035x-0.0541, r=0.524, p=0.0029). Also there was a significant association between IOP and CCT both pre-(IOP=0.0313CT-3.3, r=0.740, p<0.0001) and post-enhancement (IOP=0.0243CT-0.018, r=0.675, p<0.0001). Conclusion: LASIK enhancement with an aspheric ablation profile did not significantly impact on the average values for HOAs, IOP or CCT. For individual cases, the likely shift in magnitude of coma, trefoil and SA can be estimated and, the change in SA is correlated with changes in CCT. The change in the abscissa value linking IOP with CCT may be an indication of changes in biomechanical properties of the cornea in the central region.
Highlights
Laser in situ keratomileusis (LASIK) is the most frequently applied corneal refractive surgical procedure today [1]
Since 2000, the reported rate for retreatment averages at about 4% [10,11,12], increasing to 20% in myopic patients after 10 years according to one source [13].The original nomograms for excimer laser photoablation were based on relatively simple spherical optics
Study design This was a consecutive case-by-case series of patients referred for refractive enhancement due to non-tolerated residual refractive error and uncorrected distance visual acuity (UDVA) after primary Laser in situ Keratomileusis (LASIK) performed during 2012
Summary
Laser in situ keratomileusis (LASIK) is the most frequently applied corneal refractive surgical procedure today [1]. Since 2000, the reported rate for retreatment averages at about 4% [10,11,12], increasing to 20% in myopic patients after 10 years according to one source [13].The original nomograms for excimer laser photoablation were based on relatively simple spherical optics. This led to an increase in the magnitude of other higher order aberrations of the eye, and this was associated with reduced visual performances. Do these complex algorithms retain, reduce or increase the HOA of the eye after enhancement procedures? The evidence in the literature is inconclusive regarding enhancement procedures
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