Search

Purpose: To determine whether the eye's optical quality is correlated to the visual discrimination capacity of patients treated with LASIK using two different ablation algorithms., Methods: Visual discrimination was evaluated by the disturbance index under low illumination (Halo v1.0 software, Laboratory of Vision Sciences and Applications) in two groups of patients who underwent LASIK with two different ablation algorithms using the Allegretto Wave Eye-Q 400 Hz laser (WaveLight AG). In the first group (standard group; 30 eyes), corneal ablations were performed with the standard algorithm (preoperative spherical equivalent refraction -3.20±1.70 diopters [D]). In the second group (Q-optimized group; 38 eyes; spherical equivalent refraction -3.40±1.90 D), the ablations were made with the Q-optimized (F-CAT) algorithm. Optical quality of the eye was calculated by the Strehl ratio measured with a double-pass device (OQAS, Visiometrics SL)., Results: After LASIK, both the Strehl ratio as well as visual discrimination capacity diminished in both groups, although the changes were significantly greater in the standard group than in the Q-optimized group., Conclusions: A high correlation was found between the Strehl ratio and the disturbance index in patients who underwent LASIK, regardless of the ablation algorithm applied. Optical and visual deterioration were greater after standard ablation., (Copyright 2011, SLACK Incorporated.)

The reliability of using a reference system intrinsic to the cornea has been evaluated in order to characterize corneas of subjects after refractive surgery. Data on 90 eyes operated on by LASIK to correct myopia and astigmatism were considered. The corneal parameters (curvature radii and corneal asphericity) found with respect to this reference system are compared with the parameters provided directly by the corneal topographer. The corneal parameters referenced to the intrinsic main axes of the cornea allow a better characterization of the corneal geometry, showing lower variability and diminishing the dissimilarities between the different eyes. The use of these parameters reduces the discrepancies between the real experimental and the theoretically predicted values (21% mean relative error using intrinsic data versus 81% using the topographer data). To understand and reduce these differences is essential in refractive surgery.

We test visual performance after LASIK (laser in situ keratomileusis) for a Q-optimized ablation algorithm and one based on the Munnerlyn formula. The visual functions tested include aberrometry, monocular and binocular contrast sensitivity function (CSF), and a discrimination test under low-illumination conditions. This test is useful to quantify night-vision disturbances. A total of 102 patients took part in the experiments, and visual data were taken before (with best correction) and after LASIK. Results show a deterioration in aberrometry, CSF, binocular summation, and discrimination index for the two algorithms tested, although this deterioration is significantly lower for the Q-optimized algorithm.

Purpose: Corneal and total higher order eye aberrations and their effects on visual function were compared in two groups subjected to different emmetropization techniques-refractive surgery (LASIK) and corneal refractive therapy (CRT)., Methods: Twenty eyes of 11 patients and 22 eyes of 13 patients were examined in the CRT and LASIK groups, respectively. Mesopic contrast sensitivity function (CSF) was studied monocularly and binocularly in the two groups of patients undergoing CRT and LASIK who had approximately the same mean refractive error. Corneal asphericity and corneal and total aberrations were calculated, and the differences were analyzed between groups. Visual acuity, corneal and total ocular aberrations, corneal asphericity, and mesopic CSF were determined before and 3 months after treatment., Results: In both groups, corneal and total higher order aberrations increased after treatment, and the change in some Zernike coefficients was significant. Mesopic CSF diminished after treatment under monocular as well as binocular conditions, with the greatest decline being found in the CRT group under binocular conditions. Corneal asphericity also increased significantly in both groups, which was more accentuated in the CRT group., Conclusions: Both emmetropization techniques increased higher order ocular aberrations, implying a decline in the mesopic CSF. The increase in aberrations and the consequent deterioration in visual function was more marked in the CRT group.

We evaluate the effect of the emmetropization technique LASIK (laser-assisted in situ keratomileusis) on stereoscopic vision. For this, we used a mirror stereoscope to measure the upper disparity limit D(max) before (with best correction) and after LASIK for 30 patients. The results show that the upper disparity limit declines from 41.1 min of arc on average to 31.3 min of arc after LASIK, being significant in 83% of the patients. This deterioration is significantly correlated with an increase in the postsurgical interocular differences in higher-order aberrations, corneal asphericity, and presurgical anisometropia. New ablation algorithms should minimize interocular differences in order to improve binocular visual performance.

Purpose: To investigate if pre-surgical anisometropia influences the post-LASIK binocular mesopic contrast sensitivity function (CSF)., Methods: Pre- and post-surgical binocular CSF was measured for 54 patients under mesopic conditions. Data on visual acuity and corneal topography were also obtained., Results: The binocular contrast sensitivity declined significantly (r = 0.86; p < 0.001) with increasing pre-surgical anisometropia. Post-surgical interocular differences in corneal asphericity were also associated with increasing pre-surgical anisometropia., Conclusions: Pre-surgical anisometropia may be indicative of a possible significant deterioration of post-surgical mesopic binocular CSF, and therefore should be taken into account before surgery in analysing the possible disadvantages and limitations of refractive surgery.

Purpose: To analyze binocular visual function after LASIK., Methods: Eye aberrometry and corneal topography was obtained for both eyes in 68 patients (136 eyes). To evaluate visual performance, monocular and binocular contrast sensitivity function and disturbance index for quantifying halos were measured. Tests were performed under mesopic conditions., Results: Binocular summation and disturbance index diminished significantly (P<.0001) after LASIK with increasing interocular differences in corneal and eye aberrations. Binocular visual deterioration was greater than monocular deterioration for contrast sensitivity function and disturbance index., Conclusions: Binocular function deteriorates more than monocular function after LASIK. This deterioration increases as the interocular differences in aberrations and corneal shape increase. Improvements in ablation algorithms should minimize these interocular differences.

We present a simple device (called a halometer) to detect and quantify the phenomenon of halos after certain surgical procedures, such as refractive surgery. The task of the subject consists basically of discriminating, after dark adaptation, a small light source around a central high-luminance stimulus. The device, which is connected to a computer, provides a disturbance index to measure the effect of halos on the observer's vision. Tested with normal subjects and patients after LASIK (laser in situ keratomileusis) surgery, this apparatus proved sufficiently sensitive to quantify the halos in subjects who had undergone surgery.

Purpose: To analyze the origin of the changes in corneal asphericity (p-factor) after laser in situ keratomileusis (LASIK) and the effect of postsurgery asphericity on contrast-sensitivity function (CSF) under photopic conditions., Setting: Department of Optics, University of Granada, Granada, Spain., Methods: The p-factor and CSF (best corrected before surgery and 1, 3, and 6 months after surgery) were measured in 24 eyes., Results: An increase in the p-factor after LASIK was noted; there was an 87.2% change in the asphericity using the paraxial formula of Munnerlyn and coauthors. Other factors such as decentration, type of laser, optical role of the flap, wound healing, biomechanical effects, technical procedures, and reflection losses of the laser on the cornea could account for the greater than expected increase (12.8%) in the p-factor. The CSF measurements deteriorated after LASIK; the change was significant (P<.05) in patients with myopia worse than -4.0 diopters at frequencies of 9.2, 12, 15, and 20 cycles per degree., Conclusion: The increase in corneal asphericity after surgery, greater with a higher degree of myopia, and the deterioration in CSF with high myopia justify new ablation algorithms and further study of the variables that could modify the ablation unpredictably.