Correlations Between Central and Peripheral Changes in Anterior Corneal Topography After Myopic LASIK and Their Implications in Postsurgical Contact Lens Fitting

Comparison of Corneal Power and Astigmatism between Simulated Keratometry, True Net Power, and Total Corneal Refractive Power before and after SMILE Surgery

Purpose. To compare the mean corneal power (Km) and total astigmatism (Ka) estimated by three methods: simulated keratometry (simK), true net power (TNP), and total corneal refractive power (TCRP) before and after femtosecond laser small incision lenticule extraction (SMILE) surgery. Methods. A retrospective, cross-sectional study. SimK, TNP, and TCRP from a Scheimpflug analyzer were obtained from 144 patients before and 6 months after SMILE surgery. Km and Ka were recorded as the mean of individual paracentral rings of 1.0 to 8.0 mm (R1 to R8). The surgically induced changes in Km (delta-simK, delta-TNP, and delta-TCRP) and Ka (delta-simKa, delta-TNPa, and delta-TCRPa) were compared to the changes in spherical equivalent of the cycloplegic refraction (delta-SE) and astigmatism (delta-RA). Results. Preoperatively, astigmatism values were greatest with simKa from R1 to R5 and greatest with TCRPa from R6 to R8. Astigmatism values were smallest with TNPa from R1 to R7. Postoperatively, astigmatism values were greatest with simKa from R1 to R5 and greatest with TCRPa from R6 to R8. Delta-TCRP₃ and Delta-TCRP₄ matched delta-SE most closely, and delta-TCRPa₃ matched delta-RA most closely. Conclusions. TCRP proved to be the most accurate method in estimating corneal power and astigmatism both before and after SMILE surgery.

Changes in Peripheral Refractive Profile after Orthokeratology for Different Degrees of Myopia

PURPOSE

The purpose of this study was to evaluate the effect of orthokeratology for different degrees of myopia correction in the relative location of tangential (F(T)) and sagittal (F(S)) power errors across the central 70° of the visual field in the horizontal meridian.

METHODS

Thirty-four right eyes of 34 patients with a mean age of 25.2 ± 6.4 years were fitted with Paragon CRT (Mesa, AZ) rigid gas permeable contact lenses to treat myopia (-2.15 ± 1.26D, range: -0.88 to -5.25D). Axial and peripheral refraction were measured along the central 70° of the horizontal visual field with the Grand Seiko WAM5500 open-field auto-refractor. Spherical equivalent (M), as well as tangential (FT) and sagittal power errors (FS) were obtained. Analysis was stratified in three groups according to baseline spherical equivalent: Group 1 [M(Baseline) = -0.88 to -1.50D; n = 11], Group 2 [M(Baseline) = -1.51 to -2.49D; n = 11], and Group 3 [M(Baseline) = -2.50 to -5.25D; n = 12].

RESULTS

Spherical equivalent was significantly more myopic after treatment beyond the central 40° of the visual field (p < 0.001). FT became significantly more myopic for all groups in the nasal and temporal retina with 25° (p ≤ 0.017), 30° (p ≤ 0.007) and 35° (p ≤ 0.004) of eye rotation. Myopic change in FS was less consistent, achieving only statistical significance for all groups at 35° in the nasal and temporal retina (p ≤ 0.045).

CONCLUSIONS

Orthokeratology changes significantly FT in the myopic direction beyond the central 40° of the visual field for all degrees of myopia. Changes induced by orthokeratology in relative peripheral M, FT and FS with 35° of eye rotation were significantly correlated with axial myopia at baseline.

Spherical aberration and the sign of defocus

PURPOSE

Visual sensing of the sign of defocus is important not only for the rapid control of accommodation but also for regulating the slower long-term growth of the eye.

METHODS

We examined the possibility that ocular spherical aberration (SA) elicits a sign of defocus by optical modeling of image formation using the principles of physical optics.

RESULTS

Retinal image contrast, as measured by the area under the visually weighted modulation-transfer function, depends on both the magnitude and the sign of defocus relative to the sign of the SA. Image contrast is greater for hyperopic blur than for myopic blur when SA is positive and vice versa when SA is negative.

CONCLUSIONS

When coupled with Wallman's hypothesis that retinal activity caused by image contrast inhibits eye growth, these results provide a testable hypothesis to account for myopia progression. For example, we suggest that hyperopic blur is a risk factor for myopia progression only when the eye has a negative SA because that is the combination leading to relatively low contrast in the defocused retinal image. Because the likelihood of a negative SA increases with accommodation, avoiding long hours of near work in the presence of accommodative lag may help prevent the onset and progression of myopia.

Peripheral refraction in myopic eyes after LASIK surgery

PURPOSE

To characterize the axial and off-axis refraction across the horizontal meridian of the visual field before and after myopic laser-assisted in situ keratomileusis (LASIK) surgery. This research took place at the Clinical Ophthalmologic-NovoVisión, Madrid, Spain.

METHODS

Twenty-six ODs (mean age ± SD = 30.4 ± 4.8 years) of 26 patients who underwent LASIK surgery to treat myopia between -0.75/-3.88 D of spherical equivalent (M) were included in the study. Peripheral refraction was evaluated by an open field auto-refractor before and after LASIK surgery at 3 months. Along with a complete set of examination procedures to assess suitability for treatment, the central and peripheral refractions were measured along the horizontal meridian up to 35° of eccentricity in the nasal and temporal retinal areas in 5° visual field steps.

RESULTS

Changes in M ranged between 1.85 ± 0.93 D at center to 0.33 ± 0.73 D at 35° in the nasal retina (p < 0.029 for all eccentricities). Treatment induced was symmetric between nasal and temporal visual fields along the horizontal meridian. The degree of myopic increase in relative peripheral refractive error as represented by the spherical equivalent for 30° (r2 = 0.462, p < 0.001) and 35° (r2 = 0.717, p < 0.001) eccentric refraction was correlated with axial spherical equivalent at baseline.

CONCLUSIONS

Peripheral refraction is affected by myopic LASIK surgery. Unlike orthokeratology, which increases the peripheral myopia, LASIK reduces myopia across the horizontal visual field out to at least 35° from fixation.

Multi-aspheric description of the myopic cornea after different refractive treatments and its correlation with corneal higher order aberrations

Background

To analyse the asphericity of the anterior corneal surface (ACS) for different diameters, and correlate those values with corneal higher order aberrations (cHOA) before and after myopic treatments with corneal refractive therapy (CRT) for orthokeratology and customized (CL) and standard laser (SL) assisted in situ keratomileusis (LASIK).

Setting

Clínica Oftalmológica NovoVisión, Madrid, Spain.

Methods

The right eyes of 81 patients (27 in each treatment group), with a mean age of 29.94 ± 7.5 years, were analysed. Corneal videokeratographic data were used to obtain corneal asphericity (Q) for different corneal diameters from 3 to 8 mm and cHOA root mean square (RMS) obtained from Zernike polynomials for a pupil diameter of 6 mm.

Results

There were statistically significant differences in asphericity values calculated at different corneal diameters for different refractive treatments and their changes. The difference between asphericity at 3 and 8 mm reference diameters showed statistically significant correlations with spherical-like cHOA that was also significantly increased after all procedures.

Conclusions

The shift in corneal asphericity and the differences among different treatment techniques are more evident for the smaller reference diameters. These differences can be much reduced or even masked for a peripheral reference point at 4 mm from centre, which is used by some corneal topographers.

Retrospective analysis of changes in the anterior corneal surface after Q value guided LASIK and LASEK in high myopic astigmatism for 3 years

Background

To compare the corneal high-order aberrations (HOAs), asphericity and regularity after Q-value guided laser in situ keratomileusis (LASIK) and laser epithelial keratomileusis (LASEK) in high myopic astigmatism.

Methods

In this retrospectively comparative study, we measured the corneal HOAs, asphericity indices (Q values) and corneal regularity indices preoperatively and 36 months postoperatively in 70 eyes (35 patients) with Q-value guided surgeries. All the patients with high myopic astigmatism were divided into two groups which included 34 eyes underwent LASIK and 36 eyes underwent LASEK procedures. The main impact factors of the high-order aberrations were also analyzed.

Results

In the two groups, the efficacy index was more than 1.00 and safety index approached 1.00 at year 3 postoperatively. Statistically significant (P < 0.05) increased in Q values and main corneal HOAs (spherical aberrations and coma) following Q-value guided LASIK and LASEK procedures. Spherical aberrations increased more in the LASEK group and there was statistically difference compared to the LASIK group (P < 0.05). LASEK had better effects in correcting corneal astigmatism (P < 0.05). All the corneal regularity indices after surgeries increased and there was no significant difference (P = 0.707, P = 0.8 and P = 0.224, respectively) between the two groups. The main impact factors of spherical aberration included the optic zone size, changes of Q value, surgical procedure and the corrected refraction.

Conclusions

In high myopic astigmatism, Q-value guided ablation showed good safety, efficacy and predictability. Q value, regularity indices, spherical aberration and coma increased in both LASIK and LASEK procedures. Astigmatism could be corrected more effectively by LASEK but greater spherical aberration could be created. The difference might be related to the different healing mechanisms. Optic zone size and the corrected refraction might be the main influence factors on the anterior corneal high order aberrations.

Local steepening in peripheral corneal curvature after corneal refractive therapy and LASIK

PURPOSE

The purpose of this study was to assess the changes in curvature along the horizontal meridian of the anterior cornea occurring after refractive surgery and corneal refractive therapy (CRT).

METHODS

One hundred twenty-two eyes of 122 patients (70 female) with a mean (SD) age of 30.6 +/- 7.5 years were retrospectively analyzed in this study. Forty-three of those underwent standard laser in situ keratomileusis (LASIK) ablation, 40 had customized LASIK and 39 had CRT with orthokeratology lenses. Patients in different groups were matched to be comparable in terms of pretreatment refractive error and corneal topographic profiles. Topographical data along the horizontal meridian were collected over a 10 mm corneal diameter in 1 mm steps using the tangential power map from the computer display.

RESULTS

A statistically significant increase in corneal power (p < 0.05) was observed at the nasal and temporal locations between 2 and 3 mm for CRT and 3 and 4 mm for LASIK procedures, from corneal keratometric center. This steepening was more pronounced after CRT treatment (p < 0.05 for all comparisons against LASIK groups) but not significantly different between LASIK groups (p > 0.124, Mann-Whitney Test).

CONCLUSIONS

Both, surgical and non-surgical interventions show a mid-peripheral local corneal steepening. However, the narrower optic zone and higher midperipheral steepening with CRT seems to provide the potential to create a more relative peripheralmyopic increase in corneal power than LASIK, which may have implications in slowing down myopia progression.

Effect of pupil size on corneal aberrations before and after standard laser in situ keratomileusis, custom laser in situ keratomileusis, and corneal refractive therapy

PURPOSE

To evaluate the effect of changing the pupil size on the corneal first-surface higher-order aberrations induced by different refractive treatments: standard laser in situ keratomileusis (LASIK), custom LASIK, and corneal refractive therapy.

DESIGN

Observational study.

METHODS

Eighty-one right eyes from patients with a mean age of 29.94 +/- 7.5 years, of which 50 were female (61.7%), were analyzed retrospectively at the Clínica Oftalmológica NovoVision, Madrid, Spain. Corneal videokeratographic data were used to obtain corneal first-surface higher-order aberrations for aperture diameters from 3 to 8 mm using the Vol-CT software (Sarver & Associates, Inc). Total root mean square (RMS) and RMS for third- to sixth-order Zernike polynomials as well as spherical-like, coma-like, secondary astigmatism, and spherical plus coma-like variables were calculated.

RESULTS

We verified an increase in the higher-order aberration total RMS after treatments of 0.014 +/- 0.025 microm, 0.019 +/- 0.027 microm, and 0.018 +/- 0.031 microm for standard LASIK, custom LASIK, and corneal refractive therapy, respectively, for 3-mm pupil diameter. For the 8-mm aperture diameter, changes in total RMS increased by a factor of 50 compared with the variation for the 3-mm diameter up to 0.744 +/- 0.731 microm, 0.493 +/- 0.794 microm, and 0.973 +/- 1.055 microm for standard LASIK, custom LASIK, and corneal refractive therapy, respectively.

CONCLUSIONS

The 3 techniques increase the wavefront aberrations of the cornea and change the relative contribution of coma-like and spherical-like aberrations. For a large aperture (> 5 mm), corneal refractive therapy induces more spherical-like aberrations than standard and custom LASIK. However, no clinically or statistically significant differences existed for narrower apertures. Standard and custom LASIK did not display statistically significant differences regarding higher-order aberrations.