Equation for Corneal Asphericity After Corneal Refractive Surgery

Purpose To numerically evaluate and compare the tolerance to misalignment and tilt of aspheric intraocular lenses (IOLs) designed for three eyes: with standard cornea and with simulated corneas after myopic and hyperopic laser ablation surgery. Methods Three aspheric IOLs of +20.00 diopter (D) with different spherical aberration (SA) (Z40) values have been designed using a theoretical model eye. Drastic changes on the theoretical eye anterior corneal asphericity have been performed to simulate myopic and hyperopic refractive surgeries. The effect of IOL misalignment and tilt on the image quality has been evaluated using a commercial optical software design for the three eye models. Image quality was assessed from the modulation transfer function (MTF), root mean square (RMS) values of defocus, astigmatism, coma and spherical aberration (Z40), and retinal images obtained from a visual simulator using an aleatory optotype of 0.00 LogMar visual acuity (VA). Results IOL misalignment and tilt reduced MTF values in general, and increased wavefront aberrations errors. Aberration-free IOLs maintained best the MTF values when misalignments were applied, together with good on-axis optical quality. IOLs with negative SA (Z40) correction decreased the MTF value under 0.43 for misalignments values higher than 0.50 mm with the three corneas. The effect of misalignment on RMS astigmatism and coma was correlated with the IOL SA (Z40) and with the three corneas. Conclusions This theoretical study shows that the largest degradation in image quality arises for the IOL with the highest amount of spherical aberration (Z40). Moreover, it has been found that the aspherical design has a more influential role in misalignment tolerance than in tilt tolerance.

Download Full-text

Faculty Opinions recommendation of Topical cyclosporine a treatment in corneal refractive surgery and patients with dry eye.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.718546233.793499173 ◽

2014 ◽

Author(s):

Karl Stonecipher

Keyword(s):

Dry Eye ◽

Cyclosporine A ◽

Refractive Surgery ◽

Corneal Refractive Surgery

Download Full-text

Effect of corneal refractive surgery on accommodative and binocular dysfunctions among civilian pilots in Southwest China

BMC Ophthalmology ◽

10.1186/s12886-021-01855-0 ◽

2021 ◽

Vol 21 (1) ◽

Author(s):

Ye Wu ◽

Zhen Zhang ◽

Meng Liao ◽

Qi Li ◽

Xue Lin Tang ◽

...

Keyword(s):

Binocular Vision ◽

Refractive Surgery ◽

Visual Symptom ◽

Chi Square ◽

Visual Symptoms ◽

Significant Difference ◽

Symptom Scores ◽

Chi Square Test ◽

Corneal Refractive Surgery ◽

Normal Binocular Vision

Abstract Background To analyze whether corneal refractive surgery (CRS) is associated with the distribution of different accommodative dysfunctions (ADs) and binocular dysfunctions (BDs) in civilian pilots. A further aim was to analyze the percentages and visual symptoms associated with ADs and/or BDs in this population. Methods One hundred and eight civilian pilots who underwent CRS from January 2001 to July 2012 (age: 30.33 ± 4.60 years) were enrolled, the mean preoperative SE was − 1.51 ± 1.15 D (range: − 1.00- − 5.00 D). Ninety-nine emmetropic civilian pilots (age: 29.64 ± 3.77 years) who were age- and sex-matched to the CRS group were also enrolled. Refractive status, accommodative and binocular tests of each subject were performed. Visually related symptoms were quantified using the 19-item College of Optometrists in Vision Development Quality of Life (COVD-QOL) questionnaire. The 19 items were summed to obtain visual symptom scores that might indicate visual dysfunctions. The chi-square test was used to analyze differences in percentages of ADs and/or BDs between the CRS and emmetropic groups. The Mann-Whitney U test was used to compare visual symptom scores between pilots with ADs and/or BDs and pilots with normal binocular vision. Results No significant difference was observed between the CRS and emmetropic groups in the overall prevalence of ADs and BDs (15.7% and 15.2% in the CRS and emmetropic groups, respectively; P = 0.185). ADs were present in 4.63% and 3.03% of the CRS and emmetropic group, respectively. BDs were observed in 11.1% and 12.1% of the CRS and emmetropic group, respectively, yielding no significant differences between the groups in the prevalence of ADs or BDs (AD: P = 0.094; BD: P = 0.105). Pilots with ADs and/or BDs had significantly more visual symptoms than pilots with normal binocular vision (p < 0.001). Conclusions CRS for civilian pilots with low-moderate myopia might not impact binocular functions. ADs and/or BDs commonly occur in both emmetropia pilots and pilots who undergo CRS, and pilots with ADs and/or BDs are associated with increased symptoms. This study confirms the importance of a full assessment of binocular visual functions in detecting and remedying these dysfunctions in this specific population.

Download Full-text

Constitutive Laws for Biomechanical Modeling of Refractive Surgery

Journal of Biomechanical Engineering ◽

10.1115/1.2796033 ◽

1996 ◽

Vol 118 (4) ◽

pp. 473-481 ◽

Cited By ~ 122

Author(s):

Michael R. Bryant ◽

Peter J. McDonnell

Keyword(s):

Finite Element ◽

Material Properties ◽

Refractive Surgery ◽

Fiber Optic ◽

Transverse Isotropy ◽

Constitutive Laws ◽

Finite Element Models ◽

Corneal Refractive Surgery ◽

Best Fit ◽

Membrane Inflation

Membrane inflation tests were performed on fresh, intact human corneas using a fiber optic displacement probe to measure the apical displacements. Finite element models of each test were used to identify the material properties for four different constitutive laws commonly used to model corneal refractive surgery. Finite element models of radial keratotomy using the different best-fit constitutive laws were then compared. The results suggest that the nonlinearity in the response of the cornea is material rather than geometric, and that material nonlinearity is important for modeling refractive surgery. It was also found that linear transverse isotropy is incapable of representing the anisotropy that has been experimentally measured by others, and that a hyperelastic law is not suitable for modeling the stiffening response of the cornea.

Download Full-text