Spherical Aberration and the Sign of Defocus

Thibos, Larry N.; Bradley, Arthur; Liu, Tao; López‐Gil, Norberto

doi:10.1097/opx.0000000000000040

Cited by 54 publications

(48 citation statements)

References 75 publications

(49 reference statements)

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“…Spherical aberration values of −0.2 to −0.3 μm or less (more negative) for a 5-mm pupil required clinically significant changes (at least 0.25 D) in the best sphere correction to optimize the retinal image quality. Thibos et al 40 also performed computational modelling and investigated the coupling effect of the sign of spherical aberration and defocus on retinal image quality. They reported that positive spherical aberration may have a protective effect against myopia progression because, in combination with hyperopic defocus that is often present in young myopes with a lag of accommodation during near work, 41,42 this improved the retinal image quality in comparison with the combination of negative spherical aberration and hyperopic defocus.…”

Section: Discussionmentioning

confidence: 99%

Higher-Order Aberrations and Axial Elongation in Myopic Children Treated With Orthokeratology

Lau

Vincent

Cheung

et al. 2020

Invest. Ophthalmol. Vis. Sci.

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Citation: Lau JK, Vincent SJ, Cheung S-W, Cho P. Higher-order aberrations and axial elongation in myopic children treated with orthokeratology. Invest Ophthalmol Vis Sci. 2020;61(2):22. https://doi.org/10.1167/iovs. 61.2.22 PURPOSE. This retrospective longitudinal study aimed to examine the relationship between ocular higher-order aberrations (HOA) and axial eye growth in young myopic children undergoing orthokeratology (ortho-k) treatment. METHODS.Axial length and ocular HOA, measured under cycloplegia annually over a 2year period from the right eyes of myopic children, who previously completed ortho-k clinical trials, were retrieved. Linear mixed model analyses were applied to determine the association between ocular HOA, other known confounding variables (age, sex, and refractive error), and axial eye growth. RESULTS.Data from 103 subjects were analyzed. The root-mean square (RMS) values of total ocular HOA (third to sixth orders combined), spherical (Z 0 4 and Z 0 6 combined), and comatic (Z −1 3 , Z 1 3 , Z −1 5 , and Z 1 5 combined) aberrations increased by approximately 3, 9, and 2 times, respectively, after 2 years of ortho-k treatment. After adjusting for age, sex, and refractive error, higher RMS values of total HOA and spherical aberrations were associated with both longer axial length and slower axial elongation (all P < 0.01). For individual Zernike term coefficients, a higher level of positive spherical aberration (Z 0 4 ) was also associated with longer axial length and slower axial elongation (both P < 0.01), after adjusting for baseline HOA. CONCLUSIONS.Ortho-k for myopia control significantly increases the Zernike coefficients and therefore the RMS values for a range of total ocular HOA terms or metrics in children. These findings suggest the potential role of HOA, particularly spherical aberration, as the possible mechanism of slowing axial elongation in ortho-k treatment.

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Section: Discussionmentioning

confidence: 99%

Higher-Order Aberrations and Axial Elongation in Myopic Children Treated With Orthokeratology

Lau

Vincent

Cheung

et al. 2020

Invest. Ophthalmol. Vis. Sci.

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“…[32][33][34][35] It has been hypothesized that the increase in positive SA could provide an additional explanation for the myopia control effects obtained with different treatments in progressing myopes, due to a change in behavior of the accommodative system. [36][37][38] However, there is controversy in the results from different studies aiming to evaluate the actual changes in the accommodative system after Table 2. The slope of the linear regressions is indicative of the direct relation between refractive descriptors.…”

Section: Discussionmentioning

confidence: 99%

Morphology, topography, and optics of the orthokeratology cornea

et al. 2016

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The goal of this work was to objectively characterize the external morphology, topography, and optics of the cornea after orthokeratology (ortho-k). A number of 24 patients between the ages of 17 and 30 years (median=24 years) were fitted with Corneal Refractive Therapy® contact lenses to correct myopia between −2.00 and −5.00 diopters (D) (median=−3.41 D). A classification algorithm was applied to conduct an automatic segmentation based on the mean local curvature. As a result, three zones (optical zone, transition zone, and peripheral zone) were delimited. Topographical analysis was provided through global and zonal fit to a general ellipsoid. Ray trace on partially customized eye models provided wave aberrations and retinal image quality. Monozone topographic description of the ortho-k cornea loses accuracy when compared with zonal description. Primary (C40) and secondary (C60) spherical aberration (SA) coefficients for a 5-mm pupil increased 3.68 and 19 times, respectively, after the treatments. The OZ area showed a strong correlation with C40 (r=−0.49, p<0.05) and a very strong correlation with C60 (r=0.78, p<0.01). The OZ, as well as the TZ, areas did not correlate with baseline refraction. The increase in the eye’s positive SA after ortho-k is the major factor responsible for the decreased retinal optical quality of the unaccommodated eye.

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“…7,23 Thibos et al hypothesize that hyperopic blur can be a risk factor for the progression of myopia when the eye has a negative spherical aberration (which can lead to low contrast in a defocused retinal image). 24,25 Changes in ocular wavefront aberrations occur as accommodation attempts to compensate for retinal defocus. 11 The average change in defocus in the present study showed a clear negative relationship with increasing accommodation stimuli.…”

Section: Discussionmentioning

confidence: 99%

Wavefront aberration changes caused by a gradient of increasing accommodation stimuli

Zhou

Wang

et al. 2014

Eye

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Purpose The aim of this study was to investigate the wavefront aberration changes in human eyes caused by a gradient of increasing accommodation stimuli. Design This is a prospective, single-site study. Methods Healthy volunteers (n ¼ 22) aged 18-28 years whose refraction states were emmetropia or mild myopia, with astigmatism o1 diopter (D), were included in this study. After dilating the right pupil with 0.5% phenylephrine drops, the wavefront aberration of the right eye was measured continuously either without or with 1, 2, 3, 4, 5, or 6D accommodation stimuli (WFA1000B psychophysical aberrometer). The root mean square (RMS) values of the total wavefront aberrations, higher-order aberrations, and 35 individual Zernike aberrations under different accommodation stimuli were calculated and compared. Results The average induced accommodations using 1, 2, 3, 4, 5, or 6D accommodation stimuli were 0.848, 1.626, 2.375, 3.249, 4.181, or 5.085 D, respectively. The RMS of total wavefront aberrations, as well as higher-order aberrations, showed no significant effects with 1-3 D accommodation stimuli, but increased significantly under 4, 5, and 6 D accommodation stimuli compared with relaxed accommodation. Zernike coefficients of Z 0 4 significantly decreased with increasing levels of accommodation. Conclusion Higher-order wavefront aberrations in human eyes changed with increased accommodation. These results are consistent with Schachar's accommodation theory.

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Spherical Aberration and the Sign of Defocus

Cited by 54 publications

References 75 publications

Higher-Order Aberrations and Axial Elongation in Myopic Children Treated With Orthokeratology

Higher-Order Aberrations and Axial Elongation in Myopic Children Treated With Orthokeratology

Morphology, topography, and optics of the orthokeratology cornea

Wavefront aberration changes caused by a gradient of increasing accommodation stimuli

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