Optimization of the optical performance of variable-power and astigmatism Alvarez lenses

Peloux, Marius; Berthelot, Laurent

doi:10.1364/ao.53.006670

Cited by 15 publications

(9 citation statements)

References 11 publications

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“…17 It is suggested that children from less resourced environments, who are likely not to habitually wear spectacles were at greater risk for less accurate results with adjustable glasses possibly because such children are more tolerant of imperfectly corrected VA and were thus less inclined to carefully adjust the SRSs until optimal VA had been achieved. 17 18 In addition, in this study, the findings revealed that refractive correction using the two self-refraction spectacles were similar and produced similar SE refractive values within acceptable margins of optical error for Alvarez designs, [28][29][30] irrespective of the background of the end user. This was despite the fact that the study found low spectacle wear among the children, with only about a quarter of the study population reporting wearing spectacle, and nearly two-thirds (72.5%) of those wearing spectacles were from urban areas compared with slightly over one-third (27.5%) of rural children.…”

Section: Discussionmentioning

confidence: 60%

Refractive error correction among urban and rural school children using two self-adjustable spectacles

et al. 2023

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ObjectiveSelf-refracting spectacles (SRSs) have different optical and mechanical designs, which may affect the refractive outcome, depending on the experience of the end user. This study compared the performance of two SRS among children in Ghana.Methods and analysisA cross-sectional study of two Alvarez variable-focus SRS designs was conducted. A total of 167 children (mean age 13.6±1.6 years) identified as having refractive error were recruited from 2465 students who underwent screening. Subjects completed self-refraction using FocusSpecs, and Adlens, autorefraction and cycloplegic subjective refraction (CSR) (gold standard). Wilcoxon signed-rank test was used to compare visual outcomes and accuracy of refraction and graphically illustrated using Bland-Altman plots.ResultsEighty (47.9%) urban and 87 (52.1%) rural children were analysed and only about one-quarter 40 (24.0%) wore spectacles. The proportion who achieved visual acuity of ≥6/7.5 with FocusSpec, Adlens, autorefraction and CSR among urban schools were 92.6%, 92.4%, 60% and 92.6%, while those in rural schools were 81.6%, 86.2%, 54.0% and 95.4%, respectively. The mean±SD spherical equivalent errors for urban and rural schools using FocusSpec, Adlens and CSR were −1.05±0.61 D, –0.97±0.58 D and −0.78±0.53 D; and −0.47±0.51 D, –0.55±0.43 D and −0.27±0.11 D, respectively. The mean differences between the two self-refraction spectacles for urban and rural schools were not statistically different (p>0.00) but differed significantly when both were compared with the gold standard (CSR) (p<0.05).ConclusionBackground and refraction experience of school children did not significantly affect self-refraction.

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Section: Discussionmentioning

confidence: 60%

Refractive error correction among urban and rural school children using two self-adjustable spectacles

et al. 2023

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“…For Alvarez lenses, the simple theory presented earlier used the thin‐element approximation, in which any ray crossing the elements is assumed to exit at the same transverse position ( x,y ) on its last surface as it entered on its first surface. As has been pointed out by Peloux & Berthelot, this is not true for ophthalmic lenses, especially since wide angles may be involved and the lenses are made in meniscus form. Peloux and Berthelot show how this disturbs the uniformity of the power distribution across an Alvarez doublet, particularly towards the periphery of the lens, under various circumstances.…”

Section: Discussionmentioning

confidence: 99%

“…[6][7][8] One attractive approach, dating back nearly 50 years, is that of Alvarez. 9,10 In his design and its subsequent developments, [11][12][13][14][15] each lens consists of two closely-spaced components which are translated laterally with respect to one another. In the simplest form of the lens, 9 with the components in the 'zero power' position the thicknesses, t 1 and t 2 , of the two elements can be described by cubic functions of the area coordinates x and y with respect to the coincident centres of the elements, i.e.…”

Section: Introductionmentioning

confidence: 99%

Optical characteristics of Alvarez variable‐power spectacles

Radhakrishnan

Charman

2017

Ophthalmic Physiologic Optic

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“…Compared with other varifocal lenses that are tuned along the optical axis, the Alvarez lens has the potential to achieve a much more compact structure and a faster response, which can be useful in miniature cameras for autofocusing and zooming. Many scholars have simulated and analyzed the optical performance of the Alvarez lens [19][20][21][22][23]. With the maturity of fabrication technology, the actuator of the Alvarez lens has also been developed.…”

Section: Introductionmentioning

confidence: 99%

Experimental study on the focal length of Alvarez lens actuated by dielectric elastomer with different pre-stretched ratios and diameters

Cheng

Chen

et al. 2022

Optical Design and Testing XII

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A varifocal lens with a large focal length range is an indispensable optical part for applications such as biomedical engineering, intelligent robot, industrial image, and virtual-real. A key feature of Alvarez lenses is that the focal length can be tuned using small lateral rather than axial translation. Dielectric elastomer (DE) is a kind of ‘smart’ non-ionic electroactive polymer material. DE can be used as a soft actuator to produce the lateral translation for the Alvarez lens due to its reversibly large strains with a fast response speed, low cost, lightweight, and simple manufacturing process. When a driving voltage is applied to the compliant electrodes of the DE, an electrostatic force named Maxwell stress reduces the distance between the electrodes, thus the DE expands in the lateral directions. The focal length range of the Alvarez lens actuated by DE is not only determined by the parameters of the Alvarez lens but also by the parameters of the DE. To achieve large lateral displacement for achieving a large focal length range, three Alvarez lenses actuated by DE with different pre-stretched ratios and diameters are experimentally studied in this paper. Firstly, we develop and fabricate three Alvarez lenses actuated by DE with different pre-stretched ratios and diameters. Two Alvarez lenses, actuated by DE membranes with the same diameter of 38 mm, but with different pre-stretched ratios, i.e., 200% and 260%, respectively, are fabricated. In addition, an Alvarez lens actuated by DE membrane with a pre-stretched ratio of 260% and diameters of 30 mm is fabricated. Secondly, a driving voltage is applied to the DE membrane to actuate the Alvarez lenses. The driving voltage is generated using a function generator and the amplitude is amplified by a high-voltage converter. Lastly, the focal length ranges of the three Alvarez lenses are measured by the magnification method. A young embryo of the capsella bursa-pastoris section is selected as the imaging object and placed 2.0 mm from the fabricated Alvarez lenses. By measuring the object height in the captured image under different driving voltages using a microscope, the focal lengths of the three Alvarez lenses are obtained. The results show that the Alvarez lens actuated by a dielectric elastomer with a large pre-stretched ratio and diameter has a wider focal length range under the same driving voltage. The study is beneficial to designing and developing an Alvarez lens actuated by DE for optical imaging applications that require wide focal length tuning capacity.

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Optimization of the optical performance of variable-power and astigmatism Alvarez lenses

Cited by 15 publications

References 11 publications

Refractive error correction among urban and rural school children using two self-adjustable spectacles

Refractive error correction among urban and rural school children using two self-adjustable spectacles

Optical characteristics of Alvarez variable‐power spectacles

Experimental study on the focal length of Alvarez lens actuated by dielectric elastomer with different pre-stretched ratios and diameters

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