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Esotropia in paediatric aphakic patients: the role of botulinum toxin
Published in Jan-Tjeerd de Faber, 28th European Strabismological Association Meeting, 2020
When using high plus spectacle lenses, spherical aberration at the lens margin optically reduces vision in the deviated eye. Or a large angle of deviation can make contact lenses fitting difficult. Because of the variability of the angle, the strabismic surgery is frequently postponed until reliable measures are available. Consecutive exotropia is not unusual in these cases and amblyopia is exacerbated by the sensory deficit imposed by aphakia.
Optical and visual metrics
Published in Pablo Artal, Handbook of Visual Optics, 2017
where the Seidel coefficients At, Ad, Aa, Ac, and As represent tilt (distortion), defocus (curvature of field), astigmatism, coma, and spherical aberration, respectively. Spherical aberration affects rays from on-axis points when the optical surfaces do not have the shape needed to bring all rays to a focus. The other aberrations affect rays from points off the axis. These rays pass through a system that, from their perspective, is tilted and asymmetric; so light is not brought to a sharp focus (astigmatism and coma), images are on a curved surface instead of a flat plane (curvature of field), and, finally, images lie at a nonproportional distance from the axis (distortion).
Perceptions of potential barriers to soft contact lens wear among university students in Jordan
Published in Clinical and Experimental Optometry, 2023
Mera F Haddad, May M Bakkar, Mohammad Al Qadire
Compared to spectacles, contact lenses provide many benefits. These include better field of view, since there is no obstruction in the field of vision that could possibly be caused by frames when wearing spectacles. Contact lenses are also considered a better solution to correct high refractive errors and irregular astigmatism through providing better visual performance, reducing spherical aberration and prismatic effect associated with high refractive error.7 Contact lenses also enhance peripheral vision through lens movement during eye rotation.8 Additionally, they are more comfortable than spectacles as they do not bear any weight on the face and ears beside the preferred cosmetic appearance achieved with contact lenses compared to spectacles.9,10 Quality of life for children and teens has been greatly improved with contact lenses compared to spectacles. Contact lenses improve how children feel about their appearance, and increase participation in physical activities and social acceptance, resulting in greater satisfaction of their refractive error correction.10–12
Evaluation of Visual Quality in Pseudophakic Eyes with Different Ocular Spherical Aberrations
Published in Current Eye Research, 2019
Xuan Liao, Jia Lin, Qingqing Tan, Baiwei Wen, Jing Tian, Changjun Lan
Optical aberrations have a significant impact on the image quality of retina.1 Of all types of higher-order aberrations, spherical aberration (SA) is the only on-axis and rotationally symmetric aberration that is caused by different refraction between peripheral rays and central rays that reach the retina at the same time. In human eyes, a transparent medium such as the cornea or the crystalline lens can refract peripheral rays to cross optical axis in front of (i.e. positive SA) or behind (i.e. negative SA) the focal point of central area. To be specific, cornea is a relatively stable optical system with positive SA throughout a lifetime, while lenticular SA changes from negative to positive value with aging. Thereby, in a young eye, corneal and lenticular aberrations tend to neutralize each other, just like the coupling of two optical systems, so as to achieve optimized optical quality and visual function.2
Comparison of visual performance between two aspheric monofocal intraocular lens models
Published in Clinical and Experimental Optometry, 2023
Francisco Poyales, Nuria Garzón, Laura Rico, Ying Zhou, María S Millán, Fidel Vega
The human cornea is naturally aspheric, usually showing greater curvature in its central region and flattening out as we move towards the periphery (prolate shape). The presence of high levels of spherical aberration usually causes a decrease in retinal image contrast and affects visual quality, particularly under mesopic conditions.27 On average, corneal spherical aberration is slightly positive (between +0.27 and +0.30 µm for an entrance pupil of 6 mm)28 and remains stable throughout the lifetime of an individual. Some studies suggest that it might not be necessary to fully correct spherical aberration; in fact, it has been claimed that it is advisable to leave the eye with a slightly positive (+0.10 µm) residual aberration.29,30