Corneal Asphericity and Visual Function After Radial Keratotomy

Fleming, Joseph F

doi:10.1097/00003226-199305000-00009

Cited by 18 publications

(5 citation statements)

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“…The aspheric nature of the normal cornea is well-established 2526. A negative Q -value (prolate) is defined as progressive corneal flattening from center to periphery, whereas a positive Q -value (oblate) is defined as increasing corneal curvature moving from center to periphery 27.…”

Section: Discussionmentioning

confidence: 99%

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Anterior segment study with the pentacam scheimpflug camera in refractive surgery candidates

Hashemi

Falavarjani

Aghai

et al. 2013

Middle East Afr J Ophthalmol

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Purpose:The purpose of this study was to evaluate the anterior segment measurements according to refractive status in a sample of the Iranian population.Setting:Rassoul Akram Hospital, Tehran University of Medical Sciences.Material and Methods:In this study, refractive surgery candidates were assigned according to the refractive error to one of three groups : emmetropia, myopia, and hyperopia. Myopic eyes were further divided to four subgroups : simple myopic group, simple myopic astigmatism group, high myopic group, and high myopia with astigmatism group. Anterior segment measurements with the Pentacam Scheimpflug system were performed in the right eye of all subjects.Results:The study sample was comprised of 283 subjects with a mean age of 29.1 ± 7.5 (standard deviation) years. Mean keratometry reading, Anterior chamber depth (ACD) and volume measurements were significantly higher in the myopic group and mean keratometry reading and anterior chamber angle measurements were significantly lower in the hyperopic group (P < 0.05, all comparisons). Maximum anterior elevation (AEmax) and maximum posterior elevation (PEmax), Q value, progression index, minimum corneal thickness, and corneal volume measurements were similar for all groups (P > 0.05, all comparisons). In the myopic subgroups, AEmax and PEmax and maximum keratometry (Kmax) were significantly higher, and ACD was lower in the astigmatic groups (P < 0.05, all comparisons). The Q value was less negative in low myopia (P < 0.05).Conclusions:Myopic eyes had steeper corneas than hyperopic eyes and anterior chamber measurements were significantly higher in the myopic eyes. In myopic eyes, AEmax and PEmax and Kmax measurements were higher, and ACD measurements were lower in the astigmatic groups.

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Section: Discussionmentioning

confidence: 99%

“…The anterior chamber parameters are clinically useful for planning intraocular lens (IOL) power calculation for cataract surgery and phakic IOL placement in refractive surgery 262728…”

Section: Discussionmentioning

confidence: 99%

Anterior segment study with the pentacam scheimpflug camera in refractive surgery candidates

Hashemi

Falavarjani

Aghai

et al. 2013

Middle East Afr J Ophthalmol

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“…The effect of approximation ͑3͒ can limit the optimization of refractive surgery if the ablation depth is altered to introduce the corneal asphericity. Some practical works 4,17 have shown the influence of corneal asphericity on visual function after surgery, and some authors 5,6,8,18 have mentioned the importance of taking into account corneal asphericity in refractive surgery. In this sense, Jiménez et al 6 demonstrated that, if the algorithm given by Eq.…”

Section: Effect Of Series Expansion When Corneal Asphericity In the Amentioning

confidence: 99%

“…That is, the use of one expression rather than another implies that the postsurgical state of the cornea is different, and we know that small variations in the anterior cornea ͑the surface most responsible for ocular refraction͒ can influence the parameters of the observer's vision. 4,7,8 In this study we theoretically calculated the monochromatic modulation transfer function ͑MTF͒ for two groups of patients with average myopia who were emmetropized when the ablation depth was calculated by Eq. ͑2͒ or its approximation, expression ͑4͒, to determine the influence of this approximation on the image quality of the patient who was operated on.…”

Section: Introductionmentioning

confidence: 99%

Effects on visual function of approximations of the corneal-ablation profile during refractive surgery

2001

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We offer an analysis that shows that the approximations made for the ablation depth during practical refractive surgery, in which the square-root terms are replaced by the first two terms of the series expansion, can limit the visual function of the observer by reducing the modulation transfer function (MTF). To simulate the refractive-surgical operation, we considered two groups of myopic patients with different ametropia who were emmetropized with different ablation profiles. We made the MTF calculations by taking the spherical aberration into account. In addition, a fuller analysis showed that these approximations limit the possibility of considering surfaces that are aspherical for reshaping the anterior cornea to optimize the observer's visual function.

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“…In terms of optics, the reshaping of the cornea involves different aspects that could optimize the visual function (or performance) of the subject undergoing surgery. One with paramount influence over the resulting visual function is corneal asphericity [3][4][5][6][7][8]. Given that the anterior cornea is the surface that most determines the refractive power of the eye, corneal asphericity is decisive in the final retinal image quality of the subject, since eye aberrations (which diminish retinal image quality) depend on the shape of the anterior cornea, among other factors.…”

Section: Introductionmentioning

confidence: 99%