Corneal shape change during accommodation

Pierscionek, Barbara K.; Popiołek-Masajada, Agnieszka; Kasprzak, Henryk T.

doi:10.1038/eye.2001.246

Cited by 37 publications

(32 citation statements)

References 10 publications

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“…In the 1960s, no change in corneal shape was found to result from accommodation. 5,6 More recent studies found some change in corneal shape but the amount is small 7 and not in the central cornea. 8 The change in BFS, which was due to mydriasis, we found was different from that by Saitoh and colleagues.…”

Section: Discussionmentioning

confidence: 95%

“…They proposed that corneal steepening occurs when the ciliary muscles pull on the scleral spur, trabecular meshwork and the corneal limbus. Earlier studies 5,6 could not find significant corneal change with accommodation but recent studies have found that accommodation can affect the central 7 and mid-peripheral cornea. 8 Buehren and associates 8 using corneal topography proposed that significant cyclotorsion was found as a result of accommodation but no clear evidence of changes on corneal topography accounted for the torsional effect.…”

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confidence: 80%

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The effect of mydriasis from phenylephrine on corneal shape

Huang

Lam

2007

Clinical and Experimental Optometry

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Purpose: A previous study reported that pharmacologically-dilated pupils changed the corneal shape. Researchers used mydriatic agents with significant cycloplegic effect. The current study investigates the effect of mydriasis on corneal shape using phenylephrine alone, where phenylephrine has minimal effect on the accommodative system and whether corneal topography can be done after pupil dilation. Methods: Forty-four young healthy subjects with one eye randomly selected for mydriasis were used in this study. Twenty-two received one drop of 2.5% phenylephrine (group 1); the other 22 subjects had one drop of 0.4% benoxinate instilled prior to the application of 2.5% phenylephrine (group 2). They were matched for age and refractive error. Anterior chamber depth, pupil size and corneal parameters were compared before and after mydriasis. The corneal parameters included best-fit sphere (BFS), surface asymmetry index (SAI), surface regularity index (SRI) and the axial and tangential powers in the form of flattest and steepest powers, and in the form of M, J 0 , and J 45 vector presentation. Results: Group 1 and group 2 subjects had similar pre-mydriatic baseline ocular parameters. The mean (± SD) pupil dilation was 1.24 ± 0.59 mm for group 1 and 1.80 ± 0.95 mm for group 2. The dilation was significantly larger in group 2 (unpaired t-tests: t = 2.36, p = 0.02). There were no significant changes in corneal parameters from mydriasis in either group. Conclusions: Previous investigations used mydriatic agents, which affected not only the pupil size but also accommodation. The current study found that mydriasis from phenylephrine, with minimal effect on accommodation, did not result in significant corneal alteration, and corneal topography can be measured after pupil dilation with phenylephrine.

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Section: Discussionmentioning

confidence: 95%

mentioning

confidence: 80%

The effect of mydriasis from phenylephrine on corneal shape

Huang

Lam

2007

Clinical and Experimental Optometry

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“…Studies have found that accommodation of the lens can induce slight but measurable changes in the central corneal radius of curvature. 1 Subsequent studies have supported this 2 while others have shown that accommodation can produce changes in the shape and size of the globe. 3,4 Perhaps the most evident manifestation of ocular pliability throughout life is the development of myopia that is increasingly found to occur in adults.…”

Section: Introductionmentioning

confidence: 90%

Modelling the elastic properties of the anterior eye and their contribution to maintenance of image quality: the role of the limbus

Asejczyk-Widlicka

Sródka

Kasprzak

et al. 2006

Eye

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Purpose The elastic moduli of the cornea, sclera, and limbus for different corneal eccentricities (e) and varying levels of intraocular pressure (IOP) were modelled in order to determine how the rheological properties, especially those of the limbus, need to alter to maintain optical image quality when the eye is subjected to small variations in IOP. Methods Finite element analysis (FEA) was used to construct eyeball models with four different corneal eccentricities (e ¼ 0, 0.33, 0.5, 0.65). Three values for Young's modulus of the cornea were tested in all models (0.2 megapascal (MPa), 1.2 and 10 MPa). For each corneal modulus, scleral moduli of 3, 4, 5, 7, and 10 times that of the corneal modulus were selected. The limbal modulus was varied to optimise image quality of the eye model subjected to IOP variations of 70.8 mmHg for three different levels of IOP (8,16, and 32 mmHg). Results The elastic modulus of the limbal ring increases with an increase in corneal modulus and rises to a peak when the ratio of scleral to corneal moduli is between 5 and 7 depending on corneal eccentricity. Different levels of IOP produce only slight differences in the relative moduli required to maintain optical image quality. Conclusions The significance of a peak in the value of Young's modulus of the limbus is not clear but suggests that there may be an optimal limbal modulus that must be balanced with the moduli of cornea and sclera for preservation of image quality.

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“…Early studies, which were limited by the technology of the time, used optometers, keratometers, or photokeratoscopes to measure the cornea and suggest that little change in the cornea occurs with accommodation. [14][15][16][17] Pier scionek et al 18 used a modified keratometer to assess the effect of accommodation on central corneal shape and found that several subjects had a significant change in corneal curvature during accommodation; however, no definite trend toward steepening or flattening of the central cornea with accommodation could be demonstrated.…”

mentioning

confidence: 99%