The Performance of Four Different Corneal Topographers on Normal Human Corneas and Its Impact on Orthokeratology Lens Fitting

Cho, Pauline; Lam, Andrew; Mountford, John; Ng, Larry Hou-Yan

doi:10.1097/00006324-200203000-00012

Cited by 84 publications

(58 citation statements)

References 16 publications

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“…We did not use the Orbscan system because of its poor clinical performance. 11 The change in axial and tangential powers was not significant from the consideration of flattest and steepest curvatures. When the power vector method was applied, the changes were still small and within onesixth of a dioptre.…”

Section: Discussionmentioning

confidence: 87%

“…This topographer has been demonstrated to be reliable when taking two readings with a score over 90. 11 We adopted the same measurement procedures as in a previous study. 11 Anterior chamber depth was measured using a noncontact biometer IOLMaster (Zeiss Humphrey System, USA).…”

Section: Methodsmentioning

confidence: 99%

“…11 We adopted the same measurement procedures as in a previous study. 11 Anterior chamber depth was measured using a noncontact biometer IOLMaster (Zeiss Humphrey System, USA). 12,13 Three readings were taken and an average was calculated to serve as a baseline.…”

Section: Methodsmentioning

confidence: 99%

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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: 87%

Section: Methodsmentioning

confidence: 99%

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The effect of mydriasis from phenylephrine on corneal shape

Huang

Lam

2007

Clinical and Experimental Optometry

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“…Medidas repetidas realizadas sobre personas, muestran una desviación estándar media de 9,08 µm en los 7 mm centrales de la córnea (10). Sin embargo, la repetitividad y reproducibilidad del Orbscan es baja cuando se trata de medir la curvatura corneal (18), por lo que los valores de curvatura se determinaron mediante viedoqueratoscopía. Estudios previos muestran una alta repetitividadad en las medidas realizadas con el videoqueratoscopio, con una desviación estándar de ± 0,01 mm en personas y en bolas de calibrado (19,20).…”

Section: Sujetos Materials Y Métodounclassified

Variaciones diurnas de espesor y curvatura corneal central y paracentral

Giráldez-Fernández

Diaz-Rey²,

García-Resúa

et al. 2008

Arch Soc Esp Oftalmol

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RESUMENObjetivo: La topografía y espesor de la córnea tienen una gran importancia clínica en la adaptación de lentes de contacto y en cirugía refractiva. Sin embargo, la repetibilidad en las medidas de estos parámetros se ve comprometida por el fenómeno natural de las variaciones diurnas. Nuestro objetivo es determinar las variaciones diurnas de espesor y curvatura corneal central y paracentral durante un periodo de 10 horas. Material y método: Se determinó la curvatura y espesor corneal en los ojos derechos de 10 varones jóvenes mediante Orbscan y videoqueratoscopio respectivamente. Ambos parámetros fueron determinados para la zona central y paracentral a 1 y 2 mm del centro de la córnea, cada dos horas durante un periodo de 10 horas. Resultados: La córnea presentaba su espesor máxi-mo y curvatura mínima al abrir el ojo. Se observó una variación estadísticamente significativa de espesor (ANOVA, método de Schefféc p< 0,05) y de curvatura (ANOVA, método de Tamhane p < 0,05) a lo largo del día en todas las localizaciones estudiadas, si bien la variación y los rangos de valores en la zona paracentral eran mayores. Los valo-ARTÍCULO ORIGINAL ABSTRACT Objective: Corneal topography and thickness has clinical importance in contact lens fitting and refractive surgery, however repeated measurement of corneal thickness and curvature is complicated by the natural phenomenon of diurnal variation. Our aim was determine diurnal variations of central and paracentral corneal thickness and curvature over a period of ten hours. Materials and methods: Corneal thickness and curvature of 10 right eyes of 10 young healthy men were determined by Orbscan Topography System and EyeSys videokeratoscope respectively. Both parameters were determined for central and paracentral regions 1 mm and 2 mm from the centre of the cornea at 2-hour internals for ten hours. Results: The cornea was thickest and flattest on awakening. There was a difference in corneal thickness (ANOVA, Schfféc method p< 0.05) and curvature (ANOVA, Tamhane method p< 0.05) over time for all the corneal locations studied, with greater changes observed in the peripheral corneal data. The minimum value was 10 and 8 hours after eye opening for central and paracentral zones, respectively. Change in central and paracentral corneal

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“…Ltd., Victoria, Australia) has shown to have a high degree of accuracy and precision for measuring spherical and aspherical test surfaces [3] and high repeatability of measurements of in vivo corneas [4]. The device automatically captures four corneal topography images once the projection head, which includes the camera, is properly situated [5].…”

Section: Introductionmentioning

confidence: 99%

Open-access operating algorithms for commercial videokeratographer and improvement of corneal sampling

et al. 2013

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We present an algorithm to process images of reflected Placido rings captured by a commercial videokeratoscope. Raw data are obtained with no Cartesian to polar coordinates conversion, thus avoiding interpolation and associated numerical artefacts. The method provides a characteristic equation for the device and is able to process around 6 times more corneal data than the commercial softwares. Our proposal allows complete control over the whole process from the capture of corneal images until the computation of curvature radii.

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The Performance of Four Different Corneal Topographers on Normal Human Corneas and Its Impact on Orthokeratology Lens Fitting

Cited by 84 publications

References 16 publications

The effect of mydriasis from phenylephrine on corneal shape

The effect of mydriasis from phenylephrine on corneal shape

Variaciones diurnas de espesor y curvatura corneal central y paracentral

Open-access operating algorithms for commercial videokeratographer and improvement of corneal sampling

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