The Topography of the Central and Peripheral Cornea

Read, Scott A.; Collins, Michael J.; Carney, Leo G.; Franklin, Ross

doi:10.1167/iovs.05-1181

Cited by 100 publications

(57 citation statements)

References 44 publications

(55 reference statements)

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“…8,1,14,18,25 In our study the trend and pattern of astigmatism in different age groups present results which are comparative with the other Indian and Asian studies. 22,23,26 …”

Section: Discussionsupporting

confidence: 56%

“…In different Asian and Indian studies percentage of prevalence varies from 13 per cent to 30% or higher depending on the age or ethnic groups. [13][14][15][16][17] Human infants exhibit both high prevalence and high degrees of astigmatism, largely corneal in origin than in schoolchildren and is also known to vary with ethnicity. 8,12,16,[18][19][20][21] The reported prevalence of astigmatism in children aged 3 to 6 years varies in different studies and in different ethnicities.…”

Section: Discussionmentioning

confidence: 99%

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Profile of astigmatism in school going children at state level hospital in Uttarakhand

Gupta¹,

Vats²,

Tyagi³

2016

Int J Res Med Sci

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“…8,1,14,18,25 In our study the trend and pattern of astigmatism in different age groups present results which are comparative with the other Indian and Asian studies. 22,23,26 …”

Section: Discussionsupporting

confidence: 56%

Section: Discussionmentioning

confidence: 99%

Profile of astigmatism in school going children at state level hospital in Uttarakhand

Gupta¹,

Vats²,

Tyagi³

2016

Int J Res Med Sci

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“…11 Corneal astigmatism was classified as being stable, reducing or increasing in the peripheral cornea. Of the subjects with significant corneal astigmatism tested in this study, astigmatism was found most commonly to be reducing (47 per cent of astigmatic subjects) or stable (44 per cent) in the peripheral cornea.…”

Section: Components Of Astigmatismmentioning

confidence: 99%

A review of astigmatism and its possible genesis

Read

Collins

Carney

2007

Clinical and Experimental Optometry

230

205

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Astigmatism is a refractive condition encountered commonly in clinical practice. This review presents an overview of research that has been carried out examining various aspects of this refractive error. We examine the components of astigmatism and the research into the prevalence and natural course of astigmatic refractive errors throughout life. The prevalence of astigmatism in various ethnic groups and diseases and syndromes is also discussed. We highlight the extensive investigations that have been conducted into the possible aetiology of astigmatism, however, no single model or theory of the development of astigmatism has been proven conclusively. Theories of the development of astigmatism based on genetics, extraocular muscle tension, visual feedback and eyelid pressure are considered. Observations and evidence from the literature supporting and contradicting these hypotheses are presented. Recent advances in technology such as wavefront sensors and videokeratoscopes have led to an increased understanding of ocular astigmatism and with continued improvements in technology, our knowledge of astigmatism and its genesis should continue to grow.

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“…It is important to note that though selective individual ocular component modeling yielded the required levels of myopia and their respective models, all the parameters were found to be within the range of normal values of the population. [53][54][55][56][57][58][59][60] In this experiment, we considered the retinal surface to be a rotationally symmetric aspheric surface for all the myopic models and assumed it to be invariable over the range and types of myopic prescription chosen. The rationale was to limit the degrees of freedom so as to keep the experiment simpler.…”

Section: Discussionmentioning

confidence: 99%

Do Peripheral Refraction and Aberration Profiles Vary with the Type of Myopia? - An Illustration Using a Ray-Tracing Approach

Bakaraju

Ehrmann

Papas

et al. 2009

Journal of Optometry

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Myopia is considered to be the most common refractive error occurring in children and young adults, around the world. Motivated to elucidate how the process of emmetropization is disrupted, potentially causing myopia and its progression, researchers have shown great interest in peripheral refraction. This study assessed the effect of the myopia type, either refractive or axial, on peripheral refraction and aberration profiles. METHODS: Using customized schematic eye models for myopia in a ray tracing algorithm, peripheral aberrations, including the refractive error, were calculated as a function of myopia type. RESULTS: In all the selected models, hyperopic shifts in the mean spherical equivalent (MSE) component were found whose magnitude seemed to be largely dependent on the field angle. The MSE profiles showed larger hyperopic shifts for the axial type of myopic models than the refractive ones and were evident in -4 and -6 D prescriptions. Additionally, greater levels of astigmatic component (J180) were also seen in axial-length-dependent models, while refractive models showed higher levels of spherical aberration and coma. RESUMENSe considera que la miopía es el error refractivo más frecuente a nivel mundial en niños y en adultos jóvenes. Con el objetivo de esclarecer de qué modo se ve perturbado el proceso de emetropización, potencialmente dando lugar a la aparición de miopía y a su progresión, los investigadores se han mostrado muy interesados en estudiar la refracción periférica. Este estudio evalúa en qué medida la refracción periférica y los perfiles de aberración dependen del tipo de miopía predominante, ya sea refractiva o axial. MÉTODOS:Partiendo de modelos de ojo esquemáticos adaptados al caso de la miopía y utilizando un algoritmo de trazado de rayos, se calcularon las aberraciones periféricas, incluyendo el error refractivo, en función del tipo de miopía. RESULTADOS: En todos los modelos estudiados, se observó un cambio o desplazamiento hipermetrópico en el equivalente esférico medio (EEM), cuyo valor parecía depender mayormente del ángulo analizado (excentricidad). En los perfiles de EEM se aprecia que dicho desplazamiento hipermetrópico es mayor para los modelos de miopía de tipo axial que para los de tipo refractivo, diferencia que se hace evidente en los casos correspondientes a -4 D y a -6 D. Además, se observó que el coeficiente asociado al término de astigmatismo (J180) presentaba un valor más alto en los modelos con un mayor peso de la miopía axial, mientras que en los modelos predominantemente refractivos se obtuvieron mayores niveles de aberración esférica y de coma. CONCLUSIONES: Este estudio ha concluido que aquellos ojos miopes donde prima la componente axial pueden presentar un mayor riesgo de progresión que ojos miopes que tengan errores refractivos similares pero donde prime la componente refractiva. Esta predicción surge de los resultados teóricos obtenidos en modelos de ojos utilizando un algoritmo de trazado de rayos, por lo que necesitan ser confirmados experimentalment...

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The Topography of the Central and Peripheral Cornea

Abstract: Highly significant changes occur in the shape of the cornea in the periphery. On average, the peripheral cornea becomes significantly flatter and slightly less astigmatic than the central cornea. A conic section is a poor estimator of the peripheral cornea.

Cited by 100 publications

References 44 publications

Profile of astigmatism in school going children at state level hospital in Uttarakhand

Profile of astigmatism in school going children at state level hospital in Uttarakhand

A review of astigmatism and its possible genesis

Do Peripheral Refraction and Aberration Profiles Vary with the Type of Myopia? - An Illustration Using a Ray-Tracing Approach

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