Improved Method for Calculation of Corneal Topography for Any Photokeratoscope Geometry

Saarloos, van; Ij, Constable

doi:10.1097/00006324-199112000-00010

Cited by 33 publications

(13 citation statements)

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“…Some insights may be found in (9)(10)(11)(12)(13)(14)(15)(16)(17) , just to name a few. We will describe here only the method that we used, which may be described as the calibrated sphere algorithm (18) or the lookup table method.…”

Section: Calculating Radius Of Curvature and Powermentioning

confidence: 99%

Videokeratograph (VKS) for monitoring corneal curvature during surgery

Carvalho¹,

Romão²,

Tonissi³

et al. 2002

Arq. Bras. Oftalmol.

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Arq Bras Oftalmol 2002;65:37-41 Purpose: We have developed an instrument for computerized surgical videokeratography. A corneal central region of approximately 7.00 mm in diameter may be analyzed, providing the surgeon with information of the power and the astigmatism. Methods: The system is based on a fiber optic Placido disc projecting cone, which is attached to the objective lens of a Zeiss compatible surgical microscope. At the beam splitter we installed a monochromatic high resolution camera. A frame grabber is installed on a PC and images are digitized at a 480x640 resolution. Image processing is used for edge detection of rings. Results: Calibrating curves based on 4 spherical surfaces were generated and approximately 3600 points are calculated for each examination. Preliminary measurements on 10 healthy corneas were compared with those of an EyeSys System 2000 Corneal Topographer. Mean deviation was 0.05 for radius of curvature, 0.24 D for the power and 5.0 degrees for the cylinder. Conclusions: This surgical VKS, with some hardware and software improvements, may be used to reduce residual astigmatisms in conventional cataract and keratoplasty. It could also be used to gather preoperative data in corneal topography assisted LASIK.Videoceratógrafo para monitoramento da curvatura da córnea durante a cirurgia * Mantém vínculo com a EyeTec Equipamentos Oftálmi-cos Ltda.(www.eyetec.com.br), empresa que fabrica a versão comercial do instrumento apresentado.

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Section: Calculating Radius Of Curvature and Powermentioning

confidence: 99%

Videokeratograph (VKS) for monitoring corneal curvature during surgery

Carvalho¹,

Romão²,

Tonissi³

et al. 2002

Arq. Bras. Oftalmol.

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“…Due to its simplicity, it is widely used in undergraduate courses in optometry, ophthalmology and vision science. The improvement of corneal topography techniques in the late 80s and along the 90s [5][6][7][8][9][10][11][12][13][14] allowed the inclusion of more precise corneal surface data into schematic eye models. This represented an important progress in ophthalmology, as the cornea contributes to approximately 2/3 of the overall refractive power of the eye.…”

Section: Introductionmentioning

confidence: 99%

Different schematic eyes and their accuracy to the in vivo eye: a quantitative comparison study

Almeida¹,

Carvalho²

2007

Braz. J. Phys.

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Current ophthalmic technology allows the manipulation of eye components, such as anterior cornea and lens, of the human eye with a considerable precision and customization. This technology opens up the possibility of exploiting some characteristics of the eye in order to improve the methods of correcting optical aberrations. Moreover, product development and research for the eye-care professional has reached very high standards, since there is nowadays software available to design and simulate practically any mechanical or optical characteristic of the product, even before it is thrown into production line. Although quite similar in the general form, different human eye models simulate the image formation by considering different property combinations in the constitutive elements of the eye structure (such as refraction index and surface curvatures), producing retinal images that resemble very closely those of the biological eye. Using optical design software, we have implemented a simulation of 5 well-known schematic eyes available in the literature. These models were the Helmholtz-Laurance, Gullstrand, Emsley, Greivenkamp and Liou & Brennan. The optical performance of these different models was compared using different quantitative optical quality parameters. The model of Liou and Brennan, contains features of the biological eye that were not considered in previous models, as the distribution of a gradient refraction index and a decentered pupil. Furthermore, it has great reliability since it takes into account the mean value of empirical measurements of the in vivo eye in order to define size and parameters such as anterior and posterior curvature of cornea, lens, axial length, etc. Comparisons between the MTF (Modulation Transfer Function), spot diagrams and ray fan showed the difference in image quality between eye models, and the Strehl Ratio was also used as a parameter of comparison. A careful comparison between the different models showed that the first four schematic eyes have better optical quality than what is expected for the general and healthy emmetropic in vivo eye. Liou and Brennan schematic eye is the one that most closely resembles the in vivo biological eye. Therefore, in applications, such as research or product development for customized vision correction, which must consider optical properties intrinsic to the biological eye, we recommend this latter model; for applications that do not require refraction-limited performance, most of the other models should be a good approximation.

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“…Alguns argumentam que a região central da córnea tem formato esférico [9], outros afirmam que tem um formato elíptico [10], e os trabalhos mais recentes propõem métodos para fazer reconstruções independentes de curvas algébricas pré-determinadas [11,12,13] ou fazer utilização de técnicas de traçado de raio (ray tracing) para achar a melhor superfície que descreve a córnea [14,15]. A precisão do topógrafo está baseada na grande quantidade de anéis projetados, os quais garantem que quase toda a córnea pode ser mapeada; e nos algoritmos para fazer a reconstrução, cada vez mais sofisticados.…”

Section: Ceratômetro De Troutmanunclassified

“…Muitos estudos têm sido feitos no sentido de descrever a superfície da córnea [7,9,10,11,12,13,14,15,16,17,18]. Não é uma tarefa simples pois a córnea não é comparável a nenhum material sintético conhecido, portanto não sabemos as relações entre as diferentes tensões superficiais e os possíveis formatos que a córnea pode assumir, tornando extremamente difícil qualquer tipo de previsão.…”

Section: Os Diversos Modelos Matemáticos Para Cálculo Do Contorno Da unclassified

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Desenvolvimento de um instrumento computadorizado para medida da curvatura da cornea durante o ato cirúrgico.

Carvalho¹

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Improved Method for Calculation of Corneal Topography for Any Photokeratoscope Geometry

Cited by 33 publications

References 0 publications

Videokeratograph (VKS) for monitoring corneal curvature during surgery

Videokeratograph (VKS) for monitoring corneal curvature during surgery

Different schematic eyes and their accuracy to the in vivo eye: a quantitative comparison study

Desenvolvimento de um instrumento computadorizado para medida da curvatura da cornea durante o ato cirúrgico.

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