Publicado em: 12/12/2013

Defessa de Mestrado em Processamento Gráfico

UNIVERSIDADE FEDERAL DO RIO GRANDE DO SUL

INSTITUTO DE INFORMÁTICA

PROGRAMA DE PÓS-GRADUAÇÃO EM COMPUTAÇÃO

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DEFESA DE DISSERTAÇÃO DE MESTRADO

Aluno: André Luís Beling da Rosa

Orientador: Prof. Dr. Manuel Menezes de Oliveira Neto

Título: An Accessible Approach for Corneal Topography

Linha de Pesquisa: Processamento Gráfico

Data: 19/12/2013

Hora: 8h30min

Local: Prédio 43413 – Auditório Inferior, Instituto de Informática

Banca Examinadora:

Prof. Dr. Anderson Maciel (UFRGS)

Prof. Dr. Horacio Enrique Fortunato (UNIRITTER)

Prof. Dr. Airton Leite Kronbauer (UFRGS)

Presidente da Banca: Prof. Dr. Manuel Menezes de Oliveira Neto

Abstract:

Corneal topography consists of measuring the corneal shape, which is a key factor for visual acuity. The exam is used, for instance, in keratoconus detection, personalized contact lens fitting, in pre- and post-procedures associated with refractive surgery and corneal transplants. This thesis presents an accessible, inexpensive and portable approach to perform corneal topographies. The results obtained with our prototype show a mean difference of about 0.02 millimeters, equivalent to 0.5% of the mean corneal radius, when compared to topographies acquired with a commercial device. Our approach is based on Placido’s disks, a set of concentric disks that are placed in front of the patient’s eye and reflected on the cornea. Observing the deformation of the projected pattern, one can identify some refractive conditions (e.g., astigmatism, keratoconus) and estimate the patient’s corneal topography. We have built a clip-on device to be used with a cell phone to emit the patterns, which are then captured by the cell phone camera. We use a software pipeline to enhance the images, segment the patterns, associate the emitted pattern with the captured one to sample the signal, and finally estimate the corneal surface. The estimated shape is then decomposed using Zernike polynomials in components with specific optical meanings. We have evaluated the results obtained with our prototype in three ways: visual inspection of keratoscopies, keratoconus detection, and comparison with the results produced by a commercial corneal topographer. According to such analysis, our device can be used for screening of individuals with keratoconus, and to obtain corneal topographies with 0.02-millimeter differences with respect to the results obtained with a commercial corneal topographer.

Keywords:  Corneal topography, Image processing, Zernike polynomials, Geometric reconstruction.

Divulgação PPGC