G5 Doctoral dissertation (article)
Determining the size of retinal features : a study on the magnification of a fundus photograph and its application in the development of reaction time perimetry




List of Authors: Knaapi Laura
Publisher: University of Turku
Place: Turku
Publication year: 2018
ISBN: 978-951-29-7307-1
eISBN: 978-951-29-7308-8

Abstract

Fundus photography plays a vital part in the diagnosis and follow-up of ocular pathology. Both the camera optics and the ametropia of the given eye influence the magnification of a fundus photograph. Determining the true size of retinal features thus requires the use of mathematical equations. 

This study was aimed at evaluating the formula of Bennett et al. (1994) for determining the size of retinal features in two different clinical settings. First, its use was verified with healthy volunteers by measuring the macula-disc center distance from fundus photographs taken with the telecentric Zeiss fundus camera, and by calculating the theoretical location of the blind spot based on the macula-disc center distance. These results were compared with the results from a visual field examination using the Octopus custom made Blind Spot visual field program. The theoretical location of the blind spot, derived from calculations based on fundus photography, corresponded to the visual field examination derived location of the physiological blind spot. In addition, the magnification characteristics of the Topcon fundus camera were assessed by calculating its conversion factor. 

Secondly, the accuracy of the formula was evaluated after cataract surgery and IOL implantation. Cataract surgery and IOL implantation did not have an effect of clinical significance on the magnification of a fundus photograph taken with the telecentric Zeiss and Topcon fundus cameras even after the ametropia and the anterior chamber depth were changed due to surgery. 

Thirdly, the use of the macula-disc center distance as a reference tool for determining the size of retinal features from fundus photographs was evaluated in prematurely born children aged from 10 to 11 years. The macula-disc center distance was found to be close to a constant. 

Lastly, a novel method for examining the visual field was introduced. Reaction time perimetry was shown to be able to detect the physiological blind spot. The location of the blind spot was verified with two independent methods: First, by calculating the theoretical location of the blind spot based on the macula-disc center distance derived from fundus photographs taken with the telecentric Zeiss fundus camera, and second, by visual field examination using the Octopus custom made Blind Spot visual field program. Validating the use of reaction time perimetry in different ocular pathology requires further studies.



Internal Authors/Editors

Last updated on 2019-21-08 at 16:45