[Setting the preferential retinal locus. Part 1. Analysis of the rehabilitation results as a function of positioning]

INTRODUCTION

The aim of this study was to compare the various positions of preferred retinal locus (PRL) with the results of low vision rehabilitation to reading in view to elucidate the mechanisms involved.

MATERIAL AND METHODS

We studied 100 visually impaired subjects who came to the center for rehabilitation of low vision. The technique is based on a scanning laser ophthalmoscope recording, compared with angiofluorographic pictures to obtain the PRL position with respect to the fovea.

RESULTS

It is shown that unsuccessful rehabilitations are not related to the eccentricity or to the angular value of the PRL but are only correlated to its absence. The difficulties that arise from the multiplicity of the PRL or from the confinement of the fovea by an annular scotoma can be overcome with the help of rehabilitation.

CONCLUSION

The upper and right positions are manifestly dominant, but they do not favor reading or writing. We believe that their purpose is to favor the integration of the new visual message of visually impaired people to facilitate their daily life activities. Therefore, using one or another of these peexisting PRL during eccentric viewing training should be preferred.

[Quantitative and spatial analysis in image processing: study of drusen distribution from the foveal center in age-related macular degeneration]

Angiofluorograms were obtained from 58 patients presenting posterior pole drusen due to age-related macular degeneration. These frames underwent image processing by morphological mathematics algorithms. The detection sensitivity of this algorithm is 78%. We present a quantitative and spatial analysis of drusen distribution from the foveal center in the form of a graph. This technique may allow for multi-date comparisons, by using a graphic representation of this risk factor for age-related macular degeneration.

Mathematical morphology in computerized analysis of angiograms in age-related macular degeneration

This paper deals with image processing of numerical retinal angiograms in order to facilitate diagnosis and follow-up in age-related macular degeneration (AMD) which is currently the main cause of blindness in industrialized countries. A computerized scheme using principally mathematical morphology operators is proposed for detecting and counting drusen, which are precursor lesions of the ocular fundus. In order to check the feasibility of this approach, results relative to 58 retinal images are compared with those given by three retinal specialists independently. From manual counting measures it is found that interobserver correlation coefficients lie in the range 0.71-0.78. On the other hand, a correlation coefficient of 0.89 is obtained when the average of the three expert countings is compared with the drusen number given by the computerized method. This coefficient is improved from 0.89 to 0.93 by processing only frames captured immediately after the appearance of a dye consecutive to intravenous sodium fluorescein injection. Compared to the manual analysis which is, among other things, tedious and time consuming, the computerized analysis is both quicker and more objective. Validation by the practitioner is however necessary, given possible detection errors. The proposed computerized scheme for detecting and counting drusen may be easily automated and so should prove useful in clinical studies which involve high volume analysis of retinal angiograms.