Automatic method of analysis of OCT images in assessing the severity degree of glaucoma and the visual field loss

Robert Koprowski,Marek Rzendkowski,Zygmunt Wróbel

doi:10.1186/1475-925x-13-16

Abstract

IntroductionIn many practical aspects of ophthalmology, it is necessary to assess the severity degree of glaucoma in cases where, for various reasons, it is impossible to perform a visual field test - static perimetry. These are cases in which the visual field test result is not reliable, e.g. advanced AMD (Age-related Macular Degeneration). In these cases, there is a need to determine the severity of glaucoma, mainly on the basis of optic nerve head (ONH) and retinal nerve fibre layer (RNFL) structure. OCT is one of the diagnostic methods capable of analysing changes in both, ONH and RNFL in glaucoma.Material and methodOCT images of the eye fundus of 55 patients (110 eyes) were obtained from the SOCT Copernicus (Optopol Tech. SA, Zawiercie, Poland). The authors proposed a new method for automatic determination of the RNFL (retinal nerve fibre layer) and other parameters using: mathematical morphology and profiled segmentation based on morphometric information of the eye fundus. A quantitative ratio of the quality of the optic disk and RNFL – BGA (biomorphological glaucoma advancement) was also proposed. The obtained results were compared with the results obtained from a static perimeter.ResultsCorrelations between the known parameters of the optic disk as well as those suggested by the authors and the results obtained from static perimetry were calculated. The result of correlation with the static perimetry was 0.78 for the existing methods of image analysis and 0.86 for the proposed method. Practical usefulness of the proposed ratio BGA and the impact of the three most important features on the result were assessed. The following results of correlation for the three proposed classes were obtained: cup/disk diameter 0.84, disk diameter 0.97 and the RNFL 1.0. Thus, analysis of the supposed visual field result in the case of glaucoma is possible based only on OCT images of the eye fundus.ConclusionsThe calculations and analyses performed with the proposed algorithm and BGA ratio confirm that it is possible to calculate supposed mean defect (MD) of the visual field test based on OCT images of the eye fundus.

Highlights

In many practical aspects of ophthalmology, it is necessary to assess the severity degree of glaucoma in cases where, for various reasons, it is impossible to perform a visual field test - static perimetry
Correlations between the known parameters of the optic disk as well as those suggested by the authors and the results obtained from static perimetry were calculated
Analysis of the supposed visual field result in the case of glaucoma is possible based only on OCT images of the eye fundus

Summary

Results

The obtained result LRNFL*(θ,ρ), the ROI in the polar coordinate system (Figure 7), is the basis for further analysis. Based on the proposed ratio wBGA, its correlation with the results of perimetry was determined It was compared with the results obtained only on the basis of known software (features w(1) to w(29)). The following results were obtained: Correlation of classes 1, 2, 3 (obtained from features w(1) to w(29)) with the results obtained from perimetry is 0.78, Correlation of the proposed ratio wBGA referred to the described method of image analysis and processing with the results of perimetry is 0.86 – Figure 10.

Conclusions

Introduction

Methods