Drusen volume development over time and its relevance to the course of age-related macular degeneration

Abstract

Aims: To quantify the change in drusen volume over time and identify its prognostic value for individual risk assessment.

Methods: A prospective observational study over a minimum of 3 years and maximum of 5 years and follow-up examination every 3 months was conducted at the ophthalmology department of the Medical University of Vienna. 109 patients presenting early and intermediate age-related macular degeneration (AMD) were included, of which 30 patients concluded a regular follow-up for at least 3 years. 50 eyes of 30 patients were imaged every 3 months using spectral-domain and polarisation-sensitive optical coherence tomography (OCT). Drusen volume was measured using an automated algorithm. Data of a 6-month follow-up were segmented manually by expert graders.

Results: Gradings from 24 000 individual B-scans showed solid correlation between manual and automated segmentation with an initial mean drusen volume of 0.17 mm³. The increase in drusen volume was shown to be comparable among all eyes, and a model for long-term drusen volume development could be fitted as a cubic polynomial function and an R²=0.955. Spontaneous drusen regression was observed in 22 of 50 eyes. In this group, four eyes developed choroidal neovascularisation and three geographic atrophy.

Conclusions: Drusen volume increase over time can be described by a cubic function. Spontaneous regression appears to precede conversion to advanced AMD. OCT might be a promising tool for predicting the individual risk of progression of AMD.

Keywords: Degeneration; Imaging; Retina.

Figure 1

Calculating the drusen volume growth model. The upper left image shows the extrapolation of drusen progression based on sequential reconstruction over a long-term period. In the upper right image, the extrapolation for the preregression phase is shown, and in the bottom left image for the regression and postregression phase. In the bottom right image, the growth function is displayed.

Figure 2

Bland–Altman plot showing the agreement between the drusen volume measurements. The y-axis shows the difference between both measurements (spectral-domain optical coherence tomography (SD-OCT) minus polarisation-sensitive optical coherence tomography (PS-OCT) volume), the x-axis the mean volume of both measurements.

Figure 3

Development of drusen volume of all eyes during study period. Different colours represent the course in individual eyes. The top image shows the complete development, the image in the centre the preregression phase. In the bottom image, the drusen volume regression phase and development in the postregression phase is shown.

Figure 4

Examples of drusen development. In the top image, the volume development of three individual eyes from three different patients is shown. Fundus images, drusen maps and macular B-scans of representative visits of the blue line 1 are shown in the central three rows. The two rows below show the drusen maps and B-scans of the green line 2, which developed geographic atrophy at month 46, and the bottom two rows show the drusen maps and B-scans of the red line 3, which developed choroidal neovascularisation at month 34.