Vessel density and multispectral fractal dimensions in normal tension glaucoma

Abstract

Purpose : Impaired ocular blood flow has been proposed as an important component in the pathogeneis of glaucoma. Optical coherence tomography angiography (OCTA) measurements of vessel density (VD), a marker of ocular perfusion, are reduced in glaucoma; however, other vascular characteristics may be important. Fractal analysis, which can be used to quantify the complexity of vascular networks, is a useful surrogate of health of ocular microcirculation in several conditions including diabetic retinopathy. The aim of this study was to investigate the relationship between structural and functional markers of glaucoma severity, OCTA VD and multispectral fractal dimensions (MSFD) in patients with normal tension glaucoma (NTG).

Methods : A cross-sectional study of patients with NTG seen at a university hospital. Participants had a comprehensive ophthalmic examination including intraocular pressure (IOP) phasing, measurement of corneal hysteresis and standard automated perimetry. OCTA (RTVue XR 100 Avanti) was used to obtain 3x3 mm² macular and optic nerve head images to determine vessel density. OCT was also used to measure circumpapillary retinal nerve fibre layer (RNFL) thickness, inner macular thickness (IMT) and ganglion cell complex (GCC) thickness. MSFD was calculated using custom built software developed at the Universty of Edinburgh which automatically detects vessels in OCTA images and quantifies fractal dimensions (Vessel Assessment and Measurement Platform for Images of the Retina (VAMPIRE)).

Results : 57 eyes of 29 subjects were included, with a mean age of 66.5 years. The mean IOP at diagnosis and mean deviation (MD) were 15.7mmHg (SD 2.4) and -4.5dB (SD 4.5) respectively. OCTA vessel density was negatively associated with age (P= 0.011, R²= 0.116) but positively associated with MD, MSFD, average IMT and GCC thickness (P= 0.001, 0.005, 0.001, 0.006 and R²= 0.241, 0.133, 0.205, 0.133 respectively). There was a trend towards a negative association between age and MSFD, but this did not reach statistical significance (P= 0.062). MSFD was not associated with gender, MD, average GCC, cpRNFL or inner macular thicknes.

Conclusions : Lower macular vessel density was significantly associated with structural and functional markers of glaucoma severity. Multispectral fractal dimensions was positively associated with vessel density but was not associated with structural or functional markers of glaucoma.

This is a 2020 ARVO Annual Meeting abstract.