Table 1

Glossary of retinal imaging technologies and parameters used in studying Alzheimer’s disease

Retinal imaging technologiesParameters measured from retinal imagingDescriptions of the parameters
Spectral-domain optical coherence tomography (SD-OCT)Peripapillary retinal nerve fibre layer (RNFL) thicknessA thickness of RNFL layer in peripapillary region to assess retinal ganglion cell (RGC) axon. Traditionally, peripapillary RNFL thickness is calculated along a 3.4 mm circle around optic disc.
Macular ganglion cell inner plexiform layer (GC-IPL) thicknessA combined thickness of ganglion cell layer and inner plexiform layer in macular region to assess RGC cell bodies and dendrites.
Macular ganglion cell complex (GCC) layerA combined thickness of RNFL, ganglion cell layer and inner plexiform layer in macular region to assess RGC axon, cell bodies and dendrites.
Macular thickness or volumeA thickness or volume between inner limiting membrane and the retinal pigment epithelium at macular region.
Quantitative retinal vasculature analysis with retinal fundus photographyCentral retinal arteriole equivalent (CRAE)A summary index reflecting the average width of retinal arterioles.
Central retinal venule equivalent (CRVE)A summary index reflecting the average width of retinal venules.
Fractal dimensionA measure of a fractal structure that exhibits the property of self-similarity, characterising the distribution of the branching retinal vasculature.
TortuosityA measure of the straightness/curliness of the retinal vessels.
Length-diameter ratioA measure of the ratio of the length between two branching points to trunk vessel width.
Optical coherence tomography angiography (OCT-A)Vessel densityA measure of the area occupied by blood vessels (including capillaries) over total area within the interested region.
Foveal avascular zone (FAZ) areaA capillary-free area in the central macula with highest cone photoreceptor density and oxygen consumption.
Optical coherence tomography with enhanced depth imaging (OCT-EDI)Choroidal thickness or volumeA thickness or volume between the outer border of retina pigment epithelium and sclera-choroidal interface.
Dynamic vessel analyserFlicker-induced vessel dilationAn average percentage increase in the vessel diameter in response to the flickering-light during measurement cycles, relative to the baseline diameter size.
Retinal oximetryRetinal vessel oxygen saturationA measure of the oxygen saturation in retinal arterioles and venules to detect changes in oxygen metabolism.
Ultra-widefield retinal photographyPresence of peripheral hard drusenPresence of small and distinct yellow deposits under retina in the periphery.
Fluorescence lifetime imaging ophthalmoscopy (FLIO)Fluorescence lifetimeA measure to describe the average time a single fluorophore remains in its electronically excited state after absorbing the energy of a photon and before returning to the ground state by emitting a photon.