Imaging video plethysmography shows reduced signal amplitude in glaucoma patients in the area of the microvascular tissue of the optic nerve head

Abstract

Purpose To measure parameters of the cardiac cycle-induced pulsatile light absorption signal (plethysmography signal) of the optic nerve head (ONH) and to compare parameters between normal subjects and patients with different stages of glaucoma. Patients and methods A recently developed video ophthalmoscope was used to acquire short video sequences (10 s) of the ONH. After image registration and trend correction, the pulsatile changing light absorption at the ONH tissue (excluding large vessels) was calculated. The changing light absorption depends on the pulsatile changing blood volume. Various parameters, including peak amplitude, steepness, time-to-peak, full width at half maximum (FWHM), and pulse duration, were calculated for averaged individual pulses (heartbeats) of the plethysmography signal. This method was applied to 19 healthy control subjects and 91 subjects with ocular hypertension, as well as different stages of primary open-angle glaucoma (17 subjects with ocular hypertension, 24 with preperimetric glaucoma, and 50 with perimetric glaucoma). Results Compared to the normal subjects, significant reductions (p < 0.001) in peak amplitude and steepness were observed in the group of perimetric glaucoma patients, but no significant difference was found for time-to-peak, FWHM, and pulse duration. Peak amplitude and steepness showed high correlations with RNFL thickness (p < 0.001). Conclusions The presented low-cost video-ophthalmoscope permits measurement of the plethysmographic signal of the ONH tissue and calculation of different blood flow-related parameters. The reduced values of the amplitude and steepness parameters in perimetric glaucoma patients suggest decreased ONH perfusion and blood volume. This outcome is in agreement with results from other studies using OCT angiography and laser speckle flowgraphy, which confirm reduced capillary density in these patients. Registration site: www.clinicaltrials.gov, Trial registration number: NCT00494923

Heart rate and age modulate retinal pulsatile patterns

“…Previous studies showed that SVP were influenced by the IOP 28 , 35 , 37 , 47 and RNFL significantly correlated with RPP morphological measurements in the dataset, including population with retinal neurodegenerative disesase 4 , 19 , 43 . In our participants, the IOP and RNFL did not correlate with RPP morphology.…”

“…Therefore, the unverified biological impact of HR and age at RPP morphology was in vivo confirmed and validated. The impact of HR and age on the SVP/OCP morphology has been neglected in previous clinical research 4 , 19 , 33 , 34 , 43 and even in theoretical SVP-intracranial/intraocular pressure models 35 , 36 . The in vivo findings validate Levine and Bebie’s theory, assuming that SVP Ampl is influenced by HR 37 , 38 .…”

“…VO is inexpensive and well suited to become a diagnostic and disease monitoring tool for the real-time imaging of local microvascular blood supply and detecting various pathologies. VO is applicable in many fields of medicine such as ophthalmology (e.g., diabetic retinopathy 1 , glaucoma 2 – 4 ), neurology (e.g., Alzheimer disease 5 , multiple sclerosis 6 , stroke 7 ), or cardiology (e.g., coronary heart disease 8 , arterial stiffness 9 – 11 , hypertension 12 , diabetes 12 , 13 ).…”

“…Blood flow 14 , 15 , blood volume 4 , 16 and structural venous diameter changes 17 – 19 are the most commonly evaluated hemodynamic parameters from dynamic retinal imaging. The hemodynamic parameters are usually extracted in a manual or semi-automated fashion from specific morphological segments of a retinal vessel tree 16 – 18 , 20 – 23 .…”

“…Exactly how the in vivo video-ophthalmoscopic data (sensitive to blood flow or volume fluctuations) are affected by HR, age, or sex remains to be determined. If the impact of any variable is proved, a revisiting of clinical video-ophthalmoscopic outcomes demonstrating correlations between VO measurements and retinal neural fiber layer (RNFL) thickness 4 , 19 , 43 or other outcomes in populations of healthy subjects and those with disease conditions such as glaucoma is warranted.…”