Abstract
PurposeTo 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 methodsA 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).ResultsCompared 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).ConclusionsThe 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
Highlights
Knowledge of the perfusion of the optic nerve head (ONH) is important in the diagnosis of ocular diseases such as glaucoma and diabetic retinopathy and in basic research to Optical methods to assess ocular blood flow are based on two basic principles: light absorption by blood components or light scattering by moving blood components.In early measurements of retinal blood flow, non-imaging light absorption–based methods were used [2,3,4,5,6]
We describe the application of a light absorption–based method to measure the cardiac cycle– induced pulsatile changing blood volume in the ONH using a recently developed video ophthalmoscope
The presented low-cost video-ophthalmoscope allows the measurement of the plethysmographic signal of the ONH tissue and the calculation of different perfusion-related parameters
Summary
Knowledge of the perfusion of the optic nerve head (ONH) is important in the diagnosis of ocular diseases such as glaucoma and diabetic retinopathy and in basic research to Optical methods to assess ocular blood flow are based on two basic principles: light absorption by blood components or light scattering by moving blood components.In early measurements of retinal blood flow, non-imaging light absorption–based methods were used [2,3,4,5,6]. Knowledge of the perfusion of the optic nerve head (ONH) is important in the diagnosis of ocular diseases such as glaucoma and diabetic retinopathy and in basic research to Optical methods to assess ocular blood flow are based on two basic principles: light absorption by blood components or light scattering by moving blood components. With light absorption–based methods, only the changing fraction of the blood flow can be measured. The photoplethysmographic (PPG) principles is based upon light absorption due to the changing blood volume in the investigated tissue. We show that the PPG principles can be applied for assessment of optic nerve head perfusion with high spatial and temporal resolution using a previously published experimental ophthalmoscope and specific image and signal processing approaches.
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