Abstract
Optic nerve head (ONH) blood flow may be associated with glaucoma development. A reliable method to quantify ONH blood flow could provide insight into the vascular component of glaucoma pathophysiology. Using ultrahigh-speed optical coherence tomography (OCT), we developed a new 3D angiography algorithm called split-spectrum amplitude-decorrelation angiography (SSADA) for imaging ONH microcirculation. In this study, a method to quantify SSADA results was developed and used to detect ONH perfusion changes in early glaucoma. En face maximum projection was used to obtain 2D disc angiograms, from which the average decorrelation values (flow index) and the percentage area occupied by vessels (vessel density) were computed from the optic disc and a selected region within it. Preperimetric glaucoma patients had significant reductions of ONH perfusion compared to normals. This pilot study indicates OCT angiography can detect the abnormalities of ONH perfusion and has the potential to reveal the ONH blood flow mechanism related to glaucoma.
Highlights
Glaucoma is a leading cause of blindness [1,2] that is characterized by degeneration of the optic nerve associated with cupping of the optic nerve head (ONH)
We report the first use of optical coherence tomography (OCT) angiography to quantify human ONH blood flow
Noise predominates in pixels with low OCT signal amplitude and flow cannot be assessed in these pixels with any accuracy
Summary
Glaucoma is a leading cause of blindness [1,2] that is characterized by degeneration of the optic nerve associated with cupping of the optic nerve head (ONH). Fluorescein angiography provides useful qualitative information in health and disease [7]; it only shows the superficial ONH vessels and does not assess deep ONH perfusion [8]. Injection of dye can cause nausea and anaphylaxis [9], making it unsuitable as a tool for routine glaucoma assessment. Both laser Doppler flowmetry, which samples capillary flow over a small retinal area [3,10,11,12], and laser speckle flowgraphy, which provides a spot sample of blood velocity [13], can show differences between glaucoma and normal group [14,15,16,17]. Magnetic resonance imaging (MRI) has been proposed to quantitatively image ONH perfusion; the major limiting factor with this method is the small size of the ONH and limited resolution to detect focal or mild circulatory insufficiency [18,19]
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