Table 1.
Table summarizing the techniques of ocular blood flow measurement in myopia.
| Methods | Principle of each method | Findings in myopia |
|---|---|---|
| Laser Doppler flowmeter (LDF) | Measurement of blood cells traversing volume which are reflecting the light, and the light undergoes a Doppler shift | Retinal blood flow is decreased in highly and mild myopic eyes |
| Laser Doppler velocimetry (LDV) | Doppler shift for interfered lights reflected from blood cells | No data |
| Retinal vessel analyzer (RVA) | Measurement of the diameter of retinal vessels in relation to time and location | In high myopia, the vessels at the posterior pole have smaller diameter but are functionally comparable to control subjects |
| Retinal function imager (RFI) | Measurement of the haemodynamic parameters such as retinal blood flow velocity, oximetric state, metabolic responses to photic activation, and generation of capillary perfusion maps (CPM); RFI maps the retina to the resolution of single red blood cells moving through capillaries | No significant difference in retinal microcirculation blood flow velocity in either arterioles or venules |
| Laser speckle contrast imaging (LSCI) | Measurement of velocity distributions which are coded as speckle contrast variations | Decreased optic nerve microcirculation in eyes with myopic optic discs |
| Pulsatile ocular blood flowmeter (POBF) | Measurement with the use of a pneumotonometer, which registers changes in intraocular pressure during each cardiac cycle | In high myopes, pulsatile ocular blood flow as well as ocular blood flow amplitude and volume is decreased |
| Fundus pulsation amplitude (FPA) | Measurement of the distance between the cornea and the retina during the cardiac cycle with the use of laser interferometry | Decrease in the FPA index along with increased axial length |
| Fluorescein and indocyanine angiography (FA, ICG) | Examining the circulation of the retina and choroid using a fluorescent dye and a specialized camera | Delayed blood flow in highly myopic eyes |
| Optical coherence tomography angiography (OCTA) | Measurement of laser light reflectance of the surface of moving red blood cells | Reduced perfusion in the peripapillary retina and decreased superficial and deep retinal vascular density in annular zone of myopic eyes |
| Colour Doppler imaging (CDI) | Measurement of backscattered signals as a function of the motion of the erythrocytes toward or away from the transducer | Decreased blood flow velocity in the retrobulbar vessels, increased resistance index in central retinal artery |
| Doppler optical coherence tomography (DOCT) | Measuring the phase changes between two scans which is a quantitative value for the velocity if the time between the two measurements is known | DOCT could indicate choroidal neovascularization in pathological myopia |
| Retinal oximetry | Measurement of the optical densities of retinal vessels for two wavelengths and their ratio, which is known to be proportional to the oxygen saturation | Reduced saturation in high myopia |
| Magnetic resonance imaging | Method that provides structural, physiological, and functional image of tissue with the use of magnetic properties of certain atomic nuclei | In severe myopia, blood flow is markedly reduced |
| Blue light entoptoscopy | Measurement of average leukocyte velocity in area around the foveola by the use of entoptic phenomenon | No data |
| Ocular surface temperature (OST) | Measurement of infrared energy emitted from object | No data |