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J. Ning, J.M. Beach, B. Khoobehi; Hyperspectral Imaging Measurements of Primate Optic Nerve Head Blood Volume . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4799.
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© ARVO (1962-2015); The Authors (2016-present)
To use reflectance hyperspectral imaging to assess the relationship between intraocular pressure (IOP) perturbations and blood volume in the optic nerve head (ONH) and retinal artery/vein in normal primate eyes.
Two cynomolgus monkeys were anesthetized and IOP was monitored and raised using a needle connected to a bottle of BSS and inserted into the anterior chamber of each eye. Three hyperspectral images were taken at IOPs of 10, 30, 45 and 55 mmHg when each pressure was steady. Nine sessions were conducted for the two animals. Relative changes in blood volume were assessed using the formula modified from F.C. Delori (Reflectometry Measurements of Optic Disc Blood Volume, Ocular Blood Flow in Glaucoma, Kugler & Ghedini Publications, 1989).
The blood volume index at 10 mmHg IOP (normal) for the retinal artery, retinal vein, ONH rim (nasal, temporal, superior, inferior), and cup (nasal and temporal) were 17.14µm±0.98µm, 18.64µm±1.72, 12.43µm±0.71µm, 10.80µm±0.79µm, 13.67µm±0.53µm, 13.33µm±0.83µm, 13.01µm±0.72µm and 10.18µm±0.90µm, respectively. Blood volume decrease was not significant for retinal vessels at 30 mmHg but was significant (P=0.0006, P=0.0000003 for artery, vein, respectively) at 45 mmHg (6.4%, 12.6% decrease, respectively); and significant (for artery, P=0.00003; for vein, P=0.0000016) at 55 mmHg (9.8%, 15.6%, respectively.) Decreases for the average of the ONH rim were not significant at high IOPs (nasal: no significance; temporal: significant increase: P=0.022, P=0.022, P=0.0078 at 30, 45, 55 mmHg, respectively; superior: significant decrease at 55 mmHg (P=0.011); and, inferior: not significant increase at 30mmHg (P=0.159), not significant decrease at 45, 55 mmHg (P=0.51, 0.81 respectively) ), with an average of 1.7% increase at 30 mmHg, 0.3% decreases at both 45 and 55 mmHg; but was significant for the cup (nasal: P=0.002 at 45 mmHg, P=0.00015 at 55 mmHg; temporal: P=0.003 at 55 mmHg), with decreases of 1.4%, 4.0%, 6.7% at 30, 45, 55mmHg, respectively.
Elevation of IOP reduces blood volume of the ONH and retinal vessels. The reduction was not significant in the ONH rim but was significant in the cup, since the ONH rim receives its blood supply via peripapillary retinal arterioles, which are supplied through the central retinal artery. The prelaminar blood supply was shown to be masked by vessels in the nerve fiber layer (NFL), but not the central cup; the deeper layers of the ONH, including the prelaminar and laminar regions, would be most accessible to optical reflectometry at the central cup.
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