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A. Benavente-Perez, S. L. Hosking, N. S. Logan; Myopes Exhibit Reduced Choroidal Blood Velocity Which Is Highly Responsive to Hypercapnia. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3581.
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Low-moderate human myopia exhibits reduced pulsatile and retrobulbar ocular circulation. The choroidal circulation has been implicated as having an effect on myopic eye growth, but remains largely unexplored in humans. The purpose of this study was to assess the choroidal circulation in human myopia by the evaluation of its resting and autoregulation profile. Hypercapnia was used to induce stress on the choroidal circulation.
The choroidal haemodynamics were assessed at the central foveal avascular zone using Laser Doppler Flowmetry (LDF). Choroidal velocity (LDFvel), volume (LDFvol) and flow (LDFflow) were recorded at 2 sessions: baseline (B1, breathing room air) and isoxic hypercapnia (IH: breathing CO2 enriched air until end tidal pCO2 increased approximately 15% above B1 with constant O2 supply). B1: one eye of each of 51 healthy volunteers grouped by mean spherical equivalent (MSE): a) 23 emmetropes with MSE ±0.50 D (mean MSE 0.00 ±0.47D; mean age 42.75 ± 16.94 years), b) 28 myopes with spherical equivalent (MSE) < -1.00D (mean MSE -3.80 ± 2.12D; mean age 35.60 ± 14.94 years) were matched and assessed. IH: subgroups comprising 10 myopes (mean MSE -3.90 ± 2.06; mean age 30.90 ± 12.16 years) and 10 emmetropes (mean MSE -0.21 ± 0.30D; mean age 33.10± 10.37 years) were matched and evaluated. Blood pressure (BP), intraocular pressure (IOP), mean arterial pressure (MAP), ocular perfusion pressure (OPP) and body mass index (BMI) were established.
B1: There were no differences in BP, MAP, BMI or OPP between groups. Choroidal blood velocity was 28% lower in myopes (p=0.03). IH: BP, IOP, OPP and MAP did not change significantly. Emmetropes did not show a significant change in choroidal haemodynamics; whereas the choroidal blood velocity significantly increased in myopes (p=0.03) reaching the baseline choroidal velocity level of the emmetropes
Under room air conditions low-moderate myopia was associated with reduced choroidal blood velocity. Hypercapnia did not result in significant choroidal changes in emmetropes; whereas, myopes exhibited a significant increase in choroidal blood velocity. These results suggest that myopes have a significantly lower resting choroidal flow velocity which is highly responsive to CO2. The differences in vascular reactivity may be related to the anatomy of the myopic eye and suggest the existence of a local choroidal response.
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