The Response of Retrobulbar Vasculature to Hypercapnia in Primary Open-Angle Glaucoma and Ocular Hypertension

Abstract

Purpose: To evaluate the physiological effects of hypercapnia on the retrobulbar vasculature in ocular hypertension (OH) and open-angle glaucoma (OAG). Methods: Peak systolic velocity (PSV), end-diastolic velocity (EDV) and resistive index (RI) of the ophthalmic (OA) and central retinal arteries (CRA) were evaluated in 12 eyes with OH and 8 eyes with OAG using color Doppler imaging. Measurements were taken before and during hypercapnia. Results: Patients with OAG were found to have increased EDV (p < 0.035) of the CRA, and decreased PSV (p < 0.097) and EDV (p < 0.098) of the OA, during hypercapnia. Patients with OH had increased PSV (p < 0.062) and EDV (p < 0.072) of the CRA during hypercapnia. Patients with OH also demonstrated a greater percent change in the calculated RI (p < 0.065) of the CRA in response to hypercapnia when compared to OAG. The mean RI of the CRA decreased during hypercapnia. Discussion: Patients with OH were found to have a normal vasodilatory response within the retrobulbar vasculature during hypercapnia resulting in increased volumetric blood flow to the retina while patients with OAG did not, suggesting there is vasospasm at or downstream from the CRA resulting in decreased volumetric blood flow to the retina.

Glaucoma Risk Factors: Ocular Blood Flow

“…Patients with ocular hypertension were found to have a normal vasodilatory response within the retrobulbar vasculature during hypercapnia resulting in increased volumetric blood flow to the retina while patients with glaucoma did not, suggesting there is vasospasm at or downstream from the central retinal artery, which may result in decreased volumetric blood flow to the retina. 104 This builds upon previous research by Harris et al that found that NTG patients had reversible vasospasm apparent in the retrobulbar blood vessels. …”

“…11,125 In this capacity, the cerebral and ocular circulations may be related, and evidence suggests that systemic vascular regulatory dysfunction may also exist in NTG and POAG patients. 104,126 Furthermore, an ultrasound study of cerebral hemodynamics found diminished central visual function to be one manifestation of widespread cerebrovascular insufficiency in glaucoma. 127 The vascular dysfunction in the retrobulbar blood vessels measured by CDI may also appear as an observable vasospasm in certain glaucoma patients.…”

“…127 The vascular dysfunction in the retrobulbar blood vessels measured by CDI may also appear as an observable vasospasm in certain glaucoma patients. 104 Vasospasm within the blood vessels supplying the optic nerve head and retinal ganglion cells may lead to accelerated loss of visual function and increased rates of glaucomatous disease progression. 123,128 Specifically, Plange et al found that asymmetric glaucomatous visual field loss was associated with asymmetric flow velocities in the central retinal and ophthalmic arteries in POAG patients.…”

Ophthalmic imaging of ocular circulation for detecting disease

“…20 Select glaucoma patients may have an observable vasospasm as evidence of vascular dysfunction in the retrobulbar blood vessels measured by CDI. 21 Vasospasm within the blood vessels supplying the optic nerve head (ONH) and retinal ganglion cells may cause increased loss of visual function and increased progression of glaucoma. 18,22 In patients with OAG, asymmetric glaucomatous visual fi eld loss was associated with asymmetric blood fl ow velocities in the central retinal and ophthalmic arteries.…”

Farbduplexsonographie der retrobulbären Gefäße und Hyperkapnie bei Normaldruckglaukom

“…Auch dies wurde als partielle Reversibilität einer relativen Vasokonstriktion bei Glaukompatienten interpretiert. Sines et al [27] berichteten über einen Anstieg der EDV der A. centralis retinae unter Hyperkapnie bei Patienten mit POWG, während die Blutfließgeschwindigkeiten der A. ophthalmica sogar sanken. Venkataraman et al [28] fanden hingegen eine verminderte Antwort der retinalen Gefäße und der Perfusion des Sehnervs mithilfe der Laserdoppler-Flowmetrie bei Patienten mit unbehandeltem und fortschreitendem POWG unter Hyperkapnie.…”