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

Abstract

Abstract: : Purpose: To evaluate the physiologic effects of hypercapnea on the retrobulbar vasculature comparing patients with Ocular Hypertension (OH) and Primary Open Angle Glaucoma (POAG). Methods: At a single study visit, 12 eyes of 6 patients with OH and 8 eyes of 4 patients with POAG were evaluated. Color Doppler Imaging (Siemens Quantum 2000) was used to evaluate the Peak Systolic Velocity (PSV), End Diastolic Velocity (EDV), and Resistive Index (RI) of the Ophthalmic Artery (OA) and Central Retinal Artery (CRA). Measurements were taken before and during carbon dioxide (CO₂) supplementation sufficient to increase the end–tidal CO₂ partial pressure by 10% (Poet II). Results: In patients with POAG, hypercapnea resulted in increased CRA EDV (p<0.035), decreased OA PSV (p<0.097), and decreased OA EDV (p<0.098). Mean CRA EDV increased from 1.84 ± 0.74 mm/sec to 2.57 ± 1.28 mm/sec, mean OA PSV decreased from 32.56 ± 4.85 mm/sec to 29.06 ± 6.20 mm/sec, and mean OA EDV decreased from 9.28 ± 2.85 mm/sec to 7.56 ± 2.86. In POAG the CRA PSV was not significantly altered. In patients with OH, hypercapnea resulted in increased CRA PSV (p<0.062) and EDV (p<0.072). Mean CRA PSV increased from 8.80 ± 2.18 mm/sec to 10.25 ± 4.22 mm/sec and mean CRA EDV increased from 2.17 ± 0.76 mm/sec to 2.88 ± 1.49 mm/sec. Patients with OH also demonstrated a greater percent change in the calculated RI (p<0.065) of the CRA in response to hypercapnea when compared to those with POAG. Mean CRA RI decreased from 0.752 ± 0.064 to 0.722 ± 0.061. Conclusions: Glaucoma and OH retrobulbar vasculature react differently in response to hypercapnea. This suggests there are vascular alterations involved in the pathophysiology of POAG.

Keywords: blood supply • ischemia • imaging/image analysis: clinical