Acute IOP elevation with scleral suction: Effects on central retinal artery hemodynamics

Purpose. Mechanical and vascular factors may both contribute to glaucoma. We investigated the relationship of mechanical to vascular factors by examining how acute intraocular pressure (IOP) elevation altered flow velocity in the central retinal artery. Methods. IOP was elevated from 13.6 ± 1.4 to 42.0 ± 1.2 mmHg in 3 stages in nine healthy subjects using suction ophthalmodynamometry. During recovery from scleral suction, IOP fell below 10 mmHg. At each IOP, peak systolic and end-diastolic velocities (PSV and EDV) were measured in the central retinal artery using color Doppler imaging (Siemens Quantum 2000). Each IOP level was maintained for two minutes prior to color Doppler recordings which were completed in 3-5 subsequent minutes. Results. PSV and EDV both fell in steady progression as IOP was acutely elevated (each p<0.01). The derived resistance index ((PSV-EDV)/PSV) rose as IOP was elevated (p<0.05). At IOP of 42 mmHg, EDV was virtually absent and the resistance index was very nearly 1.0. PSV, EDV, and RI all appeared to be linearly dependent upon calculated ocular perfusion pressure (2/3 (mean arterial pressure)-IOP). Conclusion. Flow velocities in the central retinal artery are highly IOP-dependent, suggesting that vascular and mechanical factors are closely linked in this vascular bed.