ACUTE IOP ELEVATION WITH SCLERAL SUCTION - EFFECTS ON RETROBULBAR HEMODYNAMICS

Aims/background - Mechanical and vascular factors may both contribute to glaucoma. This study investigated the relation of mechanical to vas cular factors by examining how acute IOP elevation altered how velocit ies in the central retinal and ophthalmic arteries. Methods - IOP was elevated from a baseline near 14 to approximately 45 mm Hg using sucti on ophthalmodynamometry. During recovery from scleral suction, IOP fel l to near 8 mm Hg. At each IOP, peak systolic and end diastolic veloci ties (PSV and EDV) were measured in the central retinal and ophthalmic arteries using colour Doppler imaging (Siemens Quantum 2000). Eleven healthy people served as subjects. Results - Acute elevation in IOP ha d no effect upon PSV, EDV, or the derived resistance index in the opht halmic artery: how velocities in this vessel were identical at IOP of 8 mm Hg or 45 mm Hg. In contrast, in the central retinal artery, PSV a nd EDV fell, and the resistance index rose, in steady progression as I OP was acutely elevated (each p<0.01). At IOP of 45 mm Hg, EDV was vir tually absent and the resistance index was very nearly 1.0. Conclusion - Ophthalmic arterial haemodynamics are unrelated to acute fluctuatio ns of the IOP over a wide range, suggesting that ocular hypertension i tself cannot induce vascular dysfunction in this artery. In contrast, flow velocities in the central retinal artery were highly IOP dependen t, implying that haemodynamic and mechanical factors are closely linke d in this vascular bed.