Differential effects of compression and suction ophthalmodynamometry on the scotopic blue-flash electroretinogram

Several studies have investigated the effect of elevated intraocular pressure with reduced ocular perfusion pressure on visual neural function by means of compression and suction ophthalmodynamometry. We compared the effects of nominally equivalent reductions in the ocular perfusion pressure induced by compression and suction ophthalmodynamometry retinal function as measured by flash electroretinography. Scotopic blue-flash electroretinograms were recorded in five subjects for baseline conditions; during a 40% reduction in the ocular perfusion pressure effected in a first test session by compression ophthalmodynamometry; and then in a second test session some 4 hours later by suction ophthalmodynamometry. Fifteen consecutive electroretinographic sets were recorded during scleral compression or suction, and also after compression or suction was removed. Compression and suction ophthalmodynamometry decreased the electroretinogram b-wave to different degrees; overall, the electroretinogram was attenuated more by compression than by suction ophthalmodynamometry. In the recovery phase, the group averaged b-wave quickly increased to exceed baseline after both scleral compression and suction. The trends for prolonged implicit times over the duration of the study were similar for compression and suction ophthalmodynamometry.