Influence of transiently altered retinal vascular perfusion pressure on rod/cone contributions to scotopic...

The oscillatory potentials (OPs) are sensitive to vascular disturbances in the retina. Rods in man are more susceptible than cones to ischaemia. The findings in a recent study showed that the white flash OP-5 had a heightened sensitivity to altered retinal vascular perfusion pressure (RVPP), compared with earlier OPs and the b-wave. In the present study, a comparison was made of the sensitivity of scotopically matched blue and red flash OPs to dim white flash OPs, to transient stepwise changes in the RVPP, in 10 healthy young adults. After 30 minutes of dark adaptation, two consecutive 0.3 Hz flash groups (n = 20) were filtered and averaged to obtain 100 ms flash ERGs and OPs simultaneously via DTL fibre electrodes for white, blue, and red flashes. To minimize any carry-over effects across flash colour, or repeated testing, the retinal responses to each of these stimuli were measured in separate test sessions several hours to days apart. The RVPP was increased or decreased by 20% and 40% non-invasively by body inversion and scleral suction respectively. For the flash intensities used, blue and red flash OPs appeared more variable than white flash OPs. The OP index increased or decreased across all flash colours when the RVPP was increased, with blue OPs showing the greatest spread of data. Retesting in five subjects using white and red flashes against a blue background disclosed the input of both rods and cones to the white flash scotopic OPs. The provocative test conditions described here offer a potentially profitable approach for studies attempting to differentiate the effects of vascular disorders on rod versus cone function.