A new microelectrode positioner for electrophysiology in the intact mammalian eye

In vivo cannulation of retinal vessels

In vivo cannulation of retinal blood vessels has not been reported but would be useful in exploring local vascular parameters and new treatment modalities. We developed a microsurgical technique for cannulating rabbit and cat retinal vessels, using glass micropipettes with curved shanks made from standard capillary tubing. The micropipette was held by a micromanipulator, which was fitted with a fiberoptic sleeve for intraocular illumination and for micropipette tip protection during insertion through the sclera. Direct aspiration from and injection into retinal blood vessels were possible.

Differential effects of short- and long-pulsewidth laser exposures on retinal ganglion cell response

Time-dependent effects of laser exposures on rhesus monkey retinal ganglion cells were studied with a Q-switched, doubled Nd:glass laser, which produced 20 nsec pulses of 530-nm light, and a continuous-wave (CW) argon laser (514.5 nm), which produced exposures of 0.1-msec to 0.1-sec duration. Ganglion cell activity was recorded in situ by means of an intraocular electrode. Ganglion cells exposed to a single 20-nsec exposure, at a sublesion intensity, produced a 60-90 sec discharge of action potentials and exhibited a 2 log or greater elevation of light threshold, depending on beam size and intensity. At equivalent energy levels, the longer exposures produced the same or slightly weaker effects. This result is not as straightforward as it seems. Submillisecond flashes bleach no more than 50% of the visual pigment because of photoregeneration. The Dowling-Rushton relation predicts that a 50% bleach should produce only a 1.5 log loss of cone sensitivity. Exposures longer than 1 msec should not photoregenerate pigment (ie, more pigment will be bleached for a given exposure intensity). In view of the probable differences in pigment bleaching, it appears that the Q-switched laser light adapts the cells out of proportion to the visual pigment actually bleached--a single-cell analogue of Rushton's "theta" effect.