Evoked Retinal Response

Patients affected by retinitis pigmentosa (RP) and related diseases suffer loss of vision due to death of photoreceptor cells. The investigators have observed that short pulses of focused ultrasound can cause perception of light (phosphenes) when directed to spots on the retinal surface. If this phenomenon is caused by direct stimulation of the retinal nerves, which seems probable, then it might be possible to use this phenomenon to produce a form of vision in such patients. The investigators propose to conduct a study of a small cohort of patients affected by RP to determine if pulsed ultrasound will evoke a perception of light in the absence of functional photoreceptors.