U.S. flag An official website of the United States government
  1. Home
  2. Medical Devices
  3. Science and Research (Medical Devices)
  4. CDRH Research Programs
  5. Visual Sensory Devices
  1. CDRH Research Programs

Visual Sensory Devices


Ethan D. Cohen, Ph.D.


Retinal prostheses are neurosensory devices intended to stimulate the degenerate retina in blind patients to elicit sensations of light termed “phosphenes” to provide useable vision. Little is known about what levels of electrical and optical stimulation are safe for the degenerate retina. The mission of this laboratory is to develop metrics to evaluate safer and more effective methods of retinal cell stimulation by prosthetic devices. We have developed a novel transparent tube stimulation electrode method which when combined with optical coherence tomography (OCT), allows us to study neurons and retinal tissue directly under stimulus electrodes in real time during pulse train stimulation.

Stimulus Electrode and Retina Layers

Optical coherence tomography and transparent electrodes allow accurate measurement of electrode access resistance with retinal proximity.

Recorded Alpha Retinal Ganglion Cell

Confocal reconstruction of an alpha retinal ganglion cell recorded in the isolated live retina.

Overstimulated Retina Under Electrode

Example of the use of optically transparent stimulus electrodes to study in real time the effects of overstimulation of the retina directly under the stimulus electrode.

Current projects include:

  1. Optical evaluation of the relation of the stimulus electrode pulse waveform to electrode-retina proximity.
  2. Evaluation of microglia cells as indicators of retinal damage from overstimulation.
  3. Evaluation of neurotoxins in real time on retinal tissue using an optically transparent microapplicator tubes and OCT. (CDRH/CDER)

The results of these projects have provided FDA with a better understanding of how the retinal layers are activated by electrical stimulation pulses and determine what levels of electrical stimulation are safe for retinal tissue. Our projects support the regulatory review mission of the Agency, as the measurement of access resistance with tissue proximity may allow the evaluation of more efficacious electrode to target placement directly in implanted patients.

For more information, visit www.artificialvision.org.

Current funding sources

NSF Scholar in Residence
George Mason University
FDA Critical Path Initiative


FDA Staff:
Ethan Cohen, Ph.D.
Anant Agrawal, Ph.D.
Daniel X. Hammer, Ph.D.

FDA collaborators

Alex Beylin
Joseph Hanig
T. Katherine Shea
Shulei Zhao 

External collaborators

George Mason University
National Eye Institute, NIH
Naval Research Laboratories
University of Minnesota, Minneapolis, MN 

Resource facilities

  • Leica upright laser confocal physiology microscope
  • Patch clamp slice Normarski imaging workstation
  • Patch clamp retinal photostimulation with Normarski imaging workstation
  • Photomicrography fluorescence workstation 

Relevant standards & guidances

(2013) Guidance for Industry and FDA Staff: Investigational Device Exemption (IDE) Guidance for Retinal Prostheses.

Selected peer-review publications

Back to Top