title: Contrast Sensitivity With a Subretinal Prosthesis and Implications for Efficient Delivery of Visual Information.
abstract: OBJECTIVE
  To evaluate the contrast sensitivity of a degenerate retina stimulated by a photovoltaic subretinal prosthesis, and assess the impact of low contrast sensitivity on transmission of visual information.
  
  
  METHODS
  We measure ex vivo the full-field contrast sensitivity of healthy rat retina stimulated with white light, and the contrast sensitivity of degenerate rat retina stimulated with a subretinal prosthesis at frequencies exceeding flicker fusion (>20 Hz). Effects of eye movements on retinal ganglion cell (RGC) activity are simulated using a linear-nonlinear model of the retina.
  
  
  RESULTS
  Retinal ganglion cells adapt to high frequency stimulation of constant intensity, and respond transiently to changes in illumination of the implant, exhibiting responses to ON-sets, OFF-sets, and both ON- and OFF-sets of light. The percentage of cells with an OFF response decreases with progression of the degeneration, indicating that OFF responses are likely mediated by photoreceptors. Prosthetic vision exhibits reduced contrast sensitivity and dynamic range, with 65% contrast changes required to elicit responses, as compared to the 3% (OFF) to 7% (ON) changes with visible light. The maximum number of action potentials elicited with prosthetic stimulation is at most half of its natural counterpart for the ON pathway. Our model predicts that for most visual scenes, contrast sensitivity of prosthetic vision is insufficient for triggering RGC activity by fixational eye movements.
  
  
  CONCLUSIONS
  Contrast sensitivity of prosthetic vision is 10 times lower than normal, and dynamic range is two times below natural. Low contrast sensitivity and lack of OFF responses hamper delivery of visual information via a subretinal prosthesis.
authors.affiliation: Hansen Experimental Physics Laboratory, Stanford University, Stanford, California, United States 2Department of Electrical Engineering, Stanford University, Stanford, California, United States.
authors.forename: Georges
authors.initials: G
authors.lastname: Goetz
authors.affiliation: Santa Cruz Institute for Particle Physics, University of California Santa Cruz, Santa Cruz, California, United States.
authors.forename: Richard
authors.initials: R
authors.lastname: Smith
authors.affiliation: Department of Electrical Engineering, Stanford University, Stanford, California, United States.
authors.forename: Xin
authors.initials: X
authors.lastname: Lei
authors.affiliation: Department of Electrical Engineering, Stanford University, Stanford, California, United States.
authors.forename: Ludwig
authors.initials: L
authors.lastname: Galambos
authors.affiliation: Department of Electrical Engineering, Stanford University, Stanford, California, United States.
authors.forename: Theodore
authors.initials: T
authors.lastname: Kamins
authors.affiliation: Institute of Photonics, University of Strathclyde, Glasgow, Scotland, United Kingdom.
authors.forename: Keith
authors.initials: K
authors.lastname: Mathieson
authors.affiliation: Santa Cruz Institute for Particle Physics, University of California Santa Cruz, Santa Cruz, California, United States.
authors.forename: Alexander
authors.initials: A
authors.lastname: Sher
authors.affiliation: Hansen Experimental Physics Laboratory, Stanford University, Stanford, California, United States 5Department of Ophthalmology, Stanford University, Stanford, California, United States.
authors.forename: Daniel
authors.initials: D
authors.lastname: Palanker
mesh_terms: D000818:Animals; D015350:Contrast Sensitivity / Q000502:physiology*; D004195:Disease Models, Animal; D005074:Evoked Potentials, Visual; D005260:Female; D010775:Photic Stimulation; D051381:Rats; D020318:Rats, Long-Evans; D012162:Retinal Degeneration / Q000503:physiopathology / Q000601:surgery*; D012165:Retinal Ganglion Cells / Q000502:physiology*; D014792:Visual Acuity; D057488:Visual Prosthesis