June 2017
Volume 58, Issue 8
Open Access
ARVO Annual Meeting Abstract  |   June 2017
Spatial maps of the sensitivity parameter I1/2 derived from multi-electrode electroretinography (meERG) responses in healthy rat eyes and eyes with experimental lesions
Author Affiliations & Notes
  • John R Hetling
    Bioengineering, Univ of Illinois at Chicago, Chicago, Illinois, United States
    Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, Illinois, United States
  • Zahra Derafshi
    Bioengineering, Univ of Illinois at Chicago, Chicago, Illinois, United States
  • Brian Kunzer
    Bioengineering, Univ of Illinois at Chicago, Chicago, Illinois, United States
  • Footnotes
    Commercial Relationships   John Hetling, RetMap, Inc. (P), RetMap, Inc. (S), RetMap, Inc. (I); Zahra Derafshi, None; Brian Kunzer, None
  • Footnotes
    Support  UIC Colleges of Engineering and Medicine Bridge Funding
Investigative Ophthalmology & Visual Science June 2017, Vol.58, 5345. doi:
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      John R Hetling, Zahra Derafshi, Brian Kunzer; Spatial maps of the sensitivity parameter I1/2 derived from multi-electrode electroretinography (meERG) responses in healthy rat eyes and eyes with experimental lesions
      . Invest. Ophthalmol. Vis. Sci. 2017;58(8):5345.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose : Pathology can change the amount of light required for a photoreceptor to reach half-saturation (I1/2, a change in sensitivity) before measurable changes in the maximum a-wave amplitude. I1/2 can be derived from corneal electroretinogram (ERG) responses, however, pathologic changes in I1/2 restricted to local areas of the retina, as in early-stage disease, can appear within normal ranges. Here we demonstrate a technique for creating spatial corneal maps of I1/2 that can be interpreted for local changes in I1/2 at the retina.

Methods : Normally-sighted Long Evans rats (n =26) were dark adapted, anesthetized, and pupils were dilated. Multi-electrode electroretinography (meERG) was used to record a-wave potentials at 25 locations on the cornea elicited by two flash strengths, one saturating and one approximately half-saturating. At each corneal location, the a-wave amplitudes elicited by the two stimuli were fit with a function A/Am = I / (I + I1/2), where A is the a-wave amplitude for stimulus strength I, Am is the saturated a-wave amplitude, and I1/2 was the free parameter. The resulting 25 I1/2 values were then used to create corneal maps of sensitivity for each animal, and a normative range was established. Similar I1/2 maps were also created for 13 animals two days after receiving experimental retinal lesions (photo- or cryo-coagulation) resulting in complete disruption of between 0.9-14.9% (mean 5.1%) of the retina.

Results : The spatial distribution of I1/2 across the cornea of healthy rat eyes was approximately uniform (all locations within one standard deviation of the spatial mean), unlike the distinct nasal-temporal asymmetry in the a-wave potentials from which I1/2 is derived. The normal distribution of I1/2 values was altered in the presence of experimental lesions. Eyes with lesions could be classified with 77% sensitivity, 65% specificity, based on local values of I1/2.

Conclusions : Spatial differences in the distribution of photoreceptor sensitivity (I1/2) seen at the cornea are affected by local areas of damage at the retina, and may be useful for detection of early, localized pathophysiology that affects this parameter prior to cell death.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.

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