March 2012
Volume 53, Issue 14
ARVO Annual Meeting Abstract  |   March 2012
The Impact Of Acute Intraocular Pressure Elevation On Rod- And Cone-pathways In Rats
Author Affiliations & Notes
  • Tina I. Tsai
    Optometry & Vision Sciences, University of Melbourne, Carlton, Australia
  • Bang V. Bui
    Optometry & Vision Sciences, University of Melbourne, Carlton, Australia
  • Algis J. Vingrys
    Optometry & Vision Sciences, University of Melbourne, Carlton, Australia
  • Footnotes
    Commercial Relationships  Tina I. Tsai, None; Bang V. Bui, None; Algis J. Vingrys, None
  • Footnotes
    Support  NHMRC 566570
Investigative Ophthalmology & Visual Science March 2012, Vol.53, 165. doi:
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      Tina I. Tsai, Bang V. Bui, Algis J. Vingrys; The Impact Of Acute Intraocular Pressure Elevation On Rod- And Cone-pathways In Rats. Invest. Ophthalmol. Vis. Sci. 2012;53(14):165.

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

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Purpose: : To investigate the sensitivity of rod- and cone-retino-cortical-pathways to acute intraocular pressure (IOP) elevation.

Methods: : Acute, IOP elevation was achieved (10-70 mmHg, 12 minute steps) in anaesthetised (Ket:Xyl, 60:5 mg/kg) Long Evans rats. Full-field scotopic and/or photopic electroretinograms (ERG) and visual evoked potentials (VEP) were measured simultaneously in two groups of animals (n=9 each). Recovery from IOP was tracked for 1 hour after maximum IOP challenge. Scotopic ERG-VEP stimuli were brief white flashes (-4.99 and -0.52 log cd.s.m-2) that elicit the scotopic threshold response (STR) and maximal rod b-wave. Photopic ERG-VEPs were recorded at -0.52 log cd.s.m-2 following light adaptation (10 mins at 10 cd.s.m-2). IOP effects on waveform amplitudes (treated/baseline, %) were described with a cumulative normal function.

Results: : Both scotopic and photopic ERGs declined with IOP elevation. The ERG components most sensitive to IOP elevation were the negative STR (nSTR) and the photopic negative response (PhNR) (nSTR vs. PhNR, p=0.37). These were followed by the positive STR (pSTR), and the scotopic and photopic b-waves (PII). The least sensitive component was the scotopic a-wave (A-min) (2-way ANOVA, p<0.05). The photopic b-wave was significantly less sensitive to IOP elevation than was the scotopic b-wave (at 70 mmHg scotopic -98 ± 2% vs. photopic -61 ± 8%, p<0.01). During recovery, the cone b-wave amplitude returned to baseline sooner than did the rod b-wave (12 vs. ≥48 min), whereas both nSTR and PhNR amplitudes did not recover until ≥48 min. Despite significant reductions in the ERG, the VEP showed only subtle reductions in amplitude (scotopic and photopic ERG vs. VEP: -98 ± 2% vs. -32 ± 12%, and -61 ± 8% vs. -20 ± 19%, respectively at 70 mmHg). IOP profiles showed the VEP to be significantly more resistant to IOP elevation than the ERG (scotopic and photopic ERG PII vs. VEP N1P2, both p<0.05). There was no difference in the sensitivity of rod and cone mediated VEPs to IOP elevation (p<0.05).

Conclusions: : In rats, the cone retinal pathway was less sensitive and recovered faster from IOP challenge than the rod pathway. Retinal signals are more sensitive to IOP challenge than are cortical signals.

Keywords: intraocular pressure • electrophysiology: non-clinical 

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