Short-Term Moderately Elevated Intraocular Pressure Is Associated With Elevated Scotopic Electroretinogram Responses.
OBJECTIVE
Moderately elevated intraocular pressure (IOP) is a risk factor for open-angle glaucoma. Some patients suffer glaucoma despite clinically measured normal IOPs. Fluctuations in IOP may have a significant role since IOPs are higher during sleep and inversion activities. Controlled transient elevations of IOPs in rats over time lead to optic nerve structural changes that are similar to the early changes observed in constant chronic models of glaucoma. Because early intervention decreases glaucoma progression, this study was done to determine if early physiological changes to the retina could be detected with noninvasive electrophysiological and optical imaging tests during moderately elevated IOP.


METHODS
Intraocular pressures were raised to moderately high levels (35 mm Hg) in one eye of Sprague-Dawley rats while the other (control) eye was untreated. One group of rats underwent scotopic threshold response (STR) and electroretinogram (ERG) testing, while another 3 groups underwent optical coherence tomography (OCT) imaging, Western blot, or histologic evaluation.


RESULTS
The amplitudes of the STR and ERG responses in eyes with moderately elevated IOPs were enhanced compared to the values before IOP elevation, and compared to untreated contralateral eyes. Structural changes to the optic nerve also occurred during IOP elevation.


CONCLUSIONS
Although ischemic IOP elevations are well-known to globally reduce components of the scotopic ERG, acute elevation in rats to levels often observed in untreated glaucoma patients caused an increase in these parameters. Further exploration of these phenomena may be helpful in better understanding the mechanisms mediating early retinal changes during fluctuating or chronically elevated IOP.
School of Optometry and Vision Science University of Waterloo, Waterloo, Ontario, Canada.
Vivian
V
Choh
Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario, Canada.
Akshay
A
Gurdita
Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario, Canada.
Bingyao
B
Tan
Vanderbilt Eye Institute, Vanderbilt University, Nashville, Tennessee, United States.
Ratna C
RC
Prasad
School of Optometry and Vision Science University of Waterloo, Waterloo, Ontario, Canada 2Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario, Canada.
Kostadinka
K
Bizheva
Vanderbilt Eye Institute, Vanderbilt University, Nashville, Tennessee, United States.
Karen M
KM
Joos
D000818:Animals; D015153:Blotting, Western; D003623:Dark Adaptation / Q000502:physiology; D004596:Electroretinography; D007429:Intraocular Pressure / Q000502:physiology*; D008297:Male; D009798:Ocular Hypertension / Q000503:physiopathology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012160:Retina / Q000473:pathology / Q000502:physiology* / Q000503:physiopathology; D041623:Tomography, Optical Coherence