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Verleen K. McSween, Suresh Viswanathan, Joseph A. Bonanno; Inner-retinal Function During And After Acute Elevation Of Intraocular Pressure. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5483.
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To evaluate inner-retinal function before, during and immediately after acute elevations of Intraocular pressure (IOP).
Retinal function was assessed with the full-field dark-adapted electroretinogram before, during and after IOP elevations of 30, 45 or 60 mm Hg produced by reservoir cannulation of the anterior chamber of anesthetized Brown Norway rats. The Scotopic Threshold Response (STR) was used to assess inner-retinal function (-4.7 log sc.cd/m2) and scotopic a- and b-waves were used to assess rod photoreceptor and bipolar cell function (1.7 log sc.cd/m2). The duration of IOP elevation chosen for each pressure was different so that they all yielded an IOP integral (pressure x duration) of 5250 mm Hg-minutes. Control and recovery phases were also measured for 30 minutes prior to and 80 minutes after IOP elevations, respectively, at an IOP of 10 mm Hg.
Reductions in a- & b-waves and STR were seen at 60 mm Hg, whereas only the STR was reduced at 30 and 45 mm Hg. The magnitude of STR reduction was greater with increasing IOP integral with a greater reduction observed for the higher IOP at each integral (30 mm Hg: slope=-0.004, r=0.9, p<0.0001, 45 mm Hg: slope=-0.009, r=0.94, p<0.0001). The STR was reduced by 26 and 55% for 30 and 45 mm Hg respectively at the maximum IOP integral of 5250 mm Hg-minutes. When IOP was returned to baseline the STR showed 36% recovery by 80 minutes for eyes held at 45 mm Hg. But, no obvious recovery was seen for eyes held at 30 mm Hg.
Inner-retinal responses can be selectively reduced for acute elevation of IOP in the range of 30-45 mm Hg if IOP elevations are maintained for sufficiently long durations. In this nominal pressure range, while peak IOP may be the more important determinant of the magnitude of functional loss, the duration of IOP elevation may be a more important factor for functional recovery.
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