Transiently raised intraocular pressure reveals pattern electroretinogram losses in ocular hypertension

It is known that the pattern electroretinogram (PERG) of normal subjects is reduced temporarily after short-term elevation of intraocular pressure (IOP). The authors evaluated PERG changes in ocular hypertension during and after transient IOP elevation.

Steady state (8 Hz) PERGs to sinusoidal gratings (1.7 cyc/deg spatial frequency) were recorded in seven untreated patients with ocular hypertension at medium risk (maximum IOP, 22 to 25 mm Hg; cup-disk ratio, 0.6 to 0.7; normal Humphrey 30-2 visual field results; positive family history), as well as in six age-matched normal subjects. Recordings were obtained for the baseline condition during a short-term (6-minute) IOP elevation (to 30 mm Hg) by using a suction cup apparatus and during a 6-minute recovery period after removal of the apparatus.

During IOP elevation, PERG amplitudes were reduced significantly from baseline values in normal subjects and patients. However, PERG losses were significantly greater in patients (average loss from baseline after 4 minutes of IOP elevation: 72% +/- 7.6%) compared to controls (average loss after 2 minutes of IOP elevation: 40% +/- 7.5%). In the recovery phase, mean PERG amplitude returned to baseline values in normal subjects but not in patients, whose recovery took longer. In normal subjects, PERG phase did not change either during or after IOP elevation. In patients, however, PERG phase showed a delay from baseline during and after IOP elevation (average delay after 6 minutes of recovery: -41.1 degrees +/- 13 degrees).

Results indicate that increasing IOP with scleral suction produces greater PERG losses in eyes with ocular hypertension than in normal eyes. This suggests that the inner retina of eyes with ocular hypertension may have a heightened sensitivity to vascular or mechanical changes induced by transient IOP elevation.