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Ophthalmic Physiol Opt. 2015 Mar;35(2):114-24. doi: 10.1111/opo.12170. Epub 2014 Dec 19.

Provocative intraocular pressure challenge preferentially decreases venous oxygen saturation despite no reduction in blood flow.

Author information

1
Department of Optometry and Vision Sciences, The University of Melbourne, Melbourne, Australia; Department of Ophthalmology, Countess of Chester Hospital NHS Foundation Trust, Chester, UK.

Abstract

PURPOSE:

Ocular disease can both alter the retina's oxygen requirements, and decrease its ability to cope with changes in metabolic demand. We examined the influence of a moderate intraocular pressure (IOP) elevation on three outcome measures: arterial and venous oxygen saturation, blood flow, and the pattern electroretinogram (PERG).

METHODS:

We increased IOP to ˜30 mmHg in 23 healthy participants (22-39 years) using a mechanical probe applied to the eyelid, thereby lowering ocular perfusion pressure (OPP) by ~30%. The Oxymap retinal oximeter was used to measure oxygen saturation for arteries and veins. Blood flow, volume and velocity were measured using the Heidelberg retinal flowmeter and steady-state PERG waveforms (8.34 Hz) were recorded bilaterally (200 sweeps). For each outcome measure, data was obtained three times: at baseline, 1 min into sustained IOP elevation, and 1 min after the probe was removed.

RESULTS:

During IOP elevation, changes in oxygen saturation of retinal arteries failed to reach statistical significance [F(1,30) = 3.69, p = 0.05], whereas venous oxygen saturation was significantly reduced [F(1,21) = 27.43, p < 0.01]. Blood flow increased slightly [F(2,40) = 6.28, p < 0.0001], PERG amplitude significantly reduced [F(2,44) = 24.24, p < 0.0001] and PERG phase was significantly delayed [F(2,44) = 17.00, p < 0.0001]. Contralateral eyes were unchanged. OPP reduction correlated little with PERG amplitude, PERG phase or venous oxygen saturation.

CONCLUSIONS:

Mild, acute IOP elevation increases arterio-venous oxygen saturation differences primarily through lowering venous oxygen saturation, suggesting increased oxygen consumption by healthy neurons when physiologically stressed.

KEYWORDS:

blood flow; intraocular pressure elevation; oxygen saturation; pattern electroretinogram

PMID:
25528886
DOI:
10.1111/opo.12170
[Indexed for MEDLINE]

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