Retinal oxygenation after Vitrectomy
Irene A. Barbazetto, L. Zheng, J. Liang, J. P. Dillon (New York)
Recent studies suggest that vitrectomy surgery significantly increases intraocular oxygen
tension during and for prolonged period after surgery. The increase in oxygen has been linked
to post-operative complications such as cataract formation and even the development of glaucoma
years after the procedure.1,2
In this presentation we would like to discuss potential mechanisms, which maintain the oxygen
tension within the vitreous in the animal model and to validate a new technique to continuously
measure oxygen within the eye by using modified fluorphotometry.
Fluorophotometry is an established method for quantitating the permeability of the bloodretinal
barriers and the blood-aqueous barrier. In this study a Pd prophyrin was injected into
the life rabbit vitreous. Phosphorescence measurements using a modified fluorotron device
were obtained before, directly after, 5 days after injection and after scarification of the animal.
In addition in vitro oxygen measurements and HPLC analysis of isolated vitreous samples were performed. Results were
compared to control measurements obtained using a fiber-optic oxygen sensor system (optode/ Ocean Optics inc.).
Measurements with modified fluorophotometry confirmed previous study results obtained using an optode. In the normal eye
a gradient exits which decreases dramatically through the retina and more slowly towards the anterior vitreous, which is lost
after vitrectomy. In addition, there is a decrease of oxygen towards the periphery of the retina in the rabbit model. After
sacrifice the oxygen tension in the central vitreous dropped precipitously to almost zero after only 10 minutes. Although
much of this loss is due to retinal metabolism, this may not explain completely the very rapid decline. HPLC analysis showed
that losses in oxygen were paralleled by losses in ascorbic acid. These results were ascertained using either an optode or
in conjunction with the fluorotron.
Oxygen tension varies throughout the vitreous. A component of the oxygen control in the vitreous is via chemical reactions
with ascorbic acid.
The modified fluorotron technology has the potential for minimal invasive, reproducible, continuous oxygen measurements
in the eye.
1: Holekamp NM, Shui YB, Beebe DC. Vitrectomy surgery increases oxygen exposure to the lens: a possible mechanism for nuclear cataract formation.
Am J Ophthalmol. 2005 Feb;139(2):302-10.
2: Barbazetto IA, Liang J, Chang S, Zheng L, Spector A, Dillon JP. Oxygen tension in the rabbit lens and vitreous before and after vitrectomy.
Exp Eye Res. 2004 May;78(5):917-24.