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Juan Carlos Martinez, Karthik Murali, Amir H Kashani, Mark S Humayun; Modification of preretinal oxygen tension related to intraocular pressure. Invest. Ophthalmol. Vis. Sci. 2016;57(12):88.
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© ARVO (1962-2015); The Authors (2016-present)
Oxygen levels in the retina and vitreous have been extensively studied. These data have been used to estimate the oxygen retina requirements and consumption. Animal models of retinal vein occlusion (RVO) have shown that vascular changes can modify these values, triggering a decrease in the oxygen tension levels secondary to retinal ischemia. Changes in intraocular pressure (IOP) could increase vascular resistance, reducing blood flow. We hypothesize that preretinal oxygen tension is directly correlated with IOP and that has the potential to be a model of partial retinal ischemia.
Four eyes of four healthy pigmented rabbits (2-3kg of weight) were included in the study. We placed a 23G closed infusion line (B+L Stellaris) via pars plana at the lower sector. Next, we introduced an oxygen probe (Oxford Optronix) through a 27G incision 180 degrees away from the first incision. Guided by indirect ophthalmoscopy and a micromanipulator, we positioned the oxygen probe at the vitreoretinal interface, above the retinal arteries proximal to optic nerve in the temporal or nasal sector. The first oxygen tension measurement was recorded at normal IOP. We raised IOP in increments of 5mmHg (from 10 to 60mmHg) via the infusion line and recorded preretinal oxygen tension values. Time was given for the preretinal oxygen to reach steady state between each recording. The position of the oxygen probe was also adjusted after every increase in IOP to maintain its preretinal position. The relationship between IOP and oxygen tension was analyzed.
Baseline oxygen tension (pO2) was 38.08 ±6.89mmHg. By increasing the pressure above 20mmHg, pO2 decreased gradually to 7.05mmHg (see Figure). IOPMax was 60mmHg, which induced bleaching of the vessels and paling of the optic nerve, as observed by indirect ophthalmoscopy. There is a linear relationship between oxygen tension and IOP with an R squared value of 0.96. Progressive slow changes in the retinal vessel diameter and optic nerve appearance were observed as well once IOP was increased beyond 30 mmHg.
Small changes in IOP can affect preretinal oxygen tension significantly. This negative correlation shows IOP plays an important role in the regulation of intravitreal and retinal oxygen.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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