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Jeremiah Kah Heng Lim, Christine T Nguyen, Algis J Vingrys, Bang V Bui; The effect of ageing on ocular blood flow, oxygen tension and retinal function during and after intraocular pressure elevation in rat eyes. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4554.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the effect of ageing on ocular blood flow, intravitreal oxygen tension and retinal function during and after intraocular pressure (IOP) elevation in rat eyes.
Anaesthetised (60:5 mg/kg ketamine:xylazine) three (n=14) and fourteen (n=16) month-old male Long Evans rats underwent IOP elevation (anterior chamber cannulation) from 10 to 120 mmHg in 5 mmHg steps (3 min) lasting a total of 1 hour. IOP was then returned to 10 mmHg and recovery was monitored for 2 hours. Photopic (background 15 cd/m2) electroretinogram b-waves (2.03 log cd.s/m2) were recorded at each IOP step and at each minute during recovery. At the same time, ocular blood flow (OBF) and vitreal oxygen tension (pO2) were assayed continuously using a combined laser Doppler flowmeter and an oxygen sensitive fibre-optic probe, respectively. The sensor was placed in the vitreous chamber, proximal to the retina. Data were analysed at each IOP step and at 1 min intervals during recovery. Recovery dynamics were described using a bi-logistic function.
During IOP elevation, rats of both ages showed no difference in LDF (two-way ANOVA F1,19 = 2.82, p = 0.09), pO2 (two-way ANOVA, main effects, F1,19 = 1.01, p = 0.32) or ERG (two-way ANOVA, main effects, F1,19 = 3.39, p = 0.07) attenutation. On recovery, both ages showed a two-phased recovery for all three measures with the exception of the LDF in 3-month-old rats, which showed only a rapid phase. LDF recovered fastest (<1 minute), followed by pO2 (<10 minute) and finally ERG (> 1 hour). During recovery older animals showed greater hyperperfusion (3 versus 14m.o.: 104±x% versus 120±y%, P < 0.05). Young and older eye showed similar levels of pO2 recovery (134±y% versus 120±y %, P < 0.05). Despite the similar pO2 recovery, the ERG in older eyes did not recover fully (3m.o. versus 14m.o.: 105% versus 86%, P < 0.05) 2 hours after acute IOP elevation.
Young and middle aged rats showed similar pO2, OBF and ERG susceptibility to IOP elevation. Age-related differences were manifest during recovery, with older eyes failing to show full ERG recovery despite significant hyperperfusion and normal oxygen recovery. These data suggests an inherent neuronal susceptibility to IOP elevation in middle aged rat eyes.
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