Abstract
PurposeTo investigate the effect of ageing on the recovery of ocular blood flow, intravitreal oxygen tension and retinal function during and after intraocular pressure (IOP) elevation.MethodsLong Evans rats (3- and 14-month-old) underwent acute stepwise IOP elevation from 10 to 120 mmHg (5 mmHg steps each 3 minutes). IOP was then returned to baseline and recovery was monitored for 2 hours. Photopic electroretinograms (ERG) were recorded at each IOP step during stress and at each minute during recovery. Ocular blood flow and vitreal oxygen tension (pO2) were assayed continuously and simultaneously using a combined laser Doppler flow meter (LDF) and an oxygen sensitive fibre-optic probe, respectively. The combined sensor was placed in the vitreous chamber, proximal to the retina. Data were binned into 3 minute intervals during stress and 1 min intervals during recovery. Recovery data was described using a bi-logistic function.ResultsRats of both ages showed similar susceptibility to IOP elevation, with pO2 showing a closer relationship to ERG than LDF. During recovery, both ages showed a distinctive two-phased recovery for all three measures with the exception of the LDF in 3-month-old rats, which showed only 1 phase. In all animals, LDF recovered fastest (<1 minute), followed by pO2 (<10 minute) and ERG (>1 hour). 14-month-old rats showed surprisingly faster and greater LDF recovery compared to the younger group, with similar levels of pO2 recovery. However, the ERG in these middle-aged animals did not fully recover after two hours, despite showing no difference in susceptibility to IOP during stress compared to the young group.ConclusionsYoung and middle-aged eyes showed similar susceptibility to IOP elevation in terms of pO2, LDF and ERG. Despite this lack of difference during stress, older eyes did not completely recover function, suggesting a more subtle age-related susceptibility to IOP.
Highlights
Ageing is considered a major risk factor in many neurodegenerative diseases, including Parkinson’s and Alzheimer’s disease [1]
The neurodegenerative disease glaucoma is strongly associated with senescence, an observation that cannot be accounted for by only small age-related increases in intraocular pressure (IOP)
ERG during IOP elevation Figure 2 shows the effect of stepwise IOP elevation on the photopic ERG in a representative 3- and 14-month old rat
Summary
Ageing is considered a major risk factor in many neurodegenerative diseases, including Parkinson’s and Alzheimer’s disease [1]. The neurodegenerative disease glaucoma is strongly associated with senescence, an observation that cannot be accounted for by only small age-related increases in intraocular pressure (IOP) This raises the possibility that some inherent neuronal, structural or vascular susceptibility [2], places older eyes at greater risk of IOP-related injury. Retinal blood flow has been shown to decline with age, a phenomenon that has been attributed to increased vascular resistance [4,5,6,7,8], decreased metabolic consumption due to age-related cell loss [9], rheological changes [10] in blood vessels and increasing IOP with age [11,12]. Impairment in the ability for blood flow to regulate during and after IOP elevation may lead to slower functional restoration [18,19]
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