Systemic hypertension is associated with declined retinal functions via intraocular pressure (IOP)-independent mechanism 

Purpose : Systemic hypertension (HT) is a risk factor for glaucoma, although the precise mechanism remains elusive. Whether or not HT has any effect on intraocular pressure (IOP) as a contributory factor remains controversial. In this preliminary study, we evaluated the cross-sectional changes of blood pressure (BP), IOP changes and functional retinal response in rats with chronic HT.

Methods : Female spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY) aged 4 - 15 months were used. Non-invasive systolic BP and IOP measurements were determined under awake condition by the tail-cuff method and rebound tonometry, respectively. At 7 and 15 months of age, functional retinal response in retinal ganglion cells (RGCs) and cone photoreceptors of both SHR and WKY rats were determined by positive scotopic threshold response (pSTR) and photopic a-wave using full-field electroretinogram (ERG).

Results : SHR showed a sustained BP elevation throughout the studied period when compared with age-matched WKY controls. Interestingly, SHR displayed significantly lower IOP than WKY controls at 4 months (9.0 ± 0.1 vs 10.2 ± 0.1 mmHg), 7 months (9.6 ± 0.1 vs 10.3 ± 0.2 mmHg), and 15 months (9.8 ± 0.1 vs 10.8 ± 0.4 mmHg). At 7 months, pSTR reduced by 27% (N=4, p
Conclusions : The ERG data suggest that chronic HT leads to a progressive functional loss in RGCs and cone photoreceptors. In addition, impaired retinal responses observed in SHR may be mediated by an IOP-independent mechanism. Further longitudinal studies are warranted to investigate the precise relationship between IOP and the morphological and functional changes in retina over a prolonged period.