Abstract
Purpose :
Aqueous humour outflow facility determines intraocular pressure (IOP), and decreased outflow facility causes IOP elevation in glaucoma. Classic studies have argued that outflow facility is unaffected by temperature reduction (Bárány EH. Acta Soc Med Upsal. 1954) or metabolic inhibitors (VanBuskirk EM, Grant WM. Am J Ophthalmol. 1974), leading to the conventional view that outflow is passive and independent of metabolism. In this study, we re-examined the effects of temperature reduction and metabolic inhibitors on outflow facility.
Methods :
Outflow facility (C) was measured in enucleated eyes from C57BL/6 mice (male, 9-14 weeks old) using iPerfusion (Sherwood JM et al. PLoS One. 2016) within 20 minutes of cervical dislocation. All experiments were conducted in compliance with the “Statement for the Use of Animals in Ophthalmic and Vision Research”. We performed three experimental sets: 1) C was measured in contralateral eyes perfused with vehicle at 35°C versus 22°C (n = 10 pairs); 2) C was measured in contralateral eyes at 35°C perfused with inhibitors of glycolysis and oxidative phosphorylation (11mM 2-Deoxy-D-glucose + 4mM sodium azide + 100μM 3PO in PBS) versus isosmotic vehicle (n = 9 pairs); and 3) C was measured in contralateral eyes at 35°C versus 22°C where both eyes were perfused with metabolic inhibitors (n = 8 pairs). Facility at 22°C was multiplied by 1.36 to correct for higher viscosity at lower temperature. Weighted t-tests were used to detect statistical significance (Sherwood JM et al. PLoS One. 2016).
Results :
In Set 1, the temperature-corrected C was 63 [38, 78]% (geometric mean [95% CI]) lower at 22°C compared to 35°C (P = 0.0017). In Set 2, perfusion with metabolic inhibitors reduced C by 21 [9, 31]% (P = 0.0063). In Set 3, the temperature-corrected C was 44 [29, 56]% lower at 22 versus 35°C (P = 0.0006) in the presence of metabolic inhibitors.
Conclusions :
Suppressing metabolic activity, either by reducing temperature or by inhibiting glycolysis and oxidative phosphorylation, significantly reduces outflow facility in freshly enucleated mouse eyes. Classic studies examining this phenomenon used bovine or human eyes greater than 24 hours post mortem, where metabolic activity would already be suppressed. Our results suggest that active cellular metabolism contributes to the regulation of aqueous humour outflow and IOP, and disruption of these mechanisms may thereby contribute to glaucoma.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.