Intraocular Pressure And Systemic Hypercapnia And Hyperoxia

Abstract

Purpose: : To investigate the magnitude of change, if any, of intraocular pressure (IOP) to systemic gas provocations in healthy participants.

Methods: : The sample consisted of five healthy participants (mean age 24.6 ± 2.7 years) with no ocular or systemic diseases and free from any blood flow-altering medications. Following stabilization of end-tidal partial pressures of carbon dioxide (P_ETCO₂) and oxygen (P_ETO₂), three IOP measures were obtained in a randomly selected eye during each of a series of four inhaled gas conditions; baseline A (P_ETCO₂ = 38mmHg; P_ETO₂ = 100mmHg), hypercapnia 42 (P_ETCO₂ = 42mmHg; P_ETO₂ = 100mmHg), hypercapnia 46 (P_ETCO₂ = 46mmHg; P_ETO₂ = 100mmHg), baseline B (P_ETCO₂ = 38mmHg; P_ETO₂=100mmHg). Measurements were then obtained in the other eye during the following four inhaled gas conditions: baseline C (P_ETCO₂ = 38mmHg; P_ETO₂ = 100mmHg), hyperoxia 250 (P_ETCO₂ = 38mmHg; P_ETO₂ = 250mmHg), hyperoxia 500 (P_ETCO₂ = 38mmHg; P_ETO₂ = 500mmHg), baseline D (P_ETCO₂ = 38mmHg; P_ETO₂ = 100mmHg). The gas blends were achieved using the RespirAct™ (Thornhill Research Inc., Toronto, Canada) attached to a sequential rebreathing circuit (HiOx-80, VIASYS Healthcare Inc.).

Results: : The means and standard deviation of IOP at each gas provocation were: baseline A = 12.4 ± 1.9; hypercapnia 42 = 13.2 ± 1.4; hypercapnia 46 = 13.0 ± 1.4; baseline B = 12.5 ± 1.8; baseline C = 12.8 ± 3.0; hyperoxia 250 = 12.1 ± 2.2; hyperoxia 500 = 12.0 ± 1.7; baseline D = 11.9 ± 3.1. Two repeated-measures ANOVAs were performed which showed no significant differences in IOP between hypercapnia and baseline (p=0.38), nor between hyperoxia and baseline (p=0.34).

Conclusions: : Preliminary results of this study show that IOP does not appear to vary significantly with systemic hypercapnia or hyperoxia.

Keywords: intraocular pressure