Effect of Nitrous Oxide (N2O) on Intraocular Pressure in Healthy Volunteers

Overview

The purpose of this study is to learn if breathing nitrous oxide (also known as "laughing gas") changes the pressure in a person's eyes. Some patients who need regular eye exams to measure their eye pressure often need to be put to sleep with medicine in order to complete the eye exam. Some of these medicines are known to cause changes in a person's eye pressure. Because of this, such medicines are avoided if the eye doctor needs to measure the patient's eye pressure. One medicine that is frequently used to put patients to sleep is nitrous oxide. No one really knows what effect nitrous oxide might have on a persons' eye pressure. The investigators are interested to see if nitrous oxide causes an increase, decrease, or no change in eye pressure. The investigators also want to investigate if there is a difference in the effects of nitrous oxide on eye pressure between males and females. Understanding these effects of nitrous oxide is important because during such eye exams, the eye doctor uses the pressure measurements to make important decisions about treatment and surgery options for the patient. The investigators hypothesize that the use of inhaled nitrous oxide (N2O) will result in a decrease in IOP in healthy volunteers. The investigators aim to determine the magnitude and duration of change, if any, in IOP caused by inhalation of N2O, and to assess if the gender of the patient has a role in this effect.

An initial pre-anesthetic evaluation and physical examination will be performed by an attending anesthesiologist, and an eye exam will be performed by an attending ophthalmologist to determine suitability for inclusion according to the above criteria. Ideally the eye exam will take place immediately prior to conduction of the study. However, logistical restraints may require that the eye exam take place at a separate time/date prior to conduction of the study. IOPs will be measured by the attending ophthalmologist (B.E.) who will be blinded to the actual readings of the Tonopen by means of a small screen, and a single trained observer (E.F.) will record observations from the Tonopen. The nitrous oxide sedation will be managed by the attending anesthesiologist (K.L.). All patients will be monitored throughout using standardized monitoring (continuous EKG, non-invasive BP, and continuous pulse oximetry).