Correlation Between Intraocular Pressure Measurement by Tomometer and Anterior Chamber Depth Measurement by Ultrasound

Intra ocular pressure (IOP) may theoretically increase due to steep Trendelenberg position and studies showed that IOP reaches peak levels after steep Trendelenberg position on an average of 13 mmHg higher than preanesthesia induction values. Major determinants of IOP are aqueous humor flow, choroidal blood volume, central venous pressure and extra ocular muscle tone. During the robotic surgery there are two theories explaining the increase of IOP, first, gravitational forces increase central venous pressure which in turn affect orbital venous pressure and increase IOP. Second, intraperitoneal carbon dioxide causes increased choroidal blood volume which may result in IOP increase. One study reported that low end tidal carbon dioxide was a significant predictor of the IOP increase. Continuous absorption of carbon dioxide from peritoneum and increased pressure on diaphragm results in lower delivered tidal volumes and subsequently increased arterial carbon dioxide levels leading to increased choroidal blood flow and increased IOP. Hassen GW et al measured anterior chamber depth in 2 patients with glaucoma and compared the anterior chamber depth (ACD) with the intraocular pressure measured by tonometer. They concluded that bedside ultrasound could be useful in evaluating patient with suspected increased IOP, who are unable to open their eyes. It can also be used for serial examination and follow-up of treatment success. They also mentioned that, it is necessary to conduct a prospective study with a larger sample size, to evaluate if there is agreement between measurements using a tonometer and measurements of the ACD using ultrasound. In addition, it is essential to determine the cut off normal ACD for evaluation of IOP.