Effects of Body Temperature and General Anesthetics on Intraocular Pressure in Rats

Ocular hypertension has been identified as the fundamental risk factor in glaucoma which is the leading cause for irreversible blindness in the world. Understanding the different factors that affect IOP is of utmost importance in clinical management as IOP is considered as the fundamental factor in assessing the efficiency of glaucoma medications. Several studies have attempted to assess factors that could affect IOP including age, body position, blood pressure, anesthetics commonly used during eye operations, etc. However, in most of these studies IOP is measured under anesthesia using rodent models and these anesthetics could affect the IOP measurements directly or indirectly. The use of tonometry in such experiments also includes certain limitations like acquiring IOP at discrete moments in time, human error while handling the instrument and stress induced spikes in IOP while handling awake animals. This study uses a wireless continuously monitoring device to eliminate these limitations while also acquiring IOP at a higher rate. Anesthesia induction is known to lower body temperature. However, previous studies on the effects of various anesthetic agents fail to take into account this drop in body temperature which could potentially lead to erroneous results. This thesis focuses on studying the effects of two commonly used anesthetic agents, isoflurane and ketamine while accounting for loss in body temperature. The effects of changing body temperature on intraocular pressure was also studied to help understand the effects of these factors accurately. There was a statistically significant drop (p\u3c0.001) in intraocular pressure post isoflurane induction with no heat support across several animals. The addition of heat support in the next set of experiments resulted in an almost steady pressure throughout the experiment. Since the body temperature was maintained constant throughout the experiment, there was no statistically significant difference (p\u3e0.05) among IOP’s for the awake and anesthetized condition. This conclusion was then confirmed by obtaining a direct effect of changing body temperature on IOP. There was a rise in IOP while the animal was placed on a 42 degree Celsius heating pad and a drop in IOP while the animal was placed on a 20 degree Celsius surface with no heat support. The corresponding changes in body temperature were confirmed using a rectal thermometer. There were no significant changes in the IOP measured by the sensor while measuring pressure with the iCare tonolab. Applanation tonometry however produced an average mean intraocular pressure increase of 2.11 ± 1.62 mmHg