Acute Stress Increases Intraocular Pressure in Nonhuman Primates

Abstract

Purpose: To quantify intraocular pressure (IOP) change and time course during stressful activity Study Design: Experimental Study Subjects: Three nonhuman primates (NHPs) Methods: Bilateral IOP and aortic blood pressure (BP) were recorded continuously, then averaged for periods of 8-30 seconds before, during, and after a common anesthetic induction procedure (cage squeeze followed by intramuscular injection). Experiments were repeated four times in each NHP. Main Outcome Measures: IOP, BP, and heart rate (HR) change during an anesthetic induction procedure Results: IOP, mean arterial pressure (MAP), and HR increased rapidly and significantly by 27%, 38%, 34%, respectively, in anticipation of anesthetic induction (Figure; p<0.05). IOP rose ~10% within 10 seconds of hearing the technician enter the outer anteroom door, and reached its maximum within ~1 minute of first anticipating human contact. IOP fell to below baseline levels within 1 minute after anesthetic induction. Conclusions: IOP increases rapidly and significantly in response to stressful situations in the nonhuman primate.

Effect of Anesthesia on Intraocular Pressure Measured With Continuous Wireless Telemetry in Nonhuman Primates

“…Results show that changes in IOP with injectable and inhalant anesthesia relative to precontact baseline are generally small, which bodes well for clinical and animal research activities that rely on postanesthesia IOP measurements. Both this study and a recent study from our group show that acute stress associated with human contact significantly elevates IOP, MAP, and HR in NHPs, demonstrating the importance of measuring IOP using telemetry that doesn't require human contact 1. Anesthesia did lower IOP significantly when compared to IOP measured when the NHPs are in contact with staff (mean decrease of 5.4 mm Hg), but this is likely to be due to the relaxation of the animals from a stressful state and not the pharmacologic effects of the anesthesia itself, as postulated in prior NHP and human studies 1,15.…”

“…Both this study and a recent study from our group show that acute stress associated with human contact significantly elevates IOP, MAP, and HR in NHPs, demonstrating the importance of measuring IOP using telemetry that doesn't require human contact 1. Anesthesia did lower IOP significantly when compared to IOP measured when the NHPs are in contact with staff (mean decrease of 5.4 mm Hg), but this is likely to be due to the relaxation of the animals from a stressful state and not the pharmacologic effects of the anesthesia itself, as postulated in prior NHP and human studies 1,15. Previous studies have shown that changes in IOP can be modulated through relaxation of the extraocular muscles, which could be the mechanism through which anesthesia acutely lowers IOP when the subject is stressed and IOP is acutely elevated as a result 25.…”

“…We have developed and validated an implantable telemetry system (Konigsberg Instruments, Inc., Pasadena, CA, USA) that allows continuous monitoring of IOP and aortic blood pressure and records 500 measurements of IOP per second for up to 2.5 years 1,24. IOP transducers were calibrated biweekly via anterior chamber manometry from 5 to 30 mm Hg in 5 mm Hg steps, and all data were corrected for signal drift assuming a linear drift between calibration tests.…”

“…Only unilateral IOP data were acquired (OS) in NHP 9028 due to transducer failure in the right eye. We chose the precontact baseline to be the period ∼20 minutes prior to the technician entering the room to minimize acute stress and concomitant IOP, BP, and HR changes associated with the NHPs hearing the technicians preparing to enter the room 1. The preinjection baseline was the 30-second period immediately after the technician entered the room, but before touching the cage to squeeze the animal for injection.…”

“…The effects of anesthesia on IOP have been studied in both animal models and human patients using single time-point (snapshot) IOP measurements, but comparisons were not made to true naïve baseline IOP since only postcontact and/or postanesthesia IOP measurements were obtained. Studies have shown that contact with a clinician or human animal handler can acutely elevate IOP 1–7. Ketamine is an NMDA receptor antagonist anesthetic that is a commonly used in animal studies and in ophthalmic procedures involving children and uncooperative patients.…”