Advancing the health and well-being of animals and people

Fellow: Stacey Cooley
Mentor: Peter Scrivani

Department of Clinical Sciences
Email:; 607-253-3160
Sponsor: American College of Veterinary Radiology
Grant Number: N/A
Title: Ultrasonographic Measurement of the Optic Nerve Sheath Diameter in Horses
Annual Direct Cost:  $4,350
Project Period: 0701/2013- 06/30/2014

DESCRIPTION (provided by applicant): Early diagnosis of elevated intracranial pressure and the ability to monitor treatment response is critical to preventing progressive brain injury due to intracranial pressure induced reduction in cerebral perfusion. In people detecting enlargement of the optic nerve sheath diameter by transpalpebral ultrasonography is a highly accurate test for elevated intracranial pressure. Additional benefits of this test are its noninvasiveness, ease of use, accessibility, affordability, and lack of requirement for general anesthesia. We propose that this test is beneficial to horses with suspected elevated intracranial pressure; we are particularly interested in the ultimate application of this test in foals with hypoxic ischemic encephalopathy. Therefore, our first aim is to demonstrate the feasibility of making this measurement in live horses by assessing repeatability, intraobserver agreement, and interobserver agreement. Our second aim is to investigate hypotheses that optic nerve sheath diameter is positively correlated with age (presumably due to normal growth) and with body weight, which also will help establish a reference range. The study design is prospective, observational, cross-sectional, and blinded. The sample population will consist of 50 horses of variable ages and body weights that are representative of clinical practice, and without clinical signs of ocular disease or elevated intracranial pressure. Descriptive statistics will be reported for all variables. Repeatability will be assessed as the percentage of differences between duplicate measures that are <2 standard deviations from the mean difference between duplicate measures. Agreement within and between observers will be assessed using Bland-Altman plot analysis. Correlations will be investigated using Pearson’s correlation if all of the age, body weight, and optic nerve sheath diameter data are Normal and linear; otherwise, we will use Spearman’s correlations. Our overall threshold for significance will be P≤0.05 2-sided, but we will use Bonferroni adjustments to correct for multiplicity. We expect that the results of this study will both establish a reference range of optic nerve sheath diameter in horses and justify whether or not further investigations are reasonable in hospital patients (particularly foals with hypoxic ischemic encephalopathy).