Transpalpebral ultrasonographic measurement of the optic nerve sheath diameter is a non-invasive, low cost method that may serve as an additional tool to help identify cats with intracranial haemorrhage (ICH) where invasive measurement of intracranial pressure (ICP) is contraindicated or unavailable
Journal citation

Evangelisti, M.A., Carta G., Burrai G.P., et al (2020)
Repeatability of ultrasound examination of the optic nerve sheath diameter in the adult cat: comparison between healthy cats and cats suffering from presumed intracranial hypertension
Journal of Feline Medicine and Surgery 22(10), 959-965

Published October 2020

Type of study
  • Prospective, blinded, observational cross-sectional study
  • n = 57 cats
Key points
  • This is the first study of transorbital ultrasonography as a method of identifying ICH in cats
  • Clinical diagnosis of ICH is challenging in small animals
  • As direct measurement of ICP requires specialist equipment and resources, there is increased interest in the development of non-invasive techniques
  • Ultrasound measurement of the optic nerve sheath diameter (ONSD) is a rapid, non-invasive and low cost procedure which is easily performed in awake cats
  • The subarachnoid space around the optic nerve is continuous with the intracranial subarachnoid space and an increase in ICP above a certain level can displace cerebrospinal fluid from the intracranial cavity into the subarachnoid space
  • Care should be taken not to inadvertently apply excessive pressure to the eye which could cause damage
  • ONSD > 1.5 mm suggested ICH whereas ONSD 1-1.4 mm indicated an absence of ICH


  • ONSD measurements were not compared to direct ICP pressure measurement
  • The transpalpebral ultrasonographic technique is a non-invasive, feasible and reproducible method to measure the optic nerve sheath diameter and may serve as an additional tool to help identify cats with ICH where invasive measurement of ICP is contraindicated or unavailable