Porcine study supports CLOSED optic nerve ultrasound protocol: full analysis

A new in-vivo porcine study suggests that ultrasound can measure the optic nerve and optic nerve sheath with good agreement to MRI when operators use the standardized CLOSED protocol. That’s a technical finding, but an important one: optic nerve sheath diameter has been studied as a non-invasive proxy for intracranial pressure, and one of the biggest barriers to broader use has been measurement consistency across operators, machines, and species. (pubmed.ncbi.nlm.nih.gov)

The work builds on a broader push to standardize optic nerve sheath ultrasound. The CLOSED protocol was introduced in 2020 as a structured approach to sonographic assessment of optic nerve sheath diameter, aimed at improving both safety and reproducibility. Subsequent human studies using the protocol have described a consistent measurement approach: evaluating both eyes, using transverse and sagittal planes, and measuring 3 mm behind the optic disc. In parallel, a wider review literature has emphasized that methodological discrepancies remain a major reason optic nerve sheath ultrasound can be hard to compare across studies. (pubmed.ncbi.nlm.nih.gov)

That context helps explain why a porcine validation study matters. Pigs are already used as experimental models for intracranial hypertension research, and prior swine work has shown that ultrasound-measured optic nerve sheath diameter changes with intracranial pressure and correlates linearly with invasive ICP readings. Another pig study noted the lack of established normal porcine optic nerve sheath values in the literature, underscoring the need for better baseline characterization and standardized imaging methods. Against that backdrop, demonstrating that ultrasound measurements align well with MRI adds confidence that the anatomy being captured sonographically is real and reproducible, not just operator-dependent artifact. (sciencedirect.com)

The study also lands in a veterinary landscape that’s already testing this concept across species. Published work has reported transpalpebral optic nerve sheath ultrasound measurements in healthy dogs, repeatability studies in cats, MRI-based optic nerve sheath assessment in cats with and without presumed intracranial hypertension, and direct ICP-comparison work in horses. More recently, a canine clinical study examined optic nerve sheath diameter before and after mannitol in dogs with presumed intracranial hypertension. Taken together, that suggests the field is moving from proof of concept toward clinically relevant application, but it’s still doing so unevenly and with limited species-specific thresholds. (pubmed.ncbi.nlm.nih.gov)

Expert and review literature outside veterinary medicine has generally framed optic nerve sheath ultrasound as a useful screening or monitoring adjunct rather than a standalone replacement for invasive intracranial pressure assessment. A 2021 animal-model study in pigs concluded that ultrasound ONSD correlated linearly with ICP, while noting a lag in return to baseline after rapid decompression. Reviews have likewise stressed that the modality’s value depends heavily on protocol quality, image acquisition, and clinical context. That caution is relevant for veterinary teams, where case mix, sedation status, globe conformation, and access to advanced imaging can all affect implementation. (sciencedirect.com)

Why it matters: For veterinary professionals, the real significance is standardization. If ultrasound is going to help screen or monitor patients with suspected intracranial hypertension, practices need confidence that the number on the screen reflects anatomy, not technique drift. This porcine study doesn’t establish clinical cutoffs for dogs or cats, and it doesn’t replace MRI, CT, fundic exam, or neurologic assessment. But it does support a more rigorous framework for future veterinary studies, especially in emergency and critical care settings where a repeatable bedside tool could help triage unstable patients, monitor response to therapy, or support referral decisions when advanced imaging isn’t immediately available. (theultrasoundjournal.springeropen.com)

There’s also a translational angle. Because the CLOSED protocol was designed to reduce ambiguity in how optic nerve sheath measurements are obtained, validation in an in-vivo animal model may help bridge human neurocritical care methods and veterinary research. That could be especially useful for academic centers studying traumatic brain injury, hydrocephalus, inflammatory CNS disease, or other causes of raised ICP in animal patients. Washington State University, for example, has highlighted active canine research interest in optic nerve sheath diameter as a non-invasive way to estimate intracranial pressure in dogs with brain disease. (pubmed.ncbi.nlm.nih.gov)

What to watch: The key next milestones are prospective veterinary studies that define normal ranges and intervention thresholds by species, test inter-operator repeatability in real clinical settings, and show whether standardized optic nerve sheath ultrasound changes case management or outcomes for patients with suspected intracranial hypertension. (pubmed.ncbi.nlm.nih.gov)