First and second year — the floor first, then every step
On the trauma CT, read the orbits on a soft-tissue window: globe contour and volume, lens position, intraocular gas or foreign body, and retrobulbar haematoma with tenting of the posterior globe — the orbital compartment syndrome.
Orient first
Open globe injury is an ophthalmic emergency; CT is often the first test because the eye is swollen shut.
A retrobulbar haematoma raises orbital pressure; the posterior globe "tents" into a cone as the optic nerve is stretched.
Metal must be excluded before any MRI — CT is the test for a metallic foreign body.
Acquire the study
Thin-section (≤ 1 mm) CT of the orbits on bone and SOFT-TISSUE windows, with axial, coronal and sagittal reformats.
The manoeuvre
Soft-tissue window, axial: compare the globes side by side — contour, size and the anterior chamber depth.
Flat tire sign (a flattened, irregular globe contour) and reduced globe volume — open globe.
Intraocular gas or a hyperdense foreign body; streak artefact from metal.
Lens: dislocated posteriorly into the vitreous, or absent from its position.
Retrobulbar space: haematoma, proptosis measured against the interzygomatic line, and the posterior globe angle (tenting).
Bone window: orbital wall fractures and the optic canal.
What confirms it
Globe deformity, intraocular gas or foreign body, or a change in anterior chamber depth against the other eye.
What licenses you to exclude it
A normal CT does not exclude a small open globe injury — clinical examination decides.
The classic misread
Missing a wooden foreign body — it can be hypodense and mimic gas.
Calling a posterior scleral buckle or a prosthesis an injury — check the history.
Reporting the injury
Classification to use
Open versus closed globe (Birmingham Eye Trauma Terminology is the clinical system); retrobulbar haemorrhage with or without orbital compartment signs.
Measurements — and how to take them
Foreign body size in mm and its distance from the sclera; proptosis in mm beyond the interzygomatic line.
What to report
Globe contour and volume, intraocular gas/foreign body (size, location), lens position, anterior chamber depth, retrobulbar haematoma and tenting, optic canal, wall fractures.
How to report it
CT: "Left globe is reduced in volume with a flattened posterior contour and intraocular gas, in keeping with open globe injury. 2 mm metallic foreign body in the posterior vitreous. No retrobulbar haematoma."
What not to report
Do not recommend MRI when a metallic foreign body has not been excluded.
Associated injuries to look for
Orbital wall and optic canal fractures, facial fractures, intracranial injury.
What changes management
Open globe → urgent ophthalmic surgery; no pressure on the eye.
Retrobulbar haematoma with tenting → emergency lateral canthotomy.
Reference values
Each value carries the caveat that keeps it from being misused. Normal limits and diagnostic criteria are kept apart on purpose: a disease cut-off read as a normal range is the more dangerous mistake.
Normal limits
Globe · Axial length of the adult globe
approximately 22–25 mm (mean about 24 mm)
An axial length over about 26 mm indicates axial myopia with its staphyloma and detachment associations; a short globe accompanies hypermetropia and angle-closure anatomy.
USG · CT · MRI
Diagnostic criteria
Globe (integrity) · Open-globe signs — how to report them
an intact globe contour; flattened “flat-tyre” contour, intraocular gas or a foreign body, and a scleral discontinuity are the rupture clues — qualitative, not an axial-length millimetre (already registered)
US is often avoided if rupture is suspected. A normal axial length does not exclude a rupture.
CT · USG
Orbit (globe position) · Globe protrusion beyond the interzygomatic line
the anterior globe margin lies within approximately 21–23 mm of the interzygomatic line (texts differ on the exact ceiling)
Axial CT at the level of the lenses: a line is drawn between the anterior tips of the zygomatic processes, and the perpendicular distance to the anterior margin of each globe is measured.
⚠️ Texts genuinely differ on the millimetre — asymmetry over about 2 mm between sides is often the more useful observation. Head tilt and gantry angle shift the line; measure on a properly aligned axial series.
CT
See it on real cases
Direct links to Radiopaedia — the reference article and worked cases with their images. Each opens on Radiopaedia.