Orbital wall fractures
The bony structures of the orbit are very fragile, which is why they are among the first to be damaged in facial trauma. Computed tomography can reveal various fracture patterns:
- Medial and inferior wall fracture: frequently leads to enophthalmos (posterior displacement of the eyeball into the orbit) and hypoglobus (downward displacement of the globe). A dangerous complication is the herniation of orbital fat into the resulting bony defect. This, in turn, can cause displacement of the medial and inferior rectus extraocular muscles.
- Trap-door fracture (trap-door): typical for the inferior wall (floor) of the orbit. Orbital fat and the inferior rectus muscle herniate through the defect slit into the maxillary sinus cavity. Concurrently, an accumulation of blood—hemosinus—is often detected within the sinus itself.
Penetrating injuries and foreign bodies
In open globe injuries, CT often reveals a decreased depth of the anterior chamber. The causes of this may include a corneal laceration or anterior displacement of the lens. Depending on the material, foreign bodies present different radiological appearances:
- Metal: radiopaque (very dense) objects that appear bright on scans. Penetrating injuries are frequently accompanied by the entry of air bubbles into the vitreous body.
- Wood (splinters): identified as linear areas of decreased density (hypodense) that can easily be mistaken for air collections. They typically cross the structures of the eyeball, and small true air bubbles may also be visualized in the anterior chamber.
Lens pathologies and globe rupture
Traumatic impact frequently leads to displacement of the lens (luxation or subluxation). Most commonly, it is displaced posteriorly. If a bilateral subluxation is detected, the physician must rule out systemic connective tissue disorders, such as Marfan, Ehlers-Danlos, or homocystinuria syndromes.
Globe rupture (globe rupture) is accompanied by vitreous hemorrhage and an overall reduction in globe volume. A characteristic radiological marker of marked ocular hypotony is the flat tyre sign (flat tyre) — flattening of the nasal part of the globe. If the penetrating injury was severe, phthisis bulbi (phthisis bulbi) may develop in the long-term period — the globe shrinks, decreases in size, and undergoes calcification.
Retrobulbar visual pathway
The optic nerve is a bundle of nerve fibers closely associated with the meninges of the brain. Lesions of the retrobulbar pathway depend on anatomical localization rather than histology. The method of choice for assessing these structures is contrast-enhanced MRI (CT is used primarily in acute strokes with ocular symptoms).
- Intracranial part of the nerve: begins after exiting the optic canal. The prechiasmatic segment, about 10 mm long, passes between the anterior cerebral and internal carotid arteries.
- Optic chiasm: located at the floor of the third ventricle above the diaphragm of the sella turcica. A crucial feature: only those fibers crossing from the nasal half of the retina (carrying information from the temporal visual fields) decussate here. Fibers from the lateral (temporal) half do not cross.
- Optic tracts: exit the chiasm dorsolaterally and head toward the lateral geniculate body, carrying mixed information from the ipsilateral and contralateral halves of the retina.
Briefly: answers to topical questions
What clinical symptoms occur when the inferior rectus muscle of the eye becomes entrapped in an orbital floor fracture?
Entrapment of the inferior rectus muscle in an orbital floor fracture results in diplopia and restricted extraocular motility. Unrecognized fracture or scarring of displaced bone fragments leads to tissue entrapment, fibrosis, and persistent diplopia.
Which skull bones form the medial orbital wall, which is the most vulnerable in trauma?
The medial orbital wall is formed by the maxilla, frontal, ethmoid, lacrimal, and sphenoid bones. This very thin bone, known as the lamina papyracea, is easily injured.
Where do the optic tracts terminate, and what structures form the next section of the visual pathway?
The optic tracts head toward the lateral geniculate body, where the majority of their axons terminate. The next section of the visual pathway is formed by the optic radiations, which originate from the lateral geniculate body.
To remember which fibers cross in the chiasm, keep in mind: "Noses meet." The nasal retinal fibers cross, while the temporal fibers stay on their own side.
Class and exam questions
In which windows should CT be evaluated in eye trauma?
The scan must be evaluated in a bone window (to detect subtle orbital wall fractures) and a soft tissue window (to assess muscles, fat, lens, and hemorrhages).
How to distinguish a wooden ocular foreign body from an air bubble on CT?
Wooden splinters appear as linear hypodense (dark) areas. Due to the low density of wood, an inexperienced specialist might mistake them for air, but the shape (linear) and the trajectory of the wound tract help establish the correct diagnosis.
What is the "flat tyre" sign?
This is a CT sign of globe rupture. Due to the loss of intraocular fluid and hypotony, the nasal part of the eyeball loses its rounded shape and appears flattened.
What else to study on this topic
- Radiological appearance of scleral buckling and silicone oil tamponade in the treatment of retinal detachment.
- MRI visualization of the brainstem and skull base in eye movement disorders.
- The relationship between visual fields and the anatomy of the optic chiasm.
- Specific complications of extraocular muscle herniation into the maxillary sinus.
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