Can CT Detect Plastic in the Eye?
CT has limited and variable sensitivity for detecting plastic foreign bodies in the eye, with documented cases of missed plastic intraocular foreign bodies even on orbital CT scans. 1
Detection Characteristics of Plastic on CT
- Plastic visibility on CT is highly variable and depends on the specific composition of the plastic material 2, 3
- Plastic materials are generally radiolucent on plain radiographs, similar to wood and rubber 2
- While CT is 5-15 times more sensitive than radiography for foreign body detection overall, this advantage does not reliably extend to all plastic materials 2
- The utility of foreign body visualization with CT is based on the object's density—plastics that are more porous will have lower attenuation values due to air content, making them harder to detect 2
Critical Clinical Evidence
- A documented case report describes a polyvinyl chloride (PVC) plastic intraocular foreign body that was completely missed on both CT scan and B-scan ultrasonography, only being discovered during vitrectomy for posttraumatic endophthalmitis 1
- This case resulted in atypical posttraumatic uveitis that only resolved after surgical removal of the plastic foreign body 1
- Recent research has identified various plastic particles (including polyvinyl chloride, nylon 66, and polystyrene) within human vitreous humor samples, demonstrating that plastic materials can indeed be present in ocular tissues 4
Recommended Diagnostic Algorithm
When plastic foreign body is suspected in the eye:
Obtain thin-slice (1 mm) CT of the orbits without contrast as the initial imaging study, as foreign bodies may be very small and missed with thicker slices 2
If CT is negative but clinical suspicion remains high based on mechanism of injury and examination findings, maintain a high index of suspicion for retained foreign body 1
Consider B-scan ultrasonography as a complementary modality, though this also has documented false-negative rates for plastic materials 1, 5
Proceed to surgical exploration if clinical findings strongly suggest retained foreign body despite negative imaging, as inflammation, pain, or endophthalmitis may indicate occult plastic material 1
Critical Pitfalls to Avoid
- Never rely solely on negative CT imaging to exclude plastic foreign bodies in the setting of penetrating ocular trauma with high clinical suspicion 1
- The absence of a visible foreign body on CT does not rule out plastic material, particularly low-density plastics 1, 3
- Retained plastic can trigger granulomatous reactions, chronic inflammation, and superimposed infections including endophthalmitis 2, 1
- MRI is contraindicated if there is any suspicion for metallic foreign body and is not helpful for detecting plastic foreign bodies 2, 3