Ocular ultrasound in the evaluation of anisocoria following head injury: a case report

Abstract

Background

Anisocoria following severe head injury is traditionally interpreted as an impending neurological emergency, often prompting immediate empiric interventions for presumed intracranial hypertension. However, traumatic ocular injuries can present with identical pupillary findings, creating a critical diagnostic dilemma in the unresponsive trauma patient.

Case presentation

We present the case of a 70-year-old intubated male with a severe traumatic brain injury who presented with a unilateral fixed, dilated pupil. Because urgent transport for head computed tomography (CT) was delayed due to severe respiratory acidosis from an obstructed endotracheal tube, bedside ocular point-of-care ultrasound (POCUS) was performed to evaluate for ocular mimics of cerebral herniation. Using a minimal-pressure technique after excluding globe rupture, POCUS identified a posterior dislocation of the crystalline lens into the vitreous cavity. This rapid identification of a mechanical ocular etiology for the anisocoria successfully prevented the immediate management for brain herniation. Subsequent CT confirmed the ultrasound findings, and the patient ultimately underwent lensectomy and iris repair.

Conclusions

This case underscores the utility of screening ocular ultrasound in differentiating mechanical ocular complications from intracranial pathology in the acute trauma setting. POCUS serves as an invaluable extension of the physical examination when traditional neurological assessment is limited by sedation, paralysis, or intubation, thereby refining initial resuscitation pathways and avoiding unnecessary neuro-directed interventions alone.

Background

Lens dislocation refers to the displacement of the crystalline lens from its normal anatomical position. Although systemic connective tissue disorders are well-recognized causes, trauma remains a frequent etiology in acute care settings [1]. Traumatic lens dislocation is often associated with a significant blunt force impact that concurrently damages the iris sphincter, resulting in traumatic mydriasis. It may also result in visual impairment and secondary complications, including glaucoma, uveitis, and retinal detachment [1]. Patients with traumatic lens dislocation commonly present with blurred vision, decreased visual acuity, monocular diplopia, and ocular pain. Because lens dislocation may coexist with other traumatic ocular injuries, including open globe injury and retinal tears or detachment, a thorough ocular examination is essential. Clinical findings may be subtle, with phacodonesis, iridodonesis, or an abnormally shallow posterior chamber occasionally providing the only clues to lens displacement [2].

In head-injured patients, a unilateral dilated pupil often presents a cognitive trap for the treating clinician; it is instinctively interpreted as a sign of impending cerebral herniation, triggering urgent neuroimaging and empiric decompressive strategies such as hyperosmolar therapy. However, traumatic ocular causes of anisocoria may be clinically indistinguishable from these neurological cause. This distinction is especially challenging for general and critical care clinicians managing unconscious, paralyzed, or intubated patients where standard physical and neurological examinations are profoundly limited. Ocular ultrasound offers a practical bedside imaging modality for the direct visualization of intraocular structures, proving particularly valuable in diagnostic dilemmas where neurological causes are heavily suspected but cannot be immediately confirmed. This report describes a common trauma presentation with an uncommon but clinically significant diagnosis, highlighting the critical value of ocular ultrasonography in guiding early resuscitation.

Case presentation

A 70-year-old man with no known medical comorbidities was transferred to the emergency department following a fall into a pit from a height of approximately eight feet. Pre-hospital events included a brief loss of consciousness, right ear bleeding, and two episodes of projectile vomiting. He was acutely intoxicated with alcohol and had been intubated at an outside facility due to altered mental status before transfer.

On arrival, airway reassessment revealed an obstructed endotracheal tube, which required immediate re-intubation. The patient was hypertensive (160/100 mmHg) with a pulse rate of 96/minute, but otherwise hemodynamically stable. Neurological examination revealed a Glasgow Coma Scale (GCS) score of E1VTM5 under sedation. Pupillary assessment revealed a 2 mm right pupil that was reactive to light, and a 4 mm left pupil that was fixed and non-reactive. Physical examination noted a sutured laceration over the right pinna, a left eyebrow abrasion, and an inactive bleed from the right ear. The extended focused assessment with sonography for trauma (eFAST), as well as chest and pelvis radiographs, were unremarkable.

Initial arterial blood gas (ABG) analysis revealed acute respiratory acidosis (pH 7.15, pCO2 79 mmHg, HCO3 22 mmHg, AG 12), secondary to the obstructed endotracheal tube prior to exchange. Because the severe respiratory acidosis necessitated ventilator adjustments and a brief stabilization period, immediate transport for non-contrast brain computed tomography (CT) was delayed. Given the classic presentation of a unilateral blown pupil in a severe trauma patient, empiric administration of hyperosmolar therapy and hyperventilation for presumed raised intracranial pressure was considered. However, bedside ocular POCUS was rapidly performed to assess for papilloedema and screen for mechanical ocular causes of anisocoria.

Prior to the examination, the eye was visually inspected to exclude obvious signs of open globe injury (for example, uveal prolapse, irregular pupillary shape, flat anterior chamber). B-scan ultrasonography was then performed using a high-frequency linear transducer (7–13 MHz) with the patient in the supine position. A copious gel technique was employed to minimize any pressure on the globe. The eye was scanned in both transverse and sagittal planes through the closed eyelid. The scan demonstrated the absence of the crystalline lens in the anterior chamber and its posterior displacement into the vitreous cavity, whereas the right eye showed a normally positioned lens (Fig. 1). No sonographic features of papilloedema, vitreous hemorrhage, or retinal detachment were identified.

Fig. 1.

Ocular ultrasound showing normally located lens in the right eye  and posteriorly dislocated lens indicated by red arrow in left eye

Subsequent non-contrast CT of the brain revealed no acute intracranial pathology and confirmed the posterior lens subluxation, along with minimal pneumo-orbit on the left side (Fig. 2). Although CT revealed a pneumo-orbit, the volume of intraorbital air was minimal and did not generate significant sonographic artifacts (dirty shadowing) or obscure the visualization of the posterior segment during the initial ultrasound.

Fig. 2.

Normal location of the lens of the right eye, as seen in computed tomography imaging, indicated by the yellow arrow (left), and posteriorly dislocated lens of the left eye, seen in imaging, shown by the red arrow (right)

The early POCUS diagnosis successfully halted the administration of empiric neuro-resuscitative measures for herniation. The patient was managed conservatively during the acute phase, his neurological status rapidly improved, and he was extubated on day two. Following ophthalmology consultation, he underwent a lensectomy with posterior chamber intraocular lens (PCIOL) placement and iris repair.

Discussion

Traumatic lens dislocation results from the disruption of the zonular fibers following blunt ocular or craniofacial trauma [2]. In the acute trauma setting, its diagnosis may be significantly delayed because of overlapping neurological signs, particularly in the intubated patient where clinical examination is limited.

Anisocoria has been shown to correlate with greater injury severity and poorer outcomes following blunt traumatic brain injury, reinforcing its traditional role as a warning sign of significant intracranial pathology [3]. Consequently, the identification of a unilateral fixed dilated pupil frequently prompts urgent neuroimaging and consideration of empiric therapies for impending herniation. In the present case, however, bedside ocular ultrasound rapidly identified a structural ocular cause for the pupillary abnormality, allowing a more targeted diagnostic approach while definitive neuroimaging was being arranged.

Ocular ultrasound is exceptionally well-suited to acute and critical care environments, offering rapid bedside assessment without ionizing radiation. It enables reliable identification of the lens position and associated intraocular pathology, particularly when direct ophthalmoscopy is precluded [4]. Recognition of lens dislocation is clinically vital, as delayed diagnosis may predispose patients to secondary complications and necessitate more complex surgical management [5, 6]. CT remains complementary for assessing orbital fractures and intraorbital air, while magnetic resonance imaging provides detailed soft tissue evaluation but is rarely feasible acutely [7].

Most importantly for clinicians managing complex patients, this case reinforces the role of POCUS in mitigating cognitive anchoring. The discovery of a unilateral dilated pupil frequently triggers a protocolized cascade of interventions, such as the administration of mannitol or hypertonic saline. By rapidly identifying a structural ocular etiology, POCUS refined the diagnostic reasoning and prevented the inappropriate escalation of purely neuro-directed management while the patient was awaiting definitive CT imaging.

Beyond the diagnosis of lens dislocation, this case highlights the potential role of ocular POCUS as a screening tool in trauma patients presenting to the emergency department. Ocular examination may be challenging in the presence of periorbital edema, facial injuries, altered sensorium, sedation, or mechanical ventilation. In such situations, bedside ultrasound can serve as an extension of the physical examination, facilitating the early identification of clinically significant ocular injuries and helping guide timely specialist referral and further imaging.

Clinicians must practice strict safety considerations; suspected open globe injury is generally considered a contraindication for ocular ultrasound [8]. Clinicians must visually exclude obvious signs of rupture before attempting sonography, and a "copious gel" or "water bath" technique is mandatory to avoid direct transducer pressure on the cornea [9]. Furthermore, while ultrasound is highly sensitive to structural pathologies like lens dislocation, clinicians must remain aware of its limitations. Functional or microscopic causes of traumatic anisocoria, such as an isolated iris sphincter tear or direct third nerve injury, cannot be visualized sonographically [10]. Therefore, a "normal" ultrasound in the setting of a fixed dilated pupil primarily serves to rule out gross mechanical obstruction or globe rupture, rather than definitively confirming a specific diagnosis. However, a positive finding—such as a dislocated lens—provides immediate, actionable clarity.

The presence of intraorbital air (pneumo-orbit) also presents a specific diagnostic challenge, as it typically generates reverberation artifacts ("dirty shadowing") [11]. In cases of extensive orbital emphysema, these artifacts can obscure deeper structures, rendering the examination non-diagnostic [12]. In our patient, the pneumo-orbit was minimal and likely peripheral, preserving a clear acoustic window. When minimal air is suspected, clinicians can often "work around" the artifact by positioning the patient upright or angling the probe through unaffected quadrants.

Conclusions

Anisocoria following severe head injury is not invariably of neurological origin and may result from direct structural ocular trauma. POCUS serves as an invaluable extension of the physical examination, especially when traditional neurological assessments are obscured by intubation, paralysis, or sedation. Furthermore, bedside ocular ultrasound may serve as a valuable screening adjunct in trauma patients when direct ocular examination is not feasible. By rapidly differentiating between signs of raised intracranial pressure and primary mechanical ocular pathology, POCUS can refine clinical decision-making and prevent the unnecessary and potentially harmful administration of empiric neuro-resuscitative therapies.

Abbreviations

CT

Computed Tomography

POCUS

Point-Of-Care Ultrasound

GCS

Glasgow Coma Scale

eFAST

extended Focussed Assessment with Sonography for Trauma

PCIOL

Posterior Chamber Intraocular Lens

Author contributions

MSGM acquired the clinical data and drafted the initial manuscript. AVT conceptualized the report, critically revised the manuscript for important intellectual content, supervised the ultrasound interpretation, and gave final approval of the version. GRK acquired the clinical data and drafted the initial manuscript. AMM critically revised the manuscript for important intellectual content. All authors reviewed the manuscript.

Funding

This research received no specific Grant from any funding agency in the public, commercial, or not-for-profit sectors.

Data availability

No datasets were generated or analyzed during the current study.

Declarations

Ethics approval and consent to participate

Formal Institutional Review Board approval was not required for the publication of this single anonymized case report.

Consent for publication

Written informed consent was obtained from the patient for publication of this case report and any accompanying images.

Competing interests

The authors declare no competing interests.