From the Guidelines
The absence of corneal reflexes alone is not sufficient to diagnose brain death, though it is an important component of the brain death examination. Brain death determination requires multiple clinical findings including complete unresponsiveness (coma), absence of all brainstem reflexes (including pupillary, corneal, oculocephalic, oculovestibular, gag, and cough reflexes), and apnea (inability to breathe independently) 1. The corneal reflex, mediated by cranial nerve V (trigeminal) for sensation and cranial nerve VII (facial) for the motor response, tests midbrain and pontine function. Its absence indicates brainstem dysfunction but could occur in conditions other than brain death, such as deep sedation, severe metabolic disorders, or localized damage to these specific nerves.
Key Points to Consider
- A formal brain death determination requires that all brainstem reflexes be absent, confounding factors be excluded (such as hypothermia, sedative drugs, or metabolic derangements), and often includes confirmatory tests like cerebral blood flow studies or electroencephalography depending on institutional protocols 1.
- The examination must also be performed by qualified physicians, typically repeated after a waiting period, and follow specific procedural guidelines to ensure accuracy in this irreversible diagnosis.
- According to the 2015 international consensus on cardiopulmonary resuscitation and emergency cardiovascular care science, the absence of corneal reflex at 24 and 48 hours after ROSC predicted poor outcome, with 17 (9–27)% and 7 (2–20)% false positive rate (FPR) respectively 1.
Clinical Implications
- The absence of corneal reflexes should be considered in the context of other clinical findings and not used in isolation to diagnose brain death.
- Clinicians should be cautious when interpreting the absence of corneal reflexes, as it may not always indicate brain death, and consider other factors that may influence the examination, such as sedation or metabolic disorders 1.
- A comprehensive evaluation, including a thorough clinical examination and appropriate confirmatory tests, is necessary to determine brain death accurately.
From the Research
Absence of Corneal Reflexes and Brain Death
The absence of corneal reflexes is one of the criteria used to determine brain death, but it is not the sole indicator. According to 2, the absence of corneal reflexes, along with other brainstem reflexes, can be an indicator of imminent brain death.
Diagnostic Criteria for Brain Death
The diagnosis of brain death is based on the following essential findings:
- Coma
- Absence of brainstem reflexes, including corneal reflexes
- Apnea As stated in 3, these criteria are used to determine irreversible loss of brain function.
Clinical Evaluation and Confirmatory Tests
Clinical evaluation, including the assessment of brainstem reflexes, is crucial in determining brain death. Confirmatory tests, such as imaging studies, may be used to support the diagnosis, as mentioned in 4 and 5.
Importance of Corneal Reflex Testing
Corneal reflex testing is a fundamental component of the coma exam and is commonly used in neuroprognostication of unconscious patients and in brain death determination, as noted in 6. However, the variability in testing techniques among practitioners may lead to inaccuracies in critical settings.
Key Points to Consider
- The absence of corneal reflexes is one of the criteria used to determine brain death, but it is not the sole indicator.
- Clinical evaluation, including the assessment of brainstem reflexes, is crucial in determining brain death.
- Confirmatory tests, such as imaging studies, may be used to support the diagnosis.
- Corneal reflex testing is a critical component of the coma exam and should be performed accurately to avoid inaccuracies in critical settings, as referenced in 2, 6.