Introduction to Concussions and Eye Exams

A concussion is a type of mild traumatic brain injury (mTBI) caused by a blow, jolt, or bump to the head, or a hit to the body that causes the brain to move rapidly back and forth within the skull. This sudden movement can create chemical changes in the brain and sometimes stretch and damage delicate brain cells. Symptoms can be wide-ranging, affecting physical, cognitive, emotional, and sleep functions. Common signs include headache, confusion, dizziness, nausea, and sensitivity to light or noise. In Hong Kong, the Hospital Authority reported over 10,000 hospital admissions related to head injuries in a recent year, with a significant portion involving concussions from falls, sports, and traffic accidents. Given the brain's intricate control over visual processing, eye examinations have become a cornerstone in the diagnosis and management of concussions. They provide a non-invasive window into neurological function. Among the most critical and rapid assessments performed is the evaluation of the pupils, often summarized by the acronym perrla eyes. This simple check serves as a vital initial indicator of brainstem function and autonomic nervous system integrity following a head injury, guiding further diagnostic steps and management decisions.

PERRLA: A Quick Review

PERRLA is a standard clinical notation used by healthcare professionals to document a normal pupillary examination. It stands for Pupils Equal, Round, Reactive to Light and Accommodation. Each component is crucial. "Pupils Equal" refers to both pupils being the same size under the same lighting conditions. "Round" indicates their shape is circular, not irregular. "Reactive to Light" means the pupils constrict briskly when a bright light is shone into them (the direct reflex) and also show a consensual constriction in the opposite eye. "Accommodation" describes the pupils' ability to constrict when focusing on a near object, such as a finger moving toward the nose, which is part of the near vision triad alongside convergence and lens thickening. The assessment of perrla eyes is typically performed in a dimly lit room. The examiner uses a bright penlight or ophthalmoscope to observe the direct and consensual light reflexes. For accommodation, the patient is asked to focus on a distant object and then quickly shift gaze to a target held about 10-15 cm from their nose. A normal PERRLA finding suggests intact afferent (sensory) and efferent (motor) pathways of the pupillary reflex arcs, which involve cranial nerves II (optic) and III (oculomotor), and a functioning midbrain. This baseline assessment is fundamental in any neurological exam, especially after trauma.

How Concussions Can Affect PERRLA

The neurological impact of a concussion, while often considered "mild," can disrupt the finely tuned pathways controlling pupillary function. The force of the injury can cause shearing, stretching, or metabolic disruption of neuronal axons and affect brainstem nuclei responsible for autonomic control. Consequently, abnormalities in the perrla eyes assessment can be a red flag. One common finding is anisocoria, or unequal pupil sizes. While a small percentage of the population has physiological anisocoria (a normal variant), new-onset or worsening asymmetry after head trauma can indicate increased intracranial pressure, third cranial nerve palsy, or sympathetic pathway injury. Another key abnormality is a sluggish or absent pupillary light reflex. The pupils may react slowly to light or not at all. This can signal dysfunction in the midbrain's pretectal area or damage to the involved cranial nerves. It is a more concerning sign than simple anisocoria. Difficulties with accommodation are also prevalent. Post-concussion, patients may report blurry near vision or the examiner may observe a delayed or incomplete pupillary constriction when shifting focus from far to near. This is often linked to convergence insufficiency and other issues with the near vision complex, reflecting disruption in the coordination between accommodation, convergence, and pupillary constriction. These perrla eyes findings are objective signs that complement subjective patient reports.

Common PERRLA Abnormalities Observed

• Unequal Pupil Size (Anisocoria): A difference of more than 1mm in pupil diameter under the same lighting, especially if it is a new finding post-injury.
• Sluggish or Absent Light Reflex: A delayed, incomplete, or total lack of constriction to direct light stimulation. The consensual response may also be impaired.
• Accommodative Dysfunction: Impaired ability of the pupils to constrict during the near vision task, often accompanied by poor convergence.

Assessing PERRLA Post-Concussion

Following a suspected concussion, the evaluation of perrla eyes should be integrated into standardized assessment protocols, such as the SCAT6 (Sport Concussion Assessment Tool) or acute emergency department neurological checks. The examination must be systematic. The clinician first observes the pupils in ambient light for size and shape equality. Then, in a dim setting, a penlight is shone from the side into each eye separately, observing the direct and consensual response. The accommodation-convergence reflex is tested last. Crucially, serial examinations are paramount. Pupillary signs can evolve; an initially normal exam does not rule out later complications like evolving hemorrhage or swelling. Tracking changes over hours and days is essential for monitoring recovery or detecting deterioration. Beyond the subjective clinical eye, objective pupillometry is gaining traction in sports medicine and neurology clinics. These handheld digital devices provide quantitative measurements of pupil size, constriction velocity, latency, and dilation speed. They remove observer bias and can detect subtle impairments missed by the naked eye. In Hong Kong, leading sports medicine centers and hospital neurology departments are increasingly adopting this technology for more precise concussion management, creating baseline data for athletes and sensitive tracking tools for patients.

Other Eye-Related Symptoms of Concussion

While perrla eyes assessment focuses on objective pupillary signs, concussions frequently cause a host of subjective visual complaints that are equally disabling. These include blurred vision, double vision (diplopia), eye strain or fatigue (asthenopia), and pronounced sensitivity to light (photophobia). These symptoms often stem from disruptions in the brain's visual processing centers, the vestibular-ocular reflex (VOR), and the coordination of eye movements (vergence and saccades). For instance, blurred vision may result from accommodative dysfunction, which is directly linked to the "Accommodation" component of PERRLA. Double vision often arises from convergence insufficiency (eyes struggling to turn inward for near work) or subtle misalignments of the eyes due to brainstem injury. Photophobia is thought to involve overstimulation of the trigeminal nerve pathway or dysfunction in the brain's light-processing centers. It is critical to understand that a patient can have severe visual symptoms while still having technically "PERRLA" pupils. Conversely, abnormal perrla eyes findings often correlate with more severe or complex visual post-concussion syndromes. Therefore, a comprehensive neuro-optometric evaluation that goes beyond PERRLA is necessary to fully address a patient's visual dysfunction.

Treatment and Management of PERRLA Abnormalities After Concussion

The management of abnormal perrla eyes findings is intrinsically linked to the overall management of the concussion itself. The primary initial treatment for most concussion-related issues, including pupillary dysfunction, is physical and cognitive rest. This allows the brain's metabolic environment to stabilize. For persistent visual and pupillary issues, targeted vision therapy and rehabilitation are highly effective. Conducted by neuro-optometrists or occupational therapists, this therapy involves exercises to improve accommodation, convergence, eye tracking, and visual processing speed. For example, accommodative facility exercises (flipping focus between near and far targets) can directly improve the pupillary accommodation response. If underlying neurological issues are suspected, such as a structural lesion or significant autonomic dysregulation, further investigation with neuroimaging (like MRI) and management by a neurologist is warranted. In Hong Kong, multidisciplinary concussion clinics often bring together neurologists, physiotherapists, and optometrists to create integrated care plans. The goal is not merely to normalize the perrla eyes on exam but to resolve the functional visual deficits that impact daily life, such as reading, using computers, and navigating environments.

Summarizing Key Insights on PERRLA and Concussion

The assessment of perrla eyes is far more than a routine checkbox in a neurological exam following head trauma. It is a swift, non-invasive, yet profoundly informative test that provides a direct glimpse into brainstem integrity and autonomic function. Abnormalities in pupil equality, reactivity, or accommodation serve as objective biomarkers of neurological disturbance, guiding the urgency of care and the trajectory of recovery. When integrated with a full assessment of other visual symptoms and cognitive function, PERRLA becomes a powerful component of a holistic concussion management strategy. Given the potential for delayed complications, anyone experiencing a significant head injury, especially with symptoms like worsening headache, repeated vomiting, or observed changes in the eyes, should seek prompt medical attention. In Hong Kong's active urban and sporting environment, raising awareness about these signs, including the meaning of perrla eyes, can lead to earlier intervention, better outcomes, and a safer return to daily activities and sports.