Corneal reflex, absent
Corneal reflex, absent: Excerpt from Nursing: Interpreting Signs and Symptoms
The corneal reflex is tested bilaterally by drawing a fine-pointed wisp of sterile cotton from a corner of each eye to the cornea. Normally, even though only one eye is tested at a time, the patient blinks bilaterally each time either cornea is touched—this is the corneal reflex. When this reflex is absent, neither eye-lid closes when the cornea of one is touched. (See Eliciting the corneal reflex.)
The site of the afferent fibers for this reflex is in the ophthalmic branch of the trigeminal nerve (cranial nerve [CN] V); the efferent fibers are located in the facial nerve (CN VII). Unilateral or bilateral absence of the corneal reflex may result from damage to these nerves.
History and physical examination
If you can't elicit the corneal reflex, look for other signs of trigeminal nerve dysfunction. To test the three sensory portions of the nerve, touch each side of the patient's face on the brow, cheek, and jaw with a cotton wisp, and ask him to compare the sensations.
If you suspect facial nerve involvement, note if the upper face (brow and eyes) and lower face (cheek, mouth, and chin) are weak bilaterally. Lower motor neuron facial weakness affects the face on the same side as the lesion, whereas upper motor neuron weakness affects the side opposite the lesion—predominantly the lower facial muscles.
Because an absent corneal reflex may signify such progressive neurologic disorders as Guillain-Barré syndrome, ask the patient about associated symptoms—facial pain, dysphagia, and limb weakness.
Medical causes
Acoustic neuroma.Acoustic neuroma affects the trigeminal nerve, causing a diminished or absent corneal reflex, tinnitus, and unilateral hearing impairment. Facial palsy and anesthesia, palate weakness, and signs of cerebellar dysfunction (for example, ataxia or nystagmus) may result if the tumor impinges on the adjacent cranial nerves, brain stem, and cerebellum.
Bell's palsy.A common cause of diminished or absent corneal reflex, Bell's palsy causes paralysis of CN VII. It can also produce complete hemifacial weakness or paralysis and drooling on the affected side, which also sags and appears masklike. The eye on this side can't be shut and tears constantly.
Brain stem infarction or injury.An absent corneal reflex can occur on the side opposite the lesion when infarction or injury affects CN V or VII or their connection in the central trigeminal tract. Associated findings include a decreased level of consciousness, dysphagia, dysarthria, contralateral limb weakness, and early signs and symptoms of increased intracranial pressure, such as a headache and vomiting.
With massive brain stem infarction or injury, the patient also displays respiratory changes, such as apneustic breathing or periods of apnea; bilateral pupillary dilation or constriction with decreased responsiveness to light; rising systolic blood pressure; a widening pulse pressure; bradycardia; and coma.
Guillain-Barré syndrome.With this polyneuropathic disorder, a diminished or absent corneal reflex accompanies ipsilateral loss of facial muscle control. Muscle weakness, the dominant neurologic sign of this disorder, typically starts in the legs, and then extends to the arms and facial nerves within 72 hours. Other findings include dysarthria, dysphagia, paresthesia, respiratory muscle paralysis, respiratory insufficiency, orthostatic hypotension, incontinence, diaphoresis, and tachycardia.
Nursing considerations
▪ When the corneal reflex is absent, you'll need to take measures to protect the patient's affected eye from injury such as lubricating the eye with artificial tears to prevent drying.
▪ Cover the cornea with a shield and avoid excessive corneal reflex testing.
▪ Prepare the patient for cranial X-rays or a computed tomography scan.
▪ Discuss end-of-life issues with the patient's family, if appropriate.
Patient teaching
▪ Teach the patient how to protect his eye from injury.
▪ Demonstrate how to apply eye drops correctly.
Pictures
Book Source Details
- Book Title: Nursing: Interpreting Signs and Symptoms
- Author(s): Springhouse
- Year of Publication: 2007
- Copyright Details: Nursing: Interpreting Signs and Symptoms, Copyright © 2007 Lippincott Williams & Wilkins.
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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