Neuropathic Ocular Pain - Causes, Symptoms, and Treatment

Introduction

The eye may elicit pain due to numerous underlying conditions. The sensitive corneal layer that protects the eye from the external environment is heavily loaded with nerve endings (innervated). The disrupted function of the nerves in the cornea precipitates neuropathic ocular pain. It elicits a slight inclination towards the female population. However, the condition's incidence is reported to be evenly distributed globally.

What Is Neuropathic Ocular Pain?

Neuropathic ocular pain is a peculiar ophthalmic condition where the patient encounters shooting pain in the eye without significant trauma or injury. Various other names like:

1. Corneal neuralgia.

2. Neuropathic dry eyes.

3. Keratoneuralgia.

4. Corneal neuropathic pain.

5. Corneal allodynia.

Ocular pain syndrome is also known as a condition. The manifestations of neuropathic ocular pain closely resemble that of dry eyes, and at times it gets wrongly diagnosed as dry eyes. Ocular pain can be distressing and influence one's life quality.

What Causes Neuropathic Ocular Pain?

• Earlier, it was proposed that neuropathic ocular pain is a variant of dry eyes; later, further studies endorsed it as a different ophthalmic condition. However, the mechanism of neuropathic ocular pain needs to be figured out.

• Some of the hypotheses suggested its neuropathic (nerve-associated) origin. Certain diseases, chemical exposure, or impacts to the nerves within the corneal layer act as a trigger and precipitate significant nerve injury.

• Potential triggering agents include radiation exposure, eye surgeries like cataract surgery, retinal surgery, glaucoma surgery, certain eye drops, corneal abrasion, burn injury involving the eyes, viral infections like herpes, and underlying neurological issues like migraine, trigeminal neuralgia.

• Certain corneal disorders like cancer involving the cornea and recurrent corneal erosion (corneal cells under destruction) are also reported to be associated with the development of neuropathic ocular pain.

• The affected nerves then undergo healing by abnormal regeneration (nerve regrowth). Anomalous healing of the nerves gives rise to atypical, exaggerated responses and hypersensitivity toward the stimulus (triggering agent). As a result, the person begins to experience pain even for stimuli that normally do not evoke a painful response.

What Are the Signs and Symptoms Associated With Neuropathic Ocular Pain?

Neuropathic ocular pain condition is manifested in the form of diverse symptoms. The absence of specific symptoms and the simultaneous development of dry eyes often make the diagnosis troublesome. Routinely encountered symptoms of neuropathic ocular pain include the following:

• Pain: The affected person encounters debilitating pain in the eye. The pain sometimes extends in and around the eyeball, head, cheek, forehead, and ear region. The patient elicits pressure and stress over the eyes. The onset of pain can be either slow or abrupt.

• Photo Allodynia: The person suddenly develops pain when exposed to light. Light exposure never induces pain in an average person, but once the person experiences pain, it gives a clear hint of neuropathic ocular pain. In addition to light sensitivity, the person elicits a remarkable pain response upon exposure to wind. Exaggerated light and air sensitivity create trouble in performing day-to-day activities.

• Grittiness: The person encounters a feeling like something went into the eye. There will be persistent irritation in the eye.

• Burning Sensation: In addition to pain, certain patients reported having a burning sensation in the eyes, which makes the condition much worse.

• Dry Eyes: Simultaneous dryness is elicited by most patients, which eventually gets confused and misinterpreted as dry eye syndrome.

• Presence of Triggering Factors: Routinely, the pain attack is evoked by certain factors like light exposure, air pressure (wind), and sudden shift in atmospheric temperature.

• Systemic Diseases: It is often reported to be associated with certain systemic disease conditions like anxiety issues, headaches, fibromyalgia (stress-induced general weakness), and depression (mental disorder). Anxiety and depressive thoughts at times evoke suicidal tendencies in the patients.

How Is Neuropathic Ocular Pain Diagnosed?

Neuropathic ocular pain often challenges diagnosis due to general ocular symptoms mimicking other ophthalmic conditions like dry eyes. Diagnosis begins with scrutiny of the medical history and clinical findings. Furthermore, the diagnosis is confirmed with the help of relevant diagnostic tests. Some of the routinely performed diagnostic tests for neuropathic ocular pain include the following:

• Confocal microscopy: This optical imaging technique aids in identifying damages and injuries in the corneal nerves by providing a clear and close view of the internal structure of the cornea.

• Ocular pain assessment surveys: These encompass a set of questions, and the patients are instructed to frame answers. It gives a clear idea about the type and intensity of pain that the patient experiences. This analysis eventually contributes to the diagnosis.

How Is Neuropathic Ocular Pain Treated?

Effective treatment interventions are available to deal with the neuropathic ocular condition. Once the diagnosis is confirmed, the treatment strategy will be designed considering the symptoms and triggering factors for that particular patient. Widely adopted treatment therapies include the following:

• Anti Inflammatory Drugs: It aids in tackling inflammation (nerve swelling) associated with the corneal nerves. It is routinely advised in steroid eye drops like Tacrolimus 0.03% or non-steroidal anti-inflammatory tablets. Azithromycin and Doxycycline antibiotics are prescribed in case of tear gland dysfunction.

• Nerve Regenerative Drugs: Autologous serum tears regress the injured nerve. Serum tears are derived from the concerned patient's blood. Growth factors present in the autologous serum tear enhance the healing process.

• Ocular Surface Treatment: It is focused on dealing with the dryness in the eye with the help of artificial tears. It calms down the nerve endings and maintains optimum hydrogen ion concentration in the eyes, thereby hampering the hyperreactivity of the nerves in the cornea.

• Supplemental Therapies: These encompass vitamin B supplements and psychotic medicines to tackle mood disorders. If other underlying disease conditions precipitate the neuropathic ocular pain, appropriate treatment therapy should be initiated. Therapies to modulate nerve functions, like deep brain stimulations, are advised for cases that do not respond to conventional therapies.

Conclusion

Neuropathic ocular pain is a debilitating ophthalmic condition that hampers the patient's daily life. The ocular pain and irritation projected by this condition are so intense that it deteriorates the patient's quality of life. The diagnosis of neuropathic ocular pain is challenging as well as confusing. Timely detection enhances the effectiveness of the treatment and eventually projects a better prognosis. Though its causation is still vague and uncertain, effective treatment interventions can tackle the condition and boost the quality of life.