What is Ocular Neuropathic Pain?
Ocular neuropathic pain is a medical term for a condition where a person feels a strong pain sensation in their eyes due to otherwise harmless triggers. This condition is hard to diagnose because it doesn’t show obvious signs during regular eye examinations. As a result, it’s often mistaken for dry eye disease.
While ocular neuropathic pain can sometimes cause visible tissue damage in the eye, it’s mostly due to issues with how the nervous system functions. Unlike other eye conditions, extreme pain in the cornea (the clear outer layer of the eye) doesn’t always align with physical signs of damage. This mismatch is why ocular neuropathic pain is sometimes known as “corneal pain without stain” or “phantom cornea”. It’s somewhat similar to other pain conditions such as complex regional pain syndrome, systemic neuropathic pain, or reflex sympathetic dystrophy.
The condition also goes by several other names like corneal neuropathic pain, corneal neuralgia, ocular pain syndrome, keratoneuralgia, corneal neuropathic disease, and corneal allodynia.
It’s crucial to thoughtfully diagnose ocular neuropathic pain as it’s commonly mistaken for dry eye disease. The lack of clear signs and severe symptoms often lead to patients being dismissed or seen as exaggerating their pain or even having psychological issues. Case reports show that in severe cases, the overwhelming chronic pain has driven some patients to suicide. Hence, it’s essential to acknowledge and validate the patient’s experiences and symptoms when dealing with this condition.
The aim of this summary is to explain the basics of this condition and discuss treatment methods and management strategies. It also aims to make more people aware of this often overlooked disease.
What Causes Ocular Neuropathic Pain?
Neuropathic eye pain could be caused by damage to or diseases of the cornea nerves. This could happen, for example, because of an injury. When these nerves heal, they could change in ways that make them overly responsive. This could make you feel pain more intensely than normal, even from non-harmful stimuli.
Neuropathic eye pain could also be linked with various body-wide conditions that affect the body’s sensory pathway (the system responsible for feeling stimuli). These conditions can make the eyes perceive harmless things as painful.
It turns out that there are many potential causes that can trigger this increased eye pain response. Some researchers have made a detailed list of these causes (Dieckman and others).
Risk Factors and Frequency for Ocular Neuropathic Pain
Ocular neuropathic pain, a type of eye discomfort related to nerve damage, is often linked to various other health conditions. The ones it most commonly associates with include depression, anxiety, fibromyalgia, and headache. There are also several other conditions it can be associated with, such as diabetes, celiac disease, HIV, and idiopathic small fiber neuropathies – a condition of unknown cause leading to nerve damage.
Also, it’s important to note that this type of eye pain is more prevalent in females. This higher frequency may be due to women’s increased likelihood of having conditions like fibromyalgia and autoimmune diseases. Autoimmune diseases, which occur when the body’s immune system mistakenly attacks its own cells, affect 5 to 8% of the population but are observed more in women – they make up 78% of the affected population, a trend that might be contributing to ocular neuropathic pain’s higher occurrence in females.
- Ocular neuropathic pain is often associated with conditions like depression, anxiety, fibromyalgia, and headache.
- It can also link to other health issues like diabetes, celiac disease, HIV, and idiopathic small fiber neuropathies.
- This eye discomfort is more common in females than males.
- Females are more likely to have associated conditions such as fibromyalgia and autoimmune diseases.
- Autoimmune diseases affect 5 to 8% of all people, but 78% of those affected are females.
- This high incidence of autoimmune disease in women may contribute to the higher occurrence of ocular neuropathic pain in females.
Signs and Symptoms of Ocular Neuropathic Pain
Corneal dysesthesia, a type of eye pain, can cause a range of symptoms due to the complexity of the nerves involved. People may describe the feeling as a burning sensation, aching, intense heat like a hot poker, the feeling of a foreign object in the eye, or sensitivity to light. These symptoms can significantly impact a person’s daily life, often affecting their ability to carry out routine tasks.
To help understand and measure this type of eye pain, doctors might use tools like the Ocular Pain Assessment Survey (OPAS). Such surveys can not only help diagnose conditions like corneal dysesthesia, but can also gauge the effectiveness of treatment plans.
Additionally, chronic overactivity of nerves that detect pain in the cornea could lead to blepharospasm, a condition where the eyelids spasm or twitch uncontrollably.
Testing for Ocular Neuropathic Pain
If your doctor suspects that you are experiencing ocular neuropathic pain, which is pain caused by nerve damage in the eye, they may use a special tool called a confocal microscope to view your cornea (the clear layer at the front of your eye). This microscope can show if there are any issues with the nerves in your cornea. It can also help identify what may be causing the pain, understand if the pain is coming from the nerves in your eye or from your brain, and check if treatments are successful.
Your doctor may also use a device called an esthesiometer, which measures how sensitive your nerves are. If nerve sensitivity is too high or there are changes in the structure of the nerves in your cornea, this may suggest that you are experiencing ocular neuropathic pain.
However, not all doctors have access to these diagnostic methods. As a result, ocular neuropathic pain is often determined by ruling out other conditions.
Patients with ocular neuropathic pain may feel intense pain when their eyes are touched, exposed to air, or when eye drops are applied. Gathering detailed information about your symptoms and past eye issues, such as any surgeries, infections, or other diseases, can provide clues about what might be causing your symptoms. However, it can be challenging to diagnose this condition because many patients don’t show typical signs of eye problems during an eye exam.
In the initial examination, your doctor might carry out tests similar to those done to diagnose dry eye syndrome. These tests can include checking the health of your eye surface, measuring your tear production, and evaluating the quality of your tears. If your eye surface appears healthy and you still feel pain in your cornea, it might indicate ocular neuropathic pain. However, it’s important to keep in mind that dry eye and ocular neuropathic pain can occur at the same time, making the diagnosis a bit difficult.
To figure out whether the pain is originating from the nerves in your eye or from your brain, your doctor might use the proparacaine challenge test. During this test, they will apply a solution called 0.5% proparacaine hydrochloride to your eye. If your pain decreases or goes away completely, the pain likely comes from your eye. If your pain remains the same or gets worse, it might be originating from your brain, and it can be particularly complicated to treat.
Treatment Options for Ocular Neuropathic Pain
People suffering from ocular neuropathic pain, a type of eye pain, may experience severe pain, sensitivity to light, and trouble with daily activities. They may also have symptoms of anxiety and depression and, in extreme cases, suicidal thoughts.
There are several treatment strategies to help ease ocular neuropathic pain:
Ocular surface treatment:
These treatments focus on reducing eye discomfort and includes:
– Using artificial tears that help decrease the intensity of the tears and stop the over-excitement of the nerves in the cornea, the front surface of the eye.
– Using antibiotics and taking dietary supplements, such as omega3 fatty acids, to treat certain types of dry eye and eyelid inflammation.
– Using special types of contact lenses that provide a cushion of fluid over the entire cornea. While these lenses offer immediate relief for some, they might trigger pain in others due to extreme sensitivity.
– Using lacosamide, a specific type of medication that can be combined with a special contact lens.
Anti-inflammatory treatments:
These treatments help reduce inflammation and include:
– Soft steroids like fluorometholone or loteprednol.
– Non-steroidal anti-inflammatory drugs, either as eye drops or taken orally.
– Eye drops such as cyclosporine 0.5% or lifitegrast 5%, which can also help control inflammation, although their effects aren’t immediate.
– Tacrolimus 0.03% eye drops to improve tear stability and to fight inflammation.
– Antibiotics such as doxycycline or azithromycin.
Amniotic membranes can also be utilized. They provide anti-inflammatory effects and can be placed underneath a contact lens.
Neuroregeneration:
Treatments in this category aim to promote the healing and regeneration of nerves; for instance, autologous serum tears. These special kind of tears contain various growth factors that help in nerve healing and repair.
Additional treatments:
– Pain relief medications, antidepressants, and antipsychotics are often used to manage associated non-ocular pain.
– Anticonvulsants, such as carbamazepine, gabapentin, or pregabalin, which are usually used to treat nerve pain.
– Low-dose naltrexone, an opioid antagonist, and opioid agonists such as tramadol, which need careful usage due to the potential risk of dependence.
– Vitamin B, specifically B12, has also been shown to be effective in managing neuropathic pain and helping with nerve regeneration and healing of the corneal surface.
Alternative therapies:
Other therapies such as semi-weekly acupuncture and electrical stimulation to treat severe ongoing pain. In some severe, hard-to-treat cases of neuropathic pain, invasive therapies such as deep brain stimulation and intrathecal analgesic infusions may be used to help provide relief.
What else can Ocular Neuropathic Pain be?
Ocular neuropathic pain is often identified by ruling out other conditions. Doctors should consider the following possibilities before making this diagnosis:
- Trigeminal neuralgia (a facial pain condition)
- Oculofacial pain (pain in the eye and face)
- Referred pain (pain felt in a part of the body other than its actual source)
- Ocular surface disease (conditions affecting the surface of the eye)
- Sinus problems
- Ocular medication side effects
- Issues related to contact lens usage
- Corneal disorders such as abrasion, erosion, etc.
- Chemical injury to the eye
- Eye trauma
- Uveitis (inflammation of the middle layer of the eye)
- Post-herpetic neuralgia (pain that continues after a shingles infection)
Take ocular surface disease as an example. This condition is characterized by reduced tear secretion which causes inflammation. This inflammation sensitizes nerve endings, resulting in feelings of dryness and pain. Over time, this inflammation and nerve injury can change the way genes act within the trigeminal ganglion (a group of nerve cells), causing abnormal sensations and neuropathic pain in the eye. However, it’s crucial to understand that these symptoms can often lead to misdiagnosis of ocular neuropathic pain.
What to expect with Ocular Neuropathic Pain
The outcome for patients experiencing eye-related nerve pain can greatly differ. Often, these patients have long-term symptoms that need to be addressed with a combination of different treatments. It’s been noted that starting treatment early often results in better health outcomes.
Possible Complications When Diagnosed with Ocular Neuropathic Pain
Treating and managing long-lasting pain is a tough job, not just for the physical reasons you might think of. Patients dealing with ongoing pain tend to get extremely worried about it, and this worry actually makes them more prone to feeling pain. So, it’s like they’re stuck in a worry-pain loop. Long-lasting pain doesn’t just affect patients mentally, but also physically. Research has discovered that there are many other health issues that tend to come hand-in-hand with chronic pain, like ongoing tiredness, joint pain, and depression.
List of Related Complications:
- Increased anxiety
- Increased susceptibility to pain
- Chronic fatigue
- Joint pain
- Depression
Preventing Ocular Neuropathic Pain
Before you choose to have corrective eye surgery, such as LASIK, it’s recommended that you be checked for certain risk factors. These can include autoimmune diseases and conditions that cause widespread bodily pain. This action can lessen chances of you developing a type of eye pain known as ocular neuropathic pain following your surgery.
It’s equally important to be checked for any existing mental health conditions that might make you more prone to depression and thoughts of self-harm. People with positive mental health are better equipped to handle chronic pain while seeking treatment and are less likely to try and harm themselves.
Evidence shows that patients with a particular eye condition called ocular surface disease also report higher pain responses to stimulation in areas such as the forearm when compared to those without this condition. This suggests that these patients may have a lower threshold overall for pain, a condition that often accompanies dry eye.
So, two crucial steps in treating ocular neuropathic pain is believing that the condition is real and actively looking for it. These steps ensure that treatment is timely and attacks the root cause of the problem.
