Ocular Neuropathic Pain

Misdiagnised as Dry Eye Disease

Ocular neuropathic pain is a diagnosis of exclusion which refers to the heightened perception of pain in response to normally non-painful stimuli. It usually presents without any visible objective exam findings, making it extremely difficult to identify. For this reason, it is often misdiagnosed as dry eye disease.

Pain without staining

With other corneal pathologies, the intensity of corneal pain often correlates with vital dye staining. However, in patients with ocular neuropathic pain, symptoms are severe and unaccompanied by equivalent signs, which is why ocular neuropathic pain is sometimes referred to as “corneal pain without stain” or “phantom cornea.”

Patients are often dismissed

Ocular neuropathic pain is an important differential to consider because many patients get misdiagnosed due to its significant overlap with dry eye disease. The disparity between signs and symptoms often results in patients being dismissed or considered malingering, hysterical, or psychosomatic.

Higher proportion of females

The proportion of females with ocular neuropathic pain is higher than men. Females also tend to have a higher incidence of associated conditions such as fibromyalgia and autoimmune diseases.

Cornea has the most nerves and pain generators

The human cornea is often referred to as one of the most potent pain generators in the human body. Unsurprisingly, it is also among the most densely innervated tissues with approximately 7000 nerve terminals per square millimeter, making the cornea about 300 to 600 times more sensitive than skin.

View the cornia in-vivo with a confocal microscope

To verify a diagnosis of ocular neuropathic pain, viewing the cornea in vivo using a confocal microscope allows for detection of abnormalities of the corneal nerves.

Other assessment types

The ocular surface should be assessed with vital stains, tear production measured via Schirmer test, and tear quality evaluated with tear break up time, tear osmolarity, and/or tear proteomics

Central or peripheral nervous system?

Distinguishing between central or peripheral pain origins for ocular neuropathic pain can be helpful when determining treatments.

Types of treatments:

1. Ocular surface treatment: Copious lubrication with artificial tears decreases the hyperosmolarity
2. Topical and/or systemic antibiotics along with dietary supplements (omega3 fatty acids)
3. Anti-inflammatory: Soft steroids such as fluorometholone or loteprednol to dampen surface inflammation
4. Topical immunomodulators such as cyclosporine 0.5% or lifitegrast 5% is also an option, but their therapeutic effects are not immediate
5. Neuroregeneration: Autologous serum tears (20%) - Serum contains various growth factors which play a crucial role in neuroregeneration and healing

Inflammation

The mechanism is as follows: reduced tear secretion leads to inflammation. Inflammation causes sensitization of nociceptive nerve endings, which leads to feelings of dryness and pain.

Mental health association

Healthy-minded individuals are more equipped to cope with chronic pain for longer while they seek treatment and are less likely to resort to self-harm.