Ocular neuropathic pain: An update on diagnosis and manageme
Ocular neuropathic pain, also referred to as corneal neuropathic pain, is a condition where corneal pain is seen in response to normally non-painful stimuli. This results from repeated direct damage to corneal nerves.

Aberrant regeneration with upregulation of nociceptors responsible for processing of painful stimuli leads to hyper-responsivity and increased perception of pain in response to even normally unpainful stimuli. The distorted neuronal excitability which persists even after the tissue has healed is the basis of symptoms of self –sustained chronic corneal pain persisting even in the absence of stimuli and clinical signs – the so called corneal “pain without stain” or “phantom cornea’.

This condition is the ocular analogue of systemic neuropathic pain, complex regional pain syndrome or reflex sympathetic dystrophy (RDS). Ocular or corneal neuropathic pain, corneal neuropathy, corneal neuralgia, kertaoneuralgia and corneal allodynia are all terms that are used to describe the same disease entity.

DIAGNOSIS:-
1. Identification of cause

2. Quantification of pain

Ocular Pain Assessment Survey (OPAS) is used to quantify pain and impact on quality of life. Other dry eye questionnaires like OSDI may be used, but are not specific for pain.

3. Assessment of ocular surface health and function

4. Differentiating between peripheral and central neuropathic pain

Proparacaine administration helps to differentiate whether neuropathy is peripheral only with sensitization at the level of corneal nociceptors or has progressed to central sensitization.

MANAGEMENT OPTIONS:-

1. Ocular surface treatment
Eye lubrication and treatment of dry eye-like symptoms: Artificial tears are used to prevent surface dryness and provide symptomatic relief. By decreasing the hyper-osmolarity of tears, over-stimulation of the nociceptors is stopped. Tears, ointments and gels are all used depending on patient tolerance. If used more than 4 times, preservative free tears are recommended. Punctal plugs to increase the tear lake are also useful.

2. Anti-inflammatory therapies
Non-steroidal anti-inflammatory therapies: Topical cyclosporine 0.5% has been shown to decrease the surface inflammation. Also a new drug –lifitegrast has been shown to decrease surface inflammation. These agents modulate T cell mediated inflammation.

3. Neuro-regenerative therapy
Autologous serum tears – These therapies target the underlying pathophysiology of aberrant nerve regeneration subsequent to repeated injury in neuropathic pain.

4. Systemic analgesics, anti-depressives and anti-psychotics
Studies have shown that patients with neuropathic pain also have non ocular symptoms of discomfort. This disease entity is a part of the systemic complex pain syndrome.

The systemic pain intensity correlates with depression and PTSD correlate with the dry eye like symptoms. These patients are treated with tri-cyclic antidepressants, NSAIDS, dronabinol and tramadol. Gabapentin is also used with variable success.

Read in detail here: http://eyewiki.aao.org/Ocular_Neuropathic_Pain
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