Neuropathic Ocular Pain: An Important Yet Underevaluated Feature of Dry Eye

A Galor; RC Levitt; ER Felix; ER Martin; CD Sarantopoulos

Disclosures

Eye. 2015;29(3):301-312. 

In This Article

Neuropathic Ocular Pain and Implications for Dry Eye Diagnosis

As above, neuropathic pain is more likely to be chronic, difficult to treat, and therefore important to distinguish in dry eye patients. Unfortunately, the presence of neuropathic ocular pain is not currently evaluated when assessing dry eye patients. This information is important as identifying patients with a neuropathic component to their dry eye symptoms may affect subsequent treatment. The easiest way to assess for neuropathic ocular pain is with the use of questionnaires. Although self-reported measures cannot definitely diagnose the presence of neuropathic pain, some clues can be obtained through a careful history. Unfortunately, most currently used dry eye questionnaires, such as the Ocular Surface Disease Index (OSDI) and Dry Eye Questionnaire 5 (DEQ5),[100] do not capture this important dimension of dry eye. For example, pain descriptors are often different in patients with neuropathic vs nociceptive pain, with neuropathic pain often described as a burning, tingling, or electric pain.[28] Asking patients to describe their corneal pain using well-established metrics[101,102] may be a low-cost, first-line approach to identifying features of neuropathic pain in dry eye. Other features that suggest the presence of neuropathic pain include the presence of spontaneous pain and exaggerated pain response to normally nonnoxious stimuli (such as photoallodynia) and to suprathreshold noxious stimuli (such as hyperalgesia to wind).

Investigator-assessed features are more difficult to measure in dry eye as there are few commercially available instruments that can assess ocular sensory apparatus function in humans. Cochet–Bonnet aesthesiometery has been applied to dry eye and has demonstrated lower sensitivity to mechanical stimuli in dry eye patients.[103,104] The Belmonte aesthesiometer, a more robust instrument that can measure sensitivity to mechanical (air flow), chemical (CO2), and cooling stimuli, is unfortunately not commercially available. In those groups with such an instrument, most have found decreased sensitivity to all three stimuli in dry eye patients.[105,106] However, some groups have found higher sensitivity to air flow in dry eye patients,[107,108] representing a different disease subtype or patients at different points on the disease continuum. Commercially available confocal microscopy units have identified that some dry eye patients have neuronal alterations in the corneal subbasal plexus structures.[104,106,109,110] Dry eye patients, in general, have lower subbasal nerve density,[104,106] and some also display abnormal nerve morphology including increased tortuosity and beading.[110] Although not definitive, the findings of abnormal sensitivity and morphology in patients with chronic symptoms would suggest the presence of neuropathic pain.

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