Ocular Surface Pain: A Narrative Review

Abstract

Ocular surface pain is a frequent cause of visits to an eye care provider and has a substantial impact on healthcare cost, yet a complete understanding of its causative factors and tools for diagnostic workup are notably missing in many eye clinics. The cornea has the densest sensory innervation in the human body and has the potential to be a powerful producer of pain. Pain can manifest as a result of a noxious stimulus or disruption in the ocular surface anatomy (nociceptive pain), or it can result from abnormalities in the ocular surface neurosensory apparatus itself (neuropathic pain). Novel advances in neurobiology have sought to differentiate the two entities, particularly to identify when chronic dry eye symptomatology is driven by neuropathic ocular pain. In this review, we seek to provide an overview of the prevalence, physiologic factors, and management of ocular surface pain complaints.

Morphological and Functional Changes of Corneal Nerves and Their Contribution to Peripheral and Central Sensory Abnormalities

“…The measurement of corneal sensitivity in patients could provide the first evidence for somatosensory abnormalities, but practical tools are still lacking to assess hypersensitivity and hyperexcitability, as well as explore other stimuli than simple mechanical responses. The persistence of ocular pain in a subset of patients with dry eye syndromes is a major challenge in the management of ocular pain (Rosenthal and Borsook, 2016 ; Mehra et al, 2020 ). It is therefore crucial to identify diagnostic modalities that can accurately predict or identify neuropathic pain.…”

Exploring the Link Between Dry Eye and Migraine: From Eye to Brain

“…For this test, a higher result corresponds to a higher corneal sensitivity. 60 Alternatively, a Belmonte esthesiometer utilizes a non-contact air jet to provide the stimulus, which can either be mechanical (variable airflow), thermal (hot or cold pulses), or chemical (varying CO2 concentrations). In contrast to Cochet-Bonnet, lower values with the Belmonte esthesiometer correspond to increasing sensitivity.…”

Differential Effects of Treatment Strategies in Individuals With Chronic Ocular Surface Pain With a Neuropathic Component

“…The International Association for the Study of Pain (IASP) defines pain as a “an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage.” ( IASP Terminology, 2020 ) Ocular surface pain, one form of pain that is estimated to affect 5–30% individuals ≥50 years worldwide ( Mehra et al, 2020 ), is often characterized by patients as “dryness”, “burning”, “aching”, or “tenderness”, among other terms. While ocular surface pain was initially lumped under the heading of “dry eye disease”, it is now recognized that pain can exist independently from tear dysfunction.…”

“…cornea and conjunctivae) or central nerves (e.g. trigeminal subnucleus caudalis, thalamus, or higher centers), can contribute to pain, including nerve injury associated with infection, trauma, chemical exposure, and metabolic disorders ( Mehra et al, 2020 ). Finally, neuro-inflammatory, behavioral, cognitive and emotional mechanisms play a significant role in the perception and maintenance of pain and its manifestations, adding to the complexity of diagnosis and treatment of this common form of chronic pain.…”

“…conjunctivochalasis, pterygium), trauma and toxicity (e.g. topical glaucoma medications) as well as coexisting conditions ( Mehra et al, 2020 ). Neuropathic pain is a clinical diagnosis and several findings suggest its presence, including symptoms out of proportion to signs of disease ( Ong et al, 2018 ), a symptoms profile of sensitivity to wind and light (the ocular equivalents of hyperalgesia and allodynia) ( Kalangara et al, 2017 ), abnormal corneal sensitivity ( Galor et al, 2020 ), and persistent pain despite treatment of ocular surface abnormalities ( Galor et al, 2016b ).…”