Ocular pain

People who suffer from persistent eye pain typically turn to an ophthalmologist for proper clinical evaluation. But how can ocular pain be classified?

Broadly speaking, we could distinguish two macro categories:

• In all situations where pain occurs as a physiological response to an external stimulus (such as trauma, surgery or infection) the pain is called nociceptive and results from the stimulation of pain receptors, which are present throughout the body and also in the eye.¹
• When the patient complains of major symptoms compared to clinical signs or without an apparent previous trauma, the manifestation of pain falls within the scope of the pathological or neuropathic pain.¹

However, as we delve deeper into the subject, we realise that the types of eye pain are many more, let us look at them together.

Neuropathic eye pain

Neuropathic eye pain is a major challenge for ophthalmologists because, to date, there are no agreed diagnostic criteria. The current definition of neuropathic pain requires evidence of damage or injury to the somatosensory nervous system (i.e. the sensory nerve pathways that transmit signals from the outside, such as touch, heat perception and pain) and the diagnosis is stratified as possible, probable or definite neuropathic pain.¹ Neuropathic pain is out of proportion to the signs or may even occur in the absence of noxious stimuli and may cause debilitating pain without apparent physiological significance. In these circumstances, patients may experience pain in response to normally benign stimuli or present an exaggerated response to pain stimuli.² In addition, acute pain stimuli may develop into chronic pain.

It has been proposed that neuropathic pain has a genetic component that acts by affecting neurotransmission, immune response and metabolism.² The perception of ocular neuropathic pain can also be strongly influenced by psychological factors such as stress, depression and anxiety.²

 Acute eye pain

Acute eye pain is usually a physiological response to tissue damage and is relieved with pain-relieving treatments.² The causes of acute eye pain can be many.

Conditions affecting the conjunctiva or cornea begin with a stinging sensation and dull pain that becomes more intense during eye movements as the disease progresses. Redness, tearing and secretion are hallmarks of ocular surface disease. Additional symptoms (such as itching, discharge and bulbar congestion) may indicate a specific disease process, such as allergies or viral and bacterial infections.³ Other eye diseases, such as keratitis, scleritis, glaucoma, uveitis, retinal diseases, can cause acute eye pain.³

In the context of an acute trauma, surgery or infection, pain is usually transient and resolution of the pain follows promptly from treatment of the underlying condition.⁴

Ocular surface pain

Ocular surface pain may be associated with dryness, discomfort, granularity, itching, burning, stabbing pain symptoms, which may occur spontaneously or be exacerbated by environmental insults, such as wind, light or temperature changes. Acute ocular surface pain commonly occurs due to local tissue injury in the context of trauma, surgery and infection. In these contexts, the pain is usually transient and resolves with treatment of the underlying condition. Sometimes, however, pain may persist due to continued ocular surface stress or nerve abnormalities, or both.⁴

Ocular surface pain has a negative impact on a patient's quality of life. Indeed, it is often associated with insomnia and problems in social relationships, with implications that extend to activities of daily living, such as reading, driving and working. Fortunately, recent advances in understanding the pathophysiology and neurobiology of ocular surface pain may lead to the development of new therapies to alleviate the individual and social burden of this condition.⁴

Many factors have been associated with chronic ocular surface pain, including congenital or acquired anatomical abnormalities of the eyelids and conjunctiva, systemic and environmental factors.⁴

Dry eye syndrome: how and why does it become painful?

Dry eye syndrome is a very common condition in which patients report symptoms of dry eye, associated with burning, grittiness, irritation, photophobia and tired eyes that tend to close, even without injury to the eye surface. However, several studies have shown that some patients classified as suffering from dry eyes may have problems not related to proper lubrication of the ocular surface per se, but rather to a disturbance of the somatosensory system.¹

Diagnosis and treatment of eye pain

When pain occurs following trauma or surgery or due to an infectious or inflammatory process, treatment of the underlying process or pathological abnormality usually leads to its resolution.¹ Such pain, associated with surgery, injury, infection or inflammation in the front of the eye, is typically treated with both topical and systemic steroid and non-steroid anti-inflammatory drugs (NSAIDs), local lubricating ointments, gels or eye drops, bandage contact lenses or topical anaesthetic.¹

Patients with dry eye are usually treated with the aim of restoring the tear film and, once the underlying condition is resolved, the pain also disappears. However, in dry eye patients who present with symptoms out of proportion to the way the condition presents, the pain may be caused by other conditions and, in these cases, treatment aimed at restoring the tear film may be ineffective.¹

In cases of neuropathic ocular pain, the diagnosis is made on a clinical basis, with specific tests serving to support the correct diagnosis.² The aim of treatment in this case is to reduce the nerve signal that causes pain.¹ In patients with long-lasting symptoms or where symptoms do not disappear with treatment with NSAIDs or topical anaesthetics, there is likely to be mediation of pain at the central nervous system level and treatment will require systemic agents, such as antiepileptics and antidepressants.¹

Bibliography

• Jacobs DS. Diagnosis and Treatment of Ocular Pain: the Ophthalmologist's Perspective. Curr Ophthalmol Rep. 2017;5(4):271-275. doi: 10.1007/s40135-017-0152-1. Epub 2017 Nov 2. PMID: 29226029; PMCID: PMC5711963.
• Ebrahimiadib N, Yousefshahi F, Abdi P, Ghahari M, Modjtahedi BS. Ocular Neuropathic Pain: An Overview Focusing on Ocular Surface Pains. Clin Ophthalmol. 2020 Sep 25;14:2843-2854. doi: 10.2147/OPTH.S262060. PMID: 33061269; PMCID: PMC7524198.
• Murthy SI, Das S, Deshpande P, Kaushik S, Dave TV, Agashe P, Goel N, Soni A. Differential diagnosis of acute ocular pain: Teleophthalmology during COVID-19 pandemic - A perspective. Indian J Ophthalmol. 2020 Jul;68(7):1371-1379. doi: 10.4103/ijo.IJO_1267_20. PMID: 32587167; PMCID: PMC7574141.
• Mehra D, Cohen NK, Galor A. Ocular Surface Pain: A Narrative Review. Ophthalmol Ther. 2020 Sep;9(3):1-21. doi: 10.1007/s40123-020-00263-9. Epub 2020 Jun 5. PMID: 32500435; PMCID: PMC7406607.

Dr. Carmelo Chines
Direttore responsabile