Quieting the neuropathic components of ocular pain

Patients with chronic ocular pain may benefit from the use of nerve blocks generally used to treat peripheral neuropathic pain.

Pain disorders can be nociceptive, characterized by pain that arises from actual or threatened damage to non-neural tissue, such as with severe ocular surface disease, band keratopathy, and intraocular inflammation.

They can be neuropathic, as with pain resulting from damage to or changes occurring in the nervous system, such as that caused by a previous cataract, LASIK, or RK surgery; neuralgia associated with the herpes virus; and eye drops containing the preservative benzalkonium chloride, according to Ann V. Quan, MD, an ophthalmology resident, Bascom Palmer Eye Institute, University of Miami Hospital and Clinic, Miami.

Neuropathic pain is a complex process resulting from various receptors. The corneal nociceptors are comprised of polymodal nociceptors that sense chemical, thermal, and endogenous inflammatory mediators, mechanoreceptors that sense mechanical stimuli, and cold thermoreceptors that sense evaporation.

The terminal nerve endings of the corneal nociceptors interact with the external environment and by doing so, they are susceptible to damage during inflammation or repetitive environmental injuries.

RELATED CONTENT: Differentiating ocular pain: Nociceptive or neuropathic

Causes of ocular pain

The nociceptive causes of ocular pain, including inflammation, tear dysfunction, and anatomic abnormalities, are commonly treated. The pain often persists, suggesting there can be a neuropathic component.

Dr. Quan and colleagues retrospectively reviewed the medical records of patients in the Oculofacial Pain Clinic at the University of Miami from Jan. 1, 2017, to Aug. 11, 2018, to determine if use of nerve blocks can effectively treat chronic ocular pain that likely has neuropathic components. All of the patients had been treated with a nerve block as part of a treatment regimen.

Dr. Quan recounted that nerve blocks were administered using a standard injectable solution of 4 ml of bupivacaine 0.5% (Marcaine, Pfizer) and 1 ml of methylprednisolone acetate (Depo-Medrol, Pfizer) 80 mg/ml mixed in a 5-cc syringe and injected using a 25-gauge needle. The terminal branches of the trigeminal nerve were targeted. Bupivacaine blocks sodium channels, which prevents depolarization, and inhibits N-methyl-D-aspartate receptor-mediated transmission in the spinal cord and trigeminal nucleus.

Of 11 patients (7 men, 4 women; mean age, 54 years) who received nerve blocks, four developed pain after ocular surgery and one each following trauma, radiation, zoster ophthalmicus, pituitary adenoma resection, septoplasty, in the setting of neuromyelitis optica, and one with no known pain triggers. Following administration of a nerve block, seven patients reported immediate pain relief lasting for varying amounts of time (the longest period being seven months).

“We found that nerve blocks typically used to treat peripheral neuropathic pain elsewhere in the body may be successful for treating chronic ocular pain from a variety of causes,” Dr. Quan concluded.

Disclosures:

Ann V. Quan, MD
E: avq7@miami.edu
Dr. Quan has no financial interest in any aspect of this report.