CORNEA 50 EWAP MARCH 2022 by Liz Hillman Editorial Co-Director How to handle ‘pain without stain’ Contact information Galor: AGalor@med.miami.edu Jacobs: Deborah_Jacobs@meei.harvard.edu Itching, burning, aching, dry, gritty: Patients describe ocular surface pain in a myriad of ways. For some reason, said Anat Galor, MD, the corneal nerves are firing. It’s the physician’s job to figure out why, and in some cases, the reason is not so clear. “Nerves can fire for two reasons; either they’re firing because there is something in the environment causing them to fire, which would mean they’re firing appropriately. We call that nociceptive pain. Or they are firing because they’re abnormal—or both,” she said. She said that it’s unknown just how many patients have a neuropathic component to their eye pain, especially because it doesn’t necessarily exist in isolation, but alongside other conditions. Dr. Galor estimated that in her comprehensive dry eye clinic, 1–5% have pure neuropathic ocular pain without an obvious nociceptive source. In her ocular pain clinic, that percentage is higher. When a patient comes in using the variety of adjectives to describe pain, it’s time to put on your detective hat. While there is no gold standard diagnostic test to confirm that pain symptoms are coming from a neuropathic origin, Dr. Galor said there are findings on history and physical examination that can help physicians reach that conclusion. These include specific risk factors like pain that started immediately after surgery or painful comorbidities elsewhere, such as migraine and fibromyalgia. The characteristics of the eye pain can also help, such as describing burning pain or intensification of pain with exposure to wind or light. “While not definitive, these risk factors and characteristics make you think about the potential for a neuropathic source of pain,” Dr. Galor said. Signs of neuropathic pain include abnormal nerve sensitivity, which can be assessed in the clinic with the tip of a cotton swab. Patients with neuropathic pain oftentimes have abnormal sensitivity, either decreased or increased. Another sign of neuropathic pain is an abnormal response to a drop of anesthetic. Dr. Galor asks patients to rate their pain prior to the drop and reassess pain about 30 seconds after a drop of anesthetic is placed in the eye. If the pain doesn’t go away, it suggests a central or non-ocular surface source of pain. “We’re also looking for a disconnect. If the patient tells us they’re feeling painful sensations but we’re not seeing a lot of abnormalities on the ocular surface, this suggests a potential neuropathic component to pain,” Dr. Galor said. Deborah Jacobs, MD, MSc, said it’s rare to have a patient come in complaining of or referred for eye pain specifically. She said they’re often diagnosed with dry eye but found to not have responded to treatment, or they have symptoms but not much in the way of signs; then the physician considers neuropathic pain. Dr. Jacobs said her diagnosis of such patients is based on history, surveys such as OSDI and the Ocular Pain Assessment Survey, as well as examination techniques such as corneal sensation testing, vital dye staining, the proparacaine test, Schirmer testing, and sometimes confocal microscopy. “Corneal confocal microscopy can be helpful in supporting the diagnosis, distinguishing peripheral vs. central disease, and seeing evidence of inflammation, but this remains primarily a research tool as there are no standardize metrics for clinical practice,” Dr. Jacobs said. In terms of treatment, Dr. Galor said what many physicians are already doing for typical dry eye therapy is a good start. “You want to treat all nociceptive sources of pain,” she said. “Anti-inflammatories are a good choice if inflammation is present on the ocular surface as inflammation will cause nerves to function improperly. If first line therapies This article originally appeared in the December 2021 issue of EyeWorld. It has been slightly modified and appears here with permission from the ASCRS Ophthalmic Services Corp.
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