Effect of Trigeminal Nerve Stimulation on Corneal Nerves and Chronic Ocular Pain

Effect of Trigeminal Nerve Stimulation on Subbasal Corneal Nerve Plexus Density and Chronic Ocular Pain in Patients With Dry Eye

Individuals with dry eye tend to present with ocular pain which persists despite the use of topical treatment. This could be secondary to somatosensory impairment attributable to neuropathic pain. The purpose of this study is to evaluate the effect of trigeminal nerve stimulation (TNS) on corneal nerves and chronic ocular pain in patients with dry eye.

Dry eye is a multifactorial disease that produces a variety of clinical manifestations including, dryness, pain, blurred vision, and sensitivity to light or wind. Differences have been noted between the symptoms reported and the signs presented on physical examination, which suggests the involvement of somatosensory impairment. Ocular neuropathic pain is characterized by burning pain, hyperalgesia, photophobia, and sensitivity to wind. There are common physiopathological pathways, suggesting that corneal nerve sensitization contributes to the development of dry eye symptoms. Furthermore, in vivo confocal microscopy has reported a decrease in the density of the subbasal plexus in patients with a neuropathic component and dry eye, suggesting that they are not mutually exclusive conditions. Various topical treatments, as well as systemic medications are known to manage eye pain and dry eye. However, in some cases, individuals have been refractory to them, enhancing the importance of research in adjuvant therapies such as TNS. This research protocol evaluates the effect of transcutaneous stimulation on corneal subbasal plexus density and chronic eye pain in patients with dry eye. A complete dry eye examination will be performed, including completion of Ocular Surface Disease Index (OSDI) and Dry Eye Questionnaire-5 (DEQ-5). Subbasal nerves density will be measured by confocal microscopy before and after receiving treatment with TNS. In addition, monthly monitoring of the intensity of ocular pain (with a numerical scale of 0-10) will be maintained. The intensity and severity of the clinical variables will be compared before and after receiving the treatment with a paired t-test considering a value of p<0.05 as statistically significant.

Transcutaneous Electric Stimulation, In vivo Confocal Microscopy, Subbasal Corneal Nerve Plexus, Dry Eye, Neuropathic Pain

Individuals will receive treatment with trigeminal nerve stimulation for 20 minutes at a frequency of 100 Hertz (Hz). Ocular pain intensity will be recorded prior and after the use of therapy.

Applied to to the forehead using a self-adhesive electrode positioned bilaterally over the upper branches of the trigeminal nerve.The device generates electrical impulses allowing to stimulate the trigeminal nerve.

Eye pain will be evaluated prior to the use of trigeminal nerve stimulation using a numeric pain scale ranging from 0-10, "0" indicating no pain and "10" indicating the most severe pain imaginable. Pain will be evaluated posterior to therapy with trigeminal nerve stimulation with the same scale during monthly follow up.

Identify the effect of trigeminal nerve stimulation on subbasal corneal nerve plexus density in patients with dry eye.

Initial subbasal corneal nerve plexus density will be measured prior to therapy with with in vivo confocal microscopy. Density measurements will be repeated every two months with in vivo confocal microscopy posterior to trigeminal nerve stimulation use.

Inclusion Criteria: Individuals with dry eye, Ocular pain for more than 3 months, Contact lens users, Individuals using topical treatment and/or systemic medication for dry eye syndrome, Individuals with history of photo-ablative ocular surgery (Laser-assisted in situ keratomileusis (LASIK) , Photorefractive keratectomy (PRK), Small incision lenticule extraction(SMILE), Individuals with history of autoimmune disease (Lupus, Rheumatoid Arthritis, Sjögrens), Exclusion Criteria: Individuals with pacemakers or implantable defibrillators, Individuals with diagnosis of epilepsy, History of facial trauma one month prior to recruitment, Acute facial pain with unknown etiology, History of ocular surgery one month prior to recruitment, Trigeminal neuralgia, Active Herpes Zoster Ophthalmicus,

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