Transcutaneous Electrical Nerve Stimulation for the Long-Term Treatment of Ocular Pain

Abstract

Purpose: Ocular pain is a debilitating condition that is challenging to treat as therapies that target the ocular surface are often ineffective. We previously reported a short-term reduction in ocular pain after one periocular transcutaneous electrical nerve stimulation (TENS) session. The current study aims to elucidate the long-term effect of TENS on ocular pain.

Materials and methods: Fourteen individuals with eye pain were identified as candidates for a TENS device (RS Medical, Vancouver) for home use after a successful trial in clinic between February 2018 and July 2019 at the Miami Veterans Administration Hospital or University of Miami. Ten of the 14 patients were included in this retrospective review, based on the inclusion of receiving and using the device for a minimum of three months. The median age of the ten patients was 47.5 years, range 32-73 years, and eight were male. The main outcome measures were 1) frequency of long-term integration of TENS into ocular pain management and 2) patient reported ocular pain intensity (0-10) pre- vs. post-treatment.

Results: Patients reported an initial median use of the device 14.0 times per week and over time reducing the frequency to 3.0 times per week. All reported that the TENS unit was successfully incorporated into their ocular pain management routine for at least three months (median duration of use 6.5 months, range 3-14 months). Nine of ten patients reported subjective pain reduction with use of the TENS device at home. Overall, pain intensity decreased by approximately 27.4% (mean rank = 5.6, Z = -2.1, p = 0.02) post- vs. pre-treatment. No adverse events associated with TENS were reported in any patient.

Conclusion: Our preliminary data suggest that TENS can be integrated into the long-term management of ocular pain with improvements in overall pain intensity.

Keywords: Chronic ocular pain; chronic pain; neuropathic pain; pain management; transcutaneous electrical nerve stimulation.

Conflict of interest statement

Conflict of interest: No conflicting relationship exists for any author.

© 2020 International Neuromodulation Society.

Figures

Figure 1:

TENS applicators in position prior to treatment TENS=transcutaneous electrical nerve stimulation

Figure 2:

Pain scores in individual patients over time in months

Figure 3:

Nociceptive pathway in ocular pain and TENS modulation on pathway TENS=transcutaneous electrical nerve stimulation; TG=trigeminal ganglion; SP=stellate ganglion; CA=carotid artery; NCV1=nasociliary branch of V1; STT=spinal-thalamic tract; SN=spinal trigeminal nucleus; TGTT=trigeminal-thalamic tract; TH=thalamus; C=cortex; 1=1st order neuron; 2=2nd order neuron; 3=3rd order neuron The nociceptive pathway from corneal nerves travel along the nasociliary nerve of the ophthalmic branch of trigeminal (V1). Cell bodies are located within the trigeminal ganglion. These nerve fibers course through the spinal-thalamic tract within the medulla and synapse within the spinal trigeminal nucleus, nucleus caudalis, in the medulla. From here, second order neurons decussate and cross over to the contralateral medulla. Nerve fibers course anteriorly and synapse within the thalamus. Third order neurons then synapse within the somatosensory cortex. The proposed locations of TENS modulation of this pathway are in three main areas. A) TENS fiber stimulation of Aβ deep afferent fibers, as opposed to cutaneous Aβ fibers, within the nasociliary nerve. Through the Gate Control theory, it is proposed that they prevent the propagation of electrical signals through lightly myelinated and unmyelinated Aδ/C fibers., B) TENS is proposed to stimulate delta-opioid and cholinergic receptors within the spinal nucleus of the medulla, which have an inhibitory effect on ascending nociceptive fibers., C) Within the cortex, TENS has been found to eliminate hypometabolism within the orbitofrontal cortex and rostral angular cingulate cortex, which has been identified in humans via PET scans and fMRI., D) TENS may also have effects on sympathetic efferent hyperactivity. The stellate ganglion contains postganglionic sympathetic fibers that project fibers around the carotid artery. TENS may act as a sympatholytic accounting for part of its analgesic clinical effects.