A pilot study of the safety and feasibility of transcutaneous electrical nerve stimulation (TENS) for chronic ocular pain

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The aims of the proposed work are to: 1) evaluate the safety and side-effect profile of long-term Transcutaneous Electrical Nerve Stimulation (TENS) use in neuropathic ocular pain (NOP) patients; 2) assess the feasibility and acceptability of the Active and Sham TENS protocols for use in a future, randomized- controlled trial; 3) estimate the time-course of analgesic effect of long-term use of TENS for NOP; and 4) explore between-subject variability in feasibility, safety, and analgesic responsiveness to TENS for NOP. This pilot study will enroll 50 Veterans with chronic (>6 mo) NOP (without associated tear film abnormalities) of at least moderate intensity (≥ 4 on a 0 – 10 pain rating scale). Participants will be assessed with regard to baseline characteristics, including demographics, medical and pain history, characteristics and impact of ocular pain, eye exam metrics, and evoked pain sensitivity (Visit 1). Participants will then be randomized, in a 2:1 ratio, to Active or Sham TENS therapy. An initial in-lab 20-minute session of TENS will be performed and reports of side effects and ocular pain relief will be recorded at multiple time points for 120 minutes afterward (Visit 2). After participants are instructed on how to safely apply and start the TENS device, they will leave the laboratory with the Active or Sham device to initiate the 3-times-per-week treatment protocol (20 mins per session) at home, for a duration of 6 months. Participants will be assessed with regard to the frequency and severity of side-effects, frequency of use of the device, and pain ratings via bi- weekly phone calls with the study staff. At the mid-point (3 months) and end-of-treatment (6 months) time points, participants will return to the lab for assessments of pain characteristics, eye exam metrics, and evoked pain sensitivity measures (Visits 3 and 4). The utilization log recorded by the TENS device will also be downloaded at that time. Additional long-term follow-up data collection will occur via monthly phone interviews, up to 12 months, to capture the presence of any lingering side-effects and change in ocular pain ratings. The TENS device to be used is the Cefaly Dual ® (Cefaly Technology, Belgium), which delivers biphasic rectangular impulses (impulse width 250μS, frequency 60Hz) of up to 16mAmps in intensity via a single electrode that is placed on the forehead just above the eyebrows. The device has previously been shown to be effective for the reduction of migraine. Primary analyses will consist of descriptive statistics to assess: 1) the feasibility for recruitment and retention into a future efficacy trial (goal is enrollment of at least 50% of eligible patients, and retention of 80% of those enrolled); 2) the safety of the device (goal is that no more than 10% of participants report mild-moderate side effects that do not persist; and 0% report a severe side-effect related to the TENS treatment); and 3) the feasibility of the Sham TENS device (goal is that at least 50% of participants allocated to Sham TENS are unsure of which treatment arm they were assigned to). In addition, we will explore associations between variation in our outcomes (adherence to protocol, side-effect report, and analgesic effectiveness) and individual characteristics (demographics, ocular pain characteristics, ocular exam metrics, and sensitivity to noxious stimulation/evoked pain).