Alternating and Direct Current Stimulation for Neuropathic Eye Pain

Alternating and Direct Current Stimulation for the Treatment of Chronic Neuropathic Eye Pain and Cerebral Symptoms: a Pilot Study

The goal of this clinical intervention is to test if two forms of transcranial current stimulation, transcranial direct current stimulation (tDCS) or transcranial alternating current stimulation (tACS) can alleviate neuropathic eye pain in a sample of 20 patients. The main aims are: Test if tDCS/tACS can alleviate neuropathic eye pain and/or other cerebral symptoms: brain fatigue, migraine, light sensitivity, etc. Test if one stimulation method is superior to the other Patients will be treated for a total of fifteen 30-minute stimulation sessions, three times a day over a five-day period, each stimulation separated by approximately 4 hours, with either active tACS or tDCS over the scalp corresponding to primary sensory and motor areas. The patients will have questionnaires to monitor subjective experiences and pupillometry before and after treatment to monitor experimental outcomes.

Transcranial alternating current stimulation (tACS) device using 50x70 mm electrodes that are placed bilaterally between EEG coordinates C3/C5 for left hemisphere and C4/C6 for right hemisphere (corresponding to S1 and M1 of the eye). The alternating current electrodes are in-phase and have the same peak to peak stimulation 3mA, for 30 minutes duration at 10Hz. An impedance value under 15 ohms is required at all times to ensure patient comfort and safety.

Transcranial direct current stimulation (tDCS) device using 50x70 mm electrodes that has the anodal electrode placed contralateral to most prominent ocular pain or, in the case of bilateral pain symptoms, contralateral to the dominant hand between EEG coordinates C3/C5 for left hemisphere and C4/C6 for right hemisphere (corresponding to S1 and M1 of the eye), and the cathode placed on the patient's upper arm. A current peaking at 3mA will ramp up for 20 secs and be delivered for a total of 20 minutes, thereafter, ramping down for 20s. An impedance value under 15 ohms is required at all times to ensure patient comfort and safety.

Change from baseline subjective pain via neuropathic pain symptom inventory for the eye (NPSI-eye) at 1 week

Assesses pain related symptoms on a scale from 0 indicating no pain (better outcome) to10 indicating worst pain imaginable (worse outcome)

Change from baseline subjective pain via neuropathic pain symptom inventory for the eye (NPSI-eye) at 2 weeks

Assesses pain related symptoms on a scale from 0 indicating no pain (better outcome) to10 indicating worst pain imaginable (worse outcome)

Change from baseline subjective pain via neuropathic pain symptom inventory for the eye (NPSI-eye) at 1 month

Assesses pain related symptoms on a scale from 0 indicating no pain (better outcome) to10 indicating worst pain imaginable (worse outcome)

Change from baseline subjective pain effect experiences via Defense and Veteran Pain Rating Scale (DVPRS) at 1 week

Assesses pain related symptoms effecting sleep, stress, disposition, life quality, on a scale from 0 indicating no effect (better outcome) to10 indicating maximum effect (worse outcome)

Change from baseline subjective pain effect experiences via Defense and Veteran Pain Rating Scale (DVPRS) at 2 weeks

Assesses pain related symptoms effecting sleep, stress, disposition, life quality, on a scale from 0 indicating no effect (better outcome) to10 indicating maximum effect (worse outcome)

Change from baseline subjective pain effect experiences via Defense and Veteran Pain Rating Scale (DVPRS) at 1 month

Assesses pain related symptoms effecting sleep, stress, disposition, life quality, on a scale from 0 indicating no effect (better outcome) to10 indicating maximum effect (worse outcome)

Assesses mental symptoms on a scale from 0 indicating no effect (better outcome) to 3 indicating extreme effect (worse outcome)

Assesses mental symptoms on a scale from 0 indicating no effect (better outcome) to 3 indicating extreme effect (worse outcome)

Assesses mental symptoms on a scale from 0 indicating no effect (better outcome) to 3 indicating extreme effect (worse outcome)

Change from baseline subjective ocular symptoms and symptom frequency via custom ocular pain questionnaire at 1 week

Ocular pain questionnaire using a visual analog scale with 0 indicating no pain (better outcome) and 10 indicating extreme pain (worse outcome) and frequency measure from 0% indicating never occurring (better outcome) to 100% indicating always occurring (worse outcome)

Change from baseline subjective ocular symptoms and symptom frequency via custom ocular pain questionnaire at 2 weeks

Ocular pain questionnaire using a visual analog scale with 0 indicating no pain (better outcome) and 10 indicating extreme pain (worse outcome) and frequency measure from 0% indicating never occurring (better outcome) to 100% indicating always occurring (worse outcome)

Change from baseline subjective ocular symptoms and symptom frequency via custom ocular pain questionnaire at 1 month

Ocular pain questionnaire using a visual analog scale with 0 indicating no pain (better outcome) and 10 indicating extreme pain (worse outcome) and frequency measure from 0% indicating never occurring (better outcome) to 100% indicating always occurring (worse outcome)

Ocular pain questionnaire using a visual analog scale with 0 indicating no pain (better outcome) and 10 indicating extreme pain (worse outcome) and frequency measure from 0% indicating never occurring (better outcome) to 100% indicating always occurring (worse outcome)

Beta coefficients for participant demographics (sex, age, race/ethnicity) in regression model predicting adherence to treatment protocol

Exploratory regression analysis to identify associations between demographic variables and number of treatment sessions completed

Beta coefficients for participant demographics (sex, age, race/ethnicity) in regression model predicting change in pain (Numerical Rating Scale)

Exploratory regression analysis to identify associations between demographic variables and change in pain ratings (before vs. after stimulation treatment)

Inclusion Criteria: persistent eye pain for at least 6 months average eye pain intensity of 4 or more on a 0-10 numerical rating scale naive to transcranial stimulation eye pain having neuropathic-like characteristics Exclusion Criteria: contraindication to transcranial stimulation (i.e., pacemaker, cardioverter defibrillator, neuro-stimulation (brain or spinal cord), bone growth stimulations, indwelling blood pressure monitors, epilepsy, pregnancy) presence of ocular diseases that are the likely cause of pain (i.e., corneal and conjunctival scarring, corneal edema, uveitis, iris transillumination defects, etc.) current participation in another study with an investigational drug or device within one month prior to screening

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Farhangi M, Feuer W, Galor A, Bouhassira D, Levitt RC, Sarantopoulos CD, Felix ER. Modification of the Neuropathic Pain Symptom Inventory for use in eye pain (NPSI-Eye). Pain. 2019 Jul;160(7):1541-1550. doi: 10.1097/j.pain.0000000000001552.

Sivanesan E, Levitt RC, Sarantopoulos CD, Patin D, Galor A. Noninvasive Electrical Stimulation for the Treatment of Chronic Ocular Pain and Photophobia. Neuromodulation. 2018 Dec;21(8):727-734. doi: 10.1111/ner.12742. Epub 2017 Dec 28.