Description of the Technology
Microcurrent stimulation is a technique to apply electrical stimulation to nerve fibers using cutaneous electrodes. Microcurrent stimulation for macular degeneration is described as applying 200 microamperes of electricity from a nine-volt battery to eight points around the eye. This technique utilizes lower currents, on the order of 50 to 500 microamperes. The device controller provides the microcurrent using two different waveforms and four frequencies.
In comparison, transcutaneous electrical nerve stimulation (TENS) is a technique to apply millicurrents to nerve fibers using cutaneous electrodes. Short pulses of electrical current last from 9 to 350 microseconds, and are applied at frequencies of 0.3 to 294 MHz. The device controls provide for adjustment in the pulse parameters. The primary application of TENS in health care has been to relieve pain. Other reported uses include increasing circulation, enhancing closure of bone fractures, and improving wound healing.
Mechanism of Action
For age-related macular degeneration (AMD), the postulated mechanism is that microcurrent stimulation improves membrane permeability, nerve conduction velocity, protein synthesis, and adenosine triphosphate (ATP) levels. In a very small experimental study (n= 9), microcurrent stimulation was shown to increase microcirculatory blood flow in intact skin and blister wounds, as measured by red blood cell velocity.1 In an animal study, direct electric currents were shown to increase ATP concentrations in tissues and stimulate amino acid transport into rat skin.2
Definition of the Problem
Microcurrent stimulation of the macula has been proposed as treatment for patients with AMD. Age-related macular degeneration is the leading cause of irreversible severe central visual loss in Caucasian Americans 50 years and older. Typically, patients who progress to the neovascular form of the disease or have geographic atrophy involving the foveal center tend to develop severe vision loss. Laser photocoagulation, photodynamic therapy with verteporfin, and specific nutritional supplements are treatments that have demonstrated efficacy in randomized controlled trials for certain stages of AMD.
Although it has been reported by VisionWorks, Inc. (New Paltz, NY) that the Macular Degeneration Foundation plans to propose an industry-sponsored double-masked, randomized and multisite clinical trial for microcurrent stimulation of the macula for submittal to the U.S. Food and Drug Administration (FDA), this is not confirmed by the Macular Degeneration Foundation website.
Microcurrent stimulation devices currently marketed in the U.S. do not have FDA premarket approval for the indication of macular degeneration. At this time, any research studies in the U.S. using microcurrent stimulation for macular degeneration require FDA authorization and Institutional Review Board approval.3
Summary of Evidence
Search Methods and Study Selection
In August 2000, the Academy searched through MEDLINE and EMBASE in the English language from January 1970 to August 2000 for articles relating to TENS, microcurrent stimulation, and ocular conditions. No articles were identified, but a bibliographic search of related articles identified one study for the application of electrical stimulation in patients with AMD.4 This article was found in a non-peer reviewed journal.
To update the assessment, in March 2004 a search of MEDLINE and EMBASE was conducted for the period January 1968 through February 2004, with the same search strategy. No new citations were identified. Using the author names from the paper identified earlier, an Internet search using the Google search engine, located another paper in a non-peer reviewed journal.5 The Internet search found a web site (http://www.mdsupport.org/) which contained a discussion of microcurrent stimulation. Through this source an additional paper was identified.6
Statistical Issues and Study Design
Two studies found were case series, one with 25 patients4 and the other with 46 patients.5 The treatment in both studies was microcurrent stimulation and nutritional supplements. Another case series was of 43 patients treated with microcurrent stimulation. These studies have the following limitations: small study population, no control population, lack of detailed documentation on patient selection and patients who declined treatment, and lack of standardized outcome measures other than visual acuity. The two studies of microcurrent stimulation and nutritional supplements also have the limitation of insufficient methodology to distinguish between the results of antioxidant supplementation and microcurrent stimulation.
Information about the effect of an intervention should be obtained by comparing a treated group with an untreated control group similar in all the important respects. One way to assure similarity between the two groups is to use randomization. Because case series have no control group and do not use randomization, there is no way to estimate how an intervention might have changed an outcome. In addition, case series usually describe a small number of patients. Small sample sizes can lead to patient-selection bias as well as a higher likelihood that the observed effect was a result of chance. Properly documented case series can provide important insights into the potential utility of a new treatment and be valuable for those designing appropriate controlled clinical trials. Necessary documentation includes details about the patient selection criteria, the number of patients who declined surgery, and how the enrolled patients compared to the patients who refused treatment. Use of standardized follow-up intervals and outcomes assessment would further improve the quality of information, as would comparisons to the natural history of the remaining, untreated patient population. There should be appropriate study controls, such as using sham microcurrent stimulation treatment or using the fellow eye as a control.
The proposed benefits are that visual acuity is improved. In order to maintain the effects, microcurrent stimulation therapy is presumed to be ongoing or lifelong, although maintenance intervals are proposed to be less frequent than the initial treatment phase.
One study of 25 patients with AMD, aged 48 to 79 years, reported the results of both nutritional supplementation and electrical stimulation.4 Patients were treated for varying intervals, from 2 years to 7 years with a daily multivitamin and mineral supplement, and a monthly administration of electrical treatment of 200 microamperes on the closed eyelid for 7 minutes for each eye. There was no control population for comparison purposes.
The study reported the following results: 15 patients improved their visual acuity, and 10 patients had reduced acuity. The overall group lost an average of 0.30 letters of visual acuity over an average treatment period of 4.0 years.4
A second paper reported on two series of patients.5 One series of 12 patients with AMD, aged 60 to 89 years, were followed for up to 6 years and treated with nutritional supplements and microcurrent stimulation once a week for 6 weeks. The second series of 34 patients with AMD, aged 61 to 87 years, were followed for up to 6 years and treated with nutritional supplements and microcurrent stimulation several times a week. There was no control population in either series for comparison purposes. The machines used delivered 200 microamperes at ±9 volts of alternating, square wave current. The series of 12 patients showed an average loss of 3 letters of visual acuity over a 2-year period. The series of 34 patients had an average gain of 8.5 letters of acuity per eye.5
A third paper reported on a series of 43 patients (65 eyes) with macular degeneration treated with direct microcurrent of 200 microamperes for 20 minutes for 36 sessions.6 The treatment was applied for 10 minutes per eye three to four times a week. No details of patients’ ages or length of time of follow up was given. Thirty-five of 65 eyes (54%) had a 1 to 4 line improvement in visual acuity, 35% had no improvement, and 8% had a decline.
The overall rate of adverse effects from electrical stimulation appears to be low. In the studies of AMD and microcurrent stimulation, there were no reported adverse effects from the electrical stimulation. Adverse effects could include: electrical burns if electrodes are not coupled to conductive gel, dermatitis, and skin irritation at the electrode sites with repeated application. Some materials reviewed during the Internet search indicate that patients may self-apply the electrical stimulation, in which case there may be risks of incorrect application. There may also be risks if the current applied is higher than what has been studied. There may be a significant financial risk associated with the costs of these treatments over a long period of time.
Questions for Scientific Inquiry
- What is the biological basis for microcurrent stimulation for treating AMD?
- Does microcurrent stimulation reduce visual loss caused by AMD, using randomized controlled clinical trials in larger, well-designed studies with adequate statistical analyses, standardized outcome measures and sufficient follow-up intervals?
- How effective is microcurrent stimulation compared to standard therapies for AMD, i.e., laser surgery and photodynamic therapy?