**3. Results**

We have identified fourteen relevant papers covering the use of phototherapy in the management of Bell's Palsy, including four RCTs [28, 32–34], one prospective study [35], one case series [36], and eight case reports [29, 37–43], which we review.

Our review shows that the most studied PBM is LLLT [28, 32, 33, 35, 37, 39, 40, 42, 43]. Others include high-intensity laser therapy (HILT) [29, 32, 36, 41], monochromatic infrared energy (MIRE) [38] and laser acupuncture [34]. Rubis [41] combined PBM with cervical manipulation. Alayat et al. [32] compared the effectiveness of HILT and LLLT combined with facial massage and exercise. Ordahan and Karahan [33] studied the effect of LLLT on top facial exercises. Kuzmičić et al. [29] combined HILT with acupuncture and mirror book therapy, and Shoman et al. [28] compared LLLT with electrical stimulation.

Most subjects were adults, except for a case report on a pediatric patient [37] and two case reports on adolescents [40, 42]. We categorized the papers into acute, subacute, chronic, and unspecified, according to the time patients received PBM treatments. We defined "acute" as onset within 1 week of consultation, "subacute" as one to 12 weeks, and "chronic" as cases that present for more than 3 months. We found different laser protocols were used in the studies. The number of treatments varies, from as few as two to 45. Most studies last 6 weeks, and PMB treatment was performed three times a week. Laser parameters, including wavelengths, power, power density, frequency, and energy density, also differed vastly among studies. Most studies utilized House-Brackmann Scale (HB Scale) as an outcome measure. It is a facial nerve grading system that grades upon functional impairment, ranging from I (normal) to VI (total paralysis) [44]. Facial Disability Index (FDI), a patient-rated outcome measure, was also commonly used to assess the functional disability and quality of life in patients with facial palsy [45]. The more recent studies utilized the Sunnybrook Facial Grading System (SB System), a physician-graded scale, which includes the synkinesis section. The scale permits recognition of minor improvements in the range of movement, thus helping quantify the progress feedback to patients [46]. Other outcome measures included electromyography and nerve conduction study. Please refer to the table in **Appendix 1** for detailed characteristics of the included papers.

Despite the different types of photo energy used, marked varying laser parameters, and the heterogeneity of the patients, the outcome of laser treatment was similar among the studies.
