Low-Level Laser on Hearing: Is There an Effect?

This is a comment on " The effect of low-level laser therapy on hearing. " [1] The first law of photochemistry, the Grotthuss-Draper law, states that light must be absorbed by a compound in order for a photochemical reaction to take place. Thus, when targeting the cochlea with laser light, it is essential to make sure that a sufficient amount of light reaches the target. Indeed, low-level laser therapy includes secondary effects through systemic mechanisms, but the energy at target is decisive for the biological effect. The cochlea is located rather deeply in the scull, and to reach it with laser light, different strategies have been used. Some studies have used irradiation via the petrosus bone, but according to the experimental study by Tauber et al. [2], this approach is ineffective. As for transmeatal irradiation, these investigators report great variations in dose at target depending on the position of the probe in the meatus. These authors have therefore used a specially designed laser system for transmeatal irradiation in their pilot study [3], using a wavelength of 632.8 nm or 830 nm, both 20 mW and with the small probe positioned close to the tympanic membrane. After a follow-up period of six months, tinnitus loudness was attenuated in 13 of 35 irradiated patients, while two of 35 patients reported their tinnitus as totally absent. Hearing threshold levels and middle ear function remained unchanged. The aim of the study by Goodman et al. was not to treat tinnitus, but since studies on the use of LLLT for tinnitus also aim at the cochlea, it is reasonable to compare such studies with the present investigation. The use of low-powered (around 5 mW) red diode lasers for home care has been reasonably successful in some studies but not in all. Investigators using infrared lasers between 300 and 500 mW directly into the meatus report better results [4, 5]. However , most of the studies have failed to perform differential diagnoses between somatosensory (muscular origin, such as TMD) [6–11] and neurological (cochlear dysfunction) backgrounds. Both conditions can be treated with LLLT, but the methods are quite different. Light in the red spectrum has primarily been used to treat superficial conditions, due to its lower penetration through tissues. Infrared light has therefore been preferred to reach deeper areas, such as the cochlea. Kolárová et al. [12] used CCD camera technique to establish the penetration of 50 …