Stroboscopy (coined 'strobe') refers to the light source used in the endoscopy procedure which permits evaluation of the vibratory characteristics of the vocal folds. The term 'scope' refers to the endoscopy procedure which can be performed trans-nasally and/or trans-orally under either normal or stroboscopic light. For more explanation, see below.
Laryngeal endoscopy with continuous/normal/plain light (fiberoptic laryngoscopy, nasendoscopy, videofiberoptic laryngoscopy).
- A flexible fiberoptic endoscope is comprised of a bundle of optical fibers, some carrying light to the larynx and others carrying the image of the larynx back to the examiner.
- A rigid endoscope consists of a series of rods and lenses - 70° scope is best.
· Endoscopes can be attached to a video camera and monitor to give a magnified view.
· Rigid endoscopes are inserted in the mouth to the back of the tongue and not down the throat)and flexible fiberoptic endoscopes are inserted through the nose. Local anaesthetic is often sprayed in the nostril & sometimes the mouth (topical anaesthetics such as xylocaine, cophenylcaine) – anaethesia normally only needed for flexible scope.
· Risks are minimal. Remote risk of adverse reactions to the scope and anaesthetic.
Laryngeal endoscopy with stroboscopic light (laryngeal videostroboscopy)
· The stroboscope emits rapid pulses of light at a rate that can be set by the examiner or controlled by the fundamental frequency of client's voice. When the flashes of light are emitted at the same frequency as vocal fold vibration, the vocal folds appear to be motionless (unless there is irregular vibration).
· When the light is emitted at frequencies less than the frequency of vibration, a slow motion effect is produced.
· The examiner does not see fine details of a single cycle of vibration; the image is a composite picture of small sections from several cycles.
· Stroboscopic light can be used with either the rigid or flexible endoscope, although the rigid scope offers a better view because of the greater magnification.
· Vibratory behaviour is assessed using a sustained vowel, usually /i/. Vibratory behaviour cannot be assessed using connected speech or with rapidly changing pitch since it relies on tracking of the fundamental frequency.
· Stroboscopy is invaluable for accurate diagnosis of vocal pathologies.