Stroboscopy - Stimm-und-sprachtherapie.de

Stroboscopy 

Last Updated: May 25, 2006 

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Synonyms and related keywords: stroboscopy, videostrobe, 

videostroboscopy, stroboscopy, videostrobolaryngoscopy, 

strobolaryngoscopy, strobe, periodicity, amplitude, glottic closure, mucosal 

wave, vocal fold cysts, vocal fold polyps, vocal fold nodules, sulcus vocalis, 

endoscopy, vocal fold anatomy, flexible endoscopy, rigid transoral 

endoscopy, glottic area waveform, GAW, phonatory cycle, 

videokymography, glottography, kymography, videostrobokymography, 

stroboscope 

Author: Robert A Buckmire, MD, Associate Professor of 

Otolaryngology, Department of Otolaryngology, Head and 

Neck Surgery, University of North Carolina 

Robert A Buckmire, MD, is a member of the following medical 

societies: American Academy of Otolaryngology-Head and 

Neck Surgery, American College of Surgeons, and National 

Medical Association 

Editor(s): Clark A Rosen, MD, Director, University of 

Pittsburgh Voice Center; Associate Professor, Department of 

Otolaryngology and Communication Science and Disorders, 

University of Pittsburgh School of Medicine; Francisco 

Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; 

Erik Kass, MD, Chief, Department of Clinical Otolaryngology, 

Associates in Otolaryngology of Northern VA; Christopher L 

Slack, MD, Consulting Staff, Otolaryngology-Facial Plastic 

Surgery, Lawnwood Regional Medical Center; and Arlen D 

Meyers, MD, MBA, Professor, Department of Otolaryngology- 

Head and Neck Surgery, University of Colorado at Denver and 

Health Sciences Center 

Disclosure 

INTRODUCTION Section 2 of 8 

Author Information Introduction Background And Surgical Principle Instrumentation Clinical 

Application Diagnostic Findings Extended Applications Bibliography 

In the modern laryngological practice, videostroboscopy is an 

essential diagnostic procedure for the detection of vocal 

pathology. 

Many voice clinicians believe that successful voice surgery 

depends as much on stroboscopy as otology depends on 

audiometry or microscopy. Laryngologists recognize the

vibratory pattern of the vocal folds as one of the most crucial 

determinants of voice quality and production. As such, 

videostroboscopy is the most accessible and clinically relevant 

technique in the otolaryngologist's armamentarium to readily 

assess this important parameter. Results have important 

implications for both diagnosis and treatment of phonatory 

pathology. 

Over the past 3 decades, knowledge of vocal fold anatomy and 

physiology has revolutionized the clinical practice of 

laryngology. Since Hirano's original description of the layered 

microanatomy of the human vocal fold in the 1970s, 

increasingly sophisticated diagnostic and surgical techniques 

have evolved to more appropriately address this delicate and 

complex structure now than then. Innovative diagnostic 

modalities have grown out of an improved understanding of the 

critical importance of vocal-fold oscillation to voice production. 

Videostroboscopy has evolved as one of the most practical and 

useful techniques for the clinical evaluation of vocal-fold 

vibration. 

Videostroboscopy fulfills several important requirements of a 

complete voice examination. It provides useful, real-time 

information concerning the nature of vibration, an image to 

detect vocal pathology, and a permanent video record of the 

examination. As important as any of these aspects, 

stroboscopy substantially improves the sensitivity of subtle 

laryngeal diagnoses over techniques, such as rigid or flexible 

transnasal laryngoscopy, with continuous light sources. 

BACKGROUND AND SURGICAL 

PRINCIPLE 

Section 3 of 8 



The concept of stroboscopy is not new. For several centuries, 

stroboscopic images generated by using a flashing light source 

have been used to create the illusion of motion for 

entertainment. This practice is believed to date back to the 

ancient Greeks, who recreationally enjoyed these moving 

pictures. From the early 19th century, several examples 

illustrate the creation of moving-picture and optical toys, as well 

as scientific instruments. One device that used rotating disks to 

observe apparent motion, developed by a Viennese scientist 

named Stampfer, was called a stroboscope. This term is still 

used today to connote any pulsatile light-generating device 

designed to observe motion. 

The history of using a stroboscopic light source to examine the 

larynx is nearly as long as that of the continuous light source,

dating back to the introduction of the laryngeal mirror by 

Manuel Garcia in 1855. In 1895, an internist named Oertel used 

a stroboscopic light source with a laryngeal mirror to investigate 

voice production in different registers. The application of the 

stroboscopic light source allowed the observer to view the 

vibrating vocal folds in arrested or apparent slow motion, 

permitting detailed observations of the structure in the open or 

closed positions. Because of the limitations in illumination, 

precise control of the flashing frequency, poor image quality, 

and patient discomfort, members of the scientific community did 

not embrace this technique. 

In the early to mid 1900s, nearly 100 years after Plateau first 

suggested the use of an intermittent spark to illuminate moving 

objects to produce a stationary pattern for the purpose of study, 

H.E. Edgerton and associates developed gas discharge tubes 

for stroboscopy. They used an oscillator to control the 

frequency of the discharge and the flashing rate. Many of the 

principles of modern stroboscopic devices evolved from this 

early instrumentation. 

Pioneers of modern strobolaryngoscopy include Dr J.W. van 

den Berg at the University of Groningen, Dr Rolf Timke at the 

University of Hamburg, Dr Hans von Leden at the University of 

California, and Dr Elimar Schonharl in Erlanger, who wrote the 

first definitive book on stroboscopic examination of the larynx in 

1960. With the subsequent improvements in audio- and videorecording 

technology and with the ongoing advancements in 

optical image resolution and fiberoptic light-source intensity, the 

modern videostroboscopic unit can now produce a crisp, 

brightly illuminated, magnified image. 

The Talbot law takes into account the physical reality that 

images on the human retina linger for 0.2 seconds after 

exposure (persistence of vision). Therefore, sequential images 

produced at intervals less than 0.2 seconds produce the illusion 

of a continuous image. This understanding, along with the 

concept of correspondence (interpretation of a corresponding 

portion of sequential images representing an object in motion), 

allows for the illusion of motion when rapidly produced still 

images are presented. Finally, a characteristic of the visual 

system permits interpretation of a series of slightly altered still 

images by filling in the gaps between frames and completing 

the illusion of continuous motion. 

Strobolaryngoscopy takes advantage of these principles by 

producing intermittent light flashes in close relation to the 

frequency of the vocal-fold vibration. A microphone picks up the 

frequency of the examinee's sustained voice, which triggers the 

stroboscopic light source. With the provision that the vocal 

vibrations are periodic, a frequency of light flashes equal to the

vocal frequency produces a clear, still image of the same 

portion to the vibratory cycle. 

When the frequency of the flashes is slightly less than the 

vibration of the vocal fold, it causes a delay in the portion of 

each vibratory cycle illuminated, and the illusion of slow motion 

is obtained. However, in all healthy humans, vocal-fold 

vibrations are aperiodic to a greater or lesser degree. 

Therefore, strobolaryngoscopy does not demonstrate fine detail 

of each individual vibratory cycle; rather, it shows a pattern 

averaged over many successive nonidentical cycles. In this 

sense, it is a less-than-perfect illustration of the true vibratory 

nature. 

INSTRUMENTATION 

Section 4 of 8 



A videostrobe unit consists of a stroboscopic unit (light source 

and microphone), a video camera, an endoscope, and a video 

recorder. Stroboscopy can be performed by using either rigid or 

flexible endoscopes; each has its own benefits and drawbacks. 

Although flexible endoscopy is ideal for observing unaltered 

laryngeal behavior from various angles and for viewing the 

glottis through a narrow supraglottic aperture, it suffers from the 

low intensity of light carried through the long fiberoptic bundle 

to the tip of the narrow endoscope. With standard endoscopes, 

the light bouncing off objects being observed must then travel 

the length of the endoscope back to a camera or the operator's 

eye to be detected. 

The introduction of distal-chip technology to flexible 

endoscopes, in which the camera is placed at the distal end of 

the scope, effectively lessened the drawback profile of flexible 

laryngoscopes. The enhanced digital picture quality with 

improved illumination has greatly improved the quality and 

resolution of transnasal laryngeal stroboscopy. 

Rigid transoral endoscopy produces a magnified bright image 

ideal for stroboscopy but requires holding of the patient's 

tongue throughout the examination, which distorts the natural 

phonatory posture of the pharynx and larynx. Moreover, the 

patient must have suitable anatomy and the physical tolerance 

to allow the clinician to visualize the entire glottis. 

Rigid endoscopy additionally requires increased patient 

cooperation and amenable patient anatomy for successful 

visualization of the larynx. Recent research has suggested that

the application of the Mallampati classification system is useful 

for predicting the adequacy of transoral rigid laryngoscopic 

exposure for stroboscopy. 

CLINICAL APPLICATION Section 5 of 8 

Author Information Introduction Background And Surgical Principle Instrumentation Clinical Application Diagnostic Findings 

Extended Applications Bibliography 

Several parameters may be evaluated during the course of the stroboscopic 

examination. 

• Fundamental frequency: The fundamental frequency is measured by using the 

strobe unit and used to set the frequency of the light flashes. Strobe light is 

typically produced at a frequency several hertz slower than the vocal 

frequency to produce the illusion of a slow-motion vibratory cycle. An identical 

frequency is emitted in the locked mode that produces a still image of a single 

portion of the vibratory cycle. 

• Periodicity: Periodicity refers to the regularity of successive vocal motions. 

Normal vibratory activity is regular and periodic. 

• Amplitude: Amplitude refers to the lateral excursion of the vocal folds during 

their displacement away from the midline in oscillation. Typical amplitude is 

approximately one third of the total width of the vocal fold. Amplitude is 

generally graded as normal, less than normal, or greater than normal. 

• Symmetry: Normal motion of the vocal folds is symmetric, both in vibratory 

characteristic and in adductory and abductory motion. 

• Glottic closure: In the healthy person, the membranous portion of the vocal 

folds completely closes during the vibratory cycle. The posterior cartilaginous 

glottis may remain open (posterior glottic chink) in some healthy people. 

• Mucosal wave: The pattern of light traveling from mediolaterally along the 

superior surface of the vocal fold during vibration under illumination is referred 

to as the mucosal wave. It is a correlate of the pliable cover (epithelium and 

superficial lamina propria) of the vocal fold being displaced relative to the body 

of the vocal fold (vocalis muscle). Focal abnormalities of mucosal wave help to 

localize pathology in the vocal fold. 

DIAGNOSTIC FINDINGS Section 6 of 8 



By increasing the illumination and evaluation of vibratory patterns, videostroboscopy 

has vastly increased the sensitivity of laryngologic diagnoses. Despite the variations 

attributable to lesion size, concurrent vocal pathologies, and compensatory 

phonatory behaviors, generalizations can be made about stroboscopic findings 

accompanying specific true vocal-fold pathology. The most common benign laryngeal 

lesions and their typical stroboscopic findings are described below. 

Vocal-fold cysts

Vocal-fold cysts are encapsulated, benign lesions located in the superficial lamina 

propria of the vocal fold. They are generally unilateral, though several may be 

present at the time of diagnosis. On stroboscopy, the vocal fold generally has a 

rounded, full appearance on the affected side. Gaps anterior and posterior to the 

lesion may compromise glottic closure, depending on their size. The vibratory 

patterns of the 2 vocal folds are asymmetrical, with diminution of amplitude on the 

affected side. 

A substantially decreased mucosal wave is present throughout the affected side and 

absent over the cyst itself, an important finding for differentiating a cyst from a nodule 

or polyp (which may have similar appearances on continuous-light examination). An 

altered vibratory pattern is often the only physical finding in the presence of a small 

cyst that does not alter the contour of the vocal fold. 

Vocal-fold polyps 

Vocal-fold polyps may be unilateral or bilateral. These lesions represent pathology in 

the superficial lamina propria. They may be of any consistency, ranging from 

gelatinous to hyalinized. Glottic closure may be compromised, leaving gaps anterior 

and posterior to the lesion in maximal closure. The vibratory patterns of the 2 vocal 

folds are asymmetrical, with diminution of vibration near the lesion. Mucosal wave 

may be present over the polyp itself, depending on its physical consistency. 

Vocal-fold nodules 

Vocal-fold nodules are bilateral lesions that are roughly symmetrical. The relevant 

pathology occurs at the basement membrane zone between the overlying epithelium 

and the underlying lamina propria. The vocal folds have the appearance of medial 

fullness, typically at the junction of the anterior and middle third of the fold. Glottic 

closure is compromised. Mucosal wave is present bilaterally, though both it and the 

vibratory amplitude may be decreased. 

Sulcus vocalis 

Sulcus vocalis is a focal furrow in the covering of the vocal fold. These lesions most 

often are unilateral and represent a tethering of the overlying epithelium to the 

deeper connective tissue. Glottic closure is incomplete. Stroboscopy demonstrates a 

focal interruption in the mucosal wave at the site of the sulcus, and vibratory patterns 

are asymmetrical between the true vocal folds. 

EXTENDED APPLICATIONS Section 7 of 8 



Although videostroboscopy greatly expands the diagnostic sensitivity of 

laryngoscopy, its interpretation depends on the skill and experience of the clinician 

performing the study, and specifically, the skill and experience of the diagnostic 

interpreter. The quality of the images collected is directly related to the skill of the 

operator performing the procedure. In addition, recent research suggests that even, 

among the most experienced interpreters, interrater correlations for judging specific

parameters is moderate (kappa = 0.61-0.81) at best. Although increased experience 

in reviewing stroboscopic results appeared to have a modest positive effect on a 

clinician's intrarater reliability, it did not necessarily improve interrater correlation i a 

group of similarly experienced examiners. 

Several technologies have been developed to improve objective measurements of 

the amplitude of vibration and mucosal wave. Software was developed to measure 

the glottic-area waveform (GAW), a plot of the glottic area against the time of opening 

and closing of the glottis during a representative vibratory cycle (taken from of the 

stroboscopic image). From this information, glottal opening and closing rates are 

calculated. These measurements are purported to be correlates of vocal-fold pliability 

and statistically differ in preoperative and postoperative states for benign vocal-fold 

lesions. 

An admitted limitation of the stroboscopic image is that vocal-fold vibration must be 

relatively periodic to visualize a slow-motion representation of the phonatory cycle. 

Efforts to extend the sensitivity of laryngoscopy, to incorporate variations of wave 

characteristic across the glottis and in aperiodic patterns of vibration have yielded 

new techniques. 

Videokymography is a recent technique based on the principles of high-speed 

glottography. This method allows for the isolation of specific portions on the glottic 

image (obtained at rates of up to 7812 images per second), which are analyzed for 

closure. The suggested advantage over stroboscopy alone is the ability to evaluate 1 

portion of the glottis in comparison to another while avoiding the limitation of vibratory 

periodicity. This technique also allows for accurate objective measurements of the 

glottal gap without the inherent error produced by stroboscopic averaging of many 

individual glottic cycles. 

An additional effort to extend the diagnostic range by combining the 

videostroboscopic image with kymography (line drawings representing the distance 

between defined points on successive images), resulted in the creation of 

videostrobokymography. This technique uses the standard image generated during 

videostrobolaryngoscopy and digitalizes individual frames. Kymograms of multiple 

segments along the glottis are then produced. This marriage of the stroboscopic 

image and the objective measure of vocal-fold vibration as it varies across the 

surface of the glottis is a potentially powerful tool, without the need for additional 

camera technology, as is required for videokymography. On the contrary, this newer 

technique is subject to all of the technical limitations of the original stroboscopic 

imaging process. 

BIBLIOGRAPHY Section 8 of 8 



• Ferlito A: Diseases of the larynx. New York: Oxford University Press; 2000. 

• Hirano M, Bless DM: Videostroboscopic examination of the larynx. San Diego: 

Singular; 1993. 

• Hirano M: Morphological structure of the vocal cord as a vibrator and its 

variations. Folia Phoniatr (Basel) 1974; 26(2): 89-94[Medline].

• Low C, Young P, Webb CJ, et al: A simple and reliable predictor for an 

adequate laryngeal view with rigid endoscopic laryngoscopy. Otolaryngol 

Head Neck Surg 2005 Feb; 132(2): 244-6[Medline]. 

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Otolaryngol Head Neck Surg 1992 Jan; 106(1): 56-9[Medline]. 

• Noordzij JP, Woo P: Glottal area waveform analysis of benign vocal fold 

lesions before and after surgery. Ann Otol Rhinol Laryngol 2000 May; 109(5): 

441-6[Medline]. 

• Rosen CA, Murry T: Nomenclature of voice disorders and vocal pathology. 

Otolaryngol Clin North Am 2000 Oct; 33(5): 1035-46[Medline]. 

• Rosen CA: Stroboscopy as a research instrument: development of a 

perceptual evaluation tool. Laryngoscope 2005 Mar; 115(3): 423-8[Medline]. 

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videokymography. Laryngoscope 1998 Aug; 108(8 Pt 1): 1206-10[Medline]. 

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• Sung MW, Kim KH, Koh TY, et al: Videostrobokymography: a new method for 

the quantitative analysis of vocal fold vibration. Laryngoscope 1999 Nov; 

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