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Orbit
The International Journal on Orbital Disorders, Oculoplastic and Lacrimal Surgery
ISSN: 0167-6830 (Print) 1744-5108 (Online) Journal homepage: www.tandfonline.com/journals/iorb20
Spontaneous Eye Blink Analysis in the Normal Individual
Silvana A. Schellini, Amilton A. Sampaio Jr., Erika Hoyama, Antônio A. V. Cruz & Carlos R. Padovani
To cite this article: Silvana A. Schellini, Amilton A. Sampaio Jr., Erika Hoyama, Antônio A. V. Cruz & Carlos R. Padovani (2005) Spontaneous Eye Blink Analysis in the Normal Individual, Orbit, 24:4, 239-242, DOI: 10.1080/01676830590922057 To link to this article: https://doi.org/10.1080/01676830590922057
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Orbit, 24:239–242, 2005 Copyright c 2005 Taylor & Francis LLC ISSN: 0167-6830 DOI: 10.1080/01676830590922057

CLINICAL RESEARCH

Spontaneous Eye Blink Analysis in the Normal Individual

Silvana A. Schellini, MD, Amilton A. Sampaio Jr., MD, and Erika Hoyama, MD Department of Ophthalmology, Botucatu School of Medicine, Botucatu, SP, Brazil
Antoˆ nio A. V. Cruz Department of Ophthalmology, Ribeira˜ o Preto School of Medicine, SP, Brazil
Carlos R. Padovani, PhD Department of Biostatistics, Botucatu School of Medicine, Botucatu, SP, Brazil

ABSTRACT Purpose: Spontaneous eye blink activity in the primary eye position and its relationship to age and gender were assessed using digital image processing techniques to quantify blink opening and closing time. Methods: One hundred-and-eighty healthy volunteers (90 males and 90 females), divided into the age groups 0–3, 4–12, 13–20, 21–40, 41–60 and ≥60 years old, were evaluated prospectively. They were videotaped digitally in a standard setting and the images were transferred to a personal computer (Macintosh 400) and processed with the iMovie software. Blink opening and closing time were measured at 30 frames/second. The data were then subjected to statistical analysis. Results: The closing time was significantly longer than the opening time for all ages and both genders. Elderly individuals (≥41 years old) and women had significantly longer closing times. Conclusion: Image processing techniques made possible the observation of differences in spontaneous eye blink opening and closing time in relation to age and gender.
KEYWORDS Spontaneous eye blink; blink opening time; blink closing time; digital image
processing

Received 15 December 2004.
Address correspondence to Silvana A. Schellini, MD, Dep. OFT/ORL/CCP, Faculdade de Medicina de Botucatu, UNESP, Botucatu, SP, Brazil. Cep: 18618-000; Fax: +55-14-3811-6256; E-mail: sartioli@fmb.unesp.br

INTRODUCTION
The rapid opening and closing of the eyelids is known as blinking. There are two types of blink: involuntary blinking, which occurs spontaneously, and voluntary blinking which is controlled by the individual.
The involuntary blink lasts approximately 290–750 thousandths of a second and the blink rate is determined by many factors, including the local luminosity, temperature, ocular pathology and the degree of concentration on visual tasks (Siegel et al., 1997).
Involuntary blinking can be divided into spontaneous blinking, which occurs at approximately constant intervals, and the involuntary fright blink reflex in response to external corneal stimuli (Recordes, 1997).
The mean eye blink rate in normal individuals varies from 2 to 50 blinks/ minute (Monster et al., 1978). Many factors may affect the blink rate, including gender (the rate is higher in women than in men during reading (Bentivoglio et al., 1997)), the time of day (blinking is more frequent in the
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evening (Barbato et al., 2000)), the degree of concentration on visual tasks (Nakamori et al., 1997) and the presence of ocular discomfort or disease (Nakamori et al., 1997; Siegel et al., 1997). The rate of blinking may also affect the tear drainage (Sahlin and Chen, 1997) and ocular surface integrity (Nakamori et al., 1997; Tsubota and Nakamori, 1995).
Because of the influence of all of these factors, it is very difficult to evaluate the blinking pattern. The absence of an ideal method of analysis is another factor that makes evaluation difficult.
The eyelids are highly flexible and are one of the most movable parts of the body. According to Recordes (1997), the rate of eyelid closing is 14 cm/second so that dynamic evaluation of blinking is difficult by methods other than digital image analysis.
The introduction of image recording and processing techniques may make possible better evaluation of the eye blink pattern. The purpose of this study was to assess the eyelid opening and closing times during blinking and their relationship to age and gender, using a digital image processing system.
SUBJECTS AND METHODS
One hundred-and-eighty healthy volunteers (90 males and 90 females) were evaluated prospectively. They represented a wide age range, from newborns to over 60, and were divided into groups according to gender and age (0–3, 4–12, 13–20, 21–40, 41–60 and ≥60 years old).
Exclusion criteria were systemic eyelid abnormalities, ocular disease and previous ophthalmologic or eyelid surgery. Informed consent was obtained from all subjects.
Spontaneous eye blinks were recorded digitally, continuously and bilaterally, for 3 minutes with the subject fixing on a distant target in primary eye position. The camera was positioned laterally to the face at a distance of 1 meter. Recording was done indoors under artificial light and at standard temperature (21◦C). The images were transferred to a Macintosh 400 computer and then subjected to dynamic evaluation using the iMovie software.
Eyelid opening time, closing time and total blink time were measured for a period of 3 minutes using a frame speed of 30 frames/second. Opening time was defined as the interval between complete eyelid closing and the eyelid in the primary position of gaze; closing
S. A. Schellini et al.

time was defined as the interval between the eyelid in the primary position of gaze and complete closing of the eyelid; the total blink time was the sum of the opening and closing times.
The data were subjected to Kruskal-Wallis analysis for the relationship between eye blink time and age, and to the Mann-Whitney test for the relationship between eye blink time and gender.

RESULTS
The population under study included a broad range of ages and was divided into six groups according to age and gender. The closing time was longer than the opening time in both genders and all age groups. The closing time was statistically significantly longer in subjects over 41 years of age (Table 1). The closing time was longer in females than in males, but this difference was statistically significant only in the age group 41–60 years (Table 1).
There was no statistically significant relationship between opening time and age (Table 2). The opening time was, however, longer in females in the age groups 13–20 or 41–60 years and in males aged 21–40 years (Table 2). Both the opening time and the closing time showed pronounced variation.
The total blink time (the sum of the opening and closing times) was longer in the older subjects, with

TABLE 1 Eyelid Closing Times Measured at 30 Frames/Second
in Various Age Groups According to Gender

Gender

Age

Statistical

(yrs)

Male

Female

analysis

0–3

5.0 ± 2.0

5.0 ± 1.0 0.06 (P > 0.05)

(4.0; 15.0)

(4.0; 10.0)

4–13

7.0 ± 0.5

7.0 ± 1.5 1.91 (P > 0.05)

(5.0; 11.0)

(4.0; 10.0)

14–21

7.0 ± 1.0

8.0 ± 1.5 1.75 (p > 0.05)

(5.0; 9.0)

(6.0; 15.0)

22–40

7.0 ± 1.0

8.0 ± 2.0 0.58 (P > 0.05)

(6.0; 12.0)

(5.0; 16.0)

41–60

8.0 ± 11.0

10.0 ± 1.5 2.31 (P < 0.05)

(6.0; 11.0)

(7.0; 14.0)

>61

9.0 ± 1.5

8.0 + 2.0 0.40 (P > 0.05)

(5.0; 12.0)

(5.0 ; 12.0)

Statistical 11.89 (P < 0.05) 24.49 (P < 0.01)

Analysis (0–3) = (≤61) [(0–3) = (4–13)]

= (41–60)

Average ± inter-quartile semi-amplitude (minimum value; maximum value).

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TABLE 2 Eyelid Opening Times Measured at 30 Frames/Second
in Various Age Groups According to Gender

Gender

Age

Statistical

(yrs)

Male

Female

analysis

0–3

2.0 ± 0.5

3.0 ± 0.5 1.40 (P > 0.05)

(2.0; 4.0)

(2.0; 4.0)

4–13

3.0 ± 0.5

3.0 ± 0.5 1.60(P > 0.05)

(2.0; 5.0)

(2.0; 4.0)

14–21

2.0 ± 0.5

3.0 ± 0.0 1.98 (p > 0.05)

(2.0; 4.0)

(2.0; 4.0)

22–40

3.0 ± 0.0

2.0 ± 0.5 2.31 (P > 0.05)

(2.0; 4.0)

(2.0; 3.0)

41–60

8.0 ± 11.0

3.0 ± 0.5 2.15 (P < 0.05)

(2.0; 4.0)

(2.0; 4.0)

>61

3.0 ± 0.0

3.0 ± 0.5 0.42 (P > 0.05)

(2.0; 4.0)

(2.0; 5.0)

Statistical 8,15 (P < 0,05) 8,91 (P < 0,05)

Analysis (all of them) (all of them)

= (41–60)

= (22–40)

Average ± inter-quartile semi-amplitude (minimum value; maximum value).

females having statistically significantly longer total blink times than males in some age groups (Table 3).

DISCUSSION
Blinking has important functions, including lubrication of the ocular surface to prevent dessication, removal of foreign bodies, protection against external vi-

TABLE 3 Total Blink Times Measured at 30 Frames/Second in
Various Age Groups According to Gender

Gender

Age

Statistical

(yrs)

Male

Female

analysis

0–3

8.0 ± 2.5

8.0 ± 2.0 0.34 (P > 0.05)

(6.0; 20.0)

(6.0; 14,0)

4–13

10.0 ± 1.5

9.0 ± 2.0 1.88 (P > 0.05)

(8.0; 16.0)

(6.0; 13.0)

14–21

9.0 ± 1.0

11.0 ± 2.0 2.08 (p > 0.05)

(7.0; 13.0)

(8.0; 19.0)

22–40

10.0 ± 0.5

10.0 ± 2.0 0.36 (P > 0.05)

(8.0; 16.0)

(7.0; 20.0)

41–60

11.0 ± 1.5

13.0 ± 1.5 2.72 (P < 0.01)

(8.0; 14.0)

(9.0; 17.0)

>61

13.0 ± 1.5

11.0 ± 3.0 0.17 (P > 0.05)

(7.0; 15.0)

(7.0; 16.0)

Statistical 12.39 (P < 0.05) 21.31 (P < 0.01)

Analysis (0–3) = (≥61) [(0–3) = (4–13)]

= (41–60)

Average ± inter-quartile semi-amplitude (minimum value; maximum value).

241

sual stimuli, and the spread and maintenance of the tear film (Recordes, 1997).
The present study made use of a digital system with computer image processing to evaluate the blink rate. A previous study suggested a system with a miniature optical sensor connected to a portable device and compatible with a personal computer, while other workers have used standard videotape images (Siegel et al., 1997).
The iMovie software used in this study permits image capture (one frame) in one-thirtieth of a second. Such a high speed is extremely important due to the high speed of eyelid movements. The method proved successful since the images were easy to acquire and process. Using this technique, it was possible to identify differences according to gender and age groups in the parameters studied.
The spontaneous (involuntary) blink rate is a function of many variables, both internal (e.g., mood, concentration) and external (ambient dust, smoke) (Monster et al., 1978); it is therefore very important to control all the environmental factors throughout the experiment. Since local ocular surface factors could influence the blink rate (Nakamori et al., 1997; Tsubota and Nakamori, 1995), an inclusion criterion in this study was a healthy eye.
Closing time was significantly longer than opening time in both genders and all age groups. This has been reported previously in the literature (Recordes, 1997). The tendency towards longer closing than opening times was also seen in the elderly and in some female age groups. Involutional changes affecting the eyelid skin and orbital structures lead to redundant tissue that may compromise eyelid movement, thus possibly explaining the longer closing times in the elderly.
Blinking has been reported to be virtually absent at birth, increasing through adolescence and reaching a plateau that is maintained throughout adult life with little variation with age (Bentivoglio et al., 1997). This is not in agreement with our results, which revealed a longer total blink time in the elderly and some female age groups. The impaired eyelid movement in the elderly can be explained by reduced orbicularis function, laxity of the lateral canthus, and decreased motility and tone of the eyelids (Shore, 1985).
Our results are given in the form of median blink rates. These are considered to be more characteristic of the relaxed state, low blink rates being an indication of a high level of mental activity (Monster et al., 1978). Since the blink rate varies with behavior, being
Spontaneous Eye Blink Analysis

lower during reading and increasing progressively at rest and during conversation (Bentivoglio et al., 1997), we studied spontaneous blinking in healthy subjects under relaxed conditions. Our findings show that the image processing technique used in this study is adequate for the evaluation of spontaneous eye blink times.
ACKNOWLEDGEMENTS
This study was supported financially by FAPESP.
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