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Spontaneous blink rate of a normal population sample
Clinical Article
Spontaneous Blink Rate of a Normal Population Sample Mosa’ad Al-Abdulmunem, PhD, FAAO, and Stella T. Briggs, PhD
Blinking plays the essential role of spreading the pre-corneal tear film. Improper blinking can lead to dry eye, which can be a severe problem for contact lens wearers. The blink rate of 91 subjects was measured under controlled experimental conditions. While the mean blink rate was 26.13 blinks/min, there was a marked intersubject variation. In a set of 19 subjects taken from the main sample, the blink rate measured under two other experimental conditions showed that the blink rate was high during conversation and then decreased during a classroom examination. © Elsevier Science Inc. 1999 Keywords: Blink rate; mental activity; dry eye; contact lens
Introduction Blinking serves the important function of spreading the pre-corneal tear film and maintaining the moist condition of the anterior surface of the eye. Blinking may be defined as a rapid closure of the eyelids.1 If blinking is prevented, dry spots develop over the cornea and conjunctiva.2,3 Blink abnormalities (as in incomplete blinking, where the upper eyelid does not contact the lower lid or with infrequent blinking) can predispose the eye to dryness.4 Dry eye is a problem for contact lens wearers, and blinking itself plays an essential role in the ability of the patient to wear contact lenses. With blinking, there is an interchange of tears between contact lens and cornea, maintenance of optical quality of the anterior lens surface, and normal wetting of Address reprint requests to Mosa’ad Al-Abdulmunem, Department of Optometry, College of Applied Medical Sciences, King Saud University, P.O. Box 25208, Riyadh 11466 Saudi Arabia. Accepted for publication July 16, 1999. ICLC, Vol. 26, 1999 © Elsevier Science Inc. 1999 655 Avenue of the Americas, New York, NY 10010
those parts of the cornea not covered by the contact lens. Incomplete blinking in contact lens wear has been associated with severe punctate staining of the corneal epithelium.5 Contact lens wearers with abnormal blink rates may be given blinking exercises.6 Many factors have been determined to affect blink rate. Dry eye patients have been reported to have increased blink rate.7 Contact lenses disrupts the tear film, resulting in an increased blink rate.8,9 Fatigue, anxiety, and mental activities are known correlate to blink rate.9 –11 Blink rate has even been reported as an index for visual efficiency.12 Research findings indicate there are physiologic and psychological/perceptual factors associated with blinking. The fact that blindness and/or binocular enucleation did not reduce the blink rate to zero suggests there may be undetermined factors that cause endogenous blinking.13,14 It has been suggested that a blink “clock” is located in the brainstem.13 This may be the reason for the effect of mental activities on blink rates. The mechanism involved in blinking is, however, not fully understood. Reports are varied on the value of the normal blink rate, ranging from an average of 3 blinks/min to 25 blinks/ min.15–18 Supporting data are needed to understanding the multi-factorial mechanism of blinking. To the best of our knowledge, there are no reported data on blink rate of the Saudi Arabian population, so this may serve as important step for future research on blinking in this region and as general supporting scientific data. It is the aim of this study to establish the average blink rate in a population sample and to examine the effect of varying mental activity on blink rate. 0892-8967/99/$–see front matter PII S0892-8967(99)00016-4
Clinical Article
Figure 1. Blink rate distribution.
Materials and Methods Ninety-one subjects (female university students) participated in this study. They had a mean age of 22 years (range 19 –25). All had normal visual acuity following spectacle correction of low degrees of ametropia. None wore contact lenses or had any known ocular or systemic disease. The air-conditioned examination room temperature was 25°C and humidity was 45% during the study period. There was no noticeable air current from the ventilation system. Blink rate was measured by direct observation as described by Patel et al.19 To prevent the subjects from becoming selfconscious about their blinking, they were given spurious reasons as to what was being measured (e.g., eye movement measurements). Three investigators were involved in the measurements: two investigators counted the blinks independently using a mechanical counter while the other investigator talked to the subjects. The blink rate was counted for 1 minute. This was done two times by each investigator, and the average was taken as the blink rate. A set of 19 subjects from the sample was measured on two other occasions: (1) during a class examination and (2) during class lectures. This was secretly measured by just sitting in class during lectures and during an examination.
Results The average blink rate was 26.13 blinks/min (SD ⫾ 9.55, Mode ⫽ 25) with a range from 12– 62 blinks/min. Figure 1 shows the distribution of blink rate of the population sample. The two investigators obtained similar mea-
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ICLC, Vol. 26, 1999
surements for each subject. There were large inter-subject variations. Seventy-nine percent of the subjects had blink rates between 16 and 35 blinks/min. Table 1 shows, for each of the 19 subjects, the blink rate during three different experimental conditions. The average blink rate during conversation was 20.9 blinks/min, when listening to a lecture was 16.4 blinks/min, and during a class examination was 11.4 blinks/min. There was a significant difference (Student t-test, p ⬍ 0.05) among these three conditions. As seen in Table 1, subjects 8 and 9 showed little change in blink rate during conversation and when listening to a lecture, but did show decline during the class examination.
Discussion It is clear from our study that there is a large intersubject variation in the blink rate of normal individuals. This confirms the study of York et al.,9 who reported substantial differences in blink rate between individuals. Variations in individual physiology and psychological states could be responsible. The average blink rate of 26.13 blinks/min reported here is substantially higher than those reported in previous studies,9,15,16 but is in agreement with that of Collins et al.,17 who reported an average blink rate of 24.8 blinks/min. Our study, and that of Collins et al.,17 probably reflects the fact that blink rate was measured while the subjects were involved in conversation. Subjects measured while they were watching video tapes were found to have a mean blink rate of 12.55 blink/min.15 York et al.9 found the blink rate declined from 15 blinks /min to 4
Sponaneous Blink Rate: Al-Abdulmunem and Briggs Table 1. Blink Rate of Subjects under Three Different Experimental Conditions Blink Rate (blinks/min) During Subject
Examination
Lecture
Conversation
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Mean SD Mode Max Min
10 7 14 15 6 24 9 7 10 7 6 7 12 19 8 17 14 15 9 11.4 5 7 24 6
12 11 21 13 7 20 11 13 16 17 22 17 10 21 11 35 20 18 16 16.4 6.3 11 35 7
16 15 27 18 10 21 12 13 15 25 27 24 15 20 15 38 35 27 25 20.9 7.7 15 38 10
blink/min when the visual task was changed from watching a film to underlining “a”s on a text page. A comparable decline, but not quite under the same conditions, was observed in our study when the mean blink rate was reduced from 20.9 blinks/min during conversation to 11.4 blinks/min during an examination. A review of the literature by Stern et al.18 found that fatigue and anxiety can raise the blink rate, whereas visual task or task difficulty can lower the blink rate. Results from our study confirm this. During the conversational condition, subjects were somewhat anxious about the “test” and were slightly shy or even nervous during the conversation. These may have contributed to the high blink rate recorded under this condition, which then decreased during the class examination condition that had “task difficulty” involving high mental concentration. The fact that mental activity affects blink rate implies that the blink rate of an individual would vary throughout the day. Yolton et al.20 suggest that the blink clock determines the basal rate and produces rates that differ from one individual to the other. They added that the blink clock may be controlled by the part of the brain responsible for perception and/or attention. Thus, the clock is suppressed during times of intense visual and mental concentration. This is seen in the reduced blink rate during use of a video display unit.19 From the evidence in the literature, Yolton et al.20 concluded that the cornea and tears play a very minor role in determining blink rate.
Because blinking is so important in contact lens wear, baseline blink rate should be a standard test for prospective contact lens patients, especially those involved in intense mental or visual tasks.
Conclusion Our data established the blink rate of a population sample and showed that blink rate varies according to the mental activity, being reduced with intense mental activity. If ocular physiology of an individual remains relatively constant, the blink rate in any 24-hour period is partly dependent on mental activity.
Acknowledgment We are grateful to Dr. Ofelia Joaquin for her immense contribution to this study.
REFERENCES 1. Mandell RB: Contact Lens Practice. 4th ed. Springfield, IL, Charles C. Thomas, 1988, p. 52. 2. Holly FJ: Formation and rupture of the tear films. Experimental Eye Research 1973;15:515–525. 3. McDonald JE: Surface phenomena of tear film. Trans Am Ophthalmol Soc 1968;66:905–939. 4. Holly FJ: Diagnosis and treatment of dry eye syndrome. CL Spectrum 1989;4:37–44. 5. Mc Monnies CW: After care symptoms, signs and management. Contact Lenses. 3rd ed. Phillips AJ, Stone J (Eds). London, Butterworths, 1989, p. 709. 6. Mandell RB: Contact Lens Practice. 4th ed. Springfield, IL, Charles C. Thomas, 1988, p. 886. 7. Prause JU, Norn M: Relation between blink frequency and break-up time. Acta Ophthalmol 1987;65:19–22. 8. Sharma A, Ruckenstein E: Mechanism of tear film rupture and its implications of contact lens tolerance. Am J Optom Physiol Opt 1985;62:246–253. 9. York M, Ong J, Robbins JC: Variation in blink rate associated with contact lens wear and task difficulty. Am J Optom Am Acad Optom 1971;48:461–466. 10. King DC, Michels KM: Muscular tension and the human blink rate. J Exp Psychol 1957;53:113–116. 11. Stern JA, Walrath LC, Goldstein R: The endogenous eye blink. Psychophysiology 1984;21:22–23. 12. Luckiesh M, Moss F: Frequency of blinking as a clinical criterion of ease of seeing. Am J Ophthalmol 1934;22: 616–625. 13. Hart WM Jr: The eyelids. Adler’s Physiology of the Eye. 9th ed. Hart WM Jr (Ed). St. Louis, Mosby Year Book, 1992, p. 1. 14. Records RE: Eyebrows and eyelids. Duane’s Foundations of Clinical Ophthalmology. Volume 2. Tasman W, Jaeger EA (Eds). Philadelphia, Lippincott, 1992, p. 1. 15. Carney LG, Hill RM: The nature of normal blinking patterns. Acta Ophthalmol 1982;60:427–433. 16. Finnemore VM: Is the dry eye contact lens wearer at risk? Not usually. Cornea 1990;9(suppl):51–53. 17. Collins M, Seeto R, Campbell L, Ross M: Blinking and corneal sensitivity. Acta Ophthalmol 1989;67:525–531. 18. Stern JA, Walrath LC, Goldstein R: The endogenous eyeblink. Psychophysiology 1984;21:22–33.
ICLC, Vol. 26, 1999
31
Clinical Article 19. Patel S, Henderson R, Bradley B, Galloway B, Hunter L: Effect of visual display unit on blink rate and tear stability. Optom Vis Sci 1991;68:888–892.
20. Yolton DP, Yolton RL, Lopez R, et al. The effects of gender and birth control pill use on spontaneous blink rates. J Am Optom Assoc 1994;65:763–770.
Mosa’ad Al-Abdulmunem received his BSc in optometry from King Saud University, Riyadh, Saudi Arabia, in 1989 and his PhD from the Department of Optometry and Vision Sciences of the University of Manchester in the United Kingdom in 1994. In 1992 he was a visiting scholar at the Institute of Contact Lens Research, College of Optometry, University of Houston, Houston, Texas. In 1994, Dr. AlAbdulmunem became an assistant professor of clinical optometry at the Department of Optometry, King Saud University. In April 1995 he joined the King Khaled Eye Specialist Hospital in Riyadh, Saudi Arabia, as a consultant optometrist for 1 year. In 1997 Dr. AlAbdulmunem successfully completed a clinical residency in the area of advanced cornea and contact lens management at the school of optometry, Indiana University, Bloomington, Indiana. Dr. AlAbdulmunem became a fellow of the American Academy of Optometry in 1998. He is now the Head of the Department of Optometry at King Saud University and is an associate professor of clinical optometry. Stella T. Briggs, PhD, is an assistant professor of optometry, King Saud University, Riyadh, Saudi Arabia. She started her undergraduate studies at Indiana University (U.S.), and continued there for the Master of Science degree in optometry. She obtained her PhD in optometry from the University of Wales, Cardiff, U.K. Her area of specialization is contact lens/comeal physiology, a field in which she already has several publications. She is a member of the International Association of Contact Lens Educators.
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ICLC, Vol. 26, 1999
Spontaneous Blink Rate of a Normal Population Sample Mosa’ad Al-Abdulmunem, PhD, FAAO, and Stella T. Briggs, PhD
Blinking plays the essential role of spreading the pre-corneal tear film. Improper blinking can lead to dry eye, which can be a severe problem for contact lens wearers. The blink rate of 91 subjects was measured under controlled experimental conditions. While the mean blink rate was 26.13 blinks/min, there was a marked intersubject variation. In a set of 19 subjects taken from the main sample, the blink rate measured under two other experimental conditions showed that the blink rate was high during conversation and then decreased during a classroom examination. © Elsevier Science Inc. 1999 Keywords: Blink rate; mental activity; dry eye; contact lens
Introduction Blinking serves the important function of spreading the pre-corneal tear film and maintaining the moist condition of the anterior surface of the eye. Blinking may be defined as a rapid closure of the eyelids.1 If blinking is prevented, dry spots develop over the cornea and conjunctiva.2,3 Blink abnormalities (as in incomplete blinking, where the upper eyelid does not contact the lower lid or with infrequent blinking) can predispose the eye to dryness.4 Dry eye is a problem for contact lens wearers, and blinking itself plays an essential role in the ability of the patient to wear contact lenses. With blinking, there is an interchange of tears between contact lens and cornea, maintenance of optical quality of the anterior lens surface, and normal wetting of Address reprint requests to Mosa’ad Al-Abdulmunem, Department of Optometry, College of Applied Medical Sciences, King Saud University, P.O. Box 25208, Riyadh 11466 Saudi Arabia. Accepted for publication July 16, 1999. ICLC, Vol. 26, 1999 © Elsevier Science Inc. 1999 655 Avenue of the Americas, New York, NY 10010
those parts of the cornea not covered by the contact lens. Incomplete blinking in contact lens wear has been associated with severe punctate staining of the corneal epithelium.5 Contact lens wearers with abnormal blink rates may be given blinking exercises.6 Many factors have been determined to affect blink rate. Dry eye patients have been reported to have increased blink rate.7 Contact lenses disrupts the tear film, resulting in an increased blink rate.8,9 Fatigue, anxiety, and mental activities are known correlate to blink rate.9 –11 Blink rate has even been reported as an index for visual efficiency.12 Research findings indicate there are physiologic and psychological/perceptual factors associated with blinking. The fact that blindness and/or binocular enucleation did not reduce the blink rate to zero suggests there may be undetermined factors that cause endogenous blinking.13,14 It has been suggested that a blink “clock” is located in the brainstem.13 This may be the reason for the effect of mental activities on blink rates. The mechanism involved in blinking is, however, not fully understood. Reports are varied on the value of the normal blink rate, ranging from an average of 3 blinks/min to 25 blinks/ min.15–18 Supporting data are needed to understanding the multi-factorial mechanism of blinking. To the best of our knowledge, there are no reported data on blink rate of the Saudi Arabian population, so this may serve as important step for future research on blinking in this region and as general supporting scientific data. It is the aim of this study to establish the average blink rate in a population sample and to examine the effect of varying mental activity on blink rate. 0892-8967/99/$–see front matter PII S0892-8967(99)00016-4
Clinical Article
Figure 1. Blink rate distribution.
Materials and Methods Ninety-one subjects (female university students) participated in this study. They had a mean age of 22 years (range 19 –25). All had normal visual acuity following spectacle correction of low degrees of ametropia. None wore contact lenses or had any known ocular or systemic disease. The air-conditioned examination room temperature was 25°C and humidity was 45% during the study period. There was no noticeable air current from the ventilation system. Blink rate was measured by direct observation as described by Patel et al.19 To prevent the subjects from becoming selfconscious about their blinking, they were given spurious reasons as to what was being measured (e.g., eye movement measurements). Three investigators were involved in the measurements: two investigators counted the blinks independently using a mechanical counter while the other investigator talked to the subjects. The blink rate was counted for 1 minute. This was done two times by each investigator, and the average was taken as the blink rate. A set of 19 subjects from the sample was measured on two other occasions: (1) during a class examination and (2) during class lectures. This was secretly measured by just sitting in class during lectures and during an examination.
Results The average blink rate was 26.13 blinks/min (SD ⫾ 9.55, Mode ⫽ 25) with a range from 12– 62 blinks/min. Figure 1 shows the distribution of blink rate of the population sample. The two investigators obtained similar mea-
30
ICLC, Vol. 26, 1999
surements for each subject. There were large inter-subject variations. Seventy-nine percent of the subjects had blink rates between 16 and 35 blinks/min. Table 1 shows, for each of the 19 subjects, the blink rate during three different experimental conditions. The average blink rate during conversation was 20.9 blinks/min, when listening to a lecture was 16.4 blinks/min, and during a class examination was 11.4 blinks/min. There was a significant difference (Student t-test, p ⬍ 0.05) among these three conditions. As seen in Table 1, subjects 8 and 9 showed little change in blink rate during conversation and when listening to a lecture, but did show decline during the class examination.
Discussion It is clear from our study that there is a large intersubject variation in the blink rate of normal individuals. This confirms the study of York et al.,9 who reported substantial differences in blink rate between individuals. Variations in individual physiology and psychological states could be responsible. The average blink rate of 26.13 blinks/min reported here is substantially higher than those reported in previous studies,9,15,16 but is in agreement with that of Collins et al.,17 who reported an average blink rate of 24.8 blinks/min. Our study, and that of Collins et al.,17 probably reflects the fact that blink rate was measured while the subjects were involved in conversation. Subjects measured while they were watching video tapes were found to have a mean blink rate of 12.55 blink/min.15 York et al.9 found the blink rate declined from 15 blinks /min to 4
Sponaneous Blink Rate: Al-Abdulmunem and Briggs Table 1. Blink Rate of Subjects under Three Different Experimental Conditions Blink Rate (blinks/min) During Subject
Examination
Lecture
Conversation
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Mean SD Mode Max Min
10 7 14 15 6 24 9 7 10 7 6 7 12 19 8 17 14 15 9 11.4 5 7 24 6
12 11 21 13 7 20 11 13 16 17 22 17 10 21 11 35 20 18 16 16.4 6.3 11 35 7
16 15 27 18 10 21 12 13 15 25 27 24 15 20 15 38 35 27 25 20.9 7.7 15 38 10
blink/min when the visual task was changed from watching a film to underlining “a”s on a text page. A comparable decline, but not quite under the same conditions, was observed in our study when the mean blink rate was reduced from 20.9 blinks/min during conversation to 11.4 blinks/min during an examination. A review of the literature by Stern et al.18 found that fatigue and anxiety can raise the blink rate, whereas visual task or task difficulty can lower the blink rate. Results from our study confirm this. During the conversational condition, subjects were somewhat anxious about the “test” and were slightly shy or even nervous during the conversation. These may have contributed to the high blink rate recorded under this condition, which then decreased during the class examination condition that had “task difficulty” involving high mental concentration. The fact that mental activity affects blink rate implies that the blink rate of an individual would vary throughout the day. Yolton et al.20 suggest that the blink clock determines the basal rate and produces rates that differ from one individual to the other. They added that the blink clock may be controlled by the part of the brain responsible for perception and/or attention. Thus, the clock is suppressed during times of intense visual and mental concentration. This is seen in the reduced blink rate during use of a video display unit.19 From the evidence in the literature, Yolton et al.20 concluded that the cornea and tears play a very minor role in determining blink rate.
Because blinking is so important in contact lens wear, baseline blink rate should be a standard test for prospective contact lens patients, especially those involved in intense mental or visual tasks.
Conclusion Our data established the blink rate of a population sample and showed that blink rate varies according to the mental activity, being reduced with intense mental activity. If ocular physiology of an individual remains relatively constant, the blink rate in any 24-hour period is partly dependent on mental activity.
Acknowledgment We are grateful to Dr. Ofelia Joaquin for her immense contribution to this study.
REFERENCES 1. Mandell RB: Contact Lens Practice. 4th ed. Springfield, IL, Charles C. Thomas, 1988, p. 52. 2. Holly FJ: Formation and rupture of the tear films. Experimental Eye Research 1973;15:515–525. 3. McDonald JE: Surface phenomena of tear film. Trans Am Ophthalmol Soc 1968;66:905–939. 4. Holly FJ: Diagnosis and treatment of dry eye syndrome. CL Spectrum 1989;4:37–44. 5. Mc Monnies CW: After care symptoms, signs and management. Contact Lenses. 3rd ed. Phillips AJ, Stone J (Eds). London, Butterworths, 1989, p. 709. 6. Mandell RB: Contact Lens Practice. 4th ed. Springfield, IL, Charles C. Thomas, 1988, p. 886. 7. Prause JU, Norn M: Relation between blink frequency and break-up time. Acta Ophthalmol 1987;65:19–22. 8. Sharma A, Ruckenstein E: Mechanism of tear film rupture and its implications of contact lens tolerance. Am J Optom Physiol Opt 1985;62:246–253. 9. York M, Ong J, Robbins JC: Variation in blink rate associated with contact lens wear and task difficulty. Am J Optom Am Acad Optom 1971;48:461–466. 10. King DC, Michels KM: Muscular tension and the human blink rate. J Exp Psychol 1957;53:113–116. 11. Stern JA, Walrath LC, Goldstein R: The endogenous eye blink. Psychophysiology 1984;21:22–23. 12. Luckiesh M, Moss F: Frequency of blinking as a clinical criterion of ease of seeing. Am J Ophthalmol 1934;22: 616–625. 13. Hart WM Jr: The eyelids. Adler’s Physiology of the Eye. 9th ed. Hart WM Jr (Ed). St. Louis, Mosby Year Book, 1992, p. 1. 14. Records RE: Eyebrows and eyelids. Duane’s Foundations of Clinical Ophthalmology. Volume 2. Tasman W, Jaeger EA (Eds). Philadelphia, Lippincott, 1992, p. 1. 15. Carney LG, Hill RM: The nature of normal blinking patterns. Acta Ophthalmol 1982;60:427–433. 16. Finnemore VM: Is the dry eye contact lens wearer at risk? Not usually. Cornea 1990;9(suppl):51–53. 17. Collins M, Seeto R, Campbell L, Ross M: Blinking and corneal sensitivity. Acta Ophthalmol 1989;67:525–531. 18. Stern JA, Walrath LC, Goldstein R: The endogenous eyeblink. Psychophysiology 1984;21:22–33.
ICLC, Vol. 26, 1999
31
Clinical Article 19. Patel S, Henderson R, Bradley B, Galloway B, Hunter L: Effect of visual display unit on blink rate and tear stability. Optom Vis Sci 1991;68:888–892.
20. Yolton DP, Yolton RL, Lopez R, et al. The effects of gender and birth control pill use on spontaneous blink rates. J Am Optom Assoc 1994;65:763–770.
Mosa’ad Al-Abdulmunem received his BSc in optometry from King Saud University, Riyadh, Saudi Arabia, in 1989 and his PhD from the Department of Optometry and Vision Sciences of the University of Manchester in the United Kingdom in 1994. In 1992 he was a visiting scholar at the Institute of Contact Lens Research, College of Optometry, University of Houston, Houston, Texas. In 1994, Dr. AlAbdulmunem became an assistant professor of clinical optometry at the Department of Optometry, King Saud University. In April 1995 he joined the King Khaled Eye Specialist Hospital in Riyadh, Saudi Arabia, as a consultant optometrist for 1 year. In 1997 Dr. AlAbdulmunem successfully completed a clinical residency in the area of advanced cornea and contact lens management at the school of optometry, Indiana University, Bloomington, Indiana. Dr. AlAbdulmunem became a fellow of the American Academy of Optometry in 1998. He is now the Head of the Department of Optometry at King Saud University and is an associate professor of clinical optometry. Stella T. Briggs, PhD, is an assistant professor of optometry, King Saud University, Riyadh, Saudi Arabia. She started her undergraduate studies at Indiana University (U.S.), and continued there for the Master of Science degree in optometry. She obtained her PhD in optometry from the University of Wales, Cardiff, U.K. Her area of specialization is contact lens/comeal physiology, a field in which she already has several publications. She is a member of the International Association of Contact Lens Educators.
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ICLC, Vol. 26, 1999