- Asthenopia represents a subjective complaint of uncomfortable, painful, and irritable vision. There are 24 different  types  of  asthenopia  based  on  various causes. Because of its subjectivity, however, it can have a myriad of meanings to any number of people. Asthenopia can be caused from some underlying conditions  such  as  focusing  spasm,  different  vision  in  each  eye, astigmatism, hyperopia, myopia, excess light, voluntary focusing, eye coordination difficulties, and more.
- Because computer use is such a high visually demanding task, vision problems and symptoms are very common. Most studies indicate that computer operators report more eye-related problems than noncomputer office workers.  A  number  of  investigators have indicated that visual symptoms occur in  75  to  90%  of  computer  workers (Anshel, 2005).  In  contrast,  a  survey  released  by  the National Institute for Occupational Safety and Health (NIOSH) showed that only 22% of computer workers have musculoskeletal disorders.
- A survey of optometrists (Sheedy, 1992) indicated that 10 million primary care eye examinations are given annually in this country, primarily because of  visual  problems  at  computers.  This  study  eventually  culminated  in  the compilation of the series of symptoms that are now collectively known as computer  vision  syndrome  (CVS).  This  condition  most  often  occurs  when the viewing demand of the task exceeds the visual abilities of the computer user.  The American  Optometric Association  defines  CVS  as  that  “complex of eye and vision problems related to near work that are experienced during or  related  to  computer  use.”  The  symptoms  can  vary  but  mostly  include
eyestrain, headaches, blurred vision (distance or near), dry and irritated eyes, slow refocusing, neck and backache, light sensitivity, double vision, and color distortion.
It is imperative to elicit a thorough case history to distinguish the type of headache involved. The patient should  be  queried  about  the  time  of  onset,  location  of  the  pain, frequency, duration, severity, and precipitating factors such as stress, certain foods or medications. Associated signs and symptoms such as nausea, vomiting, light sensitivity, and noise sensitivity should also be noted.

Computer workers most likely get tension-type headaches. These can be precipitated  by  many  forms  of  stress,  including  anxiety  and  depression; numerous eye conditions, including astigmatism and hyperopia; improper workplace  conditions,  including  glare,  poor  lighting,  and  improper  work-station  setup.  These  types  of  headaches  are  mild  to  moderate  in  intensity, often occur on either or both sides of the head, are not aggravated by physical activity,  develop  during  the  early  to  middle  part  of  the  day,  last  from  30 minutes  to  the  rest  of  the  day,  and  are  relieved  by  rest  or  sleep.  Chronic tension headaches vary somewhat from this but have the same overall symptoms and occur much more frequently.

Visual  and  environmental  conditions  are  the  first  places  to  look  for  a solution to a headache problem. If all obvious factors have been considered, medical management is in order, often starting with a complete eye examination to rule out a visual cause.
Visual acuity is the ability to distinguish between two distinctive points at a particular distance. This requires the image formed on the retina to be well circumscribed  and  distinct.  If  the  image  focuses  in  front  of  or  behind  the retina, it will strike the retina in an unfocused state, creating the subjective
symptom of blur. This process is true for all distances with the viewing range of the human eye, which we routinely consider to be from within 20 feet to 16 inches.

A condition known as transient myopia has been shown to be more prevalent in a population of computer users. This is a condition in which a person exhibits myopia toward the end of the day but not at any other times. Many times, the myopia is not present early in the day or on weekends.

Glare  is  also  a  concern  because  of  the  eye  attending  to  the  glare  image rather  than  the  screen  image.  If  a  specular  reflection  is  noticeable  on  the screen, the eye will attempt to focus on it. The image of the glare source will appear to be somewhere behind the screen (much as your image is reflected in a mirror) and the screen image can appear blurred. This can become more noticeable as computer usage time is increased.
The lachrymal glands secrete the tears that cover the eye surface and keep the  eye  moist,  which  is  necessary  for  normal  eye  function.  The  tears  help maintaining  the  proper  oxygen  balance  of  the  external  eye  structures  and  to keep the optical properties of the eye sharp. The normal tear layer is cleaned off and refreshed by the blinking action of the eyelids.

The blink reflex is one of the fastest reflexes in the body and is present at birth. However, our blink rate varies with different activities — faster when we are very active, slower when we are sedate or concentrating. Yaginuma et al. (1990) measured the blink rate and tearing on four computer workers and noted that the blink rate dropped very significantly during work at a computer  compared  with  before  and  after  work.  There  was  no  significant change in tearing. Patel et al. (1991) measured blink rate by directly observing a  group  of  16  subjects.  The  mean  blink  rate  during  conversation  was  18.4 blinks per minute, and during computer use it dropped to 3.6 — more than a five-fold decrease.

Tsubota and Nakamori (1993) measured blink rates on 104 office workers. The mean blink rates were 22 blinks per minute under relaxed  conditions,  10  blinks  while  reading  a  book  on  a  table,  and  only  7 while viewing text on a computer. Their data support the fact that blink rate decreases during computer use, but also show that other tasks can decrease the blink rate.

EyeScience.org is a source of scientific information about visual ergonomics and human-machine interactions..
Computer Vision Syndrome (CVS)
Definition: CVS is a series of signs and symptoms that are common to those who experience computer-related eye discomfort.
Etiology: The main causes for the visual complaints are a combination of individual visual problems and poor visual ergonomics either at home or at work, or even in both environments.
Most frequent Signs and Symptoms
Al-Abdulmunem M. 1999. Relation between tear breakup time and spontaneous blink rate. Int Contact Lens Clin 26(5):117-120.
Anshel, J. 2005. Visual Ergonomics Handbook. CRC Press - Taylor & Francis Group, USA, 233 p.
Anshel JR. 2007. Visual ergonomics in the workplace. AAOHN J 55(10):414-420; quiz 421-412.
Bacher LF. Factors regulating eye blink rate in young infants. Optom Vis Sci 87(5):337-343.
Bali J, Navin N, Thakur BR. 2007. Computer vision syndrome: a study of the knowledge, attitudes and practices in Indian ophthalmologists. Indian J Ophthalmol 55(4):289-294.
Barbato G, De Padova V, Paolillo AR, Arpaia L, Russo E, Ficca G. 2007. Increased spontaneous eye blink rate following prolonged wakefulness. Physiol Behav 90(1):151-154.
Barbato G, Ficca G, Beatrice M, Casiello M, Muscettola G, Rinaldi F. 1995. Effects of sleep deprivation on spontaneous eye blink rate and alpha EEG power. Biol Psychiatry 38(5):340-341.
Barbato G, Ficca G, Muscettola G, Fichele M, Beatrice M, Rinaldi F. 2000. Diurnal variation in spontaneous eye-blink rate. Psychiatry Res 93(2):145-151.
Barbato G, Moul DE, Schwartz P, Rosenthal NE, Oren DA. 1993. Spontaneous eye blink rate in winter seasonal affective disorder. Psychiatry Res 47(1):79-85.
Bartko G, Herczeg I, Zador G. 1990. Blink rate response to haloperidol as possible predictor of therapeutic outcome. Biol Psychiatry 27(1):113-115.
Belisario A, Modiano A, Fantini A, Gennari E, Nini D, Bacchi L. 1988. [Ocular symptoms and video display terminals: study of a group of video-terminal operators]. G Ital Med Lav 10(1):39-42.
Benoit FM, LeBel GL, Williams DT. 1984. Are video display terminals a source of increased PCB concentration in the working atmosphere? One answer. Int Arch Occup Environ Health 53(3):261-267.
Bentivoglio AR, Bressman SB, Cassetta E, Carretta D, Tonali P, Albanese A. 1997. Analysis of blink rate patterns in normal subjects. Mov Disord 12(6):1028-1034.
Bentivoglio AR, Daniele A, Albanese A, Tonali PA, Fasano A. 2006. Analysis of blink rate in patients with blepharospasm. Mov Disord 21(8):1225-1229.
Bergman T. 1980. Eye care Health effects of video display terminals. Occup Health Saf 49(10):24, 26-28, 53-25.
Berrios GE, Canagasabey AF. 1990. Depression, Eye Blink Rate, Psychomotor Retardation, and Electroconvulsive Therapy-Enhanced Dopamine Receptor Sensitivity. Convuls Ther 6(3):224-230.
Blehm C, Vishnu S, Khattak A, Mitra S, Yee RW. 2005. Computer vision syndrome: a review. Surv Ophthalmol 50(3):253-262.
Bodfish JW, Powell SB, Golden RN, Lewis MH. 1995. Blink rate as an index of dopamine function in adults with mental retardation and repetitive behavior disorders. Am J Ment Retard 99(4):335-344.
Boutros NN, Hatch JP. 1988. Blink rate on routine EEGs: possible psychiatric significance. Biol Psychiatry 24(6):717-720.
Breimhorst M, Marks A, Robens S, Griefahn B. 2009. Blink rate during tests of executive performance after nocturnal traffic noise. Noise Health 11(45):217-222.
Caplan R, Guthrie D. 1994. Blink rate in childhood schizophrenia spectrum disorder. Biol Psychiatry 35(4):228-234.
Caplan R, Guthrie D, Komo S. 1996. Blink rate in children with attention-deficit-hyperactivity disorder. Biol Psychiatry 39(12):1032-1038.
Caplan R, Guthrie D, Komo S, Shields WD. 1998. Blink rate in pediatric complex partial seizure disorder. J Child Psychol Psychiatry 39(8):1145-1152.
Carta A, Pasquini L, Lucchini R, Semeraro F, Apostoli P. 2003. [Relation of asthenopia and some ophthalmological, neuropsychological, and musculoskeletal parameters in workers assigned to video display terminals]. Med Lav 94(5):466-479.
Chan RC, Chen EY. 2004. Blink rate does matter: a study of blink rate, sustained attention, and neurological signs in schizophrenia. J Nerv Ment Dis 192(11):781-783.
Chen EY, Lam LC, Chen RY, Nguyen DG. 1996. Blink rate, neurocognitive impairments, and symptoms in schizophrenia. Biol Psychiatry 40(7):597-603.
Chen WH, Chiang TJ, Hsu MC, Liu JS. 2003. The validity of eye blink rate in Chinese adults for the diagnosis of Parkinson's disease. Clin Neurol Neurosurg 105(2):90-92.
Choy EP, Cho P, Benzie IF, Choy CK. 2008. Dry eye and blink rate simulation with a pig eye model. Optom Vis Sci 85(2):129-134.
Dainoff MJ. 1983. Video display terminals. The relationship between ergonomic design, health complaints and operator performance. Occup Health Nurs 31(12):29-33.
De Padova V, Barbato G, Conte F, Ficca G. 2009. Diurnal variation of spontaneous eye blink rate in the elderly and its relationships with sleepiness and arousal. Neurosci Lett 463(1):40-43.
Depue RA, Iacono WG, Muir R, Arbisi P. 1988. Effect of phototherapy on spontaneous eye blink rate in subjects with seasonal affective disorder. Am J Psychiatry 145(11):1457-1459.
Doughty MJ, Naase T. 2006. Further analysis of the human spontaneous eye blink rate by a cluster analysis-based approach to categorize individuals with 'normal' versus 'frequent' eye blink activity. Eye Contact Lens 32(6):294-299.
Drinkwater BL, Flint MM. 1968. Telemetric monitoring of the reflex blink rate. Percept Mot Skills 26(1):303-307.
Dubois-Poulsen A, Lemaigre-Voreaux P, Plat P. 1983. [From general and visual ergonomics in adults to school ergonomics. Contribution to the study of lighting in schools]. Infirm Fr(246):19-27.
Elsworth JD, Lawrence MS, Roth RH, Taylor JR, Mailman RB, Nichols DE, Lewis MH, Redmond DE, Jr. 1991. D1 and D2 dopamine receptors independently regulate spontaneous blink rate in the vervet monkey. J Pharmacol Exp Ther 259(2):595-600.
Franks CM. 1963. Ocular movements and spontaneous blink rate as functions of personality. Percept Mot Skills 16:178.
Franks CM. 1964. The Effects of Alcohol Upon Fluctuation in Perspective, Blink Rate and Eye Movements. Q J Stud Alcohol 25:56-67.
Goldberg TE, Maltz A, Bow JN, Karson CN, Leleszi JP. 1987. Blink rate abnormalities in autistic and mentally retarded children: relationship to dopaminergic activity. J Am Acad Child Adolesc Psychiatry 26(3):336-338.
Golding TR, Bruce AS, Gaterell LL, Little SA, Macnamara J. 1995. Soft lens movement: effect of blink rate on lens settling. Acta Ophthalmol Scand 73(6):506-511.
Grajewski B, Schnorr TM, Reefhuis J, Roeleveld N, Salvan A, Mueller CA, Conover DL, Murray WE. 1997. Work with video display terminals and the risk of reduced birthweight and preterm birth. Am J Ind Med 32(6):681-688.
Haik KG. 1985. Visual difficulties from video display terminals. South Med J 78(7):887-888.
Harris CS, Thackray RI, Shoenberger RW. 1966. Blink rate as a function of induced muscular tension and manifest anxiety. Percept Mot Skills 22(1):155-160.
Helms PM, Godwin CD. 1985. Abnormalities of blink rate in psychoses: a preliminary report. Biol Psychiatry 20(1):103-106.
Iwanaga K, Saito S, Shimomura Y, Harada H, Katsuura T. 2000. The effect of mental loads on muscle tension, blood pressure and blink rate. J Physiol Anthropol Appl Human Sci 19(3):135-141.
Izquierdo JC, Garcia M, Buxo C, Izquierdo NJ. 2004. Factors leading to the Computer Vision Syndrome: an issue at the contemporary workplace. Bol Asoc Med P R 96(2):103-110.
Izquierdo JC, Garcia M, Buxo C, Izquierdo NJ. 2007. Factors leading to the computer vision syndrome: an issue at the contemporary workplace. Bol Asoc Med P R 99(1):21-28.
Jacobsen LK, Hommer DW, Hong WL, Castellanos FX, Frazier JA, Giedd JN, Rapoport JL. 1996. Blink rate in childhood-onset schizophrenia: comparison with normal and attention-deficit hyperactivity disorder controls. Biol Psychiatry 40(12):1222-1229.
Josefsson T, Nilsson R, Eriksson A, Weidenhaijn B, Weidenhaijn F. 1990. [Disorders caused by video display terminals and hypersensitivity to electricity--the affected persons experience a cruel reality]. Lakartidningen 87(45):3745-3746, 3751.
Kao KT, Powell DA. 1988. Lesions of the substantia nigra retard Pavlovian eye-blink but not heart rate conditioning in the rabbit. Behav Neurosci 102(4):515-525.
Karson CN, Goldberg TE, Leleszi JP. 1986. Increased blink rate in adolescent patients with psychosis. Psychiatry Res 17(3):195-198.
Karson CN, Kaufmann CA, Shapiro AK, Shapiro E. 1985. Eye-blink rate in Tourette's syndrome. J Nerv Ment Dis 173(9):566-569.
Karson CN, Kleinman JE, Berman KF, Phelps BH, Wise CD, DeLisi LE, Jeste DV. 1983. An inverse correlation between spontaneous eye-blink rate and platelet monoamine oxidase activity. Br J Psychiatry 142:43-46.
Kim IN, Megeda EV. 2007. [Negative impact of video display terminals on the organs of vision]. Gig Sanit(2):30-33.
Kimber TE, Thompson PD. 2000. Increased blink rate in advanced Parkinson's disease: a form of 'off'-period dystonia? Mov Disord 15(5):982-985.
King DC, Michels KM. 1957. Muscular tension and the human blink rate. J Exp Psychol 53(2):113-116.
Kitamura T, Kahn A, Kumar R, Mackintosh JH. 1984. Blink rate and blunted affect among chronic schizophrenic patients. Biol Psychiatry 19(3):429-434.
Kleven MS, Koek W. 1996. Differential effects of direct and indirect dopamine agonists on eye blink rate in cynomolgus monkeys. J Pharmacol Exp Ther 279(3):1211-1219.
Knave BG, Wibom RI, Bergqvist UO, Carlsson LL, Levin MI, Nylen PR. 1985. Work with video display terminals among office employees. II. Physical exposure factors. Scand J Work Environ Health 11(6):467-474.
Kojima M, Shioiri T, Hosoki T, Sakai M, Bando T, Someya T. 2002. Blink rate variability in patients with panic disorder: new trial using audiovisual stimulation. Psychiatry Clin Neurosci 56(5):545-549.
Kroemera KH, Marras WS. 1980. Ergonomics of visual emergency signals. Appl Ergon 11(3):137-144.
Laibson PR. 1981. Importance of blink rate. West J Med 135(2):92.
Lam DS, Cheuk W, Leung AT, Fan DS, Cheng HM, Chew SJ. 1999. Eye care when using video display terminals. Hong Kong Med J 5(3):255-257.
Lawrence MS, Redmond DE, Jr. 1991. MPTP lesions and dopaminergic drugs alter eye blink rate in African green monkeys. Pharmacol Biochem Behav 38(4):869-874.
Lemaigre-Voreaux P, Plat P. 1983. [From general and visual ergonomics in adults, to school ergonomics. Part 2]. Infirm Fr(247):17-24.
Letourneau EG. 1981. Are video display terminals safe? Can Med Assoc J 125(6):533-534.
Lichtenberg P, Even-Or E, Bachner-Melman R, Levin R, Brin A, Heresco-Levy U. 2008. Hypnotizability and blink rate: a test of the dopamine hypothesis. Int J Clin Exp Hypn 56(3):243-254.
Lovestone S. 1992. Periodic psychosis associated with the menstrual cycle and increased blink rate. Br J Psychiatry 161:402-404.
Luckiesh M, Guth SK, Eastmann AA. 1947. The blink-rate and ease of seeing. Illum Eng 42(5):584-588.
Mackert A, Woyth C, Flechtner KM, Frick K. 1990. [Increased blink rate in schizophrenic patients]. Nervenarzt 61(7):426-430.
Mackert A, Woyth C, Flechtner KM, Volz HP. 1990. Increased blink rate in drug-naive acute schizophrenic patients. Biol Psychiatry 27(11):1197-1202.
Mackert A, Woyth C, Flechtner M, Frick K. 1988. Increased blink rate in acute and remitted schizophrenics. Pharmacopsychiatry 21(6):334-335.
Mackintosh JH, Kumar R, Kitamura T. 1983. Blink rate in psychiatric illness. Br J Psychiatry 143:55-57.
MacLean WE, Jr., Lewis MH, Bryson-Brockmann WA, Ellis DN, Arendt RE, Baumeister AA. 1985. Blink rate and stereotyped behavior: evidence for dopamine involvement? Biol Psychiatry 20(12):1321-1325.
Madhan MR. 2009. Computer vision syndrome. Nurs J India 100(10):236-237.
Maisel JM. 1988. Visual complaints and video display terminals. N Y State J Med 88(6):289-290.
Malfatti P, Modiano A, Navacchia P, Giuliani MB, Fantini A, Olivetti G, Belisario A. 1985. [Ocular fatigue syndrome in subjects exposed to video display terminals: definition and evaluation in a group of VDT operators]. G Ital Med Lav 7(5-6):249-252.
Martin I. 1958. Blink rate and muscle tension. J Ment Sci 104(434):123-132.
Maurice D. 1995. The effect of the low blink rate in rabbits on topical drug penetration. J Ocul Pharmacol Ther 11(3):297-304.
McConnell CR. 1985. Video display terminals: a new source of employee problems. Health Care Superv 3(4):81-88.
Meyer DR, Bahrick HP, Fitts PM. 1953. Incentive, anxiety, and the human blink rate. J Exp Psychol 45(3):183-187.
Miyake-Kashima M, Dogru M, Nojima T, Murase M, Matsumoto Y, Tsubota K. 2005. The effect of antireflection film use on blink rate and asthenopic symptoms during visual display terminal work. Cornea 24(5):567-570.
Monster AW, Chan HC, O'Connor D. 1978. Long-term trends in human eye blink rate. Biotelem Patient Monit 5(4):206-222.
Mueser KT, Dysken MW, Sussman S, Lyons JS, Davis JM. 1984. Development of tolerance to neuroleptic-induced decreases in blink rate. Biol Psychiatry 19(4):617-621.
Nagashima K. 1998. Gravity, blink rate, and lacrimal drainage capacity. Am J Ophthalmol 126(1):152.
Nyman KG, Knave BG, Voss M. 1985. Work with video display terminals among office employees. IV. Refraction, accommodation, convergence and binocular vision. Scand J Work Environ Health 11(6):483-487.
Patel S, Henderson R, Bradley L, Galloway B, Hunter L. 1991. Effect of visual display unit use on blink rate and tear stability. Optom Vis Sci 68(11):888-892.
Powell DA, Hernandez L, Buchanan SL. 1985. Intraseptal scopolamine has differential effects on Pavlovian eye blink and heart rate conditioning. Behav Neurosci 99(1):75-87.
Rainwater G, Cogan R. 1975. Simultaneous disappearances of both images during binocular rivalry of contours and effect on eye-blink rate. Percept Mot Skills 40(1):71-77.
Reiner J. 1999. [Vision disorders in work at video display terminals caused by poor gaze orientation]. Klin Monbl Augenheilkd 215(6):aA9-11.
Roberts JE, Symons FJ, Johnson AM, Hatton DD, Boccia ML. 2005. Blink rate in boys with fragile X syndrome: preliminary evidence for altered dopamine function. J Intellect Disabil Res 49(Pt 9):647-656.
Ruiz-Padial E, Sollers JJ, 3rd, Vila J, Thayer JF. 2003. The rhythm of the heart in the blink of an eye: emotion-modulated startle magnitude covaries with heart rate variability. Psychophysiology 40(2):306-313.
Sahlin S, Chen E. 1997. Gravity, blink rate, and lacrimal drainage capacity. Am J Ophthalmol 124(6):758-764.
Sahlin S, Laurell CG, Chen E, Philipson B. 1998. Lacrimal drainage capacity, age and blink rate. Orbit 17(3):155-159.
Sandyk R. 1990. The significance of eye blink rate in parkinsonism: a hypothesis. Int J Neurosci 51(1-2):99-103.
Scheiman M. 1996. Accommodative and binocular vision disorders associated with video display terminals: diagnosis and management issues. J Am Optom Assoc 67(9):531-539.
Schuri U, von Cramon D. 1981. Heart rate and blink rate responses during mental arithmetic with and without continuous verbalization of results. Psychophysiology 18(6):650-653.
Semlitsch HV, Anderer P, Saletu B, Binder GA, Decker KA. 1993. Acute effects of the novel antidepressant venlafaxine on cognitive event-related potentials (P300), eye blink rate and mood in young healthy subjects. Int Clin Psychopharmacol 8(3):155-166.
Sheedy JE. 1992. Vision problems at video display terminals: a survey of optometrists. J Am Optom Assoc 63(10):687-692.
Sheedy JE, Gowrisankaran S, Hayes JR. 2005. Blink rate decreases with eyelid squint. Optom Vis Sci 82(10):905-911.
Shukla D. 1985. Blink rate as clinical indicator. Neurology 35(2):286.
Slagter HA, Davidson RJ, Tomer R. Eye-blink rate predicts individual differences in pseudoneglect. Neuropsychologia 48(5):1265-1268.
Sotoyama M, Villanueva MB, Jonai H, Saito S. 1995. Ocular surface area as an informative index of visual ergonomics. Ind Health 33(2):43-55.
Stern JA, Boyer D, Schroeder D. 1994. Blink rate: a possible measure of fatigue. Hum Factors 36(2):285-297.
Stewart T. 1995. Ergonomics standards concerning human-system interaction: visual displays, controls and environmental requirements. Appl Ergon 26(4):271-274.
Taino G, Ferrari M, Mestad IJ, Fabris F, Imbriani M. 2006. [Asthenopia and work at video display terminals: study of 191 workers exposed to the risk by administration of a standardized questionnaire and ophthalmologic evaluation]. G Ital Med Lav Ergon 28(4):487-497.
Tinker MA. 1949. Involuntary blink rate and illumination intensity in visual work. J Exp Psychol 39(4):558-560.
Tsubota K, Miyake M, Matsumoto Y, Shintani M. 2002. Visual protective sheet can increase blink rate while playing a hand-held video game. Am J Ophthalmol 133(5):704-705.
Tsubota K, Nakamori K. 1993. Dry eyes and video display terminals. N Engl J Med 328(8):584.
Tsubota K, Nakamori K. 1995. Effects of ocular surface area and blink rate on tear dynamics. Arch Ophthalmol 113(2):155-158.
Ustinaviciene R, Obelenis V, Ereminas D. 2004. Occupational health problems in modern work environment. Medicina (Kaunas) 40(9):897-904.
Von Stroh R. 1993. Computer vision syndrome. Occup Health Saf 62(10):62-66.
Walker JC, Kendal-Reed M, Utell MJ, Cain WS. 2001. Human breathing and eye blink rate responses to airborne chemicals. Environ Health Perspect 109 Suppl 4:507-512.
Weiner EA, Concepcion P. 1975. Effects of affective stimuli mode on eye-blink rate and anxiety. J Clin Psychol 31(2):256-259.
Weitzenhoffer AM. 1969. Eye-blink rate and hypnosis: preliminary findings. Percept Mot Skills 28(2):671-676.
Windham GC, Fenster L, Swan SH, Neutra RR. 1990. Use of video display terminals during pregnancy and the risk of spontaneous abortion, low birthweight, or intrauterine growth retardation. Am J Ind Med 18(6):675-688.
Yaginuma Y, Yamada H, Nagai H. 1990. Study of the relationship between lacrimation and blink in VDT work. Ergonomics 33(6):799-809.
Yeow PH, Sen RN. 2004. Ergonomics improvements of the visual inspection process in a printed circuit assembly factory. Int J Occup Saf Ergon 10(4):369-385.
York M, Ong J, Robbins JC. 1971. Variation in blink rate associated with contact lens wear and task difficulty. Am J Optom Arch Am Acad Optom 48(6):461-467.

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