In a comprehensive literature review, Professor Michael Doughty, of Glasgow-Caledonian University in Scotland, highlighted the ranges of blinks per minute during reading as 1.4 to 14.4, primary gaze as eight to 21 and conversation as 10.5 to 32.5. 1,13 These findings have been replicated across a series of experiments, demonstrating that one's blink rate is highly dependent upon experimental conditions. 12 Research into the task-dependent nature of the blink has supported blink-rate types in relation to four tasks: visual display unit use (e.g., computer) reading primary gaze and conversation. Indeed, even the intensity of illumination and glare has been shown to impact the frequency of blinking. Hence, adequate eyeblinks and an intact lid margin are critical to maintaining the ocular surface.īlink rate can vary across tasks and states, and can increase in frequency and completeness. 11 The lacrimal gland/oil layer reestablishes the tear film, but the tear film can only be maintained with adequate blink rate. 10 Muscles of the lower lid margin-particularly the muscle of Riolan and the intratarsal muscle-are believed to be involved with controlling meibomian gland secretion. Additionally, blinking allows for the distribution of tarsal goblet cell mucin and works to increase lipid layer thickness. The action of blinking not only protects the cornea and conjunctiva from external damage, it also enables the removal of debris from the ocular surface. The levator palpebrae motor neurons (innervated by the superior branch of the oculomotor nerve: cranial nerve III) lift the upper eyelid. Activation of the orbicularis oculi (supplied by the zygomatic branches of the facial nerve, cranial nerve VII), the abducens (cranial nerve VI) and accessory abducens motor neurons, is responsible for closing the eyelids. Blinks are carried out by a series of motor neuron activations. Evolution-wise, the momentary closure of the eye can make the difference between a captured prey and a missed meal, which may explain the decreased blink rate during stimulus tracking.Ī blink can be either a reflex response to corneal stimulation (e.g., irritation by a foreign body) or the result of stimulation of the supraorbital nerve. The reason why certain cognitive processes and activities affect blink rate depends on the situation. 8 According to a paper presented by State University of New York-Oswego researcher Kara Wallace at the XVth Biennial International Conference on Infant Studies in Kyoto, Japan, in 2006, speaking, memorizing and mental arithmetic have all been linked to an increased blink rate, while daydreaming, directing and redirecting one's attention and stimulus tracking have been associated with a decreased blink rate. Some researchers have also proposed that the blink rate is connected to mental load and is regulated by the rate of cognitive processing. Correspondingly, blocking the dopamine receptor results in a decreased blink rate. 7 The amplification of dopamine receptor 1 activity with D1 agonists has been shown to result in an increased blink rate. 5,6 Research on non-human primates has demonstrated the direct relationship between cortical levels of dopamine and spontaneous blinking. Scientists have proposed various theories for the spontaneous nature of the blink: Some have suggested the presence of an internal blink pacemaker regulated by the brain stem, 4 while others have alleged that the dopamine-related circuitry of the hypothalamus and of the caudate nucleus are involved. The spontaneity of the eyeblink has piqued the curiosity of many scientists, and more than 80 years of research has been devoted to unraveling the mechanism behind the human eyeblink. This article will examine the task-dependent nature of the blink rate and its relationship to ocular surface conditions. 3 Clinically, it is crucial to consider the role of the blink when investigating ocular conditions, as behavior modifications can be important for treatment. 2 Blinking is also influenced by internal factors including fatigue, medications, stress and affective state. 1 However, blinks are highly variable across tasks, such as reading, computer use, TV, driving, conversation and gazing. Blinks, which last between 300 and 400 milliseconds, are integral to ocular surface health, as they help maintain the tear film. There are many lines of defense protecting the ocular surface from harm, beginning with reflex-gestures and brow line, and culminating with the eyelashes, lid, tear film and epithelium.
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