Also in this week's column:
Why do babies blink less often than adults?
Asked by Cade Stevens of Nashville, Tennessee
Babies blink less often than adults. In normal circumstances, newborns blink at the rate of less than two times per minute. In childhood, the blink rate rises. Thus, by about age 14, the blink rate rises to about 10 blinks per minute. In adulthood, the blink rate remains at about 10 to 15 times per minute.
This rate changes with attention, stress, excitement, eye irritation, and amount of sleep. Generally, when one has had more sleep, one needs to blink less. There is widespread variation in blink rate among individuals. There may be a genetic component in this. There may also be a learned cultural component as well.
Blinking also may play an undetermined role in body language as it does in our non-human primate cousins. The main physiological purpose of blinking is to spread tears over the surface of the eyes.
According to Dr Samuel Salamon of the Cataract Eye Centre of Cleveland, Ohio, it is puzzling as to why babies don't suffer from dry eyes due to their lack of blinking. It could be that since babies sleep so much, and thus spend so much time with their eyes shut, perhaps dry eyes are less of a problem for them.
Also, Dr Salamon points out, a baby's eyes have smaller fissures compared with an adult's eyes. That is, much less of the front of a baby's eye is exposed to the outside world - and to its dirt, dust, and brightness - due to the shape of the infant skull. A baby's eyelid openings are smaller in relation to the eye compared with the eyelid openings of adults. Thus, a baby's eyes may need less lubrication.
Babies do not manufacture tears during their first month of life.
A dry cornea can affect the outcome of today's high tech eye scans using tomography (OCT). According to Dr DM Stein and five colleagues from the Department of Ophthalmology at the School of Medicine at the University of Pittsburgh, writing in the June 2006 Opthalmology, corneal dryness affects OCT scan quality and measured nerve fibre layer thickness after only a short exposure time. What's to be done? They write: "It is recommended to instruct those who are scanned to blink frequently or to instill artificial tears."
Stephen Juan, Ph.D. is an anthropologist at the University of Sydney. Email your Odd Body questions to firstname.lastname@example.org