Pediatric and Teen CL Care
A Closer Look at Children’s Blink Rate and Tear Film
BY CHRISTINE W. SINDT, OD, FAAO
Have you ever had a stare down with a child? I can almost guarantee you blinked first. The tear film supports and maintains corneal health while creating a smooth optical surface. It’s an ever changing structure that is inherently unstable. The tear film is reformed during each blink and will thin and break down if blinking is prevented. Children, however, have a decreased blink rate compared to adults, suggesting a more stable tear film.
Past studies have shown that 11 seconds is about the average time that normal adults can comfortably keep their eyes open (Lawrenson et al, 2005). In contrast, babies often show interblink intervals of greater than 23 seconds, frequently greater than one minute.
Infants 0 to 17 weeks old have the lowest blink rate at approximately two blinks per minute. There is a progressive increase in blink rate with age, with 36- to 53-week-olds having a blink rate of approximately five blinks per minute (Lawrenson et al, 2005). In contrast, adults have blink rates that vary from 15 to 30 blinks per minute (Doughty et al, 2006).
The lipid layer has been the focus for the reduced blink rate because it stabilizes the tear film by preventing evaporation. In infants, the lipid layer of the tear film is thicker and more stable than it is in adults (Kaercher and Welt, 2003). The meibomian secretions in younger children have greater ability to withstand repeated compression and expansion compared to those of older children (age 7 to 10 years) and to those of adults (Kaercher and Welt, 1994). This is associated with a longer tear breakup time. Increased tear stability implies excellent conditions for young contact lens wearers.
Figure 1. Slit lamp evaluation of pediatric patients will reveal any tear film abnormalities.
Stable Tear Film
Some believe that evaporation leads to eye surface cooling, which triggers a blink that in turn restores the tear film (Craig and Tomlinson, 1997). Because adults and infants show similar levels of corneal sensitivity to eye surface cooling, infants’ lower blink rate is not because of reduced sensitivity to surface cooling that results when the tear film breaks up.
It has also been hypothesized that the smaller palpebral apertures in infants account for increased tear film stability through reduced surface area (Bacher, 2010). However, eye surface area does not explain individual differences in spontaneous blink rates in infants.
A recent study showed no difference between surface area and spontaneous blink rates in 4-month-olds and similar sensitivity to eye surface cooling between adults and children (Bacher, 2010). In addition to the stability of the precorneal tear film, this study suggests that the developing neurological system may play the key role in the difference in blink rates among infants, children, and adults.
Regardless of the underlying reason, children have very stable tear film compared to adults. Their high success in contact lens wear may be due in part to this stability. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #176.
Dr. Sindt is a clinical associate professor of ophthalmology and director of the contact lens service at the University of Iowa Department of Ophthalmology and Visual Sciences. She is also the chair-elect of the AOA Contact Lens and Cornea Section. She is a consultant or advisor to Alcon, Ciba Vision, and Vistakon and has received research funds from Alcon. You can reach her at email@example.com.