discovering dry eye
The Tears of an Infant
BY KELLY KINNEY NICHOLS, OD, MPH, PHD
This month I traded in scientific journals for baby books, faculty meetings for on-line correspondence and stylish maternity wear (well, not that stylish) for sweats and a bathrobe. That's right, baby Braden Nichols finally arrived in our household. During the occasional sleep-deprived nights and the eye-open hours of the day, I have the wonderful opportunity to gaze into Brady's still-blue eyes....and to monitor his blink patterns and observe his tear film.
My scientific observation of Brady as he stares at the pots hanging on our pot rack is that he doesn't blink very frequently when he is intent and alert. Therefore, I started a mini-study of his blink patterns. On several occasions I have counted the time between blinks. I have documented a range from one minute and 45 seconds between blinks to only one to two seconds between blinks. Sometimes there are four to five blinks in a row followed by a minute between the next blink. There appears to be a small inferior tear prism, and the lipid layer is often visible like an oil layer on the top of a rain puddle.
My current scientific references (What to Expect the First Year and Caring for Your Young Baby and Young Child: Birth to Age Five) devote only short paragraphs to lacrimal disorders. The books do address the gradual development of the lacrimal system over the first six months. One book says the tears begin to be produced at about one month; the other says it will be seven to eight months before a baby "cries real tears." Adler's Physiology states "newborn babies secrete tears within the first 24 hours of life." The book cites a study that found 82 percent of infants secreted tears in the first day, and the number increased to 96 percent if the infants were stimulated to cry.
Clearly babies have tears on the surface of their eyes; however, the composition of the tear film may be very different from adult tears. My speculation, based on my observation of my son's tear film, is that the aqueous layer of the newborn tear film may be very thin, and the lipid layer is thicker than an adult tear film. This could explain the long periods of time an infant can keep the eyes open between blinks.
Yesterday I saw a piece of fuzz in Brady's eye, which did not seem to bother him in the least. His eye is not red or teary. It was as if he could not feel that there was any surface irritation. In the last few years, an increasing amount of attention has been focused on the theory of the ocular surface feedback loop. Innervation to the front surface of the cornea maintains the aqueous production and tear film. Any interruption to the feedback loop can lead to disorders of the tear film like dry eye. In the infant, the "feedback loop" may not be as developed as in the adult. In the adult world, dry eye is often considered a symptom-based disease, with symptoms possibly occurring with a breakdown in the feedback loop. With infants, all symptoms are reported the same way: crying. Tear film problems would probably be on the bottom of the "important" list of an infant.
The AOA recommends that the first eye examination occur at six months of age, in addition to screenings performed by the pediatrician at routine visits. Over-tearing in an infant could indicate that the valve of Hasner at the bottom of the lacrimal sac has not yet opened, which can be aided by massage if no infection is present. Lack of "tears" within the first few months (and crying for that matter) should be considered a welcome blessing.
Dr. Nichols is assistant professor of clinical optometry at The Ohio State University College of Optometry in the area of dry eye research.