MUC5AC overexpression in tear film of neonates

Full-term neonates produce tears normally, but neonatal tear film is modified to resist evaporation with a thick lipid layer that allows lower spontaneous blink rates. This adaptation presumably prevents drying of the ocular surface during long inter-blink periods. However, tear-film stability is not only based on the integrity of the lipid layer, but also reflects properties of the underlying mucus layer. Characteristics of the neonatal mucus tear-film layer have not yet been described.

Tear samples were obtained from eight full-term healthy neonates (four males, four females, mean age 1.7 +/- 0.5 days) and eight healthy adult controls (four males, four females, mean age 26.3 +/- 2.5 years). Characterization of tear samples' total proteins was obtained by spectrophotometry. Western blot for major secretory mucin MUC5AC was performed on the samples. Blink rate in the neonates and adults enrolled in the study was also observed and recorded.

Using the same procedure, the amount of tears collected was significantly greater in adults than in neonates (p < .01). Western Blot performed on neonatal tear samples showed a significant 76.8% increase in the expression of major secretory mucin MUC5AC as compared to healthy adult controls (p < .001). Mean blink rate recorded in neonates was significantly lower than in adults (p < .001), with a mean 1.6 +/- 0.5 blinks per minute and a mean interblink time of 33 +/- 9 seconds.

As far as we are aware this is the first description of the mucus tear-film layer in neonates. The greater tear-film stability in neonates has been so far attributed to a thicker lipid layer. In our study, we show that a concomitant increase in MUC5AC protein expression in tears is present and may contribute to this greater stability; therefore, both mucus and lipid layer should be considered while evaluating tear film stability in neonates.