Tear-film lipid layer morphology and corneal sensation in the development of blinking in neonates and infants

Abstract

The aim of the study was to evaluate the role of lipid layer thickness and corneal sensation in the development of blinking in neonates. The study group comprised sixty-four neonates and infants (mean age 27.5 +/- 15 (sd) weeks, range 3.4-52) whose mothers were attending a general practice healthy baby clinic. Spontaneous eye-blink activity was determined from digital videographic recordings; tear film lipid layer morphology wasexamined using interference patterns produced by the Keeler Tearscopetrade mark Plus over a five-point grading scale (higher grades are associated with thick and stable lipid films); corneal sensation threshold was assessed with the Non-Contact Corneal Aesthesiometer (NCCA), using the eye-blink response as an objective indication that the cooling stimulus had been felt; palpebral aperture dimensions were measured using calibrated digital still images of the eye in the primary position. The overall mean spontaneous blink-rate was found to be 3.6 (+/- 0.3) blinks min(-1), and the mean interblink time was 21.6 (+/- 2.8) s. The lowest blink-rates were observed in the 0-17-week age group (average 2 blinks min(-1)). The blink-rate showed a highly significant correlation with age (r = 0.46, P < 0.01). The overall mean lipid layer grading was 3.6 (+/- 0.2 SE) arbitrary units. Higher grades were found in the newborn and the mean grading score reduced with age (P < 0.01). The mean sensation threshold to blink (TTB) was 0.69 (0.04 SE) mbar, which did not differ from a control group of older subjects (P > 0.05). There was a rapid increase in palpebral aperture length and width from birth to 1 year old, with surface area increasing by 50% over the same period. We concluded that the low rate of spontaneous eye blink activity in neonates is associated with a thick stable lipid layer that may be a function of a small palpebral aperture. Furthermore, neonates appear to have the capacity to detect ocular surface cooling, which is a major trigger for spontaneous blinking.

Fig. 1

Measurement of horizontal and vertical palpebral aperture dimensions.

Fig. 2

Variation in blink-rate with age (means ± SE).

Fig. 3

Scatter plot showing correlation between blink-rate and age over the first year of life.

Fig. 4

Variation in tear grading with age (means ± SE).

Fig. 5

Variation in corneal sensation threshold with age.

Fig. 6

Variation in vertical width (▴) and horizontal length (▪) with age.

Fig. 7

Variation in exposed ocular surface area with age.