Study: It's all about the bottom half
This sort of felt like one of those “duh” results. I mean, unless you hold your eyes very wide open or look up a lot, the upper half of the eye seems to me like it’s much more likely to be covered than the lower half more of the time. - Especially in the age of smartphones, where we’re all looking down all the time anyway, right?
In addition, if you have - as so many of us do - a habitually poor blink, the part of the eye staying exposed the most is bound to be the lower half where the lids fail to meet. It’s always nice to see data on stuff that makes sense.
Zhuo et al, Cornea, May 2019
To investigate the temporal and spatial distribution of tear film breakup time via a noninvasive topographer in normal subjects and patients with dry eye disease (DED).
A total of 77 subjects were separated into normal and DED groups based on their symptoms and tear film instabilities. In noninvasive evaluation with Oculus Keratograph, the precorneal tear film was recorded and reconstructed into a two-dimensional map that evolved with time. Whether or not each sector broke and the breakup time if it did were recorded. The map was further grouped into 4 quadrants to reveal the spatial variation.
By the end of recording, the inferior quadrant in DED subjects had a higher number of broken sectors than other quadrants (P < 0.01). Over the recording period, the cumulative percentage of sectors that were broken rose much quicker in the inferior quadrants, and the inferior quadrant is the only quadrant that showed a significant difference between the normal and DED groups (P < 0.01). This difference peaked at 12 seconds and declined after 15 seconds. Receiver operating characteristic curve for each index always showed the largest differential value in the inferior quadrant.
Tear film breakup is not homogenously distributed, with sectors in the inferior quadrant being more likely to break and to break earlier. Between normal and DED subjects, a significant difference of tear film instability is more likely to be found in the inferior quadrant.