“Dry eye complaints used to be an ‘old lady disease,'” used to say one of my mentors. In the 21st Century, Dry Eye has become a scourge partly due to increased screen time. [I hope you are having Siri, or some other electronic voice, read you this post as I am typing most of it with my eyes closed and with FLUX in the background.]


Many papers have shed light on why women are often more commonly affected by dry eye. The below paper does a good job looking at rats and comparing it to human data. 


Here is a break down of their results:


The trigeminal system (Cranial Nerve 5 from the brain) is essential to blinking and can identify changes in the corneal tear film. It can compensate for irregularities by regulating the aqueous and lipid tear components released by the lacrimal and meibomian glands by altering blinking and by direct stimulation of the lacrimal gland.

Neurons in the spinal trigeminal complex border region (ie, between the interpolaris and caudalis subnuclei) sense corneal drying and increase the aqueous tear component by activating the lacrimal glands via the superior salivatory nucleus (Hirata et al. 2004; Katagiri et al. 2015; Okamoto et al. 2012). These neurons also drive reflex blinking and likely modulate spontaneous blinking (Kaminer et al. 2011). 


The neural adaptations of the trigeminal complex that compensate for the rapid tear film breakup of dry eye also express themselves as changes in blinking and blinking rates and durations of blinking it appears. 


With dry eye or eye irritation, trigeminal reflex blink excitability increases such that a single trigeminal blink-evoking stimulus elicits multiple blinks (Evinger et al. 2002; Peshori et al. 2001; Schicatano et al. 2002): the body is trying to compensate for the dry eye environment of the eye by blinking which tries to milk the oil from the Meibomian Gland.


The present study investigates sex differences in blink patterns created by dry eye. These differences may explain why dry eye, which can cause focal nerve issues such as benign essential blepharospasm (BEB), neuropathy, and eye pain occurs predominantly in females. 


Specifically, they looked at blink modifications in a rat model of dry eye produced by removal of the exorbital gland, a rodent lacrimal gland. They also examine the properties of trigeminal neural adaptation by looking at how dry eye affects the body’s blink response and blink amplitude.




[More details: The report three sexual dimorphisms (differences between male and female) of trigeminal reflex and spontaneous blinking in normal rodents. 


1st: The threshold current for evoking a trigeminal reflex blink was higher in males than in females. Could this imply that males can tolerate more pain before there is a physical response? Maybe


2nd: the HFS paradigm for depressing trigeminal reflex blink gain produced a significantly larger gain reduction in male than in female rats (Fig. 3E). 


3rd: the duration of spontaneous blink OOemg activity was longer in females than in males. Do females blink longer than males? In rats yes. In woman, maybe also.]


Reading this with colleagues, we wondered if the “batting eyes of a pretty woman” or “wink,” which are both known to be associated with being “more attractive to men,” is not really a symptom of underlying dry eyes. 


SLC




Sexual dimorphism is the condition where the two sexes of the same species exhibit different characteristics beyond the differences in their sexual organs.

Sex, blinking, and dry eye.