When tear production decreases or tears begin to evaporate too quickly, symptoms of dry eye can develop.
The physiology of tears is much more complex than one might initially think.
Tear Production
There are many reasons that a persons process of tear production isnt working properly.

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Your ophthalmologist can help you identify medicines that could be causing your symptoms.
This test is not meant to substitute for a visit to your eye doctor.
see to it to schedule an appointment for a medical consult and proper diagnosis.
Cleveland Clinic.Why we cry and what tears are made of.
American Optometric Association.Dry eye.
Sharma A, Hindman HB.Aging: a predisposition to dry eyes.Journal of Ophthalmology.
2014;2014:1-8. doi:10.1155/2014/781683
American Academy of Ophthalmology.How can I tell what’s causing my dry eye?