Roughly summarized, there are two main causes of dry eyes:

1. On the one hand, there may be a qualitative problem, i.e. there are enough tears, but the quality (the protective film) is disturbed. This is controlled by the meibomian glands, which are located along the upper and lower eyelid margins. They produce lipids or oils that coat the tears and protect them from excessive evaporation. When these glands do not function properly, a condition called evaporative stress occurs, in which tear fluid evaporates too quickly, resulting in an unstable tear film composition.

2. On the other hand, the amount of tears may be reduced. This refers to the aqueous portion (>90%). We have a tear gland behind the bone of the upper eyelid that constantly releases this fluid and distributes it throughout the eye. In autoimmune, allergic or rheumatic diseases, general inflammation or over the course of life, the function of this gland can be disturbed and volume deficiency stress occurs. You can well imagine that this can put a strain on the surface of the eye.