When we stare at an object, without blinking, tears roll down from our eyes. Why?
K. SANKARANARAYANAN
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When one stares at an object without blinking for a long period of time tears tend to roll down from the eyes - the cause of this phenomenon is two fold.
Tears are secreted from the tear glands and are kept spread over the anterior part of the eye. Lids play an important role of keeping the anterior part of the eye moist by evenly spreading the tears over the surface.
Volume of tears secreted per minute is approximately 0.6 to 1.1 micro litres (one drop is equal to 60 microlitres). We blink approximately 10 to 12 times a minute and this reduces to 3 to 4 times a minute during concentrated activities like reading.
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Blinking serves two functions, one is to spread the tears evenly over the eye and the second is to push the excess tears into the tear ducts situated at the inner part of the lids. This is referred to as the tear pump. Tears drain down there ducts and the lacrymal sac into the nose (this is why when one cries both eye and nose water!).
Eyes become dry when one does not blink for a long time and stares at an object continuously. This dryness causes irritation which results in increased tear secretion as a reflex. These increased tears are not drained down the natural pathway as the tear pump action of blinking is absent. Thus this increased tear secretion and lack of blinking result in tears running down from the eyes.
DR. ARULMOZHI VARMAN
Uma Eye Clinic
Chennai