The tear structure consists of four parts called mucus layer, watery layer, oily layer and lacrimal glands. The quality of our vision is directly related to the proper functioning of the lacrimal system, because otherwise 
it leads to problems such as burning, itching, dryness of the eyes, and foreign body sensation, and in advanced situations causes corneal opacity, corneal ulcer, and eye infections.
The Schirmer's test is used to assess the function of lacrimal apparatus under physiologic conditions. For this purpose, our colleagues at Noor Eye Hospital place a thin, special paper strip in the lower eyelid pouch of the patient for a specified period of time, generally for 5 minutes. It can be done with or without topical anesthesia. After removing the paper from the eye, the wetted length of the paper is measured and compared with a certain standard.
It should be noted that the length of the wetted paper in people with dry eye is less than the standard length of schirmer. Lacrimal system examination is performed with high precision at Tehran-Iran Noor Eye Hospital.