Schirmer’s test is normally used to measure the aqueous component of the tear film. It must be performed BEFORE any other ophthalmological examination requiring the use of drugs that interfere with tear secretion (reduced by local anaesthetics and parasympatholytic mydriatics, increased by parasympathomimetics). When it is necessary to perform the test AFTER administration of the above-mentioned substances, dry the eye and the palpebral fissure well and wait 10 to 15 minutes before performing the test. Manipulations and the use of dyes can cause falsely high values to be recorded.
The test is performed using sterile strips of filter paper with a notch 5 mm from one end, which acts as a guide for the folding procedure (see below). Some packages provide a strip for the right eye and one for the left eye.
Before performing the measurement it is a good idea to gently remove any traces of mucus or other substances on the cornea or in the conjunctival fornix with a cotton swab (so as not to stimulate excessive reflex lachrymation). The notch is then folded approximately 45°, keeping it turned towards the medial corner and the strip of paper is introduced into the lower conjunctival fornix towards the temporal side. The part of the strip that will become wetted should not be touched with the fingers both for reasons of sterility and because the fingers can leave fatty substances on the strip that can make the test unreliable. During the test the eye can be gently closed and kept closed with the strip inserted. The reading should be carried out as quickly as possible after the strip has been removed because the lachrymal fluid tends to impregnate it through capillary action.
The strips of filter paper used have different absorption capacities. There are packages with the reading scale printed on the strip, others with the scale printed on the box and yet others in which the strips are pre-marked with dye to facilitate the reading. At least 15 mm of the strip should be wetted (during one minute), bearing in mind that the folded part introduced into the conjunctival fornix should not be counted in the measurement. Values between 10 and 15 mm are equivocal, while a value below 10 mm should be considered pathological.
There is a type 1 Schirmer's test that measures basal lachrymation and reflex lachrymation and a type 2 test in which a local anaesthetic is used (which should eliminate reflex lachrymation, thus making it possible to measure basal lachrymation only). In this case the values obtained will logically be lower. The procedure for the latter test requires that the local anaesthetic acts for a few minutes and that the excess amount is removed with a cotton swab.