Tear breakup time TBUT This test evaluates the stability of the tear film

❖ Test: Fluorescein dye (10 ^l of a 0.125% fluorescein solution) is added to the precorneal tear film. The examiner observes the eye under 10-20 power magnification with slit lamp and cobalt blue filter and notes when the first signs of drying occur (i) without the patient closing the eye and (ii) with the patient keeping the eye open as he or she would normally.

❖ Normal: TBUT of at least 10 seconds is normal.

Rose bengal test: Rose bengal dyes dead epithelial cells and mucin. This test has proven particularly useful in evaluating dry eyes (keratoconjunctivitis sicca) as it reveals conjunctival and corneal symptoms of desiccation.

— Measuring tear secretion with Schirmer tear testing.

— Measuring tear secretion with Schirmer tear testing.

Tear Breakup Time Tbut
Fig. 3.4 A strip of litmus paper is folded over and inserted into the conjunctival sac of the temporal third of the lower eyelid. Normally, at least 15 mm of the paper should turn blue within five minutes.

Impression cytology: A Millipore filter is fastened to a tonometer and pressed against the superior conjunctiva with 20-30mm Hg of pressure for two seconds. The density of goblet cells is estimated under a microscope (normal density is 20-45 goblet cells per square millimeter of epithelial surface). The number of mucus-producing goblet cells is reduced in various disorders such as keratoconjunctivitis sicca, ocular pemphigoid, and xeroph-thalmia.

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