In a normal subject, the tear film is evident as a rim of fluid along the lid margin and a deficiency of this can be seen by direct examination. Prolonged deficiency of tears can be associated with the presence of filaments -microscopic strands of mucus and epithelial cells, which stain with Rose Bengal. Punctate staining of the corneal epithelium is also seen after applying a drop of fluorescein. In some dry eye syndromes, for example, ocular pemphigoid and Stevens-Johnson syndrome, keratin-isation of the cornea and conjunctiva with the formation of contracting adhesions between the opposed surfaces of the conjunctiva occurs. A similar change is apparent following chemical or thermal burns of the eyes.
One end of a special filter paper strip is placed between the globe and the lower eyelid. The
Figure 5.7. Schirmer's test.EQ
other end projects forward and the time taken for the tears to wet the projecting strip is measured. The test is not an accurate measure of tear secretion but it provides a useful guide (Figure 5.7).
Using the slit-lamp microscope, the time for the tear film to break up when the patient stops blinking is measured. This test is sometimes used as an index of mucin deficiency.
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