Clinical Tests - Normal Values
Here are Normal Values for some frequently used clinical tests for Dry Eyes
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Lipid Layer Thickness
Normal value: ≥ 65 ICU units (roughly equivalent to 65nm) normal up to about 100 ICU
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Incomplete Blinks – Alterations of regular Eyelid Blinking
Normal value: ca. 20% of blinks are incomplete (References in Literature differ somewhat)
Pathologic: > 50% incomplete eyelid blinks
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Tear Film - Stability
with Fluorescein (F-BUT, Break-Up Time)
Normal value: ≥ 10 seconds
(F-BUT with fluorescein is the international standard on which the present research is based and can be measured without special equipment)
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Non-Invasive BUT (NI-BUT)
Normal value: ≥ 10 Sekunden
in NI-BUT the normal values are typically higher (than in F-BUT (see below), i.e. longer stability, because the tear film is not influenced by addition of a stain. Ni-BUT is simpler to measure, more comfortable and reveals numerical values … it is theoretically more exact
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Tear-Volume/ Tear Meniscus Height (TMH)
Normal value: ≥ 0,2 mm
(Height of the tear volume on the ocular surface)
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Tear Osmolarity
Normal values: ca. 280 - 306 Osmolarity (mOsms/L), Cut-off: 306 mOsms/L
With increasing numerical value also the tear osmolarity increases (concentration of the salts and proteins).
The interpretation of tear film osmolarity requires a certain background knowledge because not only the absolute value but also differences between both eyes are relevant.
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Vital staining
Normal value: “0” - (i.e. a normal ocular surface should have no vital staining micro-defects)
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LId-Parallel COnjunctival Folds (LIPCOF)
Normal value: “0“ - ( i.e. a normal ocular surface should not have loosened conjunctival tissue that build up folds on the lid margin)
Pathological LIPCOF folds of the conjunctiva are classified by increasing number and size in typically 3 grades (1-3)
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Conjunctival redness index
Normal value: ≤ 1 (depends on the actual grading scale of the equipment)
(Increeasing redness of the ocular surface is typically graded by increasing values from 0 to 3. A certain redness is normal since the ocular surface needs a certain normal blood flow)
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MMP-9 enzyme test (detection of inflammation)
Normal value: “Negative”
A positive test indicates a level of destructive enzyme (MMP9) above a threshold that is considered as normal and is regarded to indicate an inflammatory condition.
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Schirmer-1 Tear Test
Normal value: ≥ 10 millimeter in 5 minutes
(indicates the amount of new tear production as wetted area of a paper strip)
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Meibography
Normal value: “0“
Display of the Meibomian gland mass in the eyelids: Classification from “0“ Normal (all glands are present) along increasing loss of one thirds on the glands each in the grades 1-3. In grade 3 = loss of 3/3 of glands (i.e. practically no more glands present)
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Diagnostic expression of the meibomian glands - lipid delivery
Normal value: Meibomian glands yielding liquid secretion (MGYLS)
typically indicated as: (No of secreting glands) ca. 6-10 / 15 (investigated glands)
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