Diagnosis of Keratoconjunctivitis Sicca-Fluorescein Tests
Fluorescein sodium is used for several dry eye tests . They all are mildly invasive tests. At a concentration around 0.1%, the dye is highly fluorescent, staining the tear film and epithelial defects. Once the surface layer of epithelial cells is lost, the dye spreads rapidly in the intercellular space. Fluorescein is available in the form of fluorescein-impregnated paper strips or as a 1-2% solution in a sterile, unit dose sachet. Fluorescence is with the use of a blue exciter filter in combination with a yellow barrier filter. Most slit-lamps are provided with an adequate blue light source and it is well worth purchasing a suitable Kodak Wratten 12 or 15 barrier filter.
To instil fluorescein from an impregnated strip, a drop of sterile saline is applied to the impregnated end and the excess discarded with a rapid flick. The moistened tip is then touched lightly onto the lower tarsal plate of the right and then the left eye, in sequence. Because 1-2% fluorescein is non-fluorescent, it is only appropriate to apply a small volume in order to achieve dilution and flu¬orescence. A suitable volume is 2-5 |xl applied with a micropipette.
The fluorescein tear film break-up time records the rupture of the tear film after a blink. The tear film should be evaluated after a few blinks. The average of three measurements provides a representative measure of the tear film stabil¬ity . Evaluation: >10 s: normal; 5-10 s: marginal dry eye; <5 s: dry eye.
Fluorescein staining of the interpalpebral surface of the eye has a character¬istic pattern in KCS, initially affecting the lower part of the exposed eye and later affecting the cornea and conjunctiva more extensively. In meibomian gland dys-function the staining pattern is often disposed over the lower cornea, closer to the lower lid margin. A number of suitable grading schemes exist . The Oxford grading scheme consists of a series of panels representing the cornea and the two zones of exposed conjunctiva, on which is displayed a pattern of dots representing increasing staining from grade 0 to 5 (fig. 8). The number of dots increases sequentially in a log-linear scale: from grade 0 to 1 there is a 1-log step,
which means that 10 dye spots are detected per 1 zone in grade 1. Between grade 1 and 5 there is a 0.5-log unit increase of spots, which equals 32 dye spots in grade 2, 100 dye spots in grade 3 and 316 dye spots in grade 4, always counted per 1 zone. Grade 5 is detected, when the number of dye spots exceeds 316 per 1 zone. The individual scores for each of the 3 panels are added up to give the total score. The maximum staining score for the exposed conjunctiva and cornea is 15.
An important point to note is that if the recommended filter combination is used then grading with fluorescein can be carried out on both the cornea and conjunctiva and use rose bengal can be avoided. This prevents patient discom¬fort, since in the absence of an anaesthetic, rose bengal causes intense stinging on instillation (fig. 9). Staining of the epithelium can occasionally be obscured by the fluorescence of the tear film. Asking the patient to blink several times allows the staining pattern to be viewed more clearly.
The stained meniscus can be used to estimate the meniscus volume, either simply by measuring meniscus height using the width of the slit-lamp beam, or in a more sophisticated fashion, by reflective meniscometry or by assess¬ing its profile photographically in slit section . A meniscus radius of curva¬tures <0.25 mm suggests a dry eye condition.
Fluorescein can also be used for measurements of tear turnover and of the tear fluorescein clearance .
Fluorescein sodium is used for several dry eye tests . They all are mildly invasive tests. At a concentration around 0.1%, the dye is highly fluorescent, staining the tear film and epithelial defects. Once the surface layer of epithelial cells is lost, the dye spreads rapidly in the intercellular space. Fluorescein is available in the form of fluorescein-impregnated paper strips or as a 1-2% solution in a sterile, unit dose sachet. Fluorescence is with the use of a blue exciter filter in combination with a yellow barrier filter. Most slit-lamps are provided with an adequate blue light source and it is well worth purchasing a suitable Kodak Wratten 12 or 15 barrier filter.
To instil fluorescein from an impregnated strip, a drop of sterile saline is applied to the impregnated end and the excess discarded with a rapid flick. The moistened tip is then touched lightly onto the lower tarsal plate of the right and then the left eye, in sequence. Because 1-2% fluorescein is non-fluorescent, it is only appropriate to apply a small volume in order to achieve dilution and flu¬orescence. A suitable volume is 2-5 |xl applied with a micropipette.
The fluorescein tear film break-up time records the rupture of the tear film after a blink. The tear film should be evaluated after a few blinks. The average of three measurements provides a representative measure of the tear film stabil¬ity . Evaluation: >10 s: normal; 5-10 s: marginal dry eye; <5 s: dry eye.
Fluorescein staining of the interpalpebral surface of the eye has a character¬istic pattern in KCS, initially affecting the lower part of the exposed eye and later affecting the cornea and conjunctiva more extensively. In meibomian gland dys-function the staining pattern is often disposed over the lower cornea, closer to the lower lid margin. A number of suitable grading schemes exist . The Oxford grading scheme consists of a series of panels representing the cornea and the two zones of exposed conjunctiva, on which is displayed a pattern of dots representing increasing staining from grade 0 to 5 (fig. 8). The number of dots increases sequentially in a log-linear scale: from grade 0 to 1 there is a 1-log step,
which means that 10 dye spots are detected per 1 zone in grade 1. Between grade 1 and 5 there is a 0.5-log unit increase of spots, which equals 32 dye spots in grade 2, 100 dye spots in grade 3 and 316 dye spots in grade 4, always counted per 1 zone. Grade 5 is detected, when the number of dye spots exceeds 316 per 1 zone. The individual scores for each of the 3 panels are added up to give the total score. The maximum staining score for the exposed conjunctiva and cornea is 15.
An important point to note is that if the recommended filter combination is used then grading with fluorescein can be carried out on both the cornea and conjunctiva and use rose bengal can be avoided. This prevents patient discom¬fort, since in the absence of an anaesthetic, rose bengal causes intense stinging on instillation (fig. 9). Staining of the epithelium can occasionally be obscured by the fluorescence of the tear film. Asking the patient to blink several times allows the staining pattern to be viewed more clearly.
The stained meniscus can be used to estimate the meniscus volume, either simply by measuring meniscus height using the width of the slit-lamp beam, or in a more sophisticated fashion, by reflective meniscometry or by assess¬ing its profile photographically in slit section . A meniscus radius of curva¬tures <0.25 mm suggests a dry eye condition.
Fluorescein can also be used for measurements of tear turnover and of the tear fluorescein clearance .
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