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PUPOSE To measure the stability of the tear film.
INDICATIONS
The tear break- time (TBUT) should be measured when you suspect a lacrimal insufficiency based on the patient’s symptoms or the slit lamp eva luation. A baseline TBUT should be measured prior to fitting a patient with contact lenses. The TBUT must be performed prior to instillation of a topical anesthetic or dilating agent as these may alter the composition of the tear film.
EQUIPMENT
·Biomicroscope.
·Sodium fluorescein strips
·Sterile saline solution.
SET-UP
·Adjust the biomicroscope so it is comfortable for both the patient and the examiner.
·Focus the oculars, adjust the PD, and set the magnification on the lowest setting (6× or 10×).
·Insert the cobalt blue filter and set the illumination arm approximately 30°from the straight ahead position. Open the slit to a wide parallelepiped.
STEP-BY-STEP PROCEDURE
1. Moisten the end of a fluorescein strip with one drop of sterile saline.
2. Instruct the patient to look , gently pull down the lower lid and touch the wet end of the fluorescein strip to the patient’s inferior bulbar or palpebral conjunctiva of his right eye.
3. Position the patient in the slit lamp and focus on the patient’s cornea. The tear film will appear green due to the fluorescein.
4. Instruct the patient to blink several times to evenly spread the fluorescein over the cornea and then to keep his eyes open looking straight ahead.
5. Scan the entire cornea looking for dark spots or streaks. Count the number of seconds between the last blink and the first appearance of these dry spot formations.
6. Repeat steps 4 and 5 two more times and average the results. Note the position of the first dry spots. If the tear film consistently breaks in a specific location, it may be an indication of an epithelial defect rather than an unstable tear film.
7. Instill fluorescein in the patient’s left eye as in steps 1 and 2.
8. Repeat steps 4 to 6 on his left eye.
RECORDING
·Record the results for each eye separately.
·Record the average of the three trials in seconds.
EXAMPLE
TBUT: OD 15 seconds. OS 12 seconds.
EXPECTED FINDINGS
·The normal TBUT is between 15 and 45 seconds.
·A TBUT less than 10 seconds is indicative of an unstable tear film.
·If the tear film consistently breaks in the same location, it probably indicates a defect in the corneal epithelium. |
