Micro-instillation of fluorescein with an inoculation loop for ocular surface staining in dry eye syndrome

PurposeTo describe and validate the micro-instillation of fluorescein on the ocular surface by a disposable calibrated inoculation loop to improve corneal and conjunctival staining quality. MethodsAccuracy and precision of the volume of 0.5% sodium fluorescein collected by a single use 1l-calibrated inoculation loop were measured using a precision balance. Twenty patients (40 eyes) suffering from dry eye syndrome were enrolled in a prospective interventional nonrandomized study. Fluorescein was instilled with the loop, and slit-lamp images were taken within 30seconds using cobalt blue light with and without a yellow barrier filter. For comparison, after a washout period, the same images were retaken after instillation of one drop of fluorescein from a single-dose unit. The main outcome measure was the staining quality assessed by three experts, blind to the instillation method. Patient discomfort (tolerance, by a questionnaire) was also compared. ResultsThe mean volume collected by the loop was 1.180.12l, compared with 33.70 +/- 6.10l using the single-dose unit. The loop avoided excess dye responsible for unpleasant tearing, masking of lesions and rapid diffusion into the stroma. Micro-instillation greatly improved image quality without losing information. The yellow filter further improved image contrast. Tolerance was excellent. ConclusionThe 1l-calibrated inoculation loop is a safe, convenient, inexpensive, disposable, sterile, well-tolerated tool for reproducible micro-instillation of commercial fluorescein. By greatly improving staining quality, it will help standardize assessment of dry eye severity.