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

Purpose To describe and validate the micro‐instillation of fluorescein on the ocular surface by a disposable calibrated inoculation loop in order to improve corneal and conjunctival staining quality. Methods Prospective interventional non‐randomized low risk study performed in the Department of Ophthalmology at Saint‐Etienne University Hospital. Twenty patients (40 eyes) suffering from dry eye syndrome were enrolled. Accuracy and precision of 0.5% sodium fluorescein collected by a disposable 1 μL‐calibrated inoculation loop were measured using a precision balance. Fluorescein was instilled in patients’ eyes with the loop, and slit lamp images were taken within 30 seconds 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 and to discomfort felt by patients. Results The mean amount collected by the loop was 1.18 ± 0.12 μL, compared with 33.70 ± 6.10 μL using the single‐dose unit. Tolerance was excellent. 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. Conclusions The 1 μL‐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.