Influence of Topical Fluorescein on Scheimpflug-Based Corneal Densitometry and Potential Applications

Purpose: To evaluate the effect of topical fluorescein on Scheimpflug-based corneal densitometry and to determine the optimal timing for reliable imaging. In addition, a patient with dry eye disease (DED) was examined to assess the potential of fluorescein-enhanced densitometry for detecting superficial punctate keratitis (SPK). Methods: Twenty healthy participants underwent Scheimpflug imaging at baseline and 1-, 5-, 10-, 15-, and 20-minute postinstillation of 2% fluorescein sodium. Corneal densitometry values across 3 corneal layers and 4 concentric zones and central corneal thickness (CCT) were measured. Imaging was repeated at a second visit to assess reproducibility. A linear mixed-effects model was used to analyze time-dependent changes. One patient with DED with SPK was included for a proof-of-concept examination. Results: A significant increase in corneal densitometry after fluorescein instillation was only observed in the anterior layer, with an increase in the 0- to 2-mm zone at visit 1 from 26.6 ± 2.4 gray scale units (GSU) to 62.5 ± 18.9 GSU ( P < 0.001) at 5-minute postinstillation and a gradual decrease toward baseline values by 20 minutes (32.0 ± 11.4 GSU, P = 0.045). Reproducibility between visits was high for 10- to 20-minute postinstillation examinations ( P > 0.05). In the patient with DED, fluorescein-enhanced densitometry revealed localized signal elevations consistent with SPK seen on slit-lamp examination. Conclusions: Topical fluorescein induces time-dependent changes in anterior corneal densitometry, with measurements returning close to baseline by 20-minute postinstillation in healthy eyes. In patients with DED, fluorescein may locally enhance densitometry of epithelial defects and could offer a novel, objective method for assessing corneal surface integrity. Further studies are needed to validate its clinical utility.