Lower Tear Meniscus Height Measurements Using Keratography and Swept-Source Optical Coherence Tomography and Effect of Fluorescein Instillation Methods

Purpose: The first aim of this study was to compare inferior tear meniscus height (TMH) measured by keratography and swept-source optical coherence tomography (OCT). Effect of locations of fluorescein instillation and subjects' subjective sensation, and the TMH results were also investigated. Methods: Forty-one eyes from 41 healthy adults had TMH randomly measured by keratography (K5M, Oculus, Germany) and swept-source OCT (Casia SS-1000, Tomey Corp, Japan) at baseline, followed by touching either the inferior bulbar or inferior palpebral conjunctiva, randomly assigned, with a moistened fluorescein strip. Two-way analysis of variance (ANOVA) was used to compare TMH obtained from the two devices and three measurement conditions. Subjective sensation of conjunctival touch was obtained through a 4-point scale with zero representing no sensation, and one to three representing ocular sensation in an ascending order. Results: Two-way ANOVA revealed no significant difference in TMH between keratography and swept-source OCT (Factor (devices): F = 0.579, p = .451) while there was a significant difference among fluorescein instillations (Factor (conditions): F = 10.146, p < .001). Baseline TMH was around 0.25 mm, and increased to around 0.28 mm after instillation of fluorescein sodium. Ocular sensation was similar between the two conjunctival touch, and TMH was not significantly associated with ocular sensation. Conclusions: Keratography and swept-source OCT provided similar TMH results. Applying fluorescein sodium through moistened fluorescein strip could over-estimate TMH by around 0.03 mm. Applying moistened fluorescein strip at bulbar or palpebral conjunctival led to similar subjective sensations and did not affect TMH measurement.