Investigating retention time and fluid dynamics of the vehicles in non-invasive topical ocular drug delivery systems

Efficient topical ocular drug delivery is critical for managing eye diseases, yet non-invasive approaches often suffer from limited retention time and low bioavailability. This study evaluated the retention time and spatial distribution of I-Drop MGD artificial tear, using Anterior segment Optical Coherence Tomography (ASOCT). Twelve healthy volunteers were enrolled, each assessed in both eyes across four visits, yielding a dense, paired dataset with high statistical power and reduced inter-subject variability. Baseline assessments showed a strong correlation between the central corneal thickness (CCT) measurements in fellow eyes and minimal variability across visits. Following instillation, CCT increased sharply and then decayed over time, consistent with tear film clearance. Retention time, estimated by exponential fitting, had a mean of 13. 94 ± 16.32 minutes and a median of 7.7 minutes (3.4-16.78 minutes). Qualitative image analysis revealed that thinner, well-distributed films cleared more slowly than thicker accumulations, suggesting that film morphology influenced drainage dynamics. Although the administration volume was fixed, differences in ocular surface area, due to natural variation in anatomy, appeared to affect the distribution of the formulation and, consequently, retention behavior. Statistical analyses further demonstrated that neither blinking rate nor tear film break-up time (TBUT), within physiological ranges, significantly impacted retention time for healthy subjects. Similarly, subjective discomfort levels reported after installation had no measurable effect. Statistical power analysis confirmed that the paired-eye, multi-visit design was robust, requiring as few as four subjects to detect treatment effects with approximately 81 % power based upon the tested eye drops. Overall, the findings supported the use of ASOCT for high-resolution, non-invasive assessment of ocular formulation retention and suggested that future design of ophthalmic vehicles should account for film-distribution behavior and rheological properties to optimize performance.