# A Droplet Evaporimeter for Evaluating Eye Care Formulations

## TL;DR

This paper introduces a new droplet evaporimeter system to study how eye drops reduce tear evaporation, which is important for treating dry eye.

## Contribution

The novel contribution is the development of a tunable evaporimeter system for evaluating eye drop formulations' evaporation rates.

## Key findings

- The evaporimeter system accurately measured evaporation rates and aligned with theoretical models.
- Systane Pro Preservative Free eye drops showed the greatest reduction in evaporative flux due to a synergistic effect of mineral oil and hyaluronic acid.
- The system can simulate ocular surface conditions for in vitro and ex vivo studies of eye drop formulations.

## Abstract

This study explores the development and application of a convenient droplet-based evaporimeter system as a research tool to investigate the evaporation of lubricating eye drop formulations and potentially other ophthalmic applications.

The evaporimeter integrates a goniometer with an environmental control system, allowing for precise test solution adjustment and a wide range of environmental settings. To verify the system design, pure water evaporation was conducted under various environmental conditions. Measured water evaporation rates aligned with the theoretical kinetic mass-transfer model. Evaporation evaluations were performed under conditions simulating the ocular surface in typical indoor environments. This study compared the evaporative flux of three baseline solutions and various commercial lubricating eye drop formulations.

Phosphate-buffered saline (PBS) had an evaporative flux similar to water, whereas simulated artificial tear solution (ATS), containing tear components, exhibited a lower evaporative flux. Among the tested eye drops, Systane Pro Preservative Free demonstrated the greatest reduction in evaporative flux, highlighting a potential synergistic effect between mineral oil and hyaluronic acid.

An advanced evaporation evaluation system designed for in vitro and ex vivo research has been established to provide a rapid method with tunable sample/environment conditions to assess evaporative flux from eye drop formulations. This study enables future work to investigate eye drop formulations and their interactions with tear components to better understand their effects on reducing tear evaporation in dry eye.

This work provides a reliable method to evaluate the effectiveness of eye drop formulations in reducing tear evaporation, which is essential for managing dry eye.