Designing a contact lens with atropine base using a microemulsion technique

Myopia or near-sightedness is a global vision problem. Atropine eye drops and myopia-controlling contact lenses can help to slow down its progression, but neither is sufficient alone. The present research work was conducted to design a contact lens embedded with an atropine base within a microemulsion system. The goal was to improve the stability of atropine base and facilitate its release from the lens, preventing the rapid clearance observed with atropine eye drops. Two microemulsions, one with a pH of 7.4 and the other with a pH of 6.5, were developed using the surfactant D-alpha-tocopherol polyethylene glycol 1000 succinate (TPGS), the co-surfactant polyethylene glycol 400 (PEG 400), the emulsifier Capmul MCM C8, atropine base, and phosphate-buffered saline (PBS). The microemulsions were kept at room temperature (21 °C) and the amount of the atropine base in microemulsions were checked periodically over one year using reverse-phase High Performance Liquid Chromatography (RPHPLC) to determine its stability. The globule size of the formulations was measured using a zetasizer. MiSight contact lenses were soaked in the atropine base microemulsion formulations for 24 h, and the amount of atropine base loaded into contact lenses and released in PBS was measured by a RPHPLC. ISO 10993-5 guidelines were used to measure the in vitro cytotoxicity of atropine base loaded contact lenses. The atropine base was more stable in the microemulsion at pH 6.5 (ME 6.5) with less than 4 % degradation, compared to a 10 % degradation at pH 7.4 (ME 7.4). The globule sizes of the microemulsions ranged between 17-21 nm. MiSight lenses absorbed4.25 ± 1.67 µg atropine base from ME 6.5, with the majority of the atropine base (3.52 ± 0.03 µg) released within 2 h. However, elutes from atropine base loaded contact lenses were toxic to human corneal epithelial cells (HCECs), reducing cell viability to less than 5 % after 24 h. While the microemulsions were stable and the contact lenses released sufficient amounts of atropine base, future studies are needed to address the toxicity issue.