Preclinical studies evaluating the effect of semifluorinated alkanes on ocular surface and tear fluid dynamics

Purpose: Dry eye disease (DED) is one of the most prevalent ocular surface disorders that presents clinically. Recently, the semifluorinated alkane (SFA) perfluorohexyloctane (NovaTears (R); EvoTears (R)) entered the market for the management of evaporative DED, while perfluorobutylpentane has been used as a vehicle to enhance ocular drug delivery. This study evaluated the mechanisms by which SFAS might improve therapeutic outcomes in DED. Methods: Interactions of both SFAS with the corneal surface were evaluated ex vivo using high-speed photography. The in vivo influence of SFAS on tear fluid dynamics was evaluated in healthy rabbit eyes observing changes in lipid layer grade, tear evaporation rate, tear volume and tear osmolarity. Furthermore, ocular tolerability was confirmed by clinical scoring and sodium fluorescein staining. Results: Ex vivo studies demonstrated that both SFAS rapidly spread on the ocular surface with their contact angle on the cornea being virtually zero. A significant improvement in lipid layer grade was observed immediately after instillation of both SFAS in vivo, although the improvement was more sustained upon instillation of perfluorohexyloctane with a statistically significant difference compared to saline instillation evident from day five onwards. No significant changes in tear evaporation rate, volume or osmolarity, nor any signs of ocular irritation were observed after application of either SFA over the seven-day study period. Conclusion: Both SFAS showed excellent spreading on the ocular surface. Perfluorohexyloctane improved the lipid layer grade significantly after topical application supporting its potential to stabilise the tear film lipid layer and thus provide symptomatic relief in evaporative DED.