PURPOSE: Semifluorinated alkanes (SFAs) are amphiphilic molecules with a fluorinated carbon segment (F) and a hydrocarbon segment (H) and have differing chain lengths and volatilities. These properties can influence the ability to form a long-lasting monolayer at air-liquid interfaces and inhibit evaporation. This in vitro study evaluated the impact of chain length on SFA evaporation rate (Revap) and inhibition of Revap of saline by assessing several SFAs including two dry eye drops, one consisting of 100% SFA (perfluorohexyloctane; F6H8; MIEBO) the other which includes the SFA perfluorobutylpentane (F4H5) as a vehicle (cyclosporine ophthalmic solution 0.1%; CsA 0.1%; VEVYE).

METHODS: Evaporation rates were measured gravimetrically at 35°C in a masked study. The following SFA containing dry eye drops and comparator SFAs were evaluated: F4H2, F4H5/CsA 0.1%, F6H7, F6H8 and F6H10. The Revap of 1 mL of each SFA and saline alone or saline with a 11 or 100 µL aliquot of SFA layered over the top was evaluated in a container with an exposed surface area similar to that of the human ocular surface. Total sample weight was recorded to five decimal places every 10 minutes over 100 minutes. The Revap for each sample was obtained from the slope of the best-fit line obtained by least squares linear regression analysis.

RESULTS: The mean (SEM) Revap in mg/min were 102 (25), 6.0 (0.6), 0.58 (0.20), 0.15 (0.017), and 0.12 (0.09) mg/min for F4H2, F4H5, F6H7, F6H8, and F6H10 alone, respectively (n=3-9). The Revap of saline alone was 10.53 (0.06) µm/min. Layering 100 µL F4H5/CsA 0.1% over saline had no effect on Revap (P=0.52) while F4H2, F6H7, F6H8, and F6H10 inhibited the Revap of saline by 8.4%, 16.7%, 73.9% and 60.7%, respectively (P<0.001 for all vs saline. none of the sfas had a significant inhibitory effect on revap of saline when applying a single 11 l drop except for f6h8 p><0.0001 vs saline n="10-25).">

CONCLUSIONS: The chain length and volatility of the SFAs appeared to impact their ability to inhibit the Revap of saline in this in vitro model. Shorter chain length SFAs F4H2 and F4H5/CsA 0.1% had minimal or no effect on Revap while longer chain length SFAs F6H8 and F6H10 had the maximal effect. The data reinforce the suitability of F6H8 as an anti-evaporative agent for the treatment of signs and symptoms of DED.