OTG-i is able to measure water evaporation from the tear film using the Non-intrusive Tear Evaporimeter (US patent number 4461303 A) invented by Miguel F. Refojo and Maurizio Rolando.
The device comprises of  a pair of goggles which condition the air over the test eye to a desired baseline of relative humidity and temperature. The increase in relative humidity due to water evaporation from the tears is determined over the testing period.