Radioactive sodium pentechnetate Tc 99m was added to commonly used ophthalmic drug vehicles of saline, 1% methylcellulose, 1.4% polyvinyl alcohol, and a 6:4 mixture of white petrolatum-mineral oil ointment. These drug vehicles containing99mTc were placed on both rabbit and human eyes and the rate of disappearance of the radioactivity determined. The ocular retention of99mTc by the eye was much longer in the nonblinking eye regardless of the vehicle used. The rate of loss of99mTc from the eye was fastest with saline and slowest with the ointment, with methylcellulose and polyvinyl alcohol in between. The longest contact time of the drug vehicle with the eye is afforded by the use of the ointment vehicle and the covering of both eyes.
Hardberger R, Hanna C, Boyd CM. Effects of Drug Vehicles on Ocular Contact Time. Arch Ophthalmol. 1975;93(1):42-45. doi:10.1001/archopht.1975.01010020046008