Effects of drug vehicles on ocular contact time

Radioactive sodium pentechnetate Tc 99m was added to commonly used ophthalmic drug vehicles of saline, 1% methyicellulose, 1.4% polyvinyl alcohol, and a 6:4 mixture of white petrolatum-mineral oil ointment. These drug vehicles containing 99m Tc were placed on both rabbit and human eyes and the rate of disappearance of the radioactivity determined. The ocular retention of 99m Tc by the eye was much longer in the nonblinking eye regardless of the vehicle used. The rate of loss of 99m Tc 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.