Other ocular surface agents that protect and prevent drying are the emollients, such as mineral oils and paraffin, etc. These are generally found in preparations that would fall into the thick gel or even thicker ointment categories. With very high viscosity, long residence time but reducing optical clarity, they are generally reserved for severe dry eye disease (DED) and/or nighttime use. Therefore, these polymers resist flowing off the ocular surface with varying levels of viscosity.
High viscosity makes it stay in contact with the ocular surface longer (increased residence time) but reduces optical clarity, so a balance is needed. An appealing agent might be one that has visco-elasticity, a property that has different viscosities during the blink, enough to increase its residence time but decreasing immediately after blink to increase optical clarity again.
We are fortunate that sodium hyaluronate adds this to its other beneficial properties.