How do hydrophilic Contact Bandages work?
Each soft bandage lens is packaged in isotonic sodium chloride in crimp sealed, glass vials.They are autoclaved (steam sterilized) at 250F+ degrees for 20 minutes --enough for even a stubborn sporulating organism.
At time of use, the lens is removed and may be placed in the topical medication of choice allowing it to "sponge up" to the lens' point of hydrophilicity. In other words, a 55% can retain only 55% of the desired medication. A 73% water content allow somewhat extended treatment. Soft, bandage contacts deliver in quasi-time release fashion --- much like placing a small sponge onto the eye. Alternately, drops may be applied directly to the in situ placed lens.
The best method, of course, is to measure the corneal curvature (keratometry) as well as the distance from "white to white" in millimeters. However, any measurement of corneal curvature is rare and fairly impractical in private practice. Plastic and cardboard measuring devices are mostly "illusions of accuracy". Practice and experience are the most effective metrology tools.
Rule of Thumb:The smaller the lens diameter, the steeper the curvature. For example, a 14mm diameter lens suitable for a Boston Terrier has a steep curve of 8.3mm; a 38mm diameter for a big Arabian horse has a flat curvature of 19mm. The tables above make this easier to see.
How long will they stay on? :
The influencing factors are temperature, humidity, winds, activity of the animal and lysozyme actions on the patient's eye. Lenses with higher hydrophilicity tend to remain on the eye for longer periods.