Extraocular fluid dynamics: how best to apply topical ocular medication

Blinking markedly increases outflow of solutions. During initial drug application, try to prevent squeezing or fluttering of the eyelids since this can cause a fourfold increase in lacrimal outflow. 'Half blinks' or incomplete closure of a blink has significantly less effect in removal of fluid from the eye while squeeze blinks may cause solution spillage onto the lids. Closure of the lids prevents loss of solution by inhibiting flow into the lacrimal outflow system, enhances entrapment of fluid under the lid, and increases the volume of extraocular fluid. The conjunctival sac is a potential space which holds and releases medication as much as three times slower than compared to solutions just applied to the globe. Avoid mechanical or psychic factors which will increase secondary lacrimal secretion. Do not apply drops that initially hit the cornea. Do not hit the cilia, pinch the skin, flood eye with excess solutions, or encourage anyone whom the patient has little confidence in to apply the ocular medication. Preferably, drops should be near body temperature. Apply the drug to the main area of pathology and put the head in a position where gravity will have the greatest tendency to keep the drug where medically indicated. If a significant corneal defect is present, place the patient in a position where gravity will allow filling of the defect with medication and gently close the lids. How long to keep the lids closed depends on severity of underlying disease, but they should be closed for at least 1 to 2+ minutes. Pressure, on the lacrimal sac, especially with lids closed, is a most effective method to increase ocular contact times. Theoretically, for drugs which must have a high corneal contact time to achieve intraocular penetration, the best method is inferior temporal application with eyelids closed in either the face down or the head vertical position. Theoretically, current commercial drop sizes of 50 to 75 μl are larger than necessary and may not be as effective therapeutically if drug equivalents can be given in a 15μl range.