I frequently come across patients who exhaust their eye drops in a few days only. One vial should be sufficient for a few weeks of average use but when they tell me that their eye drops have finished one week or so after the prescription, I know where things went wrong.
Routinely, we recommend only one drop of the medication in the eye. Why only one drop? Because that is how dosage of any eye drop is calculated which will produce the desired effect. The size of the drop squeezed out of the vial differs in size depending on the viscosity of the medication. In all cases, only one drop should be instilled into the eye because the conjunctival sac (broadly speaking, the space between the eyelids and the eyeball) cannot accommodate more than one drop.
Any amount more than one drop will probably overflow and will be wasted. In most cases, putting 4-5 drops, for example, of the medication at a time will not produce faster and better effects.
In my experience, most of the eye care professionals do not give importance to this simple instruction to the patients while they are counseled or explained how to use their treatment unless the patient directly asks how many drop/s he or she should instil in the eye. They should not presume that the patients already understand that one drop of the medication at a time is sufficient.
This simple point will save unnecessary effort and money for the patients.