Guttae. Eye Drops.
Eye drops are made by dissolving the required medicament in freshly sterilised and cooled distilled water, straining through sterilised cotton wool if necessary, the strength being indicated in parts per 100 parts by volume. Such strengths may be taken as equivalent to percentages when the proportion of dissolved substance is small. It may be more accurately described as w/v (weight/volume) percentage, and corresponds to grammes per 100 mils thus, a 1 per cent. weight/volume solution contains 1 gramme in 100 mils and this is equivalent to 4.375 grains per fluid ounce. In making alkaloidal solutions in water, soluble salts are employed and not the free alkaloids, the latter being, for the most part, very sparingly soluble in water.