Eye-lotions are usually weak solutions in water of one or more medicaments of an antiseptic, astringent, or sedative character- such as boric acid, mercuric chloride, alum, tannic acid, borax, or sodium bicarbonate. The medicament may itself possess strongly preservative properties. In the very dilute solution, however, in which it is used in ophthalmic practice, the quantity present may be insufficient to preserve the lotion for more than a few days. Eye-drops consist usually of a solution of an alkaloid or other material which of itself possesses no preservative property, but on the other hand probably lends itself to the action of micro-organisms.

In compounding all prescriptions for such lotions and drops it is well to adopt a general procedure of sterilisation. Use recently boiled distilled water, have the bottle and cork soaking in hot water while the prescription is being prepared, and strain through wool that has been washed with a little of the sterile water. A solution of atropine sulphate in water so prepared keeps good for quite a long time. Prescribers recognise the probability of a preservative being required, but not being quite sure how to order it, and not having the time to spare to look up the matter, they not infrequently write a prescription such as this :

In such case the conventional quantity of boric acid to use is 2 per cent. Salicylic acid has not been favourably received for preserving eye-drops, although a very small quantity is required- about 1/8 grain to the ounce. A minim of sulphurous acid in 2 ounces of sterilised water prevents eserine (physostigmine) solutions becoming red.

The following is a typical eye-lotion of the old class; commonly called 'red lotion':

Ft. lotio pro oculis.

Pour the tincture and spirit into the bottle containing 7 ounces of distilled water; dissolve the sulphate of zinc in 1/2 ounce of water and add to the contents of the bottle. In this way there is comparatively little deposit. If spring-water of ordinary hardness be used, there will be a copious deposit of carbonate of zinc and sulphate of lime,

It is generally considered that lead lotions are bad for the eyes because the lead salt is apt to produce pigmentation of the cornea, and thus cause temporary blindness. The following is an example of intentional incompatibility:

Ft. collyrium.

On compounding this a precipitate of sulphate of lead is formed. It should be filtered when required for the eyes. Unfiltered lotions similar to this are used for old wounds.

The following are the strengths of eye-lotions commonly adopted, the quantities given being for 1 ounce of distilled water or finished lotion unless otherwise stated. Those marked with an asterisk are used for dropping into the eyes, the rest for bathing them: