Why are solutions such as eye drops and contact solutions always isotonic?

Isotonic: an isotonic solution is one that has the same osmotic pressure compared to another one usually cells or body fluid.

If eye drops had high osmotic pressure they would cause the eye to be dry since fluid would move out the cells making up the eye.

If the eye drops had low osmotic pressure this would cause swelling of the eye since the cells would retain the fluid from the eye drop.