I used to put two eye drops one for allergy other for dry eye , but today accidentally , i put an old cortisone eye drop i have been taken few month ago instead of the allergic one , that is happened only one time ? so is that dangerous ?

Putting one drop of a cortisone eye drop into one of your eyes would have no adverse effect. The only thing to be careful of is infection if the tip came into contact with your eye and it is an old bottle that may not be very clean any more. So, if your eye gets red and has pus coming out of it, then see your doctor to see if you need antibiotic eye drops or ointment. Good luck!