It is common to feel a mild burning or stinging sensation immediately after using Combipat eye drops, and this usually settles within a few minutes. You can continue using the drops as prescribed. However, if the burning is severe, lasts longer than a few minutes, or if your eyes become very red, swollen, or your vision changes, stop the drops and contact your doctor, as you may be sensitive to one of the ingredients. Your doctor may suggest an alternative preservative-free drop to better manage your eye allergy.