It is hard to see. If you keep your eye drops well and the drops just overdue one or two days, it may don't cause any eye damages. Or the eye drops may loss their effectiveness and won't help your eyes. But if the eye drops expired for a long tom or not stored properly ( even if the eye drop not expire), it can risk your eyes to get infection. So, don't use expired eye drops. It is unwise to risk your eye health.
Quality guarantee period is just an approximate time, the majority of expired drugs can also maintain the original potency, but the premise is that it is unopened, and well-preserved. The bacteria of expired eye drops may exceed, it may lead to bacterial conjunctivitis, but if your eyes are neither painful nor itching, do not have redness, and eye secretions do not increase significantly, then there would be no matter. If you have above-mentioned phenomenon, you should go to the hospital.
Once the eye drops are expired, they will lose their effectiveness. However, if they are prescription eye drops, they may have some side effects. Sometimes they will cause eye infection or bglurry vision in your eyes. As you only use them only for several days over the expired date, it won't cause anything serious. As long as you don't experience anything uncomfortable, there will be no problem. If you find something wrong with you, you should go to see a doctor immediately.