anyway it is better to replace the case every 3 months to reduce the risk of get cotaminated . It is the same as we should replace our toothbrush or towels every 3 month . But most people don't aware that . For me , I will not replace my case unless someday I suddenly aware that I should have a new case . one of my friends keep her case for almost 10 years . unbelievable ,right ?lOL
Usually, i often change my contact lenses 3 months. And replace my contact lenses half a year. I feel good. In fact, whether you replace your contact lenses case is not the point. You shall always keep the cases clean. I always keep washing my contact lenses cases everyday. As long as the cases are clean and in good condition, you can use it. But As for contact lenses, you shall replace them once they are overdue. Or it may cause eye hurt.