This is a good question as we are all trying to save money however we can. However, there is a very valid reason that contact lens and glasses prescriptions are valid for only a year. This happens so that you will return to your ophthalmologist
to have a complete eye exam every year. This is important as your eye care professional will not only make sure that your contact lens are fitting correctly and that your prescription has not changed, but more importantly, they will check your eyes for serious conditions such as glaucoma, diabetes, uveitis, hypertension, macular degeneration, and retina problems just to name a few. Also, even a small change in your prescription can lead to headaches and eye strain if not corrected even if you feel that you can see just fine with your current prescription.
So, in summary, the health of your eyes is not something to scrimp on. Discuss your financial concerns with your provider as there are often ways to help if money is tight. Also your eye care professional will be able to explain why it is important for you to not go longer than a year without a complete eye health check up.