That’s the core rule. If you’re 18 or older and your eye exam happened within the last two years, your prescription is almost certainly still valid. If you’re under 18, the window is one year.
Here’s what most patients don’t realize: the prescribing doctor can shorten that window. If your optometrist or ophthalmologist writes a shorter validity period directly on your prescription form, that shorter period governs — not the state default.
Prescription validity is the legally defined period during which an eyeglass prescription remains usable under NYS Education Law. That written document — from your optometrist or ophthalmologist — authorizes lens fabrication, and its validity isn’t a suggestion. It determines whether a licensed optician in New York can legally fill your order. Once a prescription expires, no licensed dispensing optician can use it to make lenses, regardless of how recent it feels.