It is your brain (and not your eyes) that usually needs the time to adapt to any new glasses.
Assuming your prescription is accurate and balanced, this is true even with minor prescription changes and is more so in instances of large changes, changes to only one eye, or an introduction of a new element to the prescription, such as astigmatism and reading ADD power. You may feel that your glasses feel ‘too strong’, you may experience some initial depth perception changes, and you may find yourself constantly turning your head to find a ‘sweet-spot’ for clearer and comfortable vision. Interestingly, our eyes themselves are responsible for only about 10% of the actual ‘seeing’ with the rest being done by the brain’s visual system that interprets the eyes’ visual signals.
Without any change in glasses, our brain becomes accustomed to interpreting the visual signals sent by the eyes, and it uses very little of its ‘processing power’ to make sense of what you are looking at. With a change in visual signals when looking through any new eyeglass lenses, the brain cannot rely on this visual memory and has to re-calibrate itself. The message it subsequently sends back to visual systems manifest as swimming, headaches, or vague discomfort. Sometimes our brain tries to convince us that “the old glasses were better” as this initial adaptation stage is not as comfortable as with the older prescription.
Wear your glasses as much as possible for quicker adaptation.
Although most individuals experience little or no symptoms of adaptation to new eyeglasses, it can take up to 4 weeks to fully adapt. By wearing your glasses as much as possible even if you don’t require them all the time, you will likely adapt to your new glasses much quicker.