While examining a patient, the time eventually comes when the patient and I end up talking about what they should expect after receiving their prescription eyewear. At this time, if their is a change in their prescription, I will let them know how long it will take for them to adjust to their new eyewear. For most people (say 75%), the adjustment process is immediate, that is – they end up seeing well and seeing comfortably right after putting it on their face. For the other 25% or so, I will usually let give them a specified number of hours to try the glasses on for their brains and eyes to adjust. If there is a massive change in the prescription, I will usually tell them to wear them for around 80 hours for things to adjust. If there is a medium change in prescription, I will tell them to give it 40-60 hours of adjustment. And if there is a minimally-challenging change in prescription, I will usually tell them to give the glasses 20-40 hours of adjustment time.
There are so many factors that can affect why it can take so long for a patient to adjust to a new pair. First, the presence or absence of astigmatism can affect one’s adjustment. Astigmatism adjustment can mean a change in the power of astigmatism as well as the angle (axis). Second, progressive lenses create a different field of view than might have been present with a single vision lens. This can create a perceptual challenge for the brain.
If a patient does feel that things are getting easier to adjust to, usually we will have them come in to make a modification to the prescription.