If an optometrist is seeing a patient for the first time, some information will have to come from factors such as the patient's age, the patient's history with regard to frequency of spectacle power changes and when the spectacle power was last changed, whether contact lenses have been used, what type of lenses they are and when was the last time they were worn, etc.
And then the optometrist will do their own spectacle power check, with and without dilating drops if this is a pre-LASIK check.
And so, with all this information at hand, we can imagine a few scenarios.
eg. Patient says they have worn the same spectacles for 2 years, and that spectacle lens power (can be checked with lensmeters/focimeters in the office) is the same as the optometrist's own current refraction check, and any soft contact lenses have not been worn for at least the past week, then we can say the spectacle power is stable
or on the other hand
eg Patient says they just updated the glasses 6 months ago, and the optometrist's current refraction check is even higher than that of the updated glasses, then the spectacle power is probably not stable
As you can see, it depends partly on what the patient tells the optometrist, and partly on what the optometrist finds on examination. If there is any uncertainty about the stability of the spectacle power, it is usual practice to postpone LASIK until another spectacle power check in perhaps 6 months to 1 year.
