20 yrs male  myopic by -2D&-5 D ,theoretically you should have diplopia & in medical terminology it called anisometropia if difference between power  of two eyes is more than 2 D but practically  I have not seen diplopia in all cases,myopic power increases upto21 yr in male because body growth  gets completed by21 yrs .After that age you may go for LASIK ,for time being you may continue with glasses or contact lens,with regards

It will be better if you use contact lenses over glasses and make sure that you don't have double vision when you see with both eyes. Normally beyond 3 doctor power difference between 2  eyes power Patient gets double vision with glasses. But with contact lenses it can be avoided  hence you are advices to use contact Lenses.  If you are being 21 and if your vision is stable them you can go for lasik surgery.