In myopic patients, number usually tends to increase during increased periods of eye strain as in continuous studying for long time during exams, watching TV or computer screens in night time, causing excessive eyestrain. Use of glasses during this period, may help you to prevent this change in number. Usually by the age of 20, the number begins to settle down and become stable afterwards. Till it settles, use glasses (preferably cheaper ones) for whole day, eat good healthy diet, avoid continuous staring at screens and wash your eyes frequently. After your number becomes stable for atleast 1yr, you can go for Lasik ( procedure to remove specs).