I can understand your concern. Such increases in prescription can be alarming; however, I tend to agree with your optometrist's assesment that this is due to your son's growth spurt. As children grow quickly, during the pre-teen and teen, years such changes are quite common. This results from concomittant changes in the eyes' anatomy.
The reason your son can still see through his current glasses lies in his ability to accomodate the lens of his eye to still achieve clear vision through them. Still, this accomodation of the lens of the eye requires straining of the vision and can ultimately lead to headaches towards the end of the day. It is best to prescribe the proper glasses that will allow for relaxation of the lens of the eye and provide the proper vision without straining.
I do believe that this trend towards higher prescriptions is likely to continue over the next few years with stabilization somewhere in the mid to late teen years.
Having said all this, I always encourage patients to obtain a second opinion. If there are any doubts in your mind about the exam performed on your son, there is no harm in having a second doctor examine him.
I hope this helps...
I feel he has a moderately high prescription for a nine year old. There could several reasons why your husband's glasses are blurry when your son puts them on.
1. differences in pupillary distance
2. adjustment from your son's current prescription to your husband's
3. small amount of astigmatism correction in your husband's glasses
Also, initially your son's eyes may want to resist the new correction due to the prolongued accomodation of the lens of his eye in order to achive clear vision through his current glasses. He may feel a tunnel vision effect and even experience a headache on the first 1 to 2 days of wear as the eyes adjust (relaxation of the lens) to the new correction. It is important to reassure him as he goes through this process.
Remember that your son will probably be able to wear contact lenses at about 12 or 13 years old and so this will keep him from having to wear thick heavy glasses. I recommend that he starts with contact lenses once you feel he is mature enough to properly care for them.
Good Luck as you help your son through this adjustment to new glasses...