First your son would need a dilated retinal exam by an ophthalmologist Eye MD who be asked the question. If the retina exam is normal on my patients I would allow tennis playing. It is a racquet sport and the biggest risk is getting hit in the eye. Consequently he should buy a pair of sports glasses and wear them when playing NOT his reqular glasses.
Much research is being done into preventing myopia from progressing. Nothing always works. Testing is being done on drops such as atropine and a new investigational drop, bifocals, scleral reinforcement.
To the mother whose 9 year old son plays tennis 6 hours per day... how is your son doing?
I have a daughter who's playing tennis 3 - 4 times per week (about 2 hours per session) and is nearsighted (-4 right eye and -3.75 left eye). What concerns me and my wife is that her eyes worsened by -1.25 in about 9 months since the last checkup. That happened probably over this summer when we played more tennis than usual, watched about 2 hours of tv per day and played 1 hour of computer games. Besides that, she loves to read and paint.
The doctor asked us if she had a growth spurt or practices any intense sports. When we said that she plays tennis he suggested that it could be the cause.... What do you think? Is tennis a problem. I believe not, but...