no, not nessicarily. Someone I talked to in the army had 4 operations on his lazy eye. 2 before and 2 after joining the army.
From the army website (old one):
The standard personal weapon is the SA80 and this requires vision in the right eye to be correctable to no less than 6/9. Vision in the left eye must be correctable to no less than 6/36. Spectacle correction must be no greater than -7diopters or +8 in any meridian.
Certain types of surgery or laser treatment to correct visual defects are unacceptable and clarification should be sought prior to application.
The standards required by the Army Air Corps are higher than for other branches: applicants should check current standards with the Army Air Corps.