There are many medical conditions that can prevent enlistment in the Army. However, this does not include poor vision, so long as that vision can be corrected through the use of glasses or, in certain cases, through the use of corrective surgery.
Eligibility for military enlistment depends on an individual's vision once corrected by lenses. In most circumstances, the military requires your vision to corrected to at least 20/40 in the better eye.
Contacts Versus Glasses
Recruits are not allowed to wear contacts during basic training due to hygiene concerns. Instead, their vision will be tested before arriving at basic training, and if it is determined that they need glasses, two pairs of military-issue glasses will be provided to them during basic training. Once basic training is over, recruits can wear contacts or their own glasses again.
Individuals who have had surgery to correct their vision are able to join the army, but only once they provide medical documentation and obtain a medical waiver. In fact, many soldiers elect to have corrective surgery after they have completed basic training.