Why am i not allowed to smoke a day before lasik surgery?

Many reasons: Smoking has been shown to increase the risk of infection related to surgery or contact lens use. It is also associated with a higher prevalnce of cataract formation.

Dry eyes: Smoking can also decrease tear production, which can increase dry eyes. This is not a strict rule, but it will certainly help speed recovery if your eyes are more lubricated.

And after LASIK too: Smoke can increase irritation in your eyes. I usually ask my patients not to smoke for a few days after surgery. This is also not a 'rule', but a strong recommendation.

Smoking: Smoking is not contraindicated prior to lasik but it is terrible for you and surgeon probably does not want to smell it on you.