Yeah, the redness in our eyes is really uncomfortable. The time the redness lasts will depend on how much do you smoke. On other hand, if you just smoke one joint, the redness will only last for about one hour. If you smoked too much, the redness will disappear in some hours. Of course, it does not disappear for a long time and you are really worried about it, you can have a try with visine which will help you clear the dry eyes. Then, as the reasons why our eyes become red, in fact, there is another name of the redness called bloodshot. I think you know there is some marijuana in the smoke. The marijuana will increase the pulse rate, blood pressure, and heartbeat. As we all know, the increase of the blood pressure is the main reason why the eyes because bloodshot, then here will be some redness in your eyes.