Smoking can cause the amblyopia, because the oxygen will be consumed while smoking, resulting in the decrease of oxygen in the blood, and the retina of the eye is particularly sensitive to hypoxia. For the long-term effect, the optic nerve will be damaged. According to the investigation of medical experts, 20% of cataract patients are related to long-term smoking. Compared to the smokers who smoke at least 20 cigarettes a day, the non-smoking man will have twice time less chance to have amblyopic. Smoking can also cause increased intraocular pressure, and this is particularly obvious in patients with glaucoma. Glaucoma patients have been on high intraocular pressure, and the smoking can make it even worse.