Nicotine and smoking have far-reaching consequences to health beyond those most well known. While most people know about the impact on smoking to the lungs and heart, most effects on the eyes are not as well known but can lead to a number of eye conditions and even blindness.
Smoking in general causes a lowering of antioxidants throughout the body. It also compromises the immune system. Nicotine's action as a vasoconstrictor makes it harder to pump blood through constricted arteries, leading to decreased blood flow with less oxygen available.
Smokers have an increased risk of age-related macular degeneration or AMD. Macular degeneration is a condition where the central portion of the retina or the macula, that allows us to see sharp detail and color. This leads to the loss of central vision, first blurring and then darkness. Smoking at least doubles the risk of developing either type of Macular degeneration, wet or dry. Although it was thought quitting did not lessen the risk, there are recent studies that indicate this is not true and that quitting does lower the risk of developing this problem.
Age-related cataracts are another increased risk among smokers. Smoking is directly related to age-related increases in the density of the lens of the eye located behind the iris. Smokers are particularly susceptible to a type of cataract known as a Nuclear Cataract, a cataract forming in the center of the lens. It is thought that antioxidants are responsible for maintaining transparency in the eye and smoking reduces these in the body.
Tobacco amblyopia occurs when blood vessels constrict and circulation is lessened resulting in optic neuritis or swelling of the optic nerve. This swelling may lead to damage of the optic nerve. At first there may be blurring or some loss of central vision. If unchecked, blurring may spread to the peripheral field. This progressive atrophy of the optic nerve causes loss of central and color vision. In addition, smokers who smoke one pack or more daily have a greater chance of developing red/green defects, leading to color blindness.
Thyroid eye disease is a factor in Graves' disease. The thyroid becomes overactive and while eye disease is a function of the disorder, smokers are more likely to develop this complication. Starting as double vision, thyroid eye disease can lead to blindness. A general weakening of the immune system is thought to be responsible.
Optic neuropathy, or damage to the optic nerve, occurs because of blocked arteries due to smoking. Reduced blood flow damages the cells in the retina and can lead to blindness.
Diabetic retinopathy is yet another outcome possible for smokers who have diabetes. Blood vessels in the retina are more sensitive to poor blood sugar control that can lead to macular edema or swelling leading to blurred vision. Continued lack of oxygen can actually cause new blood vessels to form along the retina and in the vitreous humor but these may bleed, destroying the retina and leading to blindness.
While it may seem as though smoking does not lead directly to many diseases that can develop in the eye that cannot develop anyway, nicotine and smoking contribute to the deterioration of the eye in the presence of other conditions as well as the specialized condition of tobacco amblyopia. The likelihood of developing complications, however, is lessened by not smoking at all, or by quitting smoking as soon as possible.