Of course, there are many risk factors for these conditions, and most people who smoke will not develop these problems. However, except for cataract which is readily treatable, the conditions listed above can cause irreversible loss of vision. For more information on ocular complications of smoking and other drugs and medications, go to Tobacco. The brain is able to fill in missing information and alter our perception of images to fit expected appearances. This is why blind spots in our peripheral vision are often very difficult to locate without using complicated techniques to find them.
Optical illusions play tricks on our perception of images.
A book titled Perception by Irvin Rock explores this in more detail. One group of disorders affecting our perception of images is dyslexia. In one type of this problem, written letters or words may be perceived as being backwards. The eye itself actually receives the image of the letter correctly, but it is then reversed later by the brain. It is usually recommended for people who are being evaluated for dyslexia to have an eye examination in order to exclude any other problem that might be affecting the vision.