The first symptoms most people notice are difficulty reading fine print, particularly in low light conditions, eyestrain when reading for long periods, blurring of near objects or temporarily blurred vision when changing the viewing distance. Many extreme presbyopes complain that their arms have become "too short" to hold reading material at a comfortable distance.<unk> , like other focal imperfections, becomes less noticeable in bright sunlight when the pupil becomes smaller. As with any lens, increasing the focal ratio of the lens increases depth of field by reducing the level of blur of out-of-focus objects (compare the effect of aperture on depth of field in photography). The onset of<unk>  varies among those with certain professions and those with miotic pupils. In particular, farmers and homemakers seek correction later, whereas service workers and construction workers seek correction earlier. Scuba divers with interest in underwater photography may notice<unk>  changes while diving before they recognize the symptoms in their normal routines due to the near focus in low light conditions. Interaction with myopia People with low near-sightedness can read comfortably without eyeglasses or contact lenses even after age forty, but higher myopes might require two pairs of glasses (one for distance, one for near), bifocal, or progressive lenses. However, their myopia does not disappear and the long-distance visual challenges remain. Myopes considering refractive surgery are advised that surgically correcting their nearsightedness may be a disadvantage after age forty, when the eyes become<unk>  and lose their ability to accommodate or change focus, because they will then need to use glasses for reading. Myopes with low astigmatism find near vision better, though not perfect, without glasses or contact lenses when<unk>  sets in, but the more astigmatism, the poorer the uncorrected near vision. A surgical technique offered is to create a "reading eye" and a "distance vision eye", a technique commonly used in contact lens practice, known as monovision. Monovision can be created with contact lenses, so candidates for this procedure can determine if they are prepared to have their corneas reshaped by surgery to cause this effect permanently.
Presbyopia
Quadrantanopia
Heterotopia 
Pseudomyopia
Nyctalopia
Cerebral polyopia
Entomopia
Ocular dysmetria