By Carl DiNello
www.lasikeyesurgery.lkr-healthinformation.com
Although this article is not directly related to LASIK, it offers an easy to understand definition regarding the various levels of visual efficiency. We all understand that to be told we have 20/20 vision is great; but exactly what do all those other levels of vision mean? What's o.k., what's not o.k., what's bad? The following explanations should help clear up any confusion you might have.
20/20: This is considered good, standard normal vision.
20/25 to 20/65: Slightly subnormal vision, but not seriously impaired. Those below 20/45 will have some difficulty reading a newspaper at normal arms length, but most, upon holding it closer to their face, with good light, will still be able to read. It is still legal to drive in many states with visual acuity as low as 20/60. However, most drivers in this category will carry restricted licenses. Telescopic glasses qualify all of this group to drive so long as it is permitted in the state in which they are licensed, and if they do not also have serious field vision loss.
20/70: Mildly impaired vision. It is at this point that people really begin to feel handicapped. Without magnification, reading newspapers is very difficult, and most states will not issue a drivers license to persons with a visual acuity this low, unless they are equipped with telescopic glasses. Object and travel vision are still excellent, with the exception of those who have lost considerable field vision.
20/75 to 20/200: Moderately impaired vision. With the assistance of low vision aids, this group can still function as sighted in almost all circumstances. Object vision for this group is poorer, but is still adequate for nearly all activities. Examples; people with this vision level will see the car clearly, but may not be able to identify its make and model. They can see that a person is coming, but may not recognize if it is a friend. Travel vision is acceptable, unless there is also field vision loss.
Reading poses the most difficulty for this group, but proper visual aids and training can eliminate this problem. People in this group should be equipped, and properly trained to read with the assistance of numerous available low-vision aids. For all members of this group driving is permitted with the use of telescopic glasses unless there is also serious peripheral-vision loss, or other limiting factors.
20/200 to 20/800: Seriously impaired vision. People in this group can read with the assistance of low-vision aids. Those below 20/500 might consider learning Braille. While this isn't mandatory, it is a viable option. Even with the use of telescopic glasses, people with this level of vision will not be able to drive. Object vision is greatly diminished, but is still useful. Travel vision is adequate, however, those at the lowest end of the scale could sometimes trip over something as simple as a curb. Crossing streets can be quite hazardous for those at the lower end of this scale due to the difficulty of seeing distant oncoming cars.
20/800 to 20/1200: Severely impaired vision. At this level of visual acuity a person loses an acceptable level of travel vision. People who have suffered a substantial loss of peripheral vision may find a white cane useful, or necessary even before this point is reached. At this stage of impaired vision, the use of the white cane becomes necessary, regardless of the cause of vision loss. It may be possible for some in this group to read using very strong magnifiers, and large print publications. A +50 diopter lens will help most in this group to read textbook-size print.
20/1200 to 20/6000: Very severely impaired vision. A great many doctors refuse to recognize the use of visual acuity figures this low. Letter sizes larger than 700 do not exist on eye test charts, but there are mathematical equivalents. Doctors describe vision at this level as the ability to see a hand moving one foot away, but without the ability to count fingers. People in the 20/1200 to 20/6000 group are dependent on at least the assistance of the white cane, or more probably, the need of a guide dog for independent mobility. A video visual aid for reading is the only effective reading aid for this group. The best possible assistance available for reading is a Voice synthesizer that can convert print into speech.
This group has very little object vision, but as long as there is light perception, that vision is useful. For example, a man walking down the street with his white cane sees two shadows ahead. He can also see light between the two objects. While he probably can't recognize the objects, he knows there is enough space between them for him to pass through.
There you have it, a breakdown of the 7 levels of visual efficiency. I hope this will help you have a better understanding of just what those numbers mean at your next eye examination.
