Blind World Magazine

The Seven Steps Of The Visual Scale.




The Fred's Head Companion.
Wednesday, August 30, 2006.




20/20, 20/70, 20/200, do you ever get confused by these measurements? What do they mean? How mutch can a person really see when a doctor uses one of these measurements to describe their vision? Finally, here's the answer.


20/20: This is considered normal vision.


20/25 to 20/65: Subnormal vision, but not seriously impaired. Those below 20/45 have difficulty reading a newspaper, but most can hold it closer to their face and still read with good light. Many states will license people to drive with visual acuity as low as 20/60, but most such drivers will carry restricted licenses. Telescopic glasses allow this group to drive as long as their state permits it and if they do not also have serious field loss. These people have excellent object and travel vision, except for those who have lost considerable field vision as well as visual acuity.


20/70: Mildly impaired. This is the point where people really begin to notice a loss of vision. Reading newspapers is very difficult without magnification, and most states refuse to license persons to drive with a visual acuity this low unless they are equipped with telescopic glasses. Object and travel vision are still excellent, except for those who have lost field vision as well.


20/75 to 20/200: Moderately impaired. This group can still function as sighted in most regards with the use of low-vision aids. Object vision for this group is poorer, but it is still adequate for almost all activities. These people can see the car but may have trouble identifying its make and model. Recognizing friends may be difficult, but they see the person. Travel vision is still quite good unless there is also field vision loss. Reading is the primary difficulty of this group. All members of this group should be able to drive with telescopic glasses unless there is also serious peripheral-vision loss, or other limiting factors.


20/200 to 20/800: Seriously impaired, but still with travel vision and reduced but useful object vision. People in this group can read with low-vision aids. Those below 20/500 might consider learning Braille, but it's not mandatory. These people will not be able to drive, even with telescopic glasses. Object vision diminishes but is still useful. Travel vision is still adequate, although those at the lower end of the scale may sometimes trip over curbs. Crossing streets can be hazardous for people at the lower end of this scale because they cannot see distant oncoming cars.


20/800 to 20/1200: Severely impaired. At this level of visual acuity a person loses travel vision. People suffering a loss of peripheral vision may find a white cane useful or even necessary before this point is reached, but at this stage, use of the white cane becomes necessary, regardless of the cause of vision loss. Some in this group are able to use very strong magnifiers to read large print. A +50 diopter lens will give almost all in this group the ability to read textbook-size print.


20/1200 to 20/6000: Very severely impaired. Doctors categorize this level as the ability to see a hand moving one foot away, without the ability to count fingers. People in the 20/1200 to 20/6000 group are dependent on the white cane or a guide dog for independent mobility. A CCTV is the aid of choice for reading print and the only aid that provides visual access to print. This is the group that will use screen reading technology.



http://fredsheadcompanion.blogspot.com/2006/08/seven-steps-of-visual-scale.html




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