视力测验

定义

The visual acuity test is used to determine the smallest letters you can read on a standardized chart (Snellen chart) or a card held 20 feet (6 meters) away. Special charts are used when testing at distances shorter than 20 feet (6 meters). Some Snellen charts are actually video monitors showing letters or images.

选择的名字

Eye test - acuity; Vision test - acuity; Snellen test

如何执行测试

This test may be done in a health care provider's office, a school, workplace, or elsewhere.

Visual acuity is usually recorded as:

• "Uncorrected," which is without glasses or contact lenses
• "Best corrected," which is with the best possible glasses or contact lens prescription

对于未矫正的视力, you will be asked to remove your glasses or contact lenses and stand or sit 20 feet (6 meters) from the eye chart. 你要睁大眼睛.

You will be asked to cover one eye with the palm of your hand, 一张纸, or a small paddle while you read out loud the smallest line of letters you can see on the chart. Numbers, lines, 或图片 are used for people who cannot read, especially children. If you can't make out any of the letters, 数字, 或图片, the examiner will usually hold up some number of fingers and record at how many feet away you can correctly identify how many are being held up.

If you are not sure of the letter, you may guess. This test is done, one at a time on each eye. If needed, it is repeated while you wear your glasses or contacts. You may also be asked to read letters or 数字 from a card held 14 inches (36 centimeters) from your face. 这将考验你的近视力.

在Covid-19大流行期间, home visual acuity testing became an important part of telemedicine for eye care. A variety of home tests are available in print, on smartphone apps or the internet. These tests have been found to be almost as accurate as a test performed in a provider's office.

如何准备考试

No special preparation is necessary for this test.

考试的感觉如何

没有不适.

为什么要进行测试

The visual acuity test is a routine part of an eye examination or general physical examination, 特别是如果有 视力的改变 或者视力有问题.

In children, the test is performed to screen for vision problems. Vision problems in young children can often be corrected or improved. Undetected or untreated problems may lead to permanent vision damage.

There are other ways to check vision in very young children, or in people who do not know their letters or 数字.

正常的结果

Visual acuity is expressed as a fraction.

• The top number refers to the distance you stand from the chart. 这通常是20英尺(6米).
• The bottom number indicates the distance at which a person with normal eyesight could read the same line you correctly read.

For example, 20/20 (6/6) is considered normal. 20/40 (6/12) indicates that the line you correctly read at 20 feet (6 meters) away can be read by a person with normal vision from 40 feet (12 meters) away.

Even if you miss one or two letters on the smallest line you can read, you are still considered to have vision equal to that line.

异常结果意味着什么

Abnormal results may be a sign that you need glasses or contacts. Or it may mean that you have an eye condition that needs further evaluation by a provider.

风险

There are no risks with this test.

参考文献

查克RS, 邓恩SP, Flaxel CJ; American Academy of 眼科学 Preferred Practice Pattern Committee, 等. Comprehensive adult medical eye evaluation preferred practice pattern. 眼科学. 2021;128(1):1-29. www.aaojournal.org/article/S0161-6420(20)31026-5/fulltext. 2020年11月12日发布. 于2023年4月5日发布.

Olitsky SE, Marsh JD. 眼睛检查. 在:Kliegman RM, St. Geme JW, Blum NJ, Shah SS, Tasker RC, Wilson KM, eds. 纳尔逊儿科学教材. 21艾德. Philadelphia, PA: Elsevier; 2020:chap 637.

Rubin GS, Dunbar HMP. Visual acuity and contrast sensitivity. In: Sadda SR, Sarraf D, Freund KB, 等, eds. 瑞恩的视网膜. 7日艾德. Philadelphia, PA: Elsevier; 2023:chap 12.