We should all have the experience of physical examination, whether it is a child in the school inside the organization of the physical examination, or to go to the hospital physical examination in the ophthalmology department of the eyesight examination, basically every routine physical examination will be carried out by a project is the eyesight examination, usually in front of a table of eyesight, the medical staff to give us the instructions, need to answer the medical staff pointed out that the "E" is open in which direction, and then the test results will be converted to myopia degree. We are instructed by the health care provider to answer which way the "E" is pointing, and then the results are converted to myopia. Many people also hang a logarithmic visual acuity chart at home for daily vision testing, so is the result of the logarithmic visual acuity chart accurate? Today we give you the answer.
Logarithmic vision charts are basically accurate, but not precise
It can be said that the results of the logarithmic vision checking eyesight is basically accurate, otherwise it would not have been used for decades. The logarithmic visual acuity chart first originated in 1958, and after more than half a century of time, countless people have tested their eyesight through the logarithmic visual acuity chart, and the accuracy of the results has stood the test of time. However, for professional ophthalmologists, the results of logarithmic visual acuity charts are generally used as a reference, and after an approximate range has been detected, further tests are carried out using precise instruments. That's why we usually do a logarithmic visual acuity chart first, and then use another instrument in a dimly lit room when we get glasses.
Logarithmic visual acuity meter conversion method
Now many parents will be at home using the logarithmic visual acuity meter to their children's eyesight, at any time to detect the child's visual acuity, you can do to the early detection of nearsightedness, help to protect the eyesight, prevention of nearsightedness, so we know that the results of the vision meter test out of the point of time, so the corresponding degree is how much? What is the corresponding degree?
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Difference between International Standard Visual Acuity Scale (ISVAS) and Logarithmic Visual Acuity Scale (LVAS)
I. Crowding: When the lighting conditions are the same, the results of visual acuity examination of the same patient using the above two types of visual acuity scales are different. Found that the international standard visual acuity table to check visual acuity, the results than the logarithmic visual acuity table to be better (about a line). The reason for this was analyzed: The letter "E" in the visual scale of the International Standard Vision Scale (ISVS) is shorter in the middle than in the other two horizontal lines. On the other hand, the "E" of the standard logarithmic visual acuity scale has three equal horizontal lines. The latter is more difficult to recognize than the former because the latter is more "crowded", resulting in "difficulty in separating", i.e., "crowding phenomenon".
Second, the impact of amblyopia diagnosis and efficacy determination: amblyopia definition of corrected visual acuity ≤ 0.8 for amblyopia, while the standard logarithmic visual acuity table lacks 0.9 line. If the patient's corrected visual acuity is 0.9, the existence of amblyopia can be denied, but the patient's visual acuity is not up to 1.0. Therefore, because of the lack of 0.9 line in the standard logarithmic visual acuity chart, it is not possible to determine whether the patient is amblyopia or not, and the existence of this "blind spot" causes inconvenience to the diagnosis of amblyopia and efficacy of the judgment.
Third, the visual acuity below 4.0 can not be applied to the five-point recording method: At present, the domestic hospitals and optical stores basically use the standard logarithmic visual acuity chart, and many of them use the five-point recording method. However, when the visual acuity is lower than 4.0, there is no corresponding five-point recording method, and they have to follow the recording method of the international standardized visual acuity charts, resulting in the use of two different visual acuity recording methods for the same patient. (d) Out of line with international standards: The application of the standardized logarithmic visual acuity chart for checking visual acuity is more scientific than the international standardized visual acuity chart. However, the standardized logarithmic visual acuity chart is not commonly used internationally and lacks two lines, 0.7 and 0.9, which makes it difficult to compare with the international standardized visual acuity chart. Fifth, the vision test must be fixed reference, exclude other physical diseases, please take the first vision test location, light source, time, distance, test method for the comparison of before and after the effect of reference, otherwise the effect can not be clear.