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Myopia is a refractive error of the eye that causes the eyes to become blurred when looking at distant objects. Usually, the degree of myopia will be assessed through the Diop index. Let’s learn more about this index with Cfis.edu.vn through the article below.
What is Diop?
Diop is called a unit of measurement of curvature of the lens used to help the eye see things around more clearly . Usually, the larger the diopter, the more severe the nearsightedness and the thicker the lens.
Myopia is denoted by D , the symbol written on the surface of the lens is -D means myopia, conversely, if it is +D, it is farsightedness.
For example, -1, -2 would be equivalent to myopia of 1 degree and 2 degrees. Close 2 diop will be interpreted as close 2 degrees.
How to calculate myopia of the eye?
Normally, there will be many types of eye acuity tables, but depending on each object, there will be a way to calculate myopia with different tables.
- Landolt open-circle visual acuity chart.
- Visual vision board with objects/animals to use with children or people who are illiterate.
- Armaignac’s E-vision chart.
- Snellen alphabetical vision chart with the letters: LFDOI E.
In addition, the calculation of myopia will also be based on each person’s own near point and far point. The lying image will be within the limit of 2 near and far points, if the image is in that range, it will be clearly seen by the eye.
The far point is considered the farthest point at which an object can be clearly seen by the naked eye. Normal people have a far point called infinity, so wearing glasses is only for the main purpose of correcting the far point of nearsighted people to an infinity distance.c
For example, there is a calculation like this:
When the far point is 3m, it will be equivalent to -2D. The far point of 1m will be equivalent to near -1.5D. When the far point is 50cm, it will correspond to myopia of -2D … Thereby, you will have a conclusion and give a clear remedy for your eye condition.
How to measure myopia of the eye at home
Formula for calculating proximity
Here is the formula to estimate myopia to measure myopia at home:
Myopia = 100/Distance (cm)
For example: A distance of 50cm is considered the distance to see objects clearly, then myopia will be calculated = 100/50 = 2 degrees.
How to convert proximity
Below is a commonly used myopia conversion, the results when conducting a visual acuity measurement in letters will show how many rows you can clearly read out of a total of 10 rows.
For example: When measuring myopia with the alphabet, you will be able to read about 6 rows, eyesight is 6/10; If you can only read 2 lines, your eyesight will be 2/10.
The normal degree of myopia will correspond to a range of vision, specifically:
- Vision 6 – 7/10: The corresponding nearsightedness will be -0.5 Diop
- Vision 4 – 5/10: The corresponding nearsightedness will be -1 Diop
- Vision 1/10: Myopia will correspond to -1.5 to -2 Diop
- Visual acuity less than 1/10: Nearsightedness will be above -2.25 Diop
Measuring myopia by machine
Step 1Measure with an electronic machine
You can measure the degree of myopia of the eye through an electronic device. Using this method, the result will be some common symbols such as:
- L (Left) or OS is considered as a result of the left eye’s visual acuity.
- R (Right) or OD is considered to be the result of the right eye acuity measurement.
- S (SPH/Sphere/Bridge) is the number of degrees of the lens, followed by the symbol “+” indicating farsightedness and vice versa, the symbol “-” indicating myopia. However, to ensure accuracy, you need to perform this step many times, thereby taking the average measurement, or AVG number, to determine the degree of myopia of the eye.
- SE is referred to as the number of recommended degrees of glass to use.
- PD is the distance between the two pupils between the two eyes, the unit is millimeters (mm).
With this approach, you will be able to determine if you are nearsighted or not, then you will be taken to the next steps to give the most accurate diagnosis.
Step 2Measure eye acuity by fitting sample glasses
Besides, you can measure the visual acuity of your eyes by fitting the sample glasses on the person with eye defects to try on, the glasses will be adjusted and moved to the appropriate direction until the eyes can see clearly and feel comfortable. roof. This is considered a way to know exactly how close your friend is. Finally, the technician will cut glasses to suit each person’s nearsightedness.
The most popular methods of measuring myopia today
Here are some common methods of measuring myopia today:
- Professional meter: With this measurement will usually be applied in clinics or hospitals because this is done by professional technicians at general clinics. And this is considered to be the most accurate way.
- Myopia alphabet: This way will include Landolt table (C board), Armaignac (E table), Parinaud’s table, Snellen table, picture table and carded optometry table. This is the fastest way to detect if the eye is nearsighted or not and also the most commonly used.
- Measure with online applications: This is considered the most convenient way to assess eye condition. Some popular applications such as: Eye Care Plus, iCare Eye Test, Prescription Check, Eye exam,…
- Measure myopia at home: With this method, you can use basic tools to determine where the far and near points are, and then determine the degree of myopia. However, with this approach, it is only relative and not very accurate.
Reference: Learn 6 alphabets to measure myopia and how to use each type
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Source: Long Chau Pharmacy, Vinmec International General Hospital
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