One area of the sight test that’s always misunderstood by the affected person is in regard to explaining whether or not your eyesight has got higher or worse and does that imply the eyeglasses want changing?
There are associated, however very distinct ways to talk about and describe your eyesight. One is to talk about what your prescription is and how it has changed. The other is to talk about what line you may see on the sight test chart. The two are linked, however a change in one does not necessarily mean a change in the other. I usually say to my patients “It does not matter what prescription is in your specs as lengthy you’ll be able to see the chart. It is when you may’t see the chart, despite what we put in your eyeglasses, that we have a problem.”
The chart usually used is a called a Snellen chart. It is named after a Dutch eye physician called Hermann Snellen who designed it in 1862. The letters are giant at the top and get gradually smaller as you move down the chart. The thickness of the lines that make up the letters, is equal to the thickness of the areas between the lines. The height and width of the letters is 5 occasions the width of the lines.
You will have heard the phrase “20/20”. This is usually understood to imply perfect vision. Actually, most people with good vision have eyesight better than 20/20. It means that you may see, from 20 feet, what you ought to be able to see from 20 feet. We now actually use 6/6 instead of 20/20. This represents the change from feet to meters (20 ft equals 6 meters). For those who can see 6/5(very good eyesight), this means you’ll be able to see, from 6 meters, what it’s best to have to get to 5 meters to be able to see. If you have 6/60 (poor eyesight), it means you need to be 6 meters away to see what you should be able to see from 60 meters. There are totally different levels in between.
The first measure is called vision. This is a measure of what you’ll be able to see without any assist at all. For somebody who would not want glasses and has no eye health problems, it is normally 6/6 or a little better. As your prescription gets stronger, the second number gets higher. The top letter of the chart is often 6/60. Needing eyeglasses is just not the only cause for this number to be higher. If you have eye problems, chances are you’ll not have a prescription however still only be able to see the bigger letters. This is the place the time period visual acuity turns into important.
Your visual acuity tells us how well you’ll be able to see with the perfect prescription in your glasses. When you have something improper with your eyes akin to cataract or macular degeneration, then even with the best possible pair of specs for you, you could only see some of the bigger letters on the chart. Precisely how far down the chart you possibly can see with the most effective spectacles is your visual acuity.
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