A normal eye chart, also known as a Snellen chart, is a tool used to measure visual acuity, which is the sharpness of your vision.
Understanding the Snellen Chart
The Snellen chart is the most common type of eye chart used by eye doctors. Here's what you should know about it:
- Layout: The Snellen chart is structured with 11 rows of capital letters.
- Letter Size: The top row features a single, large letter. As you move down the chart, the rows contain increasing numbers of letters that decrease in size.
- Distance: When using a Snellen chart, you stand 20 feet away from it, without your glasses or contact lenses.
- Purpose: The purpose is to see how far down the chart you can accurately read.
How to Read a Snellen Chart
- Starting Point: You begin by trying to read the letters on the top row.
- Moving Down: If you can read the top row easily, you move down to the next row and try to read that one.
- Visual Acuity: The smallest row of letters you can read accurately determines your visual acuity, also known as your vision.
Example
- If you can read the line marked as 20/20, you have normal vision.
- If you can only read the line marked as 20/40, it means you have to be 20 feet away to see what a person with normal vision can see from 40 feet.
Why Use It?
The Snellen chart is an essential tool for assessing vision and determining if someone might need corrective lenses (eyeglasses or contact lenses). It helps in diagnosing various vision problems, including:
- Myopia (nearsightedness)
- Hyperopia (farsightedness)
- Astigmatism
The standard eye chart is the Snellen chart. It consists of eleven rows of capital letters, with the size of the letters decreasing in each subsequent row. During testing, you would stand 20 feet away from the chart without wearing corrective lenses. The smallest line of letters that you are able to read accurately determines your visual acuity.