Snellen Chart | Visual Acuity | Light Perception | Essilor

The Human Eye is an Amazing Organ

Light Perception

How do light rays allow you to see? The human eye is composed of many parts, all of which work together to convert the light rays that are going through your pupil into information your brain can interpret. Light rays travel and bounce off objects before they get to your pupil, and determine the color and brightness your brain perceives. Thanks to this complicated process, we perceive the thin band of the electromagnetic spectrum called visible light that enables us to be aware of what surrounds us.

The Wonder of Sight and How It Works

At the very back of the eye is a curved and light-sensing layer called the retina. The retina senses light rays and acts as a messenger to the brain. The brain, in turn, translates the information it receives into images.

Three things happen when you look at something:

1. Light enters your eye through your pupil. 2. The cornea and crystalline lens work together to focus the light onto the retina 3. The energy from the light is transferred to your brain and decoded into an image

Visual Acuity

How clearly do you see? Visual acuity refers to the sharpness of one's vision; it is a measure of how well a person sees. The Snellen chart test is commonly used to measure acuity.

This test determines how much detail a person can distinguish on a standardized chart of letters, when standing 20 feet away. Someone with 20/20 vision can resolve the same degree of detail at 20 feet that a standard observer can resolve at 20 feet. 20/20 does not mean perfect vision, as it is quite possible to see better than 20/20. The smaller the bottom number in the visual acuity ratio, the better the acuity.

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