How Do You Spell 20/400?

Pronunciation: [twˈɛnti slˈaʃ fˈɔːhˈʌndɹəd] (IPA)

The spelling of the number combination "20/400" can be a bit tricky, as it is not a commonly used term. However, it is commonly used to refer to visual acuity or sharpness of vision. In IPA phonetic transcription, it can be written as "twɛnti fɔr ˈhʌndrəd." The number "20" is pronounced as "twɛnti," while "400" is pronounced as "fɔr ˈhʌndrəd." The slash "/" between the two numbers is pronounced as "over" or "out of."

20/400 Meaning and Definition

  1. The term "20/400" refers to a measurement used in ophthalmology to determine a person's visual acuity or sharpness of vision. It is a fraction that compares an individual's ability to see or resolve details at a distance with the standard or average vision of a normal eye.

    In this context, the number 20 denotes the testing distance, usually measured in feet, between the person being assessed and the visual chart. The letter "E" placed at the top of a standard Snellen chart is typically used for this type of test. The denominator, 400, represents the distance at which a normal eye can see and accurately identify the same letter or symbol. Therefore, an individual with "20/400" vision can only discern or identify an object from a distance of 20 feet, while a person with normal vision can clearly perceive it from a distance of 400 feet.

    Having a visual acuity of 20/400 indicates that the person's vision is significantly impaired, with a reduced ability to distinguish small details or objects from a distance. It implies that the person would need to be at a relatively closer distance in order to perceive what a person with normal vision could see from a much larger distance. The term "20/400" is often used to describe severe visual impairment or legal blindness, thus requiring corrective measures such as glasses, contact lenses, or visual aids for day-to-day activities.

Etymology of 20/400

The term "20/400" is derived from a system known as the Snellen chart, which was created by Dutch ophthalmologist Herman Snellen in the 19th century. The term consists of two numbers, with the first number (20) representing the distance at which a person is standing from the chart, and the second number (400) representing the distance at which a person with normal vision can read the same line of letters on the chart.

In this visual acuity system, a person with 20/400 vision is able to see at 20 feet what a person with normal vision sees at 400 feet. Therefore, 20/400 vision indicates significant visual impairment, as objects need to be much closer for the individual to see them clearly.

The term "20/400" is specific to the field of ophthalmology and is used to measure visual acuity during eye examinations.