Table of Contents
- 1 Why are vision tests 6 meters?
- 2 Why is a Snellen chart 6 meters?
- 3 What is special about the fovea?
- 4 Why is 20 ft The standard distance for a Snellen eye test?
- 5 What does 6/12 vision mean for normal vision?
- 6 What is the distance visual acuity of 6/6?
- 7 What is the difference between 6/30 and 3/60 vision?
Why are vision tests 6 meters?
6/6 is the visual acuity needed to discriminate two contours separated by 1 arc minute – 1.75 mm at 6 metres. This is because a 6/6 letter, E for example, has three limbs and two spaces in between them, giving 5 different detailed areas.
Why is a Snellen chart 6 meters?
Recording Snellen Results Top number equates to the distance (in metres) at which the test chart was presented (usually 6m), Bottom number identifies the position on the chart of the smallest line read by the ‘patient’. Eg; 6/60 means the subject can only see the top letter when viewed at 6m.
How far away do you normally stand in taking a vision test?
During a vision screening, you will typically be asked to sit or stand 20 feet away from the eye chart. In instances where the optometrist’s office is not 20 feet long, the chart may be located behind you and a mirror may be placed on the opposite wall to simulate a distance of 20 feet.
What is special about the fovea?
As the fovea is responsible for high-acuity vision it is densely saturated with cone photoreceptors. A unique feature of the central fovea is the displacement of other retinal layers concentrically, which allows for the highly efficient packing of cones.
Why is 20 ft The standard distance for a Snellen eye test?
Snellen charts help to determine a baseline for your vision in each eye – a baseline typically measured against “20/20” vision. This means when you are 20 feet away from an object, you can comfortably see details that most people with normal vision can also see at 20 feet distance.
What does it mean when your near sighted?
Nearsightedness (myopia) is a common vision condition in which you can see objects near to you clearly, but objects farther away are blurry. It occurs when the shape of your eye causes light rays to bend (refract) incorrectly, focusing images in front of your retina instead of on your retina.
What does 6/12 vision mean for normal vision?
A person with normal vision can read all the lines from a distance of 6 meters. What a 6/12 vision vision would mean is that what a normal adult person with normal vision can read from 12 meters, the person with 6/12 vision can only read from 6 meters and not beyond.
What is the distance visual acuity of 6/6?
For someone with 6/6 acuity, they can resolve 1 minute of arc (in a letter 5 minutes of arc high). Distance visual acuity means, in these cases, the distance isn’t relevant, e.g. at 6m (6,000mm), the height of a 6/6 letter is 8.73mm; at 60m, it has to be 87.3mm and at 600m, 873mm etc.
How far away can you read a vision chart?
Typically, the distance can be reduced to either 10 feet (3 meters) or approximately 3 feet (1 meter). So if you can only read the top line at 10 feet, your vision will be recorded as 10/200 or 3/60. When the chart cannot be read even at closer proximity, it will be difficult to determine the exact visual acuity.
What is the difference between 6/30 and 3/60 vision?
If you have 6/30 vision, you must be as close as 6 meters to see what a person with normal vision can see at 30 meters. 3/60 vision means the eye can resolve the 6/60 letter size but at a closer distance of 3 meters. 1/60 vision means the eye can resolve the 6/60 letter size but at the closer still distance of 1 meter.