What is a Snellen chart used for?
Invented in 1862 by a Dutch ophthalmologist named Herman Snellen, the Snellen chart remains the most widespread technique in clinical practice for measuring visual acuity. [1][2] The Snellen chart serves as a portable tool to quickly assess monocular and binocular visual acuity.
How do you write a Snellen chart results?
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.
What is Snellen principle?
Snellen defined “standard vision” as the ability to recognize one of his optotypes when it subtended 5 minutes of arc. Thus the optotype can only be recognized if the person viewing it can discriminate a spatial pattern separated by a visual angle of one minute of arc.
Who uses a Snellen chart?
The Snellen chart is a familiar sight in physician and optometrist offices. It consists of 11 lines of block letters, also known as “optotypes,” which are constructed according to strict geometric rules and whose size decreases on each lower line of the chart.
What size are the letters on a Snellen eye chart?
Snellen designed stylized letters on a 5×5 grid, which he called “optotypes.” He defined the reference standard (known today as “20/20”) as the ability to recognize one of his optotypes when it subtends an angle of 5 minutes of arc. He described this as a size that can be “easily recognized by normal observers.”
What does it mean by 6 6 eyesight?
6/6 vision describes being able to see at 6 metres what an average person can see at 6 metres. While 20/20 vision describes the same ability, but at 20 feet rather than 6 metres.
How big is a Snellen eye chart?