Landolt C on:
[Wikipedia]
[Google]
[Amazon]
The Landolt C, also known as a Landolt ring, Landolt broken ring, or Japanese vision test, is an optotype—a standardized symbol used for testing vision. It was developed by the Swiss-born ophthalmologist Edmund Landolt.
The Landolt C consists of a ring that has a gap, thus looking similar to the letter C. The gap can be at various positions (usually left, right, bottom, top and the 45° positions in between) and the task of the tested person is to decide on which side the gap is. The size of the C and its gap are reduced until the subject makes a specified rate of errors. The minimum perceivable angle of the gap is taken as measure of the visual acuity. It is generally practised in the laboratory.
The stroke width is of the diameter, and the gap width is the same. This is identical to the letter C from a
The Landolt C, also known as a Landolt ring, Landolt broken ring, or Japanese vision test, is an optotype—a standardized symbol used for testing vision. It was developed by the Swiss-born ophthalmologist Edmund Landolt.
The Landolt C consists of a ring that has a gap, thus looking similar to the letter C. The gap can be at various positions (usually left, right, bottom, top and the 45° positions in between) and the task of the tested person is to decide on which side the gap is. The size of the C and its gap are reduced until the subject makes a specified rate of errors. The minimum perceivable angle of the gap is taken as measure of the visual acuity. It is generally practised in the laboratory.
The stroke width is of the diameter, and the gap width is the same. This is identical to the letter C from a Snellen chart
A Snellen chart is an eye chart that can be used to measure visual acuity. Snellen charts are named after the Dutch ophthalmologist Herman Snellen who developed the chart in 1862 as a measurement tool for the acuity formula developed by his profe ...
. The Landolt C is the standard optotype for acuity measurement in most European countries. It was standardized, together with measurement procedures, by the German DIN, as DIN 58220 (now EN ISO 8596).
Although accepted as a gold standard
A gold standard is a backed currency, monetary system in which the standard economics, economic unit of account is based on a fixed quantity of gold. The gold standard was the basis for the international monetary system from the 1870s to the ...
, this optotype has its own inherent problems, possibly due to higher brain function where the gap will appear closed near the limit of resolution. This is not due to the structure of the cornea or lens, and it is not due to astigmatic errors.The Effects of Optical Defocus on the Legibility of the Tumbling-E and Landolt-C
REICH, LEWIS N. OD, PhD, FAAO; EKABUTR, MICHELE Optometry & Vision Science:June 2002
See also
* Edmund Landolt *Visual acuity
Visual acuity (VA) commonly refers to the clarity of visual perception, vision, but technically rates an animal's ability to recognize small details with precision. Visual acuity depends on optical and neural factors. Optical factors of the eye ...
* E chart
An E chart, also known as a tumbling E chart, is an eye chart used to measure a patient's visual acuity.
Uses
This chart does not depend on a patient's easy familiarity with a particular writing system (such as the Latin alphabet). This is oft ...
* Golovin–Sivtsev table
References
External links
* {{Commons-inline Ophthalmology Optotypes