The Landolt C, also known as a Landolt ring, Landolt broken ring, or Japanese vision test, is an
optotype
__NOTOC__
An eye chart, or optotype, is a chart used to subjectively measure visual acuity. Eye charts are often used by health care professionals, such as optometrists, physicians or nurses, to screen persons for vision impairment. Ophthalmologis ...
: a standardized symbol used for testing vision. It was developed by the Swiss-born
ophthalmologist
Ophthalmology ( ) is a surgery, surgical subspecialty within medicine that deals with the diagnosis and treatment of eye disorders.
An ophthalmologist is a physician who undergoes subspecialty training in medical and surgical eye care. Followin ...
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. Many ophthalmologists and vision scientists now use an improved ...
. 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, this optotype has its own inherent problems, possibly due to higher brain function where the gap will appear closed near the limit of resolution, especially when the gap is at the 6 o'clock position. 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
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Edmund Landolt
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Visual acuity
Visual acuity (VA) commonly refers to the clarity of vision, but technically rates an examinee's ability to recognize small details with precision. Visual acuity is dependent on optical and neural factors, i.e. (1) the sharpness of the retinal ...
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E chart
An E chart, also known as a tumbling E chart, is an ophthalmological chart used to measure a patient's visual acuity.
Uses
This chart is useful for patients who are unable to read the Latin alphabet – for example, very young children. It is al ...
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Golovin–Sivtsev table
The Golovin–Sivtsev table (russian: Таблица Головина-Сивцева) is a standardized table for testing visual acuity, which was developed in 1923 by Soviet ophthalmologists Sergei Golovin and D. A. Sivtsev. In the USSR, it was t ...
References
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Ophthalmology
Optotypes