OPTOTYPES
Learn a little more about the types of fonts used in eye exams
Did you know that there are specific sources for vision screening?
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What should they have and where did they come from?
OPTOTYPES
Now let's learn a little more about the sources used and their origins.
The optometry scale is one of the methods of detecting visual acuity. We will see below the aspects of the historical process and construction of these scales.
One of the methods used to check visual acuity. It is characterized by a white board in which figures, letters or hieroglyphs of different diameters and black color are arranged, called optional, differentiated according to the scale. Their organization is in descending order. Optional items of the same size appear in the same horizontal line, each corresponding to a coefficient of vision that in general ranges from 0.1 (10%) to 1.0 (100%).
Infográfico da evolução dos optotipos.
First standardized visual acuity tests
- Küchler Chart -
Heinrich Küchler is one of the first individuals credited with creating an eye chart to test visual acuity. Küchler, a German ophthalmologist, drew a chart in 1836 using figures cut from publications made up of images of animals and musical objects.
Dr. Küchler refined his chart by publishing a new version in 1843 of typefaces of ten different graduations.
- Snellen Eye Chart -
In 1862, the Dutch ophthalmologist Hermann Snellen , in an attempt to improve the perception of objects at a distance, in which the print characters had different sizes, published the Snellen scale .
Snellen was based on the construction of his scale the visual angle threshold of 1 meter. This scale was immediately accepted and soon solidified in the ophthalmological literature.
1862, Snellen Chart [Imagem cortesia: Wikipedia, ANTI Hamar]
Acuity is marked by two numbers, in the form of a fraction, such as 20/100. The first number is the distance between the frame and the patient and the second represents the row of the smallest letters that the patient can read. Each row in the Snellen Table contains a number that corresponds to the distance at which a "normal" eye can read the letters in that row. For example, the letters in row “100” can be read by a total seer at a distance of 100 meters. This means that a patient with acuity of 20/100 can read at a distance of 20 meters what a person with total visual acuity is able to read at a distance of 100 meters, remembering that 20/20 vision is considered normal.
Snellen uses as a figure only one letter, the vowel “E” capitalized in four positions. In transforming the letter E into an optotype, each one was adapted according to the standardized values in millimeters. These numbers are related to the quantitative value of visual acuity, determining the size of each optotype for that visual coefficient. Depending on the rules determined by the International Council of Ophthalmology, the same letter or number must never be presented twice on the same line. During their use, the scales of optotypes remain in the vertical position and with the height of the examinee's eyes at 0.8 (9).
The test works as follows: at a distance of 6 meters, with one eye covered, the person reads each line. Then do it with the other eye and again with both eyes open.
There are three types of scales. The first is the most traditional, it is composed of the letters C, D, E, F, L, N, O, O, T and Z. In addition, there is the one used for illiterate people, which consists of the letter "E" with variation rotation like "ш", where the person is asked to indicate which way the letter is. And yet it can also be done with figures. The latter is used mainly for children.
Visual acuity is measured by the relationship between the distance between the observer and the object and the size of the smallest object (optotype) viewed.
- Sloan Chart -
Dr. Louise Littig Sloan was an American ophthalmologist and scientist. She is considered a pioneer in the subdivision of clinical vision research, her most notable work was in the field of visual acuity, where he developed and improved equipment.
These ten optotypes , according to Sloan, were specifically chosen from capital letters of the alphabet in an article written in 1959 , in order to reduce the existing inefficiencies present in other visual acuity test charts. The set consists of the letters Z, N, H, R, V, K, D, C, O and S , chosen for their qualities of consisting of horizontal, vertical, curved and inclined lines, which helps to perform " subjective tests for determination of the refractive error Compared to the letters Snellen, the letters Sloan have no serifs, although they follow the traditional principle that "the overall height and width are five times the width of the strokes." They are particularly effective in identifying the astigmatism.
Sloan Chart
- LogMAR Chart -
In 1976, Ian Bailey and Jan E Lovie-Kitchin , from the National Vision Institute of Australia, proposed a new graphic layout, describing their concept as follows:
"We designed a series of close-up graphics in which the font, size progression, size range, number of words per line and spacing were chosen in an effort to achieve a standardized testing task." 12
This layout replaces the Snellen rectangular chart format with a variable number of letters per line with a triangular one with five spatially proportional letters on each line.
The ten Sloan Optotypes appear on the Bailey-Lovie Chart using the same letter-to-height ratio equal to five stroke widths, excluding serifs.
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The Bailey-Lovie Chart, also called LogMAR, a term that describes the geometric notation used to express visual acuity. The "Logarithm of the Minimum Resolution Angle" or (LogMAR) tests, in 1984, were selected as the standard for visual acuity tests by the International Council of Ophthalmology.
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The LogMAR chart comprises lines of letters and is used by ophthalmologists, optometrists and vision scientists to estimate visual acuity. When using the LogMAR graph, visual acuity is marked with a minimum Resolution Angle's Log reference , as the name of the graph suggests.
An observer who can resolve details as small as 1 minute of visual angle score LogMAR 0, since the base 10 logarithm of a 0; an observer who can resolve details as small as 2 minutes of visual angle (ie, decreased acuity) marks LogMAR 0.3, since the base 10 logarithm of 2 is almost approximately 0.3; and so on.
- A World Standard -
In 1982, when the National Eye Institute needed standardized graphics for its " Diabetic Retinopathy Early Treatment Study" (ETDRS) , Dr. Rick Ferris combined the logarithmic progression and logarithmic format of Green and Bailey-Lovie Charts with the Lyrics Sloan. ETDRS charts use equal spacing between letters and lines, making the acuity chart more balanced. This graphic format has been accepted by the National Eye Institute and the FDA, and is mandatory for many clinical trials conducted worldwide.
The ETDRS test is more accurate than the Snellen or Sloan versions because the lines contain the same number of letters, the lines and letters are evenly spaced on a log scale, and the individual lines are balanced for letter difficulty. There are also three different versions of the test available to prevent memorization.
A limitation of the original ETDRS chart is the use of the Latin alphabet, making it difficult to use across Europe. To address this limitation, the Tumbling E and Landolt C graphics are used for populations who are not familiar with letters of the Latin alphabet. Recently, a modified ETDRS chart was developed using Latin, Greek and Cyrillic alphabets. For this chart, the standard letters C, D, N, R, S, V and Z have been replaced by the letters E, P, X, B, T, M and A. These letters are created using the same 5 x 5 grid and the Sloan Letters.
ETDRS Chart