My graphic design students have intercourse to design card using the classic eye chart composition , and they frequently ask “ What face should I use for this ? ” Not accept a classic answer has always been frustrating , so I decided to inquire to line up out what typeface is used on center chart .
I started my quest by asking my ophthalmologist , who enthusiastically allow a dizzying amount of expert entropy about the variety of heart charts and test plan for dissimilar consultation and middle conditions . Suddenly , a simple head became a series of discoveries . Not only is there no one letterform design or font used for oculus charts ; the letterform aim are more suitably called optotypes , of which there are several versions . There is a science to the pattern of optotypes and their legibility at specific distances .
Since I am a in writing designer and not an eye or sight expert , I will forgo the technical account and focus on optotypes used on several pregnant charts to provide a dependable understanding of this complex and fascinating topic .
centre chart are designed to test ocular acuity , or pellucidity of imagination . Each chart design has limitations and advantage , depending on the clinical setting , patient visibility , and diagnostic object lens . To understand the differences between the chart , it is helpful to know a lilliputian historical background of standardized optical acuity examination .
The First Standardized Tests
Heinrich Küchler is one of the first individuals credited with creating an eye chart to try out ocular acuity .
Küchler , a German ophthalmologist , designed a chart in 1836 using number reduce from calendars , books , and newspapers glue in rows of decrease sizes onto paper . These figures included cannons , guns , bird , farm equipment , camels , and frogs . This system was limited because the figure were not consistent in optical weight or flair .
Dr. Küchler extend to elaborate his chart , and in 1843 , published a fresh version using 12 row of Blackletter letter diminish in size . This chart was not widely adopted ( hard to reckon why ) and was published only once in 1843.1
The next meaning ontogenesis in visual acuity chart design was the Snellen Eye Chart , which is recognisable to most Americans from visit to the DMV .
The Snellen Eye Chart was designed by Dutch ophthalmologist Herman Snellen in 1862 as a way to improve the immanent nature of vision testing , which was usually accomplished by having patient record a passage of schoolbook throw their hands , or held at a aloofness by the doc . This test had obvious limitations : the results were dependent upon the recitation ability of the patient , the legibility of the typeface used , and the fact that the patient role could opine the next watchword by reading a sentence . accord to Dr. August Colenbrander , a scientist at the Smith - Ketterwell Eye Research Institute and an expert on eye chart design , Snellen begin experimenting with dingbat , or symbolic representation such as squares and circles for his optic chart , but detect that it was difficult for trial case to describe the symbolisation accurately.2
So , he go on to using letters . The characters on the first Snellen Charts were : A , C , E , G , L , N , P , R , T , 5 , V , Z , B , D , 4 , F , H , K , O , S , 3 , U , Y , A , C , E , G and L. The letter used were Egyptian Paragons or slab seriph of contrast cable heaviness with cosmetic hybridizing strokes on terminal . Snellen then theorized that test subjects would be able to distinguish non - ornamented , monoline / equally weighted letters of consistent visual size more well , and so he make optotypes.3
At first glance , it may appear that the Snellen optotypes are Lubalin Graph or Rockwell . But upon detailed exam , it is apparent that these characters are rather atypical . Unlike typical font in which missive proportions are determined by ‘ family ’ groupings ( such as n , r , m , h and u ) , Snellen optotypes are designed on a 5 x 5 power system . moreover , they comprise a very limited fictional character - set of just 9 - 10 letters . Optotypes are design using a bare geometry in which the weight of the job is equal to the negative space between lines . The height and width of an optotype is five times the thickness of the line weight.4These design considerations produce inconsistently and curiously proportioned letter . For example , in a typical typeface , C and D would appear wide of the mark than Z , but in the optotype dodge , the opposition is true .
Dr. Snellen produce Optotypes using minutes of arc rather of a typographic value system . This made it potential for his charts to be reproduced easily . The first heavy order for Snellen Charts was from the British Army in 1863 . From there , the Snellen Eye Chart became the banner for vision test for almost a century . In summation , Snellen ’s 5 x 5 control grid optotype design is the foot upon which all other optic chart scheme are establish . The Snellen Eye Chart is still the most agnise conception , which can , to some extent , contradict its strength , if , for example , the tryout field has memorized the chart.5
Most Snellen Charts hold eleven lines of engine block letters . The first line consists of a single prominent varsity letter , most often an E. Subsequent course have increasing phone number of letters that are increasingly modest in sizing . The test topic , from a length of 20 foot , cover one oculus , and , set out at the top , reads aloud the letters in each row . The smallest row that can be read accurately indicates the visual acuity in that particular eye.6
Current Snellen Charts practice nine varsity letter , C , D , E , F , L , O , P , T , Z. Note that with the exception of E and O , the letters are all consonants . The diverse shapes of the optoypes let test subjects to identify verticals , horizontals , and diagonal . These letter of the alphabet shapes are also extremely effective in name astigmia .
Although today ’s Snellen Eye Charts may vary in the number of rows , size step , and serif or sans serif design,7their commons admit the rectangular shape . This dictates the vary numbers of optotypes appearing on each line as space permits.8
As a result of continual refinement , most of today ’s Snellen Charts follow logarithmic procession , have improved alphabetic character plan , and a unvarying 25 % progression from course to line.9
Refinements and Variations
In 1868 , Dr. John Green of the St. Louis College of Physicians and Surgeons in Missouri decided to make some changes to the Snellen Eye Chart . He designed a more structured grid sport a uniform logarithmic geometrical advancement of 25 % for successive lines , and with proportional spacing . He also commute the mode of the optotypes from the blocky slab serif to sans serif . His construct became known as the “ Preferred Numbers Series , ” but his system did not become wide know until the next century when sans serif typography gain popularity . Ironically , in response to criticism that his letters looked “ bare ” , Dr. Green abandoned them in 1872 , and returned to the serif optotypes.10
In 1959 , Dr. Louise Sloan of Johns Hopkins University created ten new optotypes using sans serif letter preferred by Dr. Green . These optotypes included the letter : C , D , H , K , N , O , R , S , V , and Z. Like Snellen letters , Sloan Letters are form within a square , with the stroke width equal to one - fifth of the letter elevation and with equal visual free weight . The Sloan Chart has coherent spacing between letters and rows that are proportional to letter size . Spacing between letter is adequate to letter width , and spacing between rows is adequate to the height of the letter in the subsequent , smaller row.11Notice that , as in the Snellen Chart , all of the characters are consonant with the exception of 0 . Also note that the missive pick used on the Snellen Chart is not the same as that in the Sloan Chart . In both cases , the diverse shapes of the optoypes allow test subjects to name verticals , horizontal and diagonal — an help to discover or differentiate individual letters . The ten Sloan Letters are considered to be the most effective letter selection for adequate discernability . What ’s more , they are particularly effective at key out astigmatism .
The Sloan Letters may at first glimpse resemble Microgramma orEurostile fonts , but upon closer examination , it is evident again that the grid data format bring down upon these optotypes produces some curious and inconsistently proportioned letter of the alphabet .
New Charts and Methods
In 1976 , Ian Bailey and Jan E Lovie - Kitchin of the National Vision Institute of Australia nominate a newfangled chart layout , describing their concept as be :
We have design a series of near vision chart in which the typeface , size progression , size range , number of words per words and spacings were chosen in an endeavor to accomplish a standardisation of the test task.12
This layout exchange the Snellen rectangular chart format with a variable issue of letters per line with a triangular one with five proportionally space letters on each billet . The ten Sloan Optotypes appear on the Bailey - Lovie Chart using the same letter ratio of the varsity letter - peak adequate to five throw widths , excluding serifs .
The Bailey - Lovie Chart is an example of a LogMAR psychometric test , a term describing the geometric notational system used to extract visual acuity . “ Logarithm of the Minimum Angle of Resolution ” or ( LogMAR ) run , were selected , in 1984 , as the standard for visual acuteness testing by the International Council of Ophthalmology.13
In 1982 , when the National Eye Institute needed standardized chart for its “ Early Treatment of Diabetic Retinopathy Study ” ( ETDRS ) , Dr. Rick Ferris combined the Green and Bailey - Lovie Charts ’ logarithmic progression and data formatting with the Sloan Letters . ETDRS charts use equal space between alphabetic character and lines , making the acuity graph more balanced.14This chart format has been accepted by the National Eye Institute and the FDA , and is mandate for many clinical trials perform worldwide .
The ETDRS test is more accurate than either the Snellen or Sloan versions because the rows contain the same number of letters , the rows and letters are equally spaced on a log scurf , and individual row are balanced for missive trouble . There are also three different edition of the test available to deter memorization.15
One limitation of the original ETDRS chart is its use of the Latin alphabet , making it hard to use throughout all of Europe . To address this restriction , the Tumbling E and Landolt C chart are used for population who are unfamiliar with letters of the Latin alphabet . Recently , a modified ETDRS chart was developed using Latin , Greek , and Cyrillic ABCs . For this chart , the standard letter of the alphabet 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 create using the same 5 x 5 grid and the Sloan Letters.16
In more late year there has been a move to create electronic chart , including the British - designed Test Chart 2000 , which was the world ’s first Windows - based computerized run chart . It overcomes several hard issues such as screenland contrast , and provide the chance to change the letter successiveness , so that it can not be memorized.17
These fonts , for Mac and Windows OSs , are uncommitted for inquiry purposes . The fonts are ground on Louise Sloan ’s designs , which has been designated the US standard for sharpness testing by the National Academy of Sciences , National Research Council , Committee on Vision.18
Charts for Non-Readers
For testing patients who can not read or for those unfamiliar with the Latin alphabet , the Tumbling tocopherol Eye Chart and the Landolt C or Broken Ring Chart are used.19
The tumble atomic number 99 Chart was designed by Professor Hugh Taylor of the Centre for Eye Research Australia ( CERA ) in 1978 to test the imaginativeness of Australian Aborigine individuals in an attempt to identify those with the eye upset , Trachoma .
Professor Taylor , using the Snellen proportions , designed a human body resemble an uppercase eastward , which he set up in four direction ( up , down , right , and left ) in progressively smaller size . The patient then but describes the direction in which the twig vitamin E is facing .
The Landolt C or Broken Ring Eye Chart is also used for illiterate mortal or those persons unfamiliar with the Latin first rudiment . create by Swiss eye doctor Edmund Landolt , this test is now considered the European monetary standard . The Broken Ring ( which is the same proportions as the C from the Snellen and Sloan Charts ) is rotated by increments of 90 ° . The minimum understandable slant of the snow - break is the measurement of visual acuity.20
In accession to the topple E and Landolt light speed tests , there are charts for children in which progressively small , simple-minded pictograms of object are used . The challenge in designing these chart is creating recognizable pictograms of equal visual weight , reproducible style , and intent .
This article is not an thoroughgoing inquiry subject into the subject of center charts or their efficaciousness . There are many more model of center chart . My objective was to research the pilot of optotype design in the evolution of the center chart as a symptomatic tool . Now I can tell my scholarly person that there is , technically , not a single typeface to commend for their design ; and I can look up them to this article for more information ! study optotypes has been an eye - opening experience .
Lorrie Frearis an Associate Professor in the School of Design / College of Imaging Arts and Sciences at the Rochester Institute of Technology in Rochester , New York , where she teaches in writing design and calligraphy . Go hereto see additional footnote and author .
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