Eye chart

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Eye chart
Snellen chart.svg
Snellen chart used for visual testing. In this case, the chart should be 20 feet from the eyes.
UsesVision testing
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An eye chart is a chart used to measure visual acuity comprising lines of optotypes in ranges of sizes. Optotypes are the letters or symbols shown on an eye chart. [1] Eye charts are often used by health care professionals, such as optometrists, physicians and nurses, to screen persons for vision impairment. Ophthalmologists, physicians who specialize in the eye, also use eye charts to monitor the visual acuity of their patients in response to various therapies such as medications or surgery.

Contents

The chart is placed at a standardized distance away from the person whose vision is being tested. The person then attempts to identify the optotypes on the chart, starting with the larger ones and continuing with progressively smaller ones until the person cannot identify the optotypes. The size of the smallest optotypes that can be reliably identified is considered the person's visual acuity.

The Snellen chart is the most widely used. Alternative types of eye charts include the logMAR chart, Landolt C, E chart, Lea test, Golovin–Sivtsev table, the Rosenbaum chart, and the Jaeger chart. Eye charts do not provide doctors with information on eye diseases such as glaucoma, problems with the retina, or loss of peripheral vision. [2]

History

The concept of using eye glasses in order to improve eyesight has been prevalent since the late thirteenth century. [3] As science progressively improved, reputable doctors within the ophthalmology field like Franciscus Cornelius Donders began to describe a clear definition as to what should be done in order to improve impairments of a patient's vision. Although it slowly became clear which procedures benefitted patients, there was no uniform test to document impairment and improvement in someone's vision. Around this time, the knowledge within the field of ophthalmology grew immensely. [4]

To measure visual acuity, in 1835 German ophthalmologist, Heinrich Küchler, made the first eye chart consisting of pictures of objects of decreasing size that patients were to identify. In 1843, he published another chart comprising alphabetic letters . [3] In 1854, Austrian ophthalmologist, Eduard Jaeger created a chart comprising paragraphs with decreasing font sizes to test near vision acuity. [5] In 1862, the then most effective and popular chart to test visual acuity was published by Dutch ophthalmologist Herman Snellen. [6] Snellen was Donders' first assistant. [7] [8]

Because of Donders' fame and Snellen's natural talent towards the field of ophthalmology, many doctors were enticed to visit in order to share ideas with them in Utrecht. [8] As he worked closely through his practice, Snellen created his own chart that measured visual acuity. [9] Snellen's eye chart became the first of its type, hence it being the most scientifically reliable design in order to test vision distance in that time period. [6] Snellen's success within his charts was because they differed from past models that measured visual acuity. His chart varied the sizes of stimuli. [10] Snellen's eye chart opened the door to testing visual acuity, hence it became the global standard. [11]

The high demand for this chart was everywhere. Even japanese ophthalmologist Ema Tenko, who studied under Snellen, created an eye chart that was used in Japan. [12] Because of the creation of eye charts, examinations like vision screening (roughly beginning in 1899) within schools took place in order to test children's eyes. [13]

Procedure

Charts display several rows of optotypes, which are standardized symbols for testing vision. Optotypes are usually letters, numbers, or geometric symbols. Each row of the chart depicts optotypes of a different size. Typically the largest optotypes are in the top row. The optotypes become progressively smaller towards the bottom of the chart.

The person removes any glasses or contact lenses, and stands or sits a standardized distance from the chart (e.g., 20 feet for the Snellen chart). [14] The person is then asked to identify the optotypes on the chart, starting with large rows and continuing to smaller rows until the optotypes cannot be reliably identified any more. The row in which the person can reliably identify symbols defines the visual acuity.

One eye is tested at a time. Practically, this is accomplished by covering the other eye with a hand, piece of paper, or a small paddle. After testing without glasses or contact lenses, testing is repeated while the person wears them, if applicable. [15] Often, the use of such refractive lenses will correct visual acuity to normal. Refractive error can be corrected using a pinhole occluder. If the visual acuity improves with the use of pinholes, refractive lenses can be utilized to improve visual acuity. Squinting can achieve the same effect as a pinhole occluder.

With the Snellen chart, the visual acuity is recorded as a fraction with 20 in the numerator (top number) and values ranging from 10 to 600 in the denominator (bottom number). The denominator indicates the distance in feet at which a person with normal vision could stand to correctly identify the same symbols identified by the person tested. For example, a visual acuity of 20/20 is considered normal.

Variations

An example of the Landolt C eye chart (also known as the Japanese eye chart.) Japanese eye chart.JPG
An example of the Landolt C eye chart (also known as the Japanese eye chart.)

Numerous types of eye charts exist and are used in various situations. For example, the Snellen chart is designed for use at 6 meters or 20 feet, and is thus appropriate for testing distance vision, while the ETDRS chart is designed for use at 4 meters. [16] There is often also a need to test a subject's vision at near or occupational tasks (such as reading or computer use). For these situations, a Rosenbaum chart or Jaeger chart can be used. [17]

While the Snellen chart remains the default, some authors have argued that the logMAR chart is superior. [18] The logMAR chart presents the same number of symbols on each line, uses a typeface with letters that are equally legible at various sizes, and by varying the symbol size logarithmically, it is easier to use at nonstandard distances. As a consequence of these improvements, the logMAR chart has been proposed as a more reliable tool for measuring visual acuity.

It can be difficult to measure visual acuity in infants, young children, and illiterate adults. Special eye charts such as Lea Symbols can be used. One version uses simple pictures or patterns. Others are printed with the block letter "E" turned in different orientations, the so-called Tumbling E. The patient simply indicates which direction each "E" is facing. The Landolt C chart is similar: rows have circles with different segments missing, and the test-taker describes where each broken piece is located. The last two kinds of charts also reduce the possibility of the patient guessing the images. [19]

Parents and caregivers may test their child's eyesight from home to identify potential vision problems that require an eye care professional. Testing a child age three and older can be accomplished using the Tumbling E chart to play the "pointing game". For this test, the child sits in a chair 10 feet from the chart, gently holding an eye cover over one eye. The parent or caregiver points to each E, starting with the largest E. The child then points in the direction the E is facing (up, down, left, right). The smallest line with Es identified by the child can be recorded. The various directions the E can face should be reviewed with the child prior to home testing. Home tests are not as accurate as exams conducted by professional ophthalmologists. At home eye tests should not replace a visit to a professional eye care physician. [20] [21]

Alternatives

Computer-based alternatives to the eye chart have been developed, but are not very common prior to smart phones with high display resolution and DPI becoming popular. [22] They have several potential advantages, such as a more precise measurement, less examiner-induced bias and randomized optotypes.

If the person, particularly a young child, is unable to cooperate with visual acuity testing via an eye chart, practitioners can be alerted to possible deficits in visual acuity by asking parents whether the child appears to see well. A clue is that the child may hold objects close to the face when attempting to focus. [23] Refractive error can be estimated via photography, a technique called photoscreening. [24]

Technical details

Optotype Crowding

Research has shown that optotype "crowding" reduces visual acuity at the fovea (as opposed to eccentric visual acuity) once the optotype characters are closer than 4.4 bar widths apart. [25] This is referred to as the "critical spacing" for optotype letters at the fovea. For periphery visual acuity, the critical spacing is much greater, such that optotype characters closer than 15-20 bar widths apart negatively affect visual acuity. [26]

See also

Related Research Articles

<span class="mw-page-title-main">Visual acuity</span> Clarity of vision

Visual acuity (VA) commonly refers to the clarity of 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 influence the sharpness of an image on its retina. Neural factors include the health and functioning of the retina, of the neural pathways to the brain, and of the interpretative faculty of the brain.

<span class="mw-page-title-main">Snellen chart</span> Eye 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 professor Franciscus Cornelis Donders. Many ophthalmologists and vision scientists now use an improved chart known as the LogMAR chart.

<span class="mw-page-title-main">Eye examination</span> Series of tests assessing vision and pertaining to the eyes

An eye examination is a series of tests performed to assess vision and ability to focus on and discern objects. It also includes other tests and examinations pertaining to the eyes. Eye examinations are primarily performed by an optometrist, ophthalmologist, or an orthoptist. Health care professionals often recommend that all people should have periodic and thorough eye examinations as part of routine primary care, especially since many eye diseases are asymptomatic.

<span class="mw-page-title-main">Amsler grid</span> Tool to detect defects in central vision

The Amsler grid, used since 1945, is a grid of horizontal and vertical lines used to monitor a person's central visual field. The grid was developed by Marc Amsler, a Swiss ophthalmologist. It is a diagnostic tool that aids in the detection of visual disturbances caused by changes in the retina, particularly the macula, as well as the optic nerve and the visual pathway to the brain. Amsler grid usually help detecting defects in central 20 degrees of the visual field.

<span class="mw-page-title-main">Herman Snellen</span> Dutch ophthalmologist (1834–1908)

Herman Snellen was a Dutch ophthalmologist who introduced the Snellen chart to study visual acuity (1862). He took over directorship of the Netherlands Hospital for Eye Patients, after Franciscus Donders.

<span class="mw-page-title-main">Landolt C</span> Optotype

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.

<span class="mw-page-title-main">Lea test</span>

The LEA Vision Test System is a series of pediatric vision tests designed specifically for children who do not know how to read the letters of the alphabet that are typically used in eye charts. There are numerous variants of the LEA test which can be used to assess the visual capabilities of near vision and distance vision, as well as several other aspects of occupational health, such as contrast sensitivity, visual field, color vision, visual adaptation, motion perception, and ocular function and accommodation (eye).

<span class="mw-page-title-main">Defocus aberration</span> Quality of an image being out of focus

In optics, defocus is the aberration in which an image is simply out of focus. This aberration is familiar to anyone who has used a camera, videocamera, microscope, telescope, or binoculars. Optically, defocus refers to a translation of the focus along the optical axis away from the detection surface. In general, defocus reduces the sharpness and contrast of the image. What should be sharp, high-contrast edges in a scene become gradual transitions. Fine detail in the scene is blurred or even becomes invisible. Nearly all image-forming optical devices incorporate some form of focus adjustment to minimize defocus and maximize image quality.

<span class="mw-page-title-main">Eduard Jäger von Jaxtthal</span> Austrian ophthalmologist

Eduard Jäger von Jaxtthal was an Austrian ophthalmologist who was a native of Vienna. He was a professor at the University of Vienna, and was son to oculist Friedrich Jäger von Jaxtthal (1784-1871), and grandson to Georg Joseph Beer (1763-1821).

<span class="mw-page-title-main">E chart</span>

An E chart, also known as a tumbling E chart, is an ophthalmological chart used to measure a patient's visual acuity.

<span class="mw-page-title-main">Golovin–Sivtsev table</span> Standardized table for testing visual acuity

The Golovin–Sivtsev table 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 the most common table of its kind, and as of 2008 its use is still widespread in several post-Soviet states.

<span class="mw-page-title-main">Pinhole occluder</span> Ophthalmological testing tool

A pinhole occluder is an opaque disk with one or more small holes through it, used by ophthalmologists, orthoptists and optometrists to test visual acuity. The occluder is a simple way to focus light, as in a pinhole camera, temporarily removing the effects of refractive errors such as myopia. Because light passes only through the center of the eye's lens, defects in the shape of the lens have no effect while the occluder is used. In this way, the ophthalmologist, orthoptist or optometrist can estimate the maximum improvement in a patient's vision that can be attained by lenses to correct errors of refraction. This can be used to distinguish visual defects caused by refractive error, which improve when the occluder is used, from other problems, which do not. The pinhole occluder can also be used in testing visual acuity in mydriatic patients. In this case, the pinhole occluder compensates for the inability to contract the iris assisting the eye in obtaining a retinal projection similar to that of a non-cycloplegic eye.

<span class="mw-page-title-main">LogMAR chart</span> Eye chart

A logMAR chart is a chart consisting of rows of letters that is used by ophthalmologists, orthoptists, optometrists, and vision scientists to estimate visual acuity. The chart was developed at the National Vision Research Institute of Australia in 1976, and is designed to enable a more accurate estimate of acuity than do other charts. For this reason, the LogMAR chart is recommended, particularly in a research setting.

<span class="mw-page-title-main">Prism cover test</span>

The prism cover test (PCT) is an objective measurement and the gold standard in measuring strabismus, i.e. ocular misalignment, or a deviation of the eye. It is used by ophthalmologists and orthoptists in order to measure the vertical and horizontal deviation and includes both manifest and latent components. Manifest is defined by the eye deviating constantly or intermittently, whereas latent is where the deviation is normally controlled but becomes present when the eyes are dissociated. A PCT reveals the total deviation and cannot distinguish between latent and manifest strabismus as you are using an alternate cover test.

<span class="mw-page-title-main">Subjective refraction</span> Technique to determine the combination of lenses that will provide the best corrected visual acuity

Subjective Refraction is a technique to determine the combination of lenses that will provide the best corrected visual acuity (BCVA). It is a clinical examination used by orthoptists, optometrists and ophthalmologists to determine a patient's need for refractive correction, in the form of glasses or contact lenses. The aim is to improve current unaided vision or vision with current glasses. Glasses must also be comfortable visually. The sharpest final refraction is not always the final script the patient wears comfortably.

Childhood cataract is cataract that occurs at birth or in childhood. It may be congenital or acquired.

The Jaeger chart is an eye chart used in testing near vision acuity. It is a card on which paragraphs of text are printed, with the text sizes increasing from 0.37 mm to 2.5 mm. This card is to be held by a patient at a fixed distance from the eye dependent on the J size being read. The smallest print that the patient can read determines their visual acuity. The original 1867 chart had a text containing seven paragraphs and a corresponding seven-point scale.

<span class="mw-page-title-main">Louise L. Sloan</span> Vision scientist (1898-1982)

Louise Littig Sloan was an American ophthalmologist and vision scientist. She is credited for being a pioneer of the sub-division of clinical vision research, contributing more than 100 scientific articles in which she either authored or co-authored. Her most notable work was in the area of visual acuity testing where she developed and improved equipment. Sloan received her Ph.D. from Bryn Mawr College in experimental psychology. She spent a short period of time in both Bryn Mawr's experimental psychology program as well as the Department of Ophthalmology at Harvard Medical School. The majority of her career, however, was spent at Johns Hopkins Wilmer Eye Institute where she directed the Wilmer Laboratory of Physiological Optics for 44 years. In 1971, Sloan was the second woman awarded the prestigious Edgar D. Tillyer Award by Optica (formerly Optical Society for her many achievements in the field of vision.

The MNREAD acuity chart or Minnesota low vision reading chart is a text based chart used to measure near visual acuity in people with normal or low vision. It can also be used to measure maximum reading speed, critical print size and the reading accessibility index of a person. Digital and printed types of charts are available.

<span class="mw-page-title-main">Ophthalmic trial frame</span> Tool used in eye examination

A trial frame is a tool used by ophthalmic professionals like ophthalmologists and optometrists. It is basically an adjustable spectacle frame with multiple cells, used to hold corrective lenses, and other accessories in subjective refraction and retinoscopy.

References

  1. ↑ Nottingham Chaplin, P. Kay, and Geoffrey E. Bradford. "A Historical Review of Distance Vision Screening Eye Charts: What to Toss, What to Keep, and What to Replace." NASN School Nurse, vol. 26, no. 4, July 2011, pp. 221–228, doi : 10.1177/1942602X11411094
  2. ↑ Vimont, Celia. "All About the Eye Chart". American Academy of Ophthalmology. American Academy of Ophthalmology. Retrieved 6 November 2020.
  3. 1 2 Vogel, Wolfgang H., and Andreas Berke. Brief History of Vision and Ocular Medicine. Kugler Publications, 2009.
  4. ↑ Schett, A., and C. R. Keeler. The Ophthalmoscope. Wayenborgh Publishing, 2018.
  5. ↑ Azzam, Daniel, and Yasmyne Ronquillo. "Snellen Chart." StatPearls, StatPearls Publishing, 2021. PubMed, http://www.ncbi.nlm.nih.gov/books/NBK558961/ .
  6. 1 2 Rothenstein, Julian, and Mel Gooding, editors. A2Z+: Alphabets & Signs. Princeton Architectural Press, 2018.
  7. ↑ Schett, A., and C. R. Keeler. The Ophthalmoscope. Wayenborgh Publishing, 2018.
  8. 1 2 Snyder, Charles. Our Ophthalmic Heritage. 1967. Little, Brown and Company.
  9. ↑ Vimont, Celia. "All About the Eye Chart." American Academy of Ophthalmology, 25 Feb. 2021, https://www.aao.org/eye-health/tips-prevention/eye-chart-facts-history .
  10. ↑ Wade, Nicholas, and Mike Swanston. Visual Perception: An Introduction, 3rd Edition. Psychology Press, 2013.
  11. ↑ Goes, Frank Joseph. The Eye in History. JP Medical Ltd, 2013.
  12. ↑ Mishima, S. The History of Ophthalmology in Japan. Wayenborgh Publishing, 2018.
  13. ↑ Appelboom, Tina M. "A History of Vision Screening." Journal of School of Health 55, no. 4 (April 1985): 138-141
  14. ↑ "Medline Plus, Visual Acuity Test".
  15. ↑ "All About the Eye Chart". American Academy of Ophthalmology. 2021-02-25. Retrieved 2021-10-27.
  16. ↑ VALIDITY OF OUTCOME MEASURES. Canadian Agency for Drugs and Technologies in Health. August 2015.
  17. ↑ "Home vision tests: MedlinePlus Medical Encyclopedia". www.nlm.nih.gov. Retrieved 2015-05-09.
  18. ↑ Hussain, Badrul; Saleh, George M; Sivaprasad, Sobha; Hammond, Christopher J (2006). "Changing from Snellen to LogMAR: debate or delay?". Clinical and Experimental Ophthalmology. 34 (1): 6–8. doi:10.1111/j.1442-9071.2006.01135.x. PMID   16451251. S2CID   44724633.
  19. ↑ "Vision screening in infants, children and youth". Paediatrics & Child Health. 14 (4): 246–248. April 2009. doi:10.1093/pch/14.4.246. ISSN   1205-7088. PMC   2690539 . PMID   20357924.
  20. ↑ "What Is a Visual Acuity Test?". Optometrists Network. Optometrists Network. Retrieved 6 November 2020.
  21. ↑ Repka, Michael. "Home Eye Test for Children and Adults". American Academy of Ophthalmology. American Academy of Ophthalmology. Retrieved 6 November 2020.
  22. ↑ Claessens, Janneau L. J.; Geuvers, Judith R.; Imhof, Saskia M.; Wisse, Robert P. L. (2021-06-25). "Digital Tools for the Self-Assessment of Visual Acuity: A Systematic Review". Ophthalmology and Therapy. 10 (4): 715–730. doi:10.1007/s40123-021-00360-3. ISSN   2193-8245. PMC   8225487 . PMID   34169468.
  23. ↑ Hagan, JF (2008). Futures: Guidelines for Health Supervision. Elk Grove.
  24. ↑ "Photoscreening – EyeWiki". eyewiki.aao.org. Retrieved 2015-05-09.
  25. ↑ "Amblyopia - EyeWiki". eyewiki.aao.org. Retrieved 2019-05-20.
  26. ↑ Coates, D. R; Chin, J. M; Chung, S. T (2013). "Factors Affecting Crowded Acuity: Eccentricity and Contrast". Optometry and Vision Science. 90 (7): 628–638. doi:10.1097/OPX.0b013e31829908a4. PMC   3837536 . PMID   23770657.
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