Near visual acuity

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Near visual acuity
N notation reading chart.jpg
N notation reading chart in English and Hindi languages

Near visual acuity or Near vision is a measure of how clearly a person can see nearby small objects or letters. Near vision is usually measured and recorded using a printed hand-held card containing different sized paragraphs, words, letters or symbols. Jaeger chart, N notation reading chart and Snellen's near vision test are the commonly used charts for measuring and recording near visual acuity. Near vision testing is usually done after correcting the distance vision.

Contents

Eye conditions like presbyopia, accommodative insufficiency, cycloplegia etc. can affect the near visual acuity. According to the World Health Organization, the near visual acuity less than N6 or M0.8 at 40 cm is classified as near visual impairment.

Physiology of near vision

Duane's classical curves showing the amplitude or width of accommodation as changing with age. Mean (B) and approximate lower (A) and upper (C) standard deviations are shown. Duane (1922) Fig 4 modified.svg
Duane's classical curves showing the amplitude or width of accommodation as changing with age. Mean (B) and approximate lower (A) and upper (C) standard deviations are shown.

In human, near vision is obtained by a mechanism called accommodation. With the help of accommodation, a normal young human eye can change focus from distance (infinity) to as near as 6.5 cm from the eye. [2] [3] This change in focal power of the eye of approximately 15 diopters (the reciprocal of focal length in meters) occurs as a consequence of a reduction in zonular tension induced by ciliary muscle contraction. This process can occur in as little as 224 ± 30 milliseconds in bright light. [4]

The amplitude of accommodation declines with age. The dependency of accommodation amplitude on age is graphically summarized by Duane's classical curves. [1]

Near vision impairment

The difficulty in reading small prints or blurring at a reading distance is commonly defined as Near vision impairment (NVI). Difficulty with near vision increases with age. [5] Eye conditions like presbyopia, accommodative insufficiency, cycloplegia etc. can affect the near visual acuity. Ocular diseases that cause defective distance vision like cataract and macular degeneration, can also cause reduced near vision. [5]

According to the World Health Organization, the near visual acuity less than N6 or M0.8 at 40 cm is classified as near visual impairment. [6]

Presbyopia

Presbyopia is physiological insufficiency of accommodation associated with the aging of the eye that results in defective near vision. [7] Management of presbyopia includes corrective glasses such as a special pair of reading glasses, contact lenses, bifocals, or progressive lenses. [8]

Insufficiency of accommoation

Insufficiency of accommoation also known as Accommodative insufficiency is another condition that causes blurring of the near vision. [9] Management of accommodative insufficiency needs correcting any underlying refractive errors. [9] Vision therapy may also help improving the condition. [9]

Cycloplegia

Cycloplegia is the paralysis of the ciliary muscle causing paralysis of accommodation and defective near vision. [10] Cycloplegia can be caused intentionally by instilling some medications into the eyes, or it can occur due to some neurological disorders, or trauma to the eye. [11]

Hypermetropia

Hypermetropia, the most common refractive error in childhood, affects the near vision more than distant vision. [12]

Tests for near vision

To measure near vision, a patient is seated in a well illuminated room is asked to read the handheld near vision chart kept at a distance of 25–35 cm away from the eye. [13] The distance used for near vision testing may vary depending on the occupation or basic need of the patient. [14] The smallest test type that the patient can read is the measure of his near acuity. Commonly used tests for near vision are described below.

Jaeger chart

The Jaeger chart is a card on which paragraphs of text are printed, with the text sizes increasing from 0.37 mm to 2.5 mm. [15] 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 near visual acuity. [16]

Roman test types

Roman test types also known as N notation reading charts or Point chart, [17] uses Times New Roman font, and records near visual acuity as N5, N6, N8, N10, etc. [13] N notation is the standard near vision test in the United Kingdom and Australia. [18]

M-scale notation

The M-scale indicate the distance in metres at which the height of a lower case 'x' letter subtends a visual angle of 5 minutes of arc at the nodal point of the eye. [18] The M system is said to have sufficient advantages over other systems for near vision testing to make it a universally accepted standard method. [19] M-scale notation is widely used in North America. [18]

Snellen's near vision test

Snellens near vision chart Snellens near vision chart.jpg
Snellens near vision chart

Snellen's near vision test is a near vision chart introduced by Dutch ophthalmologist Herman Snellen, which uses the same principle of his distance vision Snellen chart. [13] Size of Snellen's near vision chart is approximately 1/17th of the normal Snellen chart. [13]

Sloan Reading Cards

Sloan reading cards which uses continuous text paragraphs with logarithmic progression of optotype sizes, was a reading chart introduced in 1960s. [20] Near acuity was recorded as 1.0 M, 1.5 M, 2.0 M etc.

Bailey-Lovie Word Reading Charts

Bailey-Lovie charts introduced in 1980s, which measures reading acuity and reading speed, uses logarithmic progression of optotype sizes. [20]

MNREAD acuity chart

The MNREAD acuity chart is a text based chart used to measure near visual acuity in people with normal or low vision. [21] It can also be used to measure maximum reading speed, critical print size and the reading accessibility index of a person. [22] Digital and printed types of charts are available. [23]

Standardization of reading charts

The concept of logarithmic progression of optotype sizes for distance vision charts was introduced by John Green, in 1868. [24] However, apart from the reading chart developed by Birkhaeuser in 1911, none of the charts in use at the time were standardized. [20] Aiming to overcome the standardization problem of Jaeger charts, N-notation was introduced in 1950s, but this too was not fully logarithmic. [20] This was followed by the introduction of logarithmic Sloan reading cards in the early 1960s and then the Bailey-Lowey word reading charts in the 1980s.

Standardization criteria established by the International Council of Ophthalmology (ICO) or EN ISO 8596 directive include the reproducibility, comparability, validity, interpretability and reliability of reading tests. [25] Reading charts which uses a logarithmic progression of print sizes, like Sloan Reading Cards, the Bailey-Lovie Word Reading Charts, the MNREAD charts, the RADNER Reading Charts, the Colenbrander Continuous Text Near Vision Cards, the Smith-Kettlewell Reading Test, the Oculus Reading Probe II, the C-Read Charts and the Arabic-BAL Chart etc. are near vision charts that meet standardization criteria published by the ICO. [25]

Conversion

Near visual acuity conversion chart
RomanJaegerSnellen
(US)		Snellen
(Metric)		DecimalM unit
N4.5J120/206/61.000.5
N5J320/306/90.670.8
N6J520/406/120.501.0
N8J620/506/150.40-
N10J720/606/180.331.2
N12J920/806/240.25-
N14J1020/1006/300.201.3

source: [26] [27]

Related Research Articles

Cycloplegia is paralysis of the ciliary muscle of the eye, resulting in a loss of accommodation. Because of the paralysis of the ciliary muscle, the curvature of the lens can no longer be adjusted to focus on nearby objects. This results in similar problems as those caused by presbyopia, in which the lens has lost elasticity and can also no longer focus on close-by objects. Cycloplegia with accompanying mydriasis is usually due to topical application of muscarinic antagonists such as atropine and cyclopentolate.

<span class="mw-page-title-main">Presbyopia</span> Medical condition associated with aging of the eye

Presbyopia is physiological insufficiency of accommodation associated with the aging of the eye that results in progressively worsening ability to focus clearly on close objects. Also known as age-related farsightedness, it affects many adults over the age of 40. A common sign of presbyopia is difficulty reading small print which results in having to hold reading material farther away. Other symptoms associated can be headaches and eyestrain. Different people will have different degrees of problems. Other types of refractive errors may exist at the same time as presbyopia. This condition is similar to hypermetropia or far-sightedness which starts in childhood and exhibits similar symptoms of blur in the vision for close objects.

<span class="mw-page-title-main">Amblyopia</span> Failure of the brain to process input from one eye

Amblyopia, also called lazy eye, is a disorder of sight in which the brain fails to fully process input from one eye and over time favors the other eye. It results in decreased vision in an eye that typically appears normal in other aspects. Amblyopia is the most common cause of decreased vision in a single eye among children and younger adults.

<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 Cornelius Donders. Many ophthalmologists and vision scientists now use an improved chart known as the LogMAR chart.

<span class="mw-page-title-main">Eye chart</span> Chart used to measure vision

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. 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.

<span class="mw-page-title-main">Refractive error</span> Problem with focusing light accurately on the retina due to the shape of the eye

Refractive error is a problem with focusing light accurately on the retina due to the shape of the eye and/or cornea. The most common types of refractive error are near-sightedness, far-sightedness, astigmatism, and presbyopia. Near-sightedness results in far away objects being blurry, far-sightedness and presbyopia result in close objects being blurry, and astigmatism causes objects to appear stretched out or blurry. Other symptoms may include double vision, headaches, and eye strain.

<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">Accommodation (vertebrate eye)</span> Focusing ability of eye

Accommodation is the process by which the vertebrate eye changes optical power to maintain a clear image or focus on an object as its distance varies. In this, distances vary for individuals from the far point—the maximum distance from the eye for which a clear image of an object can be seen, to the near point—the minimum distance for a clear image. Accommodation usually acts like a reflex, including part of the accommodation-convergence reflex, but it can also be consciously controlled.

<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.

Accommodative insufficiency (AI) involves the inability of the eye to focus properly on an object. Accommodation is the adjustment of the curvature of the lens to focus on objects near and far.

<span class="mw-page-title-main">Emmetropia</span> State of vision

Emmetropia is the state of vision in which a faraway object at infinity is in sharp focus with the ciliary muscle in a relaxed state. That condition of the normal eye is achieved when the refractive power of the cornea and eye lens and the axial length of the eye balance out, which focuses rays exactly on the retina, resulting in perfectly sharp distance vision. A human eye in a state of emmetropia requires no corrective lenses for distance; the vision scores well on a visual acuity test.

<span class="mw-page-title-main">Blurred vision</span> Medical condition

Blurred vision is an ocular symptom where vision becomes less precise and there is added difficulty to resolve fine details.

Laser blended vision is a laser eye treatment which is used to treat presbyopia or other age-related eye conditions. It can be used to help people that simply need reading glasses, and also those who have started to need bifocal or varifocal spectacle correction due to ageing changes in the eye. It can be used for people who are also short-sighted (myopia) or long-sighted (hyperopia) and who also may have astigmatism.

<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">Duochrome test</span>

A duochrome test is a test commonly used to refine the final sphere in refraction, which makes use of the longitudinal chromatic aberration of the eye. Because of the chromatic aberration of the eye, the shorter wavelengths (green) are focused in front of the longer red wavelengths. It is assumed that best vision is attained when the yellow wavelengths are focused on the retina.

The Jaeger chart is an eye chart used in testing near visual 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.

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.

References

  1. 1 2 Duane, Alexander (1922). "Studies in Monocular and Binocular Accommodation with their Clinical Applications". American Journal of Ophthalmology. 5 (11): 865–877. doi:10.1016/s0002-9394(22)90793-7. S2CID   43172462.
  2. ↑ Chen, Ai Hong; O'Leary, Daniel J.; Howell, Edwin R. (2000). "Near visual function in young children". Ophthalmic & Physiological Optics. 20 (3): 185–198. doi:10.1016/S0275-5408(99)00056-3, Fig. 5.{{cite journal}}: CS1 maint: postscript (link)
  3. ↑ That value follows from the maximum accommodative power and can be calculated as 100 cm/15 dpt.
  4. ↑ Lockhart, T. E.; Shi, W. (2010). "Effects of Age on Dynamic Accommodation". Ergonomics. 53 (7): 892–903. doi:10.1080/00140139.2010.489968. PMC   2908311 . PMID   20582770.
  5. 1 2 Varadaraj, Varshini; Lee, Moon Jeong; Tian, Jing; Ramulu, Pradeep Y.; Bandeen-Roche, Karen; Swenor, Bonnielin K. (26 August 2019). "Near vision impairment and Frailty: Evidence of an association". American Journal of Ophthalmology. 208: 234–241. doi:10.1016/j.ajo.2019.08.009. ISSN   0002-9394. PMC   6888870 . PMID   31465753.
  6. ↑ "World report on vision". World Health Organization. p. 11. Retrieved 2022-03-03.
  7. ↑ Khurana, AK (September 2008). "Asthenopia, anomalies of accommodation and convergence". Theory and practice of optics and refraction (2nd ed.). Elsevier. pp. 100–107. ISBN   978-81-312-1132-8.
  8. ↑ "Presbyopia - EyeWiki". eyewiki.aao.org.
  9. 1 2 3 Enaholo, Ehimare S.; Musa, Mutali J.; Zeppieri, Marco (2024). "Accommodative Insufficiency". StatPearls. StatPearls Publishing. PMID   36508537.
  10. ↑ Kaur, Kirandeep; Gurnani, Bharat (2024). "Cycloplegic and Noncycloplegic Refraction". StatPearls. StatPearls Publishing. PMID   35593830.
  11. ↑ "Cycloplegia: The Eye Condition That Affects Your Ability to Focus Up Close".
  12. ↑ Majumdar, Soumyadeep; Tripathy, Koushik (2024). "Hyperopia". StatPearls. StatPearls Publishing. PMID   32809551.
  13. 1 2 3 4 Khurana (2008). Theory and Practice of Optics and Refraction. Elsevier India. p. 49. ISBN   9788131211328.
  14. ↑ Caltrider, David; Gupta, Abhishek; Tripathy, Koushik (2024). "Evaluation of Visual Acuity". StatPearls. StatPearls Publishing. PMID   33231977.
  15. ↑ Blesi, Michelle; Wise, Barbara; Kelley-Arney, Cathy (2011). Medical Assisting Administrative and Clinical Competencies. Cengage Learning. pp. 888–890. ISBN   978-1133706960.
  16. ↑ G.K. & Pal; Pal; Pravati (1 February 2006). Textbook Of Practical Physiology (2nd ed.). Orient Blackswan. pp. 328–. ISBN   978-81-250-2904-5.
  17. ↑ Houf, James W. (October 2009). "Understanding Near Vision Eye Tests". The American Society for Nondestructive Testing. 8 (4).
  18. 1 2 3 ELLIOTT, DAVID B (2007). Clinical Procedures in Primary Eye Care (3 ed.). Elsevier. pp. 38–41. ISBN   9780750688963.
  19. ↑ Jose, R. T.; Atcherson, R. M. (September 1977). "Type-size variability for near-point acuity tests". American Journal of Optometry and Physiological Optics. 54 (9): 634–638. ISSN   0093-7002. PMID   596414.
  20. 1 2 3 4 Radner, W. (2017). "Reading charts in ophthalmology". Graefe's Archive for Clinical and Experimental Ophthalmology. 255 (8): 1465–1482. doi:10.1007/s00417-017-3659-0. ISSN   0721-832X.
  21. ↑ Altinbay, Deniz; Adibelli, Fatih Mehmet; Taskin, Ibrahim; Tekin, Adil (2016). "The Evaluation of Reading Performance with Minnesota Low Vision Reading Charts in Patients with Age-related Macular Degeneration". Middle East African Journal of Ophthalmology. 23 (4): 302–306. doi: 10.4103/0974-9233.194078 . ISSN   0974-9233. PMC   5141623 . PMID   27994393.
  22. ↑ Calabrèse, Aurélie; Cheong, Allen M. Y.; Cheung, Sing-Hang; He, Yingchen; Kwon, MiYoung; Mansfield, J. Stephen; Subramanian, Ahalya; Yu, Deyue; Legge, Gordon E. (1 July 2016). "Baseline MNREAD Measures for Normally Sighted Subjects From Childhood to Old Age". Investigative Ophthalmology & Visual Science. 57 (8): 3836–3843. doi: 10.1167/iovs.16-19580 . ISSN   1552-5783. PMC   4961000 . PMID   27442222.
  23. ↑ Calabrèse, Aurélie; To, Long; He, Yingchen; Berkholtz, Elizabeth; Rafian, Paymon; Legge, Gordon E. (19 January 2018). "Comparing performance on the MNREAD iPad application with the MNREAD acuity chart". Journal of Vision. 18 (1): 8. doi: 10.1167/18.1.8 . ISSN   1534-7362. PMC   5774869 . PMID   29351351.
  24. ↑ Green, John (1868). "On a New Series of Test-Letters for determining the Acuteness of Vision". Transactions of the American Ophthalmological Society. 1 (4–5): 68–71. ISSN   0065-9533.
  25. 1 2 Ntonti, Panagiota; Mitsi, Christina; Chatzimichael, Eleftherios; Panagiotopoulou, Eirini-Kanella; Bakirtzis, Minas; Konstantinidis, Aristeidis; Labiris, Georgios (18 January 2023). "A systematic review of reading tests". International Journal of Ophthalmology. 16 (1): 121–127. doi:10.18240/ijo.2023.01.18. ISSN   2222-3959.
  26. ↑ "Near visual acuity conversion chart" (PDF). UK Civil Aviation Authority.
  27. ↑ "Print Comparison of Font Sizes". Teaching Students with Visual Impairments.
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