near visual acuity

File:Duane (1922) Fig 4 modified.svg

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.{{cite journal | last1 = Chen | first1 = Ai Hong | last2 = O'Leary | first2 = Daniel J. | last3 = Howell | first3 = Edwin R. | title = Near visual function in young children | journal = Ophthalmic & Physiological Optics| volume = 20 | issue = 3 | pages = 185–198 | year = 2000 | postscript= , Fig. 5. | doi = 10.1016/S0275-5408(99)00056-3 }}That value follows from the maximum accommodative power and can be calculated as 100 cm/15 dpt. 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.{{Cite journal |pmc = 2908311|year = 2010|last1 = Lockhart|first1 = T. E.|title = Effects of Age on Dynamic Accommodation|journal = Ergonomics|volume = 53|issue = 7|pages = 892–903|last2 = Shi|first2 = W.|pmid = 20582770|doi = 10.1080/00140139.2010.489968}}

The amplitude of accommodation declines with age. The dependency of accommodation amplitude on age is graphically summarized by Duane's classical curves.{{Cite journal |doi = 10.1016/s0002-9394(22)90793-7|title = Studies in Monocular and Binocular Accommodation with their Clinical Applications|journal = American Journal of Ophthalmology|volume = 5|issue = 11|pages = 865–877|year = 1922|last1 = Duane|first1 = Alexander| s2cid=43172462 |url = https://zenodo.org/record/1529034}}

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.{{Cite journal |last1=Varadaraj |first1=Varshini |last2=Lee |first2=Moon Jeong |last3=Tian |first3=Jing |last4=Ramulu |first4=Pradeep Y. |last5=Bandeen-Roche |first5=Karen |last6=Swenor |first6=Bonnielin K. |date=26 August 2019 |title=Near vision impairment and Frailty: Evidence of an association |journal=American Journal of Ophthalmology |volume=208 |pages=234–241 |doi=10.1016/j.ajo.2019.08.009 |issn=0002-9394 |pmc=6888870 |pmid=31465753}} 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.

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.{{Cite web |title=World report on vision |url=https://www.who.int/publications-detail-redirect/9789241516570 |page=11 |access-date=2022-03-03 |website=World Health Organization |language=en}}

Presbyopia is physiological insufficiency of accommodation associated with the aging of the eye that results in defective near vision.{{cite book |last1=Khurana |first1=AK |title=Theory and practice of optics and refraction |publisher=Elsevier |isbn=978-81-312-1132-8 |pages=100–107 |edition=2nd |chapter=Asthenopia, anomalies of accommodation and convergence|date=September 2008 }} Management of presbyopia includes corrective glasses such as a special pair of reading glasses, contact lenses, bifocals, or progressive lenses.{{cite web |title=Presbyopia - EyeWiki |url=https://eyewiki.aao.org/Presbyopia |website=eyewiki.aao.org}}

Insufficiency of accommodation also known as accommodative insufficiency is another condition that causes blurring of the near vision.{{cite journal |last1=Enaholo |first1=Ehimare S. |last2=Musa |first2=Mutali J. |last3=Zeppieri |first3=Marco |title=Accommodative Insufficiency |journal=StatPearls |date=2024 |url=https://www.ncbi.nlm.nih.gov/books/NBK587363/ |publisher=StatPearls Publishing|pmid=36508537 }} Management of accommodative insufficiency needs correcting any underlying refractive errors. Vision therapy may also help improve the condition.

Cycloplegia is the paralysis of the ciliary muscle causing paralysis of accommodation and defective near vision.{{cite journal |last1=Kaur |first1=Kirandeep |last2=Gurnani |first2=Bharat |title=Cycloplegic and Noncycloplegic Refraction |journal=StatPearls |date=2024 |url=https://www.ncbi.nlm.nih.gov/books/NBK580522/ |publisher=StatPearls Publishing|pmid=35593830 }} 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.{{cite web |title=Cycloplegia: The Eye Condition That Affects Your Ability to Focus Up Close |url=https://ophthalmologybreakingnews.com/cycloplegia--the-eye-condition-that-affects-your-ability-to-focus-up-close}}

Hypermetropia, the most common refractive error in childhood, affects the near vision more than distant vision.{{cite book |last1=Majumdar |first1=Soumyadeep |last2=Tripathy |first2=Koushik |title=StatPearls |date=2024 |publisher=StatPearls Publishing |url=https://www.ncbi.nlm.nih.gov/books/NBK560716/ |chapter=Hyperopia|pmid=32809551 }}

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. The distance used for near vision testing may vary depending on the occupation or basic need of the patient.{{cite journal |last1=Caltrider |first1=David |last2=Gupta |first2=Abhishek |last3=Tripathy |first3=Koushik |title=Evaluation of Visual Acuity |journal=StatPearls |date=2024 |url=https://www.ncbi.nlm.nih.gov/books/NBK564307/ |publisher=StatPearls Publishing|pmid=33231977 }} 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.

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.{{cite book |title=Medical Assisting Administrative and Clinical Competencies |first1=Michelle |last1=Blesi |first2=Barbara |last2=Wise |first3=Cathy |last3=Kelley-Arney |publisher=Cengage Learning |year=2011 |url=https://books.google.com/books?id=7XMJAAAAQBAJ&pg=PA888 |pages=888–890|isbn=978-1133706960 }} 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.{{cite book|author1=G.K. & Pal|author2=Pal|author3=Pravati|title=Textbook Of Practical Physiology|edition=2nd|url=https://books.google.com/books?id=XpUAihQ7Ib4C&pg=PA328|date=1 February 2006|publisher=Orient Blackswan|isbn=978-81-250-2904-5|pages=328–}}

Roman test types also known as N notation reading charts or Point chart,{{cite journal |last1=Houf |first1=James W. |title=Understanding Near Vision Eye Tests |journal=The American Society for Nondestructive Testing |date=October 2009 |volume=8 |issue=4 |url=https://www.asnt.org/~/media/Files/Publications/TNT/TNT_08-4.ashx}} uses Times New Roman font, and records near visual acuity as N5, N6, N8, N10, etc.{{cite book |title=Theory and Practice of Optics and Refraction |author=Khurana |publisher=Elsevier India |year=2008 |page=49 |isbn=9788131211328 |url=https://books.google.com/books?id=qYeD3VHi8OsC&pg=PA49}} N notation is the standard near vision test in the United Kingdom and Australia.{{Cite book |last=ELLIOTT |first=DAVID B |title=Clinical Procedures in Primary Eye Care |publisher=Elsevier |year=2007 |isbn=9780750688963 |edition=3 |pages=38–41 |language=English}}

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. The M system is said to have sufficient advantages over other systems for near vision testing to make it a universally accepted standard method.{{cite journal |last1=Jose |first1=R. T. |last2=Atcherson |first2=R. M. |title=Type-size variability for near-point acuity tests |journal=American Journal of Optometry and Physiological Optics |date=September 1977 |volume=54 |issue=9 |pages=634–638 |pmid=596414 |url=https://pubmed.ncbi.nlm.nih.gov/596414/ |issn=0093-7002}} M-scale notation is widely used in North America.

File:Snellens near vision chart.jpg

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. Size of Snellen's near vision chart is approximately 1/17th of the normal Snellen chart.

Sloan reading cards which uses continuous text paragraphs with logarithmic progression of optotype sizes, was a reading chart introduced in 1960s.{{cite journal |last1=Radner |first1=W. |title=Reading charts in ophthalmology |journal=Graefe's Archive for Clinical and Experimental Ophthalmology |date=2017 |volume=255 |issue=8 |pages=1465–1482 |doi=10.1007/s00417-017-3659-0 |pmid=28411305 |pmc=5541099 |issn=0721-832X}} Near acuity was recorded as 1.0 M, 1.5 M, 2.0 M etc.

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

The MNREAD acuity chart is a text based chart used to measure near visual acuity in people with normal or low vision.{{cite journal |last1=Altinbay |first1=Deniz |last2=Adibelli |first2=Fatih Mehmet |last3=Taskin |first3=Ibrahim |last4=Tekin |first4=Adil |title=The Evaluation of Reading Performance with Minnesota Low Vision Reading Charts in Patients with Age-related Macular Degeneration |journal=Middle East African Journal of Ophthalmology |date=2016 |volume=23 |issue=4 |pages=302–306 |doi=10.4103/0974-9233.194078 |pmid=27994393 |issn=0974-9233|pmc=5141623 |doi-access=free }} It can also be used to measure maximum reading speed, critical print size and the reading accessibility index of a person.{{cite journal |last1=Calabrèse |first1=Aurélie |last2=Cheong |first2=Allen M. Y. |last3=Cheung |first3=Sing-Hang |last4=He |first4=Yingchen |last5=Kwon |first5=MiYoung |last6=Mansfield |first6=J. Stephen |last7=Subramanian |first7=Ahalya |last8=Yu |first8=Deyue |last9=Legge |first9=Gordon E. |title=Baseline MNREAD Measures for Normally Sighted Subjects From Childhood to Old Age |journal=Investigative Ophthalmology & Visual Science |date=1 July 2016 |volume=57 |issue=8 |pages=3836–3843 |doi=10.1167/iovs.16-19580 |language=en |issn=1552-5783|doi-access=free |pmid=27442222 |pmc=4961000 }} Digital and printed types of charts are available.{{cite journal |last1=Calabrèse |first1=Aurélie |last2=To |first2=Long |last3=He |first3=Yingchen |last4=Berkholtz |first4=Elizabeth |last5=Rafian |first5=Paymon |last6=Legge |first6=Gordon E. |title=Comparing performance on the MNREAD iPad application with the MNREAD acuity chart |journal=Journal of Vision |date=19 January 2018 |volume=18 |issue=1 |pages=8 |doi=10.1167/18.1.8 |pmid=29351351 |pmc=5774869 |language=en |issn=1534-7362|doi-access=free }}

It is a type of Lea chart used to assess the functional near vision in children.{{Cite book |last=Khurana |first=A. K. |url=https://books.google.com/books?id=izlmDwAAQBAJ |title=MODERN SYSTEM OF OPHTHALMOLOGY (MSO) SERIES CLINICO-INVESTIGATIVE OPHTHALMOLOGY |date=2018-10-30 |publisher=CBS Publishers & Distributors Private Limited |isbn=978-93-87964-18-1 |pages=44 |language=en}} It is also used to introduce the child to the testing procedure, before introducing a distance Lea chart.

The concept of logarithmic progression of optotype sizes for distance vision charts was introduced by John Green, in 1868.{{cite journal |last1=Green |first1=John |title=On a New Series of Test-Letters for determining the Acuteness of Vision |journal=Transactions of the American Ophthalmological Society |date=1868 |volume=1 |issue=4–5 |pages=68–71 |pmid=16691740 |pmc=1361516 |issn=0065-9533}} However, apart from the reading chart developed by Birkhaeuser in 1911, none of the charts in use at the time were standardized. Aiming to overcome the standardization problem of Jaeger charts, N-notation was introduced in 1950s, but this too was not fully logarithmic. 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.{{cite journal |last1=Ntonti |first1=Panagiota |last2=Mitsi |first2=Christina |last3=Chatzimichael |first3=Eleftherios |last4=Panagiotopoulou |first4=Eirini-Kanella |last5=Bakirtzis |first5=Minas |last6=Konstantinidis |first6=Aristeidis |last7=Labiris |first7=Georgios |title=A systematic review of reading tests |journal=International Journal of Ophthalmology |date=18 January 2023 |volume=16 |issue=1 |pages=121–127 |doi=10.18240/ijo.2023.01.18 |pmid=36659955 |pmc=9815988 |issn=2222-3959}} 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.

source:{{cite web |title=Near visual acuity conversion chart |url=https://www.caa.co.uk/media/jblh5jzp/20230817-vision-conversion-chart-v2-0.pdf |publisher=UK Civil Aviation Authority}}{{cite web |title=Print Comparison of Font Sizes |url=https://www.teachingvisuallyimpaired.com/print-comparisons.html |website=Teaching Students with Visual Impairments |language=en}}

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Category:Ophthalmology

Category:Optometry

Category:Visual perception