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Near visual acuity
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<h2 id="physiology-of-near-vision">Physiology of near vision</h2> <p>In human, near vision is obtained by a mechanism called <a href="/facts/Accommodation_(vertebrate_eye)/UqjPBp3S">accommodation</a>. 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.<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a><a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> 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 <a href="/facts/Zonule_of_Zinn/KAuNV6oN">zonular</a> tension induced by <a href="/facts/Ciliary_muscle/dxkVzBek">ciliary muscle</a> contraction. This process can occur in as little as 224 ± 30 milliseconds in bright light.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> </p><p>The amplitude of accommodation declines with age. The dependency of accommodation amplitude on age is graphically summarized by <a href="/facts/Alexander_Duane/6zpKPxFU">Duane</a>'s classical curves.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> </p> <h2 id="near-vision-impairment">Near vision impairment</h2> <p>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.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> Eye conditions like <a href="/facts/Presbyopia/SYtUhl2D">presbyopia</a>, <a href="/facts/Accommodative_insufficiency/o581a5Jh">accommodative insufficiency</a>, <a href="/facts/Cycloplegia/rehWsGgs">cycloplegia</a> etc. can affect the near visual acuity. Ocular diseases that cause defective distance vision like <a href="/facts/Cataract/RzN7k7K2">cataract</a> and <a href="/facts/Macular_degeneration/9pFARaka">macular degeneration</a>, can also cause reduced near vision.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> </p><p>According to the <a href="/facts/World_Health_Organization/YNN3bgug">World Health Organization</a>, the near visual acuity less than N6 or M0.8 at 40 cm is classified as near <a href="/facts/Visual_impairment/sFuqKj3n">visual impairment</a>.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> </p> <h3>Presbyopia</h3> <p>Presbyopia is physiological insufficiency of <a href="/facts/Accommodation_(eye)/UqjPBp3S">accommodation</a> associated with the aging of the <a href="/facts/Human_eye/a24ua4fy">eye</a> that results in defective near vision.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> Management of presbyopia includes corrective glasses such as a special pair of <a href="/facts/Reading_glasses/qRBkxeM5">reading glasses</a>, <a href="/facts/Contact_lens/0nzxq5Rm">contact lenses</a>, <a href="/facts/Bifocals/6mTNHgIl">bifocals</a>, or <a href="/facts/Progressive_lens/fMnJI3ap">progressive lenses</a>.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> </p> <h3>Insufficiency of accommodation</h3> <p>Insufficiency of accommodation also known as <a href="/facts/Accommodative_insufficiency/o581a5Jh">accommodative insufficiency</a> is another condition that causes blurring of the near vision.<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> Management of accommodative insufficiency needs correcting any underlying <a href="/facts/Refractive_error/bcWcSg2N">refractive errors</a>.<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> <a href="/facts/Vision_therapy/eHhId1hp">Vision therapy</a> may also help improve the condition.<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> </p> <h3>Cycloplegia</h3> <p><a href="/facts/Cycloplegia/rehWsGgs">Cycloplegia</a> is the paralysis of the ciliary muscle causing paralysis of accommodation and defective near vision.<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> 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.<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> </p> <h3>Hypermetropia</h3> <p><a href="/facts/Hypermetropia/h8pFNRfI">Hypermetropia</a>, the most common refractive error in childhood, affects the near vision more than distant vision.<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a> </p> <h2 id="tests-for-near-vision">Tests for near vision</h2> <p>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.<a class="footnote-ref" id="fnref:16" href="#fn:16"><sup>16</sup></a> The distance used for near vision testing may vary depending on the occupation or basic need of the patient.<a class="footnote-ref" id="fnref:17" href="#fn:17"><sup>17</sup></a> 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. </p> <h3>Jaeger chart</h3> <p>The <a href="/facts/Jaeger_chart/mjdqwvfa">Jaeger chart</a> is a card on which paragraphs of text are printed, with the <a href="/facts/Text_size/w7vz87Rm">text sizes</a> increasing from 0.37 mm to 2.5 mm.<a class="footnote-ref" id="fnref:18" href="#fn:18"><sup>18</sup></a> 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.<a class="footnote-ref" id="fnref:19" href="#fn:19"><sup>19</sup></a> </p> <h3>Roman test types</h3> <p>Roman test types also known as N notation reading charts or Point chart,<a class="footnote-ref" id="fnref:20" href="#fn:20"><sup>20</sup></a> uses <a href="/facts/Times_New_Roman_font/8hrJ2Hb2">Times New Roman font</a>, and records near visual acuity as N5, N6, N8, N10, etc.<a class="footnote-ref" id="fnref:21" href="#fn:21"><sup>21</sup></a> N notation is the standard near vision test in the United Kingdom and Australia.<a class="footnote-ref" id="fnref:22" href="#fn:22"><sup>22</sup></a> </p> <h3>M-scale notation</h3> <p>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.<a class="footnote-ref" id="fnref:23" href="#fn:23"><sup>23</sup></a> The M system is said to have sufficient advantages over other systems for near vision testing to make it a universally accepted standard method.<a class="footnote-ref" id="fnref:24" href="#fn:24"><sup>24</sup></a> M-scale notation is widely used in North America.<a class="footnote-ref" id="fnref:25" href="#fn:25"><sup>25</sup></a> </p> <h3>Snellen's near vision test</h3> <p>Snellen's near vision test is a near vision chart introduced by Dutch <a href="/facts/Ophthalmologist/024hdTWF">ophthalmologist</a> <a href="/facts/Herman_Snellen/T0WmdHvk">Herman Snellen</a>, which uses the same principle of his distance vision <a href="/facts/Snellen_chart/cR0DUR4d">Snellen chart</a>.<a class="footnote-ref" id="fnref:26" href="#fn:26"><sup>26</sup></a> Size of Snellen's near vision chart is approximately 1/17th of the normal Snellen chart.<a class="footnote-ref" id="fnref:27" href="#fn:27"><sup>27</sup></a> </p> <h3>Sloan Reading Cards</h3> <p>Sloan reading cards which uses continuous text paragraphs with logarithmic progression of optotype sizes, was a reading chart introduced in 1960s.<a class="footnote-ref" id="fnref:28" href="#fn:28"><sup>28</sup></a> Near acuity was recorded as 1.0 M, 1.5 M, 2.0 M etc. </p> <h3>Bailey-Lovie Word Reading Charts</h3> <p>Bailey-Lovie charts introduced in 1980s, which measures reading acuity and reading speed, uses logarithmic progression of optotype sizes.<a class="footnote-ref" id="fnref:29" href="#fn:29"><sup>29</sup></a> </p> <h3>MNREAD acuity chart</h3> <p>The <a href="/facts/MNREAD_acuity_chart/Fu343pGk">MNREAD acuity chart</a> is a text based chart used to measure near visual acuity in people with normal or <a href="/facts/Low_vision/sFuqKj3n">low vision</a>.<a class="footnote-ref" id="fnref:30" href="#fn:30"><sup>30</sup></a> It can also be used to measure maximum reading speed, critical print size and the reading accessibility index of a person.<a class="footnote-ref" id="fnref:31" href="#fn:31"><sup>31</sup></a> Digital and printed types of charts are available.<a class="footnote-ref" id="fnref:32" href="#fn:32"><sup>32</sup></a> </p> <h3>Lea near vision card</h3> <p>It is a type of <a href="/facts/Lea_test/GGp7o0rg">Lea chart</a> used to assess the functional near vision in children.<a class="footnote-ref" id="fnref:33" href="#fn:33"><sup>33</sup></a> It is also used to introduce the child to the testing procedure, before introducing a distance Lea chart.<a class="footnote-ref" id="fnref:34" href="#fn:34"><sup>34</sup></a> </p> <h2 id="standardization-of-reading-charts">Standardization of reading charts</h2> <p>The concept of logarithmic progression of optotype sizes for distance vision charts was introduced by John Green, in 1868.<a class="footnote-ref" id="fnref:35" href="#fn:35"><sup>35</sup></a> However, apart from the reading chart developed by Birkhaeuser in 1911, none of the charts in use at the time were standardized.<a class="footnote-ref" id="fnref:36" href="#fn:36"><sup>36</sup></a> Aiming to overcome the standardization problem of Jaeger charts, N-notation was introduced in 1950s, but this too was not fully logarithmic.<a class="footnote-ref" id="fnref:37" href="#fn:37"><sup>37</sup></a> 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. </p><p>Standardization criteria established by the <a href="/facts/International_Council_of_Ophthalmology/BFEmWkoe">International Council of Ophthalmology</a> (ICO) or EN ISO 8596 directive include the reproducibility, comparability, validity, interpretability and reliability of reading tests.<a class="footnote-ref" id="fnref:38" href="#fn:38"><sup>38</sup></a> 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.<a class="footnote-ref" id="fnref:39" href="#fn:39"><sup>39</sup></a> </p> <h2 id="conversion">Conversion</h2> Near visual acuity conversion chart<table><tbody><tr><th>Roman</th><th>Jaeger</th><th>Snellen(US)</th><th>Snellen(Metric)</th><th>Decimal</th><th>M unit</th></tr><tr><td>N4.5</td><td>J1</td><td>20/20</td><td>6/6</td><td>1.00</td><td>0.5</td></tr><tr><td>N5</td><td>J3</td><td>20/30</td><td>6/9</td><td>0.67</td><td>0.8</td></tr><tr><td>N6</td><td>J5</td><td>20/40</td><td>6/12</td><td>0.50</td><td>1.0</td></tr><tr><td>N8</td><td>J6</td><td>20/50</td><td>6/15</td><td>0.40</td><td>-</td></tr><tr><td>N10</td><td>J7</td><td>20/60</td><td>6/18</td><td>0.33</td><td>1.2</td></tr><tr><td>N12</td><td>J9</td><td>20/80</td><td>6/24</td><td>0.25</td><td>-</td></tr><tr><td>N14</td><td>J10</td><td>20/100</td><td>6/30</td><td>0.20</td><td>1.3</td></tr></tbody></table> <p>source:<a class="footnote-ref" id="fnref:40" href="#fn:40"><sup>40</sup></a><a class="footnote-ref" id="fnref:41" href="#fn:41"><sup>41</sup></a> </p> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>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) <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>That value follows from the maximum accommodative power and can be calculated as 100 cm/15 dpt. <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>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. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2908311" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2908311</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>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. <a href="https://zenodo.org/record/1529034" target="_blank">https://zenodo.org/record/1529034</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>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. 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PMID 36508537. <a href="https://www.ncbi.nlm.nih.gov/books/NBK587363/" target="_blank">https://www.ncbi.nlm.nih.gov/books/NBK587363/</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>Enaholo, Ehimare S.; Musa, Mutali J.; Zeppieri, Marco (2024). "Accommodative Insufficiency". StatPearls. StatPearls Publishing. PMID 36508537. <a href="https://www.ncbi.nlm.nih.gov/books/NBK587363/" target="_blank">https://www.ncbi.nlm.nih.gov/books/NBK587363/</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>Enaholo, Ehimare S.; Musa, Mutali J.; Zeppieri, Marco (2024). "Accommodative Insufficiency". StatPearls. StatPearls Publishing. PMID 36508537. <a href="https://www.ncbi.nlm.nih.gov/books/NBK587363/" target="_blank">https://www.ncbi.nlm.nih.gov/books/NBK587363/</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>Kaur, Kirandeep; Gurnani, Bharat (2024). "Cycloplegic and Noncycloplegic Refraction". 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Theory and Practice of Optics and Refraction. Elsevier India. p. 49. ISBN 9788131211328. <a href="9788131211328" target="_blank">9788131211328</a> <a href="#fnref:16" class="footnote-back-ref">↩</a></p></li> <li id="fn:17"><p>Caltrider, David; Gupta, Abhishek; Tripathy, Koushik (2024). "Evaluation of Visual Acuity". StatPearls. StatPearls Publishing. PMID 33231977. <a href="https://www.ncbi.nlm.nih.gov/books/NBK564307/" target="_blank">https://www.ncbi.nlm.nih.gov/books/NBK564307/</a> <a href="#fnref:17" class="footnote-back-ref">↩</a></p></li> <li id="fn:18"><p>Blesi, Michelle; Wise, Barbara; Kelley-Arney, Cathy (2011). Medical Assisting Administrative and Clinical Competencies. Cengage Learning. pp. 888–890. ISBN 978-1133706960. <a href="978-1133706960" target="_blank">978-1133706960</a> <a href="#fnref:18" class="footnote-back-ref">↩</a></p></li> <li id="fn:19"><p>G.K. & Pal; Pal; Pravati (1 February 2006). Textbook Of Practical Physiology (2nd ed.). Orient Blackswan. pp. 328–. ISBN 978-81-250-2904-5. <a href="978-81-250-2904-5" target="_blank">978-81-250-2904-5</a> <a href="#fnref:19" class="footnote-back-ref">↩</a></p></li> <li id="fn:20"><p>Houf, James W. (October 2009). "Understanding Near Vision Eye Tests". The American Society for Nondestructive Testing. 8 (4). <a href="https://www.asnt.org/~/media/Files/Publications/TNT/TNT_08-4.ashx" target="_blank">https://www.asnt.org/~/media/Files/Publications/TNT/TNT_08-4.ashx</a> <a href="#fnref:20" class="footnote-back-ref">↩</a></p></li> <li id="fn:21"><p>Khurana (2008). Theory and Practice of Optics and Refraction. Elsevier India. p. 49. ISBN 9788131211328. <a href="9788131211328" target="_blank">9788131211328</a> <a href="#fnref:21" class="footnote-back-ref">↩</a></p></li> <li id="fn:22"><p>ELLIOTT, DAVID B (2007). Clinical Procedures in Primary Eye Care (3 ed.). Elsevier. pp. 38–41. ISBN 9780750688963. <a href="9780750688963" target="_blank">9780750688963</a> <a href="#fnref:22" class="footnote-back-ref">↩</a></p></li> <li id="fn:23"><p>ELLIOTT, DAVID B (2007). Clinical Procedures in Primary Eye Care (3 ed.). Elsevier. pp. 38–41. ISBN 9780750688963. <a href="9780750688963" target="_blank">9780750688963</a> <a href="#fnref:23" class="footnote-back-ref">↩</a></p></li> <li id="fn:24"><p>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. <a href="https://pubmed.ncbi.nlm.nih.gov/596414/" target="_blank">https://pubmed.ncbi.nlm.nih.gov/596414/</a> <a href="#fnref:24" class="footnote-back-ref">↩</a></p></li> <li id="fn:25"><p>ELLIOTT, DAVID B (2007). Clinical Procedures in Primary Eye Care (3 ed.). Elsevier. pp. 38–41. 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