_id

683a162cc782e11e38d1b246

id

10060

title

Visual Acuity Testing (Snellen Chart)

full_title

Visual Acuity Testing (Snellen Chart)

short_title

Snellen Chart

med_description

Assess binocular and monocular visual acuity.

short_description

Visual acuity.

slug

visual-acuity-testing-snellen-chart

description

The Visual Acuity Testing (Snellen Chart) assess binocular and monocular visual acuity.

keywords

Visual acuity test, Snellen chart, visual acuity

complaint

[ "Any/All", "Vision Loss" ]

formula

evidence

• There are two main charts used to test visual acuity – Snellen charts, which use a geometric scale, and logMAR charts, which use a logarithmic scale.

• While both have been widely studied, Snellen charts are more widely used in clinical practice and logMAR charts are used more often in the context of research studies given the ease of statistical analysis.

• Data looking at eleven different smartphone applications found that the accuracy of the applications was limited (none were within one line of the true Snellen visual acuity) (Perera 2015).

• One study suggested that the visual acuity on smart phone apps may not be completely accurate, but the results are reproducible allowing the app to track change from baseline (Phung 2016).

• There has been one study validating the use of smartphone charts in measuring visual acuity; however, this validation was application-specific and thus more studies need to be conducted to elucidate the true validity of these charts (Bastawrous 2015).

measurements

[]

information

refrences

{ "Clinical Practice Guidelines": [], "Manufacturer Website": [], "Original/Primary Reference": [ { "href": "https://www.google.com/books/edition/Probebuchstaben_zur_Bestimmung_der_Sehsc/LEYJAAAAIAAJ?hl=en", "text": "Snellen, H. Probebuchstaben zur Bestimmung der Sehschärfe. Utrecht, Van de Weijer, 1862." } ], "Other References": [], "Outcomes": [], "Validation": [ { "href": "https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4506341/", "text": "Perera C, Chakrabarti R, Islam FMA, Crowston J. The Eye Phone Study: reliability and accuracy of assessing Snellen visual acuity using smartphone technology. Eye 2015; 29(7): 888–894." }, { "href": "https://www.ncbi.nlm.nih.gov/pubmed/26022921 ", "text": "Bastawrous A, Rono HK, Livingstone IA, et al. Development and validation of a smartphone-based visual acuity test (Peek Acuity) for clinical practice and community-based fieldwork. JAMA Ophthalmol. 2015;133(8):930-937." }, { "href": "https://www.ncbi.nlm.nih.gov/pubmed/26509223", "text": "Phung L, Gregori NZ, Ortiz A, Shi W, Schiffman JC. Reproducibility and comparison of visual acuity obtained with sight book mobile application to near card and Snellen chart. Retina Phila Pa. 2016 May;36:1009–20. " } ], "Validations": [] }

pearls

• Patients over the age of 40 may have presbyopia and often require reading glasses; thus, their near-vision test results may be unreliable if the test is administered without reading lenses.

• Alternate charts exist for illiterate patients or young children, but have limited studies evaluating their use in smartphones.

• While the Snellen chart is the most widely used method of testing visual acuity in clinical practice, it is not without its pitfalls, including difficulty with standardization of the chart, as well as test-retest reliability.

Instructions for Use:

• Ensure proper room lighting and set phone brightness to 100%.

• Hold the screen 4 feet (1.2 m) from the patient (approximately the end of a standard hospital bed if patient is sitting upright).

• Test each eye independently. The patient should completely cover the opposite eye.

• If the patient is unable to read any of the letters on the chart, the person checking vision should hold up fingers at varying distances and assess whether the patient can count them; this is recorded as counting fingers (CF) vision (e.g. CF at 4 feet, 1.2 m).

• If the patient cannot count fingers, the person checking vision should move his/her hand across the patient’s field of vision to assess whether the patient can see this; this is recorded as hand motion (HM) vision.

• Finally, if the patient is unable to see hand movements, a penlight should be swept across the patient’s eye to assess whether the patient can tell when the light is pointed at the eye. If they are able to identify when the light is pointed at the eye, this is recorded as light perception (LP) vision. If they are unable to identify the light, this is recorded as no light perception (NLP) vision.

usecase

To assess binocular and monocular visual acuity in cooperative patients.

reasons

Provides a portable and quick method to assess visual acuity.

next_advice

• Visual acuity worse than 20/25 should be evaluated by a licensed eye professional to determine whether corrective lenses or other treatments may be necessary.

• Visual acuity is not a measure of a patient’s prescription. This is a separate value that needs to be measured in an office setting.

next_actions

next_management

Any patient with sudden changes in visual acuity from baseline or new obscurations in vision requires immediate referral to an ophthalmologist for dilated fundus examination and further testing.

diseases

[ "Any/All" ]

input_schema

[ { "md_calc_info_concept": null, "option_fhir_rules": null, "type": "visual", "visual": "<img src='https://cdn-web-img.mdcalc.com/content/snellen2.png'>" }, { "conditionality": "", "default": null, "label_en": "Select lowest line that patient can read correctly.", "mdcalc_info_concept": null, "name": "line", "option_fhir_rules": null, "optional": false, "options": [ { "label": "Line 1", "value": 0 }, { "label": "Line 2", "value": 1 }, { "label": "Line 3", "value": 2 }, { "label": "Line 4", "value": 3 }, { "label": "Line 5", "value": 4 }, { "label": "Line 6", "value": 5 }, { "label": "Line 7", "value": 6 }, { "label": "Line 8", "value": 7 }, { "label": "Line 9", "value": 8 }, { "label": "Line 10", "value": 9 }, { "label": "Line 11", "value": 10 } ], "show_points": false, "tips_en": "", "type": "radio" } ]

instructions

• Ensure proper room lighting and set phone brightness to 100%.
• Hold the screen 4 feet (1.2 m) from the patient (approximately the end of a standard hospital bed if patient is sitting upright).
• Test each eye independently. The patient should completely cover the opposite eye.
• See Pearls/Pitfalls for further instructions.

published

2022-04-21T20:28:12.079Z

purpose

[ "Diagnosis" ]

search_terms

[ "Snellen chart", "eye test", "vision test", "visual acuity test" ]

seo

{ "keywords_en": "Visual acuity test, Snellen chart, visual acuity ", "meta_description_en": "The Visual Acuity Testing (Snellen Chart) assess binocular and monocular visual acuity." }

specialty

[ "Family Practice", "Internal Medicine", "Ophthalmology", "Primary Care" ]

departments

[ "Neurologic", "Ophthalmic" ]

tags

[]

version_number

1

versions

[]

related

[ { "calcId": 10061, "short_title_en": "Ishihara Test", "slug": "color-vision-screening-ishihara-test" }, { "calcId": 3982, "short_title_en": "4AT", "slug": "4-test-delirium-assessment" }, { "calcId": 3995, "short_title_en": "AMT-4", "slug": "abbreviated-mental-test-4-amt-4" } ]

ismed

true

section

[ "whenToUseViewed", "pearlsPitfallsViewed", "whyUseViewed", "nextStepsViewed", "evidenceViewed" ]

cleaned_departments

[ "neurology", "ophthalmology" ]

cleaned_use

[ "To assess binocular and monocular visual acuity in cooperative patients." ]

pub

false