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VISUAL ACUITY IN ADULTS AYESHA PATIL, MPH

MEDICAL STUDENT | UNIVERSITY OF UTAH

SOPHIA FANG, MD, MSPEDIATRIC OPHTHALMOLOGIST | CHILD EYE CARE ASSOCIATESGLOBAL OUTREACH FELLOW 2019-2020 | MORAN EYE CENTER

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ACKNOWLEDGEMENTS• Jacqueline Pullos, COMT, OSC, CTC

– Staff Education Coordinator | Moran Eye Center

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WHAT IS VISUAL ACUITY?• The clarity or sharpness of vision,

measured by the ability to recognize letters or numbers at a specific distance

[Moran Eye Center Global Outreach Division]

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THE IDEAL EYE • Light rays from a far away object will get bent/focused by the cornea

and the lens as they pass into the eye• In an ideal eye, the light rays will come to a focus at a point exactly on

the retina to produce a perfect, clear image • An ideal eye is free of disease and has a perfect visual acuity of 20/20

[https://commons.wikimedia.org/wiki/File:Emmetropia.png]

Retina

Cornea Lens

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REASONS FOR REDUCED VISUAL ACUITY

Refractive errorsExamplesMyopiaHyperopia

Astigmatism

Disease

Congenital CataractsGlaucoma

Macular DegenerationDiabetic Retinopathy

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MYOPIA • Also called nearsightedness• The eye is too long and the

image gets focused in front of the retina

• Near objects are seen more clearly whereas there is more difficulty seeing distant objects clearly

[https://commons.wikimedia.org/wiki/File:Myopia_Diagram.jpg]

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HYPEROPIA• Also called farsightedness• The eye is too short and the

image is focused behind the retina

[https://commons.wikimedia.org/wiki/File:Myopia_Diagram.jpg]

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ASTIGMATISM• Causes distorted vision• Usually due to an irregularly

shaped cornea – e.g. the corneal surface can be

more like a football, where one axis is steeper than the other, rather than a basketball that is the same all the way around

• Changes the way light rays pass through different parts of the cornea/lens, resulting in multiple focal points

[https://commons.wikimedia.org/wiki/File:Astigmatism2.svg]

[https://pixabay.com/illustrations/basketball-sport-circle-round-4061225/]

Basketball

[https://pixabay.com/vectors/american-football-ball-sport-game-311817/]

Football

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HOW DO YOU MEASURE VISUAL ACUITY?• Standard distance for

measurement is 20 ft (or 6 m)• 20/20 is defined as normal visual

acuity– The higher the bottom number, the

worse the vision– Think of visual acuity as a ratio

comparing your vision to someone who has normal vision

[Moran Eye Center Global Outreach Division]

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FACTORS THAT CAN AFFECT VISUAL ACUITY MEASUREMENT

Literacy level of the patient – i.e. if a patient cannot read Roman letters à cannot use a Snellen chart

Amount of light in the room

Duration of presentation to chart – enough time given for patient to read chart

Attentiveness of the patient – ability to focus on the chart without distractions

Developmental age (e.g. infant, toddler, developmental delay)

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QUICK REVIEW!• When we have a patient read an eye chart we are measuring their

_________ _________• In an ideal eye with 20/20 vision, where in the eye do light rays come to a

focal point?• Describe what these terms mean:

– Myopia– Hyperopia– Astigmatism

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REVIEW ANSWERS1. Visual Acuity2. Exactly on the Retina3. See Myopia, Hyperopia and Astigmatism slides

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HOW TO TEST VISUAL ACUITY • Terminology

– Right eye: OD– Left eye: OS – Both eyes: OU

• Without correction (i.e. glasses, contact lenses)– SC

• With correction– CC

• With pinhole– PH

[https://www.cleanpng.com/png-eye-cartoon-early-reading-instruction-what-science-598473/preview.html]

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CHOOSE CHART TYPE • Consider verbal ability and

literacy level of patient

[https://en.wikipedia.org/wiki/File:Snellen_chart.svg]

Snellen Chart

ETDRS Chart

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Tumbling E chart

[https://www.medexsupply.com/exam-room-equipment-vision-testing-eye-test-charts-good-lite-tumbling-e-linear-spaced-distance-chart-9-x-14-20-39--x_pid-15943.html?]

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INSTRUCTIONS1. Ensure good lighting and quiet room2. Have patient stand 20 ft/6 m away from eye

chart, with chart at eye level 3. Document with (CC) or without correction (SC)4. Test right eye first by covering left eye with an

occluder.Start with smallest line a patient can read

ORIf a patient needs help, start with the biggest letter and move down the left side of the chart, having them read the first letter of each line until they miss a letter. Then go back up to the previous line and have them read across it.

5. A patient is said to be able to read a given line if they can read at least 50% of the letters on that line.

[Moran Eye Center Global Outreach Division]

Lorgnette Pinhole Occluder

[https://www.graylinemedical.com/products/good-lite-occluder-lorgnette-ea?variant=19359208472633&gclid]

Short Single Ended Occluder

[Sophia Fang, MD]

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INSTRUCTIONS, CONT.6. Encourage your patient (say “try your best”)7. Repeat with other eye 8. If vision is not 20/20 in either eye, repeat test with

pinholes9. Make sure to record all visual acuity

measurements appropriately

[Moran Eye Center Global Outreach Division]

Lorgnette Pinhole Occluder

[https://www.graylinemedical.com/products/good-lite-occluder-lorgnette-ea?variant=19359208472633&gclid]

Short Single Ended Occluder

[Sophia Fang, MD]

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WHAT ARE PINHOLES?• Very useful tool to see if decreased

visual acuity may be due to untreated refractive error– If someone has improved visual acuity with

pinhole, there is likely a component of uncorrected refractive error

• How do they work?– Pinholes screen out all light rays which are not

perpendicular to the visual axis, reducing distortion from irregular corneas

• Use a pinhole after you have checked visual acuity through open hole. Ask patient to put black side flap down (as shown here), try to look through one of the little holes, and repeat visual acuity test. Repeat for each eye

[https://www.flickr.com/photos/communityeyehealth/14545275197]

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RECORDING VISUAL ACUITY• Find the acuity notation on the last

line of optotypes the patient can read

• Write as a fraction 20/20, 20/40, etc.• If a patient misses 1-2 letters on a

line, you can write it as:– 20/20 -2 or 20/50 -1

• If a patient gets 1 or 2 letters on the next line, you can write it as:– 20/30+2 or 20/60+1

• Encourage patient not to squint [https://en.wikipedia.org/wiki/File:Snellen_chart.svg]

20/30-2

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EXAMPLE OF RECORDED VISUAL ACUITY

[Sophia Fang, MD]

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PATIENT WITH LOW VISION• If a patient cannot see the big E on Snellen chart or top line

on other charts, here are techniques for visual acuity testing:– Finger counting (CF)

• Hold 1, 2, or 5 fingers up – ask patient how many fingers they see while covering the other eye. Record number of fingers at distance tested

– Hand motion (HM)• Determine if patient can detect hand motion in each eye and in which direction the hand is

moving – up and down or left and right

– Light perception (LP/NLP)• Shine a light in one eye at a time, determine if patient recognizes when light is shown

and/or from which direction**record all findings at distance tested (e.g. CF @ 1 ft., HM @ 3 ft.)**

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QUESTIONS?

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LET’S PRACTICE!

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