Visual Acuity in Adults

VISUAL ACUITY IN ADULTS

AYESHA PATIL, MPH MEDICAL STUDENT | UNIVERSITY OF UTAH

SOPHIA FANG, MD, MS PEDIATRIC OPHTHALMOLOGIST | CHILD EYE CARE ASSOCIATES GLOBAL OUTREACH FELLOW 2019-2020 | MORAN EYE CENTER

• Jacqueline Pullos, COMT, OSC, CTC – Staff Education Coordinator | Moran Eye Center

[Moran Eye Center Global Outreach Division]

© UNIVERSITY OF UTAH HEALTH 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

Lens Cornea

Retina

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

Examples Myopia Refractive errors Hyperopia Astigmatism

Congenital Cataracts Disease Glaucoma Macular Degeneration Diabetic Retinopathy

© UNIVERSITY OF UTAH HEALTH 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]

© UNIVERSITY OF UTAH HEALTH 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 [https://commons.wikimedia.org/wiki/File:Astigmatism2.svg] same all the way around • Changes the way light rays pass Basketball Football through different parts of the cornea/lens, resulting in multiple focal points

[https://pixabay.com/vectors/american-football- [https://pixabay.com/illustrations/basketball- ball-sport-game-311817/] sport-circle-round-4061225/]

© UNIVERSITY OF UTAH HEALTH 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]

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)

• 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

1. Visual Acuity 2. Exactly on the Retina 3. See Myopia, Hyperopia and Astigmatism slides

• Terminology • Without correction (i.e. glasses, – Right eye: OD contact lenses) – Left eye: OS – SC – Both eyes: OU • With correction – CC • With pinhole – PH

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

[https://www.flickr.com/photos/nationaleyeinstitute/7544734768] [https://en.wikipedia.org/wiki/File:Snellen_chart.svg] [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?]

© UNIVERSITY OF UTAH HEALTH INSTRUCTIONS 1. Ensure good lighting and quiet room 2. 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 OR If a patient needs help, start with the biggest letter and [Moran Eye Center Global Outreach Division] move down the left side of the chart, having them read the first letter of each line until they miss a letter. Lorgnette Pinhole Occluder Short Single Ended Occluder 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.

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

© UNIVERSITY OF UTAH HEALTH 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 pinholes 9. Make sure to record all visual acuity measurements appropriately

[Moran Eye Center Global Outreach Division]

Lorgnette Pinhole Occluder Short Single Ended Occluder

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

© UNIVERSITY OF UTAH HEALTH 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. [https://www.flickr.com/photos/communityeyehealth/14545275197] Repeat for each eye

© UNIVERSITY OF UTAH HEALTH 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 20/30-2 • 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]

[Sophia Fang, MD]

© UNIVERSITY OF UTAH HEALTH 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.)**

[https://pixabay.com/illustrations/question-mark-note-duplicate-2405197/]

[https://www.flickr.com/photos/venditti_min_min- venditti/30598426833/in/photostream/]