review of low vision evaluations - caoms statewide ... vision evals.pdfteaching points •goals:...
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Review of Low Vision Evaluations
Emily Gorski, OD
Ian L. Bailey Low Vision Resident
Marlena A. Chu, OD, FAAO
Low Vision Diplomate, American Academy of Optometry
Chief of Low Vision Services
California Association of Orientation & Mobility Specialists Conference
November 4th, 2017
Monterey, CA
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Financial Disclosure
• We have no financial conflict of interest in any equipment or products presented.
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Teaching points
• Goals:
• Provide better understanding of low vision evaluation testing procedures, prescribing, & clinical thinking
• Clarify low vision reports
• Outline of Talk:
• Case history
• Testing procedures
• Prescribing
• Review of low vision devices
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Extended History
• Review of ocular/systemic history
• Functional needs at school/work
• Functional needs at home • Cooking/cleaning • Dials on stove, microwave, washer/dryer, thermostat
• Independent travel
• Outdoor/indoor glare
• Curbs/stairs
• Driving issues
• Night vision
• Family, care givers, friends
• Charles Bonnet Syndrome
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• LogMAR Charts
• Bailey-Lovie
• ETDRS
• Lea symbols
• Allows measurement of vision up to 20/16,000!
Distance Visual Acuity Tests
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Contrast Sensitivity Testing
• Ability to detect contrast more important in day to day functioning than visual acuity
• Decreased contrast sensitivity affects all independent living skills
Mars Contrast Test
Precision Vision
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Peripheral Visual Fields
• Transilluminator:
Gross screening in exam room
• Goldmann Perimetry and/or Humphrey Field Analyzer 30-2:
Functional assessment • Berkeley Central Field Test:
Tangent screen test for low vision patients
Central Visual Fields
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Low Luminance Testing
• 4% gray transmission fitovers
• 4% visible light
• Low luminance visual acuity: Expect 8-10 letters loss
• Low luminance contrast sensitivity:
Expect 0.1 - 0.3 log units loss
• Low luminance central field: Possible enlargement of scotoma with macular conditions
With filters : : Without filters
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Refractive Evaluation
• Retinoscopy
• Trial Frame Refraction
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Reading Acuity
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Prescribing Distance Magnification
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Prescribing for Distance Vision
• BCVA 20/125
• Goal 20/40
• Usually start lower power with new low vision patients
125/40 = ~3x monocular
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Distance devices
• Monocular
• Bioptics
• Inverse monocular – visual field
expander
• Hemianopes
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Bioptics
• Driving, musicians, medical personnel
• Expensive, heavy
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Inverse monocular
• Retinitis Pigmentosa
• Glaucoma
• Low power
•Good acuity
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Hemianopes
• Peli prism glasses
• Training devices for scanning to blind side
• NOT visual field expanders
• High fresnel prism mounted on glasses intended to alert patient to objects on their blind side
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Prescribing Near Magnification
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Prescribing for Near Vision
EVD: Equivalent Viewing Distance
– Actual viewing distance for preferred angular size
“Easy to read” Θ
EVD
• Threshold: Smallest print size read
• Efficiency: Preferred angular size
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5M Fast
4M Fast
3.2M Fast
2.5M Fast
2M Slow
1.6M Slower
1.25M Slower
1M Unable to Read
Reading acuity threshold = 0.20/1.25M Reading acuity efficiency = 0.20/2.5M
Reading Acuity
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Confirm dVA = Reading Acuity Threshold
20/125 = 0.20/1.25M
Measure Reading Efficiency
0.20/2.5M
Goal is 1M (8 point)
EVD = 8cm
0.2m x
2.5M 1M = x = 0.08m = 8cm
Prescribing for Near Vision
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Calculation of EVD to Magnification
• Reciprocal of distance (cm)
1 =
0.08 +12.50D
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Near Devices Based on Calculated Magnification
• EVD = 8 cm
• Magnification = +12.50D
• Add (Glasses) = +12.50D
• Hand-Held Magnifier = +12.50D
• Stand Magnifier = Based on image distance & enlargement ratio
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Hands Free Near Devices
• Largest field of view
• Close focus distance
• High Add glasses
• Prism readers
• Microscopic Readers
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High Add
• Bifocal
≤ +4.00
• Single vision
• Set nPD for convergence for low adds
• nPD = dPD – 1.5(add)
• Monocular at high adds
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Stock Readers
• Prism Reader
• Base In prism
• 4D – 16D
• Microscopic Readers
• Used monocularly but can be ordered binocular
• 2x-12x
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Hand-held magnifiers: Diopter vs. “x”
• Many magnification formulas
Magnification = P/4
OR
Magnification = (P/4) + 1
• Companies inconsistent in formula
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Hand-Held Magnifiers
• Pocket magnifiers
•Illuminated (Lighting options)
•Near spotting
•Greater working distance
•Decreased field of view
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Dome magnifiers
• Simple
• All same power ~ 1.5x
• Image located at same distance as object
• Brightens up page
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Stand magnifiers
• Greater working distance
• Occasionally need reading glasses as image is located below object
• Focus fixed by magnifier
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Stand magnifiers
• Power (Pe)
• Distance to image focus (v)
• Enlargement Ratio (ER)
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Electronic magnifiers
• Portable CCTVs • Desktop CCTVs
• OCR technology
• Desktop CCTVs
• OCR technology
• Portable CCTVs
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Head Mounted Electronic Devices
• eSight
• IrisVision
• NuEyes
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How to Refer
• Referral pads and patient intake forms • (f) 510.642.8012 • 200 Minor Hall, Berkeley, CA 94720-2020
• (p) 510.642.5726 • Karen • Irene
Tuesday Wednesday Thursday Friday
UC Berkeley CA School for the Blind
UC Berkeley SF LightHouse
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References
• Elliott DB, Yang KCH. Visual Acuity Changes Throughout Adulthood in Normal, Healthy Eyes: Seeing Beyond 6/6. OVIS. 1995;72(3):186-191.
• Haegerstrom-Portnoy G, Brabyn J, Schneck ME, Jampolsky A. The SKILL Card: An 552 acuity test of reduced luminance and contrast. Invest Ophthalmol Vis Sci 553 1997;38:207-218.
• Lang GK. Ophthalmology: a pocket textbook atlas. 2nd Edition. Chapter 16. Thieme Publisher. 2007. New York. Pg 435-468.
• Lovie-Kitchen J, Feigl B. Assessment of age-related maculopathy using subjective vision tests. Clin Exp Optom. 2005; 88(5):292-303.
• Owsley C. Contrast sensitivity. Ophthalmol Clin N Am 2003;16:171-177.
• Thomson D. VA testing in optometric practice (Part 2: Newer chart designs). Optometry Today. 2005;(May 6):22-24.
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Questions?
• Marlena A. Chu, OD, FAAO
• 510.642.5726
• Emily Gorski, OD
• Blind & Visually Impaired Center of Monterey is hiring for a full time O&M
• 831.649.3505