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

Financial Disclosure

• We have no financial conflict of interest in any equipment or products presented.

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

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

• LogMAR Charts

• Bailey-Lovie

• ETDRS

• Lea symbols

• Allows measurement of vision up to 20/16,000!

Distance Visual Acuity Tests

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

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

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

Refractive Evaluation

• Retinoscopy

• Trial Frame Refraction

Reading Acuity

Prescribing Distance Magnification

Prescribing for Distance Vision

• BCVA 20/125

• Goal 20/40

• Usually start lower power with new low vision patients

125/40 = ~3x monocular

Distance devices

• Monocular

• Bioptics

• Inverse monocular – visual field

expander

• Hemianopes

Bioptics

• Driving, musicians, medical personnel

• Expensive, heavy

Inverse monocular

• Retinitis Pigmentosa

• Glaucoma

• Low power

•Good acuity

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

Prescribing Near Magnification

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

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

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

Calculation of EVD to Magnification

• Reciprocal of distance (cm)

1 =

0.08 +12.50D

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

Hands Free Near Devices

• Largest field of view

• Close focus distance

• High Add glasses

• Prism readers

• Microscopic Readers

High Add

• Bifocal

≤ +4.00

• Single vision

• Set nPD for convergence for low adds

• nPD = dPD – 1.5(add)

• Monocular at high adds

Stock Readers

• Prism Reader

• Base In prism

• 4D – 16D

• Microscopic Readers

• Used monocularly but can be ordered binocular

• 2x-12x

Hand-held magnifiers: Diopter vs. “x”

• Many magnification formulas

Magnification = P/4

OR

Magnification = (P/4) + 1

• Companies inconsistent in formula

Hand-Held Magnifiers

• Pocket magnifiers

•Illuminated (Lighting options)

•Near spotting

•Greater working distance

•Decreased field of view

Dome magnifiers

• Simple

• All same power ~ 1.5x

• Image located at same distance as object

• Brightens up page

Stand magnifiers

• Greater working distance

• Occasionally need reading glasses as image is located below object

• Focus fixed by magnifier

Stand magnifiers

• Power (Pe)

• Distance to image focus (v)

• Enlargement Ratio (ER)

Electronic magnifiers

• Portable CCTVs • Desktop CCTVs

• OCR technology

• Desktop CCTVs

• OCR technology

• Portable CCTVs

Head Mounted Electronic Devices

• eSight

• IrisVision

• NuEyes

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

• marlenachu@berkeley.edu

Tuesday Wednesday Thursday Friday

UC Berkeley CA School for the Blind

UC Berkeley SF LightHouse

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.

Questions?

• Marlena A. Chu, OD, FAAO

• 510.642.5726

• marlenachu@berkeley.edu

• Emily Gorski, OD

• Blind & Visually Impaired Center of Monterey is hiring for a full time O&M

• 831.649.3505