Systematic Approach to Low Vision Exams

Welcome to the first installment of a three-part series describing how I approach low vision exams and device selection! This is a good starting point for students who need a step-wise approach for executing what is often seen as one of the more difficult exams. I find having a systematic approach allows me to gather all the appropriate data and prescribe devices more effectively. Note: The articles here are by no means comprehensive and should not substitute your professional training and judgment!

• Part 1: Low Vision Work Up
• Part 2: Low Vision Device Selection
• Part 3: Low Vision Training
  

Part 1: Low Vision Work Up

1. History

Just like any other exams, history is crucial because it drives the rest of the exam. Every patient has a chief complaint or a need. It is up to the clinician to ask appropriate questions and to set a few initial goals for the patient. Don’t be satisfied with a chief complaint of “I’m just here for a low vision exam.” Questions may include:

1. Chief complaints
2. Patient’s goals: near, intermediate and distance
3. Hobbies
4. Currently using any devices or wearing glasses?
   1. Any devices patient tried in the past? Successful?
   2. Any issues with activities of daily living?
   3. Any problems with glare or lighting?
   4. Mobility issues?

2. Distance VA

1. Use patient’s current glasses
2. First attempt Snellen chart (unless VA is known to be poorer than what can be obtained with Snellen chart)
3. Alternative charts
   1. Feinbloom chart
      1. Hold chart at 5 or 10 ft for easy conversion to Snellen equivalent
      2. I always like to start a couple lines above expected VA to build patient’s confidence
      3. One disadvantage is difficulty with refraction using Feinbloom chart (unless there’s another person holding the chart for you)
   2. ETDRS
      1. Easily moveable and able to stand on own without you holding it
      2. Advantage: more letter options per line
      3. Good chart when doing refraction
4. Record both central & eccentric VAs
   1. Attempt eccentric viewing if patient is not already doing so. Record eccentric viewing from patient’s view.

3. Manifest Refraction

1. Use current specs Rx as starting point
   1. May do autorefraction or retinoscopy for starting point if patient doesn’t wear glasses
2. Use phoropter if possible
3. If patient uses any eccentric viewing, it is HIGHLY recommended to perform trial frame refraction
   1. Remember just noticeable difference!
4. Record both best corrected central and eccentric viewing VAs

4. Contrast Sensitivity

1. There are many contrast sensitivity tests. One more commonly used is the Mars Letter Contrast Sensitivity.
   1. Test OD and OS separately & with near correction
   2. Record log contrast sensitivity and level of impairment
      

5. Visual Field

1. Test monocularly then binocularly
2. Record:
   1. Horizontal and vertical field
   2. If there is any scotoma: record size and location
   3. Note the area with the largest continuous visual field- important for scanning training
3. Variety of visual field machines (we are looking for areas of useable vision)
   1. Arc perimeter
   2. Goldmann visual field
   3. Amsler grid (helps locate location of scotoma, but not size of scotoma)
   4. Humphrey visual field & Octopus may not be the best because of reduced vision

6. Color Vision

1. Test monocularly
2. Ishihara or Farnsworth D-15

7. Near VA

1. Remember to include add over manifest refraction (if patient is presbyopic)
2. Test OD/OS/OU
3. Test at 40 cm or measure distance patient prefers
4. Use good lighting!
5. Record distance tested in meters and smallest M notation read
   1. Example: 0.4m/3M
6. Record preferred eye

Acknowledgement:

Thank you Dr. Amy Huddleston, at Veteran’s Affairs Outpatient Center in Jacksonville, Florida, for guidance and tips in low vision examination.