Distance Vision: Visual Acuity

To screen for Myopia, Astigmatism and Amblyopia (Lazy Eye)

Procedures:

  1. Pick an age-appropriate visual acuity chart.
  2. Test Distance: ( 3 m: Snellen, Tumbling Es, LEA Symbols ) ( 4 m: Bailey-Lovie Chart (ETDRS))
  3. Seat participants at eye level facing the chart.
  4. Keep participant’s glasses on for testing. (If glasses are used only for reading, then they should not be worn for distance vision testing.)
  5. Use alcohol to clean the occluder after each patient and allow to air dry. Cover the left eye (LE) with an occluder and test the right eye first. Ask the patient: “Can you see the chart over there?”
  6. Start with the first symbol on the 6/12 (0.5) line and move down to the next line towards 6/6 line. If the participant cannot read that line, move up to the line above until they can read it.
  7. Proceed with the test until the lowest line can be read.

How to record?

• If the Px can read out 6/9.5 line completely plus 1 more alphabet from the next
line with glasses on in their right eye, write: OD with glasses **6/9.5+1
** • If the Px can read out most of the line on 6/9.5 but misses 1 alphabet in their left eye: OS with glasses: 6/9.5-1

Points to Remember!

Watch that participant does not “peek” through the occluder while taking VA’s.

The occluders and plus lenses should be disinfected thoroughly with alcohol after each use and allowed to air dry.

Always test right eye then left eye as a routine to avoid confusion.

Even though only one eye is occluded, participants should be instructed to keep both eyes open and read the letter symbol. MAKE SURE PARTICIPANTS ARE NOT SQUINTING THEIR EYES WHILE TESTING VISUAL ACUITIES

The LEA Symbols Matching cards may be given to the participants to assist in VA testing. Frequent cleaning of the card is also necessary after each child

Effects of Pinhole on Distance Vision

If distance vision is subnormal (e.g worse than 6/9.5 or 6/12), depending on the age of participants, there are 3 com- mon clinical causes: uncorrected refractive errors/functional problems (lazy eye) or pathology (eye disease)

You can use a pinhole to differentiate uncorrected refractive errors (VA improves with pinhole) from the others. Note: Whether VA improves or not with pinhole, note that they still failed this test if either eye has subnormal VA.

Plus Blur Lens (To Screen for Hyperopia)

This is used for those with good distance visual acuities in order to identify participants who may suffer from far-sightedness. Alternatively, the near visual acuity test may be used for hyperopia detection.

Place + 3D lens in front of the patient’s eye and ask if they can still read the letters clearly. Under normal circumstances, a plus lens should blur the letters.

Near Vision: Visual Acuity

To screen for hyperopia, focusing problems and astigmatism

Procedures:

Proper near VA chart should be used. Ask the Px to read the smallest line at 40 cm or at the participant’s habitual working distance. You should record units in M-notation.

Colour Vision Screening HRR 4th Edition, Ishihara Test Color Vision Testing Made Easy

Procedures:

  1. Glasses are allowed but not essential. The book should be placed perpendicular to the participant’s line of sight.
  2. Make sure there is adequate lighting + Working Distance = 75cm
  3. Demo Plates: Ishihara- Plate #1; HRR 4th Edition- Plates #1 to #4; CVME- Demo
  4. For HRR 4th Edition: Screening Test Plates #5 to #10 (total 6 plates):

ASK:

Number: How Many symbols do you see?

Name: What are they?

Location: Where are they?

Note the number of incorrect response(s). Fail if any errors are re- ported on the screening plates. Participants who make only 2 or less er- rors should be re-tested or tested with another test to ensure accuracy. Please follow instructions on booklet.

  1. For Ishihara: Ask the Px to identify the numbers on the following pages: 1-15 (Pages:1,2,4,8,10,14 for a very basic/quick screening). Can omit Plates #16 & 17.
  2. For CVME: Pre-School Children: Ask them to show you where the “ball” is in Plates #1-9
  3. Note the number of correct response(s).

Allow about 3 secs / plate.

If the Px is illiterate (not educated to recognize numeric signs), ask the Px to trace the lines or drawings with a cotton swab Q-tip. Remind par- ticipants not to touch the targets.

“Fail” ≤ 13/15 Plates Correct (Ishihara = 2 or more errors); For CVME: < 8/9 Balls Identified Correctly

How to record?

Eg. Ishihara Both Eyes: 2/15 correct (missing Plate #’s: 2,3…) or fail). Ab- normal colour vision

Points to Remember!

Color vision books should be closed when not in use

Never touch color plates with your fingers as the oil on your skin can damage the plates

Stereopsis (3D Testing)

This test checks for problems with depth perception.

DO NOT WIPE ALCOHOL ON THE VIEWING SURFACES OF THE POLARIZED GLASSES or INSIDE THE TEST BOOKLET

Procedures:

  1. Place the polarized glasses on the participant. If the participant wears prescription glasses, place polarized glasses over their glasses. You can entice the participant by telling them these are “magic glasses” to see special pictures only he/she can see.
  2. Be sure the participant keeps their head straight and does not tilt or move their head around during the test.

For Stereo Smile 3 Test

  1. Hold the sample raised Smiley Face test target. Ask the child to point to the figure.

  2. Practice using the sample card and blank card together by presenting the cards to the participant and asking them to point to the card with the “Smiley Face” on it.

  3. Substitute the Smiley Face test card with test cards A–>B–>D–>C (or E) according to instruction booklet.

  4. Hold the Test Card and the Blank Card about 40 cm from the participant and ask the participant to identify

    where the “picture” is. Repeat this 4 times. Record last card with 4 out of 5 times correct

Demo+Blank --> 480 sec arc+Blank --> 120 sec arc+Blank–> 60 sec arc+Blank (use 240 if 120 cannot be appreciated by the participant)