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Appendix
Setup and Administration of Binocular Vision and Accommodation Tests
Cover Test
EQUIPMENT NEEDED
Gulden fixation stick
20/30 target for distance (or two lines above threshold if acuity is not 20/30)
Occluder
SETUP
1. If the patient wears glasses for close work, these should be used.
2. For distance testing, isolate a 20/30 letter on the distance visual acuity chart.
3. For near testing, hold Gulden fixation stick 40 cm from patient’s face and direct the patient’s attention to the isolated 20/30 letter.
PROCEDURE: UNILATERAL AND ALTERNATE COVER TEST
1. Instruct the patient to fixate the letter and to “keep it clear” throughout testing.
2. Cover the subject’s right eye (RE) and watch left eye (LE) as RE is covered.
3. Cover the subject’s LE and watch RE as LE is covered.
4. Allow the subject adequate time to regain fixation.
5. Neutralize the alternate cover test (ACT) according to the following procedure:
(a) Select a loose prism nearest in power to the estimated magnitude.
(b) Cover one eye with the occluder, interposing the prism behind the occluder. (Uncovered eye is therefore fixating.)
(c) Switch the occluder and observe the eye movement behind the prism. (Only observe eye behind prism during ACT.)
(d) Interpose different magnitudes of prism until neutrality is obtained by a bracketing method.
(e) Record the amount and base of prism.
(f) Repeat the procedure at 40 cm using a single 20/30 letter on the Gulden fixation stick.
If an intermittent strabismus is present, use the intermittent exotropia scale (Table 1.3) and follow the directions below:
(a) The control scale is for both distance (3 m) and near (0.33 m) fixation.
(b) The fixation objects are accommodative and age appropriate, such as small stickers and videos for younger children and letters for older children and adults.
(c) Levels 5 to 3 are assessed during a 30-second observation period. If exotropia is observed, testing stops and the control score is recorded as 5, 4, or 3 at that distance.
(d) If no exotropia is observed during the 30-second observation period, testing continues.
(e) Levels 2 to 0 are then assessed and graded as the worst of three successive 10-second periods of occlusion. An occluder is placed over the right eye for 10 seconds, and on removal, the time required to re-fuse is noted.
(f) This process is repeated for the left eye, and then a third occlusion trial is performed on the eye that required the longest time to re-fuse.
(g) The worst of these three 10-second trials is recorded, resulting in a control score of 2, 1, or 0 at that distance.
IMPORTANT POINTS
1. Control accommodation using
(a) 20/30 target
(b) Occasional movement of target
2. The cover test is objective and can be used with young children.
Watch for small horizontal movements and small movements of the upper lashes, if a vertical phoria is suspected. With practice, clinicians can detect less than Δ heterophoria on the cover test.
Measurement of Horizontal Phoria: von Graefe Technique
EQUIPMENT NEEDED
Phoropter
Isolated 20/30 target
SETUP
1. Seat the patient comfortably behind the phoropter with the patient’s distance correction in place.
2. Use a single 20/30 letter on the distance chart.
3. Place the Risley prisms before both eyes and set the prism before the left eye at about 10 to 12 base-in. Set the prism before the right eye at 6 base-down.
PROCEDURE
1. Instruct the patient to open both eyes and ask how many targets he or she sees.
2. Ask the patient to look at the lower target (seen by right eye) and keep it clear at all times.
3. Instructions: “I will be moving the upper target from side to side until it is directly above the lower target. Look at the lower target, keep it clear, and tell me when the upper target moves directly above the lower target.”
4. Move the Risley prisms at about a rate of 2 Δ per second.
5. Record the amount and direction of prism when the patient reports alignment.
6. Repeat the procedure again, using an isolated 20/30 letter or vertical line of 20/30 print positioned at 40 cm.
IMPORTANT POINTS
1. Control accommodation by stressing the importance of keeping the target clear.
2. This test tends to have the poorest repeatability of the various tests used to assess motor alignment.