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PURPOSE To assess the patient’s flat fusion ability at distance and at near．The hand held Worth 4 Dot flashlight is also used to detect a small unilateral central scotoma．
INDICATIONS
The Worth 4 Dot test is indicated when stereopsis is below 40 seconds of arc．It is also used in the differential diagnosis of unilateral decreased visual acuity．
EQUIPMENT
Worth 4 Dot target.
Red-green glasses．
SET-UP
·The patient wears his habitual correction for the distance being tested．
·The patient wears the red-green glasses over his correction, with the red lens over his right eye and the green lens over his left eye．
·The examiner turns on the Worth 4 Dot box mounted at the end of the examination room for distance testing．The Worth 4 Dot flashlight is used for near testing and for testing for a central spression scotoma．The near target is initially held at 16 in．
STEP-BY-STEP PROCEDURE
TO TEST THE PATIENT’S FLAT FUSION ABILITY AT DISTANCE OR AT NEAR
1．Show the patient the Worth 4 Dot target with the white dot at the bottom and the red dot at the top．
2．Ask the patient how many spots of light he sees．
a. If the patient reports that he sees four dots，he has normal flat fusion．
b．If the patient reports that he sees two red dots，he is using only his right eye and is spressing his left eye．
c．If the patient repots that he sees three green dots, he is using only his left eye and is spressing his right eye．
d．If the patient reports that he sees five dots，ask the patient where the green ones(seen by the patient’s left eye)are located：to the right, left，above, or below the red ones(seen by the patient’s right eye)．Based on the patient’s response, determine the relationship of the visual axes of the two eyes．If the red dots are to the right of the green dots，the patient has an eso deviation．If the red dots are to the left of the green dots, the patient has an exo deviation．If the red dots are above the green dots，the patient has a left hyper deviation．If the red dots are below the green dots, the patient has a right hyper deviation (see Figure 2-5)．
TO TEST FOR A CENTRAL SUPPRESSION SCOTOMA
This can be done only if the patient has normal flat fusion with the Worth 4 Dot at 16 in．
1．Hold the Worth 4 Dot flashlight 16 in from the patient with the white dot at the bottom and the red dot at the top．
2．Instruct the patient to continue fixating on the flashlight and to report if the number of dots changes from four dots to either two or three dots at any time．
3．Slowly begin to move away from the patient．Ask the patient to report any changes in the number of dots he sees．
4．Stop when the patient reports a change in the number of dots．Estimate the distance at which this occurs．If the patient still repots seeing four dots at a distance of 10 feet, stop the test and record “no spression to 10 feet．”
5．Determine which eye is spressing．Then ask the patient to cover the eye that is not spressing and to report whether or not the spressed dots reappear．If the dots reappear，the patient has a spression scotoma that occurs only under binocular conditions．If the dots do not reappear，the patient has a unilateral scotoma．
RECORDING
For testing flat fusion：
·Record the distance at which the test was done．
·If the patient sees 4 dots， record “Fusion．”
·If the patient sees 2 dots, record “Spression OS．”
·If the patient sees 3 dots, record “Spression OD．”
·If the patient sees 5 dots, record “Diplopia” and the type of deviation.
a．Green dots to the left of red dots：“Eso”(uncrossed diplopia)．
b．Green dots to the right of red dots：“Exo”(crossed diplopia)．
c．Green dots above red dots：“R hyper．”
d．Green dots below red dots：“L hyper．”
e．Combinations of vertical and horizontal deviations are possible．
When using the Worth 4 Dot flashlight to detect a central spression scotoma，record the distance at which spression occurred．Which eye is spressing，and whether the dots reappeared or not when the seeing eye was occluded．
EXAMPLES
For flat fusion testing at distance or near：
Worth 4 Dot—fusion at distance
Worth 4 Dot—fusion at 16″
Worth 4 Dot—fusion at distance；spression OS at 16″
Worth 4 Dot—diplopia．R hyper eso at 16″
For central spression scotoma testing:
·Fusion at 16″and no spression to 10′．
·Fusion at 16″, spresses OS at 6′，dots reappear when OD occluded． |
