Worth four dot test assesses the client´s flat fusion ability at distance and near. The hand-held test in front of you is also used to detect a small unilateral central scotoma. The test is indicated when stereopsis is below 40 seconds of arc. It is also used in the differential diagnosis of unilateral decreased visual acuity. The traditional test is performed on a paper form. The client reports what colour the circle is. In the application, client simply taps on a coloured circle at the top of the screen and their dominant eye is displayed on the screen.
Equipment and set-up:
Put a red glass filter in front of the client´s right eye and the green filter in front of the left eye over the correction for the distance. The test is held at 40 cm. Show the client this test and ask them how many light spots they see.
Interpreting the results:
- If the client recognises four dots, they have normal flat fusion
- If the client reports that they see two red dots, they are using only the right eye, therefore they are suppressing their left eye.
- If the client reports that they see three green dots, they are using only their left eye, therefore they are suppressing their right eye.
- If the client sees 5 dots, ask where the green ones are located. Based on the response, we can determine the relationship of the visual axes of the two eyes:
- If the red dots are to the right of the green ones, the client has an ESO deviation.
- If the red dots are to the left of the green dots, the client has an EXO deviation
- If the red dots are above the green dots, the client has a RIGHT HYPODEVIATION (or left hyperdeviation)
- If the red dots are below the green dots, the client has a right RIGHT HYPERDEVIATION (or left hypodeviation).
Testing for a central scotoma:
- Hold this test at 40 cm
- Ask the patient to continue fixating four dots and to report if the number of dots drops to either 3 or 2 at any time
- Slowly start to move the test away from the patient
- Stop when the patient reports a change in number of dots and estimate the distance at which it occurs
- If the patient sees all four dots at 3 metres the test stops and you can record “no suppression to 3 metres”
Determine which eye is suppressing then ask a patient to cover the eye that is not suppressing and to report whether or not the suppressed dots reappear. If the dots reapper, the patient has a suppression scotoma that only occurs in binocular vision. If the dots do not reappear, the patient has a unilateral scotoma