The Binocular tests group includes a number of tests and stimuli to assist the clinician in determining the patients binocular vision status at near.

The test are selected from the Binocular Vision Test Options list.

Horizontal and Vertical fixation disparity

The fixation disparity test included in the Thomson Near Chart has been developed and carefully evaluated at City University.

The patient views the device binocularly through red and green filters. The entire field except for the two monocular markers (red and cyan), is seen binocularly. The patient is asked to look at the cross in the centre and report if the markers above and below the cross are in a straight line. If they are mis-aligned, appropriate prisms or lenses are used to align them in the normal manner.

It is very important that the device colours are well-matched to the spectral properties of the red and green glasses used to ensure that the bars are seen monocularly and there are no binocular cues.  The precise colour of the red and cyan bars can be adjusted by selecting Calibrate.

Binocularity test

For this test the patient views the rows of words through red/green glasses.

The first two letters are seen through the Red filter (usually right eye) and the last two letters are seen through the Green filter (usually left eye).  The central letter is seen by both eyes,

If a patient is suppressing the right eye they will only see the last three letters while if they are suppressing the left eye, they will only see the first three letters. If they are binocular, they will see all five letters.

By asking the patients to read progressively smaller letters, some grading of binocular vision is possible.

Worth 4 dot test

The Worth 4 dot test provides a quick way of establishing if a patient is suppressing one eye.

The patient views the screen through the red / green filters and is asked “how many dots can you see"?

The black dot will be seen by both eyes, the cyan dots will be seen by the right eye only and the red dot will be seen by the left eye only.

Therefore, if the patient is binocular, they will see 4 dots. If they are suppressing the right eye they will see 2 dots, if they are suppressing the left eye they will see 3 dots

Horizontal and Vertical Maddox rod targets

These screens allow for near phoria to be measured using a Maddox rod.

To measure horizontal phoria, the vertical white bar is shown and a Maddox Rod is placed in front of one eye with the grooves horizontal.

The patient will see a vertical streak through the Maddox Rod while the other eye will see the bar.  The clinician inserts horizontal prisms until the streak appears to pass through the bar.

To measure vertical phoria, the horizontal white bar is shown and a Maddox Rod is placed in front of one eye with the grooves vertical.

The patient will see a horizontal streak through the Maddox Rod while the other eye will see the bar.  The clinician inserts vertical prisms until the streak appears to pass through the bar.

Near Point of Convergence target

When assessing the Near Point of Convergence (NPC), a vertical line is slowly moved towards the patient's nose.  The patient is asked to report if/when the line goes doubled while the clinician watches for the breakpoint.  The line is placed toward the top of the screen to allow the clinician to peer over the device and get close to the visual axis.