In diplopia mapping with prisms, which method is commonly used to dissociate the eyes and determine prism values?

In diplopia mapping with prisms, which method is commonly used to dissociate the eyes and determine prism values?

• A. Maddox rod with prism dissociation.
• B. Circle test.
• C. Tonometry.
• D. Ishihara plates.

Answer: (A)

Dissociating binocular fusion is essential to reveal true misalignment, and the Maddox rod with prism dissociation is the standard way to do this. The Maddox rod turns a point light into a streak or line for one eye, so the two eyes no longer fuse their images. This makes any misalignment show up as diplopia even if the patient wouldn’t notice fusion normally. With a fixation target in view, you adjust prisms in front of one eye while the patient reports when the two images line up, recording the prism amount needed to eliminate the diplopia. Repeating this across gaze positions builds a map of prism values required to align the eyes. The other options don’t serve this dissociating purpose: a circle test is used for a different kind of screening or motility assessment, tonometry measures intraocular pressure, and Ishihara plates test color vision.

Dissociating binocular fusion is essential to reveal true misalignment, and the Maddox rod with prism dissociation is the standard way to do this. The Maddox rod turns a point light into a streak or line for one eye, so the two eyes no longer fuse their images. This makes any misalignment show up as diplopia even if the patient wouldn’t notice fusion normally. With a fixation target in view, you adjust prisms in front of one eye while the patient reports when the two images line up, recording the prism amount needed to eliminate the diplopia. Repeating this across gaze positions builds a map of prism values required to align the eyes.

The other options don’t serve this dissociating purpose: a circle test is used for a different kind of screening or motility assessment, tonometry measures intraocular pressure, and Ishihara plates test color vision.