Crossed and Uncrossed Diplopia

UNCROSSED diplopia:

 In convergent squint, the eyeball is rotated inward. Instead of falling on the fovea, the light from the object falls on the nasal side of the retina. Nasal side of the retina is is supposed to receive light from the temporal side of the visual field. So the image formed on the nasal side of the retina will be perceived by the brain as being on the temporal side of the visual field. So in convergent squint, instead of seeing a single image, 2 images will be seen in the temporal fields of each eye. The left eye sees the image on the left and the right eye sees the image on the right – This is UNCROSSED diplopia.

 CROSSED diplopia:

 In divergent squint, The eyeball being rotated outward, the image falls on the temporal side of the retina. Images formed on the temporal side of the retina is perceived as being from the nasal field by the brain. So the image seen by the left eye will be perceived as being on the right side and that seen by the right eye will be perceived as being on the left side – CROSSED diplopia.

 This video will make things more clear:

Credit: PGBLAZER

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