Double vision / diplopia

Double vision is the misalignment of the two images on the retinas of a pair of eyes - often called diplopia by doctors and opticians.  Diplopia occurs when one eye turns away from its normal axis of vision (shown in red on the diagram). This is sometimes called a squint. A PRISM is used to realign the image in the squinting eye.

A sudden onset of double vision must always be investigated immediately by an optician or doctor

Correcting double visionTypes of double vision
Normal eye, the light ray passes correctly along the optic axis
Eye with a squint, light ray is not aligned to the optic axis
Eye with corrected squint, the prism lens re aligns the light ray to the optic axis

Horizontal diplopia


Vertical diplopia


Mixed diplopia



Prisms can be worked into a spectacle lens prescription with very little detriment to the cosmetic appearance of the lenses.