Optical Axis and Visual Axis
The optical axis is the centre of a lens where light travels through and is not bent. The visual axis is where light travels through the eye to the retina and is essentially understood to not be bent.
Sometimes glasses are given with the optical axis shifted away from the visual axis. This creates a prismatic effect. Prisms can be used to diagnose and treat binocular vision and other orthoptics problems which cause diplopia such as:
- Positive and negative fusion problems
- Positive relative accommodation and negative relative accommodation problems
Read more about this topic: Eyeglass Prescription
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