A question of colour

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As long as the eye is viewing along the optical axis of a spectacle lens, it will perform perfectly and provide a point image of a point object. But as the eye moves away from the centre of the lens to gaze through the periphery, the aberrations in the lens will cause the image to deteriorate. The aberration most likely to be noticed by the patient is transverse chromatic aberration (TCA).

This is seen as coloured fringing around areas of stark contrast when viewing through the periphery of the lens. Most patients do not notice or complain about this fringing, but once they become aware of it - usually prompted by a practitioner asking, 'Do you see any coloured fringing?' - it will be impossible to ignore. This is the one aberration where the only 'cure' is to change lens material.