Method and contact lenses for treating presbyopia

A method of correcting or alleviating presbyopia in humans, comprising:

• fitting a first contact lens to a first eye, said first contact lens having an optical zone adapted to provide a corrected near and far image for said first eye;
• and
• fitting a second contact lens to the second eye, said second contact lens having an optical zone adapted to provide a corrected far and near image for said second eye,
• wherein each of said first and second contact lenses has an optical zone with a first power provided by the shape, curvature and material of the lens to provide one corrected image and a second power provided by diffractive means which is additive to, or subtractive from, said first power to provide a second corrected image, the diffractive means being arranged so that the amount of light directed into the near image by the first contact lens is substantially greater than that directed into the far image by that lens, and the light directed into the far image by the second contact lens is substantially greater than that directed into the near image by that lens, so that each of the eyes sees one of the two images as being of relatively high intensity while maintaining a large amount of stereoscopic vision.