Pair of multifocal progressive spectacle lenses

A pair of progressive ophthalmic spectacle lenses, each lens having an aspherical surface with a far vision zone, an intermediate vision zone and a near vision zone, and good monocular and binocular foveal vision along a principal meridian, each point M of the aspherical surface having a mean sphere defined by the formula:

• S = n - 1 2 ⁢ ( 1 R 1 + 1 R 2 )
• where R1 and R2 are maximum and minimum radii of curvature expressed in meters, and n is the refractive index of the lens material,
• where the aspherical surface of each lens has an addition (A) defined as the difference in mean sphere between a reference point of the near vision zone and a reference point of the far vision zone, the addition of the aspherical surface of each lens being one diopter or less,
• wherein for a given direction of sight for a point (M) in the object space a binocularity parameter is defined as the relative difference ΔS of the mean sphere for points (MD, MG) on the aspherical surface of the right and left lenses through which a wearer sees said point (M)
• said relative difference being defined by the formula Δ ⁢ ⁢ S = 100 × S D - S G ( S D + S G ) / 2
• where SD and SG are the values of mean sphere at said points (MD, MG) on the aspherical surface of the right and left lenses through which the wearer sees said point (M), and
• wherein the absolute value of the peak to valley value of the binocularity parameter, defined as the difference between the largest value and the smallest value of the binocularity parameter on one side of the sagittal plane, is about 3.28 or less.

A pair of progressive ophthalmic spectacle lenses, each lens having an aspherical surface with a far vision zone, an intermediate vision zone and a near vision zone, and good monocular and binocular foveal vision along a principal meridian, each point M of the aspherial surface having a mean sphere defined by the formula:

• S = n - 1 2 ⁢ ( 1 R 1 + 1 R 2 )
• where R1 and R2 are maximum and minimum radii of curvature expressed in meters, and n is the refractive index of the lens material,
• where the aspherical surface of each lens has an addition (A) defined as the difference in mean sphere between a reference point of the near vision zone and a reference point of the far vision zone, the addition of the aspherical surface of each lens being two diopters,
• wherein for a given direction of sight for a point (M) in the object space, a binocularity parameter is defined as the relative difference ΔS of the mean sphere for points (MD, MG) on the aspherical surface of the right and left lenses through which a wearer sees said point (M), and
• wherein the absolute value of the peak to valley value of the binocularity parameter, defined as the difference between the largest value and the smallest value of the binocularity parameter on one side of the sagittal plane, is about 8 or less.

A method of characterizing a pair of progressive ophthalmic spectacle lenses, comprising

• defining a binocularity parameter by
• selecting a direction of sight;
• selecting a point in the object space;
• tracing rays to the selected point, through the right and left lenses;
• comparing the value of the mean sphere at the respective intersection of the rays with the right and left lenses.