Progressive multifocal ophthalmic lens

A progressive multifocal ophthalmic lens comprising an aspherical surface having a mean sphere and a cylinder at every point thereof, said surface comprising:

• a distance vision portion including a control point L for distance vision,
• a near vision portion including a control point P for near vision,
• an intermediate vision portion between said distance vision portion and said near vision portion,
• a principal meridian of progression passing through said three portions,
• the said lens having:
• a power addition value A defined as a variation in mean sphere between said control point L for distance vision and said control point P for near vision,
• a base B defined as a value of mean sphere at said control point L for distance vision, and
• a width of said near vision portion varying not only as a function of said power addition value A, but also as a function of said base B, thereby ensuring presence of a substantially constant object field for various values of said power addition and said base,
• wherein said lens has a slope of mean sphere within a radius of 25 mm around a geometrical center O of the lens of a value less than a maximum value which is directly proportional to the power addition A of said lens.

A progressive multifocal ophthalmic lens comprising an aspherical surface having a mean sphere and a cylinder at every point thereof, said surface comprising:

• a distance vision portion including a control point L for distance vision,
• a near vision portion including a control point P for near vision,
• an intermediate vision portion between said distance vision portion and said near vision portion,
• a principal meridian of progression passing through said three portions,
• the said lens having:
• a power addition value A defined as a variation in mean sphere between said control point L for distance vision and said control point P for near vision,
• a base B defined as a value of mean sphere at said control point L for distance vision, and
• a width of said near vision portion varying not only as a function of said power addition value A, but also as a function of said base B, thereby ensuring presence of a substantially constant object field for various values of said power addition and said base,
• wherein for each value of said base B, all points of coordinates (A, L.sub.VP) plotting a possible width L.sub.VP of said near vision portion for a possible value of said power addition A, in a plot of L.sub.VP against A, are in an area comprised between
• a first straight line represented by equation
• L.sub.VP =A.sub.0 +A.sub.1min .multidot.(A-0.5)
• and
• two intersecting half lines one of which is defined, for values of power addition A on said plot less than or equal to 2.00 diopters, by equation:
• L.sub.VP =A'.sub.0 +A.sub.1max .multidot.(A-0.5)
• and another of which, for values of power addition on said plot greater than or equal to 2.00 diopters, is substantially horizontal,
• said half lines intersecting at a point whose coordinate along said power addition axis of said plot is 2.00,
• where A.sub.0 and A'.sub.0 are expressed in mm and vary as a function of said base B, A.sub.1min and A.sub.1max are fixed value coefficients, expressed in mm per diopter, that are independent of said base B, and A is the power addition of said lens expressed in diopters.

A family of progressive multifocal ophthalmic lenses having various values of base and/or power addition values, wherein each lens comprises an aspherical surface having a mean sphere and a cylinder at every point thereof, said surface comprising:

• a distance vision portion including a control point L for distance vision,
• a near vision portion including a control point P for near vision,
• an intermediate vision portion between said distance vision portion and said near vision portion,
• a principal meridian of progression passing through said three portions,
• the said lenses having:
• a power addition value A defined as a variation in mean sphere between said control point L for distance vision and said control point P for near vision,
• and a base B defined as a value of mean sphere at said control point L for distance vision, and
• a width of said near vision portion corresponding to an object field of a select size, wherein said width is defined as a function of said power addition value and said base which has a form that the width maintains said object field of said select size for varying values of said power addition value and said base thereby ensuring presence of a substantially constant object field for various values of said power addition and said base.

A method of manufacturing a progressive multifocal ophthalmic lens, said lens comprising an aspherical surface having a mean sphere and a cylinder at every point thereof, said surface comprising:

• a distance vision portion including a control point L for distance vision,
• a near vision portion including a control point P for near vision,
• an intermediate vision portion between said distance vision portion and said near vision portion,
• a principal meridian of progression passing through said three portions,
• the said lens having:
• a power addition value A defined as a variation in mean sphere between said control point L for distance vision and said control point P for near vision,
• a base B defined as a value of mean sphere at said control point L for distance vision, and
• a width of said near vision portion,
• said method comprising:
• selecting a power addition value and a base,
• defining an object field of select size,
• determining the width of said near vision portion to correspond to said object field by calculating said width as a function of said power addition value and said base.