Balanced progressive lens

A series of progressive ophthalmic lens elements, each lens element including a lens surface having

• an upper viewing zone having a surface power to achieve a refracting power corresponding to distance vision;
• a lower viewing zone having a different surface power than the upper viewing zone to achieve a refracting power corresponding to near vision;
• and
• an intermediate zone extending across each lens element having a surface power varying from that of the upper viewing zone to that of the lower viewing zone;
• the progressive ophthalmic lens series including
• a first set of lens elements having a base curve(s) suitable for use in providing a range of distance prescriptions for a first specified category of patient, each lens element within a set differing in prescribed addition power and including a progressive design, such that
• one or more of the upper, intermediate and lower viewing zones of each lens element is designed optically to reduce or minimise a selected measure of blur for the corresponding range of object distances, and wherein the selected measure of blur is the RMS power error, the surface integral of the weighted RMS power error being minimised over an area limited by a prescribed variable distance from the visual fixation locus in one or more of the upper, intermediate and lower viewing zones;
• at least a portion of the peripheral region of each lens element surface being designed to reduce or minimise one or more surface characteristics known to correlate with the sensation of swim.

A progressive ophthalmic lens element including a lens surface having

• an upper viewing zone having a surface power to achieve a refracting power corresponding to distance vision,
• a lower viewing zone having a different surface power than the upper viewing zone to achieve a refracting power corresponding to near vision, and
• an intermediate zone extending across the lens element having a surface power varying from that of the upper viewing zone to that of the lower viewing zone;
• one or more of the upper, intermediate and lower viewing zones being designed optically to reduce or minimise a selected measure of blur for the corresponding range of object distances, and wherein the selected measure of blur is the RMS power error, the surface integral of the weighted RMS power error being minimised over an area limited by a prescribed variable distance from the visual fixation locus in one or more of the upper, intermediate and lower viewing zones;
• at least a portion of the peripheral region of the surface of the lens element being designed to reduce or minimise one or more surface characteristics known to correlate with the sensation of swim;
• and
• the degree of zone congruence of the lens element in the intermediate zone is increased, and consequently in the lower viewing zone is slightly decreased.

A method of designing a progressive ophthalmic lens element including a first lens surface having

• an upper viewing zone having a surface power corresponding to distance vision, a lower viewing zone having a different surface power than the upper viewing zone to achieve a refracting power corresponding to near vision, and
• an intermediate zone extending across the lens element having a surface power varying from that of the upper viewing zone to that of the lower viewing zone;
• one or more of the upper, intermediate and lower viewing zones of each lens element is designed optically to minimise a selected measure of blur for the corresponding range of object distances;
• and
• at least a portion of the peripheral region of each lens element surface being designed to minimise one or more surface characteristics known to correlate with the sensation of swim;
• which method includes
• selecting a base surface function for the lens surface
• wherein, for a symmetrical design, the base surface function is a Taylor expansion
• as follows:
• z
• ⁡
• (
• x
• ,
• y
• )
• =
• z
• 0
• ⁡
• (
• y
• )
• +
• h
• ⁡
• (
• y
• )
• 2
• ⁢
• x
• 2
• +
• x
• 4
• 12
• ⁡
• [
• g
• 0
• ⁡
• (
• y
• )
• +
• g
• 2
• ⁡
• (
• y
• )
• ⁢
• x
• 2
• +
• ⋯
• ]
• wherein
• the functions z0(y) and h(y) are determined by the desired eye path power progression profile p(y)
• the functions gi(y) tare free coefficients;
• and
• for an asymmetric design, the x-coordinate is substituted by the transformed equivalent ζ=x−u(y)
• wherein the function u(y) describes the variation of the inset along the eye path;
• and
• odd powers of ζ are added in the Taylor expansion;
• selecting a first merit function to minimise the weighted ray traced RMS power error within the optical zones;
• computing the coefficients gi(y) of the surface function that minimise the first merit function within the upper and lower viewing zones of the ophthalmic lens element;
• separately selecting a second merit function to minimise one of more surface characteristics known to correlate with the sensation of swim, within at least the peripheral region;
• computing the coefficients of the surface function that minimise the second merit function within the peripheral region of the ophthalmic lens element;
• and
• fabricating an ophthalmic lens element having a lens surface shaped according to said modified surface function.