JP2004309588A

JP2004309588A - Progressive power lens and its design method

Info

Publication number: JP2004309588A
Application number: JP2003099623A
Authority: JP
Inventors: Tadayuki Kaga; 唯之加賀
Original assignee: Seiko Epson Corp
Current assignee: Seiko Epson Corp
Priority date: 2003-04-02
Filing date: 2003-04-02
Publication date: 2004-11-04

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new progressive power lens having eyesight compensating ability and astigmatism correcting ability on the same refractive surface by providing a new composing expression for composing a progressive refractive surface and a toric face. <P>SOLUTION: A refractive surface 2 on an eyeball side or a refractive surface 3 on an object side is formed as a curved surface expressed by a composed refractive surface 14+15 where an original progressive refractive surface 14 set only to achieve desired eyesight compensating characteristic and an original toric surface 15 set only to achieve desired astigmatism correcting characteristic are composed by using the composing expression shown by a composing expression (1). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、視力補正能力と乱視矯正能力とを有する累進多焦点レンズ及びその設計方法に関する。
【０００２】
【従来の技術】
累進多焦点レンズは、屈折力の異なる２つの視野部分と、これらの間で屈折力が累進的に変わる視野部分とを備えたレンズであり、これらの視野部分に境目がなく外観的に優れ、さらに、１つのレンズで異なる屈折力の視野を得ることができる。このため、老視などの視力の補正機能を備えた眼鏡レンズとして多く用いられている。
【０００３】
図７（ａ）に、眼鏡レンズとして多く用いられている従来の累進多焦点レンズの一般的な構造を示す。この累進多焦点レンズ１００は、遠距離の物を見るための視野部分である遠用部１１が上方に設けられ、近距離の物を見るための遠用部１１と異なる屈折力を備えた視野部分が近用部１２として遠用部１１の下方に設けられている。そして、これら遠用部１１と近用部１２が、遠距離と近距離の中間距離の物を見るために連続的に変化する屈折力を備えた視野部分である累進部１３によって滑らかに連絡されている。
【０００４】
眼鏡用に用いられる単板のレンズにおいては、図７（ｂ）に示すように、眼球側の屈折面２と、注視する物体側の屈折面３の２つの屈折面によって眼鏡レンズに要求される全ての性能、例えば、ユーザーの度数に合った頂点屈折力、乱視を矯正するための円柱屈折力、老視を補正するための加入屈折力、さらには斜位を矯正するためのプリズム屈折力などを付与する必要がある。このため、図７（ｂ）に示すように、従来の累進多焦点レンズ１００ａにおいては、これら遠用部１１、近用部１２及び累進部１３を構成するために連続的に変化する屈折力を与える累進屈折面１４が物体側の屈折面３に形成され、眼球側の屈折面２は乱視矯正用のトーリック面１５などとして用いられている。
【０００５】
このような従来構造の累進多焦点レンズ１００ａに対し、本出願人は、累進多焦点レンズの遠用部１１と近用部１２の倍率の変動に起因する像の揺れや歪みを改善できる累進多焦点レンズを提供することを目的として、累進多焦点レンズの倍率に与える累進屈折面の配置に着目し、累進屈折面を眼球側の屈折面２に形成したいわゆる内面累進多焦点レンズ１００ｂを開発した。この発明に関しては特許文献１に記載されている。
【０００６】
この特許文献１に記載されている内面累進多焦点レンズ１００ｂは、遠用部と近用部における倍率の差を縮小でき、これに起因する像の揺れや歪みを大幅に低減できる。
【０００７】
このような内面累進多焦点レンズ１００ｂにおいては、眼球側の屈折面２に累進屈折面１４を設けるので、眼球側の屈折面２に乱視矯正用のトーリック面１５を合成することができる。眼球側の屈折面２が視力補正特性と乱視矯正特性を有する累進多焦点レンズ１００ｂは、遠用部と近用部の倍率差を必要最小限に止めることができ、像の歪みや揺れが少なく、しかも、乱視を矯正することが可能であり、乱視を有するユーザーに対してもさらに快適な視野を提供することができる。
【０００８】
眼球側の屈折面２に視力補正特性と乱視矯正特性とが付加された累進多焦点レンズ１００ｂは、眼球側の屈折面が所望の視力補正特性を発揮することのみを目的として累進屈折面（以降においてはオリジナル累進屈折面）を求める第１の工程と、眼球側の屈折面が所望の乱視矯正特性を発揮することのみを目的としてトーリック面（以降においてはオリジナルトーリック面）を求める第２の工程と、累進多焦点レンズの眼球側の屈折面を、オリジナル累進屈折面及びオリジナルトーリック面から求める第３の工程とを有する設計方法を用いることにより設計することができる。
【０００９】
上述した特許文献１では、第３の工程において、オリジナル累進屈折面とオリジナルトーリック面とを一体化する合成式が提案されている。
【００１０】
特許文献１で提案された合成式を用いて眼球側の屈折面２に累進屈折面１４とトーリック面１５を合成した累進多焦点レンズ１００ｂにおいては、従来の累進多焦点レンズ１００ａと同様に、主注視線１６のほぼ全域にわたって乱視矯正を目的とした視力補正能力が害されることがなく、しかも非点収差が非常に安定して確保できることが認められる。
【００１１】
【特許文献１】
ＷＯ９７／１９３８２
【００１２】
【発明が解決しようとする課題】
しかしながら、トーリック面とは、ある子午面内では最大の屈折力を持ち、それに直角な子午面では最小の屈折力を持つ、互いに直交する断面での曲率半径を異にした表面と定義されるが、最大の屈折力を有する子午面及び最小の屈折力を有する子午面のそれぞれの断面形状は円弧であり、これらの間の曲面形状は、特に決められていない。即ち、トーリック面の面形状の種類は無限に存在するといえる。特許文献１で提案された合成式は、計算が比較的容易であるという利点があるものの、トーリック面の形状をｘ軸方向の曲率とｙ軸方向の曲率とがそれぞれ一定であるとみなして合成しているに過ぎない。
【００１３】
従って、トーリック面の面形状を表す他の合成式を提供することにより、より優れた乱視矯正能力を有する累進屈折面とトーリック面との合成屈折面を提供できる可能性がある。
【００１４】
本発明は、上記事情に鑑みてなされたもので、累進屈折面とトーリック面とを合成する新規な合成式を提供することにより、視力補正能力と乱視矯正能力とを同一の屈折面に備える新規な累進多焦点レンズを提供することを目的とする。
【００１５】
また、本発明は、かかる累進多焦点レンズの設計方法を提供することを目的とする。
【００１６】
【課題を解決するための手段】
本発明の累進多焦点レンズは、乱視軸方向の断面と乱視軸方向と直交する方向の断面がそれぞれ円弧であるトーリック面のそれぞれの円弧間の補間を曲率をサインカーブで分布させる式を用い、これと累進面とを合成する合成式（１）を用いて得られた合成屈折面を眼球側の屈折面又は物体側の屈折面に有するものである。
【００１７】
このような累進多焦点レンズは、所望の視力補正特性を発揮することのみを目的として累進屈折面（以降においてはオリジナル累進屈折面）を求める第１の工程と、所望の乱視矯正特性を発揮することのみを目的としてトーリック面（以降においてはオリジナルトーリック面）を求める第２の工程と、曲率をサインカーブで分布させて円弧間を補間したオリジナルトーリック面とオリジナル累進屈折面とを合成する合成式（１）から合成屈折面を求める第３の工程とを有する設計方法を用いることにより設計することができる。
【００１８】
従って、請求項１記載の発明は、異なる屈折力を備えた遠用部及び近用部と、これらの間で屈折力が累進的に変化する累進部とを備えた累進屈折面を眼球側の屈折面又は物体側の屈折面に有する視力補正用の累進多焦点レンズにおいて、前記眼球側の屈折面又は物体側の屈折面が、所望の視力補正特性を発揮することのみを目的として設定されたオリジナル累進屈折面と、所望の乱視矯正特性を発揮することのみを目的として設定されたオリジナルトーリック面とが合成された合成屈折面であり、物体側から眼球側に前記累進屈折面の中心を通る軸をｚ軸、前記オリジナルトーリック面の乱視軸方向をｘ軸、ｚ軸とｘ軸とに直交する軸をｙ軸としたとき、前記オリジナル累進屈折面の近似曲率Ｃｐ、ｘ軸方向の曲率Ｃｘ、ｙ軸方向の曲率Ｃｙを用いて、前記合成屈折面の任意の点Ｐ（ｘ_ｐ，ｙ_ｐ，ｚ_ｐ）における前記値ｚ_ｐが、次の式（１）で表されることを特徴とする累進多焦点レンズを提供する。
【００１９】
【数３】

【００２０】
請求項２記載の発明は、請求項１記載の累進多焦点レンズにおいて、前記合成屈折面が設けられた面と反対側の眼球側の屈折面又は物体側の屈折面が、球面又は回転対称非球面であることを特徴とする累進多焦点レンズを提供する。
【００２１】
請求項３記載の発明は、異なる屈折力を備えた遠用部及び近用部と、これらの間で屈折力が累進的に変化する累進部とを備えた累進屈折面を眼球側の屈折面又は物体側の屈折面に有する視力補正用の累進多焦点レンズの設計方法において、
前記眼球側の屈折面又は物体側の屈折面が視力補正特性を発揮することのみを目的とするオリジナル累進屈折面を求める第１の工程と、前記眼球側の屈折面又は物体側の屈折面が所望の乱視矯正特性を発揮することのみを目的とするオリジナルトーリック面を求める第２の工程と、前記眼球側の屈折面又は物体側の屈折面として、所望の視力補正特性を発揮することのみを目的として設定されたオリジナル累進屈折面と、所望の乱視矯正特性を発揮することのみを目的として設定されたオリジナルトーリック面とが合成された合成屈折面を求める第３の工程とを有し、前記第３の工程が、物体側から眼球側に前記累進屈折面の中心を通る軸をｚ軸、前記オリジナルトーリック面の乱視軸方向をｘ軸、ｚ軸とｘ軸とに直交する軸をｙ軸としたとき、前記オリジナル累進屈折面の近似曲率Ｃｐ、ｘ軸方向の曲率Ｃｘ、ｙ軸方向の曲率Ｃｙを用い、前記合成屈折面の任意の点Ｐ（ｘ_ｐ，ｙ_ｐ，ｚ_ｐ）における前記値ｚ_ｐを、次の式（１）から求めることを特徴とする累進多焦点レンズの設計方法を提供する。
【００２２】
【数４】

【００２３】
【発明の実施の形態】
以下、本発明の累進多焦点レンズ及びその設計方法の実施の形態について説明するが、本発明は以下の実施の形態に限定されるものではない。
【００２４】
本発明の累進多焦点レンズは、異なる屈折力を備えた遠用部及び近用部と、これらの間で屈折力が累進的に変化する累進部とを備えた累進屈折面を眼球側の屈折面又は物体側の屈折面に有する。
【００２５】
図１（ａ）に示すように、本発明の累進多焦点レンズ１は、遠距離の物を見るための視野部分である遠用部１１が上方に設けられ、近距離の物をみるために遠用部１１と異なる屈折力を備えた視野部分が近用部１２として遠用部１１の下方に設けられている。そして、これら遠用部１１と近用部１２が、遠距離と近距離の中間距離の物を見るために連続的に変化する屈折力を備えた視野部分である累進部１３によって滑らかに連絡されている。
【００２６】
本発明の累進多焦点レンズでは、これらの遠用部１１、近用部１２及び累進部１３を備える累進屈折面１４を、図１（ｂ）に示すように、物体側の屈折面３（凸面、外面ともいう）に設けた外面累進多焦点レンズ１ａとしてもよい。あるいは、図１（ｃ）に示すように、累進屈折面１４を眼球側の屈折面２（凹面、内面ともいう）に設けた内面累進多焦点レンズ１ｂとしてもよい。
【００２７】
内面累進多焦点レンズ１ｂは、外面に累進屈折面１４を有する累進多焦点レンズ１ａと比較して、遠用部１１と近用部１２における倍率の差を縮小でき、これに起因する像の揺れや歪みを大幅に低減できる。眼球側の屈折面２に累進屈折面の曲率を付与すると、主注視線１６に沿った累進屈折面の曲率（曲率半径の逆数）は、遠用部１１と比較し近用部１２の方が小さくなる。また、遠用部１１においては少なくとも一部の領域で累進屈折面の曲率が主注視線１６から離れるに従って小さくなっており、また、近用部１１においては少なくとも１部の領域で累進屈折面の曲率が主注視線１６から離れるに従って大きくなる。
【００２８】
さらに、累進屈折面１４としては、主注視線１６上において累進屈折面を構成する上での非点収差を最小限とすることが望ましく、そのためには、主注視線１６の少なくとも１部の領域で、累進屈折面の曲率は直交する２方向の曲率が等しくなるようにすることが望ましい。
【００２９】
本発明の累進多焦点レンズ１においては、物体側の屈折面３と眼球側の屈折面２のいずれか一方の屈折面が視力補正能力と乱視矯正能力の両方の能力を有する合成屈折面１４＋１５で構成されている。図１（ｂ）に示す外面累進多焦点レンズ１ａの場合、物体側の屈折面３に設けられている合成屈折面１４＋１５と反対側の眼球側の屈折面２は、球面又は回転対称非球面である。図１（ｃ）に示す内面累進多焦点レンズ１ｂの場合、眼球側の屈折面２に設けられている合成屈折面１４＋１５と反対側の物体側の屈折面３は、球面又は回転対称非球面である。眼球側の屈折面２に合成屈折面１４＋１５を設けると、上述したように、乱視を矯正することが可能であると共に、遠用部１１と近用部１２の倍率差を必要最小限に止めることができ、像の歪みや揺れが少ないため、乱視を有するユーザーに対してもさらに快適な視野を提供することができる。
【００３０】
このような一方の屈折面が視力補正能力と乱視矯正能力の両方の能力を有する累進多焦点レンズの設計は、所望の視力補正特性を発揮することのみを目的として設定された累進屈折面（以降においてはオリジナル累進屈折面）を求める第１の工程と、眼球側の屈折面２又は物体側の屈折面３が所望の乱視矯正特性を発揮することのみを目的として設定されたトーリック面（以降においてはオリジナルトーリック面）を求める第２の工程と、オリジナル累進屈折面及びオリジナルトーリック面から合成式を用いて合成屈折面を求める第３の工程とで行うことができる。
【００３１】
第１の工程では、ユーザーの老視の程度や眼鏡の使い方などの状況に合わせたパラメータによってオリジナル累進屈折面を求め、その結果を座標あるいは曲率などとして記憶する。
【００３２】
第２の工程では、乱視軸に沿った断面と乱視軸と直交する方向の断面がそれぞれ円弧である円弧間の補間方法として曲率をサインカーブで分布させた面形状を想定して、オリジナルトーリック面を求める。
【００３３】
そして、第３の工程では、オリジナル累進屈折面とオリジナルトーリック面とが合成された合成屈折面を、次の合成式（１）で求める。
【００３４】
【数５】

【００３５】
ここで、図１（ｂ）、（ｃ）及び（ｄ）に示すように、眼鏡装用状態において、物体側から眼球側に累進屈折面の中心を通る軸をｚ軸、オリジナルトーリック面の乱視軸方向をｘ軸、ｚ軸とｘ軸とに直交する軸をｙ軸としたとき、ｚ_ｐは物体側又は眼球側の屈折面の垂直方向のｚ座標を示す。物体側の屈折面３に対しては物体側の屈折面３とｚ軸が交わる点を原点に、眼球側の屈折面２に対しては眼球側の屈折面２とｚ軸が交わる点を原点とする。
【００３６】
曲率Ｃｐは、オリジナル累進屈折面の任意の点Ｐ（ｘ_ｐ，ｙ_ｐ，ｚ_ｐ）における近似曲率であり、曲率Ｃｘはｘ軸方向の曲率、曲率Ｃｙはｙ軸方向の曲率である。近似曲率Ｃｐとしては、例えば半径方向の平均曲率を採用することができ、オリジナル累進屈折面上の任意の点Ｐ（ｘ_ｐ，ｙ_ｐ，ｚ_ｐ）を含みｚ軸（レンズ中心または内側頂点（０，０，０）を通る）に垂直なｘｙ平面において、点Ｐと回転対称にある点Ｐ’（−ｘ_ｐ，−ｙ_ｐ，−ｚ_ｐ）及び内側頂点（０，０，０）又は外側頂点（０，０，０）の３点を通る円の半径の逆数を用いる。
【００３７】
次に、上記合成式（１）の算出手順について説明する。図２に示すような、０度，１８０度，３６０度の時、ｘ軸方向の曲率Ｃｘとなり、９０度，２７０度の時、ｙ軸方向の曲率Ｃｙとなるようなサインカーブによる補間を考える。このときの式は
【００３８】
【数６】

【００３９】
となる。この式を変形する。
【００４０】
【数７】

【００４１】
この式をｘ、ｙ座標に変換する。
【００４２】
【数８】

【００４３】
であるので、次の式（４）が得られる。
【００４４】
【数９】

【００４５】
トーリック面として、乱視軸に沿った断面と乱視軸と直交する方向の断面が円弧である円弧間の補間方法として曲率をサインカーブで分布させる面形状を想定する。ｚ座標は曲率ｃ_{（ｘ，ｙ）}の中心からの距離
【００４６】
【数１０】

【００４７】
の円弧であるので、円弧を表す次の式（５）で表せる。
【００４８】
【数１１】

【００４９】
式（５）に式（４）を代入すると、次の式（６）が得られる。
【００５０】
【数１２】

【００５１】
この式（６）で表される面形状がオリジナルトーリック面である。ｃ_ｘ、ｃ_ｙにそれぞれＣ_ｐを合成すると、下記合成式（１）が得られる。
【００５２】
【数１３】

【００５３】
なお、オリジナル累進屈折面と前記オリジナルトーリック面の座標系が乱視軸の角度ａｘだけずれている場合は、オリジナル累進屈折面の座標系において、以下の（ｐｘ，ｐｙ，ｐｚ）における近似曲率Ｃｐを用いればよい。
【００５４】
【数１４】

【００５５】
上記合成式（１）は、特許文献１で提案された合成式と比較するとやや計算量が多くなる。また、眼球側の屈折面２をこの合成式（１）で表されるトーリック面と累進屈折面とを合成した合成屈折面１４＋１５とした内面累進多焦点レンズ１ｂは、遠用部と近用部における倍率の差を縮小でき、これに起因する像の揺れや歪みを大幅に低減できる。
【００５６】
なお、乱視矯正特性を備えたオリジナルトーリック面を構成するためのｚ座標の値に、視力補正特性を備えたオリジナル累進屈折面を構成するｚ座標の値を付加して乱視矯正特性を備えた累進屈折面を構成すると、従来の乱視矯正用の累進多焦点レンズと全く同等の視力の補正と乱視矯正能力は得にくい。
【００５７】
また、物体側の屈折面又は眼球側の屈折面に累進屈折面を設けた累進多焦点レンズにおいても、基底２７０度方向のプリズムを付加することにより、薄型化することが可能である。
【００５８】
このように、累進屈折面とトーリック面とを一体化させた累進多焦点レンズの合成屈折面の座標値を求めた後、この座標値に基づいて、数値制御研磨装置を用い、物体側の屈折面又は眼球側の屈折面のいずれかを球面又は回転対称非球面としたレンズ成形品の反対側の面を切削、研削、鏡面研磨等で合成屈折面を創成することにより、本発明の累進多焦点レンズを製造することができる。
【００５９】
【実施例】
＜実施例１＞
本例の累進多焦点レンズは、物体側が球面であり、ベースカーブは４．００Ｄで一定である。トーリック面を合成する前のオリジナル累進屈折面は、眼球側へ設けられ、遠用部の平均面屈折力が４．００Ｄ、近用部の平均面屈折力が２．００Ｄ、加入度数が２．００Ｄに設定されている。オリジナルトーリック面は、乱視軸が９０度で、球面屈折力Ｓが−２．００Ｄ、円柱屈折力Ｃが−２．００Ｄである。これらのオリジナル累進屈折面とオリジナルトーリック面とを合成式（１）を用いて合成屈折面を求めた。また、レンズ中心厚さｔが３．０ｍｍ、レンズ径ｄが７０．０ｍｍとなっている。
【００６０】
図３に、実施例１の累進多焦点レンズの眼球側のｚ座標値を示す。また、図４（ａ）に、従来の外面側に累進面を設け、内面側へトーリック面を設けた外面累進多焦点レンズの非点収差分布を示す。また、図４（ｂ）に、同じ累進面とトーリック面を合成式（１）を用いて合成した合成屈折面を内面側に設けた累進多焦点レンズの非点収差分布を示す。
【００６１】
図４から、内面に累進屈折面とトーリック面とを合成式（１）を用いて合成した合成屈折面を有する実施例１の累進多焦点レンズは、物体側に累進面を設け、眼球側にトーリック面を設けた外面累進多焦点レンズと同等の性能を有することが認められる。
＜実施例２＞
本例の累進多焦点レンズは、物体側が球面であり、ベースカーブは４．００Ｄで一定である。トーリック面を合成する前のオリジナル累進屈折面は、眼球側へ設けられ、遠用部の平均面屈折力が４．００Ｄ、近用部の平均面屈折力が０．５０Ｄ、加入度数が３．５０Ｄに設定されている。オリジナルトーリック面は、乱視軸が４５度で、球面屈折力Ｓが０．００Ｄ、円柱屈折力Ｃが−６．００Ｄである。これらのオリジナル累進屈折面とオリジナルトーリック面とを合成式（１）を用いて合成屈折面を求めた。また、レンズ中心厚さｔが３．０ｍｍ、レンズ径ｄが７０．０ｍｍとなっている。
【００６２】
図５に、実施例２の累進多焦点レンズの眼球側のｚ座標値を示す。また、図６（ａ）に、従来の物体側に累進面を設け、眼球側へトーリック面を設けた外面累進多焦点レンズの非点収差分布を示す。また、図６（ｂ）に、同じ累進面とトーリック面を合成式（１）を用いて合成した合成屈折面を眼球側に設けた累進多焦点レンズの非点収差分布を示す。
【００６３】
図６から、眼球側に累進屈折面とトーリック面とを合成式（１）を用いて合成した合成屈折面を有する実施例２の累進多焦点レンズは、物体側に累進面を設け、眼球側にトーリック面を設けた外面累進多焦点レンズと同等の性能を有することが認められる。
【００６４】
【発明の効果】
本発明の累進多焦点レンズは、累進屈折面とトーリック面とを合成した合成屈折面を有し、物体側又は眼球側のいずれか一方の屈折面に視力補正能力と乱視矯正能力を付与することができる。
【００６５】
また、本発明の累進多焦点レンズの設計方法は、物体側又は眼球側のいずれか一方の屈折面に累進屈折面とトーリック面とを合成した合成屈折面を付与した累進多焦点レンズを設計することができる。
【図面の簡単な説明】
【図１】本発明の累進多焦点レンズの概略構成を示すもので、（ａ）は正面図、（ｂ）は物体側の屈折面に合成屈折面を付与した断面図、（ｃ）は眼球側の屈折面に合成屈折面を付与した断面図、（ｄ）はｘ座標が乱視軸と一致することを示す平面図である。
【図２】曲率をサインカーブで分布させることを説明するグラフである。
【図３】実施例１の累進多焦点レンズの眼球側のｚ座標値を示す座標の分布図である。
【図４】（ａ）は、物体側に累進面、眼球側にトーリック面を設けた多焦点レンズの非点収差図、（ｂ）は、眼球側に累進面とトーリック面を合成した実施例１の累進多焦点レンズの非点収差図である。
【図５】実施例２の累進多焦点レンズの眼球側のｚ座標値を示す座標の分布図である。
【図６】（ａ）は、物体側に累進面、眼球側にトーリック面を設けた多焦点レンズの非点収差図、（ｂ）は、眼球側に累進面とトーリック面を合成した実施例２の累進多焦点レンズの非点収差図である。
【図７】従来の累進多焦点レンズの概略構成を示すもので、（ａ）は正面図、（ｂ）は物体側の屈折面に累進屈折面を付与した例の断面図、（ｃ）は眼球側の屈折面に累進屈折面を付与した例の断面図を示す。
【符号の説明】
１：累進多焦点レンズ、２：眼球側の屈折面、３：物体側の屈折面、１１：遠用部、１２：近用部、１３：累進部、１４：累進屈折面、１５：トーリック面、１６：主注視線[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a progressive multifocal lens having an ability to correct visual acuity and an ability to correct astigmatism, and a design method thereof.
[0002]
[Prior art]
A progressive multifocal lens is a lens having two visual field portions having different refractive powers and a visual field portion in which the refractive power changes progressively between them, and these visual field portions have no boundary and are excellent in appearance, Further, a single lens can provide a field of view with different refractive power. For this reason, it is often used as a spectacle lens having a function of correcting visual acuity such as presbyopia.
[0003]
FIG. 7A shows a general structure of a conventional progressive multifocal lens often used as an eyeglass lens. In this progressive multifocal lens 100, a far vision portion 11 which is a field portion for viewing a distant object is provided above, and a visual field having a different refractive power from the distance vision portion 11 for looking at a short distance object. The portion is provided as a near portion 12 below the far portion 11. The distance portion 11 and the near portion 12 are smoothly connected by a progressive portion 13 which is a visual field portion having a continuously changing refractive power to view an object at an intermediate distance between a long distance and a short distance. ing.
[0004]
In a single-plate lens used for spectacles, as shown in FIG. 7B, the spectacle lens is required by two refraction surfaces, that is, an eyeball-side refraction surface 2 and a gazing object-side refraction surface 3. All performances, e.g., vertex power for user power, cylindrical power for correcting astigmatism, addition power for correcting presbyopia, and prism power for correcting oblique position. Must be given. For this reason, as shown in FIG. 7B, in the conventional progressive multifocal lens 100a, the refractive power which continuously changes in order to configure the distance portion 11, the near portion 12, and the progressive portion 13 has a refractive power. The progressive refracting surface 14 to be provided is formed on the refracting surface 3 on the object side, and the refracting surface 2 on the eyeball side is used as a toric surface 15 for correcting astigmatism.
[0005]
In contrast to the progressive multifocal lens 100a having such a conventional structure, the present applicant has proposed a progressive multifocal lens capable of improving image fluctuation and distortion caused by a change in magnification of the distance portion 11 and the near portion 12 of the progressive multifocal lens. In order to provide a focusing lens, focusing on the arrangement of the progressive refracting surface that gives the magnification of the progressive multifocal lens, a so-called inner surface progressive multifocal lens 100b in which the progressive refracting surface is formed on the refracting surface 2 on the eyeball side has been developed. . This invention is described in Patent Document 1.
[0006]
The inner surface progressive power multifocal lens 100b described in Patent Literature 1 can reduce the difference in magnification between the distance portion and the near portion, and can significantly reduce image shaking and distortion due to the difference.
[0007]
In such an inner surface progressive multifocal lens 100b, since the progressive refracting surface 14 is provided on the refracting surface 2 on the eyeball side, a toric surface 15 for correcting astigmatism can be combined with the refracting surface 2 on the eyeball side. The progressive multifocal lens 100b in which the refracting surface 2 on the eyeball side has a visual acuity correction characteristic and an astigmatism correction characteristic can reduce the magnification difference between the distance portion and the near portion to a necessary minimum, and reduces image distortion and shaking. In addition, astigmatism can be corrected, and a more comfortable visual field can be provided to a user having astigmatism.
[0008]
The progressive multifocal lens 100b in which the visual acuity correction characteristic and the astigmatism correction characteristic are added to the refraction surface 2 on the eyeball side is a progressive refraction surface (hereinafter referred to as a refraction surface) only for the refraction surface on the eyeball side to exhibit a desired vision correction characteristic. A first step for obtaining an original progressive refractive surface) and a second step for obtaining a toric surface (hereinafter referred to as an original toric surface) solely for the purpose of the eyeball-side refractive surface exhibiting desired astigmatic correction characteristics. And a third method for determining the refracting surface on the eyeball side of the progressive multifocal lens from the original progressive refracting surface and the original toric surface.
[0009]
In the above-mentioned Patent Document 1, in the third step, a synthetic formula for integrating an original progressive refractive surface and an original toric surface is proposed.
[0010]
In the progressive multifocal lens 100b in which the progressive refracting surface 14 and the toric surface 15 are combined with the refracting surface 2 on the eyeball side using the combining formula proposed in Patent Document 1, similar to the conventional progressive multifocal lens 100a, It is recognized that the visual acuity correcting ability for correcting astigmatism is not impaired over almost the entire area of the gaze line 16 and that astigmatism can be secured very stably.
[0011]
[Patent Document 1]
WO97 / 19382
[0012]
[Problems to be solved by the invention]
However, a toric surface is defined as a surface that has a maximum refractive power in a certain meridional plane and a minimum refractive power in a perpendicular meridian plane and has different radii of curvature in cross sections orthogonal to each other. The cross-sectional shape of each of the meridional plane having the maximum refractive power and the meridional plane having the minimum refractive power is an arc, and the curved shape between them is not particularly defined. That is, it can be said that there are infinite types of surface shapes of the toric surface. Although the synthesis formula proposed in Patent Document 1 has an advantage that calculation is relatively easy, synthesis is performed by regarding the shape of the toric surface assuming that the curvature in the x-axis direction and the curvature in the y-axis direction are constant. It is just doing.
[0013]
Therefore, there is a possibility that it is possible to provide a combined refractive surface of a progressive refractive surface and a toric surface having more excellent astigmatism correcting ability by providing another combined expression representing the surface shape of the toric surface.
[0014]
The present invention has been made in view of the above circumstances, and by providing a new combining formula for combining a progressive refraction surface and a toric surface, a new refraction surface having vision correction capability and astigmatism correction capability on the same refraction surface. It is an object of the present invention to provide a progressive multi-focal lens.
[0015]
Another object of the present invention is to provide a method of designing such a progressive multifocal lens.
[0016]
[Means for Solving the Problems]
The progressive multifocal lens of the present invention uses an equation that distributes the curvature in a sine curve by interpolating between the respective arcs of the toric surface in which the cross section in the astigmatic axis direction and the cross section in the direction orthogonal to the astigmatic axis direction are arcs, respectively. This has a combined refraction surface obtained by using the combination formula (1) for combining the refraction surface and the progressive surface on the refraction surface on the eyeball side or the refraction surface on the object side.
[0017]
Such a progressive multifocal lens exhibits a first step of obtaining a progressive refraction surface (hereinafter, an original progressive refraction surface) solely for exhibiting desired visual acuity correction characteristics, and exhibits desired astigmatic correction characteristics. A second step of obtaining a toric surface (hereinafter referred to as an original toric surface) solely for the purpose of the above, and a combining formula for combining an original toric surface and an original progressive refractive surface interpolated between arcs by distributing a curvature by a sine curve. It can be designed by using a design method having a third step of obtaining a combined refractive surface from (1).
[0018]
Therefore, the invention according to claim 1 provides a progressive refracting surface on the eyeball side including a distance portion and a near portion having different refractive powers, and a progressive portion in which the refractive power changes progressively therebetween. In a progressive power multifocal lens for vision correction having a refraction surface or an object-side refraction surface, the eyeball-side refraction surface or the object-side refraction surface is set only for the purpose of exhibiting desired vision correction characteristics. An original progressive surface and a synthetic refractive surface obtained by combining an original toric surface set only to exhibit desired astigmatic correction characteristics, and passes through the center of the progressive surface from the object side to the eyeball side. When the axis is the z-axis, the astigmatic axis direction of the original toric surface is the x-axis, and the axis orthogonal to the z-axis and the x-axis is the y-axis, the approximate curvature Cp of the original progressive refractive surface and the curvature Cx in the x-axis direction , The curvature Cy in the y-axis direction Used, any point P of the combined refracting surface _{_{(x p, y p, z}} p) the value z _p in is, provide a progressive multifocal lens which is characterized by being represented by the following formula (1) I do.
[0019]
[Equation 3]

[0020]
According to a second aspect of the present invention, in the progressive multifocal lens according to the first aspect, the refracting surface on the eyeball side or the refracting surface on the object side opposite to the surface provided with the synthetic refracting surface is spherical or non-rotationally symmetric. A progressive multifocal lens characterized by being spherical.
[0021]
According to a third aspect of the present invention, a progressive refracting surface having a distance portion and a near portion having different refractive powers and a progressive portion having a refracting power progressively changing between them is a refracting surface on the eyeball side. Or in a method of designing a progressive multifocal lens for vision correction having a refracting surface on the object side,
The first step of obtaining an original progressive refraction surface only for the purpose of the eyeball-side refraction surface or the object-side refraction surface to exhibit visual acuity correction characteristics, and the eyeball-side refraction surface or the object-side refraction surface is The second step of obtaining the original toric surface only for exhibiting the desired astigmatic correction characteristics, and as the refractive surface on the eyeball side or the refractive surface on the object side, only exhibiting the desired visual acuity correction characteristics. An original progressive refraction surface set for the purpose, and a third step of obtaining a combined refraction surface combined with the original toric surface set only for the purpose of exhibiting the desired astigmatic correction characteristics, In the third step, the axis passing through the center of the progressive refraction surface from the object side to the eyeball side is the z axis, the astigmatic axis direction of the original toric surface is the x axis, and the axis orthogonal to the z axis and the x axis is the y axis. And , Approximate curvature Cp of said original progressive refractive surface, x-axis direction curvature Cx, using curvature Cy in the y-axis direction, an arbitrary point _P of the combined refracting surface _{_{(x p, y p, z}} p) the value of z _A method of designing a progressive multifocal lens, wherein _p is obtained from the following equation (1):
[0022]
(Equation 4)

[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of a progressive multifocal lens and a design method thereof according to the present invention will be described, but the present invention is not limited to the following embodiments.
[0024]
The progressive multifocal lens of the present invention refracts a progressive refracting surface having a distance portion and a near portion having different refractive powers, and a progressive portion having a refracting power progressively changed between them, on the eyeball side. It is provided on the surface or the refracting surface on the object side.
[0025]
As shown in FIG. 1 (a), the progressive multifocal lens 1 of the present invention is provided with a far vision portion 11, which is a visual field portion for viewing a distant object, at an upper portion. A field portion having a refractive power different from that of the distance portion 11 is provided below the distance portion 11 as a near portion 12. The distance portion 11 and the near portion 12 are smoothly connected by a progressive portion 13 which is a visual field portion having a continuously changing refractive power to view an object at an intermediate distance between a long distance and a short distance. ing.
[0026]
In the progressive multifocal lens of the present invention, the progressive refracting surface 14 including the distance portion 11, the near portion 12, and the progressive portion 13 is connected to the object-side refracting surface 3 (convex surface) as shown in FIG. , Outer surface). Alternatively, as shown in FIG. 1C, an inner surface progressive multifocal lens 1b in which the progressive surface 14 is provided on the eyeball side refractive surface 2 (also referred to as a concave surface or an inner surface) may be used.
[0027]
The inner surface progressive multifocal lens 1b can reduce the difference in magnification between the distance portion 11 and the near portion 12 as compared with the progressive multifocal lens 1a having the progressive refraction surface 14 on the outer surface, and image fluctuation caused by this can be reduced. And distortion can be greatly reduced. When the curvature of the progressive refraction surface is given to the refraction surface 2 on the eyeball side, the curvature (the reciprocal of the radius of curvature) of the progressive refraction surface along the main gazing line 16 is smaller in the near portion 12 than in the far portion 11. Become smaller. Further, in the distance portion 11, the curvature of the progressive refraction surface decreases in at least a part of the region as the distance from the main gazing line 16 increases, and in the near portion 11, the curvature of the progressive refraction surface in at least one portion of the region. The curvature increases as the distance from the main gazing line 16 increases.
[0028]
Further, as the progressive refracting surface 14, it is desirable to minimize astigmatism in forming the progressive refracting surface on the main gazing line 16; It is desirable that the curvature of the progressive refraction surface be equal in two orthogonal directions.
[0029]
In the progressive multifocal lens 1 of the present invention, one of the refracting surface 3 on the object side and the refracting surface 2 on the eyeball side is a combined refracting surface 14 + 15 having both the ability to correct visual acuity and the ability to correct astigmatism. It is configured. In the case of the outer surface progressive multifocal lens 1a shown in FIG. 1B, the refracting surface 2 on the eyeball side opposite to the combined refracting surface 14 + 15 provided on the refracting surface 3 on the object side is a spherical surface or a rotationally symmetric aspheric surface. is there. In the case of the inner surface progressive multifocal lens 1b shown in FIG. 1C, the refracting surface 3 on the object side opposite to the combined refracting surface 14 + 15 provided on the refracting surface 2 on the eyeball side is a spherical surface or a rotationally symmetric aspheric surface. is there. By providing the combined refracting surface 14 + 15 on the refracting surface 2 on the eyeball side, astigmatism can be corrected as described above, and the magnification difference between the distance portion 11 and the near portion 12 can be minimized. Since the image distortion and shaking are small, it is possible to provide a more comfortable field of view even to a user having astigmatism.
[0030]
The design of a progressive multifocal lens in which one of the refractive surfaces has both the ability to correct visual acuity and the ability to correct astigmatism is based on a progressive refractive surface (hereinafter referred to as a progressive refractive surface) that is set only to exhibit desired vision correction characteristics. In the first step, a toric surface (hereinafter referred to as an original progressive refraction surface) and a toric surface (hereinafter referred to as a toric surface) set only for the purpose that the refraction surface 2 on the eyeball side or the refraction surface 3 on the object side exhibits desired astigmatism correction characteristics. Can be performed in a second step of obtaining an original toric surface) and a third step of obtaining a combined refraction surface from the original progressive refraction surface and the original toric surface using a combination expression.
[0031]
In the first step, an original progressive refraction surface is obtained by parameters according to the situation such as the degree of presbyopia of the user and how to use glasses, and the result is stored as coordinates or curvature.
[0032]
In the second step, the original toric surface is assumed as a surface shape in which the curvature is distributed by a sine curve as an interpolation method between arcs whose cross section along the astigmatism axis and the cross section in the direction orthogonal to the astigmatism axis are arcs. Ask for.
[0033]
Then, in the third step, a combined refraction surface in which the original progressive refraction surface and the original toric surface are combined is determined by the following combination expression (1).
[0034]
(Equation 5)

[0035]
Here, as shown in FIGS. 1 (b), 1 (c) and 1 (d), in the spectacle wearing state, the axis passing through the center of the progressive refraction surface from the object side to the eyeball side is the z axis, and the astigmatic axis of the original toric surface. when an axis perpendicular to the direction x-axis, in the z-axis and x-axis and y-axis, z _p denotes a vertical z-coordinate of the refractive surface on the object side or the eyeball side. For the refracting surface 3 on the object side, the origin is the point where the refracting surface 3 on the object side intersects with the z-axis. For the refracting surface 2 on the eyeball side, the origin is the point where the refracting surface 2 on the eyeball side intersects the z-axis. And
[0036]
Curvature Cp is any point of the original progressive refractive surface _{P (x p, y p,} z p) are approximate curvature at, the curvature Cx of curvature in the x-axis direction, the curvature Cy is the curvature in the y-axis direction. The approximate curvature Cp, for example can be employed mean curvature of the radial, any point on the original progressive refractive surface _{P (x p, y p,} z p) z -axis comprises (lens center or inner vertices ( in xy plane perpendicular to the passing 0,0,0)), P point which is rotationally symmetrical with the point _{_{P '(- x p, -y}} p, -z p) and an inner vertex (0, 0, 0) or The reciprocal of the radius of the circle passing through the three points at the outer vertex (0,0,0) is used.
[0037]
Next, the calculation procedure of the above-described synthesis formula (1) will be described. As shown in FIG. 2, interpolation using a sine curve is considered such that the curvature is Cx in the x-axis direction at 0, 180, and 360 degrees, and the curvature Cy is in the y-axis direction at 90 and 270 degrees. . The equation at this time is:
(Equation 6)

[0039]
It becomes. Transform this equation.
[0040]
(Equation 7)

[0041]
This equation is converted into x and y coordinates.
[0042]
(Equation 8)

[0043]
Therefore, the following equation (4) is obtained.
[0044]
(Equation 9)

[0045]
As the toric surface, a surface shape in which the curvature is distributed in a sine curve is assumed as an interpolation method between arcs having a cross section along the axis of astigmatism and a cross section orthogonal to the axis of astigmatism. The z coordinate is the distance from the center of the curvature c _{(x, y).}
(Equation 10)

[0047]
Therefore, it can be expressed by the following equation (5) representing the arc.
[0048]
(Equation 11)

[0049]
By substituting equation (4) into equation (5), the following equation (6) is obtained.
[0050]
(Equation 12)

[0051]
The surface shape represented by the equation (6) is the original toric surface. c _x, when synthesizing the _{C p} respectively _{c y,} the following synthesis equation (1) is obtained.
[0052]
(Equation 13)

[0053]
When the coordinate system of the original progressive refractive surface and the original toric surface are shifted by the angle ax of the astigmatic axis, the approximate curvature Cp in the following (px, py, pz) is calculated in the coordinate system of the original progressive refractive surface. It may be used.
[0054]
[Equation 14]

[0055]
The synthesis formula (1) requires a relatively large amount of calculation as compared with the synthesis formula proposed in Patent Document 1. Further, the inner surface progressive multifocal lens 1b, in which the refracting surface 2 on the eyeball side is a combined refracting surface 14 + 15 obtained by combining the toric surface and the progressive refracting surface represented by the combining formula (1), has a distance portion and a near portion. Can be reduced, and image shaking and distortion due to this can be greatly reduced.
[0056]
In addition, by adding the z-coordinate value forming the original progressive refractive surface having the visual acuity correction characteristic to the z-coordinate value for forming the original toric surface having the astigmatism correction characteristic, the progressive having the astigmatism correction characteristic is added. When the refracting surface is formed, it is difficult to obtain the same correction of visual acuity and the ability to correct astigmatism completely equivalent to those of the conventional progressive power multifocal lens for correcting astigmatism.
[0057]
Also, in a progressive multifocal lens in which a progressive refracting surface is provided on the refracting surface on the object side or the refracting surface on the eyeball side, it is possible to reduce the thickness by adding a prism in the direction of 270 degrees at the base.
[0058]
After calculating the coordinate value of the combined refractive surface of the progressive multifocal lens in which the progressive refraction surface and the toric surface are integrated as described above, based on the coordinate value, a numerically controlled polishing device is used to refract the object side. By forming a synthetic refraction surface by cutting, grinding, mirror polishing or the like on the opposite surface of a lens molded product in which either the surface or the refracting surface on the eyeball side is spherical or a rotationally symmetric aspheric surface, the progressive power of the present invention is Focus lenses can be manufactured.
[0059]
【Example】
<Example 1>
The progressive multifocal lens of this example has a spherical surface on the object side, and has a constant base curve of 4.00D. The original progressive refraction surface before combining the toric surface is provided on the eyeball side, the average surface refractive power of the distance portion is 4.00D, the average surface refractive power of the near portion is 2.00D, and the addition power is 2. 00D is set. The original toric surface has an astigmatic axis of 90 degrees, a spherical refractive power S of -2.00D, and a cylindrical refractive power C of -2.00D. These original progressive surfaces and original toric surfaces were used to determine a combined refractive surface using the combining formula (1). The lens center thickness t is 3.0 mm and the lens diameter d is 70.0 mm.
[0060]
FIG. 3 shows z coordinate values on the eyeball side of the progressive multifocal lens of the first embodiment. FIG. 4A shows the astigmatism distribution of an external progressive multifocal lens in which a conventional progressive surface is provided on the outer surface side and a toric surface is provided on the inner surface side. FIG. 4B shows an astigmatism distribution of a progressive multifocal lens provided on the inner side with a combined refraction surface obtained by combining the same progressive surface and toric surface using the combination formula (1).
[0061]
From FIG. 4, the progressive multifocal lens of Example 1 having a combined refraction surface obtained by combining a progressive refraction surface and a toric surface on the inner surface using the combination formula (1) has a progressive surface provided on the object side and a progressive surface provided on the eyeball side. It is recognized that it has the same performance as the outer surface progressive multifocal lens provided with the toric surface.
<Example 2>
The progressive multifocal lens of this example has a spherical surface on the object side, and has a constant base curve of 4.00D. The original progressive refraction surface before the synthesis of the toric surface is provided on the eyeball side, the average surface refractive power of the distance portion is 4.00D, the average surface refractive power of the near portion is 0.50D, and the addition power is 3. It is set to 50D. The original toric surface has an astigmatic axis of 45 degrees, a spherical refractive power S of 0.00D, and a cylindrical refractive power C of -6.00D. These original progressive surfaces and original toric surfaces were used to determine a combined refractive surface using the combining formula (1). The lens center thickness t is 3.0 mm and the lens diameter d is 70.0 mm.
[0062]
FIG. 5 shows z coordinate values on the eyeball side of the progressive multifocal lens of the second embodiment. FIG. 6A shows the astigmatism distribution of a conventional progressive multifocal lens having a progressive surface on the object side and a toric surface on the eyeball side. FIG. 6B shows an astigmatism distribution of a progressive multifocal lens provided on the eyeball side with a combined refraction surface obtained by combining the same progressive surface and toric surface using the combination formula (1).
[0063]
As shown in FIG. 6, the progressive multifocal lens of Embodiment 2 having a combined refractive surface obtained by combining a progressive refracting surface and a toric surface on the eyeball side using the combining formula (1) is provided with a progressive surface on the object side, It is recognized that the lens has the same performance as an external progressive multifocal lens provided with a toric surface.
[0064]
【The invention's effect】
The progressive multifocal lens of the present invention has a combined refraction surface obtained by combining a progressive refraction surface and a toric surface, and imparts a visual acuity correcting ability and an astigmatic correction ability to one of the refracting surfaces on the object side or the eyeball side. Can be.
[0065]
In addition, the progressive multifocal lens designing method of the present invention designs a progressive multifocal lens in which a combined refractive surface obtained by combining a progressive refractive surface and a toric surface is provided on one of the object-side and eyeball-side refractive surfaces. be able to.
[Brief description of the drawings]
1A and 1B schematically show the configuration of a progressive multifocal lens according to the present invention, wherein FIG. 1A is a front view, FIG. 1B is a cross-sectional view in which a synthetic refraction surface is added to an object-side refraction surface, and FIG. FIG. 10D is a cross-sectional view in which a synthetic refraction surface is provided on the side refraction surface, and FIG. 10D is a plan view showing that the x coordinate coincides with the astigmatic axis.
FIG. 2 is a graph illustrating that a curvature is distributed by a sine curve.
FIG. 3 is a distribution diagram of coordinates indicating z coordinate values on the eyeball side of the progressive power lens according to the first exemplary embodiment.
4A is an astigmatism diagram of a multifocal lens having a progressive surface on the object side and a toric surface on the eyeball side, and FIG. 4B is an embodiment in which a progressive surface and a toric surface are combined on the eyeball side; FIG. 2 is an astigmatism diagram of No. 1 progressive multifocal lens.
FIG. 5 is a coordinate distribution diagram showing z-coordinate values on the eyeball side of a progressive multifocal lens according to a second embodiment.
6A is an astigmatism diagram of a multifocal lens having a progressive surface on the object side and a toric surface on the eyeball side, and FIG. 6B is an embodiment in which a progressive surface and a toric surface are combined on the eyeball side; FIG. 3 is an astigmatism diagram of a progressive multifocal lens No. 2;
7A and 7B show a schematic configuration of a conventional progressive multifocal lens, wherein FIG. 7A is a front view, FIG. 7B is a cross-sectional view of an example in which a progressive refraction surface is added to an object-side refraction surface, and FIG. FIG. 3 shows a cross-sectional view of an example in which a progressive refraction surface is provided on the refraction surface on the eyeball side.
[Explanation of symbols]
1: progressive multifocal lens, 2: refracting surface on the eyeball side, 3: refracting surface on the object side, 11: distance portion, 12: near portion, 13: progressive portion, 14: progressive refraction surface, 15: toric surface , 16: Main gaze

Claims

Having a progressive refractive surface with a distance portion and a near portion having different refractive powers, and a progressive portion in which the refractive power changes progressively between them on the refracting surface on the eyeball side or the refracting surface on the object side. In progressive multifocal lenses for vision correction,
The refracting surface on the eyeball side or the refracting surface on the object side is an original progressive refractive surface set only for exhibiting desired visual acuity correction characteristics, and set only for exhibiting desired astigmatic correction characteristics. Is a combined refraction surface combined with the original toric surface,
When the axis passing through the center of the progressive refraction surface from the object side to the eyeball side is the z-axis, the astigmatic axis direction of the original toric surface is the x-axis, and the axis orthogonal to the z-axis and the x-axis is the y-axis, the original approximate curvature Cp of the progressive refractive surface, the curvature of the x-axis direction Cx, with curvature Cy in the y-axis direction, an arbitrary point _P of the combined refracting surface _{_{(x p, y p, z}} p) is the value _{z p} in And a progressive multifocal lens represented by the following formula (1).

The progressive multifocal lens according to claim 1,
A progressive multifocal lens, wherein the refracting surface on the eyeball side or the refracting surface on the object side opposite to the surface provided with the combined refracting surface is a spherical surface or a rotationally symmetric aspherical surface.

Having a progressive refractive surface with a distance portion and a near portion having different refractive powers, and a progressive portion in which the refractive power changes progressively between them on the refracting surface on the eyeball side or the refracting surface on the object side. In a method of designing a progressive multifocal lens for vision correction,
A first step of obtaining an original progressive refraction surface only for the purpose of the eyeball-side refraction surface or the object-side refraction surface to exhibit visual acuity correction characteristics,
A second step of obtaining an original toric surface only for the purpose of the eyeball-side refraction surface or the object-side refraction surface to exhibit desired astigmatic correction characteristics,
As the refraction surface on the eyeball side or the refraction surface on the object side, an original progressive refraction surface set only for exhibiting desired visual acuity correction characteristics, and set only for exhibiting desired astigmatism correction characteristics A third step of obtaining a combined refraction surface combined with the original toric surface that has been combined,
In the third step, the axis passing from the object side to the eyeball side passing through the center of the progressive refraction surface is the z-axis, the astigmatic axis direction of the original toric surface is the x-axis, and the axis orthogonal to the z-axis and the x-axis is y. when an axis, the original progressive approximation curvature Cp of the refractive surface, the curvature of the x-axis direction Cx, using curvature Cy in the y-axis direction, an arbitrary point P of the combined refracting surface _{_{(x p, y p, z}} p) Wherein the value z _p is obtained from the following equation (1).