Progressive power lens and progressive power lens design method
A progressive power lens including a distance portion for visual recognition of a far working distance, a near portion for visual recognition of a near working distance, and an intermediate portion provided between the distance portion and the near portion, the intermediate portion including a position of an amount of intermediate inset in which a visual line when the intermediate working distance is visually recognized passes an eyeball side surface of the progressive power lens, and addition at intermediate position for viewing an intermediate working distance smaller than the far working distance and larger than the near working distance being set to the position of the amount of intermediate inset.
1. A progressive power lens comprising:
a distance portion for visual recognition of a far working distance,
a near portion for visual recognition of a near working distance, and
an intermediate portion provided between the distance portion and the near portion,
wherein an addition of the intermediate portion that is required for viewing an intermediate working distance, which is smaller than the far working distance and larger than the near working distance, is set at a position of an intermediate inset where a line of sight intersects an eyeball side surface of the progressive lens when viewing the intermediate working distance.
2. The progressive power lens according to claim 1 , wherein, given that
an intermediate vision pupillary distance as a distance between the position of the intermediate inset for left eye and the position of the intermediate inset for right eye is MPD and a far vision pupillary distance when the far working distance is visually recognized is OPD, an amount of the intermediate inset ML is obtained from the following formula
ML =( OPD−MPD )÷2.
3. The progressive power lens according to claim 1 , wherein, given that
a necessary amplitude of accommodation is F, the intermediate working distance is ml, and refractive power in a resting position of accommodation showing an adjustment state under physiological tension without adjustment or stimulation is mf, the addition at the intermediate portion MF is obtained from the following formula
MF=F−mf =(1 /ml )− mf.
4. A progressive power lens design method for desinging the progressive power lens according to claim 1 , comprising:
obtaining an intermediate vision pupillary distance;
setting an amount of the intermediate inset based on the intermediate vision pupillary distance; and
setting the addition at the position of the intermediate inset in the intermediate portion for viewing the intermediate working distance.
5. The progressive power lens design method according to claim 4 , wherein, given that a direction defining the amount of intermediate inset is x, a direction orthogonal to the direction x is y, and an intersection of the direction x and the direction y is a start point of progressive power set in the distance portion, a position in the y direction for setting the addition at the intermediate portion is obtained from a relationship between an average power change between the start point of progressive power and an endpoint of progressive power set in the near portion and positions of the start point of progressive power and the end point of progressive power.