Variable power spectacles

Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses

Reexamination Certificate

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C351S158000

Reexamination Certificate

active

06318857

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to variable power spectacles whose refractive power is adjustable to supplement accommodation power of eyes.
Japanese Patent Provisional Publication Nos. Sho 55-64209 and Sho 63-24217 disclose the variable power spectacles. The variable power spectacles are provided with a pair of variable power lenses and an adjusting mechanism that adjusts the focal power of the variable power lenses. The variable power lens disclosed in the publications has a flexible hull that is filled by transparent liquid. The adjusting mechanism infuses or discharges the transparent liquid into or from the flexible hull to deform the variable power lens, which changes the curvature of the lens, varying the focal power of the lens continuously.
However, since the variable power lens disclosed in the publications only adjusts the focal power (i.e., focal length), the adjustment disturbs balance between accommodation and vergence of eyes, which becomes a burden on the eye when the spectacles are worn for a long time. Further, the extreme unbalance disables binocular vision.
According to a physiological optics research, it has been understood that accommodation and vergence of eyes should be balanced for good binocular vision and the unbalance disturbs comfortable binocular vision. The vergence means convergence when lines of sights move to inside and means divergence when liens of sights move to outside.
FIG. 12
is a graph showing a relationship between the accommodation and the vergence. It has been known that binocular vision is possible only when the relationship between the accommodation and the vergence is represented by a coordinate point included within the area surrounded by a curve
50
in FIG.
12
.
However, the adjustment in the conventional variable power spectacles is represented by a straight line
66
, for example. If the focal power is adjusted along the line
66
, the balance between the accommodation and the vergence is disturbed to disable the binocular vision at the small accommodation.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide improved variable power spectacles, which is capable of keeping a comfortable binocular vision even when the spectacles are worn for a long time without disturbing the balance between the accommodation and the vergence.
For the above object, according to the present invention, there is provided variable power spectacles that includes a pair of visual optical systems, which include:
a first adjusting mechanism for adjusting focal power of the visual optical systems;
a second adjusting mechanism for adjusting prismatic power of the visual optical systems; and
a linking mechanism for associating the adjustment by the first adjusting mechanism with the adjustment by the second adjusting mechanism to link one of the adjustments with the other adjustment.
Namely, the characteristic point of the present invention is to change the prismatic power of the visual optical systems as the focal power varies.
With this construction, variation of an object distance changes both of the focal power and the prismatic power, which keeps the balance between the accommodation and the vergence.
The linking mechanism may control the second adjusting mechanism to increase the prismatic power in base-in direction as the first adjusting mechanism increases the focal power. In such a case, it is preferable to satisfy the following condition:
0
<PR/AD<
3.5  (1)
where
AD [Dptr] is the additional focal power, and
PR [&Dgr;] is the additional prismatic power in base-in direction.
In one embodiment, each of the visual optical systems includes a variable power lens and a variable angle prism. In such a case, the first adjusting mechanism adjusts the focal power of the variable power lens, and the second adjusting mechanism adjusts the apex angle of the variable angle prism. When the object distance varies, the apex angle of the variable angle prism is changed as the focal power is changed, which keeps the balance between the accommodation and the vergence of eyes.
In the other embodiments, each of the visual optical systems includes a variable power lens. In such a case, the first adjusting mechanism adjusts the focal power of the variable power lens, and the second adjusting mechanism moves the optical center of the variable power lens in a temporal side or a nasal side. The movement of the optical center in the temporal side or the nasal side changes the prismatic power of the variable power lens as well as the change of the apex angle of the variable angle prism, which also keeps the balance between the accommodation and the vergence of eyes.
The term “optical center” is defined as the intersection of the straight line that links a center of paraxial curvature of the front surface (object side) and a center of paraxial curvature of the back surface (eye side) with the front surface. Further, the position of the optical center when no additional focal power is added is defined as an “original optical center. That is, the original optical center is the optical center at the minimum focal power.
The variable power lens can be moved as a whole to move the optical center, while the mechanical construction becomes too complicated to apply it to the spectacles. Thus, the variable power lens is preferable to change the focal power and the position of the optical center by deformation thereof. In such a case, the first and second adjusting mechanisms deform the variable power lens to simultaneously adjust the focal power and the prismatic power.
When the variable power lens has a positive focal power, the optical center should be moved in the nasal side as the focal power is added to increase the absolute value thereof. When the variable power lens has a negative focal power, the optical center should be moved in the temporal side as the focal power is added to decrease the absolute value thereof.
Further, when the variable power lens has a positive focal power (AD>0.5, DF+AD>0, where DF [Dptr] is the minimum value of the focal power of the variable power lens), a moving amount IN [mm] of the optical center in the nasal side direction with reference to the original optical center preferably satisfies the following condition (2):
0
<IN<
35
×AD
/(
DF+AD
)  (2).
Still further, when the variable power lens has a negative focal power (AD>0.5, DF+AD<0), a moving amount OUT [mm] of the optical center in the temporal side direction with reference to the original optical center preferably satisfies the following condition (3):
0<OUT<−35
×AD/
(
DF+AD
)  (3).


REFERENCES:
patent: 5229885 (1993-07-01), Quaglia
patent: 5526067 (1996-06-01), Cronin et al.
patent: 5684637 (1997-11-01), Floyd
patent: 5966239 (1999-10-01), Shirayanagi et al.
patent: 6040947 (2000-03-01), Kurtin et al.
patent: 0837603 (1998-04-01), None
patent: 55-64209 (1980-05-01), None
patent: 63-24217 (1988-02-01), None
patent: 2-166417 (1990-06-01), None
patent: 8-179239 (1996-07-01), None
patent: 91/17463 (1991-11-01), None
Handbook of Ophthalmic Optics, Second Edition, Japan Ophthalmic Professional School, pp. 64-66, ISBN4-307-77000-5, with English translation.

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