Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Eyeglass lens for the correction of nearsightedness
The present invention relates to an eyeglass lens
for the correction of nearsightedness, comprising a base
lens of a highly refractive glass or other materials in
which a circular or oval lenticular portion is ground
out.
It is difficult to provide myopes with suitable eye-
glass lenses because of the thickness of the periphery
of the lenses to be worn; this brings along enormous weight
problems and limits the choice of the eyeglass-frames.
Also the so-called "bull's eye" effect is disadvantageous
with these lenses. The weight problems and the esthetic
short-comings are not removed even with the presently
available eyeglass lenses having lenticular ground-out
portions. The lenses of the customary type are represented
in fig. 1 and 2. The embodiment according to fig. 1 consists
of a positive base lens having a circular lenticular ground
-out portion. The embodiment according to fig. 2 consists
of a planar base lens having equally a circular lenticular
ground-out portion.
The British patent 2 034 498 A describes ophthalmic
lenses for myopes the negative base lens of which has
been ground both on the front and the back faces thereof.
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Such eyeglass lenses have bad optical properties
and on the top of it an unesthetic aspect. Because of
1:he fact that the front face of the negative base lens is
not shaped spherically (cylindrically), but has a posi-
1:ive to negative ground-out portion causing an enormous
reflexion, the optical image formation is deteriorated,
as is the case e.g. with the bi-convex eyeglass lenses
represented in Fig. 6 of this patent. The thickness of
the periphery of the eyeglass lenses produced in this way
is comparatively only insignificantly reduced so that the
undesired "bull's eye" effect is not completely removed.
It is an object of the present invention to
provide an eyeglass lens for the correction of nearsight-
edness by which the above mentioned shortcomings of the
eyeglass lenses of the customary type are eliminated.
Besides, the transition of the lenticular ground-out
portion into the base lens should be largely camouflaged
and made practically invi~ible. According to the present
invention there is provided an eyeglass lens in which the
base lens is a negative lens and the correction of the
lenticular portion is ground into and continuous with the
negative base lens on the back face thereof.
It is advantageous when the back face of the
negative base lens has a planar to positive shape in the
area thereof extending from said lenticular portion
toward the peripheral rim of said base lens.
In one aspect of the present invention there is
provided an eyeglass lens for the correction of nearsight-
edness, comprising a base lens of highly refractive glass
or other materials in which a circular or oval lenticular
portion is ground out, characterized in that the base lens
is a negative lens having a back face and the correction
of the lenticular portion is ground into and continuous
with the negative base lens on the back face.
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In a furth~r aspect of the present invention
there is provided an eyeglass lens for the correction
of nearsightedness, comprising a base lens of highly
refractive glass in which a circular or oval lenticular
portion is ground out, wherein the base lens is negative
lens having back and front faces and the correction of
the lenticular portion is progressively ground into (and
continuous with) the negative base lens on the back face
thereof and asperically shaped to be continuous with the
base lens thereby providing a substantially imperceptible
transition between the base lens and the lenticular
portion.
In a further aspect of the present invention
there is provided an eyeglass lens comprising a negative
base lens having front and back faces and a lenticular
portion formed in only a selected area of the back face
of the base lens to provide an optical correction, the
lenticular portion being shaped aspherically by meeting
the remaining portion of the negative base lens along a
continuous flattened curve thereby providing a substantially
imperceptible transition between the base lens and the
lenticular portion.
The invention is illustrated by way of example
in the accompanying drawings wherein:
Fig. 1 shows a section of an eyeglass lens of
the customary type consisting of a positive base lens having
a circular lenticular ground-out portion,
Fig. 2 shows a section of an eyeglass lens of the
customary type consisting of a planar base lens having a
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circular lenticular ground-out portion,
Fig. 3 shows a section of the inventive eyeglass
lens consisting of a negative base lens having a cir-
cular or oval lenticular ground-out portion,
Fig. 4 shows a section of the inventive eyeglass
lens having a continuous transition of the lenticular
ground-out portion into the negative base lens in asphe-
rical form, and
Fig. 5 shows a section of the inventive eyeglass
lens consisting of a base lens which is planar to positive
in the area extending toward the peripherical rim of the
base lens.
Principally, the eyeglass lenses 1 according to fig.
3 to 5 are made of highly refractive glass (e.g. highlite
flint, index of refraction 1,7). A lenticular ground-out
portion 2 having a variable dimension is ground into a nega-
tive base lens 1 according to the required definite correc-
tio~. The correction of the lenticular is ground into the
negative base lens 1 in a circular or oval form whereby the
dimensions of such a lenticular ground-out portion are
usually smaller than those of the lenticular ground-out
portions of the customary art. The transition edge 2a of the
lenticular ground-out portion 2 into the base lens 1 is
continuous and in aspherical form (see fig. 4 and 5).
The diameter of a circular lenticular ground-out
portion as well as the thickness of the base lens are in
accordance with the necessary correction to be carried out
with the client and have therefore to be individually
determined. Accordingly, at a defficiency of sight of e.g.
-14 dptr. a base lens of - 3,0 dptr. having a sufficient
central thickness is ground, which lens allows a lenticular
ground-out portion of - 14,0 dptr. with a diameter of
approx. 22 to 25 mm and a subsequent central thickness of
approx. 0,7 mm (see fig. 3). Equally,
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a correction of the lenticular in an oval form can be
ground into the base lens of e.g. sph. -l,0 - cyl. - 3,0.
In order to make now the edge 2a of the lenticular
ground-out portion invisible, the same will be progressively
polished with a hard rubber or a similar flexible material
(see fig. 4 and 5).
Another possibility how to produce the lenticular
ground-out portion and its continuous transition into
the base lens is to provide a proper grinding tool for each
correction corresponding exactly to the definite form of the
lenticular ground-out portion and the base lens. The transi-
tion of the lenticular ground-out portion into the base lens
will be also here automatically progressively polished. That
means that the curve runs out aspherically into approx. -3,0
dptr. at the outgoing section of the optically effective
zone (lenticular ground-out portion).
The grinding tools can be flattened from the lenti-
cular ground-out portion over the minus lens to the
peripheral rim la in a planar to positive way. In this
way the thickness of the peripheral rim and so the weight
of the eyeglass lenses will be still more reduced (see
fig. 5)
With the astigmatic eyeglass lenses the cylinder
will be applied to the front face of the base lens; thus
e.g. a circular lenticular ground-out portion will be
maintained.
The above described eyeglass lens having a smaller
lenticular ground-out portion than the lenticular ground-
out portion of the known eyeglass lenses is substantially
thinner and therefore lighter than the eyeglass lenses
of the customary type. As it is known, a heavy correction
of the eyeglass lens brings along with it chromatic or
spherical aberrations, curvatures of image field etc.,
as soon as the eye leaves the optical center. Thus, the
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peripheral zones of each strong eyeglass lens are not
utilized. The forfeit of the field of vision with the
above described eyeqlass lenses is not felt to be in-
convenient. It has already earlier turned out that even
small lenticular ground-out portions do not work out in a
negative sense provided that they are brought closely in
front of the eye.
The esthetic effect noticeable by an observer is
satisfactory, because the "bull's eye" effect of the eye-
glass lenses of the customary type has disappeared. Theeyeglass lens brought closely in front of the eye diminishes
only the same and not the face behind it. The effect has
been improved in the way that a strong definite correction
of the lenticular has been ground already into the negative
base lens whereby also the transition of the lenticular
ground-out portion into the base lens is camouflaged.
