Variable powered contact lens

A soft contact lens of soft opthalmic plastic material with an anterior portion resiliently deformable by movement of the eye. The lens is of the scleral-corneal type, and has a base-down prism portion which moves under the lower eyelid. When the eye gazes downwardly and inwardly, pressure of the lower lid on the thickened portion of the lens causes a bulging of the anterior portion of the lens near the center, creating an increase in diopter power. A slab-off bevel of the lens sides shapes the bulge into proper spherical condition for clearer vision.

TECHNICAL FIELD 
This invention relates generally to contact lenses, and more particularly 
to soft contact lenses having multiple focal lengths. 
BACKGROUND OF THE INVENTION 
Contact lenses have been utilized for many years for the correction of 
various visual disorders. However, contact lenses have been less 
successful in the treatment of presbyopia. Presbyopia is characterized by 
loss of elasticity of the crystalline lens, and hence, loss of the ability 
of the eye to adjust to clearly see objects which are close and also those 
which are more distant. 
Two common methods for correcting presbyopia are the use of bifocal 
eyeglass lenses and bifocal contact lenses. Eyeglass lenses generally have 
two portions ground for two viewing distances. Since the eye will move in 
relation to the lens, the patient can easily view through either lens. 
Two types of multi-focal contact lenses are presently known. One type is 
quite similar to eyeglasses, in that it moves relative to the eye in order 
to place the correct portion of the lens over the pupil for viewing. Such 
lenses are generally categorized as translating lenses; one such lens 
being described in U.S. Pat. No. 4,418,991 to Breger. These lenses have a 
lower portion which is engaged by the lower eyelid when the patient looks 
down, causing the lens to move upwards on the cornea relative to the 
pupil. Translating lenses are difficult to fit because the amount of 
movement of the lens will vary for each patient, making it difficult to 
determine the appropriate height of the bifocal segment. 
Soft contact lenses are typically of a diameter large enough to extend 
beyond the cornea and into the scleral area. A thick peripheral portion 
fits into the natural notch created in the limbal area where the flatter 
scleral meets the steeper cornea. Such lenses can be of the translating 
type (described above), or of the simultaneous type. Simultaneous type of 
lenses, one being described in U.S. Pat. No. 4,199,231 to Evans, utilize a 
lens which does not move on the cornea, but rather causes the light rays 
to focus within a specific range forward and behind the retina. Such 
lenses require an increase in the distance prescription power for normal 
distance viewing in order to bring the near vision focal point within an 
acceptable range. This, in affect, will slightly blur the distance vision, 
since the focal point will be moved from the retina to a point slightly 
beyond the retina. Obviously, it is much more desirable to have the focal 
point of light rays from an object at any distance to be focused directly 
on the retina, and not merely within an "acceptable range" of the retina. 
It is therefore an object of the present invention to provide an improved 
variable power contact lens. 
Another object is to provide a variable power contact lens which is neither 
translational nor simultaneous and therefore suffers none of the problems 
associated with those lenses. 
Yet another object of the present invention is to provide a contact lens 
which will provide a variety of focal lengths through the same portion of 
the lens. 
These and other objects will be apparent to those skilled in the art. 
SUMMARY OF THE INVENTION 
A soft contact lens is provided which is comprised of soft, opthalmic 
plastic material which is resiliently deformable by movement of the eye. 
The lens is of the scleral-corneal type, and has a base-down prism portion 
which moves under the lower eyelid. When the eye gazes downwardly and 
inwardly, pressure of the lower lid on the thickened portion of the lens 
causes a bulging of the lens near the center, creating an increase in 
diopter power. A slab-off bevel of the lens sides shapes the bulge into 
proper spherical condition for clearer vision.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, in which the reference numerals describe 
similar or corresponding parts throughout the several views, the improved 
contact lens of this invention is designated generally at 10 in FIG. 1, 
with a prior art contact lens 11 shown in broken lines. Additional 
structure added to prior art lens 11 to form the lens 10 of this 
invention, is shown cross-hatched. 
Like prior art contact lenses, the lens 10 of this invention is made with a 
thickened area 14 around its perimeter which fits into the natural notch 
created in the limbal area 16 where the flatter scleral 18 meets the 
steeper cornea 20. The anterior face 10a of the contact lens 10 is smooth, 
for comfort under the upper and lower eyelids 22 and 24, respectively. 
The lower anterior portion of the lens is thicker than conventional lenses, 
and has a base-down prism 26, the purpose of which is described in more 
detail hereinbelow. 
The lens is composed of a soft, opthalmic plastic material which is 
resiliently deformable, and is thereby caused to deform with a slight 
bulge 28 at the center of the lens when pressure from the lower eyelid is 
exerted on the lens (see FIG. 4). One material capable of meeting the 
desired deformable characteristics is a high water content hydrogel. Other 
materials, such as a very soft silicone, could also be used with this 
invention. Bulge 28 creates an increased thickness and smaller radius 
curve in lens 10, and thereby increases the diopter of the lens 10 at 
bulge 28. 
In order to shape bulge 28 into the proper spherical shape, a slab off, or 
bevel, on both the temporal 30 and nasal 32 sides of the anterior surface 
10a of the lens 10 are necessary. The temporal bevel 30 must be slightly 
wider (when viewed in front elevation) than the nasal bevel 32 since the 
opening in the eye socket is slightly wider on the temporal side. Bevels 
30 and 32 begin along the upper perimeter of lens 10, spaced away from the 
center upper point. Bevels 30 and 32 widen (in front elevation view) to 
their widest point approximately half way down the lens 10, and then 
narrow again at the bottom. Bevels 30 and 32 increase in steepness and 
merge with the perimeter of the lens approximately at the center of the 
bottom of the lens. This bevel structure not only serves to shape the 
bulge 28, but also helps to keep the lens 10 from rotating on the eye. The 
close fit and additional surface area against which the lower eye lid 24 
will be pushing prevents rotation and helps to center the upward pressure 
of the lower lid when gazing downward. 
A lower bevel 34 on the posterior surface 10b of lens 10 aids in easing 
lens 10 into the lower fornix of the eye, and also aids in holding lens 10 
from translation upward. 
The lens 10 of this invention utilizes known characteristics of the anatomy 
of the eye to assist in the deformation of the lens 10. Upper lid 22 is 
firmer than lower lid 24, while lower lid 24 is more loose and has 
slightly less room than upper lid 22. Thus, insertion of the contact lens 
10 will cause the space under the lower eyelid 24 to be immediately filled 
by prism portion 26 of lens 10. Since near vision requires the eyes to 
move not only downwards but also toward the nasal fornix, this will cause 
additional pressure to assist in creating bulge 28 on lens 10. 
Since the eye blinks by moving only upper lid 22, the lens will not change 
shape or power during this natural phenomena, thus eliminating one of the 
problems associated with some translational lenses. 
FIGS. 3 and 4 diagrammatically show the changes which occur when the viewer 
directs his vision from a straight, distant view (FIG. 3) to a downward, 
near view (FIG. 4). Light rays 36, from a distant source, will pass 
through lens 10 and focus on retina 38. Thus, lens 10 is manufactured to 
correct the distance vision of the wearer in its "normal", undeformed 
shape. In order to view a closer object, the eye is moved downwardly and 
inwardly until lens 10 has a bulge 28 of the appropriate curvature so that 
light rays 40 are bent at a steeper angle and focused on retina 38. Thus, 
the natural movement of the eyes inwardly upon viewing a nearer object 
will actually help vary the power of the lens to maintain objects in 
focus. Because the lens 10 is made of a soft, resiliently deformable 
material, the lens 10 will return to its original shape as the eye gazes 
straight ahead for distance vision. 
It can therefore be seen that an infinite variety of powers and foci are 
available with this lens 10, making vision clear continuously from distant 
vision to very near vision. For this same reason, a nearly universal lens 
is possible with the present invention. Those who need only slight 
correction need only gaze slightly downward to obtain the necessary 
correction. Those who need larger amounts of correction could use the same 
lens by gazing downwardly (and inwardly) at a steeper angle for near 
vision. Obviously, a more "custom" fit is also possible. For example, for 
those wearers who need only a slight correction, the thickness of the 
prism portion 26 is less than for those who require greater correction. 
Because of the thickness, of the prism, lens 10 will help to mask smaller 
astigmatic errors. For higher astigmatic errors, a toric surface could be 
made on the posterior surface 10b of lens 10. 
It can therefore be seen that this invention fulfills at least all of the 
above objectives.