Contact lens bifocal with switch

A bifocal contact lens which contains two optical powers and a structure which serves as a switch to determine which power is operative as the wearer looks alternatively at objects located at various distances. The lens switch is designed so as to be triggered by the upper lid as it covers and uncovers various portions of the contact lens when the lens wearer is looking alternatively at objects located at various distances.

Bifocal contact lenses are lenses which provide at least two optical 
powers, such powers being selected so as to correct the refractive error 
of a patient's eye for two or more distances. This invention relates to a 
bifocal contact lens construction in which the two optical powers are made 
operative on an alternating basis by a switch on the contact lens that is 
triggered from the difference in lid position when viewing far and near 
objects. 
BACKGROUND OF THE INVENTION 
At the present time, several bifocal contact lenses are available for 
public use but these are not considered very successful by the eyecare 
professions (see Bennett et al, 1990). Most present bifocal contact lenses 
may be divided into two major types and several alternate designs of each 
type based on the location of the optical zones. Optical zones are those 
regions of the lens which provide an optical correction for good vision at 
specified distances for the wearer. 
The two major types of bifocal contact lenses are the concentric zone type 
and the vertically separated zones or segment type as described in U.S. 
Pat. No. 3,684,357 and Josephson 1990. Each bifocal lens type may be 
formed of either hard or soft materials. The concentric type is the oldest 
form of bifocal contact lens. It has two optical zones which are placed 
concentrically in a bullseye fashion. Depending on the lens design either 
the distance or near optical zone may be in the most central portion of 
the lens which is surrounded concentrically by the alternative of the 
distance or near portion. The optical zones are produced by having two 
different radii of curvature on either the anterior or posterior lens 
surface. 
The concentric bifocal lens usually functions by what is known as the 
simultaneous vision principle. To accomplish this, the optical portion of 
the lens must have such dimensions that, when worn on the eye, both the 
distance and near optical zones cover a portion of the wearer's entrance 
pupil so that light passing through both distance and near zones will 
contribute to the retinal image. The disadvantage of the simultaneous 
image principle is that the retinal image is composed of light from both 
distance and near objects of view simultaneously and the image is never 
completely clear. When the subject looks at a distant object the light 
from near objects which passes into the entrance pupil forms an 
out-of-focus veiling effect on the retinal image and when the subject 
looks at near objects there is the same type of veiling effect from the 
distance light. This retinal veiling, sometimes called fogging, or blur, 
has severely limited the ability of most subjects to tolerate a 
simultaneous vision type of lens correction, although in a few 
circumstances the patient may learn to ignore the veiling image and use 
the lens with a limited degree of success. Vision may also be enhanced if 
some translating movement of the lens occurs to shift the lens either up 
and down or sideways so that the subject sees through a greater proportion 
of either the distance or near optical zone. Unfortunately, the shifting 
action of the lens is usually insufficient or unreliable to be effective 
in producing the necessary lens translation to move the lens back and 
forth in order that the wearer may see alternatively between distance and 
near optical zones to accomplish the alternating form of visual 
correction. 
Another design of the concentric bifocal contact lens consists of a lens 
with aspherical curves on either the front or back surface as revealed in 
U.S. Pat. No. 3,482,906. The back surface of the lens has a varying radius 
of curvature which, beginning in the geometric center of the lens, has the 
radius needed to produce the contact lens power for the eye's correction 
for its distance refractive error and changes to radii that are longer and 
longer in lens positions towards the periphery. This lens has the 
advantage that there is no sharp transition between the distance and near 
optical zones of the lens, but rather a continuous optical power change in 
going from the center to the periphery of the lens. The aspheric bifocal 
lens suffers from the same drawbacks as other concentric lens designs, 
however, in that when worn on the eye, there is a variation of optical 
power of the lens for light which passes into the subject's entrance 
pupil, which produces a retinal image that does not have the optimal focus 
for the individual. An aspheric bifocal may function more effectively if 
the lens can be made to shift as the subject looks from distance to near, 
but it is an exceptional patient when this occurs reliably so that the 
patient can see well at both far and near distances. As an alternate 
design, an aspheric bifocal can be produced by forming an aspherical curve 
on the front surface of the contact lens, such lens functioning on the eye 
in essentially the same way as when the aspherical curve is on the 
posterior surface. 
A novel variation of the concentric zone bifocal is the diffraction bifocal 
design, which utilizes a series of concentric surface zones in the form of 
a Fresnel half-wavelength zone plate as revealed in U.S. Pat. No. 
4,210,391; U.S. Pat. No. 4,641,934 and U.S. Pat. No. 4,655,565. This lens 
is sometimes termed a "full aperture bifocal" and has been made from both 
RGP and hydrogel materials. The principle of diffraction has considerable 
advantage over refraction, in that it requires no appreciable lens 
thickness which is greater than single-vision designs. 
The mechanism for the deviation of light by diffraction requires a fine 
facet or eschelet only a few .mu.m high on the posterior lens surface 
which asymmetrically retards transmitted light such that it is in phase at 
the near focal point. The finer the structure, the greater the deviation. 
The rulings on a contact lens take the form of concentric circles, and the 
greater deviation angle required at the periphery of the lens means that 
the separation between the circles becomes less towards the periphery. By 
careful selection of the zone widths, it is possible to manipulate the 
light mainly into two images and create a simultaneous vision contact 
lens. 
In contrast to the two-zone bifocals, the diffractive bifocal always has 
many zones covering the area of the pupil, and hence the division of the 
incident light into two images occurs at every small area of the lens. 
Consequently, as the pupil changes size, the proportion of light for the 
distance and near remains constant. In addition, this ratio is constant 
for various patients with different pupil diameters. 
The principle disadvantage of the diffractive bifocal is that out-of-focus 
light is always superimposed on the image that is in focus. Hence, when 
the patient looks at distance, the out-of-focus light from near objects 
produces a blurring or hazing of the visual field. In this respect, the 
lens suffers from the same drawback of simultaneous vision as a two-zone 
bifocal, although less hazing effect is claimed. Most complaints occur 
when the lens is worn at night. 
The second major type of bifocal contact lens is the vertically stacked 
zone lens or segmented bifocal as described in U.S. Pat. No. 3,597,055. 
This lens design requires some method of stabilizing meridional 
orientation of the lens when worn on the eye so that the distance optical 
zone stays at the uppermost position of the lens, a design feature which 
is usually accomplished by the use of prism ballast. The lens is generally 
fitted so that its lower edge will rest upon the lower lid when the wearer 
looks at a distant object. As the eye looks down to view a near object, 
the cornea moves downward relative to the lower lid with the result that 
the lens is pushed upward by the lower lid. This positions the lower 
optical zone of the lens, which contains the optical correction for near 
vision, in front of the pupil. This type of lens depends upon translation 
of the lens to the proper position whenever the eye gazes from distance to 
near or returns. This lens often fails because of the lack of adequate 
movement of the lens to bring the near optic zone to a position in front 
of the entrance pupil, when viewing near objects. In addition, the lens 
often fails because of discomfort which may be due to the thick lower edge 
of the prism ballast design or other methods which are used to establish 
meridional orientation. In general, mechanical forms of bifocal lens 
shifting by the lids have been too unreliable for a high degree of 
success. 
Previous bifocal contact lens designs have utilized the lids to move all or 
part of the contact lens so as to position the desired distance or near 
optical zone in front of the entrance pupil at the desired time such as 
revealed in U.S. Pat. No. 4,302,081; U.S. Pat. No. 4,614,413 and U.S. Pat. 
No. 4,728,182. A contact lens has also been revealed in U.S. Pat. No. 
4,702,573 in which the lid induces a change in lens shape to produce an 
optical power change. 
It should be noted that all of the bifocal lens designs which have been 
described have been composed of either rigid or flexible materials 
including PMMA, silicone methacrylate, fluorosilicone acrylates, 
fluoropolymers, silicone resin, silicone elastomer, hydrogel contact 
lenses of water contents ranging from 30 to 90% (it would be no different 
for water contents outside this range), butylacrylates and all similar 
materials known to have properties which allow the construction of a 
contact lens. My following invention will also apply to lenses made from 
all of these materials as well as other materials suitable for making 
contact lenses of any rigidity. 
PRESENT INVENTION 
The present invention differs from all previous bifocal contact lenses in 
that it contains a switch in the form of a sensor material or body which 
changes the optical correction for distance or near vision, such switch 
being initiated by one or both lids acting as a trigger. An objective of 
the present bifocal contact lens invention is to activate the lens power 
change by triggering a sensing mechanism on the lens with the lid, without 
moving the lens, although some lens movement may occur without nullifying 
the invention. The invention involves the placing of a sensor material on 
the contact lens in such a way so as to convey a signal from the lid or 
lids that either the optical power for distance or near vision correction 
is required.

PREFERRED EMBODIMENTS OF THE INVENTION 
For the average individual, when the eye is open and gazing straight ahead 
at a distant object, the lids in a natural position are separated by a 
distance of about 10.5 to 11.5 mm. When the average person looks down to 
read, the upper lid moves downward by a distance of 3 to 4 mm and there is 
a small inward movement of the lower lid. For a person who is wearing a 
contact lens, the area of the contact lens that is covered by the lids is 
therefore much greater in the reading position. If the periphery of the 
contact lens now contains a material which is sensitive to some stimulus 
that is induced by the upper lid, then the lid coverage of the lens 
periphery during reading can act as a trigger or initiator of the method 
for transforming the lens into a near power correction. 
One embodiment of this invention consists of a rigid concentric bifocal 
lens made from silicone acrylate material and modified in the following 
way. A cross section of the lens is shown in FIG. 1 in which the front 
surface consists of a distance optical zone with outer diameter 1 and 
inner diameter 2 containing a gold wire 3 located about two millimeters 
from the lens edge 4 and surrounding concentrically a near optical zone 5 
located at the center of the lens. After cutting and polishing the front 
surface of the lens to produce the appropriate power for a distance 
refractive correction, the lens, which is still mounted on the arbor with 
pitch, is remounted on the lathe and the diamond cutting tool advanced 
forward at a position approximately two mm inward from the lens edge 
towards the center. A narrow groove 6 is cut in the front surface of the 
contact lens in the region of the distance optical zone, such cut being 
formed by the shape of the diamond tip to produce a small semi-circular 
groove 6 of approximately 0.5 mm chord width. With the lens still 
remaining on the arbor, a small gold wire 3 is fixed into the newly formed 
groove on the contact lens with epoxy. FIG. 1 illustrates the groove 6 
both without the wire and with the gold wire 3 for illustration only and 
the final lens will contain the wire 3 throughout the entire groove as 
shown in FIG. 2. When the epoxy is set, the lens is remounted on the lathe 
and a new surface cut is made to trim excess gold material and bring the 
surface of the gold into a continuous curve with the distance optical zone 
front surface. Next, the lens is removed from the arbor and finished in 
the usual way by adding any required peripheral curves on the posterior 
surface and edging. The lens is next coated with a liquid crystal material 
on the front surface, over the area of the gold wire and immediately 
adjacent thereto to cover the distance optical zone from its inner 
diameter 2 to its outer diameter 1. The liquid crystals are sensitive to 
heat and are transformed at about 95.degree. F. For this embodiment of the 
invention the gold wire 3 and the liquid crystal material constitute the 
lens switch. 
FIG. 3 illustrates a cross section of the bifocal lens along with the 
ocular structures consisting of the lower lid 7 cornea 8 pupil margin 9 
iris 10 crystalline lens 11 and upper lid of the eye 12. When the contact 
lens of FIG. 1 is placed on a subject's eye, it is found that as long as 
the subject looks straight ahead as shown in FIG. 3 the eyelids 7 and 12 
are held away from the gold wire 3 on the contact lens and the area of the 
contact lens immediately adjacent to the gold wire consisting of the 
distance optical zone remains clear. However, when the subject looks down 
to read as in FIG. 4, it is found that the upper lid 12 partially covers 
the lens and the gold wire 3. Soon afterward the area of the distance 
optical zone of the contact lens which was over the gold wire, or 
immediately adjacent to it, becomes darkened. This darkening effect is 
produced by the conduction of heat from the inner surface of the lid 
around the gold wire. Since the normal corneal temperature is about 
92.degree. F. and the temperature beneath the upper lid is about 
96.degree. F. or higher, there is a heat differential between the lid and 
the cornea. 
By placing the gold wire 3 in the distance optical zone of the contact 
lens, it is found that the subject can gaze in the straight ahead 
position, without the lid covering the wire. At the straight ahead 
position, both the distance and near optical zones of the contact lens 
remain clear. When the subject looks at a near object, however, the upper 
lid then covers a portion of the gold wire and heats the wire throughout 
its circle on the contact lens. This action produces a darkening in the 
distance optical zone in which the gold wire resides by transforming the 
liquid crystal coating of the distance optical zone to a darkened state 
adjacent to the wire leaving only the central near optical zone in the 
lens optically clear. This improves the optical properties contributing to 
the retinal image formation by eliminating light from the distance optical 
zone from entering the pupil. 
It is possible to place the gold wire at different positions on the lens to 
accommodate the variations in lid structure of different patients and the 
dimensions described may vary for different lens diameters or patient eye 
dimensions. With some lens configurations the lower lid may also play a 
role in activating the lens switch. 
It is recognized that various combinations of distance and near viewing 
areas could be produced on the lens by the appropriate placement of the 
gold wire and a combination of the temperature sensitizing material. A 
bipartite arrangement in which each half of the lens was given either a 
distance or near refractive correction would still allow lens rotation 
without image shift if a monocentric construction were used. 
It is also noted that many different materials are available which can be 
used for this purpose but are too toxic to be allowed to come in contact 
with the eye. This problem can be solved by layering the wire and 
photosensitive material inside the contact lens in a sandwich arrangement. 
The same principle described here might also be used with prism ballast 
and/or stacked type bifocals to eliminate a portion of the lens area from 
light transmission during distance or near gaze. Furthermore, any present 
type of bifocal contact lens design would be amenable to modification and 
incorporation of this technique. 
Another alternate form of this invention might consist of a contact lens in 
which the central portion has a second layer which consists of material of 
variable refractive index which is sensitive to temperature change. A gold 
wire is placed around the periphery of the variable index section. As the 
lid moves down over the upper portion of the gold wire during near 
viewing, the lid trigger to the gold wire initiates a change in the 
refractive index of the material. By increasing the refractive index, the 
refractive power of the central portion of the contact lens is increased 
which allows for a proper correction for near vision. When the lid is 
raised, the area is cooled and the refractive index is lowered which 
establishes the proper central lens power to correct for distance vision. 
By the proper choice of material and temperature conditions, it is 
possible for this lens to have a continuously variable power in proportion 
to the temperature change that is produced as the lid covers a greater and 
greater area of the wire. Hence, this would result in a truly continuous 
focus lens. It is also recognized that more than one gold ring may be used 
in a pattern of spokes, or some other configuration which may better 
conduct the heat from the lids to a more central portion of the contact 
lens. 
Another alternate form of my lens would be an improvement of the currently 
available diffraction bifocals. These bifocals suffer because only 40% of 
the light passing through the visual area of the lens is available for 
either distance or near vision and there is a veiling effect from the 
unfocused light. The lid sensor principle may be used with diffraction 
bifocals to selectively block out the unwanted lens areas during either 
distance or near vision. Alternatively, liquid crystals may be used to 
form a pattern on the lens which will produce images by diffraction. Since 
liquid crystals function on the basis of light interference, the heat 
sensor principle may be used to alter the state of the crystals when 
vision is changed back and forth between distance and near vision so that 
two or more lens focal powers are produced. 
The principal of the present invention may be applied to a corneal lens, in 
which the lens diameter is less than the cornea or a scleral lens, in 
which the lens diameter is equal to or grater than the corneal diameter. 
The principal of the present invention may be applied to trifocal or 
multifocal contact lenses by applying the switch structure to the lens in 
such a way that the lid will activate the switch in sequence with the 
various optical zones which are desired to be operative. 
It should also be noted that this same method may be used to measure 
temperature beneath the eyelids and by using different sensor materials 
could be used to form sensors which are sensitive to other body functions 
such as pH, pO.sub.2, or pCO.sub.2.