Contact lens having position stabilization

Contact lenses having position stabilization are utilized in order to fix the position of the contact lens on the cornea of the eye of a person wearing the lens. For this purpose, thickened regions for adjusting a specific orientation relative to the eye of the wearer are provided on the convex outer surface of the contact lens outside of the optical zone. A reliable position stabilization of a contact lens on the eye is achieved in that at least two thickened regions are provided laterally of the vertical center axis. These thickened regions extend essentially below a horizontal center axis between the optical zone and the edge region and it is very advantageous if these thickened regions lie at least at one point on the lower eyelid when the eye is open. In this way, a rotation of the contact lens is avoided when the eye is open. Furthermore, it is advantageous when the contact of the thickened regions on the lower eyelid is maintained. Additional thickened regions can be provided on the outer surface by which the movement of the upper eyelid encounters resistance when moving downwardly. These additional thickened regions are arranged above the first-mentioned thickened regions. With this combination, an optimal position stabilization of the contact lens on the cornea of the eye is achieved. The possibility is also presented that the thickened regions can be configured that they provide static as well as dynamic position stabilization.

FIELD OF THE INVENTION 
The invention relates to a contact lens with positional stabilization which 
is placed on the cornea of an eye of a person wearing the contact lens. 
The contact lens has a convex outer surface and has means for adjusting a 
specific orientation of the contact lens relative to the eye of the 
contact lens wearer. These means are provided outside of an optical zone 
on a peripheral region of the outer surface of the lens. 
BACKGROUND OF THE INVENTION 
Contact lenses having positional stabilization of the lens on the human eye 
correct, for example, axially-dependent ametropia of the eye such as 
astigmatism. The stabilization of the axial position of the contact lens 
prevents the rotational movement of the contact lens on the eye and 
assures the orientation of the contact lens even after a blinking of the 
eyelid. Various stabilization principles are known in order to obtain a 
positional stabilization of a contact lens on an eye. 
The rotation of the contact lens on the eye can be prevented with a toric 
posterior surface if the corneal astigmatism of the eye is sufficiently 
great as disclosed in U.S. Pat. No. 4,787,732. However, this prerequisite 
is fulfilled only in the rarest of cases. 
A very limited area of application is also provided for contact lenses 
which have an optical effect only for near vision. In this connection, 
reference may be had to German Patent 3,308,570 and U.S. Pat. Nos. 
4,850,689 and 3,591,264. 
Contact lenses having prismatic ballast have a stabilized position on the 
eye because of different thicknesses along the periphery of the contact 
lens and only a limited rotational movement occurs. Because of the 
increased weight of the lens in the lower region, the lens drops after 
each movement of the eyelid which pulls the lens out of the stabilized 
position and returns it to its use position as disclosed, for example, in 
U.S. Pat. No. 4,874,234. However, this thickening at the lower lens edge 
causes many wearers of contact lenses to experience a foreign-body 
sensation and the lens is therefore perceived as being disturbing. The 
same applies to contact lenses having a thickened edge in the lower lens 
region as suggested in German Patent 2,046,389 and German Utility Model 
Registration 7,034,876. A further disadvantage of contact lenses 
stabilized in this manner is that the oxygen permeability of a contact 
lens is greatly dependent on the thickness of the lens material in 
addition to the material itself and a high permeability with respect to 
oxygen must be required for a good compatibility of the contact lens on 
the eye. 
German Patent 3,003,985 suggests that a stabilization can be achieved by 
permanently supporting the lens on the lower eyelid. However, the lower 
eyelid is subjected to a permanent irritation with the continuous support 
of the contact lens thereon with its entire weight. This irritation is 
perceived by the wearer of the contact lens especially when blinking. 
The solutions for stabilization described above utilize static 
stabilization in order to suppress the movement of a contact lens on the 
eye of the wearer. However, there are also solutions for achieving 
stabilization which utilize dynamic stabilization. The dynamically 
stabilized contact lenses utilize the movement of both eyelids when 
blinking. In this way, the stabilization of the contact lens on the eye of 
the wearer takes place when the eyelids are closed. 
A solution is known wherein the dynamic stabilization takes place by a 
reduction of the thickness at the outer surface of the lens at two regions 
which lie symmetrically to each other as suggested in U.S. Pat. No. 
4,095,878 and British Patent 2,041,557. These regions are symmetrical to a 
center plane which is horizontal in the supporting position of the contact 
lens and these regions have a crescent-shaped configuration. In this way, 
the contact lens becomes thicker in the horizontal center plane than in 
the two crescent-shaped regions. When the eyelids are closed, the upper 
and lower eyelids of the eye glide over the contact lens and a pressure is 
applied to the contact lens because of the gradually increasing thickness 
of the contact lens in the crescent-shaped regions. This pressure is 
dependent upon the position of the contact lens on the eye and leads to an 
alignment of the contact lens. The alignment takes place with each blink 
of the lids whereas no stabilization takes place while the eye is open. 
A further solution according to the dynamic stabilization principle is 
disclosed in U.S. Pat. No. 4,859,049 in which the contact lens is 
deliberately thickened in two outer regions in the horizontal center axis. 
These thickened regions lead to a targeted alignment of the contact lens 
when the eyelids are closed. Here too, the alignment takes place with each 
blink whereas no stabilization takes place when the eye is open. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide a reliable positional 
stabilization of a contact lens on the eye of a wearer thereof which 
considers the eyelid geometry and the movement thereof. 
An optimal fit to the position of the eyelids in the majority of contact 
lens wearers is obtained by arranging the regions of different thickness 
essentially below the horizontal center axis. If, in contrast, these 
regions are arranged on the horizontal center axis, then the lower eyelid 
separates too soon from the stabilizing regions. This leads to an 
uncontrolled separation within certain limits from the thickened regions. 
In order to make stabilization possible and according to a feature of the 
invention, two thickened regions are provided essentially below a center 
axis which is horizontal when the contact lens is in the position in which 
it is worn by the wearer. The size, the position, and the minimum height 
of the thickened regions are determined from the eyelid geometry and the 
eyelid mechanics. The thickened regions are arranged in an outer zone 
between the optical zone and the edge region of the contact lens so as to 
be lateral to a vertical center axis in order to provide an optimal lever 
action. 
It is advantageous to provide at least one further means on the outer zone 
of the contact lens which offers a slight resistance to the downward 
movement of the upper eyelid during a blinking of the eyelids. This means 
must be arranged above the thickened regions on the outer zone of the 
contact lens. 
The form of the thickened regions is advantageously so selected that each 
of the thickened regions lies against the lower eyelid at least at one 
point of its lower limit when the eye is opened. In addition to the 
dynamic position stabilization acting with each blink of the eyelids, a 
static positional stabilization is obtained also when the eye is open so 
that a separation of the upper eyelid from the thickened region provides 
no disturbance of the stabilization. For each movement of the eyelids, the 
means arranged above the thickened regions align the thickened regions on 
the lower eyelid. 
With the contact lens according to the invention, a dynamic position 
stabilization can be combined with a static position stabilization for the 
first time and in this way a precise orientation of a contact lens on the 
cornea of the eye of the lens wearer is ensured at every point in time 
with the position stabilization not being dependent upon the thickness of 
the material of the overall contact lens. The stabilization of the contact 
lens on the cornea of the eye is then characterized by an alignment on the 
lower eyelid. 
The thickened regions are configured so as to extend longitudinally and for 
this reason the stabilization of the contact lens on the eye can be 
characterized by a "latching" in the palpebral fissure. 
The two thickened regions can also be used for the dynamic components of 
the stabilization. In that these two thickened regions are positioned in 
the lower contact lens half, the condition is achieved that the upper 
eyelid experiences only the slightest hindrance after a stabilization of 
the contact lens on the cornea. The contact lenses in this way provide a 
comfort similar to known spherical contact lenses. 
It is advantageous to manufacture the entire contact lens from a blank so 
that the thickened regions and the remainder of the contact lens are made 
of one and the same material thereby reducing production costs. 
A substantial reduction of the foreign-body sensation is obtained in that 
the thickened regions are beveled on mutually opposite ends. In this 
connection, it is especially advantageous that the upper and lower bevel 
each define a concave surface while the inner and outer bevels each have a 
convex surface. 
The stabilization of the contact lens achieved according to the invention 
makes it possible to configure the optical zone so as to be almost 
circularly shaped with the size of this optical zone being very large 
relative to the diameter of the overall contact lens. This enables the 
optical zone to be provided with a toric surface in order to correct 
directionally-dependent ametropia or to make possible sharp viewing at 
several distance ranges. 
A better fit to the form of the upper eyelid is achieved in that the upper 
boundary line of the thickened regions is aligned to the center point of 
the lens. 
Means can be provided on the surface of the outer zone of the lens for 
determining the position of the contact lens on the eye in order that the 
position of the contact lens relative to the cornea of the eye can be 
better determined with a fit and check by a technician. This means, or if 
required, other means is also advantageous to facilitate a 
position-correct seating of the contact lens on the cornea of the eye of 
the wearer thereof. 
It is irrelevant if the contact lens is made of soft or hard material; 
however, the stabilization principle is especially advantageous for a soft 
contact lens.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
The circular contact lens 1 shown in FIGS. 1 to 5 is made of a soft 
material. The lens 1 has a convex outer surface 14 and a concave inner 
surface 15. When worn, the contact lens is seated with the inner surface 
15 on the cornea of the eye 17. The inner surface 15 of the contact lens 1 
is fitted in its form to the form of the cornea of the eye 17. The outer 
surface 14 of the contact lens 1 is subdivided into several zones. 
The optical zone 8 is disposed in the central part of the contact lens 1. 
This optical zone 8 has a shape which is virtually circular and has the 
lens center 9 at its circular center. The outer surface 14 has a toric 
surface in the region of the optical zone 8. 
A connecting zone 6 is provided between the toric optical zone 8 and a lens 
outer zone 4. In this connecting zone 6, the adaptation of the outer 
surface 14 from the torically formed optical zone 8 to the spherically 
formed lens outer zone 4 takes place. 
The peripheral region 2 follows after the lens outer zone 4 which is 
essentially spherical. The peripheral region 2 is so formed that the 
contact lens 1 generates the least possible resistance for the slide-on 
movement of the eyelids (21a, 21b) when a movement on the cornea of the 
eye takes place. This is important so that the contact lens 1 will be 
perceived as being comfortable by the wearer of the contact lens on the 
eye 17. 
The region of the optical zone 8 corrects for the ametropia of the contact 
lens wearer. In principle, the optical zone 8 can also have a spherical 
surface. In this case, a position stabilization of the contact lens 1 on 
the eye 17 would then not be necessary. Especially axis-dependent 
ametropia can be corrected with a torically formed surface of the optical 
zone 8. With an appropriate configuration of the surface of the optical 
zone, several distance ranges can be clearly recognized by an ametropic 
contact lens wearer. 
Two thickened regions 12 are disposed on the lens outer zone 4. These 
thickened regions 12 are arranged below a center axis 18, which is 
horizontal in the wearing position of the contact lens 1, and are arranged 
symmetrically to a vertical center axis 19. The regions 12 adjust a 
specific position orientation of the contact lens 1 relative to the eye 17 
of the contact lens wearer. 
The thickened regions 12 lie with at least one point 20 of their lower 
boundary line on the lower eyelid 21a in order to ensure a reliable 
orientation with respect to position at any time. 
The thickened regions 12 are made of the same material as the remainder of 
the contact lens 1 and are produced by surface processing the outer 
surface 14 of the contact lens 1. The regions 12 have a longitudinal form 
and have a central rise 16 which extends longitudinally with the thickened 
regions 12 extending only on the outer zone 4 of the lens. Laterally, the 
thickened regions 12 terminate on the one hand at the partition line 3 
between the edge region 2 and the outer zone 4 and, on the other hand, at 
the partition line 5 between the lens outer zone 4 and the connecting zone 
6. The extent of the thickened regions on the ring-shaped lens outer zone 
4 is greater along the periphery of the outer zone 4 than between the two 
partition lines (3, 5). 
The two thickened regions 12 are beveled on all sides with the upper and 
lower bevels (10a, 10b) being steeper than the inner and outer bevels 
(11a, 11b). With this measure, the condition is obtained that the central 
rise 16 has an angle a flat as possible and, with an eyelid closure, the 
central rise 16 is not perceived as being disturbing by an eyelid after 
sliding upon the thickened region 12. The steeper dropping upper and lower 
bevels (10a, 10b) provide for a good positioning of the contact lens 1 on 
the eye 17. 
An angle .alpha..sub.1 is conjointly defined by the horizontal center axis 
18 and the upper boundary of the thickened region 12. An angle 
.alpha..sub.2 is conjointly defined by the horizontal center axis 18 and 
the center point of the lower boundary of the thickened region 12. The 
angle .alpha..sub.1 lies in the range of .+-.30.degree. about the 
horizontal center axis 18; whereas, the angle .alpha..sub.2 can lie in the 
range between 5.degree. and 80.degree.. However, it is more advantageous 
if angle .alpha..sub.1 lies in the range of 0.degree. to 20.degree. and 
.alpha..sub.2 in the range of 40.degree. to 80.degree.. The angle 
.alpha..sub.3 between the center point of the lower boundary of the 
thickened region 12 and the lower boundary line of the thickened region 12 
can lie in the range of 20.degree. to 80.degree. and is advantageously in 
the range between 35.degree. and 75.degree.. An excellent combination of 
angles has been determined as follows: .alpha..sub.1 =10.degree.; 
.alpha..sub.2 =60 .degree.; and, .alpha..sub.3 =65.degree.. 
The angles between the upper and lower bevels (10a, 10b) can lie in the 
range of between 5.degree. and 45.degree. with an optimal angle of 
approximately 12.degree.. The angle of the inner bevel 11a lies 
advantageously in the range between 20.degree. and 45.degree. and the 
angle between the outer bevel 11b in the range between 55.degree. and 
65.degree.. The angles are referred to an imaginary concentric line on the 
outer zone 4 of the lens. The upper and lower bevels (10a, 10b) are 
configured as inwardly curved surfaces. The inner and outer bevels are 
surfaces curved outwardly so that the central rise 16 is unrecognizably 
present since a continuous course from the inner to the outer bevel is 
provided. The inwardly curved surfaces of the upper and lower bevels (10a, 
10b) make possible on the one hand a smooth slide-on of the upper eyelid 
21b and, on the other hand, a contact of the lower boundary of the 
thickened region 12 on the lower eyelid 21a which is perceived as being 
comfortable. The bevels (11a, 11b) are arcuately curved outwardly and 
inwardly and provide for a central rise 16 with a continuous surface which 
is as flat as possible. This can be improved by polishing. The outer 
surfaces (10a, 10b; 11a, 11b) are in this configuration of the surfaces 
(10a, 10b; 11a, 11b) segments of a cylindrical wall. 
The connecting zone 6 falls off at an angle .alpha..sub.4 which can amount 
to at most 70.degree. with a range between 30.degree. to 60.degree. being 
advantageous. 
The two thickened regions 12 have the same extent in FIG. 1. With a 
different size of the two thickened regions 12, an improved action of the 
position stabilization can be achieved (see FIG. 4) with the longer 
thickened region 12a being disposed on the side of the eye facing toward 
the nose. In this way, the individual eyelid relationships of the wearer 
of the contact lens can be considered in that the magnitude of the 
thickened regions 12 can be carried out pursuant to a prescription. 
The thickened regions 12 must have a minimum elevation in order to fulfill 
their assigned task in a proper manner. If the elevation above the normal 
outer surface 14 is measured at the location of the central rise 16, then 
an optimal elevation lies at approximately 0.4 mm. This elevation is 
dependent upon the eyelid geometry such as eyelid radius, position of the 
eyelids to one another, form of the palpebral fissure, position of the 
eyelids on the cornea of the eye 17 and the mechanics of the eyelids such 
as eyelid closure frequency and eyelid pressure. An optimal fine 
adjustment can be obtained for each contact lens wearer with a limited 
number of experiments. 
The lens has an inscription 13 or engraving in its lower region at the area 
of the outer zone 4 thereof so that the contact lens 1 can be more easily 
fitted by the technician to the cornea of the eye 17 of a contact lens 
wearer. This identifies the lens and determines the axial position of the 
main sections. The inscription 13 is so configured that a plus sign 
characterizes the position of the vertical center axis 19. Signs are 
arranged to the left and right of this plus sign by means of which each 
outer vertical line facing away from the plus sign defines an angle (for 
example 10.degree.) to the next outer vertical graduation of the next sign 
or to the vertical graduation of the plus sign. 
The visibility of the characterization especially in a slit-lamp microscope 
makes it possible that the perpendicular line indicates in the ocular of 
the microscope when there is an overlap of the plus sign with the vertical 
(90.degree./270.degree. in accordance with the "Technische Ausschuss fur 
Brillenoptik" of the German optical industry). The overlap with the right 
or left outer vertical graduation of a number laterally of the plus sign 
amounts to a deviation of +10.degree. or -10.degree. so that the 
technician can carry out the fine adjustment in a simple manner. 
A special problem when seating the contact lens in the open eye 17 of the 
contact lens wearer is that the contact lens 1 must be seated in its 
correct position on the cornea of the eye 17. For this reason, the contact 
lens 1 has a color point 23 having a diameter of approximately 1 mm on the 
vertical center axis 19 in the upper lens region on the outer zone 4. This 
color point 23 is subsequently colored onto the already swollen contact 
lens and assists the wearer thereof to correctly seat the contact lens 1. 
The contact lens 1 of the invention is distinguished by the feature that 
its material thickness is independent of the position stabilization. In 
this way, an optimal supply of the eye with oxygen is assured. If the 
permeability DK of a contact lens 1 is considered then the close 
relationship between lens thickness and oxygen permeability is recognized. 
Since the position stabilization is independent of the material thickness 
of the optical zone and of the lens zone 4, an excellent oxygen supply of 
the eye is assured with the contact lens 1 by a suitable selection of the 
material. 
In FIGS. 2 and 3, the form of the contact lens 1 in the vertical center 
axis 19 and of the horizontal center axis 18 is almost the same. The 
connecting zone 6 has its greatest extent in the horizontal center axis 18 
and disappears almost completely at the vertical center axis 19. 
For the open eye 17, the contact lens 1 normally lies only at a point 20 on 
the lower eyelid 21a. With an optimal selection of the angles 
.alpha..sub.2 and .alpha..sub.3, one obtains a line or surface contact on 
the lower eyelid 21a which is advantageous because of the pressure 
distribution on the lower eyelid 21a. 
The upper and lower regions (4a, 4b) of the lens outer zone 4 lie above and 
below the eyelids (21a, 21b) as shown in FIG. 4. This is advantageous so 
that the wearer of the contact lens perceives the presence of the lens as 
little as possible. With each closure of the eyelids, the contact lens 1 
is again pressed against the lower eyelid with which the lens is in light 
contact engagement even when the eye 17 is open. In this way, an optimal 
position stabilization of the contact lens 1 on the cornea of the eye is 
assured at every point in time. 
The contact lens 1 which utilizes this stabilization process can be made of 
hard as well as soft materials. The overall diameter of the contact lens 1 
is advantageously between 12 and 15 mm. The stabilization principle is 
especially advantageous for contact lenses 1 made of silicone rubber. 
It is possible to apply the thickened regions 12 afterwards to an otherwise 
finished contact lens 1. This is especially easy with dry soft lenses or 
hard lenses. With forms which can be precisely positioned, blanks (that 
is, contact lenses which are completed except for the thickened regions) 
can thereafter be supplied with the thickened regions 12. This makes it 
especially possible to considerably reduce the variety of lenses which 
have to be maintained in inventory. 
In lieu of one thickened region 12 laterally of each side of the vertical 
center axis, two thickened regions (22, 23) can be provided on the outer 
zone 4 of the lens as shown in FIG. 6. Accordingly, at least one 
additional thickened region 23 is provided above the two thickened regions 
(22, 22a) on the outer zone 4a of the contact lens 1. The thickened region 
23 defines a certain resistance to the downward movement of the upper 
eyelid 21b when the eyelids blink. A second additional thickened region 23 
can be provided above the thickened region 22a. 
Also, further means can be provided on the outer surface of the contact 
lens. This further means can be thickened regions (for example two 
regions) or a sickle-shaped bevel of the upper outer surface of the 
contact lens. The means should then advantageously provide a slight 
resistance with each movement of the upper eyelid in order to provide a 
directed alignment of the thickened regions on the lower eyelid. From 
these considerations, it follows that this means must be disposed above 
the thickened regions on the outer surface of the contact lens. The lower 
thickened regions can function as a supporting surface on the lower eyelid 
and the contact lens is stabilized when the eye is open. The other 
stabilization means would then be defined by a slight resistance for the 
movement of the upper eyelid when the eyelids are blinked and for aligning 
the two lower thickened regions relative to the lower eyelid. 
It is understood that the foregoing description is that of the preferred 
embodiments of the invention and that various changes and modifications 
may be made thereto without departing from the spirit and scope of the 
invention as defined in the appended claims.