Quadrilateral lens

An arcuately molded lens for eyewear such as goggles or eyeglasses is provided. The lens is single pane, unitary lens defining upper and lower edges. The lower edge may have a nosepiece opening formed therein for mounting the lens on a nose of a wearer. The lens has a horizontal arcuate cross-sectional configuration which defines opposing lateral segments and a central zone interposed therebetween. The lateral segments each have a first radius of curvature designated R1, and the central zone has a second radius of curvature designated R2. The lens can also have a vertical arcuate cross-sectional configuration which has a third radius of curvature designated R3. In a preferred embodiment, R1<R2≦R3.

BACKGROUND

The present invention relates generally to a lens for sunglasses, and more particularly to a uniquely configured quadroradial lens having a dual radius horizontal curvature and a constant radius vertical curvature for minimizing the prismatic shift of the lens. As discussed in greater detail below, embodiments of the present invention maximize the interception of peripheral light, while, at the same time, mitigating prismatic shift to enhance optical resolution for the wearer. An optional frusto-conical as worn configuration of the lens also permits construction of sunglasses which conform closely to the front and sides of the wearer's head. The resulting low profile glasses utilizing the lens of the present invention are particularly suited for demanding situations which require precise optical resolution and interception of peripheral light, such as competition skiing or bicycle racing.

Sunglasses have long been designed with the general objective of blocking the sun or other sources of bright light from one's eyes. Initially, numerous designs of dual lens glasses were developed, differing essentially only in aesthetic features. However, the unitary lens was later developed, and together with existing dual lens designs, has been geometrically modified in response to various optical considerations such as optical clarity and resolution, field of vision, light wave refraction, and others.

Although prior dual lens designs are useful for some purposes, the conventional dual lens system is inherently incapable of meeting the demands of certain activities. For example, the frame on dual lens glasses presents a substantial obstruction to one's peripheral vision, which can be extremely disadvantageous in any fast-paced activity. Even in dual lens glasses without a frame along the lower edges of the lenses, the edge of each lens disrupts peripheral vision. Simply providing a larger lens that is typically stamped or molded from a flat plane or a spherical blank, causes the glasses to extend too far tangentially away from the side of the head, leaving the glasses with an undesirably bulky profile.

At the same time, conventional dual lens glasses only intercept sunlight directly in front of the eye, leaving a large, unprotected periphery about each lens. Momentary flashes of light around the lens during activity cause constriction of the pupils, with a fleeting blindness as one attempts to readjust through the darkened lens.

Prior art attempts to block this peripheral light (aside from opaque blinders) included bending (e.g., thermoforming) a flexible lens in a posterior direction near the lateral edge. Although this improved the interception of peripheral light, the resulting optical resolution was unacceptable for high speed competition situations. This is due to the phenomena that even minor irregularities in the radius of curvature, which inherently result when bending a lens, cause an irregular diffraction of light waves passing through that region of the lens and distort the field of vision.

A unitary, molded, frusto-conical lens blank was then developed, such as that disclosed in U.S. Pat. No. 4,515,448 issued to Tackles. The frusto-conical lens was designed to conform closely to the wearer's head, having lateral edges that curved and extend interiorly to block peripheral light that would otherwise pass around the lenses of a dual lens design. In addition, diffraction gradients common in the bent, flexible lens, were minimized by molding the frusto-conical lens with a predetermined curvature. Nevertheless, the potential for improvement remained for several reasons.

The next improvement in specialty unitary eyewear utilized a unitary cylindrical lens which was curved about an axis having a substantially constant radius throughout, such that the lens defined a portion of the wall of a cylinder. This lens is the subject of U.S. Pat. No. 4,859,048, issued to Jannard. The cylindrical lens demonstrated improved optical properties and interception of peripheral light. Further, it provided a sleek, low profile design that also improved ventilation. Nevertheless, the cylindrical lens produced a measurable prismatic shift in each of the vertical and horizontal planes, particularly at off axis viewing angles.

Another improvement in specialty unitary eyewear utilized a toroidal lens that was curved along each of two substantially perpendicular axes to produce a lens of generally toroidal configuration. This lens is the subject of U.S. Pat. No. 4,867,550, also issued to Jannard. The toroidal lens configuration was characterized by having arcuately configured horizontal and vertical cross-sections. The arc of each respective cross-section corresponded to a given radius. Thus, the toroidal lens can be defined by two different radii, and is configured to substantially conform to the wearer's head. In addition, the lens thickness was tapered to further reduce prismatic shift.

Yet another improvement in unitary lens eyewear utilized an elliptical lens. This lens is the subject of U.S. Pat. No. 5,774,201, also issued to Tackles. The elliptical lens is characterized as having a horizontal cross-section that substantially conforms to an elliptical shape. The vertical cross-section of the elliptical lens can be defined by any of various geometric shapes, such as a cylinder, a cone, an ellipsoid, or an ellipsoid of revolution. The elliptical lens was introduced to improve the optical characteristics of specialty eye wear, including refraction between medial light entering at the front of the lens and peripheral light entering at the lateral ends of the lens.

Notwithstanding the many advantages presented by this progression of unitary lens designs, there is a continuing need for a specialty lens having excellent optical qualities and providing reduced light wave defraction of medial, lateral and peripheral light, while at the same time providing a low profile, aerodynamic configuration that allowed for adequate ventilation and maximum comfort. Preferably, the lens will exhibit good impact resistance, as well as minimal prismatic shift in both the horizontal and vertical axes.

BRIEF SUMMARY

In accordance with an embodiment of the present invention, there is provided an arcuately molded lens for eyeglasses. The lens is suitable for participation in active sports, such as biking, skiing, and the like. The lens comprises a single pane, unitary lens defining upper and lower edges. The lower edge has a nosepiece opening formed therein for mounting the lens on a nose of a wearer. The lens has a first arcuate cross-sectional configuration in a horizontal direction.

The first arcuate cross-sectional configuration defines opposing lateral segments and a central zone interposed therebetween. In an embodiment, the central zone can be substantially symmetrically located with respect to the nosepiece and the lateral segments. The lateral segments each have a first radius of curvature designated R1, and the central zone has a second radius of curvature designated R2.

In another embodiment, the lens can have a second arcuate cross-sectional configuration in a vertical direction. The second arcuate cross-sectional configuration can have a third radius of curvature designated R3. According to various embodiments disclosed herein, R1is preferably not equal to R2. For example, R1can be less than or equal to R2(R1≦R2). Further, R2is preferably not equal to R3. In this regard, R2can be less than or equal to R3(R2≦R3).

In some embodiments, R1can be in the range of about 1½ to 3 inches, and most preferably, approximately 2½ inches; R2can be in the range of about 4 to 10 inches, and most preferably, approximately 5 inches; and R3can be in the range of about 4 to 11 inches, and most preferably, approximately between 5-10 inches.

In addition, the lens can be configured wherein R3varies along a horizontal plane of the lens. For example, R3can increases along the horizontal plane from the central zone toward the lateral segment of the lens. Thus, R3can vary between about 4 to 11 inches.

The lens can also be formed to include transition sites disposed intermediate the opposing lateral segments and the central zone. The transition sites can define a transition radius of curvature designated RT. In one embodiment, the first radius of curvature can be coincident to the second radius of curvature at the respective transition sites. According to another embodiment, R1can be less than or equal to RT, and RTcan be less than or equal to R2(R1≦RT≦R2). For example, the lens can be configured with RT=R2at an end point of the central zone and further be configured such that RTdecreases in the transition site until RT=R1at a beginning point of the lateral segment. In one implementation, the transition radius of curvature RTcan decrease at a constant rate from R2to R1.

In accordance with yet another embodiment, the lens can define inner and outer surfaces and a thickness therebetween. An average thickness of the lens in the lateral segments of the lens is less than an average thickness of the lens in the central zone. In addition, the lens can be formed such that the thickness of the lens in at least one point in the central zone can be greater than the thickness of the lens at any point within at least one of the lateral segments. In some embodiments, the thickness of the lens can taper from a central point of the lens gradually to a reduced thickness in the lateral segments. The average lens thickness can preferably be in the range of about 0.061 to 0.068 inches. However, the thickness of the lens in the central zone can be between about 0.060 and 0.070 inches and taper to between about 0.050 and 0.060 inches in the lateral segments.

DETAILED DESCRIPTION

While the present description sets forth specific details of various embodiments, it will be appreciated that the description is illustrative only and should not be construed in any way as limiting. Furthermore, various applications of such embodiments and modifications thereto, which may occur to those who are skilled in the art, are also encompassed by the general concepts described herein.

Referring now to the drawings wherein the showings are made for purposes of illustrating preferred embodiments of the present invention, and not for purposes of limiting the same,FIG. 1is a perspective view of an eyeglass or eyewear10having a unitary lens12and a mounting frame14. The lens12is configured to extend in the path of a wearer's left and right eye fields of vision. As shown inFIG. 1, the curvature of the lens12permits it to conform closely from side to side to the wearer's face, thus maximizing the interception of sun and other strong light sources, while at the same time providing comfort and pleasing aesthetic characteristics.FIGS. 1 and 2illustrate an exemplary embodiment of the eyeglass, including exemplary dimensions and shapes of the lens12and mounting frame14. However, embodiments of the present invention principally relate to the curvature of the lens12, an exemplary embodiment of which is illustrated inFIGS. 3-5. As explained in greater detail below, such embodiments provide enhanced optical qualities, for example, by tending to reduce prismatic shift of light rays passing through the lens12, throughout the wearer's field of view. Further, other properties of the lens12, such ballistic impact strength and aesthetic appeal can also be modified and enhanced utilizing the teaching herein. These, as well as other advantages are described herein.

Referring toFIG. 1, it should be noted that the particular mounting frame14is not essential to the embodiments disclosed herein. The frame14can be of varying configurations and designs, and the illustrated embodiment shown inFIGS. 1 and 2is provided for exemplary purposes only. As illustrated, the frame14may include a top frame portion16and a pair of ear stems18that are pivotably connected to opposing ends of the top frame portion16. Further, the lens12may be mounted to the frame14with an upper edge20of the lens12extending along or within a lens groove and being secured to the top frame portion16. For example, the upper edge20of the lens12can be formed in a pattern, such as a jagged or non-linear edge, and apertures or other shapes around which the top frame portion16can be injection molded or fastened in order to secure the lens12to the top frame portion16. Further, the lens12can be removably attachable to the frame14by means of a slot with inter-fitting projections or other attachment structure formed in the lens and/or top frame portion16.

It is also contemplated that the lens12can also be secured along a lower edge22thereof, with the frame14being configured to attach to the lower edge22of the lens12. Various other configurations can also be utilized. Such alternative configurations can include the direct attachment of the ear stems18to the lens12without any frame, or other configurations that can reduce the overall weight, size, or profile of the eyeglasses. In addition, various materials can be utilized in the manufacture of the frame14, such as metals, composites, or relatively rigid, molded thermoplastic materials which are well known in the art, and which can be transparent or available in a variety of colors. Indeed, the mounting frame14can be fabricated according to various configurations and designs as desired.

Similarly, the front two-dimensional profile of the lens12, as illustrated in the front views ofFIGS. 2 and 3, can also be variously configured. The lens12can be of a single pane of material. Thus, the lens12can be unitary or have a dual lens design. A nosepiece opening24can be formed along the lower edge22of the lens12, which can be sized and configured to accommodate the nose of a wearer. In addition, the nosepiece opening22can also accommodate a nosepiece26adapted to flex and closely fit the opposite sides of the wearer's nose. Furthermore, the lower edge22of the lens12can also be shaped to substantially conform to the wearer's facial profile, thus allowing some embodiments to be closely fitted to the wearer's head while not contacting the skin of the wearer's face.

In addition, lenses in accordance with the present invention can be manufactured by any of a variety of processes well known in the art. Preferably, the lens12is injection molded and comprises a relatively rigid and optically acceptable material such as polycarbonate. The curvature of the lens12would thus be incorporated into a molded lens blank. A lens blank will include the desired curvature and taper in its as-molded condition. One or two or more lenses of the desired shape may then be cut from the optically appropriate portion of the lens blank as is understood in the art. Preferably, the frame14is provided with a slot or other attachment structure that cooperates with the molded and cut shape of the lens to minimize deviation from, and even improve retention of its as-molded shape.

Alternatively, the lens12can be stamped or cut from flat sheet stock and then bent into the curved configuration in accordance with an implementation of the present invention. This curved configuration can then be maintained by the use of a relatively rigid, curved frame14, or by heating the curved sheet to retain its curved configuration, as is well known in the thermoforming art. However, this method is less desirable because bending the lens12can result in stress fractures or other compression or expansion induced flaws which can impair the optical qualities of the lens12.

FIG. 4illustrates a first arcuate cross-sectional configuration of the lens12, as shown in a horizontal direction. The sectional view ofFIG. 4illustrates an embodiment wherein the first arcuate cross-sectional configuration defines opposing lateral segments28and a central zone30interposed therebetween. The lateral segments28each have a first radius of curvature, designated R1. These radii of curvature R1are measured from independent focal points32shown inFIG. 4. In addition, the central zone30has a second radius of curvature, designated R2.FIG. 4also shows transition sites34of the lens12. The transition sites34are disposed on either side of the central zone30intermediate the central zone30and the opposing lateral segments28. According to a preferred embodiment, the transition sites34can be a coincidence point along the lens12where the radius of curvature of the lens12transitions from R1to R2, and vice versa. Also represented inFIG. 4is a pair of eyes35of the wearer.

Referring now toFIG. 5, the lens12can also have a second arcuate cross-sectional configuration in a vertical direction. The second arcuate cross-sectional configuration has a third radius of curvature, designated R3. As shown inFIGS. 4 and 5, the lens12has an inner surface36and an outer surface38. In this regard, each of the radii of curvature R1, R2, and R3are preferably measured from the inner surface36of the lens12, although the outer surface38can also be used in other embodiments. As explained further herein, embodiments of the lens12provides various advantageous optical qualities for the wearer, including reducing the prismatic shift of light rays passing through the lens12.

The human eye collects millions of light rays at a time and uses them to form an image. If the light rays collected by the eye are shifted, the image will also appear to be shifted. As illustrated inFIGS. 6 and 7, prismatic shift can be characterized as a first order optical distortion in which light rays shift as they pass through a transmissive medium. In essence, prismatic shift occurs when a light ray40entering a transmissive optical element42is deflected while traveling through the optical element42. The light ray40is redirected from an initial true direction44to a perceived direction46upon passing through the optical element42. The difference between the true direction44and the perceived direction46is referred to herein as prismatic shift48. Prismatic shift can occur in an eyeglass lens as light rays pass through the lens and are detected by eye of the wearer. The wearer actually sees an incorrect “perceived” location of the image due to the prismatic shift of the light rays. Prismatic shift presents a challenging problem for lens manufacture and design, and is explained in greater detail below.

Prismatic shift is related to the optical principle of refraction of light. Refraction can be defined as the “deflection of a wave on passing obliquely from one transparent medium into a second medium in which its speed is different, as the passage of a light ray from air into glass.” See The Columbia Electronic Encyclopedia, 6th Edition (Columbia University Press 2003). Referring toFIG. 7, the light ray40traveling through air along the initial true direction44(or vector) will be deflected in a different refracted direction50upon reaching and passing through an optical element42, such as glass. Point A illustrates where the light ray40intercepts the optical element42. AlthoughFIG. 7illustrates the optical element42as being made of glass, various other optically transmissive transparent and translucent materials, such as plastics, similarly illustrate the principal of refraction. When the light ray40exits the optical element42at point B, the light ray40is again deflected. In the example shown inFIG. 7, where the optical element42is flat and has parallel, planar first and second surfaces, the light ray40will be deflected at point B such that the perceived direction46is parallel to the initial true direction44, but laterally shifted by an offset distance or prismatic shift48. The refracted direction50of the light ray40as it travels through the optical element42, as well as the perceived direction46, can be determined according to the law of refraction.

The law of refraction considers an angle at which the light ray40approaches the first surface52of the optical element42, which angle is referred to as the angle of incidence56. This angle56is measured from the light ray40to a normal line58which is normal to the first surface52. A normal line is one that is perpendicular to a tangent line at the point where the tangent line intersects a curve (two dimensional, tangent line) or surface (three-dimensional, tangent plane). A line or plane is tangent if it that intersects the respective curve or plane at only one point. In addition, the law of refraction also considers an angle of refraction60, which is the angle between the refracted direction50of the light ray40and a normal line62. The relationship between the angle of incidence56and the angle of refraction60is established using a mathematical relationship that compares the speed at which light travels through both media (air and the optical element), and a physical property of each medium known as the index of refraction. This mathematical relationship is known as Snell's Law, and can be stated in terms of the indexes of refraction of the two media and the angles of incidence and refraction. This equation is shown below:

In the above equation, the variable ρ is representative of the angle of incidence56; the variable θ is representative of the angle of refraction60; the variable Nρis the index of refraction for a first medium (such as air); and Nθis the variable representative of the index of refraction of the second medium (in this case, glass). In most cases, the indices of refraction of the media are known, as well as the angle of incidence56of the light ray40. Thus, through manipulation of the mathematical equation, the angle of refraction60, θ, can be determined.

Thus, as illustrated inFIG. 7, the light ray40will be deflected within the optical element42at the angle of refraction60, θ, and proceed through the optical element42along a new refracted direction50until reaching the second surface54of the optical element42, which point is represented as point B inFIG. 7.

At point B inFIG. 7, the light ray40is deflected again as it passes from one medium into another, in this case, from glass back into air. The above mathematical analysis would again be performed in order to determine the perceived direction46of the light ray40. However, as mentioned above, if both the first and second surfaces52,54are parallel, the perceived direction46of the light ray40as it exits the optical element42will be parallel to the initial true direction44of the light ray40. This fact simplifies the present discussion, and is illustrated inFIG. 7.

The prismatic shift48of the light ray40can be determined by comparing the offset between the perceived direction46of the light ray40and its initial true direction44, as shown inFIG. 6. By understanding the effect of the prismatic shift48on the light ray40, it is understood that the perceived direction46of the light ray40is an incorrect representation of the true direction44of the light ray40. Thus, the perceived direction46of the light ray40detected by the eye of the wearer represents an image that is “shifted” from the true location of the image. Thus, light passing through a eyeglass lens can be distorted and be improperly perceived by the wearer.

Prismatic shift can be an especially significant drawback for an eyeglass wearer engaged in active sports, such as biking, skiing, and the like. As mentioned above, the deflection of the light ray40as it passes from one medium into another can cause the wearer to perceive an incorrect location of an object. As similarly described above, as millions of light rays enter the eyeglass wearer's eye, the retina of the eye detected the light rays and forms an image of the object. The location of the object, its dimensions, and other perceived physical attributes of the object, as detected by the eye, are determined in large measure as a result of the direction of the light rays as they enter the eye. If the light rays pass without obstruction from the object to the eye, the eye will detect a true image of the object according to its location and other physical attributes. However, if the light rays reflected off of the object pass through an intermediate optical medium prior to entering the eye, the light rays may undergo a prismatic shift, which will cause the eye to falsely perceive the true location or other physical attributes of the object. In active sports, such as cycling, basketball, baseball, and the like, the immediate detection of the location and dimension of moving objects is critical to the wearer.

Referring now toFIGS. 8-10, the optical performance of various prior art lens designs are illustrated.FIG. 8schematically illustrates refraction in a prior art unitary lens100of constant radius horizontal cross-section, having a uniform thickness102. With such a unitary lens100, neither of a pair of eyes104are positioned at the center of curvature106. Thus, the angle of incident rays from the lens100to each eye104changes throughout the angular range of vision. For example, a ray which shall be referred to as a medial light ray108strikes the lens100at an angle α to a normal line110. As discussed above, bending of light at transmitting surfaces depends in part upon the angle of incidence of light rays. In this example, because the lens100is a cylindrical lens of uniform thickness, the ray108is refracted or bent in opposite directions at each of an outer surface112and an inner surface114of the lens100, which results in a transmitted ray116parallel to the incident ray108, which accounts for prismatic shift118. The transmitted ray116is displaced, relative to the path of the medial incident ray108, by a distance corresponding to the prismatic shift118. This displacement is a first order source of optical distortion.

As also shown inFIG. 8, prismatic shift120is even more pronounced at a lateral end122of the lens100due to a greater angle of incidence β. A peripheral incident ray124thus experiences greater prismatic shift120(i.e. displacement) than the medial incident ray108. The discrepancy between the prismatic shift120of the peripheral ray124and the prismatic shift118of the medial ray110results in a second order of optical distortion.

FIG. 9illustrates an effort to compensate for the optical distortions caused by prismatic shift. Similar to the cylindrical lens100of uniform thickness discussed above, light is bent within the tapered lens200. However, tapering produces a smaller lens thickness202in the direction of lateral end204, relative to a lens thickness206at a more medial point208. This smaller lens thickness202reduces an amount of displacement, i.e. prismatic shift210, of a peripheral ray212relative to the prismatic shift120of the peripheral ray124through the untapered lens100ofFIG. 8. In other words, lesser lens thickness202at the lateral end204of the tapered lens200compensates for a greater angle of incidence β′, relative to the thickness206and angle of incidence α′ at the medial point208. The lesser lens thickness202of the tapered lens200therefore results in a smaller difference between the prismatic shift210of the peripheral ray212and the prismatic shift214of the medial ray216on the lens200. This difference is also smaller than the corresponding difference of the untapered lens100inFIG. 8, which results in a comparative reduction in the second order optical distortion. Note that the degree of correction of the second order distortion depends upon the differential thickness from the apex218to each lateral end204.

In yet another attempt to reduce the prismatic shift of incident rays,FIG. 10illustrates an elliptical tapered lens300. The light rays pass through the lens300toward the wearer's eye302more closely normal to lens outer and inner surfaces304,306, throughout the wearer's angular range of vision. This results in a lesser prismatic shift308,310at each respective point312,314along the lens300, relative to non-elliptical lenses100,200, and thus lessens first order optical distortion. This result is due to the shape of the elliptical lens300which can generally be characterized as having a curvature that increases toward the lateral ends316, which accounts for some light rays passing more closely normal to the lens outer and inner surfaces304,306. The tightening curvature of the lens300towards the lateral ends316also accounts for the lower discrepancy between the prismatic shift308of a medial ray318and the prismatic shift310of a peripheral ray320.

By way of contrast, a central horizontal meridian of an embodiment of the quadroradial lens12of the present invention is shown inFIG. 11. As mentioned with respect toFIG. 4, the lens12has opposing lateral segments28and the central zone30disposed therebetween. Each lateral segment28has a first radius of curvature, designated R1that is measured from respective centers of curvature32. Thus, medial and peripheral light rays400,402pass through the lens12to the wearer's eyes35at a closer angle to normal to the lens12inner surface38in the lateral segments28of the lens12.

Thus, as illustrated inFIG. 11, incident medial and peripheral light rays400,402are transmitted through the lens12and undergo substantially minimal or negligible refraction and consequently, prismatic shift will tend to be lessened. In fact, in the embodiment shown inFIG. 11, the ray400can pass nearly perfectly normal to both of the lens inner and outer surfaces36,38because the ray400passes through the lens12at approximately at the transition site34. Further, ray402can also pass substantially closer normal in such an embodiment.

As a result, transmitted medial and peripheral light rays404,406are not substantially deflected relative to the incident medial and peripheral light rays400,402. In this regard, first order optical distortion is substantially eliminated for the transmitted medial light ray404, and minimal for the transmitted peripheral light ray406. In addition, with minimal or negligible prismatic shift in the transmitted medial and peripheral light rays404,406, second order optical distortion is also substantially eliminated. The configuration of embodiments can be variously modified to further enhance the elimination of first and second order optical distortion. For example, the first and second radii of curvature, as well as the first and second centers of curvature, can be altered in order to optimize optical characteristics of the lens12, including the elimination of prismatic shift and first and second order optical distortion.

These exceptional optical characteristics of embodiments, including the substantial reduction or elimination of prismatic shift in the lateral segments28of the lens12can be further explained with reference to the lens geometry in the lateral segments28and Snell's Law. In the embodiment of the lens12illustrated inFIG. 11, the inner and outer surfaces36,38of the lateral segments28may be substantially parallel curvilinear surfaces and the wearer's eyes35may be positioned approximately at the respective centers of curvature of these lateral segments28.

As illustrated, the transition site34can be disposed along a circular path408, the center of which is the focal point32and the radius of which is the first radius of curvature R1. The eye35can be positioned along a linear path409intermediate the focal point32and the transition site34, which places the eye35in such a position that any rays incident upon the lens12at or nearby the transition site34will be normal to the inner and outer surfaces36,38of the lens12. This results because, as illustrated inFIG. 11, and as mentioned above, a normal line410of the circle408is one that is perpendicular to a tangent line412of the circle408at the point of intersection414of the circle408and the tangent line412. Thus, the normal line410will pass through the center32of the circle408and ultimately can also be collinear with the radius R1of the circle408. In this embodiment, the normal line410can be representative of the transmitted medial and peripheral rays404,406.

In another embodiment, the centers of rotation32can be respectively disposed approximately at the centers of the eyes35. In such an embodiment, since the transmitted medial and peripheral rays would be approximately normal to the inner surface of the lens, the path of the incident light rays while passing through the lens will also be approximately normal to the inner surface. Finally, if the inner surface of the embodiment is approximately parallel to the outer surface and the incident medial and peripheral rays are approximately normal to the inner surface, the incident medial and peripheral rays must be about normal to the outer surface as well. Thus, the incident light rays would be normal to the outer surface. In this regard, no prismatic shift would occur in the lateral segments of the lens in such an embodiment, and therefore there is no first or second order optical distortion in the lateral segments of embodiments of the lens.

As shown inFIG. 11, in accordance with another embodiment, the lateral segment28of the lens12can also be formed to transition to posterior segments420. The posterior segments420can represent that portion of the lens12adjacent the lateral segments28and extending posteriorly to enhance lateral protection of the eyes35. In one embodiment, the posterior segment420can begin at a peripheral point422along the lens12where the inner surface36of the lens12diverges from the first radius of curvature R1. The posterior segments420of the lens12can thus extend beyond the wearer's field of vision in order to block light rays and physical debris from entering from the rear of the lens12.

In another embodiment shown inFIG. 11, the lens12in the posterior segments420can taper to a reduced lens thickness424. Such an embodiment can be beneficial for light rays that pass through the posterior segments420of the lens12to the eyes32of the wearer, if the lens is configured such that the posterior segments420remain within the wearer's field of view. For example, light rays passing through the posterior segments may undergo slight prismatic shift. In order to reduce this prismatic shift in the posterior segments420, the lens12can taper to a reduced thickness424in order to minimize the angle of incidence and the angle of refraction corresponding to a light ray passing through the posterior segment of the lens12.

One of the benefits associated with the implementation of tapered posterior segments420is that the lens12can be configured to extend posteriorly beyond the limit of the wearer's normal field of vision. Little or no prismatic shift may occur should the wearer desire to look laterally through the posterior segments420. This can be accomplished without requiring that the lens12follow a continuation of the arcuate path defined by the first radius of curvature R1. In other words, the lens12can substantially conform to the shape of the wearer's head and thus have an aerodynamic and sleek configuration.

Referring again to the embodiment shown inFIG. 11, the central zone30of the lens12is illustrated as conforming to the second radius of curvature R2. The second radius of curvature R2can be measured from a second center of curvature430to the inner surface38of the lens12, and generally follow along a circular path431designated thereby. According to various embodiments disclosed herein, R1is preferably not equal to R2. For example, R1can be less than or equal to R2(R1≦R2). Further, R2is preferably not equal to R3. In this regard, R2can be less than or equal to R3(R2≦R3).

In preferred embodiments, the second radius of curvature R2can be greater than twice as much as the first radius of curvature R1, as shown in the equation: 2×R1≦R2. However, in some embodiments, R1can be in the range of about 1½ to 3 inches, and most preferably, approximately 2½ inches; R2can be in the range of about 4 to 10 inches, and most preferably, approximately 5 inches; and R3can be in the range of about 4 to 11 inches, and most preferably, approximately between 5-10 inches.

In accordance with another embodiment of the quadroradial lens12, the lens12can be tapered. As described herein, embodiments of the lens12are preferably configured to exhibit good ballistic impact strength and durability. The inner surface36and the outer surface38define a thickness432therebetween along the central zone30of the lens12. The central zone30of the lens12can be symmetrically disposed with respect to the lateral segments28. In this regard, the central zone30can define a central point434which lies equidistant from either of the lateral segments28. The lateral segments28, as well as the posterior segments420, can also be symmetrically disposed in the lens12relative to the central zone30. For example, the central point434can be the point about which horizontal planes of the lens12exhibit symmetry. In this regard, the lens12can also be configured to be symmetrical about the central point434.

The thickness432of the lens12can taper from a thickest point at the central point434of the lens12approaching the lateral segments28of the lens12. Preferably, the thickness432of the lens12tapers at a substantially even rate from the central point434toward the opposing lateral segments28.

In an additional implementation, the reduction in the thickness432of the lens12can occur only in the central zone30, and the lateral segments28can be uniformly maintained at a lateral thickness436. However, it is also contemplated that the thickness432of the lens12can taper from the central point434of the lens12continuously through the lateral segment28and, if so configured, the posterior segment420.

In some embodiments, the average thickness of the lens12in the lateral segments28can be less than the average thickness of the lens12in the central zone30. Additionally, the thickness432of the lens12in at least one point in the central zone30can be greater than the thickness432of the lens12at any point within at least one of the lateral segments. For example, the thickness432of the lens12can be within the range of 0.050 to 0.070 inches. In such an embodiment, the thickness432of the lens12in the central zone can be between about 0.060 and 0.070 inches and taper to between about 0.050 and 0.060 inches in the lateral segments. Most preferably, the thickness432of the lens12falls within 0.061 to 0.068 inches. In other embodiments, the thickness432of the lens12in the central zone30is 0.068 inches and gradually tapers to 0.061 inches at the lateral segments28of the lens12.

Referring still toFIG. 11, the lens12can be configured such that the wearer's eye35is spaced from the inner surface36of the lens12at a vertex distance440. The vertex distance440can be defined as the straight-ahead distance to the lens12as measured from the eye35. The vertex distance440can preferably be between 1-2 inches.

Further, the eye35can also be positioned such that the eye35is spaced relative to the lens12at the vertex distance440and angularly spaced from the transition site34at an angle442, as shown inFIG. 11. In other words, the angle442can represent the angular spacing between a path from the eye35along the vertex distance440and a path from the eye35toward the transition site34. In a preferred embodiment, the angle442can be between 25° and 60°. As indicated above, the modification of these parameters and configurations can be performed in order to enhance the optical qualities of the lens12.

Referring still toFIG. 11, an additional embodiment of the lens12can be configured with the lateral segments28transitioning to the posterior segments420at a point where the lens12intersects with a meridian line444. As illustrated inFIG. 11, the meridian line444can be defined as the line along which the eyes35lie. The configuration and spacing of the vertex distance440, the angle442, and the meridian line444can be variously modified in order to accommodate different users and head types. Such modifications may be performed by one of skill in the art provided these teachings.

Referring again toFIG. 11, embodiments of the quadroradial lens12can also include the transition sites34. As mentioned briefly above, the transition sites34are disposed intermediate the opposing the lateral segments28and the central zone30. The transition sites34can be defined as that portion of the lens12intermediate an end point of central zone30and a beginning point of the lateral segment28. In accordance with a preferred embodiment, the transition sites34can be the point at which the central zone30, defined by the circular path431of the radius of curvature R2, is coincident with the lateral segments28, defined by the circular path408of the radii of curvature R1. However, the transition site34can also be a section of the lens12wherealong the curvature of the lens12varies.

In some embodiments, each transition site34can have a corresponding transition center of curvature for a given point along the inner surface38of the lens12. The center of curvature for a given point along a given transition site34may vary in location and may not be located at the same position for another given point along the inner surface36of the lens12at the given transition site34. In such an embodiment, the transition radius of curvature can vary continuously. It is contemplated that the transition radius of curvature can increase or decrease at a constant rate, which can provide preferred optical characteristics. However, the transition radius of curvature can also increase or decrease at a variable rate, such as by an exponential rate corresponding to a comparison of R1and R2and a length of the transition site34. Thus, the transition radius of curvature can vary as desired between the first and second radii of curvature R1and R2.

For example, according to one embodiment of the lens12, the transition site34may have a transition radius of curvature that can be equal to the second radius of curvature R2of the central zone30and subsequently decrease through the transition site34toward the lateral segment28until being equal to the first radius of curvature R1at the lateral segment28. Such a configuration can tend to mitigate any optical distortion due to irregular contouring of the lens12that may occur during a transition between the first and second radii of curvature R1and R2. In particular, such a configuration may be particularly beneficial if used along the inner surface36of the lens12in order to minimize or eliminate prismatic shift.

In accordance with yet another embodiment, the transition radius of curvature can be constant throughout the transition site34. It is also contemplated that the transition site34can be substantially linear according to a horizontal cross-sectional view of the transition sites. However, in such embodiments, the transition site34may not form a smooth, continuous contour, but may instead be marked by an elbow or ridge line between adjacent portions of the lens12. Such an attribute can be disadvantageous for certain applications, but is nevertheless a contemplated alternative feature in embodiments of the lens12. Preferably, the transition sites34can be formed to provide a smooth arcuate transition from the central zone30to either of the respective lateral segments28of the lens12.

Referring yet again toFIG. 5and additionally to FIGS.12-13A-C, the second arcuate cross-sectional configuration of the lens12in a vertical direction is shown. As mentioned above, the second arcuate cross-sectional configuration of the lens12has a third radius of curvature designated R3. Corresponding to this third radius of curvature R3is a third center of curvature450. In an embodiment of the quadroradial lens12, the third center of curvature450can be disposed in the same horizontal plane as the wearer's eyes in the as-worn orientation. Alternatively, the third center450can be elevated vertically to a point above the horizontal plane of the wearer's eye center, to rake the lens and conform more closely to certain head forms. In certain helmet shields and other applications, the third center450may be positioned below the eye level, to tilt the shield upwardly depending upon the desired performance.

According to another embodiment of the present invention illustrated inFIG. 12, the lens12can be tapered in the vertical direction. As similarly indicated above with respect to the posterior segments420, in order to reduce the prismatic shift in the upper and lower sections454,456, the lens12can taper from a central thickness458to a reduced distal thickness460in order to minimize the angle of incidence and the angle of refraction corresponding to a light ray passing through the upper section454or lower section456of the lens12.

FIGS. 13A-Cshow cross-sectional views taken alongFIG. 2according to yet another embodiment of the lens12. As illustrated therein, the third radius of curvature R3, i.e. vertical radius of curvature, can change moving along the lens12in the horizontal plane. For example, the third radius of curvature R3′ in the central zone30of the lens12(illustrated inFIG. 13A) can differ from the third radius of curvature R3″ at the transition site34of the lens12(illustrated inFIG. 13B), and both the R3′ and R3″ can differ from the third radius of curvature R3″ in the lateral segments28of the lens12(illustrated inFIG. 13C). In the embodiment shown inFIGS. 13A-C, the third radius of curvature increases moving along the lens12in a horizontal direction, such as from the central zone30to the transition site34to the lateral segment28.

For example, the third radius of curvature can increase (or decrease) beginning from the central zone30(perhaps from the central point434) and continue to increase through the transition site34moving toward the lateral segments28of the lens12. Further, although the third radius of curvature R3can increase to any distance, such as within a range of 7 to 40 inches, the third radius of curvature R3is preferably a maximum of 10 inches. For example, in an embodiment where the third radius of curvature R3is 5 inches throughout the central zone30, the third radius of curvature R3can increase toward 10 inches in the lateral segments28. In addition, the third radius of curvature R3can increase throughout the lens12or increase only through a portion of the lens12.

According to an implementation, any increase in the third radius of curvature R3can be done at any rate, and can be altered to achieve desired optical characteristics. For example, the third radius of curvature R3can increase in a mathematically linear fashion, as illustrated in the cross-sectional views ofFIGS. 13A-C. However, the third radius of curvature R3can become increasingly greater, as desired. These teachings can be utilized to variously modify the geometry of the lens12regarding the placement and rate of change of the third radius of curvature R3. Prismatic shift can further be minimized and aesthetic quality of the lens12can be improved through implementation of these teachings.

It is contemplated that the third radius of curvature R3can be within a broad range, such as about 6 to 14 inches. In addition, it is further contemplated in embodiments of the quadroradial lens12, that the third radius of curvature R3be much greater than either of the first or second radii of curvature R1or R2, as illustrated in the following mathematical relationship: R1<<R2≦R3. The third radius of curvature R3can also correspond to be equal to the first and second radii of curvature R1and R2, which can advantageously reduce prismatic shift for light ray entering through an upper section454or lower section456of the lens12.

In a preferred embodiment of the present invention, the lens thickness is tapered along each of a central horizontal meridian and a central vertical meridian. The taper may be accomplished by de-centering the radii of curvature of the front and rear surfaces, thereby creating an optical center line through the lens or in association with the lens. Preferably, the eyeglass is mounted such that the optical center line remains within about 12°, preferably within about 8°, and, more preferably, within about 5° of a wearer's reference line of sight. The wearer's reference line of sight may be a theoretical straight ahead normal line of sight. Details concerning the relationship of lens tapering, optical center lines and straight ahead lines of sight for the purpose of minimizing prismatic shift are disclosed in U.S. Pat. No. 4,515,448 to Tackles, U.S. Pat. No. 4,859,048 to Jannard, and U.S. Pat. No. 6,168,271 to Houston, et al., the disclosures of each of which is hereby incorporated by reference in its entirety herein.

As noted above with respect toFIG. 2, the vertical curvature and front shape of the lens12can advantageously be shaped. Other optical advantages, including as the reduction or elimination of prismatic shift, can similarly be obtained through manipulation of the vertical configuration of the lens12. In this regard, the third radius of curvature R3can be varied, higher or lower than the 4-11 inch range, in order to avail the wearer of such additional optical benefits.

Although this invention has been described in terms of certain preferred embodiments, other embodiments that are apparent to those of ordinary skill in the art are also within the scope of this invention. Accordingly, the scope of this invention is intended to be limited only by the appended claims.