Patent Description:
Every waking moment our eyes transmit images to our brain. The brain also receives feedback regarding the current orientation of our eyes. Our brain then takes the images from each eye, as well as the orientation information, and synthesizes a three-dimensional picture that we use for visually orienting throughout our daily lives. This synthesis is performed quickly and subconsciously at a core level of our brain.

When we need to move our eyes from a present target to a new one, such as to the next word during reading, or to the next road sign during driving, our brain calculates the amount our eyes need to rotate in order to view the new target. In asymptomatic patients, the peripheral vision correctly calculates how our eyes need to move to align our central vision, centered on the fovea, to the new target. In symptomatic patients, our peripheral vision miscalculates the amount of movement, or rotation, that is required to align our central vision with the new target. This miscalculation of the direction of the new target is caused by the peripheral vision not being seamlessly integrated, or coordinated, with the central, foveal vision. This inconsistency between peripheral and central vision typically leads to incorrect initial movements by our extraocular muscles that are responsible for rotating the eyes, and force the brain to take additional steps to realign central binocularity onto the fovea. The mechanism responsible for the coordination of the central vision, the peripheral vision, and the eye movements in our proprioceptive system.

The lack of efficient coordination between these systems, if it persists over time, can lead to excess signaling, or rogue signals, coordinated via the ophthalmic division of our trigeminal nerve. The resulting symptomology is from our proprioceptive system, and results in a type of eye-strain, or asthenopia.

Another source of asthenopia is convergence insufficiency. With normal vision, an individual is able to focus at objects located at different distances. Ideally, an individual is able to focus on distant objects, referred to as distance-vision, and on near objects, referred to as near-vision. The optical system of the eye uses numerous muscles to focus for both distance-vision and for near-vision. These muscles adjust various aspects of the eye when transitioning between distance-vision and near-vision. The muscle adjustments include making subtle changes to the shape of the crystalline lens to adjust the focus of the lens, rotating the eyeballs to rotate their optical axes, and changing the size of the pupils.

Presbyopia is a natural deterioration of near vision caused by loss of flexibility in the eye's crystalline lenses as one ages. Presbyopia can be partially compensated by wearing "reading" glasses for reading that correct near-vision refraction errors so that the eye does not have to strain as much to focus as strongly when gazing at near objects. Presbyopic persons need different optical corrections for near-vision and for distance-vision. However, using two glasses, and changing them with great frequency is distracting. To avoid continually exchanging eyeglasses, a combination of glasses and contact lenses are used by some patients. Others use bifocal glasses that offer different optical corrections for near-vision and for distance-vision. The transition between these two vision regions can be abrupt, or it can be gradual. The latter eyeglasses are called Progressive Addition Lenses (PALs). Abrupt change bifocals have a visible line separating the two vision regions, while PALs have no lines or edges visible between the regions with different dioptric powers. Recently, contact lenses also appeared in bifocal and other advanced forms.

In spite of all this progress with glasses and contact lenses, vision-related discomforts still persist. One of these discomforts is related to a shift of habits in the modern, digital lifestyle. A large and increasing fraction of professions require workers to spend a large and increasing fraction of their working time focusing at close-distance digital interfaces, including computer screens and mobile devices. The same is true for the private lives of many, spending hours playing video games, texting and checking updates on cell phones. All these professional and behavioral shifts rapidly increased the time people spend looking at digital screens, devices, displays, and monitors at a much closer distance than before. The increased time of the eye being trained at near-vision targets places excessive demands on the extraocular muscles involved in near-vision, often straining them beyond the comfort zone. This can lead to fatigue, discomfort, pain, and eventually to digitally induced migraines. And when the eyes' ability to remain trained for long times at near objects decreases because of muscle fatigue, or increasingly incorrect peripheral vision, a convergence insufficiency can develop, that leads to other forms of asthenopia. Up to now, there is no widely accepted consensus on the precise causation mechanism of these digital-device related visual discomforts, pains and migraines. Therefore, there is a need for new and inventive glasses and contact lenses that can provide relief for digital eye discomforts. <CIT> describes methods and lenses for alleviating asthenopia. <CIT> relates to a contact lens.

The invention provides a prismatic contact lens, comprising: a first prism zone in a central circular region, having a first prism and a first optical power; a progressive prism zone, adjacent to the first prism zone and in a ring around the central circular region, having a progressive prism that varies from the first prism to a second prism, wherein the second prism is different from the first prism; and at least one of an orientation mark, and a ballast in a lower region of the prismatic contact lens, for orienting a refraction direction of the prismatic contact lens in a horizontal direction. The prismatic contact lens can further comprise a second prism zone, adjacent to the progressive prism zone, having the second prism and a second optical power.

The invention further provides a prismatic contact lens, comprising: a first prism zone in a central circular region, having a first prism and a first optical power; a second prism zone, adjacent to the first prism zone, having a second prism and a second optical power, wherein the second prism is different from the first prism and wherein the second prism zone includes one of a ring and an annulus around the central circular region; a sharp transition between the first prism zone and the second prism zone; and at least one of an orientation mark, and a ballast in a lower region of the prismatic contact lens, for orienting a refraction direction of the prismatic contact lens in a horizontal direction.

The invention also provides a method of making a prismatic contact lens, the method comprising the steps of: providing an injection mold, with a negative shape of a prismatic contact lens with a first prism zone in a central circular region, having a first prism and a first optical power; and a progressive prism zone, adjacent to the first prism zone and in a ring around the central circular region, having a progressive prism that varies from the first prism to a second prism, wherein the second prism is different from the first prism; and at least one of an orientation mark, and a ballast in a lower region of the prismatic contact lens, for orienting a refraction direction of the prismatic contact lens in a horizontal direction; heating a soft contact lens material to a molten contact lens material; injecting the molten contact lens material into the injection mold to create a molded contact lens; cooling the molded contact lens by cooling the injection mold; and removing the cooled, molded contact lens from the injection mold. The providing step may further comprise providing the injection mold with the negative shape of the prismatic contact lens having a second prism zone, adjacent to the progressive prism zone, having the second prism and a second optical power.

Embodiments of the invention are capable of reducing various sources of eye-strain, or asthenopia, such as fixation disparity and convergence insufficiency. It has been suggested that an underlying common driver of these eye conditions is proprioceptive feedback, or proprioceptive overstimulation. Convergence insufficiency emerges when the gaze of the two eyes converges on a nearby object during binocular fixation, but the optical axes do not converge properly. Looking at nearby objects, such as computer screens, over a long time, especially through positive power lenses can strain the extraocular muscles excessively and thus can cause such a convergence insufficiency. Recently, it has been proposed that convergence insufficiency can be reduced by introducing a prism in the optical pathway.

Fixation disparity, and the underlying proprioceptive overstimulation impacts the vision when the viewer decides to look at a new target that is peripheral relative to the optimal, foveal region, or when the eye and the target move relative to each other, and the tracking of the same target requires following its image to a peripheral visual region. It is quite remarkable that even as little as a <NUM> degrees deviation from the optimal foveal spot on the retina leads to a decrease of the retinal resolution by about <NUM>%. For example, when one reads a word in a text, the <NUM> degrees difference translates to only one or two words ahead in the text. These numbers underline the importance of properly locating the new target, so that the head and the rotation of the eye optical axes to acquire the new target, such as the next word, can be performed with high precision and often. The person's brain acquires the new target in the peripheral vision region, and initiates adjustments of the neck, the head, the rotational state of the eye and the optical system of the eye to move the image of the new target to the central, foveal region. When the eye controlling systems and the peripheral vision do not work seamlessly together, these adjustments will not track the existing targets, or will not acquire the new targets correctly, resulting in fixation disparity, proprioceptive feedback, or proprioceptive overstimulation, and eye-strain. The amount of prism that corrects fixation disparity is sometimes called associated phoria. Notably, inserting a prism into the optical pathways can correct this misalignment, just like the above described convergence insufficiency.

As a background, it is recalled that there are four principal systems that control and operate the eye movements. These four systems have their own neurological pathways. Although they are distinct from each other, there is significant overlap between them. These systems are the following.

Also, even for stationary targets that are close to the viewer, such as computer monitors, when using positive optical power lenses for vision correction, the optical axes of the eye need to be turned toward each other even harder by the vergence movements, because the relative angle of the two surfaces of the positive power lens induces a light-refracting prism effect. This can cause or exacerbate convergence insufficiency, as it strains the extraocular muscles excessively.

In sum, these four vision control systems have to function seamlessly and in a coordinated manner with the peripheral and central vision of our eyes, and with our feedback systems. When they do not function well together, and are not in good synchrony with each other, the relative motion of the target and the viewer, the mechanism of acquiring new targets, and the convergence insufficiency creates eye-strain and asthenopia, causing substantial discomfort, as described next.

The eye-strain symptoms can include headaches. When the saccadic movements drive adjustments that move the image of a peripheral target to the central fovea by quick bursts to conjugate eye muscles, but the adjustments do not yield good foveal alignment, conflicting binocular signals from the eye control systems sometimes over-stimulate the trigeminal nerve, or send rouge proprioceptive signals through it. Either of these can cause substantial headaches, possibly evolving into migraines.

Another asthenopia symptom is neck pain. Once the peripheral retinal perception of the new target has been signaled to the cortical and subcortical visual areas, this signal is translated into an ocular motor system and is used to initiate the saccadic eye movement and corresponding head and neck movements. The eye and the head are moved by amounts deduced from the peripheral retinal signals. If the peripheral visual information was incorrect, or the communication and translation between peripheral visual perception and the eye-control systems is not synchronized well, the resulting tracking and vergence movements will yield fixation disparity, stimulating the proprioceptive feedback mechanism.

Visual disparity can lead to muscle pain because the extraocular muscles and neck muscle afferents show considerable convergence with the retinal afferents within the superior colliculus. A relevant study in cats found that nearly <NUM>% of the cells that originate with the colliculospinal tract receive convergent input from extraocular muscle, neck muscle afferents, as well as from the retina.

The above sections summarized the pathophysiology of various forms of asthenopia. These sections also suggest that improving the synchronity, cooperation, and overlap between the peripheral vision and the central vision by optical systems that refract the light between them can alleviate several of the drivers of asthenopia.

A natural optical system that refracts the light can be a convergence-reducing lens and a prismatic eyeglass. Convergence-reducing glasses have been described in the commonly owned <CIT>. In the embodiments below, these convergence-reducing ideas are adapted and transformed, with additional substantial insights and key modifications, to the other large class of vision correction system, contact lenses.

To establish a context and platform for these later-described prismatic contact lenses, we first summarize key features of the convergence-reducing and prismatic eyeglasses.

<FIG>illustrate how the refraction angle, induced by a positive power lens, increases the convergence of the gaze of glass-wearers.

<FIG> illustrates that when a person is gazing at a remote object, then the gazing-directions of the left and right eyes are essentially parallel, and thus there is no convergence of the gazing-directions. Therefore, the extra-ocular muscles are not strained at all. In such cases, the two z-axes <NUM>, pointing to the remote object through the center of the eye <NUM>, coincide with the two eye-optical axes <NUM>. The light from the remote object is entering the eye <NUM> through the eye-lens <NUM> on its way to hitting the retina. These parallel z-axes <NUM> will be used next as references to characterize the gaze-convergence angles of gazes directed at near objects.

<FIG> illustrates that when a person is gazing at a near object <NUM>, the gazes of the left and right eyes are tilted, or rotated, towards each other, each gaze making a non-zero gaze-convergence angle β with the z-axes <NUM>. Since the gaze-convergence angle β characterizes the convergence of the gazes of the two eyes towards each other, in what follows the gaze-convergence angle β will refer specifically to the x-component of the overall gaze-rotation angle of the eye. This makes the gaze-convergence angle β analogous to an x-component to a refraction angle αX of a lens.

As mentioned before, the eyeballs are rotated by extraocular muscles attached externally to the eye. In particular, the lateral, x-directional, rotations are controlled by the medial rectus and the lateral rectus muscles, and the vertical rotations are controlled by the superior rectus and the inferior rectus, and inferior oblique muscles. When the medial rectus muscles of the left-eye and the right-eye contract, the gazes of these eyes converge towards each other. A person, training his/her eye on a near object, such as an electronic screen, a digital screen, a screen of a mobile electronic device, work-related papers, or even a book, for extended periods requires the continuous contraction of the medial rectus muscles, thus exerting substantial strain on them. This "digital eye-strain" can lead to fatigue, leading to headache, eventually culminating in migraines, caused by the demands of the modern, digital lifestyle.

The digital lifestyle can induce other forms of asthenopia, or eye-strain, and other types of convergence-disorders, including proprioceptive overstimulation and/or fixation disparity. Proprioceptive overstimulation, and fixation disparity are related to the imbalance between where the eyes are consciously focused and the nonvisual perception of where the object is located in space. This disparity often varies with space. The brain of a patient with excited proprioceptive overstimulation and/or fixation disparity, can compensate this disparity to a degree in order to maintain a clear image of the target. However, when the disparity becomes too big to be compensated, the trigeminal nerve can get overstimulated, resulting in patients experiencing headaches, eye fatigue, pain around the eyes, blurred vision, neck pain, dry eyes, and other general symptoms of asthenopia.

A class of symptoms especially worthy of mentioning is Computer Vision Syndrome (CVS), which is estimated to affect more than <NUM> million Americans. Computer Vision Syndrome is the physical eye discomfort felt after gazing for a prolonged amount of time at a nearby digital device, causing an array of asthenopia symptoms, and negatively effecting productivity.

Another large class of symptoms is known by the name of Chronic Daily Headaches (CDH). CDH symptoms are estimated to affect more than <NUM> million Americans. These patients suffer from an over-stimulation of the trigeminal nerve that manifests itself in the form of chronic daily headaches. Various factors and triggers are believed to contribute to the debilitating issue of chronic daily headache. As a result, patients suffering from CDH are limited to treatment options that merely seek to dull the symptoms. A large subset of chronic daily headache patients (believed to be as large as <NUM>% of the population) shows objective signs of a misalignment between how the central visual system, peripheral visual system and neurological system interact.

<FIG> illustrates that positive power spectacles <NUM> can exacerbate the symptoms of eye-strain, asthenopia, Computer Vision Syndrome, fixation disparity, and proprioceptive overstimulation caused by digital devices, because looking at digital devices, or objects <NUM> that are nearby, forces the wearer to gaze through the lower-inferior nasal quadrant, the "near-vision" region, of their glasses. In this off-center near-vision region positive power monovision lenses <NUM> of the regular glasses <NUM> refract the light by a refraction angle α. A ray that propagates from the near object <NUM> to the retina with the refraction angle α forces the wearer to rotate her eye to a greater gaze-convergence angle β than a ray's direction that propagates from the same object to the same retina but without the refraction α by the lens <NUM>. Therefore, positive power lenses <NUM> of regular glasses <NUM> force an increased gaze-convergence angle β and thus cause an increased strain on the medial rectus muscles when the wearer is looking at near objects. The sustained and excessive contraction of the medial rectus muscles increases the tendencies for a digital migraine that affect and possibly debilitate the wearer.

<FIG> illustrates embodiments of a convergence-reducing lens <NUM>' in a convergence-reducing spectacle <NUM>' that can reduce, and often eliminate the symptoms of eye-strain, asthenopia, Computer Vision Syndrome, fixation disparity and proprioceptive overstimulation. The convergence-reducing, or prismatic spectacles <NUM>' with convergence-reducing lenses <NUM>' have a refraction-angle α that is modified by a base-in prism that reduces the gaze-convergence angle β when their wearers look at a nearby object <NUM>, such as at a digital device. This reduction is shown by the nasally pointing, solid curved arrows. Reduced gaze-convergence angles β require a lesser rotation of the eyes in the nasal direction, and therefore relieves the continuous contraction and strain of the medial rectus muscles of the eyes. This reduced muscle strain reduces and often eliminates the symptoms of asthenopia.

There are several ways to characterize and describe embodiments of convergence reducing and prismatic lenses. Some of these are described in <CIT>. Some embodiments include an eye-strain-reducing lens, wherein a central normal of the eye-strain-reducing lens defines a z-axis, and a central region of the eye-strain-reducing lens defines a tangential, centered x-y plane, together defining an x-y-z coordinate system of the eye-strain-reducing lens, the eye-strain-reducing lens comprising a distance-vision region, having a distance-vision optical power, configured to refract a light ray directed by a source at a distance-vision region point at a distance-vision x-distance from a center of the coordinate system, to propagate to an eye-center-representative location; and a near-vision region, having a near-vision optical power, configured to refract a light ray, directed by the source at a near-vision region point at a near-vision x-distance from the center of the coordinate system, to propagate to the same eye-center representative location; wherein the near-vision x-distance is smaller than the distance-vision x-distance.

Some other embodiments include a prismatic lens of a low-convergence spectacle, wherein a central normal of the convergence-reducing lens defines a z-axis, and a center of the convergence-reducing lens defines a tangential, centered x-y plane, together defining an x-y-z coordinate system of the convergence-reducing lens, the convergence-reducing lens comprising a distance-vision region, having a distance-vision optical power, configured to refract a light ray, directed parallel to the z-axis at a distance-vision region point at an x-distance from a y-z plane of the coordinate system, to intersect the y-z-plane at a distance-vision intersection z-distance; and a near-vision region, having a near-vision optical power, configured to refract a light ray, directed parallel to the z-axis at a near-vision region point at the x-distance of the distance-vision region point, to intersect the y-z-plane at a near-vision intersection z-distance that is greater than the distance-vision intersection z-distance.

The above highlighted ways to characterize the introduction of, and to verify the presence of a prism in optical lenses and spectacles, are described further in substantial detail in the commonly owned <CIT>.

The utility and efficacy of convergence-reducing lenses and spectacles can serve as a starting point from where additional insights and key modifications can assist the adaptation of prismatic effects to the other large class of vision correction devices: contact lenses. This idea and insight is developed and described in the embodiments below. <FIG>set the baseline of regular, non-prismatic contact lenses, <FIG>illustrate a single prism contact lens. <FIG>illustrate a two-prism contact lens, and a challenging aspect of its optical performance. Motivated by the challenge of <FIG> and <FIG>, <FIG> illustrate a progressive prismatic contact lens with an improved optical performance.

<FIG> illustrates a regular, non-prismatic contact lens <NUM>, positioned on a proximal, corneal surface of an eye <NUM>. A sclera <NUM>, an iris <NUM> and a pupil <NUM> of the eye <NUM> are also indicated.

<FIG> illustrates the imaging by the non-prismatic contact lens <NUM>, looking straight along the optical axis <NUM> of the eye-lens system. Here only the pupil <NUM> is shown, the rest of the peripheral elements of the eye <NUM> are omitted for clarity. When the non-prismatic contact lens <NUM> images a centrally positioned line-like object <NUM>, directed upward from the optical axis <NUM>, the image <NUM> on the retina will be a line, directed downward from the optical axis <NUM>. The upward and the downward pointing lines are aligned with each other. The line-like object <NUM> can be an actual thin rod or wire, or it can be a laser beam stretched into a sheet of light, generated by sending a laser beam through a cylindrical lens. For reference, an x-y coordinate system is also shown. Using this system as a reference, "upward" translates to the line-like object <NUM> being directed along the positive y-axis, "downward" translates to the image <NUM> being directed along the negative y-axis.

<FIG> illustrates a single-prism contact lens 18sp imaging the same line-like upward-pointing object <NUM> into a downward-pointing image <NUM>, just like the non-prismatic contact lens <NUM>. However, the prismatic effect of the single prism contact lens 18sp shifts, or displaces, the image <NUM> sideways along the x-axis by a shift Δ. An often-used nomenclature is to call the prism "base-in", if its base, or widest portion, is closest to the nose, and its thin, apical portion is farthest from the nose. This nomenclature is particularly clear and selfevident for simple, triangular prisms.

<FIG> illustrates this prismatic effect in some detail. The prismatic effect can be generated by two optical refractive surfaces, such as the proximal and distal surfaces of the single-prism contact lens 18sp, or by the flat surfaces of a triangular glass prism <NUM>, that are tilted relative to each other by a prism, or tilt, angle α. The line along which the tilted surfaces, or their extensions, meet is called an apex 19a of the prism. In the simple case of the triangular glass prism <NUM>, the edge along which the two sides of the triangle meet is the apex 19a. Visibly, if the apex 19a is pointed upward, vertically aligned with the y-axis, then the prismatic shift Δ is in the x direction. Orienting the prismatic apex 19a along the upward, vertical, or y-direction is a typical utilization of a prismatic lens, let it be a spectacle lens or a contact lens, as this prism orientation shifts the image <NUM> in the horizontal, or x direction. A horizontal, or x shift of the image <NUM> is well-suited to alleviate the convergence insufficiency, computer vision syndrome, and other forms of eye-strain, as discussed above.

The degree of prismatic shift is often characterized in term of prismatic diopters. A lens is said to have a prismatic power, or prismatic diopter of 1D, if it deflects a paraxial light beam by the prismatic shift Δ=<NUM> on a screen positioned <NUM> behind the lens.

To summarize, a prism has a prismatic power and a refraction direction. The prismatic power describes how much the prism refracts an incoming light beam. The refraction direction captures that in which direction the prism refracts the incoming light beam. The prism refraction direction is typically orthogonal to the prism apex 19a. It is also noted that in most prismatic lenses the prism angle α is small, and therefore the two refractive surfaces do not meet in the apex 19a, only their extensions meet.

<FIG>illustrate a challenge that emerges during the design of more complex prismatic lenses. With advancing age, the eye's ability to adapt is diminishing. In the context of diminished accommodation of the optical powers, this phenomenon is called presbyopia. A widely-used prescription for presbyopia is an eye-glass with bifocal lenses that have different optical powers in their upper, distance vision region, and in their lower, near-vision region.

In an analogous manner, in some lenses it can be advantageous to have different prismatic powers in different regions. For example, the lower, near-vision region of a bifocal lens may need a prism implemented to correct convergence insufficiency, or to reduce eyestrain from excessive extraocular muscle strain. At the same time, since the upper, distance-vision region is typically not used to gaze at near objects, it may not need the implementation of a prism.

<FIG> illustrates that in some designs, such as in a prismatic contact lens <NUM>, a central first prism zone <NUM> of the prismatic contact lens <NUM>, through which a patient is looking at a present target, may need little or no prism. At the same time, a peripheral, or annular, second prism zone <NUM> of the prismatic contact lens <NUM>, through which the peripheral vision is already training on the next target, such as the next word during reading, may need a prism implemented in order to alleviate symptoms of asthenopia. In a more general sense, the first prism zone <NUM> can have a first prism, and the second prism zone <NUM> can have a second prism. According to the previous general discussion of prisms, the first prism has a first prismatic power and a first prism refraction direction, and the second prism has a second prismatic power and a second prism refraction direction.

<FIG> illustrates, again concentrating on the pupil <NUM> of the eye <NUM>, that the first prism zone <NUM> of the prismatic contact lens <NUM> may shift the image <NUM>-<NUM> in the horizontal, x direction by a Δ<NUM> amount, while the peripheral second prism zone <NUM> may shift the image <NUM>-<NUM> by a larger Δ<NUM> amount in the same x direction, where Δ<NUM> is proportional to a first prismatic power, or first prism diopter of the first prism zone <NUM>, and Δ<NUM> is proportional to a second prismatic power, or second prismatic diopter of the second prism zone <NUM>.

Notably, in bifocal lenses, different optical powers are generated by different lens curvatures, which generate a visible, high-scatter sharp line between the distance-vision and the near-vision regions. To avoid generating such an undesirable sharp line, in a new generation of lenses the transition has been made gradual and smooth. By varying the lens curvature gradually, and not in a step-like manner along the y-direction, the optical power in these "progressive" lenses progressively transitions from the distance-vision optical power to the near-vision optical power.

<FIG> illustrates key elements of a solution to avoid generating a visible sharp transition <NUM> between zones with different prismatic power. Embodiments can include the prismatic contact lens <NUM> that comprises the first prism zone <NUM>, having a first prism and a first optical power; and a progressive prism zone <NUM>, adjacent to the first prism zone <NUM>, having a progressive prism that varies from the first prism to a second prism. As discussed above, this can mean that a prismatic power of the progressive prism varies from a first prismatic power to a second prismatic power, and a prism refraction direction of the progressive prism varies from a first prism refraction direction to a second prism refraction direction.

<FIG> illustrates that such a progressive prismatic contact lens <NUM> images with its central first prism zone <NUM> an upward-pointing linear target <NUM> into a downward-pointing line-like image <NUM>-<NUM>, shifted horizontally along the x-axis by Δ<NUM>, proportional to the first prismatic power. Further, the prismatic contact lens <NUM> can create an additional downward-pointing bent image <NUM>-p by the progressive prism zone <NUM>, whose endpoint is shifted by Δ<NUM>, proportional to the second prismatic power. This figure captures a marked aspect of the optics of the progressive prismatic contact lens <NUM>.

<FIG> illustrates that such progressive prismatic contact lenses <NUM> can have the additional second prism zone <NUM>, adjacent to the progressive prism zone <NUM>, having the second prism and a second optical power. The second prism zone <NUM> can be a ring, or an annuus, around the progressive prism zone <NUM>. Such a prismatic contact lens <NUM> can be formed without creating a visible, undesirable sharp transition line <NUM> between its prismatic zones <NUM> and <NUM>, as the progressive prism of the progressive prism zone <NUM> can smoothly interpolate between the first prism of the first prism zone <NUM> and the second prism of the second prism zone <NUM>.

In a noteworthy embodiment, the first prism zone <NUM> in a central circular region, combined only with the progressive prism zone <NUM> as a ring, or annular region, around the central circular region, can already deliver useful medical benefits without having the separate, second prismatic zone <NUM>, as shown in <FIG>.

In some embodiments, the prismatic power of the first prism can be in the <NUM>-<NUM> (prism) D range, while the prismatic power of the second prism can be in the <NUM>-<NUM> (prism) D range. In some other embodiments, the prismatic power of the first prism can be in the <NUM>-<NUM> (prism) D range, while the prismatic power of the second prism can be in the <NUM>-<NUM> (prism) D range.

In some embodiments, the first optical power can be consistent with distance vision, and the second optical power can be consistent with near vision. These embodiments are bi-focal and bi-prismatic at the same time.

In some embodiments, a difference between the first optical power and the second optical power can be less than <NUM> D. In some cases, the first and second optical powers can be essentially the same. Such lenses can be characterized as monofocal and bi-prismatic, or monofocal with a progressive prism. Since the sources of presbyopia and eyestrain can be quite distinct, a substantial fraction of patients may develop eye-strain before developing presbyopia, and thus may need such monofocal and bi-prismatic/progressive prismatic lenses.

As discussed, the different types of asthenopia are associated with different vision modalities. Convergence insufficiency can be associated with refractive challenges or shortcomings specifically in the nasal-temporal direction. These can be alleviated efficiently with a "horizontal prism", i.e. with a prism that has an apex along the y-axis, and thus has a refraction direction along the x-axis. In progressive prismatic implementations, this horizontal prism can vary vertically, along the y-axis. If the additional feature of enhanced nasal prism is desired only in a lower nasal quadrant, instead of the entire lower half of the prismatic contact lens <NUM>, then, however, the prism can vary progressively along a tilted meridian, along a non-vertical line that makes an angle with the y-axis, such as a line that is tilted towards the lower nasal quadrant.

Proprioceptive overstimulation is associated with the lack of synchronism between the central vision and the peripheral vision. This condition may be alleviated by a prism that varies progressively in a radial direction, or with an increasing radius.

Articulated in general terms, in embodiments of the prismatic contact lens <NUM>, the progressive prism can be progressive in the context of its prismatic power, or its prism refraction direction, or both. In some embodiments, the prismatic power may vary progressively, while the refraction direction remains steady through the progressive prism zone <NUM>. In other embodiments, the prismatic power may remain unchanged, but its refraction direction may vary progressively through the progressive prism zone <NUM>. Finally, in some embodiments, both the prismatic power and the refraction direction may vary progressively. The progressive variations of the prismatic power and the refraction direction can be independent from each other in some embodiments. In others, they can follow a predetermined mathematical relation.

In some embodiments of the prismatic contact lens <NUM>, the prismatic power of the progressive prism can vary progressively in a radial direction, with an increasing radius, along an x-axis, along a y-axis, or along a tilted meridian, making an angle with the x-axis and the y-axis.

In some embodiments of the prismatic contact lens <NUM>, the prism refraction direction of the progressive prism can vary progressively in a radial direction, with an increasing radius, along an x-axis, along a y-axis, or along a tilted meridian, making an angle with the x-axis and the y-axis.

In a class of embodiments, the overall prism can be designed as a combination, or superposition, of a y-directionally progressive and a radially progressive prism, or some other combination of the previously described prismatic effects. Such combination prismatic contacts lenses can address and alleviate more than one sources of asthenopia.

In some embodiments, at least one of the prism refraction direction of the first prism, the prism refraction direction of the progressive prism, and the prism refraction direction of the second prism may be tilted relative to the horizontal, x-axis.

<FIG>illustrate another way to characterize and recognize the presence of a prismatic effect in a contact lens. The shown embodiments can be characterized via a description of the curvatures of the lens surfaces and the off-center locations of their corresponding centers of curvatures.

In some detail, embodiments of the contact lens in general can have a central normal of the contact lens that defines a z-axis <NUM>, or optical axis <NUM>. The central zone of the contact lens can further define a tangential, centered x-y plane. The z-axis <NUM> and the x-y plane together define an x-y-z coordinate system.

<FIG> illustrates, as a baseline comparison, that a non-prismatic contact lens <NUM> can be a meniscus lens with a non-negative optical power, having a front surface 40f with a radius of curvature Rf and a center of front surface curvature CCf, and a rear surface 40r with a radius of curvature Rr and a center of rear surface curvature CCr. In this baseline, non-prismatic contact lens <NUM>, the centers of curvature CCf and CCr are on the optical axis <NUM>/z-axis <NUM> of the contact lens <NUM>.

<FIG> illustrates that a prismatic contact lens <NUM> can have a front surface 140f with a radius of curvature Rf and a center of front surface curvature CCf, and a rear surface 140r with a radius of curvature Rr and a center of rear surface curvature CCr that are off the z-axis <NUM> because the front surface 140f makes a front prism angle αf with the front surface 40f of the corresponding non-prismatic contact lens <NUM>; and the rear surface 140r makes a rear prism angle αr with the rear surface 40r of the corresponding non-prismatic contact lens <NUM>.

The location of the centers of curvature CC relative to the z-axis is a well-defined way to characterize the prism in a lens. Since the prism of the prismatic contact lens <NUM> is varying from zone to zone, the curvatures of the first, progressive, and second prism zones are determined separately. Embodiments of the prismatic contact lens <NUM> can be described by an x-coordinate of the center of front surface curvature x(CCfp) of the progressive prism zone <NUM> being nasal relative to an x-coordinate of the center of front surface curvature x(CCf1) of the first prism zone <NUM>; or an x-coordinate of the center of rear surface curvature x(CCrp) of the progressive prism zone <NUM> being temporal relative to an x-coordinate of the center of rear surface curvature x(CCrp) of the first prism zone <NUM>, or both. Here the indices "<NUM>" and "p" were added to indicate that the centers of curvatures corresponded to the first prism zone <NUM>, or to the progressive prism zone <NUM>.

The above attributes can be expressed via inequalities by defining the directionality of the x-axis to point away from the nose, such that points farther from the nose (in <FIG> to the right) have greater x coordinates than points closer to the nose (in <FIG> to the left). With this directionality, the above characterizations can be written that at least one, possibly both inequalities hold for embodiments of the prismatic contact lens <NUM>: <MAT> <MAT>.

Here, the centers of front and rear surface curvatures CCfp and CCrp of the progressive prism zone <NUM> may not be single points. Instead, they may progress and cover an interval as the progressive prism zone <NUM> is traversed. The inequalities (<NUM>)-(<NUM>) hold for the points along this interval. Analogous inequalities relate the centers of curvature CCf2 and CCr2 of the second prism zone <NUM> to those of the first prism zone <NUM>.

In some typical embodiments, the first prism may be zero, as the central, distance vision first prism zone <NUM> may not need a refractive prism. In such embodiments, the CCf1 front and CCr1 rear centers of curvature of the front and rear surfaces 140f and 140r of the first prism zone <NUM> can be located on the z-axis <NUM>, and therefore, their x coordinates can be zero. In formal terms, x(CCf1)=x(CCr1)=<NUM>. In such embodiments of the prismatic contact lens <NUM>, x(CCfp), the x-coordinate of the center of the front surface curvature CCfp of the progressive prism zone <NUM> being nasal relative to the z-axis <NUM> of the coordinate system can be written as: <MAT>.

x(CCrp), the x-coordinate of the center of rear surface curvature of the progressive prism zone <NUM> being temporal relative to the z-axis <NUM> of the coordinate system can be written as: <MAT>.

In general, embodiments of the prismatic contact lens <NUM> are "off-axis center of curvature" lenses. In some context, the prism created by the centers of curvatures being offset according to the above inequalities is referred to as a "base-in prism", as the created prism's base is directed toward the inner center, the nose of the wearer.

The above-described coordinates and x-distances of the centers of curvature x(CCf1), x(CCr1), x(CCfp), and x(CCrp) can be determined with specialized tools and devices, such as spherometers and lens profilometers.

The optical powers of the different prism zones <NUM>, <NUM>, and <NUM> of the prismatic contact lens <NUM> can be engineered using the lensmaker's equation f(R<NUM>, R<NUM>)=(n-<NUM>) (<NUM>/R<NUM>-<NUM>/R<NUM>) for thin lenses, and its appropriate extensions for thicker lenses. These relations assume that the centers of curvatures are on the main optical axis of the lens. As discussed above, a small prismatic refraction can be introduced into embodiments of the prismatic contact lens <NUM> by tilting the lens surfaces and thus moving the centers of curvature off the optical axis without impacting the optical performance of the contact lens negatively. In other words, in leading approximation, the optical powers and the prismatic powers of the various zones of the prismatic contact lens <NUM> can be tuned independently from each other.

<FIG>illustrate another class of the prismatic contact lens <NUM>, which is not claimed herein, where the first prism zone <NUM> can include an upper region of the prismatic contact lens <NUM>; and the progressive prism zone <NUM> can include a lower region of the prismatic contact lens <NUM>. Such aspects bear closer resemblance to the lenses of the "top-bottom", or "D-segment" designs of bifocal progressive glasses.

<FIG> illustrates that in some cases (not claimed herein) the prismatic contact lens <NUM> can include a second prism zone <NUM>, where the first prism zone <NUM> includes an upper region of the prismatic contact lens <NUM>, the progressive prism zone <NUM> includes a middle region of the prismatic contact lens <NUM>, and the second prism zone <NUM> includes a lower region of the prismatic contact lens <NUM>. As discussed above, such designs may be useful for prismatic contact lenses <NUM> where the first prism zone <NUM> has an optical power consistent with distance vision, while the second prism zone <NUM> has an optical power consistent with near vision.

<FIG> illustrates an aspect which is not claimed herein, without a progressive prism zone <NUM>: it only contains a first prism zone <NUM> and a second prism zone <NUM>, separated by a sharp transition <NUM>.

<FIG> illustrates another class of embodiments of the prismatic contact lens <NUM>. These embodiments are called multi-zone prismatic contact lenses <NUM> that can include first prism zones <NUM>-<NUM>, <NUM>-<NUM>,. , collectively referenced as <NUM>-i (that include the first prism zone <NUM>), having a first prism and a first optical power. These multi-zone lenses <NUM> can also include progressive prism zones <NUM>-<NUM>, <NUM>-<NUM>,. , collectively referenced as <NUM>-i (that include the progressive prism zone <NUM>), having a progressive prism that varies from the first prism to a second prism. Finally, they can include second prism zones <NUM>-<NUM>, <NUM>-<NUM>, having the second prism and a second optical power. Multi-zone contact lenses in general can reduce astigmatism and other aberrations relative to contact lenses with fewer zones.

<FIG> illustrates the particular embodiment of the multi-zone prismatic contact lens <NUM>, wherein the first prism zones <NUM>-i include a central region and first prism rings; the progressive prism zones <NUM>-i include progressive prism rings; and the second prism zones <NUM>-i include second prism rings.

<FIG>, in analogy to <FIG> and <FIG>, illustrates the related embodiment where the multi-zone prismatic contact lens <NUM> does not have the progressive prism zones <NUM>-i, and thus the first prism zones <NUM>-i are separated from the second prism zones <NUM>-i by sharp transitions <NUM>-i. General features of these "sharp-transition embodiments" will be discussed below in more detail.

<FIG> illustrates yet another aspect of multi-zone prismatic contact lenses <NUM>, which is not claimed herein, wherein the first prism zones <NUM>-i can include radial first prism zone segments, the progressive prism zones <NUM>-i can include radial progressive prism zone segments; and the second prism zones <NUM>-i can include radial second prism zone segments. As before, such multi-zone embodiments may reduce astigmatism and aberrations relative to embodiments that have only single zones <NUM>, <NUM>, and <NUM>.

<FIG> illustrates an analogous "sharp transition" aspect which is not claimed herein, where the radial first zone segments <NUM>-i are separated from the radial second zone segments <NUM>-i only by sharp transitions <NUM>-i.

<FIG> illustrates that, in yet another class of the multi-zone prismatic contact lenses <NUM> which is not claimed herein, the first prism zones <NUM>-i can include horizontal first prism zone strips; the progressive prism zones <NUM>-i can include horizontal progressive prism zone strips; and the second prism zones <NUM>-i can include horizontal second prism zone strips.

<FIG> illustrates that in an analogous "sharp transition" aspect which is not claimed herein, the first prism zone strips <NUM>-i may be adjacent to the second prism zone strips <NUM>-i without intervening progressive prism zone strips <NUM>-i, only separated by sharp transitions <NUM>-i.

<FIG>illustrate further aspects of the prismatic contact lens <NUM> which are not claimed herein, which are less symmetric than the previously described designs. <FIG> illustrates an aspect, where the progressive prism zone <NUM> is in the lower nasal quadrant, in an off-center arrangement. <FIG> illustrates a design where the progressive prism zone <NUM> transitions into a second prism zone <NUM>, even further off center in the lower nasal quadrant. As mentioned before, these designs have connections to the bifocal lenses that offer a near-vision optical power in the lower nasal quadrant.

To extend the scope of the overview of possible embodiments, we return to the embodiments that have a sharp transition <NUM>. As mentioned, these embodiments may have a less desirable visible transition line, but their visual space does not include a progressive zone where the prism and optical power may be varying - a feature, which may be preferred by a fraction of the patients. The progressive prism contact lenses <NUM> of <FIG>, and the sharp transition contact lenses <NUM> of <FIG> may each be adopted by a segment of the overall patient population, as they offer distinct medical benefits.

The sharp-transition prismatic contact lenses <NUM> include the embodiment of <FIG> that shows a prismatic contact lens <NUM>, with a first prism zone <NUM>, having a first prism and a first optical power; a second prism zone <NUM>, adjacent to the first prism zone <NUM>, having a second prism and a second optical power; and a sharp transition <NUM> between the first prism zone <NUM> and the second prism zone <NUM>. In these prismatic contact lenses <NUM>, the first prism zone <NUM> can be a central circular region; and the second prism zone <NUM> can include an annulus, or ring, around the central circular region, as shown in <FIG>.

The simplest prismatic contact lens may address eyestrain symptoms by including a prism in its central zone, and no prism in its peripheral zone. Next, several embodiments will be described that go beyond this simplest contact lens design, providing distinct additional medical benefits.

To summarize, the above (<NUM>)-(<NUM>) embodiments of the prismatic contact lens <NUM> offer substantial additional medical benefits over the simplest prism contact lens design.

<FIG> illustrates an aspect of the prismatic contact lens <NUM> which is not claimed herein, where the first prism zone <NUM> can include an upper region of the prismatic contact lens <NUM>, and the second prism zone <NUM> can include a lower region of the prismatic contact lens <NUM>.

Finally, embodiments of the prismatic contact lens <NUM> can include a multi-zone prismatic contact lens <NUM> in general that includes first prism zones <NUM>-i, including the first prism zone, having the first prism and the first optical power; second prism zones <NUM>-i, having the second prism and the second optical power; and sharp transitions <NUM>-i, between the first prism zones <NUM>-i and the second prism zones <NUM>-i.

<FIG> illustrates that particular examples include the prismatic contact lens <NUM>, where the first prism zones <NUM>-i include a central region and first prism rings; and the second prism zones <NUM>-i include second prism rings, separated by sharp transitions <NUM>-i.

<FIG> illustrates aspects of the prismatic contact lens <NUM> which are not claimed herein, in which the first prism zones <NUM>-i can be radial first prism zone segments; and the second prism zones <NUM>-i can include radial second prism zone segments, the two separated by sharp transitions <NUM>-i.

<FIG> illustrates aspects of the prismatic contact lens <NUM> which are not claimed herein, in which the first prism zones <NUM>-i can include horizontal first prism zone strips; and the second prism zones <NUM>-i can include horizontal second prism zone strips, the two separated by sharp transitions <NUM>-i.

Finally, <FIG>illustrate prismatic contact lenses <NUM> which are not claimed herein where the second prismatic zone <NUM> is asymmetric, extending in the direction of the lower nasal quadrant, and it is connected to the first prismatic zone <NUM> with a sharp transition <NUM>, without a progressive prism zone <NUM>.

As summarized above, these two-zone, sharp transition prismatic contact lenses <NUM> can have the medical benefit of larger fraction of their area having well-defined radius of curvature, a feature that a fraction of the patients may find sufficiently valuable to make up for the visible transition line.

<FIG> is a comprehensive table to illustrate the earlier stated principle that the optical powers and the prismatic powers of the prismatic contact lens <NUM> can be engineered independently, within some limits. The Table of <FIG> shows in its column headers the previously described prism designs: zero prism, single-prism zone (e.g. <FIG>), concentric two-prism zones with sharp prism transition between (e.g. <FIG>), concentric two-prism zones with progressive prism transition between them (e.g. <FIG>), top-and-bottom prism zones with sharp prism transition in between (e.g. <FIG>), top-and-bottom prism zones with progressive prism transition in between (e.g. <FIG>), and multizone prisms (<FIG><FIG> and 11A-B). Additional prism embodiments are also part of the comprehensive list, and were not shown expressly only because of space limitations. They include the designs, where the first prism zone <NUM> is combined only with the progressive prism zone <NUM>, as in <FIG>and <FIG>The comprehensive list also includes the asymmetric designs, such as the ones in <FIG>And finally, yet another class of embodiments is the prism lenses with a prism refraction direction not being directed horizontally, but at some angle with the x-axis.

Further, the row headers of the Table of <FIG> show the various designs for the optical power, including: zero power, concentric two-zone with sharp power transition, concentric two-zone with progressive power transition, top-bottom two-zone with sharp power transition, top-bottom two-zone with progressive power transition, and a variety of possible multi-zone optical power lenses.

In describing the components of the lenses, we articulated the transitions in more specificity, distinguishing prism transitions and optical power transitions. This was necessary because the power and prism can be largely designed independently. Therefore, a prismatic contact lens <NUM> can be designed with a progressive prism transition, yet with a sharp optical power transition, for example.

<FIG> illustrates that a large number of embodiments were contemplated based on the underlying principle of the prismatic contact lens <NUM>, combined with various optical power lenses, wherein these two design drivers and the transitions between them can be varied largely independently.

<FIG> illustrates further aspects of the prismatic contact lenses <NUM>. Since directionality and orientation are important to orient the prism and its apex correctly, some embodiments can utilize stabilizing, or orienting, structures. For example, the claimed prismatic contact lenses <NUM> have at least one of a ballast <NUM> in a lower region of the prismatic contact lens <NUM>, and an orientation mark <NUM>. The extra weight of the ballast <NUM> will tend to rotate the prismatic contact lens <NUM> so that the ballast <NUM> will be positioned at the bottom of the prismatic contact lens <NUM>. This will orient the refraction direction of the prismatic contact lens <NUM> in the intended direction, typically along the x-axis, or close to it. Further, the orientation mark <NUM> can be used by the wearer to insert the prismatic contact lens <NUM> into the eye <NUM> with the correct, or prescribed, orientation.

Here a distinction is made. There has been a description of a contact lens with a "prism" before. However, the function of the described "prism" was not optical, or refractive. It was to serve as a ballast for the contact lens, analogous to the ballast <NUM> of <FIG>. The different functionalities manifest themselves in different structures. The ballast "prism" has a horizontal prism apex, and its thicker base is oriented downward, in the negative y direction to serve as a ballast. While its optical performance is not the intended function, but rather, an unintended consequence, this ballast-prism refracts light in the vertical, positive y direction. In contrast, the here-described optical prisms of the prismatic contact lens <NUM> serve primarily an optical function, to refract the light in the nasal direction, along the x-axis. In broad terms, the roles of the x and y axes are interchanged between optical prisms and ballast "prisms", and therefore these two classes of prisms are different both for their function and for their structures, and thus constitute distinct classes.

Since the prismatic contact lenses <NUM> typically employ an orienting system, such as the ballast <NUM>, they are capable of supporting other, orientation-dependent optical functions which regular, non-oriented contact lenses are unable to. One of these orientation-dependent optical functions is to correct various types of astigmatisms. These contact lenses are often referred to as toric lenses. Accordingly, in some embodiments of the prismatic contact lenses <NUM> at least one of the first prism zone <NUM> and the progressive prism zone <NUM> can also be toric. Any combination of optical power designs, and prismatic designs from the previous embodiments of <FIG> can be additionally combined with toricity.

Finally, some embodiments of the prismatic contact lens <NUM> can include Freshnel-like sawtooth-shaped surfaces, or index-of-refraction modulations.

The material of the prismatic contact lenses <NUM> can be soft hydrogel, silicone hydrogel, any gas permeable material, or PMMA. Also, various hybrid designs that use more than one of the listed materials can be used. In some other embodiments, the prismatic contact lens <NUM> can be a harder material, which can be capable of floating on the tear film of the eye, and is kept in place by the top of the lower eye-lid. In the case of such hard contact lenses, the eye <NUM> can be able to rotate relative to the prismatic contact lens <NUM> to some degree, thus amplifying the benefit of the contact lens's separate prism zones <NUM>, <NUM> and <NUM>.

The type of the use of the prismatic contact lens <NUM> can be daily disposable, frequent replaceable, or reusable.

Finally, the invention provides a method <NUM> of making a prismatic contact lens <NUM>, the method including:.

An alternative method <NUM> can include:.

Many additional steps of known methods of manufacturing a contact lens can be practiced in conjunction with the methods <NUM> and <NUM>.

Claim 1:
A prismatic contact lens (<NUM>), comprising:
a first prism zone (<NUM>) in a central circular region, having a first prism and a first optical power;
a progressive prism zone (<NUM>), adjacent to the first prism zone and in a ring around the central circular region, having a progressive prism that varies from the first prism to a second prism, wherein the second prism is different from the first prism; and
at least one of an orientation mark (<NUM>), and a ballast (<NUM>) in a lower region of the prismatic contact lens (<NUM>), for orienting a refraction direction of the prismatic contact lens (<NUM>) in a horizontal direction.