Patent Publication Number: US-8967797-B2

Title: Adjustable focus spectacles

Description:
BACKGROUND 
     Good human vision depends upon properly focusing light incident on the front of the eye onto the retina. To this end the human eye includes an internal lens, and muscles that exert forces on that lens. In youth these muscles can change substantively the focal length of the internal lens, thereby enabling focusing on objects at various distances. With increasing age the ability of these muscles to affect focus decreases until, after about forty-five, most people can no longer focus at both far and near . . . even after any innate hyperopia, or myopia, and/or astigmatism is corrected. Optometrically speaking, people evidencing this condition are called ‘presbyopes’. 
     Variable focus eyeglasses have been devised that enable a presbyopic wearer manually to adjust focal length, and thereby to focus—on demand—at any distance. See Kurtin, U.S. Pat. Nos. 5,138,494 and 5,668,620 and US Patent Application Publication No. 2008/0084532. The eyeglasses disclosed in the aforementioned patents typically include a) for each eye a fixed optical power equal to the intended wearer&#39;s required refractive correction for far vision, together with b) a manually adjustable, bilaterally tracking, spherical ADD power. The maximum ADD can, in some instances, be as large as about 2.75 diopters, which amount is sufficient to permit a change in focus from far viewing to somewhat closer than ‘reading distance’ (usually assumed to be about 16 inches). Emerging presbyopes {those who retain some natural focusing ability} usually require a lesser amount of maximum ADD. 
     Adjustable focus eyeglasses as just described will suit most presbyopes. Some, however, suffer also from fluctuating vision. This means that the spherical optical power required to correct their far vision varies from time to time (i.e., from hour to hour, or from day to day). Fluctuating vision can arise as a consequence, for example, of diabetes, dry eye, hyperthyroidism, menopause, or possibly other conditions. 
     While statistically comprehensive information is seemingly not available, published clinical data indicates that in many instances the fluctuation is primarily as to sphere, and can exceed two diopters. More to the point, when an individual with fluctuating vision presents him- or herself for a refraction there is often no conclusive way in which the optometric practitioner can be confident as to i) the relevant range of fluctuation, ii) whether or not that range is static, and iii) where within that range the patient&#39;s vision is just then situated. Hence what is needed is eyeglasses which will allow the user, from time to time, to modify his/her spherical refractive correction to offset corresponding biological fluctuations. 
     SUMMARY OF THE INVENTION 
     This application describes an eyeglass invention which allows its user to update (as to each eye separately), from time to time, his/her spherical refractive correction for far vision. For convenience the invention is described in connection with eyeglasses of the type disclosed in US Patent Application Publication No. 2008/0084532. These previously disclosed glasses are primarily intended for use by conventional presbyopes. The underlying technology can, however, via the invention described herein, be modified to be suitable for i) additionally, or ii) alternatively, compensating for fluctuating vision. Accordingly, the disclosures of that publication are incorporated herein by reference. 
     For use by presbyopes with fluctuating vision the preferred embodiment disclosed here includes actuator means (located in the bridge of the glasses) whereby bilateral ADD can be adjusted by the user [in addition to, and separately from, the each-eye-separately correction for fluctuating vision which is the subject of this invention]. If the user is not presbyopic it will not be necessary to include this actuator. In any event, said actuator is described in US Patent Application Publication No. 2008/0084532. 
     The invention can also be applied to other variable focus eyeglasses, but the one discussed herein is the presently preferred embodiment. 
     The variable lens described in US Patent Application Publication No. 2008/0084532 includes a rigid lens (referred to as the “rear” lens) spaced away from a distensible membrane, the intervening space being filled with a transparent optical liquid. Both the rigid lens and the membrane are held by spaced rings (which, in the preferred embodiment, are circular). A flexible sealing member in the space between the rings keeps the optical liquid from escaping. The inter-ring spacing at a point near the bridge is varied by an actuator located within the bridge, and the inter-ring spacing at a point substantially opposite said point near the bridge is set by a leaf hinge. If said inter-ring spacing near the bridge is changed, a portion of the optical liquid is displaced . . . thereby forcing the membrane incrementally either to bulge or to recede, and correspondingly increasing or decreasing the optical power of the lens. If the portion of the membrane that is free to bulge/recede is circular, and its boundary is flat, the resulting optical power will be essentially spherical. 
     In the present invention the leaf hinge mentioned above is replaced by a hinge means with controllable axial length (‘H/CAL’) which can be manually set by the wearer. Consequently, as further described below, by setting the axial length of each H/CAL the baseline sphere optical power provided to each eye can be altered in a controlled manner (for example, by up to approximately ±1.4 diopters). Accordingly, said hinge means together with directly related items are sometimes herein called a ‘fluctuating vision compensation mechanism’. 
     Operation of the fluctuating vision compensation mechanism can be understood as follows: 1) whenever the H/CAL is caused to alter the inter-ring spacing it controls, the volume between the front and rear rings will change correspondingly; 2) the optical liquid, having a constant volume, will thereupon cause the distensible membrane to incrementally bulge or recede; and 3) the baseline optical power of the lens will thereby change [e.g., by up to approximately ±1.4 diopters]. 
     For embodiments including an actuator, the amount of bilateral ADD, as determined by adjusting the actuator and hence by further displacing of optical liquid, will—for both eyes—increment the optical power set by the H/CAL. 
     Accordingly the invention is expected, for example, to be used as follows:
         i) An individual presents him/herself for refraction. Assuming that there is no basis on which the practitioner can assess the then-current effect of fluctuating vision, the resulting refraction is identified as ‘Clinical Refraction 1’ (CR1), and is taken as nominal.   ii) Front Lenses 14 are prescribed, each with the sphere power per CR1 less some offset. For example, assuming an implementation of the invention offering 2.75 diopter of fluctuation correction, for purposes of clear description we shall assume an initial Front Lens sphere power offset of −1.375 diopter. In this manner, when the H/CAL is set to mid travel . . . and therefore provides +1.375 D of counter-offset . . . the user will enjoy far vision per CR1, thereby correcting i) any astigmatic and/or manifest prismatic error, as well as ii) his/her nominal spherical error.   iii) From time to time; as his/her vision fluctuates, with the actuator set for far vision the user will notice that his far vision is no longer sharp. Thereupon the user can, separately for each eye, simply by directing his gaze to a distant object and modifying the setting of the H/CAL, dial in sharp vision.   iv) If CR1 was, by happenstance, in fact nominal—or if the extent of the user&#39;s vision fluctuation is sufficiently moderate—no further action need be taken. If not, then the user will find that on occasion he runs out {in either the positive, or negative, direction} of the ability adequately to offset his/her vision fluctuation. On so reporting to his/her practitioner, by modifying the specified offset to CR1 more appropriate front lenses can be prescribed . . . thereby allowing the vision fluctuation correction provided by the invention to be better utilized.       

    
    
     
       DESCRIPTION OF THE FIGURES 
         FIG. 1  is a front view of a pair of eyeglasses according to the present invention. 
         FIG. 2  is a partially exploded cross sectional view of one of the lens units of the glasses of  FIG. 1 , taken at  2 - 2  of  FIG. 1 . 
         FIG. 3A  is an enlarged view of that portion of the cross section of  FIG. 2  indicated by the numeral ‘ 3 ’.  FIG. 3A  shows the H/CAL set to provide minimum sphere optical power. 
         FIG. 3B  is similar to  FIG. 3A  except that the H/CAL is set to provide maximum sphere optical power. 
     
    
    
     DESCRIPTION OF AN EMBODIMENT OF THE INVENTION 
     The invented fluctuating vision compensation mechanism is shown herein as applied to a pair of variable focus spectacles similar to those described in Patent Application Publication 2008/0084532. For convenience, each component that also appears in the patent publication is shown having the same identification number as in that publication, including, in particular, the distensible membrane  22 , the transparent optical liquid  16 , rear lens  15 , bridge  12 , the actuator link  13 , and the tab  11  of the rear ring  20 . The link  13 , which is a part of the above-mentioned actuator, pushes the tab  11  to accomplish a change of the inter-ring spacing at a point near the bridge as described earlier. Components that are unique to the fluctuating vision compensation mechanism are given numbers over  100 . 
       FIG. 1  shows two fluctuating vision compensation mechanisms  100  incorporated in a pair of preferred embodiment variable focus spectacles. One mechanism is incorporated in each lens unit in place of the leaf hinge that would otherwise be present (i.e., approximately opposite the actuation point of the actuator). The mechanisms are shown with a slotted round head, as for adjustment with a screwdriver. Other types of heads, such as hex heads, internal sockets, and heads suitable for grasping by the fingers, would be satisfactory alternatives. Enlarged sectional views of the mechanism are shown in  FIGS. 3A and 3B .  FIG. 3A  shows the mechanism set to provide minimum optical sphere, whereas  FIG. 3B  shows the mechanism set to provide maximum optical sphere. 
     In this embodiment the mechanisms are attached by means of a front tab  110  and a rear tab  111 , welded to the front ring  19  and rear ring  20  respectively. Controllable spacing screw  112  is threaded to match a tapped hole in the front tab, and is turned down at its end to match a hole in the rear tab. This assemblage forms a connector connecting the front ring  19  to rear ring  20 . The threads of screw  112  are made somewhat loose, allowing angular motion between the front and rear rings. Retainer  113 , welded at the end of controllable spacing screw  112 , keeps this screw from coming out of tab  111 . Additionally, the thread length of screw  112  is preferably kept short enough that the screw disengages from tab  110  before any interference occurs between the front and rear ring assemblies. And also, as to rotation of the screw in the other direction, the bottom of the screw head  114  bottoms on tab  110  to limit its travel. 
     As to embodiments with an actuator means, when said actuator is moved the front tab  110  and rear tab  111  move angularly about screw  112  as a pivot; for this reason the screw threads and/or the fit of the screw body into the hole in rear tab  111  must be loose enough to allow adequate unimpeded angular motion. Accordingly it is further preferred that the lens unit be filled such that its internal pressure is positive when the front and rear rings are at their maximum separation. 
     In the present figures screw  112  is shown at a circumferential location corresponding to the filling location in US Patent Application Publication No. 2008/0084532. Hence, for convenience, in the present invention filling is preferably accomplished by injecting optical liquid through the wall of the sealing member at a somewhat different, but nearby, location. Additionally, since in use the spacing between the front and rear rings ( 19  and  20 ) is expected to vary from time to time at each point around the periphery of the lens unit, the bellows  21  preferably has a substantially bellows shape at each section; and hence, unlike as shown in Publication No. 2008/0084532, the sealing member will not have a solid portion at the filling location. 
     An alternate embodiment of the invention (not illustrated) could be comprised of a flexure [substituted for the leaf hinge in the referenced patent publication], the active length of which is controlled by a slider.