Patent Application
20200073146
Vision is a very precious possession. The quality of our vision is such that what we see we consider to be reality, in contrast to any other image that mankind is able to produce. It is very difficult to imagine that what we see is actually just an image projected in our brain.
The image is exceedingly wide-angled, has depth perception, is perfectly color-corrected and is of high resolution. It is stabilized, varifocal and is able to fuse the two images provided by the two eyes into a single image. All this has been achieved with the use of a single lens element per eye, giving the human optical designer pause. On the other hand, human vision is affected by the imperfections of this world. In many cases aberrations, like lack of focus, astigmatism and misalignment are in need of correction. This situation makes it worthwhile to consider how we can best accommodate the vision imperfections in the design of optical instrumentation. And, if so desired or needed, how we can best assist the accommodation ability of our vision.
An optometrist provides a custom prescription for the correction of the above-mentioned aberrations. This prescription is valid for unaccommodated eyes, that is for eyes in their rest position. The eyes are then focused at infinity and their convergence is zero, approximately. The correction prescribed by the optometrist is also valid for reading distances because focusing does not incur any change in the aberrations. No further testing by the optometrist is required for current bifocal glasses. The user decides only on the strength of the desired focal assistance.
In addition to the custom prescription by the optometrist, there is a large class of optical instruments that assists humans in seeing more and better, like microscopes and binoculars. Also, these instruments are basically designed to deliver their images to unaccommodated eyes. Although the eyes are varifocal, they are focused at infinity in the unaccommodated position.
Eyes have very large angle of view. Yet, their convergence is closely controlled, that is the relative alignment of their visual axes. In order to observe close objects, the two images formed by the two eyes must coincide. This is accomplished by convergence of the visual axes of the eyes at the object. One reason for keeping the relative alignment under tight control is that only a small part of the retina, called the fovea, provides high resolution. Normal eyes at their rest position keep the visual axes centered on the fovea area. Note that the visual axes of the eyes do not coincide with the optical axes. They are separated by a few degrees.
The alignment of the eyes in the unaccommodated position can be demonstrated by alternately opening one eye at a time. If the object is close, a separation of the two images can be observed, due to the separation of the two eyes. When both eyes are opened this separation is quickly eliminated by the brain by turning the eyes towards each other. Nevertheless, it is important to note the existence of a definite unaccommodated position of the eyes. It is the position at which normal eyes are at rest, are focused at infinity and the convergence is zero, approximately. The visual axes are then parallel and centered on the fovea. Binocular instruments therefore generally provide images to unaccommodated eyes. Also, the optometrist prescribes custom glasses for this position. Unaccommodated eyes serve all day long without experiencing any strain or fatigue.
However, when observing close objects, like reading a book, the eyes have to accommodate the situation in two ways. Reading requires considerable focusing effort but also considerable converging effort of the visual axes. Both efforts are sizeable and large compared to the accuracy required for the formation of a clear image. From here on this condition will be called the reading mode. It includes all situations in which objects are close. The pronounced preference of the eyes for their unaccommodated position also indicates that the reading mode takes considerable effort. Yet, the eyes are well-equipped to deal with the reading mode as young readers can testify.
However, the ubiquitous use of reading glasses indicates the need for reading assistance. Reading glasses are used for comfortable reading, for watching electronic displays, for special working conditions as well as for older people with limited eye flexibility. Current reading glasses provide focal assistance to allow the eyes to observe written matter while focused near infinity. But the eyes still have to provide the necessary convergence of the visual axes in order to obtain coincidence of the two images produced by the two eyes. Although the brain makes the correction very quickly, which is rarely observed by the user, the required effort is nevertheless considerable.
Cases that require focal assistance may naturally be expected to need convergence assistance as well. Convergence assistance may not always be essential for reading glasses but it will always further relax the eyes, whether noticed, appreciated or not. Several reasons exist that this convergence is not provided by current reading glasses. The operation directed by the brain is so quick that it is rarely observed. Also, the incorporation of convergence assistance in generic reading glasses used to be technically difficult. And the rubbing of the eyes after an hour of intense close-up observation does not indicate the cause of it. Once convergence assistance is tried, it will be greatly appreciated.
With modern technology, producing generic reading glasses that provide convergence assistance in addition to focus assistance can be accomplished at a relatively small additional expense. These new generic prism reading glasses present written material to the unaccommodated eyes, that is to eyes in their rest position. This new type of reading assistance can also be provided in a partial measure, if so desired. The claims leave the amount of assistance open.
A pair of eyes have a definite rest position at which they are focused at infinity and have their visual axes parallel. In this position they perform tirelessly all day.
Close-up conditions however require the eyes to provide focal adjustment as well as convergence of their visual axes in order to cause the two images to coincide. Current generic reading glasses and the generic bifocal part of prescription glasses only provide focal assistance. The present invention provides generic reading glasses and the generic bifocal part of prescription glasses with focal assistance combined with convergence assistance in order to provide a significantly improved and more restful reading experience.
A pair of normal eyes have a definite rest position. They are then focused at infinity and their visual axes are parallel, approximately. In this position they perform tirelessly all day, without showing any strain.
This situation is recognized by optical instrument designers so that their binocular instruments generally provide at least a pair of images that are focused at infinity and have parallel optical axes, approximately.
Close-up conditions however require considerable effort from the eyes in two ways. First, the eyes have to provide focal adjustment and, second, the eyes have to provide convergence in order to cause the two images to coincide at the very point of observation. These efforts are substantial for optimal observation and are continually changing. The depth of focus of vision is about 0.4 diopter while a reading distance of 13 inches requires 3 diopters of additional focal power, which amounts to an 8× ratio. A reading distance of 13 inches requires a convergence of the visual axes of about 5 degrees while the resolution ability of the eye is 1/60 of a degree, which amounts to a 300× ratio. Maintaining high convergence accuracy while continuously changing the subject matter, as is the case with reading, is likely to cause considerable strain, more so than the relatively relaxed focal accuracy requirement.
It is therefore important to add convergence assistance to reading glasses. The amount of convergence assistance can be commensurate with the optical power of the reading glasses and can thus be added on a generic basis. The present invention claims generic reading glasses which provide focal assistance combined with convergence assistance. The claim includes the generic addition of convergence assistance to the bifocal parts of prescription glasses.
