Optics: eye examining – vision testing and correcting – Eye examining or testing instrument – For interpupillary distance measuring or lens positioning
Reexamination Certificate
1999-11-18
2001-09-11
Manuel, George (Department: 3737)
Optics: eye examining, vision testing and correcting
Eye examining or testing instrument
For interpupillary distance measuring or lens positioning
Reexamination Certificate
active
06286957
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and a system for adjusting a pair of progressive lenses for mounting into the frame of a patient's spectacles, utilizing a device for measuring the patient's pupils locations relative to the frame in his natural habitual reading mode.
BACKGROUND OF THE INVENTION
Progressive lenses, also known as PAL (progressive addition lens), are widely used, especially by patients with weak eyesight in both reading and distance visions, like many presbyopes. There are different designs of progressive lenses produced by various manufacturers. As is known in the art, the two main features characterizing all designs of the progressive lens are optical power distribution and distortion distribution within the lens.
FIGS. 1A and 1B
illustrate two different examples, respectively, of these features for the same lens. There is practically no way of eliminating all the distortions.
The example of
FIG. 1B
presents a typical distortion map of a standard progressive lens. The lens has prescribed parameters of optical powers required for a patient's distance and reading visions and also cylinder parameters when necessary. The lens is formed with four main zones, wherein zone
2
is a far vision zone corresponding to the patient's distance vision, zone
3
is a near vision zone corresponding to the patient's reading vision, zones
5
are peripheral zones of concentrated optical distortion, defining a fourth zone
4
therebetween which is stretched between zones
2
and
3
. This fourth zone
4
is a narrow passage, called “corridor”, which is free of distortions and in which power varies continuously. All these features of the progressive lens are well known per se, and, therefore do not need to be described in detail, except to note that each standard semi finished PAL is characterized by its “addition” value (ADD), defined as the difference between the far and near vision powers.
The entire process conventionally carried out for providing a patient with PAL spectacles includes the following stages:
(1) determining for each eye values of the optical power required for the patient's reading and distance visions;
(2) selecting for each eye a semi finished lens of a suitable standard kind according to its “addition” value, and processing the inner side of the semi finished lens according to the prescribed values of the optical power and cylinder when necessary; and
(3) cutting the lens, and mounting it in the frame of the spectacles (previously chosen by the patient) in such a position that the pupil location of the patient for far vision matches a Fitting Cross marking on the lens.
As illustrated in
FIG. 2
, the Fitting Cross
6
A is a marking on the lens provided by the lens manufacture, and indicates the position of the far vision point that should be located in front of the patient's pupil center when looking at a far object. Generally, the only apparent relevant information about the lens supplied by the manufacturer to the optician is in the form of the following four standard stamped markings on the surface of the lens:
the Fitting Cross
6
A which is the recommended position to mount the lens relative to the patient's pupil in distant vision;
a horseshoe marking
6
B, which is the location recommended by the manufacturer for measuring the far vision power of the lens;
a Horizontal Fitting Line
7
, which is the reference orientation line that should be horizontal when the lens is mounted in the frame; and
a circle
8
is the center of the near vision zone, namely the location where the patient's line of sight is expected to pass when the patient reads.
In
FIG. 2
, numbers
9
A and
9
B designate “real” pupil locations (unmatched) for distance and reading vision, respectively, as found for a specific individual. The borders of the distortion zones
5
shown in dashed lines are typically unknown to the optician (concealed from view), and can only be detected by special instruments, mostly available to manufacturers, but still not to opticians. The location of the distortion zones
5
cannot practically be determined by the conventional equipment the optician has at his disposal.
Thus, by using the conventional techniques for adjusting lenses while mounting them into the spectacles' frame, the borders of the distortion zones
5
are not taken into consideration. Obviously, if while reading, the patient, for any reason, even slightly misses the recommended reading zone
8
, his line of sight might pass through the highly distorted zone
5
and/or not at the appropriate power. This may result in blurred vision, eyestrains, focusing difficulty and itchy eyes. Reasons for missing the reading zone may be, for example, the result of erroneous fitting of the lens into the frame or, in other cases, when the patient holds the reading object (e.g., his book) too high or too low, or too far or too close from the position where the lens designer assumed it to be.
Although the rate of success in fitting progressives was appreciated to be relatively high according to past surveys, newly released independent surveys disclose that one out of three presbyopes is not satisfied with his PAL glasses. These unsatisfied patients use their progressive spectacles mainly for far sight and occasionally for near vision, but not for actual reading. For reading, they constantly turn to their usual reading glasses. The discrepancy between past and recent surveys is probably due to the fact that past surveys relied on the rate of progressives returned to the practitioners as a sole indicator. As it turned out, many unsatisfied customers for various reasons failed to return their unsuccessful progressives to their dispensers.
Apparently, one of the most significant rationale for the unsuccessful adaptation of a patient to his PAL glasses, is that the design of the PAL is performed according to statistical data. For example, it is well known that for most people, reading distance is about 35 cm, and, accordingly, the design of most progressives relies on this presumption. However, older individuals may, over time, develop different reading habits by positioning the reading material in various distances and angles relative to the body. This may have a devastating effect on the functioning of the progressive lens. The problem becomes even more complex, because for this age group, it is difficult, often painful, and sometimes even impossible, to change their reading habits.
Evidently, it is impractical to custom design a lens for every patient. On the other hand, very little can be done by the optician during the lens' mounting process, if he does not receive full and accurate information about the lens, as well as about his patient's habits. Moreover, even with enough information about the lens, the optician should be provided with means to apply a set of considerations and reasoning as to how many distortions and power errors should be allowed in order to ensure optimal fitting.
The typical procedure performed by the optician is illustrated in FIG.
3
. The optician measures the far vision pupil's location relative to the selected frame independently for each lens, or alternatively derives this information from the measured inter pupillary distance. The respective data, as well as the spectacles' frame itself is input into a so-called “edger” device. The construction and operation of the edger are known per se, and therefore need not be specifically described, except to note that the edger is typically used for the circumferential cutting of a lens to fit the frame. Upon detecting that the pupil location for the distance vision overlaps the Fitting Cross
6
A marked on the lens, the optician operates the edger for cutting the lens.
It is often the case that such a process of adjusting progressive lenses for a patient's spectacles renders unsatisfactory results, and many patients feel uncomfortable with their new spectacles for a long time. One of the reasons for this is that the adjustment
Browdy and Neimark
Manuel George
PDA Advanced Optic Systems, Ltd.
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