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Claims  |
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I claim:
1. A method of obtaining information related to blood-glucose concentration
in a living subject, comprising the steps of:
obtaining a test measure of the optical power of at least one eye of such
subject; and
then comparing the test measure with a calibration measure of optical power
that corresponds to a reference blood-glucose level in such subject, to
obtain such glucose-related information.
2. The method of claim 1, further comprising the steps of:
before the test-measure-obtaining step, obtaining the calibration measure
of optical power; and
substantially contemporaneously with the calibration-measure-obtaining
step, determining the reference blood-glucose level in such subject.
3. The method of claim 2, wherein:
the determining step comprises analysis of the patient's blood.
4. The method of claim 1, wherein:
the comparing step comprises noting whether the test measure is higher or
lower than the calibration measure; and
such glucose-related information comprises the conclusion that such
patient's blood glucose level is, respectively, higher or lower than the
reference level.
5. The method of claim 1, wherein:
the reference level is unhealthfully high;
the comparing step comprises noting whether the test measure is or is not
lower than the calibration measure; and
such glucose-related information comprises the conclusion that such
patient's blood-glucose level is or is not, respectively, improved
relative to the unhealthfully high reference level.
6. The method of claim 1, wherein:
the comparing step comprises comparing the test measure with a plurality of
calibration measures of optical power that correspond to a respective
plurality of reference blood-glucose levels in such subject; and
such glucose-related information comprises an estimate of blood-glucose
concentration in such subject, calculated from the plurality of
calibration measures, the corresponding plurality of reference levels, and
the test measure.
7. The method of claim 1, wherein the test-measure-obtaining step
comprises:
projecting an image through an external optical system, and through the
cornea and lens of such subject's eye onto such subject's retina;
during the projecting step, monitoring the sharpness of focus of the image
on such subject's retina;
during the monitoring step, modifying the conditions of projection of the
image and determining the relationship between the projection conditions
and the sharpness of focus; and
using the relationship to obtain the test measure.
8. The method of claim 7, particularly adapted for such subjects who are
presbyopic, and wherein:
the external optical system has adjustable optical power, and has means for
indicating the value of optical power to which the system is adjusted;
the modifying and determining step comprises adjusting the optical power of
the external optical system to focus the image on such subject's retina as
sharply as possible, and while the optical power is so adjusted reading
the optical power of the external system from the indicating means; and
the using step comprises using the power so read as the test measure.
9. The method of claim 7, particularly adapted for such subjects who are
presbyopic, and wherein:
the image is an image of an object that is at an adjustable effective
distance from such subject's eye;
the external optical system comprises means for indicating the effective
distance to which the object is adjusted;
the modifying and determining step comprises adjusting the effective
distance of the object to focus the image on such subject's retina as
sharply as possible, and while the effective distance is so adjusted
reading the effective distance from the indicating means; and
the using step comprises using the distance so read as the test measure.
10. The method of claim 1, particularly adapted for such subjects who are
substantially not presbyopic, and wherein:
the test-measure-obtaining step is performed at the far point for such eye.
11. The method of claim 1, particularly adapted for such subjects who are
substantially not presbyopic, and wherein:
the test-measure-obtaining step is performed at the near point for such
eye.
12. The method of claim 2, particularly adapted for such subjects who are
substantially not presbyopic, and wherein:
the test-measure-obtaining step is performed at the near point for such eye
and comprises:
projecting an image of an object through the cornea and lens of such
subject's eye onto such subject's retina from an external optical system
whose optical power is preadjusted to focus such subject's eye at a
relatively large distance when the eye muscles are relaxed and when such
subject's blood-glucose concentration is substantially at said reference
level;
during the projecting step, monitoring the sharpness of focus of the image
on such subject's retina;
during the monitoring step, progressively changing the position of the
object, from a starting position which to such subject appears at a
relatively large distance, toward subsequent closer positions;
determining the closest position at which sharpness of focus of the image
on such subject's retina is maintained; and
using said closest position as the test measure of optical power at the
near point.
13. The method of claim 7, wherein:
the monitoring step is performed by means of such subject's own visual
sensation of the image on the retina.
14. The method of claim 9, wherein:
the monitoring step is performed by means of such subject's own visual
sensation of the image on the retina.
15. The method of claim 12, wherein:
the monitoring step is performed by means of such subject's own visual
sensation of the image on the retina.
16. The method of claim 13, wherein:
such subject performs the projection-condition modifying step.
17. The method of claim 14, wherein:
such subject performs the optical-power adjusting step.
18. The method of claim 15, wherein:
such subject performs the effective-object-distance adjusting step.
19. The method of claim 13, wherein:
the image is an image of the retina of a particular one of such subject's
own eyes; and
the projecting step comprises illuminating the retina of that particular
eye to project an image of that retina outward through the lens and cornea
of that particular eye to the external optical system, for projection
through the external optical system and onto the retina recited in claim
13.
20. The method of claim 7, wherein:
the projecting step comprises projecting an image that has an intensity
gradient;
the monitoring step comprises automatically scanning the image of a
photoelectric detector along the gradient.
21. Apparatus for obtaining information related to blood-glucose
concentration in a living subject who has at least one eye that includes a
lens and a retina; said apparatus comprising:
means for projecting, under adjustable projection conditions, an image of
an object through an external optical system and through such eye lens
onto such retina;
means for adjusting the projection conditions of the external optical
system in response to the optical power of said eye; and
an indicator, responsive to the adjusting means and graduated in units of
blood-glucose concentration, for indicating the approximate blood-glucose
concentration in such subject that corresponds to the projecton conditions
of the external optical system.
22. Apparatus for obtaining information related to blood-glucose
concentration in a living subject who has at least one eye that includes a
lens and a retina; said apparatus comprising:
means for projecting, under adjustable projection conditions, an image of
an object through an external optical system and through such eye lens
onto such retina;
means for adjusting the projection conditions of the external optical
system; and
an indicator, responsive to the adjusting means and graduated in units of
blood-glucose concentration, for indicating the approximate blood-glucose
concentration in such subject that corresponds to the projection
conditions of the external optical system wherein the adjustable
projection conditions comprise the optical power of the external optical
system.
23. Apparatus for obtaining information related to blood-glucose
concentration in a living subject who has at least one eye that includes a
lens and a retina; said apparatus comprising:
means for projecting, under adjustable projection conditions, an image of
an object through an external optical system and through such eye lens
onto such retina;
means for adjusting the projection conditions of the external optical
system; and
an indicator, responsive to the adjusting means and graduated in units of
blood-glucose concentration, for indicating the approximate blood-glucose
concentration in such subject that corresponds to the projection
conditions of the external optical system wherein the adjustable
projection conditions comprise the effective distance of the object from
such eye lens.
24. Apparatus for obtaining information related to a blood-glucose
concentration in a living subject who has at least one eye that includes a
lens and a retina; said apparatus being paritcularly adapted for such
subjects that are presbyopic, said apparatus comprising:
means for projecting, under adjustable projection conditions, an image of
an object through an external optical system and through such eye lens
onto such retina;
means for adjusting the projection conditions of the external optical
system;
an indicator, responsive to the adjusting means and graduated in units of
blood-glucose concentration, for indicating the approximate blood-glucose
concentation in such subject that corresponds to the projection conditions
of the external optical system;
automatic means for sensing sharpness of focus of the image on such retina;
means responsive to the automatic sensng means, for controlling the
adjusting means to maximize the sharpness; and
whereby the apparatus automatically focuses the image on such retina to
maximum sharpness and indicates the blood-glucose concentration level in
such subject that corresponds to the power of the external optical system.
25. Apparatus for obtaining information related to blood-glucose
concentration in a living subject who has at least one eye that includes a
lens and a retina; said apparatus being particularly adapted fro such
subjects that are presbyopic, said apparatus comprising:
means for projecting, under adjustable projection conditions, an image of
an object through an external optical system and through such eye lens
onto such retina;
means for adjusting the projection conditions of the external optical
system; and
an indicator responsive to the adjusting means and graduated in units of
blood-glucose concentration, for indicating the approximate blood-glucose
concentration in such subject that corresponds to the projection
conditions of the external optical system and wherein:
the adjusting means are manually adjustable by such living subject; and
the sharpness of focus of the image on such retina is perceptible by such
subject's own visual sensation of the image on such retina;
whereby such subject can focus the image on such retina to maximum
sharpness and can read from the indicator such subject's own blood-glucose
concentration level that corresponds to the power of the external optical
system.
26. The apparatus of claim 23, further comprising:
automatic control means for controlling the adjusting means to
progressively vary the effective object distance from a relatively long
distance toward a relatively short distance;
automatic means for sensing sharpness of focus of the image on such retina;
and
automatic means, responsive to both the automatic control means and the
automatic sensing means, for causing the indicator means to indicate the
blood-glucose concentration that corresponds to the shortest effective
object distance at which a substantially sharp focus is sensed by the
automatic sensing means.
27. The apparatus of claim 23, further comprising:
manually manipulable control means for use, by such subject or by an
assistant, in controlling the adjusting means to progressively vary the
effective object distance from a relatively long distance toward a
relatively short distance;
automatic means for sensing sharpness of focus of the image on such retina;
and
automatic means, responsive to both the manually manipulable control means
and the automatic sensing means, for causing the indicator means to
indicate the blood-glucose concentration that corresponds to the shortest
effective object distance at which a substantially sharp focus is sensed
by the automatic sensing means.
28. The apparatus of claim 23, further comprising:
manually manipulable control means for use, by such subject or by an
assistant, in controlling the adjusting means to progressively vary the
effective object distance from a relatively long distance toward a
relatively short distance;
whereby such subject, while perceiving by such subject's own visual
sensation the degree of sharpness of focus of the image on such retina,
can cause the manually controlled progressive variation of effective
object distance to be halted when such subject perceives that the image is
not substantially sharp; and
whereby the indicator means can be read to obtain the blood-glucose
concentration that corresponds to the shortest effective object distance
at which the subject perceives a substantially sharp focus.
29. The apparatus of claim 21, wherein: the external optical system
comprises a spectacle lens that is particularly adapted to:
correct such subject's vision, including astigmatism if present, and
focus such subject's eye at a relatively large distance,
when the eye muscles are relaxed and when such subject's blood-glucose
concentration is at a predetermined reference level.
30. The apparatus of claim 29, wherein: the relatively large distance is
infinity.
31. Apparatus for obtaining information related to blood-glucose
concentration in a living subject who has at least one eye that includes a
lens and a retina; said apparatus being particularly for use if such
subject's eye has glycemia-induced astigmatism and such astigmatism is
characterized by an axis meridian, and comprising:
means for projecting, under adjustable projection conditions, an image of
an object through an external optical system and through such eye lens
onto such retina;
the image of said object on such retina including a plurality of parallel
lines that are aligned substantially perpendicular to the axis meridian of
glycemia-induced astigmatism in such subject's astigmatic eye;
means for adjusting the projection conditions of the external optical
system in response to the optical power of said eye; and
an indicator, responsive to the adjusting means, for providing as
indication related to the projection conditions of the external optical
system;
whereby the indicator provides an indication related to the approximate
blood-glucose concentration in such subject that corresponds to the
projection conditions; and
whereby sharpness of focus of the image onto such retina is substantially
independent of glycermia-induced astigmatism exceeding that which
corresponds to said predetermined blood-glucose reference level.
32. Apparatus for obtaining information related to blood-glucose
concentration in a living subject whose has at least one eye that includes
a lens and a retina; said apparatus being particularly for use with such
subjects whose eye-pupil dilation capability is substantially normal to at
least well beyond five-millimeter pupil diameter, and comprising:
means for projecting, under adjustable projection conditions, an image of
an object through an external optical system and through such eye lens
onto such retina, said image appearing on a field, and said image and
field being characterized by brightness;
means for adjusting the brightness of the image to a level that causes the
pupil diameter of such subject's eye to be approximately five millimeters;
means for adjusting the projection conditions of the external optical
system in response to the optical power of said eye; and
an indicator, responsive to the adjusting means, for providing an
indication related to the projection conditions of the external optical
system;
whereby the indicator provides an indication related to the approximate
blood-glucose concentration in such subject that corresponds to the
projection conditions; and
whereby the relationship between said indication and such glucose
concentration has a sensitivity that is substantially optimized for depth
of field and aberrations.
33. The apparatus of claim 32, wherein:
the object is illuminated at roughly two to ten candelas per square meter. |
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Claims |
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Description |
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BACKGROUND
1. Field of the Invention
This invention relates generally to monitoring the medical condition of a
living subject, and more particularly to novel methods and apparatus for
noninvasive monitoring of blood-glucose concentration.
The invention is particularly intended for human subjects, but veterinary
applications are also within the scope of my invention.
2. Prior Art
Effective diagnosis and treatment of various medical conditions requires a
continuing sequence of information about the concentration of glucose in
the blood. For example, patients with diabetes mellitus should tailor
their diets and insulin dosage, if needed, to their blood-sugar levels.
For many such purposes average or mean values are preferable to
instantaneous values, since the latter may reflect very brief fluctuations
that are not significant or that could be misleading if used as a basis
for treatment.
Ideally, average or mean glucose-concentration measurements should be
available on short notice, at low cost, and as frequently as once or twice
a day.
Present methods of monitoring the concentration of glucose in the blood of
a living subject, however, require withdrawing a sample of blood and
analyzing the sample chemically. The process of taking and analyzing a
blood sample is not simple, is moderately expensive, is rarely done
continually, and provides only instantaneous values.
There is another area of prior art that is relevant to my invention,
although it has not heretofore been given a practical use in connection
with blood-glucose measurement. It is well known to ophthalmologists that
the eye is slowly responsive to the level of glucose in the blood.
Abnormally increasing blood glucose causes the focus of the eye to shift
toward the patient.
For example, if an old person, with no control over the accommodation
(i.e., focus) of her or his eyes, happens to have far vision focused at
infinity when that person's blood sugar is normal, the focus will shift to
perhaps three feet--causing blurring of distant objects--with increasing
abnormal blood sugar.
Because this effect is slow it is not responsive to short-term changes, but
integrates blood-sugar content over a time period of about a day.
Yet another relevant area of prior art that has not heretofore been
connected with blood-glucose measurement is the general field of
optometry. Highly refined methods and apparatus are available for
measurement and analysis of vision as such--but, as is well known, the
purpose of optometry is to obtain information for correction of vision
itself, rather than information for diagnosis or treatment of any other
condition.
OBJECTIVES OF THE INVENTION
Primary objectives of my invention are to provide quick, easy and
inexpensive mean blood-glucose measurements that do not require withdrawal
of a blood sample and that can be performed even while the patient is at
home.
For those patients who are not alert or mechanically inclined, another
objective of my invention is to provide such measurements without active
participation by the patient.
BRIEF SUMMARY OF THE DISCLOSURE
I have invented an instrument and a process whereby an untrained person can
noninvasively measure and thus control his or her blood glucose
expeditiously.
The process is to measure the blood glucose by determining the change in
the "optical power" of the patient's eye optical system, and may also
include using that information in planning the patient's diet, medication
or personal habits, or any combination of these.
The apparatus is a device that projects an image, preferably with sharp
boundaries (say a Ronchi ruling) upon the retina of the patient. The
projection conditions or parameters of the instrument are variable. The
instrument may also have some arrangement for determining the sharpness of
the retinal image, or this function may be provided by the visual
sensation of the patient himself. Any of several projection parameters of
the instrument may serve as a measure of blood glucose.
More precisely, my invention provides a method of obtaining information
related to blood-glucose concentration in a living subject. The method
includes the steps of obtaining a test measure of the optical power of at
least one eye of the subject, and then comparing the test measure with a
calibration measure of optical power, to obtain the glucose-related
information. The calibration measure corresponds to a reference
blood-glucose level in the subject.
While this is the fundamental method of my invention, several variants are
particularly important and may be mentioned at this point. First, the
method may also include the steps of obtaining the calibration measure of
optical power and determining the reference blood-glucose level in the
subject. These steps are carried out substantially contemporaneously with
one another, but generally before the step of obtaining the test measure.
The step of determining the reference level may include analysis of the
patient's blood.
Further, the "comparing" step may include noting whether the test measure
is higher or lower (in terms of optical power) than the calibration
measure. In this case, the glucose-related information that is obtained
includes the conclusion that the patient's blood-glucose level is,
respectively, higher or lower than the reference level.
(The validity of this last statement depends upon the understanding, which
is to be observed throughout this document unless otherwise specified,
that the test measure is considered in terms of optical power. This
convention is adopted for definiteness since, as will become clear, actual
numerical values used as indicia of the test and calibration measures may
increase in either direction--depending upon the particular parameter
monitored and the arbitrary selection of scale for the readout device
employed.)
Also, the method may be performed with a reference level that is
unhealthfully high, in which case the comparing step advantageously
includes noting whether the test measure is or is not lower (again, always
considered in terms of optical power) than the calibration measure. In
this case, the glucose-related information includes the conclusion that
the patient's blood-glucose is or is not, respectively, improved relative
to the unhealthfully high reference level.
It will be understood that the calibration measure establishes only one
point on a blood-glucose concentration scale. Since the amount of change
in optical power per unit of change in blood-glucose concentration varies
from one subject to another, the calibration measure cannot establish the
scale expansion. Truly quantitative estimates of concentration therefore
cannot be obtained from a single calibration measure.
On the other hand, it should also be understood that a typical scale
expansion can be assumed for any given subject, and the calibration
measure can be used to place the subject's response correctly on the scale
at one point. The scale will then be at least roughly correct at other
points, particularly at points near the calibrated point. In these cases
the glucose-related information obtained may be regarded as loosely
quantitative or semiquantitative
Next, the comparing step may include comparing the test measure with not
one calibration measure but a plurality of calibration measures of optical
power--corresponding to a respective plurality of reference blood-glucose
levels in the subject. In this case the glucose-related information
includes a more quantitative estimate of blood-glucose concentration in
the subject. The estimate is calculated from the plurality of calibration
measures, the corresponding plurality of reference levels, and the test
measure.
Still with reference to the principal variants of my novel method, the
test-measure-obtaining step preferably includes these four substeps:
(1) projecting an image through an external optical system, and through the
cornea and lens of the subject's eye, onto the subject's retina;
(2) during the projecting step, monitoring the sharpness of focus of the
image on the subject's retina;
(3) during the monitoring step, modifying the conditions of projection of
the image and determining the relationship between the projection
conditions and the sharpness of focus; and
(4) using the relationship to obtain the test measure.
I wish to emphasize that in implementing the method of my invention and its
principal variants as described above, a great number of different
specific detailed procedures may be used.
In particular with regard to the conditions of projection in the third
substep mentioned just above, any of several different parameters of the
external optical system may be varied to modify the conditions of
projection, and thus may be part of the relationship between the
conditions of projection and the sharpness.
Thus any of these various parameters may serve as the test measure of
optical power of the subject's eye, as will be set forth in the detailed
description that follows.
Now as to the apparatus of my invention, it is apparatus for obtaining
information related to blood-glucose concentration in a living subject who
has at least one eye that includes a lens and a retina. This apparatus
includes some means for projecting an image through an external optical
system and through the eye lens onto the retina. For purposes of speaking
generally, this part of the apparatus will be called the "projecting
means."
The projecting means operate under adjustable projection conditions (or in
other words projection "parameters"), and the apparatus also includes some
means for adjusting these projection conditions of the external optical
system. This part of the apparatus will be called--again for purposes of
generality--the "adjusting means."
The apparatus also includes an indicator, responsive to the adjusting
means, for indicating the approximate blood-glucose concentration in the
subject that corresponds to the projection conditions of the external
optical system. This indicator is preferably graduated in units of
blood-glucose concentration.
The adjustable projection conditions utilized may include, for example, the
optical power of the external optical system, or alternatively the
effective distance of the object from the patient's eye lens. Other
conditions (or parameters) may be substituted that provide a discriminator
for the focal condition of the patient's eye.
Other forms of my invention that are of primary interest include provision
for rendering insignificant any glucose-induced astigmatism in the
patient's eye, and for optimizing the sensitivity of the measurement.
These provisions will be discussed briefly at this point.
Not only overall optical power but also astigmatism of a subject's eye
varies with blood-glucose level. Effects of the baseline component of
astigmatism (that which is present at the reference level of glucose
concentration in the subject's blood) can be eliminated by using a
corrective lens that is similar to the patient's ordinary eyeglass lens.
Since the two glycemia-induced variations (in overall optical power and in
astigmatism) are not simply correlated, however, the glycemia-induced
component of astigmatism can seriously interfere with the measurement of
overall optical power and thus with the determination of glucose level.
In an embodiment of the apparatus of my invention that is particularly for
use if the subject's eye is astigmatic, the "object" whose image is
projected consists of a plurality of parallel lines that advantageously
are aligned essentially perpendicular to the axis meridian of the
glycemia-induced component of astigmatism for the particular subject's
eye. The glycemia-induced component of astigmatism can then only introduce
a variation in optical power along an axis that is parallel to the
plurality of parallel lines of the object.
The resultant variation in blurring is then limited to longitudinal
blurring of the extreme ends of the image lines, as distinguished from
transverse blurring of the portions of the lines between the ends. It is
the latter that naturally will be considered in evaluating the sharpness
of focus at the retina. Sharpness of focus of the image onto the retina is
thereby rendered substantially independent of glycemia-induced astigmatism
differing from that which corresponds to the predetermined blood-glucose
reference level. As to measurement sensitivity, it is useful to recognize
that the pupil diameter of the subject's eye affects sensitivity in two
ways. The pupil diameter of a subject's eye varies, as is well known, with
illumination. At high light levels the pupil diameter is very small,
leading to long depth of focus. Determination of optical power of the eye
lens is rendered difficult under such circumstances, since the retinal
image will be sharply focused for a considerable range of projection
conditions surrounding the nominal-focus or best-focus condition. The ends
of this extended sharp-focus range are relatively gradual and indistinct.
On the other hand, at low light levels the pupil diameter is very large,
leading to use of the peripheral regions of the eye lens and consequently
to the usual aberrations that are characteristic of such regions.
Determination of optical power of the eye lens is difficult in these
circumstances too, though for the opposite reason: the retinal image is
not sharply focused for any projection condition, including the nominal-
or best-focus condition.
In both of these extreme cases it is difficult to find the nominal-focus
condition, and thus difficult to obtain the desired measure of
blood-glucose level. These extreme cases are avoided by bringing the pupil
diameter to an intermediate value, ideally about five millimeters for the
normal adult human subject.
The method of my invention preferably includes determining and using for
the individual subject the illumination level that produces this
intermediate value of pupil diameter. Each particular apparatus of my
invention preferably includes means for customizing the apparatus to the
individual subject who will use the particular apparatus--by controlling
the illumination level to a value that is determined to produce the
optimum pupil diameter in the individual subject, and by using a spectacle
lens.
In apparatuses of my invention that will be used by most subjects whose
eye-pupil dilation capability is substantially normal to at least well
beyond pupil diameters of five millimeters, the object is illuminated in
the range of roughly two to ten candelas per square meter.
As in the case of the method of my invention, the apparatus may be embodied
in any of a great number of specific forms--several of which are detailed
below.
All of the foregoing operational principles and advantages of the present
invention will be more fully appreciated upon consideration of the
following detailed description, with reference to the appended drawings,
of which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is primarily a group of four related optical schematic diagrams
showing generally preferred arrangements for practicing the method of my
invention, and also showing preferred forms of the apparatus of my
invention. In addition to the optical elements, FIG. 1 also includes in
abstract block-diagram form a small number of electronic and mechanical
components.
FIG. 2 is a group of two diagrams showing how sharpness of focus on the
subject's retina can be determined automatically in nonastigmatic and
astigmatic subjects.
FIG. 3 is a graph showing the relationship between optical power and
readout in one embodiment of the apparatus of my invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The procedure and apparatus of my invention have various embodiments for
use with different types of subjects. First, in theory the form of the
procedure depends on the subject's ability to substantially change the
focus of the eye--that is, on whether the subject is presbyopic or
nonpresbyopic. In practice, however, as will be seen the actual procedural
manipulations are almost identical in these two cases.
Secondly, the form of the apparatus depends on the subject's sapience,
competence and dexterity--that is, on whether the subject is a human being
and able to think clearly and perform simple tasks with the hands and
eyes. Depending on the subject's capabilities there is a corresponding
range of equipment types, from fully manual and very inexpensive to fully
automatic and relatively costly.
These points will be now be taken up in order.
If the subject is presbyopic, then in principle it is only necessary to
determine the single value of optical power that the subject's eye can
produce. As already explained, this can be done by finding the particular
parameters of an external projection system that result in a sharp focus
on the subject's retina--and then using those projection conditions as a
measure of the eye's optical power, and thus as a measure of glucose
concentration.
As a practical matter, however, in almost every case there will be some
depth of focus of the eye. Regardless of the external apparatus used to
determine sharpness of focus, therefore, near the point of nominal best
focus the sharpness of focus will usually vary only slowly with changes of
the external projection parameters.
Under these circumstances it will usually be necessary to find not one
point but the two ends of the range of projection conditions that produce
a generally sharp focus. These two points will produce two scale
readings--or the equivalent in automatically collected data--which can be
averaged to find a single value for use as the measure of glucose level.
Thus a human subject using a manual device may start at one end of the
adjustment range of the device and slowly adjust the device through the
range of adjustments at which the image appears sharpest, stopping and
making a reading just as the image begins to blur again--and then
adjusting the device in the opposite direction and again stopping for a
reading just as the image begins to blur.
An automatic device for a presbyopic subject will perform virtually the
same procedure, although with automatic equipment it is typically just as
accurate to find the two ends of the sharp-focus region while moving
continuously in one direction. Whether performed manually or
automatically, this two-point procedure may be regarded as simply a
procedure for finding the setting that maximizes the sharpness of focus.
In the case of automatic equipment it may be preferred to use one or the
other of the two values taken singly as the measure, since automatic
apparatus can identify a particular degree of blurring more reproducibly
than can a human observer. The automatic device may be programmed to use
either the "near point" or "far point" of clear vision as the
glucose-level measure.
If the subject is nonpresbyopic, the subject of course can focus on objects
at a great range of distances. In adult humans with normal vision or with
a corrective lens, this range extends from infinity to less than ten
inches. Such a subject is not only able to focus on any object in this
range, but must exert a concentrated effort to avoid doing so when
attention is drawn to such an object. Hence an absolute measurement of the
optical power of the subject's eye is only meaningful at one or the other
end of the subject's range of focus.
A suitable measurement strategy in accordance with my invention is to lead
the subject's eye from focusing on an object that is readily within the
focal range to an extremum of that range. At the instant when the
subject's eye is no longer able to focus, the optical power of the eye may
serve as a measure of glucose concentration.
Again, any of various projection parameters of the external optical system
at that instant will provide an index to the optical power of the eye and
thus the glucose concentration. Interestingly, among other available
parameters, the distance itself at which the subject can no longer focus
may serve as the measure of both optical power and glucose level.
I emphasize that for purposes of this document, phrases such as "a measure
of the optical power of at least one eye of the subject" encompass
measurement of the distance to the "near point" or "far point" of the
subject's focal range.
The similarity of this measurement strategy for nonpresbyopic subjects to
the procedure previously described for presbyopes should now be noted.
Although the underlying reasons are different, in both instances the
external apparatus is adjusted from a projection condition that produces a
fairly sharp focus until the image begins to blur, and the projection
condition at that point is the measure of glucose level.
In fact, the presence of depth of focus is a factor in nonpresbyopes as
well as presbyopes, but in nonpresbyopes depth of focus will normally
(with suitable illumination) amount to only a slight extension of the
already long focal range. Also, in the nonpresbyopic case as well as the
presbyopic case, the "far point" of vision may be used as the focal-range
"edge" where the measure is obtained; and for best reproducibility both
the "near point" and "far point" may be used.
Now I will turn from the topic of presbyopia as it affects the method of my
invention to the matter of the subject's ability to aid in making the
measurement.
If the subject has the mental and physical capacity to operate a simple
mechanical device while viewing an image, the ability to determine when an
image is sharply focused, and the mental alertness to deal adequately with
the information generated, then the apparatus of my invention can be a
completely manual device. The apparatus can be, as an example, roughly the
size and configuration of a small kaleidoscope. The subject operates a
single control that varies a projection parameter, stopping when the image
begins to blur, and reads an indicator pointer against a graduated scale.
As will be apparent, the pointer and scale can be replaced by a digital or
other type of readout if desired. Further, the glucose-level readout can
be in the form of instructions for medication or the like, rather than in
terms of glucose level as such.
There are many circumstances under which such an apparatus will not be
appropriate. At one extreme, the subject is not necessarily a human being:
various animals may require treatment for disorders relating to glucose
concentration. At another extreme, the subject may be an elderly person
who is slightly feeble, or lacks manual dexterity due to neural disorder,
or is slightly disorganized, and thus unable to make the measurement or
use the resulting data appropriately. Between these extremes, the subject
may be a person who is completely incapacitated, or senile, or infantile.
Yet another possibility is that the subject may be a participant in a
multiparameter medical screening program that monitors the patient's
overall condition--one of the parameters being blood-glucose
concentration.
In such cases the apparatus of my invention includes some means for
automatically sensing sharpness of focus of the image on the retina.
At least for use with presbyopic subjects, the apparatus may also include
some means for controlling the previously mentioned "adjusting means" to
maximize the sharpness. By operation of these sensing and control means
the apparatus automatically focuses the image on the retina to maximum
sharpness--and then indicates the blood-glucose concentration level in the
subject that corresponds to the projection conditions of the external
optical system.
If the depth of focus in the subject's vision is too great for accurate
location of the sharpest-focus point, then instead of means for
controlling the adjustment to maximize the sharpness the automatic
apparatus may include means for controlling the adjustment to
progressively vary the adjustment from projection conditions in which the
effective distance of the object is, for example, at infinity toward
conditions in which the effective distance of the object is very small.
Alternatively the effective distance can be varied in the opposite
direction. Either or both of these can be accomplished by varying the
actual object distance, or by adjusting the position or power of a focal
element in the external optical system as will be shown.
With this form of the apparatus the automatic sensing means operate as
before, depending upon the accommodation of the subject's eye to "follow
the object in" until it is no longer possible to do so. The measure of
glucose concentration is found from the projection conditions at the
instant when the automatic sensing means determine that the retinal image
is no longer sharply focused. As previously mentioned, this determination
is to be regarded as one way of determining the optical power of the eye.
FIG. 1 shows, in the topmost portion titled "a. CALIBRATION," how to set up
for practice of the method of my invention, and also the basics of
construction of an apparatus according to my invention. The example
illustrated will be most pertinent to use for a presbyopic subject with
very short depth of focus, and that context will be assumed for the
present.
The retina R and eye lens EL of the subject's eye appear at the right end
of the drawing. The subject's eye is focused at infinity, either by virtue
of the focal capability of the eye alone or (as will more commonly be the
case for presbyopes) in combination with an ocular lens CL that is
customized to the particular subject. A far-vision spectacle lens may be
employed for this purpose and also for correction of baseline astigmatism.
Thus the retina R receives converging rays 15 from the eye lens EL, and
these rays are derived from parallel rays 13 within the apparatus. If the
unaided eye lens EL is unable to achieve this condition, then the custom
ocular lens CL is present--and from the parallel rays 13 this custom
ocular lens CL produces refracted rays 14 between the ocular lens CL and
the eye lens EL. The inclination of these refracted rays 14 is such that
the eye lens EL can focus them onto the retina.
The source of the parallel rays 13 is in turn an object or target T that is
separated from an objective lens BL by the focal length f of that lens. By
virtue of this spacing the objective lens BL funct | | |
