[0001] This invention relates to a device for the training and measurement of the human
visual accommodation system. Accommodation is the automatic adjustment of the eye
for seeing at different distances and is effected by changes in the convexity of the
crystalline lens. Specifically, the device is a training aid for teaching subjects
to relax the eye muscles which are used to focus a sharp image on the retina of the
eye and to instead focus at infinity. This is called relaxation of accommodation.
[0002] A normal, or emmetropic, eye will focus light rays from a distance on the retina
by means of complementary deflections of the cornea, crystalline lens, and fluid of
the eye. Light rays reflected from a distant object (beyond 7.62 m) are considered
to be parallel. With a nearer object, however, the reflected rays tend to diverge
so that unless some correction is made, the rays will not focus on the retina. The
correction is known as accommodation and is achieved through alteration of the anterior
lens surface curvature by action of the ciliary muscle so that a retinal focus is
obtained. It is often necessary or desirable, for both medical and research purposes,
to cause a person to relax his eye accommodation, that is to focus on a plane as far
distant as possible, theoretically at infinity for a normal eye. Perhaps a most common
instance when relaxation of accommodation is desirable is when an ophthalmologist
examines a patient to determine whether or not he needs glasses. The ophthalmologist
accomplishes this by using drugs to paralyze the eye muscles which control the eye
lens or by changing a series of glass lenses in front of the patient's eye, using
a technique called "fogging". Thus, one objective of an ophthalmologist is to prescribe
glasses which allow the patient to see far-away objects clearly, provided his accommodation
is fully relaxed. In order for the ophthalmologist to do this, the accommodation must
first be fully relaxed before refraction measurements are taken. Accommodation relaxation
can be important for a number of purposes other than just determining prescriptions
for glasses as the inventor has discovered.
[0003] There are many situations where keen distant vision is very important. For example,
it is necessary for all pilots to be able to perceive the existence of other aircraft
in the airspace immediately ahead of their aircraft. Additionally, military pilots
need to be able to detect other aircraft and identify them as friendly or hostile
at the farthest distance possible. A need has developed for a device to train one
to overcome empty field myopia and to provide therapy for behavioral myopia. Some
past optometers employed such complex electro-mechanical systems that their operation
was beyond nearly all people except the originators. For example, when the Cornsweet
and Crane optometer, citation below, was turned over to a skilled Government scientist,
it took the scientist over two months of concentrated study and practice to even make
the device work with modest success. If training human visual accommodation is ever
to have wide application and become a real social benefit then a really practical,
simple and inexpensive device must be provided. Accordingly, it is an object of the
present invention to provide a device that is economical to fabricate, simple to operate,
maintain, and transport that will: train the human visual accommodation system independently
of other visuo- muscular systems; provide an accommodation stimulus and measurement
tool in vision research; measure the accommodation resting position and the visual
near and far points.
[0004] There is no known prior art device capable of performing all of these functions let
alone one that is simple to operate and economical to constrct. An examplary prior
art relaxer is disclosed in U.S. Patent No.3,843,240 wherein a defocused flashing
source of light is viewed through a pin-hole aperture to produce relaxation of the
eye's accommodation powers. U.S. Patent No.1,475,698 issued to Henker shows an apparatus
for the objective measurement of the refraction value of the principal point of the
eye. U.S. Patent No.3,602,580 pertains to a method and appa= ratus for simultaneously
refracting both eyes of a patient wherein a narrow beam of light is directed into
each eye at a point spaced from the optical axis of the eye. An optometer of the Scheiner
type is revealed in U.S. Patent No.1,235,170 issued to Thorner. Expensive, servo-controlled
optometers that are large,. complex and difficult to use are mentioned in the following
publications: Servo-Controlled Infrared Optometer, Cornsweet and Crane, Journal of
the Optical Society of America, Vol. 60, No.4, April 1970, pp. 548-554; Volitional
Control of Visual Accommodation, R.J. Randle, AGARD Conference Porceedings No.82 on
Adaptation and Acclimatisation in Aerospace Medicine, September 1970; and Accurate
Three-Dimensional Eye- tracker, Crane and Steele, Applied Optics, Vol.17, March 1,
1978, pp.691-705.
[0005] The object of the present invention is therefore achieved by an apparatus according
to the appended claim 1.
[0006] In summary, the present invention is an apparatus for training the human visual accommodation
system and for measuring the accommodation, the accommodation resting position, and
the visual near and far points. The training of the visual accommodation system is
accomplished through a defocus feedback that is external to the natural, blurred-retinal-image
feedback loop. The apparatus employs very few components and is very easy to use.
The apparatus comprises a stationary base with a movable stage mounted on one end
of the base. Five elements are mounted on the movable stage: a light source mounted
at one end of the sage; a target mounted at the middle of the stage; a lens mounted
on the stage between the light source and the target; another lens mounted at the
opposite end of the stage; and a plurality of apertures are mounted on the stage between
said lens and the target. An eyepiece is mounted on the opposite end of the base;
and a further lens is mounted on the base between the eyepiece and the lens mounted
on the stage. The elements of the invention mounted on the movable stage are all in
fixed relationship to each other and in movable relationship to the further lens and
the eyepiece.
[0007] The invention will be more fully understood from the following detailed description
taken in conjunction with the accompanying drawings in which:
- figure 1 is a perspective view of the invention,
- figure 2 is a schematic diagram showing the elements of the invention and the location
of the image of target 36.
[0008] Figure 1 shows a presently preferred embodiment of the invention for laboratory use,
designated generally by the numeral 10. In the center of the figure is shown a stand
12 having a rod 14 extending upward vertically from a base 16. Attached to the top
of stand 12 is a base plate or rail 18. Mounted on one end of base plate 18 is movable
stage 20 which is driven by means of a rack 24 and pinion gear (not shown). Rotatable
knob 22 is coupled to the pinion gear. Stage 20 may be moved toward or away from eyepiece
70 on base plate 18 by rotating knob 22 clockwise or counter-clockwise. A diopter
and/or distance scale 23 is affixed to base 18 adjacent to rack 24 as for example
by etching or painting. Scale 23 is read by using the edge 25 of stage 20 as a pointer.
[0009] A number of elements of the invention are all mounted on movable stage 20 in fixed
relationship to each other. Vertically adjustable rod 26 affixed to stage 20 supports
rectangular box 28 which contains a light source 30 and a lens 32 mounted in holder
34. A target 36 is situated on end 38 of box 28. The target may transmit light therethrough
from light source 30 with the area adjacent thereto being opaque or viceversa. End
38 of box 28 may be, for example, a photographic transparency with a desired image
centrally positioned.
[0010] Mounted on vertically adjustable stand 40 adjacent to target 36 is a "wide open"
aperture 42 about 8mm in diameter. The aperture is positioned so that the optical
axis 74 of lens 32 and the other lenses passes centrally therethrough. Apertures 48
and 52 supported by pivotable arms 50 and 54, respectively may be moved onto the optical
axis 74 by means of high speed solenoids 44 and 46, respectively. Aperture 48 is a
"pinhole" aperture with an orifice of approximately 0.3 mm in diameter, whereas aperture
52 is a "Scheiner" aperture having two orifices about 0.5 mm in diameter, separated
by 3.0 mm. When solenoid 46 is actuated, aperture 52 is moved to the position where
the optical axis 74 bisects the two orifices. Apertures 42, 48 and 52 are not depicted
to scale in Fig.1. When the device is in use there is either one aperture on the optical
axis (42) or two (42 and 48, or 42 and 52). As it is intended that aperture 42 be
larger than aperture 48 or aperture 52, there is only one effective aperture on the
optical axis at any given time (the smaller one). A switching circuit 78 (see Fig.2)
housed in cabinet 31 energizes solenoids 44 and 46. Specifically, the switching circuit
provides these selectable modes of operation:
1. The energization of solenoid 44 to move aperture 48 to the optical axis 74.
2. The energization of solenoid 46 to move aperture 52 to the optical axis 74.
3. The automatic alternate energization of the solenoids so that apertures 48 and
52 are alternately on optical axis 74. In this mode, it is preferable that the switching
circuit include a user-selectable timing circuit so that the "on-axis" interval of
aperture 52 may by varied.
[0011] Cabinet 31 also houses a power supply to provide power to lamp 30.
[0012] The orifices of Scheiner aperture 52 are covered with different colored filters 75
and 76, respectively. These filters may be, for example, red and green. These filters
provide a cue for the direction of defocus when the image is split. On the proximal
end of stage 20 is mounted a vertically adjustable stand 56 with lens 58 and lens
holder 60.
[0013] On the proximal end of rail 18 is a vertically adjustable stand 62 which supports
lens holder 66 and lens 64. Also attached to stand 62 is a bracket 67 supporting eyepiece
70.
[0014] Figure 2 shows the preferred spacing of certain items in the trainer-tester. Back-lighted
target 36 is a fixed distance from lens 58, twice the focal length (f) of lens 58.
An image 72 of target 36 is formed the same distance on the other, left, side of lens
58. Of course as stage 20 is moved with respect to base 18 by means of knob 22, image
72 is moved with respect to stationary lens 64. Eyepiece 70 is situated one focal
length from lens 64 and lamp 30 is spaced one focal length from lens 32. The field
of view of the target is determined by the size of the aperture 42,48 or 52 and the
distance of the target from the aperture.With the aperture diameters mentioned above
and if lens 58 has a focal length of 10 centimeters, for example, there will be sufficient
field of view abailable to stimulate a large portion of the retina of the viewing
eye 79 and thus, a full accommodation response.
[0015] The several modes of operation of the apparatus will now be described.
Measurement of the Far Point of Vision
[0016] The vision far point (punctum remotum of accommodation) is defined in the Dictionary
of Visual Science, Schapero, M., et al., Chilton Co., Phila., New York, 1960 as:
The conjugate focus of the retina (fovea) when the accommodation is relaxed or at
its minimum.
In emmetropia, the far point is said to be at infinity; in myopia, it is at some finite
distance in front of the eye; in hyperopia, it is at some finite (virtual) distance
behind the eye.
[0017] What needs to be determined, therefore, is the optical distance from the subject's
eye, at, and beyond which, the image of target 36 can no longer be kept in focus,
i.e., when accommodation is fully relaxed. If the point at which the image can no
longer be kept in focus is in front of the focal plane 80 of lens 64 the far point
is closer than infinity and the eye is said to be myopic or "near-sighted". On the
other hand, if the point is behind focal plane 80 (to the right of the plane in Fig.2)
the far point is said to hyperopic, (hypermetropic) or "far-sighted". If the point
is right at the focal plane 80, the eye is then deemed emmetropic (normal).
[0018] For the measurement of the far point of vision the subject is preferably seated in
front of device 10 with the entrance pupil plane of one eye placed at the eyepiece
70. The lamp 30 is illuminated and the wide-open aperture 42 is in place on optical
axis 74. An image of target 36 is found at 72. This image is the object for lens 64
and the eye, and thus becomes the visual stimulus for the eye, The position of stage
20 is determined by the rotation of knob 22 which in turn determines the position
of the subject's stimulus with respect to lens 64.
[0019] To start the measurement process the stimulus is initially placed by the examiner
between lens 64 and focal plane 80. This requires the subject to exert some accommodative
effort, an amount that is dependent upon where the stimulus has been placed with respect
to lens 64. The scale 23 imprinted on base 18 and corresponding pointer (proximal
end of stage 20) enables the measurement of the diopter value of power required at
the eye to focus the stimulus (image 72). For convenience, scale 23 may also include
avision distance scale in addition to the dioptric scale to save the examiner the
time needed to make the conversion from diopters to distance. The subject is requested
to rotate the knob 22 to move the accommodation stimulus toward focal plane 80 and
to stop the movement when the stimulus first appears to blur. When the blurring first
occurs the point or scale 23 aligned with the pointer is read.
[0020] Because of the high variability in biological response systems, it is preferable
to measure the far point by approaching it from both directions and then taking the
average reading after several trials. That is, the subject moves the stimulus away
from lens 64, from a position set by the examiner, until the stimulus blurs, the examiner
reads the scale, the subject moves the stimulus, from a position selected by the examiner
towards lens 64 until the blurring of the stimulus stops, and the examiner reads the
scale. This cycle is repeated for as many times as is deemed appropriate by the examiner
and an average value of the dioptric distance is computed. This mean dioptric distance
is the refractive error of the eye under test, and when converted to distance (through
scale 23 or a simple calculation) is the monocular far point of vision of that eye.
Measurement of the Near Point of Vision
[0021] The Djctionary cited above defines the accommodative near point (punctum proximum)
as:
The point representing the maximum dioptric stimulus to which the eye can accommodate.
Hence, usually the nearest point anteriorly on which the eye can focus.
[0022] The measurement process for determining the near point of vision is quite similar
to the previous process. The measurement begins when the examiner, using knob 22,
places the stimulus between lens 64 and focal plane 80. The subject then uses the
knob 22 to move stage 20 and stimulus 72 toward him thus increasing the accommodative
power required at the eye at eyepiece 70 to focus the stimulus. When the stimulus
first starts to blur, the subject stops the movement of the stage 20 and the examiner
notes where the pointer has stopped on scale 23. The bracketing procedure used above
is also preferably employed here. In accordance with that procedure the examiner places
the stimulus close to lens 64 such that it is too close to be focussed and will be
observed as blurred. The subject then moves the stage 20 away from him until the stimulus
first appears in focus. When the movement is stopped, the examiner reads scale 23.
This blurring and clearing (approaching and receding stimulus) procedure is repeated
as many times as is considered necessary by the examiner and a mean value of the several
scale readings is calculated. This average value of accommodation, when converted
to distance from diopters, is the monocular near point of vision of that eye.
[0023] It is well known that as a visual stimulus approaches the eye the pupil decreases
in size as accommodation increases. The decreased pupil size causes increased depth
of field and facilitates accommodation. This often results in a lazy or lagging response
which does not necessarily indicate the true capability of the visual neuro-muscular
system. To insure that the full accommodation range of the subject will be tested,
the examiner may dilate the subject's eyes with a mydriatic. The mydriatic keeps the
pupil large, deprives the eyes of great depth-of-fleld, and fully taxes the accommodation
capabilities.
[0024] Normally a defocused image is a blurred image. However, if an optical aperture having
two laterally displaced orifices is placed in front of a lens, a single image of a
point (or extenden) source will be formed in a plane on the other side of the lens,
conjugate to the object; all other planes are not conjugate to the object--they are
defocused-- so two images of the source will be formed. These images will be separated
by a distance dependent upon the distance between the two small apertures and the
distance of the images from the conjugate plane. Between the conjugate plane and the
lens each image will lie on the same side of the optical axis as the aperture which
formed it; on the side of the conjugate plane away from the lens each image will lie
on the opposite side of the optical axis. Such a two-orifice aperture is known as
a Scheiner aperture.
[0025] For measuring both the near point and the far point, the Scheiner aperture 52 may
be used instead of, or alternately, with the wide open aperture 42. When aperture
52 is moved to the optical axis 74 by means of solenoid 46, the subject sees a single
target image 72 only when it is in focus; the retina is conjugate to72. For other
situations, namely when image 72 is defocused, the eye at eyepiece 70 observes two
displaced target images, each a different color ceased on the colors of filters 75
and 76). The separation of the images is a function of the amount of defocus. It is
easier for the subject to distinguish two displaced and different colored images than
defocus blur of one image so greater accommodation measurement accuracy can be expected
when aperture 52 is used for the near and far vision measurements.
Measurement of the Resting Position
[0026] When the eye has great depth-of-field, a position of tonic equilibrium occurs between
the sympathetic and parasympathetic nervous systems and the eye is said to be at the
resting position. The peno- menon, also called empty or dark field myopia, is an unconsciuos
process and the resting position is almost never at infinity focus. Empirical studies
indicate that normal eyes focus, on the average, about one meter in front ot the eye.
For a comprehensive study see, "The Dark Focus of Accommodation: Its Existence, Its
Measurement, Its Effects," Nicholas M. Simonelli, AFOSR Technical Report Bel-79-3/AFOSR-79-7,
prepared by the Behavioral Engineering Laboratory, New Mexico State University, November
1979.
[0027] Herein the eye is made to settle to its resting position by removing the defocus
blur accommodation retinal stimulus. This is accomplished by placing pinhole aperture
48 on optical axis 74 by means of solenoid 44. The aperture increases the depth-of-field
so much that no stimulus blur is apparent to the eye under test.
[0028] In accordance with this measurement, lamp 30 is illuminated, aperture 48 is initially
placed on optical axis 74, the subject's eye to be tested is placed at eyepiece 70,
and the subject's other eye is occluded or covered. Stage20 is moved so that stimulus
72 is positioned at the subject's previously measured far point and the subject is
allowed a reasonable time for accommodation to settle (more than one minute). After
sufficient time has been allowed for settling, solenoid 44 is de-energized moving
aperture 48 off of the optical axis and aperture 52 is moved thereon by solenoid 46.
After an interval shorter than the accommodation latency period, about 250 milliseconds,
aperture 52 is removed from optical axis and aperture 48 is returned to it. During
the brief period that aperture 52 is on the optical axis, the eye under measurement
will observe two displaced images, each differently colored, if the eye has drifted
to its resting position. This is an easy pattern to discern even during the brief
period that aperture 52 is on the optical axis.
[0029] At regular intervals aperture 52 is brought back to the optical axis for a brief
period while aperture 48 is moved to its off-axis position. As the alternation occurs,
the subject is directed to move stage 20 in a direction that will cause the two colored
images to be superimposed. The correct direction to ove the stage will be immediately
apparent to the subject because of the orientation of the two colored images. When
the images are superimposed and the stage is brought to rest, the pointer for scale
23 indicates the empty field myopia, that is, the resting position of the eye.
Training Visual Accommodation
[0030] The subject invention has three salient visual accommodation training features: (1)
It can open the accommodation loop (nullify defocus blur) to allow volitional control
to be brought into play; (2) It can provide a defocus cue (feedback) that is not normally
available in real world visual tasks; and (3) It allows accommodation to be decoupled
from binocular vergence by using only one eye, thus limiting it to a more pure accommodation
response. Inasmuch as willed control is initiated and completed in higher neural centers
than at each individual eye, both eyes benefit when only one eye is trained.
[0031] The subject invention is so versatile that it permits many strategies for training
the volitional control of accommodation. Hereinafter is but one training strategy,
that of volitionally controlling one's focus to one's far point (normally infinity)
from a position of myopia due to functional causes. The functional causes could be
due, for example, to a behavioral accommodative spasm or the effects of an empty field.
Other strategies will be apparent to a skilled clinician.
[0032] To implement the training, the device 10 is operated as it is for the measurement
of the resting position and the subject's eye not in the eyepiece is either occluded
or covered. As aperture 52 is periodically and briefly positioned on optical axis
74 (alternately with aperture 48), the subject is instructed to not touch knob 22,
but to exert volitional control on the eye so as to fuse together the two different
colored images. After some practice, trainees can learn how to drive their accommodation
in the appropriate direction to achieve the superimposition of images. It is not known
how this is accomplished nor have users of the device been able to explain how they
fuse the images. Some trainees have been able to achieve the task with as little as
one hour of training. After some practice and reinforcement a trainee is weaned from
the device and can utilize the new accommodation skill in the real world. To enhance
the training and make it possible for the trainee to alternately view real world objects
and stimulus 72 without leaving eyepiece 70, a 50/50 beamsplitter may be added to
the apparatus. When the beamsplitter is added, the eyepiece is rotated 90 degrees
so that its viewing axis is orthogonal to optical axis 74. The beamsplitter is placed
where the two axes cross. Thus, the subject may either look through the beamsplitter
at the real world or look on the beamsplitter for stimulus 72. When operated thusly,
neither eye is occluded, binocular viewing is in force, and binocular accommodation
is measured.
[0033] The components of the instrument need not be supported on tall stands or on a base
as large as 18. The instrument may be repackaged in much smaller volume. It is possible,
for instance, to helmet-mount the device for dynamic studies in piloting aircraft,
driving cars, operating computer terminals, and other human engineering investigations
without intervention in the on-going visual task.
[0034] The advantage of this invention over present day devices is that it brings together
multiple accommodation measurement/training features in one instrument that is easy
to operate and economical to construct. This invention combines in one ophthalmic
instrument a device for: (a) training the human visual accommodation system independently
of other visuo- muscular systems; (b) measuring the visual near and far points; (c)
measuring the accommodation resting position; and (d) use as an accommodation stimulus
and measurement device in vision research.
1. An apparatus for training and measuring the human visual accommodation system characterized
by a base (18); an eyepiece (70) and a stage (20) mounted on opposite ends of said
base (18); a first lens (64) mounted on said base between said eyepiece (70) and said
stage (20); means (22,24) for moving said stage (20) toward or away from said first
lens (64); a plurality of elements mounted on said stage (20) in linear optical alignment
comprising a light source (30) mounted on the end of said stage (20) farthest from
said first lens (64); a target (36) mounted on said base near the middle portion of
said stage; a second lens (32) mounted on said stage between said light source (30)
and said target (36); a third lens (58) mounted on the end of said stage (20) nearest
said first lens (64) whereby an image of said target (36) is produced between said
first lens (64) and said third lens (58) and said image is moved with respect to said
eyepiece (70) when said stage (20) is moved; and a plurality of interchangeable apertures
(42,48,52) mounted on said stage (20) between said third lens (58) and said target
(36).
2. An apparatus as set forth in claim 1 wherein said light source (30) and said second
lens (32) are enclosed within a chamber (28) and said target (36) comprises a portion
of one wall (38) of said chamber.
3. Apparatus as set forth in claim 1 further characterized by having a diopter readout
(23) to show the relationship between the movable stage (20) and the first lens (64).
4. The apparatus of claim 1 wherein said light source (30), first (64), second (32)
and third (58) lenses and said eyepiece (70) are aligned on a single optical axis
(74) and wherein only one aperture (42) is effectively on said optical axis at any
given time.
5. The apparatus of claim 4 wherein said aperture (42) is at the focal plane of said
third lens (58), said target (36) is two focal lengths from said third lens (58) and
said target image is two focal lengths from said third lens (58) and between said
first lens (64) and said third lens (58).
6. The apparatus of claim 1 wherein said interchangeable apertures (42,48 and 52)
comprise a wide-open aperture (42),a pinhole aperture (48) and a two-hole aperture
(52).
7. The apparatus of claim 6 wherein each hole of the two-hole aperture is covered
by a different colored filter (75,76) to provide a defocus cue.
8. Apparatus as set forth in claim 6 wherein means (44,46) are provided for moving
at least one of said apertures on and off of the optical axis.
9. Apparatus as described in claim 6 wherein means (78) are provided for alternately
positioning the pinhole aperture (48) and the two-hole aperture (52) at the optical
axis (74).