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Description  |
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This invention relates to objective refractors. More particularly, this
invention discloses an objective refractor utilizing knife-edge optics and
remote image detection at necessarily low light levels.
SUMMARY OF THE PRIOR ART
Knife-edge optics have not heretofore been practically used with remote
objective refractors. This is because the images produced by knife-edge
optics in conjunction with the eye are of extremely low light levels.
These low light level images are extremely difficult to remotely detect.
Low light level detectors are subject to noise. Specifically in detecting
across a broad detection surface a difference of photosensitivity, the
impedance or resistance between adjacent portions of the same
photosensitive surface is low. Where the resistance is low, and the
corresponding electron movement high, the signal-to-noise ratio quickly
becomes destructive of the image difference trying to be sensed. There
results a severe practical difficulty in trying to detect low light level
images.
Objective refractors have heretofore been sensitive to the positioning of
the eye. Precise positioning of the eye has been required before accurate
objective refraction can be made. Automatic positioning has not been
provided for, especially in a form where the positioning information is
non-interactive, separate and distinct from the refractive information.
Moreover, prior art objective refractors have included sensitivity to the
light level returned from the eye. Where, for example, a retina has a
variation across its surface on light returned to the observer, heretofore
variations in the prescriptive readings have occurred.
SUMMARY OF THE INVENTION
An objective refractor for the eye is disclosed in which knife-edge optics
are utilized. The knife-edge optics cause characteristic illumination of
the retina so that components of sphere and astigmatism can be identified.
Provision for remote reading of the characteristic images is provided with
the result that two orthogonally disposed knife-edge images can identify
the sphere, cylinder and axis required for prescriptive patterns giving
the direction and magnitude of required prescriptive change. A system of
at least two orthogonally disposed, (and preferably four), knife edges
with weighted lighting is disclosed for detection. Utilization of the
knife-edge images is made possible by the detection of the low light level
images at a detector having low noise level. A photo-sensitive element
divided into a plurality of photo-discrete segments has light from the
images proportionally dispersed over its surface. Such dispersion occurs
through a matrix of wedge-shaped segments or alternately in the form of
optical elements having cylindrical components. This dispersion of the
light when used in combination with push-pull knife-edge patterns herein
disclosed produces detectable low level refractive signal. An embodiment
using an optic having a plurality of side by side optic elements, each
element having the effect of crossed cylinders, is disclosed with the
detector. Separate independent and non-interactive positional information
on one hand, and refractive information on the other hand is provided.
Consequently the disclosed refractor is insensitive to adjustment and can
accommodate a large range of pupil configuration with insensitivity to
local retinal variations in light emission.
OBJECTS, FEATURES AND ADVANTAGES
It is an object of this invention to disclose a knife-edge test with
tell-tale illumination patterns on the retina of the human eye. According
to this aspect of the invention, a light source with a knife-edge
terminator projects collimated rays to the eye. Typically, a projection
system is incorporated between the knife edge and the eye and is
simultaneously used to project the resultant image from the eye to an
image detector. The light patterns returned from the pupil of the eye have
characteristic shape relative to the knife edge. Boundaries between light
and dark portions of the pupil with components parallel to the knife edge
indicate components of sphere and astigmatism. Boundaries with components
normal to the knife edge indicate components of astigmatism along axes at
an angle to the knife edge.
An advantage of utilizing knife-edge testing with respect to the human eye
is that a tell-tale pattern of pupil illumination is present, which
pattern indicates not only refractive error, but gives the sense and
magnitude of correction required. Consequently, the output of the detector
does not require hunting in order to determine optimal correction.
A further object of this invention is to disclose measurement of the human
eye by objective refraction utilizing at least a light source, at least
one knife edge, combined projection and reception optics and a
photodetector. The source shines into the eye through an aperture formed
such that at least a portion of the aperture boundary has a straight
terminator, thereby acting as a knife edge barrier on the outgoing beam.
The outgoing beam passes through the optics in a projecting capacity,
images on the eye and thereafter is passed to the detector by the same
optics acting in a reception capacity. A single knife edge can be used,
and functions as a knife edge for light projected to and returning from
the eye. Indeed any such boundary which is straight and knife edge like in
character and which serves as an aperture edge for both outgoing and
returning light simultaneously will do, providing that the side of the
boundary which is clear for the outgoing beam is opaque for the returning
beam and vice versa.
A further object of this invention is to disclose a sequence of edge
illumination of preferably four knife edges for interrogation of the eye.
These knife edges are preferably divided into opposing pairs. One pair of
knife edges is illuminated from opposite directions parallel to a first
axis; the other pair of knife edges is illuminated from opposite
directions parallel to a second axis, this second axis being at right
angles to the first axis. This opposing and opposite illumination of knife
edges produces a "push-pull" effect in the resultant images. Image changes
due to changing optical prescription in sphere, cylinder and axis can be
segregated out from other image degradations, such as specular reflection
from other portions of the eye as well as optical flare and the like from
within the interrogating optical train. Additionally, reduced sensitivity
to eye position is achieved.
An advantage of the disclosed push-pull knife edge interrogation of the eye
is that two separate and non-interactive information bases are generated.
The first is positional information. The second is refractive information.
Each of these respective positional and refractive information bases is
separate and non-interactive.
A further advantage of the disclosed detector is that accurate refractive
measurements of the eye can be taken over a wide area. The instrument
contains insensitivity to adjustment. Hence, accurate refraction can occur
even though relatively substantial movement of the patient may take place
during the measurement.
A further advantage of the disclosed detector is that it can accommodate a
large range of pupil configurations. Moreover, pupil retinas having
irregularities in their light transmission to the downstream detector can
be measured. Such refractive measurement is insensitive to local retinal
variations in the amount of light returned to the detector.
An advantage of this aspect of the invention is that a single detector can
interrogate peripheral illuminating edges in sequence. By this sequential
interrogation, the components of required optical correction can be
identified sequentially in magnitude and sense.
An additional advantage is that the knife edges can each be separately
provided with frequency coded light. Simultaneous interrogation of
multiple knife edges can occur.
A further object of this invention is to disclose a preferred matrix of
four knife edges for interrogating the eye. Knife edges are aligned in
normally disposed pairs.
An advantage of the disclosed knife edge projection systems and light level
detectors is that they can be incorporated in instruments of varying
length. Moreover, and by using infrared illumination, the subject can view
along a first path an illuminated target and be interrogated along the
same path for perfection of the retinal image. A preferred embodiment of
light-emitting diode interrogation in the infrared spectrum is disclosed.
An object of this invention is to disclose a preferred detector matrix for
detecting low level light returning from an eye subject to knife edge
testing. According to this aspect of the invention, the detector matrix is
divided into four discrete quadrants. Each of these quadrants is
photodistinct in that the photosensitive elements are electrically
isolated one from another. By the expedient of delivering light to a
photodistinct portion, a signal is emitted from the photodetector which
has a low signal noise ratio.
A further object of this invention is to disclose in combination with a
detector having photodistinct elements specialized optics for the
distribution of light. According to this aspect of this invention,
multi-element lenses are inserted between a low light level image in the
pupil of the eye and the detector. When the low light level image is
centrally located, light is equally distributed to all four detector
quadrants. With a linear change of position of the centroid of the low
level light image, a corresponding linear change of image intensity occurs
on all detector quadrants. The detector emits a signal in proportion to
the displacement of the centroid of the low light level image.
An advantage of this aspect of the invention is that the detector is
particularly suited for detecting the center of low light level images
such as those returned from knife edge testing of the eye. The optical
center of a low light level image can be rapidly indicated. Corresponding
corrections can be applied to the eye to determine objectively the
refractive correction required.
Yet another object of this invention is to disclose a mode of measuring at
the detector segments the returned low level light images. According to
this aspect of the invention, a summing process is disclosed in which the
image on a pair of quadrants is summed and differentiated with respect to
the image on a remaining pair of quadrants. By the expedient of striking a
ratio of the image intensity differences relative to the light received on
all quadrants, an image signal is received which is proportional to the
displacement of low light level images projected.
Yet another object of this invention is to disclose lens configurations for
utilization with low level light detection aspects of this invention.
According to a first embodiment, the resultant knife-edge image is relayed
to a matrix of deflecting optical wedges or prisms. This matrix of
deflecting prisms varies in deflecting intensity as displacement is varied
from a neutral position.
A further object of this invention is to disclose a class of image
dispersing optics, which optics may be utilized for the displacement of
light with optical detectors preferably of the discrete photoquadrant
variety. According to this aspect of the invention, an optic matrix is
generated having an overall optical effect that may best be described
using lens optics of the cross cylinder variety. A first group of
cylinders (of either positive or negative power) is laid in a first
direction to in effect generate a first light deflective effect. A second
group of cylinders is laid in another direction (preferably at right
angles) and disposed to generate a second light deflective effect. The
cylinders used may be chosen from pairings which are positive and
positive, negative and negative, or positive and negative (regardless of
order). There results an overall matrix of optical elements, which matrix
of optical elements causes distribution of light to each of the quadrants
of photodiscrete detectors.
An advantage of the disclosed lens elements for utilization with
photodiscrete detectors is that the greater the number of discrete
elements, the less critical the alignment of the lens elements with
respect to a knife edge becomes. For example, where a large number of
randomly placed elements is used, the need for precise alignment of knife
edges with respect to the elements disappears altogether.
Yet another object of this invention is to disclose other configurations of
lens elements that will serve to distribute light among photodiscrete
detector segments in proportion to the displacement of low intensity
images. By way of example, conical and randomly aligned prismatic segments
all have an effect which can be used with the photodiscrete detectors
herein disclosed.
An additional and preferred embodiment of this invention includes a matrix
generated by cylindrical lenses of positive and negative power. These
cylinders are laid in side-by-side disposition. Along one side of the lens
positive and negative cylinders are aligned in a side-by-side array. Along
the opposite side of the lens positive and negative cylinders are aligned
in a side-by-side array at preferred right angles to the first array.
There results a matrix of crossed cylinder lenses, including positive
sphere, negative sphere, cylinder in a first orientation and cylinder in a
second and 90.degree. rotated direction. This specialized lens has the
advantage of dispersing light evenly in a pattern not unlike that
generated by the trace of various Lissajous figures.
An advantage of this lens is that when it is combined with a knife edge
cutting across the lens matrix, the knife edge at the boundary can
generate symmetric patterns for detection. These patterns evenly
distribute light over a given area, which distributed light may then be
detected by photodiscrete detecting elements.
An advantage of the knife edges utilized with the matrix of cylindrical
lenses is that the electrical signal out from the detector is directly
proportional to the intensity of the image and the image displacement.
Moreover, extremely low light levels can be sensed. Segments of the
photosensitive surface can all be electrically isolated one from another.
An advantage of the cylindrical embodiment is that the overall projection
system required for the detection of light is shortened. Consequently,
this projection system lends itself to compactness in the disclosed
detector.
A further object of this invention is to disclose a preferred embodiment of
the lens elements in front of a four quadrant detector. According to this
aspect of the invention, negative lens surfaces are distributed in
side-by-side random relationship over an optical surface, preferably a
refractive surface. Specifically, these surfaces are of random alignment
and closely spaced. An easily constructed lens element results.
An advantage of this aspect of the invention is that the optical surface
can be easily constructed. For example, it has been found that by
utilizing a positive mold, such as a ballbearing impressed upon an optical
surface or replicating media for an optical surface, one obtains a
perfectly satisfactory optical element.
A further advantage of this invention is that the disclosed randomly made
optical surface or "pebble plate" does away with the need for precisely
aligning the knife edge with respect to an axis of the plate. Instead,
both the pebble plate and the optic elements utilized with it can be
randomly placed one with respect to another.
A further object of this invention is to disclose a preferred embodiment of
the matrix of cylindrical lenses in combination with a knife edge. Light
from the knife edge is projected through the specialized optics to the eye
and light received from the eye passes again through adjacent portions of
the specialized cylindrical lens. These results in the passage of light to
the eye of Lissajous-like dispersement of light along the knife edge.
Consequently, only a portion of the light so projected can be seen over
the knife edge. The remaining portions of the light projected to the eye
from the knife edge are not returnable to the detectors as the physics of
the knife edge test renders these rays not visible. The portion seen over
the knife edge images back to a position immediately above the segment of
the cylindrical matrix from which projection originally occurred. At this
segment of the lens a complimentary deflection of the light occurs. There
results an enhanced displacement of the light.
An advantage of this aspect of the invention is that the physics of a
knife-edge test is used in combination with the predictable dispersion of
light at the knife edge to screen out all that light, save and except that
which has a desired projection angle which can be seen upon return. There
results a low level light signal of enhanced sensitivity returning from
the eye.
A further advantage of this invention is that the returning light hits a
segment of the cylindrical matrix lenses, which segment produces a
complimentary deflection. This complimentary deflection not only further
deflects the light, but produces an image center of gravity which is an
enhanced, and improved signal.
A further object of this invention is to disclose a flare control
illumination pattern. According to this aspect of the invention, the
projected light is weighted in intensity about the center of the detector.
Preferably, two light sources are projected on opposite sides of the knife
edges being utilized. One area is remote from the knife edge, the other
area is adjacent the knife edge. Specularly reflected images are a
function of the illumination of both areas and are symmetrical or
cancelling in their effect. These specular reflections form a uniform
background to the detector which can be ignored. The remaining image
changes are solely a function of the knife edge, which knife-edge images
can be utilized to determine the sense of required correction.
A further object of this invention is to disclose a preferred knife edge
and aperture combination for a detector utilizing the invention set forth
herein. According to this aspect of the invention, a detector with five
apertures is disclosed. The detector includes a central aperture having a
dimension of approximately two units by two units. Four peripheral
apertures are placed for the sensing of light with each aperture being on
a one by one basis. Knife edges are aligned to each aperture. The central
aperture includes four inwardly mounted knife edges about the periphery of
the two by two central aperture. The peripheral one by one apertures
include paired knife edges. These knife edges are each aligned parallel to
a knife edge of the central aperture and faced in an opposite direction.
An advantage of this aspect of the invention is that all the light sources
in the detector head are active. No light sources are located merely for
the emitting of light, which light is not utilized in a knife edge
testing.
A further advantage of the preferred detector head is that it is
particularly adapted to use in opposing detecting configurations. For
example, the detector head can be utilized for examination of the produced
images on a push-pull basis.
A further advantage of the preferred knife edge configuration of this
invention is that the eye positional information and the eye refractive
information are separate and non-interactive.
A further object of this invention is to disclose an apparatus and method
for locating an eye first for tests. This apparatus and process utilizes
the specialized detector head immediately described above. First, knife
edges are illuminated along co-linear borders of the central aperture and
the two peripheral apertures. The single knife edge of the central
aperture faces in a first direction and is generally of two units of
length. The paired knife edges of the peripheral aperture face in the
opposite direction and are each one unit of length. All knife edges are
examined together. The central two unit length of knife edge illuminates
the eye on one side of an axis. The paired and peripheral portions of the
knife edge illuminate the eye on the opposite side of the same axis. Since
the eye is illuminated from both sides of the optical axes sensitivity to
refractive error is eliminated. However, by using parallel spaced apart
co-linear borders, both positioning of the optical axis to the eye and
proper distancing of the eye can occur. There results a detector which is
particularly sensitive to the placement of the eye in front of it.
An advantage of the disclosed sequence for positioning the eye is that
prescriptive refractive effects are cancelled. As each of the knife edges
are opposed and of equal length, the resultant projection of light is not
sensitive to the particular refractive error possessed by the eye.
Instead, the detectors evenly illuminate all classes of eyes and permit
these eyes to be centered both transversely and towards and away from the
detector.
A further object of this invention is to disclose a particularly suitable
knife edge combination, which combination is sensitive to prescriptive
errors and insensitive to the positioning of the eye. According to this
aspect of the invention, portions of the apertures are illuminated at
their knife edges. Typically, a knife edge faced along the central
aperture is illuminated. Corresponding knife edges on the peripheral
apertures are illuminated. The corresponding knife edges face in the same
direction, are parallel, but are separated by the width of the central
aperture. There results a knife edge alignment all in the same direction.
An advantage of this aspect of the invention is that prescriptive
refractive effects only are picked up; effects due to the positioning of
the eye are in large measure ignored.
Yet a further object of this invention is to disclose a sequence of
examination of the eye. According to this aspect of the invention, the eye
is first positioned utilizing knife edges illuminated in opposite
directions along co-linear portions of the aperture. Thereafter, knife
edges aligned in the same direction along differing portions of the
aperture are illuminated. During this last knife edge measurement, the
optical prescription of the eye is determined.
An advantage of the sequence of examination of the eye using the preferred
detector of this invention is that two discrete measurements with the
preferred detector can occur. First, and using knife edge pairs, each
member of the pair being co-linear but opposed knife edges, the centroid
of the eye is determined. Thereafter, and using different knife edge
pairs, each member of the pair being parallel aligned spaced apart but
with knife edges faced in the same direction, refractive information is
determined. This information originates in the difference sensed at the
detector in the light level returned from the eye between the
interrogations of the second and different knife edge pairs. This
difference contains prescriptive information which is insensitive to and
separate from the positional information.
A further advantage of this invention is that the output of the detector
readily adapts itself to driving motors in corrective optics. Motors can
be activated to null errors and produce emmetropic refraction of the eye
through corrective optics.
An advantage of this apparatus and method is that the eye is first
positioned with precision with respect to the objective refractor. During
this position, all ambient optical errors in the eye are ignored.
Thereafter, and once the eye is properly measured for position, the
optical errors of the eye are determined. This is determined even though
minute movements of the eye being tested may naturally occur. Such minute
movements are ignored.
Other objects, features and advantages of this invention can be understood
after referring to the following specification and attached drawings in
which:
FIGS. 1A-1H are respective illustrations and projections of light rays
through the human eye from a knife edge and illustrating in schematic form
the shape of knife-edge images to be viewed;
FIG. 1A illustrates an eye with a "near-sighted" or myopic condition;
FIG. 1B is a schematic of the characteristic image produced by such eye;
FIG. 1C is a deflection schematic of a positive spherical lens producing
such a condition;
FIG. 1D is a schematic of an eye with a "far-sighted" or hyperopic
condition;
FIG. 1E is a schematic of the characteristic image produced by such an eye;
FIG. 1F is a vector schematic of a lens for producing such a condition;
FIG. 1G is a combined vector schematic, knife edge and characteristic image
schematic of an eye having astigmatism oriented along
45.degree./135.degree. axes; and
FIG. 1H is a combined vector schematic, knife edge and characteristic image
schematic of an eye having astigmatism oriented along 0.degree./90.degree.
axes;
FIG. 2 is a perspective view of a prior art image detector illustrating an
embodiment in which high noise levels are present;
FIG. 3 is an embodiment of a low level light detector according to to this
invention wherein an image of a light source is focused to dispersing
prism wedges and these wedges proportionally displace the resultant image
to discrete photosensitive surfaces;
FIG. 4A is a perspective view of a specialized cylindrical lens matrix
utilized with this invention, the cylindrical lens matrix having an
underlying schematic drawing for explaining the function of the lens;
FIG. 4B is a diagram of illustrated segments of the cylindrical lens, this
diagram illustrating respective segments of positive sphere, negative
sphere and two components of astigmatism along opposite axes;
FIG. 5 is a perspective illustration of a four element lens projected by a
spherical lens system from a light souce to an imaging plane;
FIG. 6 is a perspective similar to FIG. 5 with multiple lens segments being
illustrated;
FIG. 7 is a perspective view similar to FIG. 6 with three knife edges
disposed at an angle over the face of the lens element;
FIGS. 8A, 8B and 8C are respective representations of lens elements and
resultant images on detecting planes of a plurality of knife edges
disposed over the specialized lens element of my invention;
FIG. 9 is a perspective view of a low light level detector according to the
preferred emboodiment of this invention, special note being made that the
resultant matrix of photodiscrete segments is subject to coordinate
transformation to measure the applicable deflection;
FIG. 10A is a side elevation schematic of a knife edge test on the eye of a
myope illustrating the factors involved in the image produced in the eye
during knife edge testing;
FIG. 10B is an illustration of a knife edge with the cylindrical matrix of
this invention only schematically shown illustrating the preferred
enhancement of the image utilizing the cylindrical matrix and knife edge
in combination;
FIG. 11 is a preferred embodiment of the projection system of this
invention utilizing a projection lens, with weighted illumination surfaces
being present for both control of flare and background specular
reflection; and,
FIG. 12 is an alternate embodiment of the system of this invention
utilizing a lens matrix to both project light to the eye and receive light
from the eye.
FIG. 14A is an optical schematic illustrating with respect to the lens
element originally illustrated in FIG. 4A how adjacent optical elements
detour light to particular detector quadrants;
FIG. 14B is an illustration of detector quadrants fabricated from equal
cross cylinders, here shown as negative cylinders combining to be negative
lenses, which detector quadrants in turn may be divided into four portions
with each portion detouring the light impinging thereon to a particular
and discrete detector segment;
FIG. 14C is an illustration demonstrating how a multiplicity of elements
reduces the criticality of knife edge alignment with respect to the lens
segments;
FIG. 15A is a schematic illustration of knife edges cutting the lens
element of FIG. 13B with distribution of the light being shown over the
detector segments;
FIG. 15B is a schematic illustration of displacement in the X direction of
the image shown in FIG. 14A, and particularly useful for explaining the
weighting of the image with respect to the Figure;
FIG. 15C is an illustration similar to FIG. 14B with the displacement of
the image here occurring in the Y direction;
FIG. 16A is a schematic of the improved detector head of this invention
illustrating the two by two central aperture, and the four one by one
peripheral apertures with the respective alignment of the knife edges set
forth;
FIG. 16B is a plan view of the detector of FIG. 15A illustrating the
apertures and knife edges;
FIG. 16C is an illustration omitting a portion of the optical train and
illustrating how the detector of this invention is utilized to place an
eye in proper position for measurement, three detector states being
illustrated, the detector states being the eye too close for examination,
the eye too far away for examination, and the eye properly positioned for
examination;
FIG. 16D is an illustration similar to FIG. 15C with the knife edges being
illuminated in an interrogating sequence designed for determining the
refractive corrections necessary for the eye;
FIG. 16E is a perspective embodiment of an eye having imaged light sources
therein with the light sources relayed to a position in front of the
specialized optics with resultant projection to a detector illustrated;
FIG. 16F is an illustration of the detector plane illustrating how specular
reflection is eliminated as a consideration where interrogation by the
objective refractor occurs;
FIG. 16G is a perspective representation similar to FIG. 15E utilizing one
knife edge, which knife edge when incorrectly placed towards and away from
the detector screen produces error in the resultant signal;
FIG. 16H is a view of the detector of FIG. 15G;
FIG. 16J is a perspective view similar to FIG. 15E, 15G with the
utilization of three knife edges being illustrated;
FIG. 16K is a view of the detector surface of FIG. 15J illustrating the
detector correctly placed and focused;
FIG. 16L is a view of the detector of FIG. 15J showing a placement of the
detector in an incorrect alignment with the respective images on the
detector still registering the correct optical prescription;
FIG. 17A is a perspective view of the preferred "pebble plate" of this
invention wherein side by side negative lens surfaces are impressed on a
refractive element with FIG. 17B being a section along lines 17B-17B of
FIG. 17A;
FIGS. 18A-18D are respective schematic illustrations of a knife edge and
detector surface illustrating the so-called "push-pull" knife edge
interrogation of the eye; and,
FIG. 19 is a reproduction of portion of U.S. Pat. No. 4,070,115
incorporated in this patent by reference.
Referring to FIG. 1A, a human eye E having a cornea C and a lens L.sub.3 is
shown viewing a knife edge K. Knife edge K includes an illuminated portion
14, an edge portion 15 and a point 16 (shown by an X) immediately above
edge 15 from which observation of the illuminated portion of the pupil of
the eye is made. The knife edge is typically placed at an optically
infinite distance from the eye by the expedient of collimating optics (not
shown). Alternately, projection of the knife edge may occur to any known
optical distance.
It will be appreciated that although the side 14 of knife edge K is
illuminated or luminous, this illumination terminates along edge 15. Thus
no light can be incident through lens L.sub.e onto the rear retina R of
the eye from points above edge 15.
Hereinafter, when the term "knife edge" is utilized, it will be understood
that three discrete functions are referred to.
First, there is a light source. Secondly, the light source terminates along
a boundary defining a straight line or knife edge terminator. Thirdly, the
knife edge terminator defines immediately thereover an optical path to a
detector element.
The illuminated surface below knife edge 15 will produce illumination on
the retina R. FIG. 1A assumes that eye E is afflicted with myopia. The
image plane 18 of knife edge K through lens L.sub.e will be in front of
the plane of the retina of the eye. A point along this image will form an
illuminated oval shape 20 on the retinal surface of the eye.
Placing an observer at point 16 and having the observer peer just over the
top of the knife edge, will cause light to be collected from an oval area
21 on the retina of the eye.
It will be seen that the area of illumination 20 and the area 21 overlap.
This area of overlap is indentified by the numeral 24. Rays from area 24
may be traced back to the portion of the lens L.sub.e that will appear to
an observer at 16 to be illuminated. Specifically, the light will appear
to be apparently from the bottom of lens L.sub.e.
Referring to FIG. 1B, an image of how lens L.sub.e will appear is drawn.
This image of lens L.sub.e shows the illuminated portion caused by light
returning from sector 24 within the circle of possible returning light 20
from point 16 above knife edge 15.
It is important to note that this view is a characteristic of the knife
edge. It indicates that lens L.sub.e is excessively positive and the eye E
has myopia.
Immediately above FIG. 1B is a schematic diagram 1C. Schematic diagram 1C
illustrates in vector format the excessive positive power of lens L.sub.e
and/or C in FIG. 1A.
Turning to FIGS. 1D, 1E and 1F, farsightedness or hypermetropia is
illustrated. Knife edge K with illuminated portion 14 stopping at
terminator 15 projects light to the retina R of an eye through a cornea C
and a lens L.sub.e. As previously shown, the focal plane 18' is here
behind the retina R. Projection of the knife edge to optical infinity is
assumed and not shown.
Taking projected light from the eye, an oval of illumination 23 from one
point of source area 14 will be shown on the retina.
Viewing from a point 16 above the terminator 15 of knife edge K, will allow
the person to collect light from oval area 25. The viewer will see light
returning from an illuminated portion 23 of area 25.
FIG. 1E is a view of lens L.sub.e and how lens L.sub.e appears to be
apparently illuminated. Referring next to FIG. 1F, a schematic
representation of the negative deflection of the lens L.sub.e or C is
illustrated in vector format.
Referring to FIG. 1G, only a schematic representation of a lens L, a knife
edge K and a retina R is illustrated. Lens L is illustrated in the
schematic vector format similar to FIGS. 1C and 1F. In FIG. 1G, lens L is
a cross-cylinder lens having power obliquely aligned to edge 15. This lens
has astigmatism along 45.degree.-135.degree. meridians. Lens L has a
positive power along meridian 30 and a negative power along meridian 31.
It will be noted that the respective meridians 30 and 31 are at preferred
45.degree. angles to edge 15 of knife edge K. Noting the meridians 30, 31,
the deflecting power in the vicinity of these meridians can be shown. For
example, and commencing clockwise from the right, at the three o'clock
position 32, light will be deflected downwardly. At the six o'clock
position 33, the light will be deflected to the right. At the nine o'clock
position 34, light will be deflected upwardly. Finally, at the 12 o'clock
position 35, light will be deflected to the left.
Analyzing the action of such a lens in conjunction with a knife edge K can
be quickly understood. Light on one lateral half of the lens passing above
the knife edge K will be deflected to the examined eye where it can be
viewed. Light on the opposite segment of the lens L will be deflected into
the knife edge K where it may not be viewed. Consequently, the image of
the retina R will have a terminator T at right angles to the edge 15 of
knife edge K. One segment of the lens L will be illuminated. The
illuminated portion of the lens L is shown at 36. As previously set forth,
the terminator will not be sharp but rather have a blurred edge. The term
"terminator" should be understood in this manner as it is used hereafter.
The case of a lens L having 0.degree.-90.degree. astigmatism can be
understood with reference to FIG. 1H. Specifically, in FIG. 1H, positive
cylinder is placed along meridian 40 which is normal to edge 15 of knife
edge K. Negative cylinder is placed along meridian 41 which is parallel to
edge 15 of knife edge K. The imaged at the retina R includes an
illuminated portion 46 with a terminator T that is parallel to knife edge
K.
Referring back to FIGS. 1B and 1E, it can be seen that the terminators T
are in substantially the same horizontal direction as the knife edge. This
being the case, it will immediately be realized that astigmatism with axes
either parallel to or normal to the edge 15 of knife edge K will appear
the same as spherical components. Consequently, and when utilizing only
one knife edge, only one component of astigmatism can be measured. The
measurements of components of astigmatism normal to or parallel to the
knife edge cannot be made. We can only say that the information produced
from such a measurement is an indication of a "meridiodinal" power. This
measurement can be shown to make sense and be collated to knife edges K
having alignments normal to the edge 15. For example, the reader is
invited to review my U.S. Pat. No. 4,070,115, issued Jan. 24, 1978,
wherein knife edges of differing angles are utilized for the testing of
common lenses.
Having set forth the characteristic light patterns that may be produced on
the retina of the human eye with knife-edge testing and directly observed,
reference can now be made to the problems encountered in using knife-edge
images for remote detection.
Specifically, and where any kind of an image is projected onto the retina
of the human eye, the intensity of that image must necessarily be low.
Where the image is in the visible spectrum, the glare problems on the
retina are obvious. Where the image is either visible or infrared, the
images must be of a sufficiently low intensity so that the eye is not
burned. Remembering that the rays are in effect focused by the lens L on
the retina R of the eye, one can immediately understand that the projected
light must simply be of a low light level.
When the optics of the eye are utilized to view the illuminated retina, as
in the classical case of conventional objective refraction, only a faint
image will be visible. This faint image must be remotely detected if an
objective refractor is to be automated. Moreover, the edge or "terminator"
of the image will be far from sharp. The overall image must then be
located on "weighted" basis. The problems associated with the projection
of such faint images will now be discussed.
Referring to the prior art apparatus illustrated in FIG. 2, a low level
light detector is illustrated. Light source S movable about an XY plane P
is imaged through a lens L to a photosensitive surface D. Photosensitive
surface D typically includes a single and continuous photosensitive
surface, either of the photoconductive or photoresistive variety.
Typically, such surfaces have a "common" first connection 50 and are
monitored by evenly spaced electrodes 51, 52, 53, 54.
Terminals 51-54 are symmetrically spaced about the periphery of
photosensitive surface D. Each of the terminals is typically connected by
leads to the input of an amplifier 55. Amplifier 55 is of conventional
design and amplifies the difference in electrical signal to produce an
output proportional to X and Y at 56.
When the embodiment of FIG. 2 is applied to a source S of extremely low
light level, a difficulty arises. Typically, all the terminals 51-54 are
connected to a single continuous and conductive layer of the
photosensitive material. All these terminals have substantial conductivity
between them. This relatively low resistance and high conductivity must be
sensed at amplifier 55 in order to generate a signal at terminals X and Y
which is proportional to the displacement of image of source S.
Where a high conductivity and hence low resistance is present across
electrical terminals, the intervening random motion of electrons creates
noise. This noise when received at amplifier 55 and suitably amplified
along with the outputs for X and Y results in a low signal to noise ratio.
Signal is rapidly lost as the intensity of source S diminishes. For
example, where source S images at S' on detector D, the predominant
signals at terminals 51, 52 could well be lost in the resultant noise.
The problem therefore becomes one of designing complimentary optics and
photodetectors which suppress the tendency of the detector shown in FIG. 2
to produce resultant noise at low image intensity levels.
I will disclose two embodiments. The first of these embodiments will be
illustrated with respect to FIG. 3 and illustrates a first conceived and
less preferred way of acquiring low light level sensitivity.
Thereafter, and with respect to the remaining illustrations, I will
illustrate a preferred knife edge and lens array. This preferred knife
edge and lens array illustrates not only a new and useful lens, but
additionally discloses the new light detector of my invention.
Referring to FIG. 3, and in understanding my first invention, I will first
set forth the configuration of a plate W. After discussing my plate W, I
will thereafter set forth the remaining optics and operation of the
system.
Plate W consists of a matrix of optical wedges. This matrix has a first and
upper side 60 and a second and lower side 62.
For the convenience of the understanding of the reader, lens W here is
shown of composite manufacture. A first roof prism 64 is positioned in the
middle of lens W.
The processing of light received uniformly over the top of prism 64 is easy
to understand. A first portion of the light will be directed to detector
segments D.sub.1 and D.sub.2. A second portion of the light incident upon
prism 64 will be deflected to detectors D.sub.3, D.sub.4.
Turning now to an outboard prism 65, it can be seen that this prism 65 only
includes one facet. This facet will cause light incident uniformly over
the top of prism 65 to be deflected only to segments D.sub.1, D.sub.2. No
portion of prism 65 is disposed to def | | |
