Improvements in Optometers or Instruments Designed for Use by Oculists in Testing Eyesight for the Purpose of Fitting Glasses Accurately thereto, and for other Purposes.
Year: 1886

page_text: Date of Application, 10th Nov., 1886.
Specification Accepted, 25th Jan., 1887.
[Communicated from abroad by HOWARD CULBERTSON, of Zonesville, in the County
of Muskingum and State of Ohio, United States of America, Inventor.]
Improvements in Optometers or Instruments Designed for Use by
Oculists in Testing Eyesight for the Purpose of Fitting Glasses
Accurately thereto, and for other Purposes.
I, WILLIAM PHILLIPS THOMPSON of the Agency for Foreign Patent Solicitors
6, Lord Street Liverpool in the County of Lancaster, and 323, High Holborn in the
County of Middlesex, Civil Engineer, do hereby declare the nature of this invention
and in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement :-
This invention relates to instruments for measuring the abnormal defects of the eye
for the purpose of fitting glasses accurately thereto, and also for oculists' uses; and it
consists in an instrument composed of a suitable frame or head-piece, at or near the centre
of which is fitted a rotating prism holder or carrier, in which holder is fitted a single
or double faced prism or a pair of prisms, so arranged that the eye of a person looking
through the instrument shall receive rays of light through both prisms or prism-faces,
where two prisms are used, or a double faced single prism, or through the prism and
the adjacent space or plane glass, where a single one faced prism is used, and by this
means the eye shall receive upon the retina two images of an object, and thereby the
condition of the eye as to its refractive power, whether normal, myopic, or hyper-
metropic, shall be ascertained by the relative positions of the said images, as herein-
after set forth; and in connection with the above-named rotating prism or prisms a
suitable circle degree scale, to determine the meridian or angular position of the
myopic or hypermetropic portion or portions of the eye when abnormal; also, a lens
holder for applying an adjusting lens on the instrument, and an object circle on a
suitable screen for use in forming the test images with the eye all as hereinafter
specified.
Figure 1 is a side elevation of the instrument. Figure 2 is an edge view of the
screen. Figure 3 is a front elevation of Figure 1 and at right angles to same.
Figure 4 is a face view of the screen showing the natural form of the image thereon.
Figure 5 is a similar view showing the apparent double images. Figure 6 is a cross
section of Figure 3 in line and enlarged. Figure 7, is a series of diagrams

page_text: illustrating the refractive action of the prism in looking through the instrument.
Figures 8, 9, and 10 are views of different forms of prisms.
A, shows a disk or head, preferably of circular form, supported by a tripod, bracket,
or other supporting device, F, in such a manner if desired, that it can be raised or
lowered. This disk or head is marked off on one side with a scale of degrees occupy-
ing a half-circle or more, as shown at a Figure 3.
B, is a circular holder of metal, or other suitable material, set accurately into the
frame A, and capable of rotation therein a part or a whole of a circle. It is provided
with a handle, by which it is turned, the handle also serving as a pointer moving
over the scale of degrees before described.
C is a small prism set centrally in the holder and turning with it. The prism has
two faces with the bases meeting, as shown in Figure 8 or the apices meeting as
shown in Figure 9, or a single faced prism may be used, as in Figure 10, the angle at
the acute edge being sufficiently increased to show a complete image distinct from the
image seen outside of the prism.
Preferably, however, the form shown in Figure 9, is used. It may be made of one
solid piece of glass, or of two pieces placed in juxtaposition, as the same result will be
produced in either case.
D, is a half-circular holder attached to the frame A in position to receive trial
lenses in front of the prism.
E, is a separate screen, on which is painted or otherwise made a circular or equiva-
lent form of image, c which is distinct in color from the background of the screen, and
has a clearly defined outline.
When properly constructed, the angle of the prism or prisms is such and the
diameter of the object circle c and its distance from the prism are so calculated that
there are formed upon the retina of the normal eye, two images of the object circle
tangent to each other or touching at their adjacent edges. With the prism or prism's
arranged with the apices toward each other, as shown in Figure 9, to the myopic eye,
the two images will appear to overlap to a greater or less extent, according to the
degree of myopia characteristic of the eye, and to the hypermetropic eye the images
will appear separated from each other more or less, according to the degree of
hypermetropia possessed by the eye. On the other hand, with the prism or prisms
arranged with the bases toward each other, as shown in Figure 8, to the myopic
eye the images appear to be separated, and to the hypermetropic eye the images
appear to overlap Diagrams as follows are shown in Figure 7. No. 1 illustrates
the action of the prisms, as in Figure 8. to the normal eye, the dotted lines
showing the images tangent to each other, No. 2 shows the images separated, as in a
certain degree of myopia, and No. 3. shows the images overlapped, as in a certain
degree of hypermetropia.
:
The single-faced lens, Figure 10, may be used with its apex in the centre line of
sight acting as the double prism in Figure 9, or with its base in the centre line of
sight acting, as the double faced prism in Figure 8.
The instrument is used by the person placing his eye to the tube behind the prism
in a central or proper position, and looking through the prism at the object circle,
which is adjusted to the proper distance away from the lens and directly before it.
The images of the object circle will at once indicate the degree of myopia or hyper-
inetropia, if any, belonging to the eye tested. By rotating the prism one image will
travel around the other, and the eye can be tested in each meridian, and the presence
and degree of astigmatism can be ascertained. Having ascertained that the
eye has
a curvature that is abnormal, a convex or concave lens is placed in the holder D, that
will make the double images on the screen touch in all the points of circuit, thus
ascertaining the degree of ammetropia and the lens necessary for its correction.
Having now particularly described and ascertained the nature of the said invention,
and in what manner the same is to be performed, as communicated to me by my
foreign correspondent, I declare that what I claim is :-.
1. The combination of a prism holder a prism or prisms arranged in the holder with

page_text: a terminal edge of the prismatic face or faces in the central line of sight, through the
said prism or prisms, and an object circle arranged concentrically in the line of sight,
substantially as herein specified, and for the purpose set forth.
2. The combination of a sustaining disk or frame, a prism holder adapted to be
rotated on its axis in the said disk or frame, a prism or prisms arranged in the holder
with a terminal edge of the prismatic face or faces in the central line of sight through
the said prism or prisms coincident with the axis of the holder, and an object circle
arranged concentrically in the central line of sight, and with the axis of the holder
substantially as and for the purpose herein set forth.
3. The combination of a supporting disk or frame provided with the degree
marks upon its face, a prism holder adapted to be rotated on its axis in the said disk
or frame, a prism or prisms arranged in the holder with a terminal edge of the
prismatic face or faces in the central line of sight through the said prism or prisms
coincident with the axis of the holder, and an object circle arranged concentrically
in the central line of sight and with the axis of the holder, substantially as and for the
purpose herein set forth.
4. The combination of a supporting frame or disk, a prism-holder adapted to be
rotated on its axis in the said disk or frame, a prism or prisms arranged in the holder
with a terminal edge of the prismatic face or faces in the central line of sight through
the said prism or prisms coincident with the axis of the holder, and a lens holder
attached to the disk or frame in front of the prism or prisms, and with its axis coinci-
dent with the axis of the prisin-holder, substantially as and for the purpose herein set
forth.
WM. P. THOMPSON & Co.,
Agents for the Applicant.