Improvements in Ophthalmometers.
Year: 1899

page_text: Date of Application, 4th Aug., 1899-Accepted, 16th Sept., 1899
COMPLETE SPECIFICATION.
Improvements in Ophthalmometers.
We, CHARLES CHAMBERS INSKEEP, and JOHN EDGERLY CHAMBERS, both of 146,
State Street, Chicago, in the County of Cook, and State of Illinois, United States
of America, Manufacturing Opticians, 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: -
Our invention relates to ophthalmometers, or instruments for measuring the
differences in the curvature of the cornea for the correction of corneal astig-
matism, which as is well known, results from said differences of curvature, where-
by the rays of light transmitted through the cornea are refracted to different
foci, rendering a clear image of the object of vision impossible. The general
principle on which the measurement of the said, differences of curvature is based
is the observation of images of illuminated objects reflected from the corneal
surface in different meridians viewed through a telescope with means for quanti-
tatively determining the relative departure of said images from their normal
position with reference to a given meridian. The illuminated objects are known
in the art as mires,"
," and the unit of the differential scale of refractive power
is the "diopter."
Our improvements consists in certain new and useful modifications in instru-
ments of this class whereby we are enabled to use mires which are constantly
fixed relatively to the rotating disc which supports them instead of movable
thereon as heretofore; in the employment of mires which are self luminous, or
illuminating by transmitted instead of reflected light; in the employment of mires
showing bands at right angles instead of areas broken up into steps, for promoting
the approximate estimation of refractive differences in diopters; in the use of a
double prism in the optical axis made movable and adjustable therein, whereby
the optical images of the mires can be approximated or separated by said move-
ment and adjustment; by the employment of a rotary scale graduated in any
convenient unit of measurement, as for example in diopters and fractions thereof,
for indicating accurately the relative approximations and separations of said
optical images dependent on the relative position of said prism, and by other
minor details of construction hereinafter specified.
In the drawings forming a part of this specification
Figure 1 is a vertical section of that portion of the instrument necessary to
exhibit the improvements above referred to.
Fig. 2 is a side elevation of a portion of the optical tube of the telescope, show-
ing the arrangement of the rotary scale attached thereto, and its fixed index.
Fig. 3 is a front elevation of the parts shown in Fig. 2 with the tubes in
section:
>
Fig. 4 is a face view of the graduated circular scale n, with tubes in section.
Fig. 5 is a view of the insulation rings through which current is sent to the
lights borne on the rotary disc.

page_text: mires and transmitted therethrough, as shown in the drawings. In the form
illustrated in Figs. 1 and 7, 12, 12 are hemispherical shells containing the
illuminants, which are preferably small electric light bulbs v, v, connected by
conductor wires through posts 14, 14 with a suitable source of electrical energy,
the connection being kept unbroken during the rotation of the disc by insulated
rings 8, 8 with which contact is made by springs 17, 17, connected with the
posts 14, 14, by the wires 18, 18. The insulated rings are in electrical connec-
tion with the source of energy by means of conductor wires 15, which are concealed
within the hollow standard or stem t. The mires are made of translucent or
semitransparent material, such as ground glass, milky, opalescent or cryolite
glass, horn, &c., said mires being inserted in the disc in front of the illuminated
shells 12, 12.
In order to be able to utilize mires fixed in position instead of employing those
movable and adjustable in position as heretofore we resort to the means now
about to be described.
f is the inner or sliding tube of the telescope. This tube carries the double or
birefringent prism h, whose refractive plane is in the plane of the mires. The
said prism may be made of any suitable refractive and transparent material,
either in one piece or in two pieces and is fixed in its position in the inner tube f
so as to slide with it. Said tube has attached to it a means for moving the
same, preferably a rack o, projecting through a slit m in the outer tube d, and
engaged by a pinion p, by which the inner tube can be traversed back and forth
in the said outer tube. The pinion p is sustained by a pinion block r secured to
the outer tube d by suitable fastenings. On the axis of the pinion p is a milled
head for turning the said pinion, and a disc y, preferably in duplicate, graduated
on its outer face on a scale of any convenient unit, as millimeters, and on its
edge so as to be read from the front to indicate diopters and fractions thereof of
refraction corresponding to the apparent separation of the visual images of the
mires, the effect of moving the prisms longitudinally back and forth as described
being to approximate or separate the concurrent pencils of rays forming the
said visual images in the eye piece of the telescope, in the plane of the mires.
z is the pointer, arranged in duplicate, so as to point to both dials and indicate
the graduations on both the edges and the faces of the same.
instrument
of the
A longitudinal scale of a suitable unit of graduation may also be placed on
the outer tube, with a pointer attached to the moving rack piece o, or vice versa.
In Figs. 8 and 9 are illustrated the improved standard in prefered use with
this instrument. 20 is the base
only partially
shown. 21 is the slide, having a longitudinal motion on said base, with
suitable means for operating the same, as screw 31. Said slide is open at 22 to
permit the conductor wires ordinarily used in connection with the electric
illuminating apparatus to pass down within the hollow standard to the base,
slotted beneath the slide for that purpose. 23 is the tubular lower portion of
the standard, securely fixed in the slide 21. Said tubular part 23 has a thickening
or inward enlargement at 24 which bears at one side a key or spline 25, for a
purpose presently to be explained. 26 is a hollow screw, telescoping within the
tubular enlargement 24 and loosely traversing therein, longitudinally grooved
at 27, which groove or channel is engaged by the spline 25, whereby the screw is
prevented from rotating, while free to traverse up and down. 28 is a sleeve
nut, internally screw-threaded at 29 to engage with the threads of the screw 26.
Said nut has a knurled ring 30 taking a bearing on the top of tube 23 and pro-
jecting outwards beyond the same to afford a means for turning the screw by
hand. Said sleeve nut has a thickened portion g at top loosely fitting and support-
ing the screw. There is a stop screw 32 in the screw to limit the vertical play
thereof so that the screw shall not be drawn out of engagement with the key
or spline 25. There is an annular channel 33 in the exterior surface of the
sleeve nut, into which fits the screw 34, for the purpose of preventing the sleeve
nut from climbing out of its place when rotated. Within the upper end of the

page_text: The chief advantage of employing fixed, self illuminating mires are, (1) that
the images thereof are always thrown on the cornea at a fixed angle, thereby
eliminating one source of error, as when the distance between the mires has to
be constantly adjusted and readjusted for each variation of corneal curvature.
(2) The luminous mires give a much clearer and brighter image as reflected from
the cornea to the eye of the observer than when white mires illuminated by mere
reflected light are used, one reflection being saved. (3) The readings being made
by the hand of the operator by rack and pinion adjustment, on a single scale,
are much more convenient than where a plurality of sliding scales are employed,
and the use of our improved mires gives the maximum of accuracy, inasmuch as
nothing is left to estimation, or guess work, but the exact difference in the
separation of the images is mechanically recorded, up to the limits of the powers
of observation.
Having now particularly described and ascertained the nature of our said
invention and in what manner the same is to be performed, we declare that what
we claim is: -
1. In an ophthalmometer, the combination of a telescope, a pair of mires
fixed relatively to the axis of said telescope, and means within the telescope for
causing approximation and separation of the images of said mires reflected from
the corneal surface under observation into said telescope, substantially as
specified.
2. In an ophthalmometer, a telescope, mires external to said telescope, and
means for causing said mires to shine by non-reflected light, substantially as
specified.
3. In an ophthalmometer, a concave disc, a pair of translucent mires borne
thereon at fixed distances from the center thereof on a diametral line, and means
for illuminating said mires by light transmitted therethrough, substantially as
specified.
4. In an ophthalmometer, a telescope, means for causing luminous images to
be reflected from the corneal surface under observation into said tele-
scope, a double or birefringent prism located within said telescope, and
means for moving said prism longitudinally backwards and forwards within the
telescope, whereby the said luminous images are caused to visually approximate
and separate, substantially as specified.
5. In an ophthalmometer, a telescope consisting of an outer tube provided with
an object lens and an eyepiece, an inner tube, a double or birefringent prism
borne in said inner tube, means for moving said inner tube and prism backwards
and forwards within said outer tube, and means for causing luminous images to
be reflected from the corneal surface under observation into said telescope, sub-
stantially as specified.
G. In an ophthalmometer, a telescope, a disc bearing luminous mires, a double
or birefringent prism within said telescope in the path of the optical rays, means
for moving said prism longitudinally backwards and forwards within said tele-
scope, and means for indicating the relative position of said prism in graduations,
substantially as described.
7. In an ophthalmometer, a telescope having a tube and customary lenses, a
disc bearing luminous mires, an inner tube movable within said telescope tube,
a double or birefringent prism borne in said inner tube, a rack and pinion for
moving said inner tube and said prism longitudinally in said telescope tube, a
rotary scale borne on the shaft of said pinion for indicating the position of said
prism, and a fixed pointer for said scale substantially as specified.
8. In an ophthalmometer, a telescope, a concave disc fixed thereon, a support-
ing sleeve in which said telescope may be rotated, luminous mires fixed on said
dise on a diametral line and at equal distances from the axis of rotation, and a
birefringent prism within said telescope with means for moving said prism back
and forth, whereby the visual images of the mires reflected from the corneal surface
under observation may be approximated or separated, substantially as specified.

page_text: 21. In ophthalmometers, a pair of mires each having a luminous perimeter
which is an incomplete circle, a luminous horizontal band, terminating at the
incomplete side of the circle, and each having a luminous band at right angles
to the diametral band, one above and one below the horizontal line, substantially
as shown and described.
22. In ophthalmometers, a pair of mires located on a blackened disc, each having
a luminous perimeter which is an incomplete circle, a luminous horizontal
diametral band terminating at the incomplete side of the circle, and a luminous
band at right angles to the said diametral band, one above and one below the hori-
zontal line, located at a distance of one fourth part of the diameter from the inner
ends of said diametral bands respectively, substantially as shown and described.
Dated this 2nd day of Angust 1800
W. P. THOMPSON & Co.,
Of 6, Lord Street, Liverpool, Agents for the Applicants.