Improvements 111 Optometers.
Year: 1887

page_text: Improvements 111 Optometers.
I LEOPOLD ENGELHARD of 54 Maner Strasse Berlin in the Empire of Germany
Doctor of Medicine, 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 improvements in Optometers or instruments for ascer-
taining the limits of distinct vision in different individuals for the purpose of selecting
lenses of the proper degree of refraction to correct defective vision. By means of
this improved instrument the tedious and unreliable process of testing the eyesight by
trying the effect of a series of glasses or lenses in order to find the form of lense
required for remedying defects of vision involving the use of spectacles or eye-glasses
is enabled to be dispensed with and medical men or oculists and opticians are enabled
to ascertain the extent and nature of the defect independently of the statements of the
patient and to check or verify the accuracy of their own diagnosis. These results are
obtained by means of the improved instrument or apparatus hereinafter described.
And in order that my said Invention may be fully understood I shall now proceed
more particularly to describe the same and for that purpose shall refer to the several
figures on the annexed sheets of drawings the same letters of reference indicating
corresponding parts in all the figures.
Figures 1 and 2 of the accompanying drawings represent respectively a front and
side elevation (the latter partly in section,) of one part of the improved instrument
or apparatus arranged according to this Invention-The eye of the patient or person
whose sight is to be tested is supported by a funnel shaped eye piece c which is
attached to a plate d capable of vertical adjustment by means of a sleeve or collar e
sliding telescopically on a pillar or support being fixed in any desired position
thereon according to the height of the patient by a catch g engaging with ratchet
teeth on the pillar f.
The apparatus is provided with two discs a and al arranged one behind the other
the front disc a carrying concave and convex cylindrical lenses of different foci the
hinder disc a' being provided with a corresponding number of spherical lenses two

page_text: plain glasses being also provided in each disc-These discs are capable of turning on
an axis so that any lense can be fixed by a locking device in front of the eye of
the patient.
The axis on which the discs revolve is carried by an arm h
(figs. 1 and 4) capable of turning on a fixed tube p fig. 2 and of being fixed by
means of a spring catch (Figure 1 and 4) engaging with teeth on the periphery of
a disc or plate on the tube p fig. 3 in any desired meridian corresponding with
divisions of a graduated scale marked on the plate (figure 3). The apparatus is
provided with a bar or rail which carries a sliding support connected with a part
of the apparatus hereinafter described and is graduated or divided in such a manner
that each concave lense in the disc corresponds with one of the graduations on the
said bar b.
A plane mirror about three feet square, not shewn on the drawing, is arranged in
front of the funnel or eye piece of the apparatus at a distance of nine feet.
Inside the tube p there is a set of lenses for the purpose of bringing the far point
of a normal eye to a point from 32 to 40 centimetres distant from the cornea-This
point corresponds with the zero mark on the bar corresponding with the plane
glasses in the discs a a'. In certain cases as hereinafter explained a prism p
figures 1 and 1 with a frame p2 is placed in the tube p being capable of being turned
or adjusted at any desired angle by means of a pinion » gearing with teeth von the
frame p².
P
It is evident that by duplicating the parts the test can be applied to both eyes at
once. Figures 2 and 2b show the arrangement for shifting the tubes p in such double
apparatus (binocular optometer) for the purpose of adjusting the tubes to the inter
ocular distance or distance between the pupils of the patient the said adjustment being
effected by turning a screw q whereby the left hand tube the support of which is
constructed to slide upon a bar connected to the right hand tube can be readily
shifted to the required position.
The second part of the instrument provided with a mirror chamber is illustrated on
sheet 2 figure 6 showing it in plan and Figures 7 and 8 in sections taken along the
lines and y y respectively-This part of the apparatus is placed on a pivot z of
the sliding support hereinbefore referred to-The eye of the patient is placed in front
of chamber m being illuminated by the light proceeding through a tube 2 branching
off at an angle of 45 degrees from the conducting tube r the light being caused to
fall on and be reflected from a mirror s-The rays of light proceed through a
contracted tube to the conducting tuber at the end of which they are received by
a three and a half inch achromatic lense and directed to the chamber m-
lense can be taken out when required according as the plane mirror s or the concave
mirrors or 2 (figure 9) are placed in position-In the chamber m a plane glass w is
arranged at an angle of Forty five degrees with the axis of the tube n the rays passing
through the reflector and being directed to the eye.
-The
A tube n in direct communication with the chamber m is arranged at right angles
to the conducting tube r. The rays proceeding from the eye under examination and
reflected by the glass pass through a convergent lense of 2 or 4 inches focus at o
and an 8 inch ocular lense o' to the eye of the observer.
The tube n can be drawn out or lengthened as required-The patient looks with the
other eye through a tube t (likewise adjustable in a horizontal plane being pivoted
on the support k as shewn in figure 11) at a distant object such as a white card with
blue rings thus relaxing the accommodation or ciliary muscle of the eye that is being
examined.
Before proceeding with the correction of the distorted refraction it is necessary in
the first place to ascertain the acuteness of vision-This is accomplished according to
Snellen's method by the aid of test letters placed at the side of the patient and viewed
in the aforesaid plane mirror reflecting the image of the letters at the apparent distance
of 18 feet and when the combination of lenses is used by placing the letters at the
extreme end of the bar-the rays being parallel in both cases-When test letters
which would be distinguished by a normal eye at a distance of twenty feet cannot be
distinguished by the patient except at a distance of thirty or forty feet the acuteness

page_text: of vision is equal to 38-28-28 and so on. These indications may however be
produced by abnormal refraction disturbances of the retina etc. or other organic or
functional injury or defect. In order to decide this question concave or convex lenses
of 0.75 to 1.25 d are placed alternately before the eye and according as the one or the
other produces an improvement the case is known to be myopia or hypermetropia.
The Number of the lense which gives the most distinct image shows the extent of the
defect in the refraction.
In case neither concave nor convex lenses improve the sight the eye should be
examined for astigmatism and this is not discovered the distortion must be attributed
to some other defect.
The test letters on the bar are preportioned according to Snellens principle
correspondingly to the distance in order to accurately ascertain the degree of acuteness
of vision being arranged at Snellens angle of vision of 5 feet and the diameter of the
letters correspondingly adjusted to five millimeters. In order to ascertain the
acuteness of vision according to Snellens method when the smallest letters of five
millimeters diameter are read say V the next letters being half as large again when
these are the smallest that can be read then and so on to
The lenses are
employed solely for ascertaining the acuteness of vision and the far point and are
invariably removed in examination for the near point.
20
20
20
40
20
200
The far point and the acuteness can thus be ascertained either by means of lenses
with test letters on the bar or by means of the plane mirror (after removing the
lenses). In the latter case the letters are seen in the mirror at an apparent distance
of 18 feet. The two methods may be combined in order to ensure correctness of the
diagnosis by comparison of the results thus obtaining a degree of accuracy seldom
attained in complicated cases by the methods hitherto employed.
The angular movement of the arm / carrying the revolving dises a a¹ hereinbefore
described and enabling the lenses in the dises to be turned upon the axis of vision
serves in cases of astigmatism to find the proper adjustment or combination of the
cylindrical and spherical glasses required to make the necessary correction or compen-
sation. These glasses are known when the discs are adjusted to suit the patient by
reading off the indications on the graduated scale on the back of the plate on the
tube p fig. 3. This scale consisting of a circle divided into 360 degrees begins at the
left hand end of the horizontal diameter of the circle and going over the lower
semicircular surface towards the right to the opposite end of the horizontal diameter
of this half circle ending here at 180° and going thence from right to left along the
half circle on the upper semicircular surface ending with 180 at the opposite end of
the diameter thus the lower half circle of the scale counts or is read from left to right
whilst the upper half circle of the scale counts from right to left and has the zero
point on the opposite side of the diameter. This division is for determining the
achromatic meridian.
The extent of the defect in the refraction is ascertained by shifting the test letters
on the bar towards or away from the patient until they are clearly seen and noting
the No. corresponding to this position on the scale on the bar. In order to check or
verify the result thus obtained the test letters are placed at the extreme outer end of
the bar, and the disc a is rotated until the concave lense corresponding to the No.
indicated by the scale on the bar is brought into position the lenses in the tube
being removed and the results are compared.
P
The funnel shaped eye piece which serves as a support for the eye of the patient is
provided with a slot for the reception of a piece of colored glass in order to
facilitate the examination for double vision in cases of strabism. To measure the
angle of distortion the adjustable prism p' (hereinbefore described with refererence to
figures 1 and 1 is used being first placed at zero and then turned or inclined until
it arrives at the position where the two images are caused to coincide. This exami-
nation is applicable in cases where the remedy is to be found in the use of prisms as
well as in cases where strabotoney is resorted to and serves to ascertain whether the
operation should be performed on one or on both of the eyes of the patient.

page_text: When by means of the examination hereinbefore described the patient has been
provided with glasses of suitable form for correcting the defects of his vision a third
test of the correctness of the indications is applied by means of the apparatus as next
hereinafter explained.
The eye
is placed before the ocular orifice o" of the metal case m (figs. 6 and 7) in
a line with the axis of light and the optometer is adjusted according to the degree of
false refraction such as astigmatism etcetra in the patient. The operator then
arranges the tube n and lenses o o¹ according to the requirements of the case until he
sees the reflection of the retina he then uses an 8 inch convex lense at the end of the
tube n which is drawn out as far as possible whilst the patient looks with the
disengaged eye through the tubet fig. 11 at the card with blue marks. The entire
retina is then visible with the papilla in the centre. In order to obtain the highest
magnifying power a 4 inch convex lense is used for the opening in the chamber of
the examining tube n with the 2 inch examining tube in position and drawn out to
the full length. This proves the perfection of the correction for the far point and the
correction can be verified in like manner for the near point by suitably adjusting the
instrument. The methods of examination with the chamber, the mirror and lenses
can be employed with the monocular as well as with the binocular optometer according
to the object of the examination. These comparative methods are necessary for obtaining
an absolutely certain confirmation of a diagnosis unattainable by the methods
heretofore employed.
Having now particularly described and ascertained the nature of this Invention and
in what manner the same is to be performed I declare that what I claim is:
First An apparatus or instrument for examining or testing the eyes, consisting
of a tube (p) provided with lenses (l, fig. 2) or with a prism (p³ fig. 1b) two lense
carrying discs (a, a¹) revolving so as to present the lenses into turn before the said
tube on a support capable of turning on the axis (¹) of the said tube and a support
sliding on a bar and carrying test letters substantially as herein before described
with reference to the accompanying Drawings.
Second-The instrument provided with a chamber m and consisting of a con-
ducting tube (r) which receives light admitted through a light tube (2) inclined at
an angle of 45 degrees, the said light being reflected into the chamber by a mirror at
the end of the said conducting tube so as to illuminate the eye of the patient and
transmit an image thereof to the eye of the operator by means of a reflector as and
for the purpose substantially as hereinbefore described with reference to the accom-
panying Drawings.