HOW THE SKI-OPTOMETER ASSISTS IN REFRACTION
The construction of the Ski-optometer has now been fully explained, and
the reader realizes that since the instrument contains all the lenses
necessary in making an examination, greater operative facility is
afforded through its use than where the trial-case lenses are employed.
The Ski-optometer is “an automatic trial-case” in the broadest sense
of the term, wholly superseding the conventional trial-case. It should
therefore be employed throughout an entire examination, wherever
trial-case lenses were formerly used. To fully realize its labor saving
value in obtaining accurate examination results, it is only necessary
to recall the tedious method of individually handling and transferring
each lens from the trial-case to the trial-frame, watching the stamped
number on each lens handle, wiping each lens and in the case of
cylindrical lenses setting each one at a designated axis—all being
needless steps where the Ski-optometer is employed.
THE USE OF THE SKI-OPTOMETER IN SKIOSCOPY
In skioscopy, the Ski-optometer offers the refractionist assistance of
the most valuable character.
For example, assuming that extreme motion in the opposite direction
with plane or concave mirror is obtained with a +1.25D. spherical
lens before the patient’s eye; by quickly turning the Ski-optometer’s
single reel until the two white zeros again appear, +2.50D is secured,
as explained in the previous chapter. If this continues to give too
much “against motion,” the lens power should be quickly increased to
+3.75 or +5.00D if necessary (Fig. 4). Should the latter reveal a
shadow in the reversed direction, the refractionist is assured that it
is the weakest lens that will cause its neutralization. Practically
but few lenses have been used to obtain the final result proving
the instrument’s importance and time-saving value in skioscopy, and
demonstrating the simplicity with which tedious transference of
trial-case lenses is avoided.
Furthermore, it should be noted that where the Ski-optometer is used
in skioscopy, it is not necessary to remove the retinoscope from the
eye or to constantly locate a new reflex with each lens change. This
permits a direct comparison of the final lens and eliminates the usual
difficulty in mastering skioscopy. The chief cause of this difficulty
is due to the fact that the transferring of the trial-case lenses makes
it practically impossible for the student to determine whether the
previous lens caused more “with” or “against” motion.
[Illustration: Fig. 9—The Woolf ophthalmic bracket. A convenient and
portable accessory in skioscopy and muscle testing; can be used with or
without Greek cross.]
Where the indirect method is employed in skioscopy, best results
are secured through the use of the Woolf ophthalmic bracket and
concentrated filament lamp, together with an iris diaphragm chimney.
The latter permits the reduction or increase of the amount of light
entering the eye, as it is agreed that a large pupil requires _less_
light, a small pupil requiring _more_ light. The bracket referred to
permits the operator to swing the light into any desired position
(Fig. 9), while the iris diaphragm chimney serves as a shutter. This
apparatus may also be employed for muscle testing, as described in a
subsequent paragraph.
A SIMPLIFIED SKIOSCOPIC METHOD
In using the Ski-optometer, instead of working forty inches away from
the patient in skioscopy and deducting 1.D., the refractionist will
find it more convenient to work at a twenty inch distance, deducting
2.D. This working distance may be accurately measured and maintained by
using the reading rod accompanying the instrument. Instead of deducting
2.D. from the total findings, however, it is preferable to insert a
+2.D. trial-case lens in the rear cell of the instrument directly next
to the patient’s eye. After determining the weakest lens required to
neutralize the shadow in both meridians, the additional +2.D. lens
should be removed and the total result of the examination read from the
instrument’s register.
To illustrate a case in skioscopy where spherical lenses are employed
to correct both meridians, assume that the vertical shadow requires
a +1.25D lens to cause its reversal, while the horizontal requires
+2.00D. Employment of the customary diagram, illustrated in Fig. 10,
would show the patient required +1.25 sph. = +.75 cyl. axis 90°, which
when transposed is equivalent to +2.00 sph. = -.75 cyl. axis 180°.
[Illustration: Fig. 10—Where spherical lenses are employed in
skioscopy, above indicates patient requires]
+1.25 Sph. = +.75 Cyl. Axis 90°
or +2 Sph. = -.75 Cyl. Axis 180°
It should be noted that the total spherical power is +2.00D, as the
Ski-optometer’s register shows, while the difference between the two
meridians is 75, which is the required strength of the cylinder. By
then turning the cylinder reel to .75, and setting the axis indicator
at 180° (because by using minus cylinders, the axis must be reversed)
the patient should read the test-type with ease if the skioscopic
findings are correct. Thus with the Ski-optometer, it is not even
necessary to learn transposition, since the instrument automatically
accomplishes the work, avoiding all possibility of error.
EMPLOYING SPHERES AND CYLINDERS IN SKIOSCOPY
Another commonly used objective method may be employed with even
greater facility through the combined use of both the Ski-optometer’s
spherical and cylindrical lenses. As previously suggested, insert the
+2.00 spherical trial-case lens in the rear of the instrument, working
at a twenty inch distance, then proceed to correct the strongest
meridian first.
It was assumed that it required a +2.00 spherical to neutralize
the strongest, or horizontal meridian, as shown in Fig. 10. The
refractionist should then set the axis indicator therewith, which is
the axis of the cylinder, or 180°.
It is then merely a matter of increasing the Ski-optometer’s
cylindrical lens power until the reversal of the shadow in the weakest
meridian is determined. Assuming this proves to be -.75 cylinder, axis
180°, the patient’s complete prescription +2.00 sph. = -.75 cyl. axis
180°, would be registered in the Ski-optometer without any further lens
change other than the removal of the +2.00 working distance lens.
However, regardless of the method employed, the Ski-optometer greatly
simplifies skioscopy. In fact, the instrument was originally intended
to simplify retinoscopy or skioscopy, as the subject should be termed,
the name “Ski-optometer” having been derived from the latter.
USE OF THE SKI-OPTOMETER IN SUBJECTIVE TESTING
In subjective refraction, especially where the “better or worse”
query must be decided by the patient, it is commonly understood that
the refractionist is compelled to first increase and then decrease
a quarter of a diopter before the final lens is decided. With the
Ski-optometer, the usual three final changes are made in far less
time than it takes to make even _one_ lens change from trial-case to
trial-frame.
For example:
Assuming, with a +1.25D spherical lens before the patient’s right
eye, he remarks that he “sees better” with a +1.D. while +.75D is not
as satisfactory. The refractionist can then quickly return to +1.D.,
simply turning the Ski-optometer’s single reel _outward_ to increase,
or _backward_ to decrease, the lens strength. So rapidly have these
lens changes been made, that the patient quickly sees the difference of
even a _quarter_ diopter, and quickly replies, “better” or “worse.”
This is made possible because the eye does not “accommodate” as quickly
as the lens change made with the Ski-optometer. It should also be noted
that the eye receives an image on its retina within one-sixteenth of
a second; otherwise, the patient is forced to accommodate, making it
difficult to see the difference of even a quarter diopter. On the
other hand, in transferring trial-case lenses, with its slow, tedious
procedure, the patient, being unable to detect the slight difference of
only a quarter diopter, unhesitatingly replies, “no difference,” merely
because they are compelled _to accommodate_.
A SIMPLIFIED SUBJECTIVE METHOD
The following simplified method of procedure is suggested for
subjective testing with the Ski-optometer, although as previously
explained, the refractionist may employ his customary method,
overcoming the annoyance of transferring trial-case lenses and the
setting of each cylinder individually. The Ski-optometer has been
constructed and based upon the golden rule of refraction: “As much plus
or as little minus spherical, combined with as little minus cylinder
power as the patient accepts.”
By applying this rule as in the above method and starting with +5.D.
spherical, watching the two zeros (Fig. 4) and rapidly reducing +1.25D
each time, we will assume that +1.25D gives 20/30 vision; as a final
result +1.D. will possibly give 20/25 vision.
The patient’s attention should next be directed to the most visible
line of type, preferably concentrating on the letter “E” or the clock
dial chart—either of which will assist in determining any possible
astigmatism. Since the Ski-optometer contains concave cylinders
exclusively, the next move should be the setting of its axis indicator
at 180°, commonly understood as “with the rule.” One should then
proceed to determine the cylinder lens strength by turning the reel
containing the cylindrical lenses (Fig. 8). Should the patient’s vision
fail to improve after the -.50D. cylinder axis 180° has been employed,
the refractionist, in seeking an improvement, should then slowly move
the axis indicator through its entire arc.
With the cylinder added, regardless of axis, poor vision might indicate
the absence of astigmatism. If astigmatism exists, vision will usually
show signs of improvement at some point, indicating the approximate
axis. Once the latter is ascertained, the refractionist may readily
turn the Ski-optometer’s cylinder reel and obtain the correct cylinder
lens strength, after which the axis indicator should be moved in either
direction in order to obtain the best possible vision for the patient.
The refractionist should always aim to obtain normal (or 20/20) vision
with the weakest concave cylinder, combined with the strongest plus
sphere, or weakest minus sphere.
PROCEDURE FOR USING MINUS CYLINDERS EXCLUSIVELY
For the benefit of those who have never used minus cylinders
exclusively in making their examinations, we will assume that the
patient requires O.U. +1.D sph. = -1D cyl. axis 180° for final
correction; the latter, in its transposed form, being equivalent to
+1.D. cylinder axis 90°. Unquestionably the best method is the one that
requires the least number of lens changes to secure the final result.
To obtain this, the following order of lens change should be made:
First, +1.D. sphere is finally determined and allowed to remain in
place. Concave cylinders are then employed in quarters until the final
results of +1.D. spherical, combined with -1.D. cylinder axis 180° is
secured. This necessitates the change of but _four_ cylindrical lenses
as shown in routine “A” as follows:
ROUTINE “A” ROUTINE “B”
(Made with _minus_ cylinder) (Made with _plus_ cylinder)
Sph. +1.D. Cyl. Axis Sph. +1.D. Cyl. Axis
Step 1 +1.D. = -.25 ax. 180° equal to +.75 = +.25 ax. 90°
Step 2 +1.D. = -.50 ax. 180° equal to +.50 = +.50 ax. 90°
Step 3 +1.D. = -.75 ax. 180° equal to +.25 = +.75 ax. 90°
Step 4 +1.D. = -1 ax. 180° equal to 0 +1 ax. 90°
In brief the method of using minus cylinders exclusively in an
examination, as explained in routine “A”, necessitates the change of
the cylinder lenses only after the _strongest_ plus sphere is secured.
On the other hand, notwithstanding innumerable other methods where plus
cylinders are used, routine “B” shows that the best spherical lens
strength the patient will accept, is also first determined. Then both
spheres and cylinders are changed in their regular order by gradually
building up in routine, by increasing plus cylinder and next decreasing
sphere, a quarter diopter each time, until the final result is secured.
While it is conceded that both routine “A” and “B” are of themselves
simplified methods, by comparing routine “A” where minus cylinders
are used with routine “B” where plus cylinders are used in their
corresponding steps, the refractionist will note by comparison that
one is the exact equivalent and transposition of the other. Where
_plus_ cylinders are employed, eight lens changes are made before final
results are secured; while but four lens changes are necessary where
_minus_ cylinders are used.
The refractionist should also note by comparison that the use of minus
cylinders reduces focus of the plus sphere, but only in the meridian
of the axis. It has not made the patient myopic. Furthermore, a plus
cylinder will bring the focal rays forward, while minus cylinders throw
them backward toward the retina.
This is but another reason for the exclusive use of minus cylinders in
refraction.
The method of using _minus cylinders_ exclusively in an examination,
necessitates the change of the cylinder lenses _only_. On the other
hand, the method of using plus cylinders makes it necessary to change
spheres and cylinders in routine.
In brief, since using the minus cylinder is merely a matter of
mathematical optics, their use even in a trial-case examination is
strongly urged.
The maximum value of the Ski-optometer is fully realized only when the
advantages of using minus cylinders exclusively in every examination is
clearly understood.
CONSTANT ATTENTION NOT REQUIRED
With the Ski-optometer, when the examination is completed, the
sum-total of final results—whether spherical, cylinder, axis, or all
combined—are automatically indicated or registered ready to write the
prescription. _Until then_, the foci of the various lenses that may be
employed are of no importance.
In short, in using the Ski-optometer, it is not necessary to constantly
watch the registrations during examinations. The automatic operation
of the instrument is an exclusive feature, so that the refractionist
should unhesitatingly employ it. Hence, by eliminating the perpetual
watch on the lenses in use, the refractionist is enabled to give his
undivided attention to the patient rather than to the trial lenses.
Where a special dark-room is used for skioscopic work, an additional
wall bracket or floor stand will necessitate only the removal of
the instrument itself. This enables the refractionist to use the
Ski-optometer for subjective or objective work, without disturbing the
patient’s correction.