Retinoscope assembly with scale

Techniques and retinoscopic apparatus for measuring or determining a patient's optical error are disclosed. The techniques include overrefraction and can be performed from a fixed position, avoiding the practitioner's need to move back and forth relative to the patient's eye. Equipment associated with the apparatus is adapted to record the location of the retinoscope slide (relative to its upper or lower position) during the examination to provide information concerning the optical error present in the patient's eye. Other associated equipment can include discs of spherical lenses and devices for limiting relative movement of components of the retinoscopic apparatus. Alternatively, the apparatus may include a scale graduated in suitable units for determining the patient's optical error.

FIELD OF THE INVENTION 
The present invention relates to apparatus and methods for measuring or 
determining optical errors in the eyes of humans (or animals) and more 
particularly to techniques for doing so using a modified streak 
retinoscope. 
BACKGROUND OF THE INVENTION 
U.S. Pat. No. 3,597,051 to Copeland, incorporated herein in its entirety by 
this reference, illustrates an exemplary streak retinoscope assembly. One 
such commercial assembly, the "Optec 360" retinoscope 10 of FIG. 1, 
includes a thumb slide 12 adapted to move relative to the retinoscope 
shaft. As shown in FIG. 2A, advancing slide 12 to its upper position 
causes the light rays emanating from the retinoscope to be approximately 
parallel. FIG. 2B, by contrast, illustrates the convergence of the light 
rays that occurs when slide 12 is moved to its lower position. 
Current refraction techniques use the streak retinoscope for neutralizing 
optical errors. Such techniques are described in, for example, Videotape 
No. 5063 of the American Academy of Ophthalmology's Continuing Ophthalmic 
Video Education series, entitled "Retinoscopy: Plus Cylinder Technique," 
and require use of a phoropter, trial frames, or additional lenses. 
According to these techniques, the slide of the retinoscope remains in the 
upper position throughout the retinoscopic process. Only if greater than 
one diopter of astigmatic error is present do these techniques suggest 
"enhancing" the patient's cylinder power by lowering the retinoscope 
slide. By contrast, "enhancing" the streak to estimate the sphere power 
does not occur. 
After the practitioner neutralizes the patient's error by changing the 
phoropter or trial frame lenses, the values of those lenses are consulted 
to determine the patient's ocular correction. These refraction techniques 
essentially use the phoropter or trial frame lenses to make the light rays 
emanating from the retinoscope conjugate to the patient's fundus. 
(Although these rays are generally assumed to be parallel for these 
techniques, my recent empirical studies suggest that they are not for 
commercially-available retinoscopes.) Doing so in turn causes the rays 
backscattered by the patient's fundus to be conjugate to the 
practitioner's eye, permitting neutralization of optical error at a 
specified working distance. 
According to Videotape No. 5063, prior retinoscopic estimating techniques 
were complex and thus rarely learned or used by the average practitioner. 
Such "two-handed" techniques require the practitioner to rotate a collar 
or sleeve on the retinoscope while simultaneously moving the slide up and 
down, effectively creating "spiral" movement of the slide and sleeve. To 
perform these techniques, moreover, the practitioner must move back and 
forth relative to the patient, thereby alternately approaching and 
receding from the eye under examination. The patient's optical error is 
then typically estimated based on the width of the focused streak of light 
emanating from the retinoscope as seen by the practitioner on the 
patient's pupil. Following "straddling" and other movements of the streak, 
the patient's cylindrical error axis can ultimately be estimated by 
comparing the longitudinal axis of the streak to a scale on the phoropter. 
Moreover, as discussed on page 21 of Dr. J. C. Copeland's manual for 
"Steak Retinoscopy" printed by Optec, Inc. (which manual is incorporated 
herein in its entirety by this reference), these prior estimating 
techniques were "best . . . perform[ed] . . . on the naked eye" and thus 
did not involve overrefraction of existing prescription lenses. 
SUMMARY OF THE INVENTION 
The present invention provides retinoscopic techniques for measuring or 
determining a patient's optical (sphere and cylinder) error. Unlike prior 
methods, the present techniques can be performed from a fixed position, 
avoiding the practitioner's need to move back and forth relative to the 
patient's eye. They also need not involve straddling and can be performed 
whether or not the patient is wearing existing prescription glasses. 
During the examination, equipment connected to the modified streak 
retinoscope of the invention senses the position of the slide relative to 
some nominal location (e.g. its upper or lower position), providing 
information concerning the optical error present in the patient's eye. 
This information can be used to calculate the resulting power and cylinder 
axis of appropriate corrective lenses. By contrast with prior retinoscopic 
techniques, the present invention uses this positional displacement of the 
lamp filament from the fixed condensing lens within the retinoscope to 
permit the rays emanating from the device to be conjugate to the patient's 
fundus. 
The Optec 360 retinoscope 10 of FIG. 1 contains a +20.00D condensing lens 
14 and a bi-pin lamp 16. When slide 12 is in its upper position (FIG. 2A), 
the filament of lamp 16 is approximately five centimeters from condensing 
lens 14. The rays emanating from the filament pass through lens 14 as 
essentially parallel, therefore, thereby focusing those rays at infinity. 
Displacing slide 12 from its upper position converges the emanating rays 
relative to condensing lens 14 according to the formula: 
EQU P=D+(d.times.D.times.D)-W 
where 
P=total vergence power of retinoscopic light rays at the patient's pupil 
(in diopters) 
D=vergence power of emerging retinoscopic light rays (in diopters) 
d=distance from the patient's pupil at which retinoscopy is performed (the 
"working distance") (in meters) 
W=working distance (in diopters) 
(Equation 1) 
In the slide's lower position on the Optec 360 retinoscope 10 (FIG. 2B), 
the lamp filament is approximately 6.6 centimeters from condensing lens 
14. Accordingly, displacing slide 12 of retinoscope 10 can generate 
dioptric power ranges as shown below for various (exemplary) working 
distances: 
______________________________________ 
Working Distance 
Generated Powers 
(centimeters) (diopters) 
______________________________________ 
0.0 0.00 to +4.83 
2.54 -39.40 to -33.98 
10.0 -10.00 to +2.83 
20.0 -5.00 to +4.50 
25.0 -4.00 to +6.67 
33.0 -3.00 to +9.50 
50.0 -2.00 to +12.59 
66.0 -1.50 to +18.80 
100.0 -1.00 to +26.00 
______________________________________ 
By measuring the slide's displacement from, e.g., its upper position, 
therefore, information concerning the optical power generated using the 
retinoscope can be obtained at various times during the examination 
(including when the streak fills the pupil). Embodiments of the modified 
streak retinoscope of the present invention use a momentary switch and 
potentiometer connected to the retinoscope to convert this slide 
displacement quantity into an electrical resistance. This resistance can 
in turn be measured and used to calculate the optical power necessary to 
correct the patient's error. The calculation can be performed 
electronically by a computer adapted to receive the resistance value, for 
example, permitting the computer to determine the optical correction 
needed for an overrefracted patient merely by appropriately combining the 
resistance with the patient's current prescription. 
An additional embodiment of the invention provides a scale on the 
retinoscope graduated in diopters (or portions thereof or of other 
appropriate units). Such scale permits the practitioner to determine 
immediately the optical error of the patient merely by comparing the slide 
displacement with the corresponding value of the scale. It also avoids the 
need to compute the optical correction electronically for each patient and 
to connect the retinoscope to a computer or similar equipment. The scale 
may be affixed or connected to the retinoscope using any suitable means or 
may be integrally molded as part of or otherwise formed with the 
retinoscope itself. 
Other embodiments of the apparatus of the present invention can incorporate 
lens discs or carriers permitting substitution of other power lenses for 
the +20.00D condensing lens included in the Optec 360 retinoscope 10 of 
FIG. 1. Alternatively, the powers of these additional lenses can be 
combined with that of the condensing lens, or the slide displacement can 
be increased, to enhance the dioptric range of the device. Because the 
operating principles of some commercial retinoscopes are opposite those of 
the Optec 360, yet other embodiments of the invention function exactly 
opposite the manner described above. Further embodiments of the invention 
include means for limiting the movement of the lamp filament relative to 
the condensing lens to accommodate, for example, manufacturing variances 
in existing lamps and lenses. 
It is therefore an object of the present invention to provide refraction 
techniques using a streak retinoscope. 
It is another object of the present invention to provide refraction 
techniques that can be performed by a practitioner from a fixed position 
relative to a patient. 
It is also an object of the present invention to provide overrefraction 
techniques using a streak retinoscope. 
It is a further object of the present invention to provide equipment 
connected to a streak retinoscope that senses the position of the 
retinoscope slide relative to some nominal location (e.g. its upper or 
lower position). 
It is yet another object of the present invention to provide a streak 
retinoscope connected to a momentary switch and potentiometer for 
converting slide displacement into an electrical resistance. 
It is an additional object of the present invention to provide electronic 
means for converting the sleeve displacement value (and patient's existing 
prescription if overrefraction is performed) into a resulting optical 
correction for the patient's eye. 
It is also an object of the present invention to provide a scale as part of 
a retinoscope, permitting determination of the patient's optical error 
through comparing slide displacement with a corresponding value appearing 
on the scale. 
Other objects, features, and advantages of the present invention will 
become apparent with reference to the remainder of the text and the 
drawings of this application.

DETAILED DESCRIPTION 
1. Apparatus 
As referenced above, FIG. 1 shows an Optec 360 retinoscope 10 having thumb 
slide 12, condensing lens 14, and lamp 16. Lamp 16 includes a linear 
filament designed to create the "streak" reflex or reflection seen by the 
practitioner from the retina of the eye of the patient being examined. 
Slide 12 moves approximately 1.6 cm along handle 18 so that, in its upper 
position, the filament of lamp 16 is approximately 5.0 cm from lens 14, 
which has power of +20.00D. In its lower position, therefore, the filament 
of lamp 16 is approximately 6.6 cm from lens 14. 
In use, light rays emanating from lamp 16 are reflected by mirror 19 
approximately 45.degree. into the patient's eye. The practitioner can view 
the rays backscattered from the patient's retina through a small opening 
20 in mirror 19, effectively focusing the backscattered rays into his 
pupil. In essence, the phoropter or trial frame lenses subsequently placed 
before the patient are designed to place the patient's eye in focus with 
the practitioner's eye peering through opening 20. 
FIGS. 3-4 illustrate a modified streak retinoscope 22 of the present 
invention. Retinoscope 22 may be a modified Optec 360 retinoscope 10 (FIG. 
1) or any other suitable device having a displaceable slide 24 or some 
other means for moving a lamp relative to a lens. As shown in FIGS. 3-4, 
retinoscope 22 includes a potentiometer 28 coupled to slide 24, providing 
means for converting displacement of the slide 24 along handle 30 into an 
electrical resistance. This resistance can in turn be measured by ohmmeter 
32 connected to potentiometer 28 and used by a computer 36 or other 
appropriate mechanism to calculate the optical power necessary to correct 
a patient's error. Merely by appropriately combining the resistance 
measured by ohmmeter 32 with the patient's current prescription using 
known equations, computer 36 can rapidly and easily determine the optical 
correction needed for an overrefracted patient. 
FIG. 4 details the coupling between potentiometer 28 and slide 24. Wire 40 
directly attaches slide 24 to the recording wire or contact arm 44 of 
potentiometer 28 so that, as slide 24 is displaced (upward or downward) 
along handle 30, contact arm 44 moves in a corresponding manner. 
Accordingly, potentiometer 28 tracks movement of slide 24, indicating its 
deviation from a nominal position. Those skilled in the art will recognize 
that other means may be used to sense the position of slide 24 along 
handle 30, including mechanisms electrically or optically coupled to slide 
24 or uncoupled but otherwise capable of providing the necessary 
information. A momentary switch 48 or other suitable device may be 
included as part of computer 36 (FIG. 3), retinoscope 22, or elsewhere in 
the circuitry to provide means for indicating the point at which the 
practitioner determines that a displacement measurement needs to be 
recorded. 
2. Exemplary Operations 
To refract a patient's eye using retinoscope 22, the practitioner need 
merely assume a (fixed) position a known distance (e.g. 50 cm) from the 
patient. 
A. 
For a patient having a solely spherical error between approximately -1.75D 
and +2.75D, for example, activating retinoscope 22 with slide 24 in its 
upper position initially provides to the practitioner the streak reflexive 
image shown in FIG. 5A. Because no astigmatic error is present in this 
example, neither the width nor intensity of the streak varies as collar or 
sleeve 50 is rotated .+-.90.degree.. Lowering slide 24 widens the 
reflected streak (FIGS. 5B-C) until it fills the patient's pupil as 
illustrated in FIG. 5D. Again, because the patient has no astigmatic error 
in this example, rotating sleeve 50 diminishes neither the width nor 
intensity of the streak (FIG. 5E). At this point momentary switch may be 
depressed, providing computer 36 information concerning the distance slide 
24 has been displaced from its upper position. 
B. 
For a patient having a (solely) spherical refractive error of -2.00D, a 
retinoscope 22 located 50 cm from the patient's eye, and slide 24 in its 
upper position, the practitioner will initially view the images of FIGS. 
5D-E. Accordingly, no further refractive effort is needed and the initial 
position of slide 24 is immediately converted into an electrical 
resistance and transmitted to computer 36. 
C. 
For a patient having a myopic (solely) spherical refractive error greater 
than -2.00D, the images of FIGS. 5D-E are likely not attainable for 
working distances of 50 cm or greater. To accommodate these larger 
spherical errors, the practitioner can place a phoropter or trial frame 
lens of, for example, between -3.00D and -12.00D before the patient (or 
use the patient's existing prescription lens) and continue lowering slide 
24 until the images of FIGS. 5D-E are obtained. Again, at that point the 
practitioner can simply activate computer 36 to record the displacement 
information obtained through potentiometer 28. In this case, however, the 
power of the phoropter, trial frame, or existing prescription lens must be 
included in the final corrective calculation (either as a separate input 
to computer 36 or manually after the displacement information is converted 
into the refractive error). Alternatively, the practitioner can move 
toward the patient, decreasing the distance between the retinoscope and 
eye under examination, until he views the images of FIGS. 5D-E. This 
decreased working distance must be determined and appropriately factored 
into the value obtained from computer 36, however. 
D. 
For a patient having a (solely) spherical error greater than +12.59D, the 
images of FIGS. 5D-E are similarly not likely to be obtained at a working 
distance of 50 cm. The practitioner in such a case can place a phoropter 
or trial frame lens of, for example, between +3.00 and +12.00 before the 
patient (or again use the patient's existing prescriptive lens). With this 
lens in place, the practitioner can continue lowering slide 24 until the 
images of FIGS. 5D-E are obtained, at which point he can activate computer 
36 to record the displacement information obtained through potentiometer 
28. As in connection with the prior example, the power of the phoropter, 
trial frame, or existing prescription lens must be included in the final 
corrective calculation. 
E. 
FIGS. 5F-I and 6A-D illustrate reflections viewed for a patient having a 
cylindrical error in addition to the spherical errors mentioned in 
examples A-D. In FIG. 5F-I, the axis of the patient's spherical error is 
180.degree., while in FIG. 6A-D the axis is 45.degree.. For the patient 
having a cylindrical error principally in the 180.degree. meridian, the 
practitioner determines the spherical error in the same way as discussed 
above. Upon rotating sleeve 50 by .+-.90.degree., however, the image of 
FIG. 5F is obtained and the angular orientation of the streak (i.e. 
180.degree.) is noted or estimated by the practitioner. The practitioner 
again lowers slide 24 (FIGS. 5G-H) until the streak fills the pupil (FIG. 
5I), at which point computer 36 is utilized to record the displacement of 
the slide 24. The noted cylinder axis can then be included with the 
measurements to produce a final corrective prescription. 
Embodiments of retinoscope 22 can also incorporate lens discs or carriers 
to permit lenses of other powers to be substituted for or combined with 
lens 14. For example, including a disc of spherical lenses in +0.50D 
increments capable of being optically aligned with opening 20 would 
enhance the practitioners ability to use retinoscope 22 accurately at any 
working distance from 0-100 cm. Incorporating a distance finder into 
retinoscope 22 would additionally permit electronic measurement of the 
working distance for input into computer 36, while electrically or 
otherwise coupling the lens disc to the computer would allow direct input 
of the added spherical power into the computer 36 for use in later 
calculations. 
Other embodiments of retinoscope 22 function opposite the manner described 
earlier, recording, for example, the distance slide 24 is displaced from 
its lower position. These embodiments are designed to accommodate the 
operating principles utilized in some commercial retinoscopes, in which 
the light rays from lamp 16 are either focused at infinity (or slightly 
divergent according to my recent empirical studies) when slide 12 is 
completed lowered. Yet other embodiments of retinoscope 22 contemplate 
permitting slide 24 to move more than 1.6 cm, providing a greater range of 
dioptric powers available for refraction. 
FIGS. 7A-B and 8 illustrate an embodiment of retinoscope 22 adapted as 
described above to incorporate a disc 100 of spherical lenses 104. Disc 
100 is designed to be rotated by the practitioner as needed to align a 
particular lens 104 with opening 20. Use of disc 100 increases the 
flexibility of retinoscope 22, permitting, for example, a presbyopic 
practitioner to view a clearer pupillary image. While maintaining a fixed 
retinoscopic working distance, disc 100 can also be rotated to provide 
more or less exact spherical correction. Exemplary lenses 104 for disc 100 
may have spherical powers between 0.00 and +5.00D (in 0.25 or 0.50D 
increments). 
Also shown in FIGS. 7A and 8 is knob 108, which may be a set screw or other 
adjustable device suitable for limiting movement of the filament of lamp 
16 relative to lens 14. Empirical evidence suggests that the distance 
between lens 14 and the filament of lamp 16 when slide 12 is in the upper 
position differs significantly between versions of existing commercial 
retinoscopes. Using knob 108 to limit upward travel of the filament of 
lamp 16 permits retinoscope 22 to be calibrated to neutralize not only 
this discrepancy, but other manufacturing and assembly variances 
(including those in lens 14) as well. 
Calibration of retinoscope 22 can easily be accomplished by clamping it, 
for example, 50 cm from a -2.00D (myopic) schematic eye. The position of 
slide 12 or 24 can then be adjusted until the streak fills the pupil of 
the schematic eye and knob 108 set to preclude further upward travel of 
the filament of lamp 16. Similar calibration can occur whenever lamp 16 is 
replaced. Although the embodiment of retinoscope 22 shown in FIGS. 7A-B 
and 8 may be coupled directly or indirectly to computer 36, it need not be 
and is useful manually in improving existing retinoscopic techniques. 
Manual versions of retinoscope 22 could also be adapted to include an 
infrared or other distance finder for measuring and displaying the 
resulting working distance. 
FIG. 9A-B detail embodiments of retinoscope 22 incorporating scale 120 
(FIG. 9A) or (hyperopic) scale 124 (FIG. 9B). Also shown in FIG. 9A-B is 
indicator 130, which when aligned with a gradation of scale 120 or 124 
permits determination (or provides information from which to calculate) a 
patient's optical error. Indicator 130 may be formed (as, e.g., a groove) 
in or otherwise associated with collar 132, which in turn is coupled to 
slide 24. In use, therefore, indicator 130 moves relative to scale 120 or 
124 as slide 24 is displaced along handle 30. 
Scale 120 is designed primarily for use in determining low myopic and 
hyperopic errors. It accordingly may be graduated in 0.25D or larger 
increments if desired and extend from -1.75D to +1.75D as illustrated in 
FIG. 9A. Scale 124, by contrast, has greater utility in estimating larger 
hyperopic errors between approximately +1.00D and +3.00D and, in FIG. 9B, 
is so marked. Those skilled in the art will recognize that other 
gradations and dioptric ranges may be used for scales 120 and 124 if 
necessary or desired. Scale 120 contemplates use of conventional endpoints 
during retinoscopy, furthermore, while enhancements phenomenon endpoints 
may alternatively be used in connection with retinoscopic methods 
employing scale 124. 
Each of scales 120 and 124 is derived for a specified retinoscopic working 
distance and may be computer generated according to Equation 1 (printed 
earlier) and the following Equation 2: 
EQU D=B-(100/(F+U)) 
where 
D=vergence power of emerging retinoscopic light rays (in diopters) 
B=back vertex power of the biconvex lens of the retinoscope (in diopters) 
F=distance of the lamp filament from the back surface of the biconvex lens 
within the retinoscope when the slide is displaced from the uppermost 
position (in centimeters) 
U=displacement of the slide from the uppermost position (in centimeters) 
For a value of U equalling zero, D equals the negative of the sphere 
required to focus the diverging light rays of retinoscope 22 onto a wall 
at twenty feet. Sample values obtained from Equations 1 and 2 appear 
below: 
______________________________________ 
(Chart 1) 
Focus Distance 
Retinoscopic Distance 
(cm/in) (diopters) 
______________________________________ 
127/50.0 +1.25 
106/41.4 +1.50 
90/35.4 +1.75 
80/31.5 +2.00 
70/27.5 +2.25 
67/26.4 +2.50 
64/25.2 +2.75 
54/21.3 +3.00 
______________________________________ 
To retrofit an existing retinoscope with scale 120 or 124, a practitioner 
may perform a regular manifest refraction for distance vision using 
conventional refraction techniques. Thereafter, the practitioner may 
assume his or her "regular" retinoscopic working distance and lower slide 
24 until the light streak emanating from the retinoscope fills the 
patient's pupil. Slide 24 should then be clamped in order to calibrate the 
retinoscope and to measure the practitioner's retinoscopic distance. 
To calibrate the retinoscope, indicator 130 is aligned with the "0.00D" 
gradation of scale 120 or the "+2.00D" marking of scale 124. To measure 
his or her working distance, the practitioner may approach a wall (or 
analogous structure) until the projected image of the retinoscopic beam is 
sharply focused onto the wall. The focus distance from the midpoint of the 
retinoscope to the wall is then measured. The retinoscopic distance may 
thereafter be determined from Chart 1 (which is derived from Equations 1 
and 2) and recorded and slide 24 unclamped. Chart 1 is also utilized to 
recalibrate the retinoscope whenever the retinoscopic bulb is changed. 
A practitioner may determine the optical error of appropriate patient's by 
using the techniques of retinoscopy described herein and merely comparing 
the position of indicator 130 relative to scale 120 or 124. If the 
patient's optical error exceeds the boundaries of the scale, lenses of 
additional power may be held before the patient's eye until retinoscopy 
can be completed. In such case the error may be calculated simply by 
adding the additional power of the lenses to the final value read from the 
scale. 
A new technique of retinoscopy, which I call "converging infinity 
retinoscopy," can be performed with retinoscope 22 as illustrated in FIGS. 
3, 7A, and 9A. Converging infinity retinoscopy occurs when the reflected 
retinoscopic rays from the patient's retina are focused at infinity. To 
perform this retinoscopy, the convergence or focal point of the light rays 
must be as stated in Chart 1. With retinoscope 22 of FIG. 3, for example, 
slide 24 is moved until computer 36 indicates "0.00D." Likewise, for 
retinoscope 22 of FIG. 9A, indicator 130 is placed at "0.00D" on scale 
120. To perform converging infinity retinoscopy with retinoscope 22 of 
FIG. 7A, slide 24 is fixed in position using knob 108 after performing the 
calibration technique described above. 
Advantages of converging infinity retinoscopy (as compared to conventional 
retinoscopy) include: 
eliminating divergences of retinoscopes and bulbs which give the impression 
that the patient is accommodating 
endpoints which are clearer, brighter, and of better optical qualities 
having a relative speed of the pupillary reflex that is the same as the 
intercept rather than of infinite speed as in conventional retinoscopy 
allowing patient's to read the Snellen chart while the retinoscopist is 
evaluating the retinoscopic endpoints, since no fogging is required as in 
conventional retinoscopy 
eliminating cycloplegics except for non-cooperating patient's 
being easier to teach since the retinoscopic endpoints are more consistent 
with the manifest refraction; and 
allowing performance of any retinoscopic estimation technique or 
conventional retinoscopy when desired. 
The foregoing is provided for purposes of illustrating, explaining, and 
describing embodiments of the present invention. Modifications and 
adaptations to these embodiments will be apparent to those skilled in the 
art and may be made without departing from the scope or spirit of the 
invention.