Several design changes have been made to Improve the sensitivity of the existing experimental Badal type photoretinoscope apparatus to make the instrumentation more practical as a screening device. The design changes include the use of: aspheric lenses; a narrow pass light filter; a decreased exit pupil diameter; and a single luminous object used with a coincidence (vernier) Scheiner system implemented with a pair of vertically oriented pinhole apertures to test the vertical meridian of the test eye. The resolution of the apparatus (using an emmetropic human eye analogue) was well under 1.0 D. Further modifications contemplated for the future include: a second pair of pinholes, horizontally oriented, to test the horizontal meridian, and the ability to axially rotate the pinholes along with the doubling prisms so as to sample oblique meridians, if necessary. Finally, the entire apparatus will need to be miniaturized and lightened to make it portable for field use (screening)

Fleming, J Scott

English

CommonKnowledge

Pacific University 
CommonKnowledge 
College of Optometry Theses, Dissertations and Capstone Projects 
1992 
Further development of a Badal type photoretinoscope 
J Scott Fleming 
Pacific University 
Recommended Citation 
Fleming, J Scott, "Further development of a Badal type photoretinoscope" (1992). College of Optometry. 
985. 
https://commons.pacificu.edu/opt/985 
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Further development of a Badal type photoretinoscope 
Abstract 
Several design changes have been made to Improve the sensitivity of the existing experimental Badal type 
photoretinoscope apparatus to make the instrumentation more practical as a screening device. The 
design changes include the use of: aspheric lenses; a narrow pass light filter; a decreased exit pupil 
diameter; and a single luminous object used with a coincidence (vernier) Scheiner system implemented 
with a pair of vertically oriented pinhole apertures to test the vertical meridian of the test eye. The 
resolution of the apparatus (using an emmetropic human eye analogue) was well under 1.0 D. Further 
modifications contemplated for the future include: a second pair of pinholes, horizontally oriented, to test 
the horizontal meridian, and the ability to axially rotate the pinholes along with the doubling prisms so as 
to sample oblique meridians, if necessary. Finally, the entire apparatus will need to be miniaturized and 
lightened to make it portable for field use (screening). 
Degree Type 
Thesis 
Degree Name 
Master of Science in Vision Science 
Committee Chair 
Niles Roth 
Keywords 
Refraction, infant/children refraction, Badal optometer 
Subject Categories 
Optometry 
This thesis is available at CommonKnowledge: https://commons.pacificu.edu/opt/985 
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FURTHER DEVELOPMENT OF A 
BADAL TYPE PHOTORETINOSCOPE 
By 
J. SCOTT FLEMING 
A thesis submitted to the faculty of the 
College of Optometry 
Pacific University 
Forest Grove, Oregon 
for the degree of 
Doctor of Optometry 
Advisers: 
Niles Roth, O.D.,Ph.D. 
Professor, Pacific University College of Optometry 
Paul Kohl, O.D. 
Associate Professor, Pacific University College of Optometry 
FURTHER DEVELOPMENT OF A 
BADAL TYPE PHOTORETINOSCOPE 
/lid~~ 
Niles Roth, M.Opt.,Ph.D. 
Thesis Advisor 
Professor 
Pacific University 
College of Optometry 
Fourth Professional Year 
Pacific University 
College of Optometry 
Thesis Advisor 
Associate Professor 
Pacific University 
College of Optometry 
Jeffrey Scott Fleming was born in Lancaster, California. His family moved 
to Torrance, California when he was age four. He began working in his 
father's practice during his last two years in high school. He received his 
Associate in Arts degree from El Camino Junior College, and then his 
Bachelors in Biology from California State University, at Long Beach. He 
has held employment throughout his education, including working m 
several practices, supervising the finishing department of a large 
ophthalmic laboratory, and being sole proprietor of his own ophthalmic 
finishing laboratory. He has also been very active m local and national 
optometric student politics, holding positions such as the American 
Optometric Student Association (AOSA) Trustee, Chairman of the AOSA 
Membership Development Committee, Chairman of the AOSA Benefits 
Committee, AOSA National Liaison to the Optical Laboratories Association 
(OLA), and AOSA Treasurer. He is listed in the 1990-91 Who's Who Among 
Students in American Universities and Colleges, and was given the AOSA 
Service A ward for his devoted service to A OSA in 1991-92. His goals are 
to enjoy his own private professional optometric practice providing quality 
care in all facets of the ophthalmic field. 
Several design changes have been made to Improve the sensitivity of 
the existing experimental Badal type photoretinoscope apparatus to make 
the instrumentation more practical as a screening device. The design 
changes include the use of: aspheric lenses; a narrow pass light filter; a 
decreased exit pupil diameter; and a single luminous object used with a 
coincidence (vernier) Scheiner system implemented with a pair of 
vertically oriented pinhole apertures to test the vertical meridian of the 
test eye. 
The resolution of the apparatus (using an emmetropic human eye 
analogue) was well under 1.0 D. Further modifications contemplated for 
the future include: a second pair of pinholes, horizontally oriented, to test 
the horizontal meridian, and the ability to axially rotate the pinholes along 
with the doubling prisms so as to sample oblique meridians, if necessary. 
Finally, the entire apparatus will need to be miniaturized and lightened to 
make it portable for field use (screening). 
Refraction, infant/children refraction, Badal optometer 
The most common preschool vision problems at the present time are 
strabismus and amblyopia. The estimate for their occurrence is near 5% 1. 
The work of Ingram et al 2 shows that infants with errors of 2.50 diopters 
of hyperopia or more at age one, are 20 times more likely to develop 
strabismus and amblyopia than children with a refractive status closer to 
emmetropia. This raises the possibility that refractive screening of the 
population in infancy could identify children at risk of these disorders 3 
Another factor in screening infants is the ability to record accurate 
objective findings in a short amount of time. Given these points, and the 
ever escalating costs of today's health care, a portable, easily used, 
refractive screening device which can be used by paramedical personnel 
after a short training period would be useful. 
Photoretinoscopy is an objective method of determining the refractive 
state from a photograph of a luminous fundus image. There are many 
types of photoretinoscopic devices, but the principles involved are similar. 
Typically, the subject is in a cycloplegic state when a form of photography 
records an image from the fundus on film for subsequent evaluation of the 
refractive status. 
Urness et al 4 designed the original prototype of the system 
discussed in this paper, and also included a summary of several other types 
of photoretinoscopic devices. The design of Urness et al 4 was incorporated 
into a working laboratory prototype apparatus reported by Lim et al 5. 
Several modifications have been made to this prototype and these are the 
subject of this paper. 
1 
Modifications 
The previous Badal type photoretinoscope system constructed by Lim 
et al 5 was modified as follows: 
1) First quality aspheric lenses where used for Ll and L2 (formerly 
Pl and P2) to improve the optics of the system (Figure 1). 
2) The exit pupil of the system was more accurately positioned at the 
entrance pupil of the test eye, and was reduced in diameter to 3.5 mm. The 
foregoing necessitated replacing L3 with a +3.00 D spherical lens (formerly 
+2.00 D), reducing the working distance from 50 to 37 em. 
3) A sharp cutoff yellow filter was introduced to improve the Image 
quality by reducing the effects of chromatic aberration. 
4) Several attempts were made to use opaque objects with the idea 
that they would provide easier fabrication and a less critical need for flux 
uniformity in the fundus images. However, the opaque objects presented 
an inadequate resolution of the image which led to the readoption of the 
original luminous type 6 object. 
5) The object was further modified to a single luminous source used 
with a coincidence (vernier) Scheiner system (CSS). 
6) Image retrieval is achieved via a beamsplitter less than one focal 
length from L 1. This allows a fundoscopic view of the vernier images. 
Explanation of the Apparatus (Figure 1) 
Light originates from a coiled tungsten filament (S ), and is collected 
by lens L to form the image of S at S'. 0 is a 0.8 mm diameter aperture 
located at the focal point of Ll and transilluminated by S'. Thus, 0 acts as 
a luminous object with its image at infinity. AS, a circular stop close to L, 
2 
limits the light reaching S' and acts as the entrance pupil for the entire 
system. PR is a prism placed halfway in the cone of light leaving 0, its 
ultimate purpose is to produce horizontal doubling of the image(s) of 0 
formed on the fundus of the test eye. The horizontal doubling is what 
makes this a coincidence (vernier) system. The Scheiner feature results 
from the placement of a vertically oriented double pinhole (D A, 1 mm 
diameter apertures) to the right of L 1. Thus, only the vertical meridian of 
the eye is tested. 
YF is a sharp cutoff yellow filter (t = 50% of max. at about 555 nm) 
intended to improve image sharpness by reducing the effects of chromatic 
aberration. B S, a beam splitter with about 50:50 t:r ratio, allows collimated 
light to pass to L2 which forms a double image of S' at F2, and F3, a 
common focal point between L2 and L3. Ml and M2, front surfaced 
mirrors, fold the optical path for more efficient use of space. L3 provides 
collimated light to the eye's entrance pupil, 37 em away, in the form of two 
narrow beams (due to D A). The end result is the formation of two 
horizontally oriented images of 0 on the fundus of the test eye. If the 
latter is emmetropic, the images are vertically aligned; if ametropic, the 
images are misaligned by an amount proportional to the degree of 
ametropia. The direction of the misalignment corresponds to the sign of the 
ametropia. 
Up to this point the description pertains only to input light. The 
output consists of light emerging from the eye and retracing its path 
through all the optical elements until reaching B S. About half the light 
hitting B S is reflected into a detector (eye or camera); the rest is 
transmitted through B S and lost. 
3 
Schematic eye (human eye analogue )(Figure 2) 
The schematic eye consists of a single methyl methacrylate biconvex 
lens in air with a diffusing screen acting as a fundus. The latter is fine 
grained lint-free paper attached to a piece of thin cardboard. The fundus 1s 
mounted on a screw-operated translator (Baling-Beck, England). 
Calibration of the schematic eye was done using a TOPCON 3 
Coincidence Refractionometer (Ser. No. 110030), patterned after the 
Hartinger Refractionometer (Carl Zeiss, Jena). 
Procedure 
Video recordings of the fundus images were made for subsequent 
evaluation. The effects of three kinds of procedures were recorded: 
A) Lenses of various powers were placed in front of the schematic 
eye, which was set at emmetropia, to simulate refractive ametropia. 
The following lenses were used (in diopters): plano; + 1.00; -1.00; 
+2.00; -2.00; +3.00; -3.00. 
B) A plano lens was used while the fundus of the schematic eye was 
moved to various positions to simulate axial ametropia. The following 
amounts of ametropia were represented (in diopters): plano; -2.00; -
4.00; +2.00; +4.00. 
C) Lenses of relatively low power were placed in front of the 
schematic eye to test the sensitivity of the system. The powers used 
were as follows (in diopters): plano; +0.50; -0.50; plano. 
4 
The present system produces vernier images on the fundus. The field 
of view, although small (7 deg.), is more than adequate for present 
purposes. The image offset data is given below (Table 1), followed by a 
graphical representation (figure 3). Visual inspection of offsets due to 
changing lens power by as little as 0.50 D shows sensitivity to this amount 
of change. The telescopic system used (cathetometer) was not as sensitive, 
but could measure changes well under 1.0 D. 
There have been significant improvements made in the apparatus as 
described in this paper. However, further improvements are recommended 
before human trials are preformed. These improvements include: 
1) A second pair of pinholes, horizontally oriented, to test the 
horizontal meridian. 
2) The ability to axially rotate the pinholes along with doubling 
prisms so as to sample oblique meridians, if necessary. 
3) The use of infrared (IR) light, and an IR camera (either video or 
photographic) in order to avoid the obtrusive effects of visible light. 
4) An optoelectronic scanner to Improve the sensitivity of Image 
offset evaluation. 
5 
5) A second object at a different optical distance for internal 
calibration purposes. This would enable a more accurate calibration 
(the amount of vernier offset per unit diopter of refractive error 
varies with posterior nodal distance of the test eye). 
6 
1. Amigo G. Pre-school vision study. Br J Ophthalmol 1973; 57: 125-32. 
2. Ingram RM, Traynar MJ, Walker C, Wilson JM. Screening for refractive 
errors at age 1 year: a pilot study. Br J Ophthalmol 1979; 63: 243-50. 
3. Atkinson J, Braddick OJ, Durden K, Watson PG, Atkinson S. Screening for 
refractive errors in 6-9 month old infants by photorefraction. Br J 
Ophthalmol 1984; 68: 105-12. 
4. Urness J. A theoretical proposal for the design of a photoretinoscopic 
apparatus. Senior Research Thesis, Pacific University College of Optometry, 
May 1985. 
5. Lim HO. A continuing study on the feasibility of a badal-type 
photoretinoscopic apparatus. Senior Research Thesis, Pacific University 
College of Optometry, May 1991. 
6. Kaastrup JD, Woods MP. The feasibility of an objective photoflash eye 
refractionmeter. Senior Research Thesis, Pacific University College of 
Optometry, November 1978. 
7 
DIAGRAM OF PHOTOTRETINOSCOPE APPARATUS 
ASOF03MAY1991 
FIG. 1 
• In order to inspect the images visually, the video 
camera can be replaced by an observer's eye. 
L 3 
-~ F2,F3 
Lt SPECIFICATIONS:Pt=+14.12 D; P2=-1.00 D; t=0.008 m; PV=+14.25; PN=+13.12 
n=1.523 (assumed) fv=7.34 cm;fN=7.60 em 
L2SPECIFICATIONS:Pt=+5.12 D; P2=-3.25; t=0.002; PV=+1.90; PN=+2.01 
n=1.523 (assumed) fv=52.60 em ;fN=49. 7 em 
SYMBOLS 
Pl= convex surface power 
P2= concave surface power 
t= center thickness 
Pv=back vertex power = Vfv 
PN=front vertex power= VfN 
Ai and Ai+l are front and back vertices, respectively. 
0=0.8 mm diameter aperture 
YF=yellow filter 
BS=beam splitter; DA= double aperture (1 mm Diam.) 
AS=aperture stop; Pr=prism 
S=coiled tungsten filament 
S'=image of tungsten filament (S) 
8 
MOVABLE 
FUNDUS 
: -Apprcix-. -$ca1e: 
' ' 
, 1 em= 2.5 mm 
' ; 
A2 --~~=======-~~~~------~------~~~ 12----••­
F2 
FIG. 2 
P1 = +57.65 D; P2 = + 18.15 D; Pv = + 125.76 D; fv = 8.0 mm (approx.) 
A1F2 = 20 mm 
REFR . SCALE REFR. SCALE 
ERROR RDG. ERROR RDG. 
+5.0 l.l 
-0.5 2.05 
+4 .0 1. 2 
-1.0 2.15 
+3.0 1.45 
-2.0 2.35 
+2.0 1.6 
-3.0 2.45 
+1. 0 1.75 
-4.0 2.6 5 
+0 .5 1.85 
- 5.0 2.8 
"-MYOPIA 
"-HYPEROPIA 
PLANO 1.9 
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SIMULATED 
HYPEROPIA 
LENS SIMULATED 
POWER (D) MYOPIA 
zero point 
to 0,0 
FIG. 3 . VERNIER IMAGE OFFSETS VERSUS LENS 
POWER PLACED IN FRONT OF SCHEMA TIC EYE . 
LENS RT RDG LT RDG DIFF 
(VERNIER 
OFFSET) 
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-3 2886 2910 -2 4 
TABLE 1 
POSITIVE 
DIFFERENCES 
MEAN THAT 
THE RIGHT 
IMAGE IS 
HIGHER 
THAN THE 
LEFT IMAGE . 
THE READINGS IN COLUMNS 2 AND 3 ARE ARBITRARY, TAKEN 
FROM THE VERNIER SCALE OF THE CATHETOMETER (1/10 MM 
RESOLUTION) . 
* THIS READING SHOULD BE CLOSE TO ZERO (SEE THE GRAPH). 
10 


Further development of a Badal type photoretinoscope

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Further development of a Badal type photoretinoscope

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