NOVEMBER, 1939

Fundus Photography without Cycloplegics

KATHYRN LOUISE STONECollege of Optometry, Ohio State University, Columbus, Ohio

AND

M. L. POOL

Department of Physics, Ohio State University, Columbus, Ohio

(Received August 28, 1939)

With the use of the new H6 water-cooled 1000-watt mercury arc lamp, two Polaroids, a newfast film of Weston rating 140, and a simple optical system photographs of the fundus of theeye have easily been made without the use of drugs that dilate the pupil.

INTRODUCTION

PHOTOGRAPHS of the fundus of the livinghuman eye have been made for many years

and have been of the utmost value in the diag-nosis and prognostic observation of manyaffections of the eye. This photographic aid, how-ever, has been limited to the oculist and ophthal-mologist. They alone are permitted to use cyclo-plegics which dilate the pupil, and pupillarydilation is essential for the satisfactory operationof retinal cameras now available. Of these theNordenson retinal camera is used almost uni-versally.

It is the purpose of this paper to describe asimple camera unit which is relatively inex-pensive, eliminates the necessity for usingcycloplegics and removes the customary cornealreflex.

OPTICAL ARRANGEMENT

Figure 1 shows a schematic diagram of theoptical system used in illuminating the fundus ofthe eye. The light from the source S1 is condensedby the lens L1 onto the variable slit SL. Thislight then passes through the shutter SH andinto the lens L 2 which focuses the light in thepupil of the eye at E1 . The light passes on intothe eye and merely illuminates the fundus. Mland M 2 are plane and nearly transparent mirrorsmade of thin pieces of good quality glass. Thesource S2 is placed at such a position that itsimage produced by the lens L 2 is also at E1 . Thesource S3 is placed at the primary focus of thelens L4. The distance from E1 to E 2 is the inter-pupillary distance.

Figure 2 shows a schematic diagram of theoptical system involved in the emission of the

QS,

1.i

L S L SL.Li

I i LaS H.

FIG. 1. Optical system for illumination of the fundus.

463

I I

L3P . I - ----- -- -

I II I

I II II I

I I

A', 1B PH.

VOLUME 29J. . S. A.

K. L. STONE AND M. L. POOL

B A

F

iQ2

M2

L3

Al [B PH

FIG. 2. Optical system for light emitted from the fundus.

light from the illuminated fundus. Since thepoints A' and B' are both in the primary focalplane of the compound lens system of the eye,the light leaving these points and defined by theiris consists of two diverging beams of parallellight. A portion of the camera lens L 3 interceptsthese two beams and focuses them on the photo-graphic plate PH at the points A and B, respec-tively. This lens L 3 should have a large aperturein order to be able to receive light from widelyseparated portions of the fundus and a focallength as short as possible in order to reduce thesize of the image and thus increase the speed ofthe camera. The focal lengths of the lenses L,and L 2 are 35 mm and 60 mm, respectively. Forthe lens L 3 the following have been used: focallengths 75, 50 and 25 mm with speeds, respec-tively, f: 1.8, f: 1.5 and f: 1.3.

SOURCES, FILTERS, POLAROIDS AND FILM

For the primary source Si, the new highintensity type H6 1000-watt water-cooled mer-cury arc lamp has been used with excellentsatisfaction.' Its very high intrinsic intensity,the narrow capillary source and the spectralenergy distribution are particularly suited for

1 Gen. Elec. Rev. 42, 46 (1939).

the photographic requirements in this work. Thecontrast on the photographic film between theblood vessels and the surrounding medium thatcomposes the fundus of the eye is brought outbest with green light illumination. The H6 arclamp fortunately emits a large percent of itstotal radiation in the yellow-green line, 5461A.2

In comparison with other types of mercuryarcs there is from this new lamp a very pro-nounced continuous spectral background. Theenergy in this background, nevertheless, is smallcompared with the energy in the principalmercury lines. The principal lines 4358, 4047 and3660A should not be allowed to enter the eye andmay be removed by filters. The Jena filter GG11or the Wratten filters K-2, G or the mono-chromatic No. 77 have been found about equallysatisfactory. The circulating water, used incooling, absorbs about 90 percent of the infra-redradiation. 3

For a very simple light source, although notquite as satisfactory as the H6 lamp, the newhigh efficiency tungsten coiled filament lamp hasbeen used.4 This 120-volt, 60-watt lamp in clearglass with the C6 filament is used at about 210volts. Since the filament is very small and straightit can be sharply focused on the slit S and alarge portion of the radiant output energy thusutilized. It is now necessary to be more carefulin the selection of the filters. The Jena filters BG19 and GG 11, used together, have been foundadequate.

P1 in Fig. 1 is a Polaroid which is rotated insuch a way that the light from the slit Si ispolarized in a plane perpendicular to the plane ofthe figure. Light reflected from the cornea re-mains, for the most part, polarized and thatreflected from the fundus is depolarized. Sincethe intensity of the light reflected from thecornea is comparable to that from the fundus, itis therefore necessary to rotate the Polaroid P2in such a way as to cut out all light polarized inthe original plane. Consequently, only depolar-ized radiation from the fundus gets through thesecond Polaroid and onto the photographic film.

The new commercial Eastman Tri-X pan-chromatic film has been found more satisfactory

2 L. J. Buttolph, J. Opt. Soc. Am. 29, 124 (1939).3 E. B. Noel and R. E. Farnham, J. Soc. Mot. Pict. Eng.

31, 221 (1938).4 E. W. Beggs, J. Opt. Soc. Am. 29, 117 (1939).

464

FUNDUS PHOTOGRAPHY

than any other of a number of films and profes-sional plates tried. This film has a Weston speedrating of 140 when developed in DK 60a.

RESULTS

In taking a picture of the fundus the procedureis first to close the shutter SH and turn on thesource S2 which is weak and can be varied to justvisibility. The eye in position E1 then sees a faintgeneral red glow when adjustments are correct.The only purpose of this weak source is to makeit possible for the patient to put his eye, the oneto be photographed, in the proper position whileit is dark adapted. The patient as well as thecomplete apparatus is housed in a darkenedbooth. Should the light from the strong source SI(about 10,000 times as strong as the source S2)be admitted through the shutter SH for thepurpose of making preliminary adjustments, theiris of the patient would contract to so small asize that subsequent photography would be im-possible. If the iris were prevented from con-tracting by the use of cycloplegics, then the

FIG. 3. Photograph of the fundus.

source S2 would obviously be unnecessary andthe source S1 could be used in making the pre-liminary adjustments.

Since the amount of light from the weak sourceS2 falling upon the fundus is just enough to giveto the patient the sensation of light, the amountof light reflected back from this faintly illumi-nated fundus and onto the photographic film isindeed very feeble. Consequently, it is not neces-sary to use a shutter on the camera lens itself.

The eye in position E 2 is relaxed and sees atinfinity the virtual image of the source S3. Sincethe eye at position E1 is therefore also relaxed,it is only necessary to set the camera unit tofocus parallel light in order to get a sharp pictureof the fundus. When these preliminary adjust-ments have been made, the shutter SH is thenopened for a predetermined short length of timeto allow the light from the very strong primarysource Si to illuminate the fundus.

Figure 3 is a picture of the fundus obtainedwith the H6 arc source and the GG 11 filter. Thepupil was only moderately dark adapted, and theexposure time was 1/10 sec. In the picture can beseen the whitish optic nerve head or optic disk,the retinal blood vessels, both arteries and veins,and some choroidal vessels dimly in the back-ground. One notices no abnormalities and soconcludes that this is a normal fundus.

When the C6 filament lamp is used it isnecessary to lengthen the exposure time to atleast 1/5 sec.; in addition the excellent photo-graphic detail and contrast is always somewhatlacking. Since eye movements are frequentlynoticeable it is advantageous to keep the ex-posure time as short as possible.

Some progress has already been made withusing colored 35-mm films. Since these films havean appreciably slower emulsion speed, a widerslit and the full intensity of the H6 arc sourcemust be used. Report on this work will be reservedto a later date.

465