The Swinging Flashlight Test to DetectMinimal Optic Neuropathy

John A. Stanley, MD, and George R. Baise, MD, Winston-Salem, NC

Patients with prior optic neuritis were examinedfor the presence of an unilaterally impaired pupil-lary response to light by a method which is be-lieved to be superior to conventional testing ofpupillary constriction. A positive pupil sign wasfound in ten eyes with 20/20-2 or better vision.The clinical sensitivity of the test is highlightedsince conventional tests of pupillary light constric-tion did not reveal a pupilmotor deficit. Each ofthe patients showing a positive swinging flashlighttest had mild unilateral optic nerve pallor. The re-sults further indicate that in mild optic nerve dam-age, a positive swinging flashlight test is more

consistently present than a color vision deficit or ademonstrable visual field scotoma.

A HE diagnostic value of observing impair¬ment of the direct light reaction of a pupilin optic neuritis was pointed out by Mar¬cus Gunn in 19051 and more recently byKestenbaum.2 The purpose of this paper isto investigate by a swinging flashlight testthe presence of a defective direct pupillarylight response in minimal but definite casesof unilateral optic nerve damage, and tocompare the findings with other parametersof optic nerve function.

The Swinging Flashlight TestSince the demonstration of a unilateral

pupilmotor deficit to direct light stimulationin patients with minimal optic neuropathy isthe crux of this paper, it is important thatthe test used to uncover such a deficit beexplained. Conventional pupil testing in theauthors' opinion is not particularly sensitiveto detection of mild to moderate impairmentof direct light reaction. A nearly instanta¬neous comparison of the direct light reactionbetween a patient's pupils is the key to a

sensitive test and is best made by a swinging

flashlight test as first used by Levatin.3Essentially the test consists of a series of

comparative observations rather than theconventional single annotation of pupillaryconstriction. After illuminating one pupil, abright focal light source is rapidly moved tothe fellow pupil, and an observation is madeof pupillary behavior. Normally the secondpupil does not change very much in size,perhaps alternately dilating and constrictingup to 0.5 mm. The light is then rushed backto the first eye and another observation ismade of pupillary behavior. As before, thenormal pupil does not change in size. Thisswinging of the light between the two pupilsis repeated until the examiner can concludethat either the pupils behave similarly or

dissimilarly. In normal individuals, there isno particular dilatation or constriction ofeither pupil to the swinging light. It is thedifference in pupillary behavior to theswinging light which is the crucial finding ofthe test. A difference is considered abnormal.In a few normal circumstances, there may bea moderate amount of pupillary movementin the face of focal illumination, but suchpupillary unrest or hippus is equal and sym¬metrical in the two eyes and should not beconfused with a unilateral abnormality todirect light.The reason that the pupils normally do

not change in size on alternately swinging a

light from one eye to the other is that thedirect and consensual pupillary responsesare clinically identical. Shining a brightlight in only one eye induces no anisocoriain humans4 because roughly 50% of theoptic nerve fibers decussate in the opticchiasm. The equality of the direct and con¬sensual pupillary responses imparts excep¬tional sensitivity to the swinging flashlighttest. Rapidly moving a light from one eye toanother instantly substitutes a direct lightresponse for a consensual response. If thereis unilateral optic nerve damage, the directlight response in this pupil is less than the

Submitted for publication July 8, 1968.From the Department of Ophthalmology, Bowman

Gray School of Medicine, Wake Forest University,Winston-Salem, NC.Reprint requests to the Department of Clinics,

North Carolina Baptist Hospital, Winston-Salem27103 (Dr. Stanley).

Downloaded From: http://archopht.jamanetwork.com/ by a Missouri S & T User on 10/10/2013

Patients With Prior Unilateral Optic Neuritis

Age513921483835521943563853

SexPositive Swinging

Light TestOP~

OPOSOP~

OSOS00NoneÖSOSÒ~PNone

Vision inAffected Eye20/2020/20+120/2020/2020/2020/20—220/2020/20+120/2020/20—2_20/15—120/15

PisePallorOPOPOSOPOSOSOPNoneOSOSOPNone

PericentralScotomaNoneNoneOSNoneOSNoneOPNoneOSNoneop"None

ImpairedColor Vision

NoneOPNoneOPNoneOSNoneNoneOSOSOPNone

consensual response obtained from the nor¬mal eye so that when the flashlight is movedfrom a normal eye to one with optic nerve

damage, the pupil dilates. On returning thelight to the normal eye, the pupil constricts.Such an asymmetry of pupillary behavior tothe swinging light is a positive test.The authors tested the pupils of 100 pa¬

tients thought to be free of ocular abnormal¬ities and did not find a single positiveswinging flashlight test. Drews5 also foundthe test to be free of false positives. Exactequality of pupillary reaction to light bothdirectly and consensually in normal individ¬uals was reported by Lowenstein andFriedman6 using the sensitive laboratorymethod of electronic pupillography. Thiswas later confirmed by Thompson.7The test is of limited value in cases of

bilateral optic nerve damage. Randomlymixed among the patients examined were

cases of patients with previous bilateral op¬tic neuritis, and in no such instance was a

positive swinging flashlight test recorded.Unilateral involvement would seem to benecessary since it is a normal pupillary re¬

sponse which needs to be compared with a

possible diminished response from the otherpupil.

Method

Called for examination were patients whotwo to six years prior to this study had had an

unequivocal episode of optic neuritis. Each pa¬tient was particularly tested for the following:(1) impairment of direct pupillary light reac¬tion by the swinging flashlight test, (2) defec¬tive color vision by reading the Ishihara testplates, (3) visual field defects by tangent screenexamination, using a low intensity projector

light, which experience has shown to be ap¬proximately equivalent to the 1/2000 whiteisopter, and (4) the presence of optic atrophyby comparing color and number of capillarieson the temporal margin of the two optic nerveheads. The patients were examined indepen¬dently by the two authors except for visualfield testing which was done only once (J.A.S.).Testing and recording were done without priorknowledge of which eye or whether both eyeshad had optic neuritis. No patient in the studywas found to have an impairment of the extra¬ocular motions nor a fundus abnormality exceptfor optic atrophy as reported here.The authors tested the pupillary reaction to

light in a very dimly lit room with the patientfixing on an object 20 feet distant in order toeliminate reflex pupillary motions to accommo¬dation. All patients in this study were testedwith a bright muscle light held approximately 2inches from the cornea and moved rapidlyacross the bridge of the nose. Each pupil wasilluminated by as bright a light as practical.Observation was made of each pupil for two orthree seconds, and these observations were re¬

peated until a decision was reached in eachcase as to the equality of pupillary behavior. Apositive test was taken to be a consistent dilata¬tion of one pupil in the face of a direct lightwhich had been moved rapidly from the othereye and a consistent constriction of the otherpupil when the light was rapidly moved back.

Results

Analysis of the recall examination showedthat 12 patients met the criteria of havinghad a well-documented episode of unilateraloptic neuritis which subsequently was clini¬cally inactive for at least two years withrecovery of vision to 20/20-2 or better. Dur¬ing the acute episode of optic neuritis, theinitially measured visual acuities ranged

Downloaded From: http://archopht.jamanetwork.com/ by a Missouri S & T User on 10/10/2013

from 20/70 to light perception only. Of the12 patients, two had an established diagno¬sis of multiple sclerosis.An unequivocally positive swinging flash¬

light test was found by both authors in 10 ofthe 12 patients. In none of the patients did aconventional test of pupillary response todirect light uncover an abnormality. Tenpatients were judged to have unilateral opticatrophy of mild degree. The two patientsnot believed to have optic atrophy were alsothe patients with normal pupils. A unilater¬al defect in color vision was found in sixpatients and pericentral scotomata were

plotted in five patients. One patient had a

unilaterally enlarged blind spot in the pre¬viously affected eye for which the authorshave no obvious explanation. All defects incolor vision were of mild degree with onlythree or four of the Ishihara color platesbeing missed. Further details of the recallexamination are found in the Table.

CommentNone of the patients in this study would

have been judged to have a defective pupil¬lary response to light by conventional test¬ing (observation of the magnitude of an

isolated individual pupillary constriction).Nevertheless, all the patients had had a

prior episode of unilateral optic neuritis andeven though all had recovered 20/20-2 orbetter vision in the involved eye, 10 of the12 patients were thought to have a unilater¬ally pale optic nerve head. Each of these tenpatients was independently judged by bothauthors to show a positive swinging flash¬light test, indicating a unilaterally impairedpupillary response to direct light stimula¬tion. The authors believe that judgement of apositive swinging flashlight test is also moreobjective and subject to less uncertaintythan abnormal pallor of an optic nerve head.Unilateral alternating contraction aniso¬

coria of Lowenstein8 produces pupillograph-ic asymmetry of the direct pupillary lightresponses, but the authors are unaware ofthe clinical detection of this condition.Sometimes the consensual pupillary re¬

sponse lags slightly behind the direct lightresponse, but practically this is of no conse¬

quence if each pupil is observed in turn forat least two seconds. However, it is impor¬tant to the clarity of the test that the light

source be moved rather rapidly across thebridge of the nose in order to reach theother pupil before it has "escaped" from itsconsensual reaction.The results indicate that optic nerve dam¬

age can be suspected if a positive swingingflashlight sign is present. The performanceof this test can be of great value in thediagnostic evaluation of papillitis vs unilat¬eral papilledema, unilateral retrobulbar neu¬ritis vs functional amblyopia, and optic neu¬

ropathy vs unilateral physiologic disc pallor.In acute retrobulbar neuritis, demonstrationof a difference in direct light response be¬tween the involved and uninvolved eye isthe only possible objective finding to sub¬stantiate the diagnosis. Such an objectivefinding can differentiate a unilateral opticneuropathy from malingering, hysteria, or

amblyopia ex-anopsia. In a patient having adense cataract which precludes fundus ex¬

amination, a positive swinging flashlight testcasts doubt on the integrity of the opticnerve. The more extensive the optic neuro¬

pathy, the more striking is the result of theswinging flashlight test, but even mild de¬grees of optic nerve damage reliably resultin positive tests. With very little practicethe swinging flashlight test is reproducibleand the interpretation of the results clear-cut. A positive test can be taken as evidenceof optic nerve damage whether it is second¬ary to optic neuritis, optic nerve tumor, orextensive damage to the retinal ganglioncells as occurs in arterial occlusive disease,widespread chorioretinitis, or long standingretinal detachment.

References1. Gunn, R.M.: On Retro-ocular Neuritis, Ophthal

Rev 24:285-299, 1905.2. Kestenbaum, A.: Clinical Methods of Neuro-

ophthalmologic Examination, ed 2, New York: Grune& Stratton, Inc., 1961, pp 136-137.3. Levatin, P.: Pupillary Escape in Disease of the

Retina or Optic Nerve, Arch Ophthal 62:768-779(Nov) 1959.4. Jones, I.S.: Anisocoria: Attempted Induction

by Unilateral Illumination, Arch Ophthal 42:249-253(Sept) 1949.5. Drews, R.C.: The Gunn Pupil Sign, Amer J

Ophthal 54:1109-1113 (Dec) 1962.6. Lowenstein, O., and Friedman, E.D.: Pupillo-

graphic Studies, Arch Ophthal 27:969-993 (May)1942.7. Thompson, H.S.: Afferent Pupillary Defects,

Amer J Ophthal 62:860-873 (Nov) 1966.8. Lowenstein, O.: Alternating Contraction Aniso-

coria, Arch Neurol and Psychiat 72:741-757 (Dec)1954.

Downloaded From: http://archopht.jamanetwork.com/ by a Missouri S & T User on 10/10/2013