The Hess Screen Test

Gill Roper-Hall, D.B.O.T., CO., C.O.M.T.

ABSTRACT

The Hess screen test was designed by Walter Rudolf Hessin 1908 with subsequent modifications.' - Hess was a fa-mous neurophysiologist who was awarded the Nobel Prizein 1949 for his research into the functional organization ofthe vegetative nervous system.' '̂ The original test used ablack screen on which was marked a square-meter tangentscale. The tangent nature of the coordinate lines convertsequidistant points, seen in a virtual sphere like a perimeter,into a two-dimensional chart. The test relies on color dis-sociation using red/green complementary filters. This max-imizes the ocular deviation. A red target is illuminated orprojected at the juncture where each tangent line crosses. Agreen light is projected by the patient and each plot isrecorded. The test is repeated for the opposite eye result-ing in a chart showing an inner and outer range of ocular ro-tation for each eye.

EARLY SCREEN TESTS

Methods of documenting the field of ac-tion of individual muscles in various gazefields date back as far as 1874 by Hirsch-herg, who marked a tangent scale on thewall of his examining room. However, thetest relied upon the separation of diplopic

From tbe St, Louis University Eye Institute, St. Louis. Mis-souri.

Requests for reprints should be addressed to: Gill Roper-Hall, D.B.O.T., CO.. C.O.M.T, St. Louis University Eye In-stitute, 1755 S. Grand Blvd., St, Louis, MO 63104- e-mail:grb@slu.edu

Supported in part by a ^an t from Research to PreventBlindness, New York, New York.

images described by the patient that weresubsequently joined with prisms. This didnot allow for full dissociation of the devia-tion.^

In 1907, Ohm designed a black clothscreen based on Hirschberg's tangent scalewith blue strings outlining the coordinates.Complimentary red and blue filters usedwith a red arrow created color dissociation.He subsequently constructed a transpar-ent screen from wire mesh so that the pa-tient could be observed from the other sideof the screen.•*

In 1908, Krusius also designed a glassscreen through which the examiner couldobserve the eye movements in differentgaze fields, but mostly relied upon cor-

©2006 Board of Regents of the University of Wisconsin System, .American Orthoptic Journal, Volume 56, 2006, ISSN 0065-955X, E-ISSN 1553-4448

166

ROPER-HALL

neal reflections for interpretation.^ In1927, Sattler designed a black screen us-ing red/green dissociation, but employeda system of green coordinate lines.^ Fur-ther details and analyses of these modifi-cations are described in the AOS thesis bySloane.^-'"

HESS SCREEN TEST

Hess designed several versions of hisscreen. The original screen was construc-ted of black cloth 80 x 80 cm on which redembroidered dots were stitched where thetangent coordinates crossed. A pointer 50cm long was used, on the end of which wasa green arrow. One version had a stringwith a counterweight attached to thepointer, the string passing through the cen-ter of the screen.^ Later versions showed aY-shaped string with the top part extend-ing from each corner and the lower part at-tached to the pointer."

Hess used red/green color dissociation inall his versions, including the more recentscreens. The patient wore complementaryred and green glass lenses mounted in aspectacle frame. The cloth screens could berolled to store or transport them or un-rolled and hung on the wall. They werelightweight and portable.

Other screen tests were designed or mod-ified after Hess, the best known being theLancaster red-green test, initially calledthe Lancaster-Hess test and the Leesscreen.̂ "̂̂ "̂

MODERNIZING THE HESSSCREEN TEST

With the advent of electricity and the in-troduction of plastics, new equipment be-came available. By the late 1960s, thescreen was gray, wall-mounted, and avail-able in an electrically operated version.

The red and green glass lenses were re-placed with Armstrong goggles, made

from Kodak Wratten complementary redand green filters. These were molded toconform better to the midface and wereheld on by an adjustable elastic band.

Eoster torches were designed and dis-tributed by Clement Clarke in London.These can run off an electrical source orbatteries. A goalpost filament is used toproject a linear beam of light. A gray plas-tic sleeve with the matching complemen-tary red or green filter at its distal end isslipped over the end of the flashlight. Bymoving this sleeve up or down, the imagemay be focused on the screen. These gen-erally come as a pair and are used togetherto project a red fixation light onto thescreen by the examiner while the patient,wearing the Armstrong goggles, aims thegreen line at the red one. The fixating eyecan be changed by switching the goggles,so the red filter is on the opposite side, orby the examiner and patient exchangingthe Eoster torches.'"

The modern electric Hess screen is agray board on which is scored a tangentscale. The screen is mounted on the wall ofthe examining room. Small red lights atthe juncture where each scored line crossescan be illuminated in turn by bulbs behindthe screen. The examiner presses a keypadto switch on a specific target while the pa-tient projects the green line and bisects thered dot. Since the red lights are an integralpart of the screen, the goggles must be re-versed to obtain the plots for the oppositefield. The keypad is conveniently placed ona clipboard next to the chart being plotted(Figure 1).

Since the invention of personal comput-ers, several newer versions of the Hess orLancaster screens have been designed.̂ *^^^These are used in research settings and insome clinics, but are not yet in wide use.Some of the advantages include storageand manipulation of data retrieved dur-ing testing. Maintaining a distance of atleast 33 cm is necessary to avoid inducing

American Orthoptic Journal 167

HESS SCREEN TEST

accommodative or convergence influences.If this can be surmounted, perhaps by alarger screen, the test may be used reliablyon a laptop computer and allow the test tobecome portable again. Recent variationsinclude a three-dimensional Hess test andtesting aniseikonia on a computerized Hessscreen.̂ •'•̂ ^

PRINCIPLE OF THE HESSSCREEN TEST

The Hess screen test can be described asa fovea-to-fovea (maculo-macular) test.This occurs because two different coloredtest objects are used. Each fixation targetis red and the projected light is green.Wearing complementary red and greenfilters means that neither eye can see theopposite test object. This is in contrastto a regular diplopia test (maculo-paramacular) or the Worth lights where

red/green filters are used, but a white lightis common to each eye. This means thatthe deviation in the Hess screen test is di-rect, or drawn as if each fovea were look-ing directly at the screen at the point towhich it deviated. An esotropia lookscrossed on the board in the same directionas the deviation. In contrast, in a regulardiplopia test a white light is used and theimages will appear uncrossed or homony-mous. Each fovea perceives the image ofits respective target to be located straightahead. This is maculo-macular projectionor confusion (Eigure 2).

PLOTTING THE CHART

Armstrong goggles are worn by the pa-tient during the test. The patient is seated0.5 m from the screen with the head erectand immobile using a chin or headrest. Theexamining room lights are dimmed to re-

FIGURE 1: The electric Hess screen.

168 Volume 56, 2006

ROPER-HALL

Hess screen

= Fovea• RedH Green

F F

Left eye Right eye

FIGURE 2: Fovea-to-fovea projection used to dissociate the eyes.

move fusional background cues and furtherdissociate the eyes. This is usually suffi-cient to reveal a well-controlled heteropho-ria. The patient projects a green line ontothe screen and is asked to bisect each reddot with the green line as each dot is illu-minated in turn. It is usually easier to plota predominantly horizontal deviation, suchas a sixth nerve palsy, with the green lightprojecting a vertical line and plot a verti-cal deviation, such as a fourth nerve palsy,with a horizontal line. Each dot is testedand plotted in turn—first for the innerfield, then the outer. Once this task hasbeen completed, the goggles are reversed,the patient still projecting a green line, andthe test repeated.

The dots are joined by the examinerforming an inner and outer field for eacheye. These can be thought of as isopters orlines joining points of equal value, the com-monality being the distance from primarygaze in each direction. At 0.5 m each squarerepresents 10-̂ so the inner square mea-sures 30-̂ or about 15°. This is about therange an individual will move the eyes to

view a target away from primary gazewithout moving the head. The outer fieldsmeasure twice that amount, representingan exaggerated excursion, one that nor-mally is accompanied by a head turn. De-fects appearing on the inner field are likelyto be more symptomatic.

INTERPRETATION OF THEHESS CHART

Once the chart is drawn, the examinercan assess the overall pattern to identifythe eye with the muscle(s) involved (thesmaller field), the biggest overactions inthe opposite field (whether the overallpattern shows incomitance or concomi-tance), and generally whether the patternlooks paralytic or restricted (Figure 3).One of the most valuable roles that se-quential Hess charts can provide is usefulinformation about the course ofa disorder,indicating whether it is resolving, pro-gressing, or stabilizing. This will permitappropriate management decisions to bemade (Figure 4).

American Orthoptic Journal 169

HESS SCREEN TEST

FIGURE 3: Hess chart in a patient with a longstanding concomitant hyperdevi-ation.

ADDITIONAL TECHNIQUES

Sometimes a patient will show variahil-ity during testing that is suggestive of ocu-lar myasthenia. The test can he repeatedusing Tensilon®, with those parametersalready plotted used as a haseline in theTensilon-Hess test (Figure 5).'^^ The pres-ence of an intermittent or variahle condi-tion such as superior ohlique myokymia,superior ohlique click syndrome, or ocularneuromyotonia can also he documentedduring testing.

Occasionally, the patient's view of thescreen will he obstructed hy ptosis, a heavyhrow, swelling from injury or surgery or theposition of the goggles. The red and greenfilters overlap in the center of the goggles.This excludes all light hecause the colorsare complementary and the goggles musthe adjusted. In patients with marked ex-ophthalmos, care must he taken to avoidtouching the cornea; it is helpful to ask pa-tients if they can hlink freely when the gog-gles are first introduced.

Torsion cannot he interpreted easily ona Hess chart as it is difficult to relate theangle of the torted image when projectinga line of light onto a tangent scale. Thetest certainly can reveal the presence oftorsion, hut this is hetter quantitatedusing standard methods such as douhle

Maddox rods or other methods such as theHarms or Lancaster screens.

On occasion, a patient will demonstratedifficulty in locating the next target, whennothing is ohstructing their view. It is pos-sihle to detect scotomata in glaucoma pa-tients or even suspect a hemianopic visualfield defect from the manner or direction inwhich a patient hesitates during plotting.

Patients with Parkinson disease, ataxia,or other balance prohlems should be mon-itored during the test, perhaps assisted hya family member, to ensure that they re-main seated upright in the darkened room.A helpful hand behind the patient's headwill keep the head erect and not tilted,keep the forehead on the headrest and offerassurance that they will not fall. If there ispronounced dysmetria or tremor, holdingthe green light with both hands close to thechest is helpful.

It can be challenging to perform the teston someone with a hearing problem. It isnot possible to lip-read while wearing gog-gles in the dark, with the examiner stand-ing hehind the patient. It may he neces-sary to give instructions face-to-face beforethe test hegins, making sure the patientcan understand. In patients with suppres-sion or ARC it may not he possible to ob-tain responses on a Hess chart as the prin-ciple of the test relies on normal retinal

170 Volume 56, 2006

ROPER-HALL

HESS SUIEEH OURT

FIGURE 4: Hess charts (top, bottom) demonstrating resolving, bilateral fourthnerve paralyses.

HESS SCfl£EN CHART

FIGURE 5: A T^nsilon-Hess test in a patient suspected of having ocular myas-thenia.

correspondence. However, sometimes thefovea-to fovea dissociation used is suffi-cient to disrupt suppression and the chartcan be plotted. This is useful in a patientwith a longstanding deviation with sup-

pression and a newly acquired paralysis.It is sometimes possible to plot incomi-tance in a patient with paralysis or re-striction with ARC but the angle of anom-aly should be noted.

American Orthoptic Journal 171

HESS SCREEN TEST

HESS CHARTS IN DIFFERENTIALDIAGNOSIS

Hess charts are invaluable in the differ-ential diagnosis of many different clinicalconditions. Characteristic patterns are re-vealed on the chart in congenital disorderssuch as Duane or Brown syndrome. An ob-vious restriction in the affected gaze posi-tion does not produce the usual overactionof the ipsilateral antagonist as it would ina paralysis (Figure 6). The chart may helpdifferentiate these conditions from sixthnerve palsy or an inferior oblique weak-ness, respectively.

Observing the nature of concomitanceand spread of muscle sequelae can help dif-ferentiate a recently acquired paralysisfrom a longstanding and recently decom-pensating one (Figure 3). It is particularlyuseful in planning surgery on a patientwith a stable superior oblique muscle palsyby comparing the overactions of the ipsi-lateral antagonist (inferior oblique) versusthe contralateral synergist (opposite in-ferior rectus) in deciding which muscleshould be weakened, or weakened first iftwo-staged surgery is planned.

Unilateral and bilateral fourth nervepalsies can be identified by their char-acteristic patterns (Figure 4). The Hesschart of a patient with an acquired supe-

rior oblique weakness often reveals asym-metric bilateral involvement not apparenton other clinical testing.

Most restrictive conditions such as or-bital fractures with entrapment or thyroidrestrictive disease have an accompanyinghistory to guide tbe diagnosis. However,these can be differentiated from paralysisby the different patterns each condition ex-hibits (Figure 7).

A Hess chart can be instrumental in cor-rectly identifying the affected eye whenother clinical signs suggested otherwise. Asledding accident caused an orbital floorfracture in a 64-year-old grandmother. Thefracture was confirmed by CT scan. Shecomplained of vertical diplopia. The Hesschart revealed that she had sustained amild traumatic fourth nerve palsy in theside opposite the fracture. The fracture wasallowed to heal without intervention; thefourth nerve palsy also resolved.

CONCLUSION

A Hess screen is a valuable addition toany strabismus clinic, particularly one inwhich a high percentage of adults is seen.The test can be performed quickly andprovides extensive information about therespective motility disorder. The baselinechart is used in differential diagnosis, and

FIGURE 6: Hess chart of a patient with Brown syndrome. Note absence of anyobvious problem in down-gaze.

172 Volume 56, 2006

ROPER-HALL

FIGURE 7: Hess chart ofa patient with an orbital floor fracture with mild en-trapment demonstrating restriction on both up and down-gaze in the right eye.

comparison of subsequent charts is im-portant in management. It comparesfavorably with other screen tests, and pro-vides graphic representation for interpre-tation.

ACKNOWLEDGMENT

The author wishes to thank Antonia Ra-sicovici, CO., for her assistance in trans-lating some of the more difficult Germanpassages.

REFERENCES

1. Hess WR: Eine Neue Untersuchungsmethode beiDoppelbildern. Arch Augenheilkunde 1908; 62:233-238.

2. Hess WR: Ein einfaches messendes Verfahren zurMotilitatsprufung der Augen. Zeitschrift fiir Au-genheilkunde 1916;15: 201-219.

3. Roper-Hall G: Walter Rudolf Hess (1881-1973):Ophthalmologist and Nobel Pnze winner. Am Or-thoptJ2006: 56: 184-188,

4. Huber A: WR Hess, the ophthalmologist. Experi-entia 1982; 38: 1397^000.

5. Hirschberg J: Uber Blickfeld messung. Arch Au-gen Ohrcnheilkd 1874; 4: 273.

6. Ohm J: Neue Instrumente, Medikamente, usw,ein Apparat zur Untersuchung des Doppelsehens.Central bldtt fur praktishe Augenheilkunde 1907;31:201-203.

7. Krusius F: tjber die Schetben-Deviometer. Archivfur Augenheilkunde 1908; 59: 867-868.

8. Sattler CH: Uber die genaue Measung and Dar-

stellung von Bewegungsstorungen der Augen.Klinische Monatsblatter fur Augenheilkunde1927;78: 161-178.

9. Sloane A: Analysis of methods for measuringdiplopiafields.AMAArc/iOp/K/in/1951; 277-310.

10. Roper-Hall G, Burde RM: Clinical analysis ofextraocular muscle paralysis. In: Adler's Physiol-ogy of the Eye, 7th ed. Moses RA, ed. St. Louis: CVMosby Co.; 1981. pp. 166-183.

11. von Noorden GK. Binocular Vision and OcularMotility. Theory and Management of Strabis-mus. Chapter 12. St. Louis: CV Mosby Co.; 1990.p. 181.

12. Lancaster WB: Detecting, measuring, plottingand interpreting ocular deviations. Arch Oph-thalmol 1939; 22: 867-880.

13. Lees VT: Anew method of applying the screen testfor interocular muscle balance. Br J Ophthalmol1949; 33: 54-59.

14. Lees VT: The Hess screen with mirror dissocia-tion. Br Orthopt J 1949; 6: 50-55.

15. Dulley B, Harden A: Cyclotorsion: A new methodof measurement. Br Orthopt J 1974; 31: 70-77.

16. Christoff A, Guyton DL: The Lancaster Red-Green te.st. Am Orthopt J 2006; 56:157-165.

17. Harms H: Uber die Untersuchung der Augen-muskellahmungen. Graefes Arch Clin Exp Oph-thalmol 194\; 144: 129.

18. Tyedmers M, Roper-Hall G: The Harms tangentscreen test. Am Orthopt J 2006; 56: 175-179.

19. Mackensen G: Die Tangentskala nach Harms. In:Augenmuskellcihrnungen Buvherei d. Augenarz-tes. 46. Stuttgart: Ferdinand Enke Verlag; 1966.

20. Assaf AA: Computerization of Hess and Leesscreen testing. In: Advances in Amhlyopia andStrabismus. Transactions of the Vllth Intern-tional Orthoptic Congress, Nuremberg, 1991,p. 403.

American Orthoptic Journal 173

HESS SCREEN TEST

21. Rouse MW, Calloroso E: A new method of con-comitancy testing. Am J Optom Physiol Opt 1980;57: 56-63.

22. Bowman K-J, Swann PG: An electronic Hessscreen system. Clin Exp Optom 1984; 67: 23-24.

23. Thomson WD, Desai N, Russell-Egitt I: Anew sys-tem for the measurements of ocular motility usinga personal computer. Ophthalmic Physiol Opt1990:10:137-143.

24. Bergamin O, Zee DS, Roberts DC, Landau K,Lasker AG, Straumann D: Three-dimensionalHess screen test with binocular dual search coils

in three-field magnetic system. IOVS 2001; 42:660-667.

25. Hirai T et al.: Dynamic aniseikonia on Hess chart?Binocul Vis Strabismus Q 2004; 19: 234-245.

26. Coll GE, Demer JL: The edrophonium-Hessscreen test in the diagnosis of ocular myasthenia.Am J Ophthalmol 1992; 114: 489-493.

Key words: Hess screen, Lancasterscreen, Lees screen, Harms tangent screen,diplopia, confusion, Walter Rudolph Hess

AOJ Now Available OnlineWe are proud to announce that subsaibers to American Orthoptic journalnow receive free access to complete issues oiAO] Online.

Simply go to the UW Press - Journals web site at: www.wisc.edu/wiscomin-press/joumals, select American Orthoptic Journal, click on "electronic edi-tion" and follow the simple instructions.

To order subscriptions or for information, contact:The University of Wisconsin Press, Journals Division1930 Monrm St., Madison, WI 53711 • tel: 608-263-0654, fax: 608-263-1] 73

www.wisc.edu/wiscoiisinpress/jonnials

174 Volume 56, 2006