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Ocular Rotations and the Hirschberg Test Pacific University CommonKnowledge College of Optometry Theses, Dissertations and Capstone Projects 3-1-1977 Ocular rotations and the Hirschberg test A John Carter Pacific University Recommended Citation Carter, A John, "Ocular rotations and the Hirschberg test" (1977). College of Optometry. 448. https://commons.pacificu.edu/opt/448 This Thesis is brought to you for free and open access by the Theses, Dissertations and Capstone Projects at CommonKnowledge. It has been accepted for inclusion in College of Optometry by an authorized administrator of CommonKnowledge. For more information, please contact [email protected]. Ocular rotations and the Hirschberg test Abstract The Hirschberg test is an objective means of determining the angle of strabismus by noting the distance the corneal reflex of a light source is from the center of the entrance pupil. A scale factor is used in converting the amount the reflex distance is in millimeters ot prism diopters. Recent studies have demonstrated this factor to be 22 prism diopters for each millimeter. This study notes how axial length would effect this scale factor. Using ultrasound axial lengths of thirty eyes were measured and compared to the results of a Hirschberg simulation. A small effect results from this comparison. The mean values of scale factor determination noted twenty-three prism diopters per millimeter. Degree Type Thesis Degree Name Master of Science in Vision Science Committee Chair Niles Roth Subject Categories Optometry This thesis is available at CommonKnowledge: https://commons.pacificu.edu/opt/448 Copyright and terms of use If you have downloaded this document directly from the web or from CommonKnowledge, see the “Rights” section on the previous page for the terms of use. If you have received this document through an interlibrary loan/document delivery service, the following terms of use apply: Copyright in this work is held by the author(s). You may download or print any portion of this document for personal use only, or for any use that is allowed by fair use (Title 17, §107 U.S.C.). Except for personal or fair use, you or your borrowing library may not reproduce, remix, republish, post, transmit, or distribute this document, or any portion thereof, without the permission of the copyright owner. [Note: If this document is licensed under a Creative Commons license (see “Rights” on the previous page) which allows broader usage rights, your use is governed by the terms of that license.] Inquiries regarding further use of these materials should be addressed to: CommonKnowledge Rights, Pacific University Library, 2043 College Way, Forest Grove, OR 97116, (503) 352-7209. Email inquiries may be directed to:[email protected] submitted in artial fulfillment of the Doctor cf Optomct:r.�' degree A. ,John Carter \\"'1! 31�r- .. -. 11 1 1, . 077..-· . ABSTRACT The Hirschberc test is an objective means of determining the angle of strabismus oy noting the distance the corneal reflex Of a light �our6e· is 'ftom thb ·center pf.the entrance pupil. A scale factor is used in convertinc the amount the reflex distance. is In miliimeters to prism diopters. Recent studies have demonstrated this factor to be 22 pr.ism diopters for each millimeter. This study note::; how axial length would effect this scale ·factor. Using ultrasound axial lenr,ths of. ts thirty eyes were. mea�-;ured and compared' to the re:::iul of a._ Hirschberg s:i.mulation. A small effect results from this. comparison. 'I'he mean values of scale factor determination noted. twenty-three prism diopters per. m111:1.met'er � I would like to 0,xtend an appreciation t() Dr§ Niles Roth my a.dviser, for the many hours, thought, foresie.ht, knowledge, and assistance he· has put in·this project� 1 ' I I 1�• i ! Te �:;t t - �]e\rictt.. os relative rOtational 11ostion of the eyi"!� "" " i , , '- + . ,·· · ·n ' _ o u r e.... _. + L •J • •• . .!p•1�- -� _ r;-,.-,··1..\ formGd .1"'�' ··;:1 .l' 1rld.J.� -i 'n'' b o, J. ·--GI l v ,:_, 1.. .....,. J0"'i .·f'rcr+ .. >'- ' cf".. i-1·pJ ;,.,. ·1·, ct.... ,.1 c., J. l t..o c . 1.u having. him fixate the _The ·smooth corne� 0111 reflect an image of the light visible to the �xaminor. The position of the reflex relative to the entre:"3.nCt'� pup1l, cl�''pends OD where the eye is fixa.tin.g. An eye wh�ch w.111 r5.x3.te the J.ic,ht _._, source rl, ("",I l'D"� ; o" .•11 ...l.....,, \1 'I will have L·H8 reflex n•.?.ar the center .of the cntra.nce pupil of tho eye or rnorr::� common:J.y :3.bout 0.25 mj_lli- · �- -1,._,·}·1·-" •. __ ./ �-· n,e·l · ...... r�":!... .. -t...,. o','•'!O''-·' . -"..· · ·d �� · !"i . ',c-' ... 4 -... 0 .... ..... .) � ("',_,..... �,,. \.J -,,. J,.A.(1.."" '°'"'i::.' �·J.,. c.. 1 t • s:o_-,"'.l ]_- r.:: _ .1 t·1,:.>. B1·,t· + ,_J.:.t.::, ": r··,�.:."j r1. f: ·t: t ·'• l point other than the.fixation target, as happens in strabisw1�, the corneal light reflex seE·n by t..:he examiner w j 11 be in "'· • · •' .... •. .. .. - . "' �- ..... .1 , j .. 1:'no� :.i.i·tJ"on c'1 ·e+ n vr�1" n p � . b/ "h c d 1;:;via.t ion accurate ·r ixat1onw. fi Julius H.i:rsc-hhrg - , who originated th.e mrothod, c.1. ted relationships between ocular devia.tion and app:J.r<;:nt location of the corneal reflex. Theso are, Page 2 1) Tf the corn0a1·1ight reflex is seen within the pupil- lary ·area, the deviatio� can ranee from 0-20 decrees of a�c. 2) if thP reflex is seen within the interval �ounded by the pupillary margin and th.e limbus of the cc.rnc;:1_, the dnviation Ca.n ra.nge fr<:Hn 0-lJ_52 degree S, 3) sclerc-:.) L if the ref lex 1 ies outside the limbus (on the ·I then the deviation is greater than 45 dec,ree:3. l L Krims};:y9 notedthat the radius of curvature of the cornea is about eight millimeters. He reasoned that each millimeter on the corneal curvat.un� would correspond to ��even 8.1'.'C degrees.· His reasoninc is that e�ch millimetbr the reflex deviates from the �enter of the entrance pupil, or the apex a:f the cornea, corresponds to seven a,�grees of arc, or o.bont tw1.;::lve prism diopters deviatiori. Other investigators have used similar scale factors :for . 1� angular deviation per millimeter. Among them are Scobee-� who claims·t.11-t eight.degrees deviation ls noted for ·each milli- ...... � . meter. Burian and van Noorden� agree with the seven degrees or t1..velve prism diopters quoted by Krimsky. Nore rccent1y Optometric the Weekly18 in a series of articl��s a.bout strab- L ismus for optometric assistants, .claim that the amount of s6ven Page _,1. prism diortet�s degrees or tw.:'.)lve . for each milL�_mr-:te�::- :f:corn the center of the entrance pupil. is the scale factor to use. Krims1cy9 noted. that the rotation of the eye was the crucial factor, not the 6urvatur� of the cornea. 1\lth.0:1;.ri1._, the rotation. isn • t directly me2wured. in th� Hirschber0 test, the amount of the strabismic devis.tion of eye s.hould equal the amount of rotation of a normal eye to that deviating position. He points of the cornea o�t that th� curvature doesn·t .affect the rotation the strabismus the or and that apex of the cornea would move with the rest of the eye. This idea was further D.dvanced by Jones a.nd Eskridge who noted that their recrnlts using J\rimsk.y's conversion ratio crossly miscalcul ated actual d•2viations they 8 e measured. They theorized that th distance from the center the of curvature of the cornea and center of thE� entrance pupil was constaLLt at all rotations of the e-:,1E�. · And that· the center of curvature of th8 cornea moved as well <JS the reflex i.n the various rotations of the eye. mathematical formula They der.ived a which rletermin(Jd the position of. the corneal reflex with a.ny rotation of the eye� between the reflex and . The distance the centtC)T of the entrance pupil they labelled lt. The distance between the corneal center 1�i ,- TA.BI.J E Center o:f' Rot3.tion Determined by ;_i;a:cl:i Ir-.vestiDa.ton_:; recorded in millimeters behind tho cornea f:rr;motropic E;ye AxiaJ_ 1,ength 2J • .53 25.55 22.10 Doncers 1. 3 ' _5.1+ 1q., 52 lJ.Ol lJ.?J .13.22 .·.1 :J.r' :)•-!l'.'f ! �- of curvatur8 and the entrance pup:il center, they labelled This distance (h) equalled the distance r times the sine of· two rotation of the (0) angJes 1 the 8.ngle of. eye {G) and anc,le Kappa ,y ' 1 6 or h= r sin (G+,0) • Using St ens t rom s - data for the eye, an average £ of 2.9J millimeters was introduced giving an average h of one millimeter equalling 12.2 degrees or 21.6 prism diopters • . They tested the ab6ve ratio (21.6 prism diopters/millimeter) in sulijects who were asked to fixate a t:.irr.et at various d i��ta.'11ces on either sid f� of the straightforward posit:i.on. By photo2,i:-a1-ih;y, 'they were able to determine how much the corneal light reflex deviated from the center of the entrance pupil of th(� eye (.!}.) and the relation of this deviation to known amounts the eye had rotated (G). Their averaged results clofJely resembled the scale factor �heir mathematici predicted.
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