ORIGINAL ARTICLE. Validity and Reliability of the Revised Convergence Insufficiency Symptom Survey in Children Aged 9 to 18 Years

Transcription

1 /03/ /0 VOL. 80, NO. 12, PP OPTOMETRY AND VISION SCIENCE Copyright 2003 Americn Acdemy of Optometry ORIGINAL ARTICLE Vlidity nd Relibility of the Revised Convergence Insufficiency Symptom Survey in Children Aged 9 to 18 Yers ERIC J. BORSTING, OD, MS, FAAO, MICHAEL W. ROUSE, OD, MS, FAAO, G. LYNN MITCHELL, MS, FAAO, MITCHELL SCHEIMAN, OD, FAAO, SUSAN A. COTTER, OD, FAAO, JEFFREY COOPER, OD, MS, FAAO, MARJEAN TAYLOR KULP, OD, MS, FAAO, RICHARD LONDON, MA, OD, FAAO, nd THE CONVERGENCE INSUFFICIENCY TREATMENT TRIAL GROUP Southern Cliforni College of Optometry, Fullerton, Cliforni (EJB, MWR, SAC), The Ohio Stte University College of Optometry, Columbus, Ohio (GLM, MK), Pennsylvni College of Optometry, Phildelphi, Pennsylvni (MS), Stte University of New York, College of Optometry, New York (JC), Pcific University College of Optometry, Forest Grove, Oregon (RL) ABSTRACT: Purpose. To ssess the vlidity nd relibility of the Convergence Insufficiency Symptom Survey (CISS) in children ged 9 to 18 yers. The CISS is the primry outcome mesure for pilot study evluting two different tretments for convergence insufficiency (CI). Methods. Children with CI were given the CISS twice to ssess relibility. CISS scores for the first dministrtion were lso compred with scores from children with norml binoculr vision to ssess the vlidity of the CISS. Results. Forty-seven children with CI nd 56 children with norml binoculr vision prticipted in the study. Relibility ws ssessed using intrclss correltion nd 95% limits of greement for the children with CI. For children with CI, the intrclss correltion ws 0.77 (95% confidence intervl, to 0.873), nd the 95% limits of greement were 10.2 to The men ( SD) CISS score ws for the children with CI nd for the children with norml binoculr vision. These mens were significntly different (p < ). Good discrimintion (sensitivity, 96%; specificity, 88%) ws obtined using score of >16. Conclusions. Children with CI showed significntly higher CISS symptom score thn children with norml binoculr vision. The results of the study indicte tht the CISS is vlid nd relible instrument to use s n outcome mesure for children ged 9 to 18 who re enrolled in clinicl reserch concerning CI. (Optom Vis Sci 2003;80: ) Key Words: convergence insufficiency, symptom survey, relibility, vlidity, children The Convergence Insufficiency Tretment Tril (CITT) group hs been conducting series of pilot studies in preprtion for rndomized clinicl tril compring two tretment modlities for convergence insufficiency (CI). One criticl issue fced by the group ws developing method to ssess the effect of tretment on ptient s symptoms. With nonstrbismic binoculr vision disorders such s CI, the success or filure of tretment is determined by chnges in clinicl signs s well s chnges in ptient symptoms (i.e., does the ptient hve n improvement in visul comfort nd performnce fter the therpeutic intervention). Although scled symptom surveys hve been developed nd used in the pst, 1 3 there is no stndrdized instrument tht is designed for ssessing chnges in symptoms ssocited with tretments for CI or other nonstrbismic binoculr vision disorders. Developing such survey is essentil for determining the success of tretment for nonstrbismic binoculr disorders. CI is common binoculr vision disorder 4 9 nd hs been ssocited with symptoms such s visul ftigue, hedches, nd double vision primrily in dults The ssocition of CI nd symptoms in children hs recently been ssessed in clinicl 13 nd popultion-bsed 14 smples of children using 13-item Convergence Insufficiency Symptom Survey (CISS) developed by the Convergence Insufficiency nd Reding Study (CIRS) Group. The CISS llows two-fctor nlysis of symptoms: first, whether the symptom is present nd second, how frequently the symptom occurs. To test the vlidity of the CISS, cse comprison method 13 ws used to compre 14 school-ged children (ged 8 to 13 yers) with CI nd 14 children with norml binoculr vision

2 (NBV) of the sme ge recruited from clinic popultion. Borsting nd collegues 13 found tht the children with CI scored significntly higher (i.e., were more symptomtic) thn the children with NBV. In subsequent study, 14 modified version of the CISS ws dministered to 392 children, ged 8 to 15 yers, who pssed vision screening of visul cuity nd refrctive sttus. Eighteen of the children (4.6%) hd three signs of CI, nd this group hd symptom scores tht were significntly higher thn the NBV group. The results of these two studies indicte tht the CISS cn discriminte between children with CI nd children with NBV in both clinic- nd popultion-bsed groups of school-ged children ged 8 to 15 yers. Borsting nd coworkers 15 lso investigted the relibility of the CISS by dministering the survey twice over 1- to 2-week period to group of children with two or three signs of CI. The between-session relibility ws found to be excellent (intrclss correltion coefficient of 0.93). Although our initil studies with the CISS were promising, severl issues needed to be ddressed before the survey could be used in clinicl tril. The originl CISS rnked severity of symptoms using three or four response ctegories, which is dequte for discriminting between the CI nd NBV groups, but my not be sensitive enough to trck chnges observed during therpeutic interventions. 16 In ddition, the relibility of the CISS hs not been estblished with the proposed five response ctegories. Finlly, dt on children with NBV re necessry to estblish the norml vrince of symptom scores in school-ged popultion. To ddress these issues, the CISS ws modified nd then dministered to two groups of 9- to 18-yer-old children, one group of children with CI nd the other with NBV. Convergence Insufficiency Symptom Survey Borsting et l. 833 METHODS Survey Development The originl CISS 13 ws modified to broden the type of ner work ctivities nd trck chnges in symptoms during tretment (See Tble 1 for revised CISS). Insted of sking bout symptoms during reding nd studying, subjects were sked bout symptoms present when reding nd performing close work becuse we felt tht this included broder rnge of ctivities (e.g., video gmes, hobbies, nd plesure reding) thn only sking bout reding nd studying. Two items on the originl CISS were divided into two seprte questions to better clrify the specific symptoms. For exmple, one question on the originl CISS sked whether the child s eyes were tired or uncomfortble when reding or studying. This ws chnged to two seprte questions, one relted to tired eyes nd the other to uncomfortble eyes. We lso chnged the scle for clssifying frequency from four to five choices. The new version used the following response choices: never, infrequently, sometimes, firly often, nd lwys. Incresing the number of response choices to five mkes trcking chnges during therpeutic intervention more sensitive. 16 In ddition, the response option lbels were chosen in such mnner s to hve equl perceived spcing. The lbels were chosen using dt on the numeric rting of frequency terms from 20 studies in the socil science literture. 17 Subjects Children, ged 9 to 18 yers, were recruited from five optometric teching clinics s prt of pilot study evluting the efficcy of TABLE 1. Distribution of responses on ech item of the Convergence Insufficiency Symptom Survey (CISS) for children with convergence insufficiency (CI) nd children with norml binoculr vision (NBV) Symptom Firly Never Infrequently Sometimes Alwys Often CI NBV CI NBV CI NBV CI NBV CI NBV 1. Do your eyes feel tired when reding or doing close Do your eyes feel uncomfortble when reding or doing close Do you hve hedches when reding or doing close Do you feel sleepy when reding or doing close Do you lose concentrtion when reding or doing close Do you hve trouble remembering wht you hve red? Do you hve double vision when reding or doing close Do you see the words move, jump, swim or pper to flot on the pge when reding or doing close 9. Do you feel like you red slowly? Do your eyes ever hurt when reding or doing close Do your eyes ever feel sore when reding or doing close Do you feel pulling feeling round your eyes when reding or doing close 13. Do you notice the words blurring or coming in nd out of focus when reding or doing close 14. Do you lose your plce while reding or doing close Do you hve to re-red the sme line of words when reding?

3 834 Convergence Insufficiency Symptom Survey Borsting et l. two different tretments for CI. The inclusion nd exclusion criteri for CI subjects re listed in Tbles 2 nd 3. The dignosis of CI ws mde when the child presented with the following three signs: exophori t ner tht ws t lest 4 greter thn fr, 5 filure of Sherd s criterion 18 or minimum normtive positive fusionl vergence (brek 15 ), 19 nd receded nerpoint of convergence ( 6 cm). 20 Additionlly, potentil CI subjects were given the originl 13-item CISS to determine whether their symptom score met the inclusion criteri of Subjects with ttention deficit disorder, lerning disbility, or currently tking mediction tht could ffect ccommodtion or vergence were excluded. Children identified s hving CI were scheduled for n eligibility exmintion, which included dministrtion of the revised CISS long with other tests for dignosing CI. Children in the ge rnge of 9 to18 yers with NBV were recruited from ech of the five optometric teching clinics. The inclusion criteri re listed in Tble 4, nd the exclusion criteri, which were essentilly the sme s for children with CI, re listed in Tble 3. Ech CITT study site received pprovl from its ffilited institutionl review bord (Southern Cliforni College of Optometry, Pennsylvni College of Optometry, The Ohio Stte University College of Optometry, Stte University of New York College of Optometry, nd Pcific University College of Optometry). Centrlized humn subjects pprovl ws obtined from the Biomedicl Sciences Institutionl Review Bord t The Ohio Stte University, including pprovl of the individul informed consent documents. A prent or gurdin provided consent, nd ech child provided ssent before ny testing ws done. Procedure TABLE 2. Inclusion criteri for children with convergence insufficiency (CI) Age 9 to 18 yers Best-corrected visul cuity 20/25 in both eyes t distnce nd ner Approprite distnce refrctive correction worn for 2 weeks Willing to continue to wer eyeglsses/contct lens to correct refrctive error Exophori t ner 4 greter thn t fr 5 Filed Sherd s criterion 18 or minimum normtive positive fusionl vergence of 15 BO brek 19 Receded nerpoint of convergence of 6 cm 20 Pssed stereocuity (500 sec Rndot forms) Originl Convergence Insufficiency Symptom Survey score 9 points 13 No previous CI tretment (ny office-bsed vergence therpy or completed pencil push-up therpy) Hs not used plus dd t ner or bse-in prisms for t lest the pst 4 weeks Hd cycloplegi refrction within pst 12 months TABLE 3. Exclusion criteri for children with convergence insufficiency (CI) or children with norml binoculr vision Amblyopi (two-line difference in best corrected visul cuity between the two eyes) Constnt strbismus History of strbismus or refrctive surgery Anisometropi 1.50D difference between the two eyes Monoculr estimte method (MEM): with motion with 1.75D or ccommodtive mplitude 5D Verticl heterophori 1 Dignosed with multiple sclerosis, Grves thyroid disese, mystheni grvis, dibetes, or Prkinson s disese Chronic use of ny mediction tht might ffect ccommodtion or vergence or use of ny of these medictions in previous 24 hours Mnifest or ltent nystgmus Currently dignosed with lerning disbility for which school ws providing intervention Dignosed by physicin with Attention Deficit Hyperctivity Disorder nd currently tking mediction for this disorder Regulr use of medictions for sthm Household member or sibling lredy enrolled in Convergence Insufficiency Tretment Tril Exclusion for only potentil CI subjects. TABLE 4. Inclusion criteri for children with norml binoculr vision Age 9 to 18 yers Best corrected visul cuity 20/20 in both eyes t distnce nd ner Approprite refrctive correction worn for 2 weeks Willing to continue to wer eyeglsses/contct lens to correct refrctive error Heterophori t ner between 2 esophori nd 8 exophori 21 Negtive fusionl vergence t ner 7 BI-brek/5 BIrecovery 22 Positive fusionl vergence t ner 10 BO-brek/7 BOrecovery 22 Nerpoint of convergence closer thn 6.0 cm brek 20 Monoculr mplitude of ccommodtion ge 23 Pssed stereocuity (500 sec Rndot forms) No previous convergence insufficiency tretment (ny officebsed vergence therpy or completed pencil push-up therpy) Hs not used plus dd t ner or bse-in prisms Hd cycloplegi refrction within pst 12 months The CISS (Tble 1) ws dministered to ech of the children with either CI or NBV. To ssess relibility, CI subjects were given the CISS second time when they returned for their initil tretment visit. Subjects with NBV were given the CISS t the eligibility exmintion, but did not prticipte in the relibility portion of the study. Questions from the CISS were red to ech subject while he or she looked t printed copy of the response options. The questions were red, in order, exctly s written nd were repeted if the subject did not respond or requested to her the question gin. After ech question, the exminer recorded the subject s response. The survey ws scored s follows: never (0), infrequently (1), sometimes (2), firly often (3), nd lwys (4). The totl score ws then

4 Convergence Insufficiency Symptom Survey Borsting et l. 835 obtined by summing the points for ll 15 items, which could rnge from 0 to 60. RESULTS Subjects Forty-seven children with CI nd 56 children with NBV were enrolled in the study. The men ( SD) ge ws yers for the CI group nd yers for the NBV group. In the CI group, 57.5% of the subjects were femle, nd in the NBV group, 45.5% were femle. The distribution of children by center is listed in Tble 5. The Pennsylvni College of Optometry center recruited the most CI nd NBV subjects, but the symptom score ws not significntly different when compring the Pennsylvni College of Optometry to the other centers (men t Pennsylvni College of Optometry, 31.56; men t other sites, 30.79; p 0.124). The vlues for ner heterophori, positive fusionl vergence, nerpoint of convergence, nd ccommodtive mplitude re shown in Tble 6. The CI group hd significntly different vlues thn the NBV group on ll three signs of CI (p ). The internl consistency of the survey ws ssessed using Cronbch s lph coefficients. The coefficient ws 0.92, nd no item ws negtively correlted with the totl. This indictes tht the internl consistency of the CISS ws good to excellent nd tht the items within the survey were not redundnt. Relibility of the CISS for the children with CI ws ssessed using the intrclss correltion coefficient (ICC) 24 nd 95% limits of greement. 25 The men time between dministrtion ws dys. The men difference between the first nd second dministrtion ws points, indicting minimum bis between the two dministrtions (one-smple t-test, 1.14; p ). The ICC ws 0.77 (95% confidence intervl, to 0.873), nd the 95% limits of greement were 10.2 to 12.1 (Fig. 1). The men score on the CISS t the eligibility visit ws for the children with CI nd for the NBV children. The children with CI scored significntly higher thn the NBV group (t 15.4, p ). In ddition, the ge of the child did not correlte with the symptom score (r 0.052, p 0.728). The distribution of response option on ech item for children with CI nd children with NBV is shown in Tble 1. We hve lso grphiclly presented the distribution of the percentge of children with CI nd children with NBV responding firly often or lwys on the CISS (Fig. 2). To ssess the bility of the CISS to correctly clssify subjects s TABLE 5. Number of subjects enrolled t ech site Site CI NBV Pennsylvni College of Optometry Southern Cliforni College of Optometry 8 15 Stte University of New York, College of Optometry 7 5 The Ohio Stte University 3 7 Pcific University College of Optometry 1 1 Totl CI, convergence insufficiency; NBV, norml binoculr vision. TABLE 6. Men SD CI-relted mesures nd CISS symptom score CI or NBV, sensitivity nd specificity vlues were clculted using vrious cutoff vlues for the CISS score. A cutoff vlue of 16 (i.e., CISS 16) yielded sensitivity of 95.7% nd specificity of 87.5%. This vlue ws lso 1 SD bove the men for the NBV group. A list of cutoff vlues nd corresponding sensitivity nd specificity vlues re shown in Tble 7. We hve lso grphiclly shown the distribution of CISS scores for the CI nd NBV groups (Fig. 3). DISCUSSION Test CI Subjects NBV Subjects Heterophori t fr ( ) XP XP Heterophori t ner ( ) XP XP PFV brek ( ) PFV recovery ( ) NPC brek (cm) NPC recovery (cm) Accommodtive mplitude (cm, OD) CISS score CI, convergence insufficiency; CISS, Convergence Insufficiency Symptom Survey; NBV, norml binoculr vision; NPC, ner point of convergence; PFV, positive fusionl vergence. FIGURE 1. A plot of 95% limits of greement showing the individul differences between repet dministrtions of the Convergence Insufficiency Symptom Survey. The solid line shows the men bis, nd the dshed lines show the 95% limits of greement. The results of this study indicte tht the CISS is vlid nd relible instrument for use s primry outcome mesure for 9- to18-yer-old children enrolling in the CITT. Children with CI scored significntly higher thn the NBV group on the CISS, suggesting tht the survey is vlid. In ddition, n ICC of pproximtely 0.8 indictes tht the CISS hs good relibility. The results of this study re similr to those found by Borsting nd collegues. 13, 14 Both studies found tht children with CI hd significntly higher symptom scores thn children with NBV. The

5 836 Convergence Insufficiency Symptom Survey Borsting et l. FIGURE 2. Distribution of the percentge of children with convergence insufficiency (CI) nd children with norml binoculr vision (NBV) responding firly often or lwys on the Convergence Insufficiency Symptom Survey. TABLE 7. Sensitivity nd specificity vlues for vrious cutoff vlues for the CISS Cutpoint Sensitivity 9 18-Yer Olds Specificity CISS, Convergence Insufficiency Symptom Survey. totl symptom score in this study is higher thn tht found in both of our previous studies 13, 14 ; this is primrily becuse of the incresed number of questions (13 to 15) nd the expnded response ctegories (3 or 4 to 5) in the modified CISS. Our results re lso consistent with those of McKeon nd collegues, 26 who used the Vision Function Scle in ptients with intermittent exotropi. The Vision Function Scle hs mny items tht re similr to the revised CISS (e.g., How often do you lose your plce?). The intermittent exotropi group ws found to hve higher symptom score thn the visully norml group. This study ssessed the test-retest relibility of the CISS, which is importnt for evluting chnges in symptoms occurring before nd fter specific tretment. The 95% limits of greement were 10.2 to 12.1 with men bis of This mens tht FIGURE 3. Distribution of Convergence Insufficiency Symptom Survey scores for children with convergence insufficiency (CI) nd children with norml binoculr vision (NBV). The suggested symptomtic score of 16 is lso shown. chnge of more thn 10 points would be considered cliniclly meningful nd outside the rnge of norml vribility. For exmple, child with CI who scored 32 on the CISS before tretment would hve to score 21 fter tretment for the chnge to be considered significnt. These dt llow both the prctitioner nd the resercher to determine whether tretment hd cliniclly meningful effect on the ptient s symptoms. The prctitioner cn use the results of this study to distinguish between children with norml nd bnorml levels of symptoms ssocited with CI by using symptom score of 16. This score is more thn 1 SD from the men of the children with NBV nd hs high sensitivity (95.7) nd specificity (87.5). Using this vlue, only one CI subject ws considered symptomtic, nd seven NBV

6 subjects were considered symptomtic. We cn only speculte on why seven NBV subjects were symptomtic given our current dt. The NBV subjects my hve hd binoculr dysfunction tht we did not ssess (e.g., vergence fcility) or n undignosed lerning disorder. Although it is hs been suggested tht CI is not common in children, nd the ssocited symptoms, such s blur nd diplopi, cn be the result of the child s interprettion of norml physiologicl phenomenon, 27 no dt hve been presented to support this position. However, we cn indirectly investigte this clim by looking t our dt nd compring the occurrence of blur nd diplopi s reported by children with CI nd NBV. If blur nd diplopi were the result of the child s interprettion of norml physiologicl phenomenon, one would expect both groups to report these symptoms with equl frequency. However, we found tht the children with CI reported blur s firly often or lwys in 40.5% of cses, wheres only 4.4% of NBV children reported blur this frequently. For diplopi, we found tht the children with CI reported diplopi s firly often or lwys in 36.5% of cses, wheres no child with NBV reported diplopi in the firly often or lwys ctegories. Children with NBV my report blur or diplopi s Wright nd Boger 27 suggest, but the occurrence tends to fll into the infrequently ctegory (19.6% for blur nd 7.1% for diplopi). Thus, in our study, children with CI hd significntly greter occurrence of blur nd diplopi s well s ll other symptoms on the CISS thn children with NBV (Fig. 2). The CISS ppers pproprite to use in children presenting with symptoms ssocited with convergence insufficiency. Even though this study did not ddress the use of CISS for other nonstrbismic disorders of ccommodtion nd vergence, the symptoms described in the literture tend to be similr cross these vision conditions. 28 For exmple, hedches nd eyestrin re reported in both CI nd ccommodtive dysfunction. This hypothesis is lso supported by recent reserch conducted by Borsting et l., 14 who found tht the CISS ws ble to discriminte between children with ccommodtive insufficiency nd NBV. As result, future studies should look t the use of the CISS in other disorders of ccommodtion nd vergence. In conclusion, children with ll three signs of CI showed significntly higher CISS symptom score thn children with NBV. This study dds further evidence to support previous reserch 7, 13, 14 indicting tht CI hs significnt number of ssocited symptoms. In ddition, the results of this study demonstrte tht the CISS is vlid nd relible instrument for evluting symptoms in 9- to 18-yer-old children. Future studies should evlute the CISS in dults nd lso evlute the use of the CISS in other binoculr vision disorders. ACKNOWLEDGMENTS This Convergence Insufficiency nd Tretment Tril Study Group pilot study ws supported by Ntionl Eye Institute, Ntionl Institutes of Helth plnning grnt EY Presented t the Americn Acdemy of Optometry Meeting, December 2001, Phildelphi, PA. Received Jnury 21, 2003; revision received July 21, Convergence Insufficiency Symptom Survey Borsting et l. 837 REFERENCES 1. Sheedy JE, Sldin JJ. Phori, vergence, nd fixtion disprity in oculomotor problems. Am J Optom Physiol Opt 1977;54: Sheedy JE, Sldin JJ. Assocition of symptoms with mesures of oculomotor deficiencies. Am J Optom Physiol Opt 1978;55: Cooper J, Selenow A, Ciuffred KJ, Feldmn J, Fverty J, Hokod SC, Silver J. Reduction of sthenopi in ptients with convergence insufficiency fter fusionl vergence trining. Am J Optom Physiol Opt 1983;60: Cooper J, Duckmn R. Convergence insufficiency: incidence, dignosis, nd tretment. J Am Optom Assoc 1978;49: Dum KM. Convergence insufficiency. Am J Optom Physiol Opt 1984;61: Letourneu JE, Ducic S. Prevlence of convergence insufficiency mong school children. Cn J Optom 1988;50: Rouse MW, Hymn L, Hussein M, Soln H, Convergence Insufficiency nd Reding Study (CIRS) Group. Frequency of convergence insufficiency in optometry clinic settings. Optom Vis Sci 1998;75: Rouse MW, Borsting E, Hymn L, Hussein M, Cotter S, Flynn M, Scheimn M, Gllwy M, De Lnd PN, Convergence Insufficiency nd Reding Study (CIRS) group. Frequency of convergence insufficiency mong fifth nd sixth grders. Optom Vis Sci 1999;76: Porcr E, Mrtinez-Plomer A. Prevlence of generl binoculr dysfunctions in popultion of university students. Optom Vis Sci 1997; 74: White JW, Brown HW. Occurrence of verticl nomlies ssocited with convergent nd divergent nomlies: clinicl study. Arch Ophthlmol 1939;21: Hirsch MJ. A study of forty-eight cses of convergence insufficiency t the ner point. Am J Optom Arch Am Acd Optom 1943;20: Kent PR, Steeve JH. Convergence insufficiency, incidence mong militry personnel nd relief by orthoptic methods. Milit Surgeon 1953;112: Borsting E, Rouse MW, De Lnd PN, Convergence Insufficiency nd Reding Study (CIRS) Group. Prospective comprison of convergence insufficiency nd norml binoculr children on CIRS symptom survey Optom Vis Sci 1999;76: Borsting E, Rouse MW, Delnd PN, Hovett S, Kimur D, Prk M, Stephens B. Assocition of symptoms nd convergence nd ccommodtive insufficiency in school-ge children. Optometry 2003;74: Borsting E, Rouse MW, De Lnd PN, Convergence Insufficiency nd Reding Study (CIRS) Group. Survey instruments in the convergence insufficiency nd reding study. Optom Vis Sci 1998; 75(Suppl): Kirshner B, Guytt G. A methodologicl frmework for ssessing helth indices. J Chronic Dis 1985;38: Mosteller F, Youtz C. Quntifying probbilistic expressions. Stt Sci 1990;5: Sherd C. Zones of oculr comfort. Am J Optom Arch Am Acd Optom 1930;7: Scheimn M, Herzberg H, Frntz K, Mrgolies M. A normtive study of step vergence in elementry schoolchildren. J Am Optom Assoc 1989;60: Hyes GJ, Cohen BE, Rouse MW, De Lnd PN. Normtive vlues for the nerpoint of convergence of elementry schoolchildren. Optom Vis Sci 1998;75: Morgn MW. Anlysis of clinicl dt. Am J Optom Arch Am Acd Optom 1944;21:

7 838 Convergence Insufficiency Symptom Survey Borsting et l. 22. Wesson MD. Normliztion of prism br vergences. Am J Optom Physiol Opt 1982;59: Hofstetter HW. A comprison of Dune s nd Donders tbles of the mplitude of ccommodtion. Am J Optom Arch Am Acd Optom 1944;21: Fleiss JL. The Design nd Anlysis of Clinicl Experiments. New York: Wiley, Blnd JM, Altmn DG. Sttisticl methods for ssessing greement between two methods of clinicl mesurement. Lncet 1986;1: McKeon C, Wick B, Ady LA, Begley C. A cse-comprison of intermittent exotropi nd qulity of life mesurements. Optom Vis Sci 1997;74: Wright JD Jr, Boger WP III. Visul complints from helthy children. Surv Ophthlmol 1999;44: Scheimn M, Wick B. Clinicl Mngement of Binoculr Vision: Heterophoric, Accommodtive nd Eye Movement Disorders, 2nd ed. Phildelphi: Lippincott Willims & Wilkins, Eric Borsting Southern Cliforni College of Optometry 2575 Yorb Lind Blvd. Fullerton, CA e-mil: eborsting@scco.edu