ISSN(print) 1226-5012 22(4):443-448, December 2017 < 초청논문 > http://dx.doi.org/10.14479/jkoos.2017.22.4.443 The Influence of Binocular Single Vision Intervened Fusional Vergence and Diplopia on The Risk of Falling Sang-Yeob Kim*, Kwang-Keun Oh, Hyeong-Su Kim, Dong Hoan Kim 1, Byeong-Yeon Moon, Dong-Sik Yu, and Hyun Gug Cho Dept. of Optometry, Kangwon National University, Samcheok 25949, Korea 1 Dept. of Physical Therapy, Gangneung Yeongdong University, Gangneung, 25521, Korea (Received October 23, 2017: Revised November 13, 2017: Accepted November 16, 2017) Purpose: This study was performed to investigate the influence of visual conditions such as binocular single vision intervened fusional vergence and diplopia on the risk of falls in static posture. Methods: Forty-two subjects of average age 23.40±2.70 years were participated in this study. In order to induce binocular single vision with fusional convergence (FC) and fusional divergence (FD), BI BO prism lenses of 4Δ and 8Δ were added, respectively, and to induce vertical vergence (VV), OD-BU 1Δ/OS-BD 1Δ was added in a trial frame fully corrected subject s refractive error. We detected the minimum amount of prism that diplopia was occurred in each subject and applied for inducing diplopia in each direction of vergence. Using the TETRAX biofeedback system, the fall risk index (FI) was measured at each test condition and compared with that without prism effect. Also, the difference of FI depending on the amount of breakpoint in horizontal vergence was investigated. Results: FI was increased significantly when involved FC and VV for maintaining binocular single vision, but, FI decreased to the state without prism effect while diplopia is occurred. FI showed a higher tendency in the group with low BO break point. Conclusions: Even if binocular single vision was maintained, the visual state intervened FC and VV was analyzed as a factor that more increasing the risk of falling than the diplopia state. Key words: Fusional vergence, Vertical vergence, Binocular single vision, Diplopia, Fall risk index 서 론 균형유지능력을감소시킨결과로설명하였고, De Boer 등 [7] 의연구에서는대비감도의저하를, Nevitt 등 [8] 은불량한 낙상은지면, 바닥또는낮은곳으로예기치않게넘어지는것으로정의할수있다. [1] 최근보건복지부자료에따르면, 우리나라노인의 25.1% 가지난 1년간낙상을경험한것으로조사되어, [2] 낙상은노인의건강을위협하는주요위험요인중하나로인식되고있다. 또한자신감저하, 우울증및낙상두려움등과같은심리적문제를불러일으키며, [3] 이러한심리적문제로인해신체활동은감소되고, 줄어든활동으로인한약화된신체는낙상사고의재발률을높이는악순환으로작용한다. [4] 낙상의위험요인으로는연령증가, 보행및균형능력저하, 인지기능감소, 심혈관질환및치매등으로다양하지만, [5] 시각적문제또한낙상의위험을증가시키는주요원인으로대두되고있다. 시각상태와낙상위험에관한이전연구를살펴보면, Langley와 Mackintosh [6] 는저시력자의빈번한낙상사고를공간인지및사물인식능력의저하가 입체시를낙상의위험을증가시키는요인으로각각보고하였다. 저자들은이전연구에서미교정된근시와원시성굴절이상의정도가클수록신체안정성을더욱감소시키고, 낙상의위험은미교정된원시가존재할때더욱민감한것으로보고한바있다. 이를통해굴절이상의존재도정적자세의전반적인균형능력의안정성을떨어뜨려낙상의위험을증가시키는요인임을알수있었다. [9,10] 또한, Glasauer 등 [11] 은주시가고정된상태보다추종안구운동이발생할때신체흔들림이증가되는것을발견했고, Kim 등 [12] 의연구에서는추종안구운동의속도가증가함에따라신체불안정성도비례적으로높아지는것을밝혀냈다. 따라서본연구에서는복시와같은부적절한시각상태나양안단일시가유지되더라도이향운동의자극이개입된시각상태가낙상위험에영향을미치는요인으로작용하는지조사해보고자하였다. *Corresponding author: Sang-Yeob Kim, TEL: +82-33-540-3413, E-mail: syk@kangwon.ac.kr 443
444 Sang-Yeob Kim, Kwang-Keun Oh, Hyeong-Su Kim, Dong Hoan Kim, Byeong-Yeon Moon, Dong-Sik Yu and Hyun Gug Cho 대상및방법 대상본연구의취지에동의한평균연령 23.79±2.81세의 42 명 ( 남 28, 여 14) 을대상으로측정 평가하였고, 실험대상자의등가구면굴절력은평균 3.62±2.74 D이었다. 문진을통해빈번한낙상경험이나신체균형과관련있는신경근육이나근골격질환, 전신질환, 그리고안질환및이와관련된약물복용경험이없음을확인하였다. 단안교정시력이 1.0이하, 시기능검사를통해안위상태및융합력등이정상평균기댓값 [13] 을벗어나는경우, 그리고복시와같은비사시성양안시이상과관련된자각증상을경험했던경우대상에서제외하였다. 방법 1. 측정장비및평가항목낙상의위험도를평가하기위해 TETRAX the biofeedback system(tetrax Protable Multiple System, Tetrax Ltd, Ranmat Gan, Israel) 을사용하였다 (Fig. 1). 사용된측정장비는 A( 오른발뒤꿈치 ), B( 오른발앞꿈치 ), C( 왼발뒤꿈치 ), D( 왼발앞꿈치 ) 로표시되어있는 4개의지면반력감지장치를통해정적자세에서의신체흔들림영역, 길이, 속도등의분석을통해낙상지수 (fall risk index; FI) 값을측정한다. [14] FI는미끄러지거나위에서아래로떨어지는등의급격한체위이동으로인해신체에상해를입는낙상의위 험정도를나타내며, 낮은위험도 (0~35), 중등도 (36~57), 높은위험도 (58~100) 의세등급으로분류된다. [15] 2. 측정방법대상자의완전교정굴절력은수동포롭터 (Ultramatic RX Master, Reichert, USA) 를이용한자각적굴절검사를통해검출하였고, 수정된토링톤법 (modified thorington method) 으로원거리안위상태를확인하였다. 그리고최대한의이향운동량을발휘한상태에서도양안단일시를유지할수없는한계지점인분리점 (break-point) 값을포롭터내로타리프리즘을이용하여각이향운동방향에따라측정하였다. FI 측정전, 대상자마다다른동공간거리에따른프리즘영향을제거하기위해단안 PD를설정할수있는시험테 (Trial Frame TF-3, Topcon, Japan) 를사용하여완전교정굴절력값을장입하였고, 조절개입을최소화하기위해 6 m 전방에위치시킨 LCD 시력표의점광원을주시타깃으로하였다. 원거리주시상태에서수평 수직방향의이향운동이개입된양안단일시및복시상태를유발시키기위해완전교정굴절력값앞에프리즘렌즈를덧대었다. 먼저수평이향운동방향에서융합성개산 (fusional divergence) 이개입된양안단일시를유발하기위해 BI 4Δ과 8Δ, 융합성폭주 (fusional convergence) 가개입된양안단일시를유발하기위해 BO 4Δ과 8Δ을각각사용하였고, 전체프리즘굴절력은각눈에반으로나누어장입하였다. 또한수직이향운동 (vertical vergence) 이개입된양안단일시를위해총 2Δ의굴절력을모든대상자의오른쪽눈에 BU 1Δ, 왼쪽눈에 BD 1Δ으로각각나누어장입하였다. 복시상태를유발하기위해서는앞서측정한이향운동량의분리점을참고하여대상자마다각기저방향에서복시가발생하는최소프리즘을검출한후적용하였다 (Table 1). FI의측정을위해우선대상자에게완전교정굴절력이장입된시험테를착용시키고, TETRAX 측정장비의지면반력장치위에올라서도록하였다. 4개의지면반력장치위에양발을정확하게정렬시키고해부학적자세 ( 팔을늘어뜨리고양손바닥을앞으로향한채똑바로서있는자세 ) 를취하게한뒤, 정 Table 1. Break point of vergence of subjects participating in the study Fig. 1. Equipment for measuring parameters of postural control (The TETRAX biofeedback system). Break point of vergence Means±SD (Δ) Min. (Δ) Max. (Δ) BI 10.43±1.43 9 14 BO 17.52±7.26 10 36 BD (OD-supra) 3.17±0.49 3 5 BU (OD-inpra) 3.38±0.73 3 6 (n=42)
The Influence of Binocular Single Vision Intervened Fusional Vergence and Diplopia on The Risk of Falling 445 적자세로 10초간유지시킨후측정매뉴얼에따라 32초간측정을실시하였다. 그런다음, BU/BD, BI, 그리고 BO 프리즘에의한양안단일시유지및복시상태에서각각반복측정한후완전교정상태에서측정된값과비교하였다. 동일한프리즘기저방향에서의측정은무작위순서로실시하였고, 프리즘렌즈의기저방향이바뀔때마다각 5분, 부가되는프리즘렌즈의굴절력이바뀔때마다각 1분의휴식시간을제공하였다. 3. 분석데이터분석은 IBM SPSS Statistics 23 프로그램을이용하여반복측정분산분석 (repeated measures ANOVA) 과독립표본 t-검정 (independent two-sample t-test) 을실시하였고, p<0.05일때통계적으로유의한차이가있다고판단하였다. 결과및고찰 1. 수평및수직프리즘에의해유발된각시각상태에서낙상지수 (FI) 값의변화 Fig. 2는수평프리즘에의한수평융합이향운동이개입된양안단일시와복시상태에서 FI값의변화를나타낸것이다. BI 프리즘의영향에의한각시각상태에서는 FI값의현저한차이가없었지만 (p>0.05), BO 4Δ과 8Δ에인해양안단일시를유지시키기위한융합성폭주의개입정도가증가할수록 FI값도현저하게증가하였다가복시상태에서는오히려프리즘영향이없었던상태로감소되었다 (p<0.05). 마찬가지로 Fig. 3에서양안단일시를유지하기위해 2Δ의 Fig. 2. The changes of fall risk index according to visual condition induced by horizontal prism. *p<0.05: significantly different from single vision without prism according to repeated measures ANOVA n=42 (for each condition) Fig. 3. The changes of fall risk index according to visual condition induced by vertical prism. *p<0.05: significantly different from single vision without prism according to repeated measures ANOVA n=42 (for each condition) 수직융합이향운동이개입될때 FI값은현저하게증가하였다가복시상태에서는프리즘영향이없었던상태로다시감소되었다 (p<0.05). 정상적인자세조절은감각신경계 ( 시각계, 전정계, 고유수용감각계 ) 와운동신경계의복잡한상호조화에의해완성된다. [16] 외안근고유수용감각신호 (extra-ocular proprioceptive cues) 는공간과신체간의위치파악뿐만아니라몸전체의자세를조절하는데필수적이고, [17,18] 융합성이향운동의신호또한고유수용감각의정보를포함하고있어정적자세조절에중요한역할을하는것으로알려져있다. [19] Roll 등 [18] 은외안근의진동만으로도자극된근육에따라두드러진신체흔들림을이끌어내며, 특히수직방향운동을담당하는작용근을자극시키면앞-뒤방향으로신체기울임을유발하였다고보고하였다. 본연구에서이미정상적인이향운동시스템이형성되어있는대상자에게양안단일시를위해발생한변형된이향운동신호는자세조절과관련된체성-고유수용감각루프 (somatosensory-proprioceptive loops) 를일시적으로교란시켜신체흔들림을유발하고, [20] 이런결과로낙상의위험도증가시킨것으로판단된다. 하지만본연구결과에서 BI 프리즘에의한융합성개산이개입되더라도 FI값의의미있는변화는찾아볼수없었다. Kapoula와 Lê [19] 의연구에따르면, 실제로개산운동보다폭주운동이발생할때 ERP(event-related potential) 활성정도는더욱강하게생성된다고설명하였다. 결국수평방향에서는동일한양의융합성이향운동이요구되더라도신경자극에대한활성정도가약한융합성개산이발생될때에는자세조절을위한피드백루프의교란에미치는영향은상대적으로미미한것으로추측된다.
446 Sang-Yeob Kim, Kwang-Keun Oh, Hyeong-Su Kim, Dong Hoan Kim, Byeong-Yeon Moon, Dong-Sik Yu and Hyun Gug Cho Bronstein [21] 은사시안에서나타나는안구정렬이상및복시로인해변경된안구운동고유수용감각신호 (oculomotor proprioceptive signal) 는자세안정성을감소시키는원인이될수있다고하였다. 정상안위를가진대상자로한본연구에서 BO과 BU/BD 프리즘을이용해원거리수평및수직복시를유발하였을때낙상지수는오히려프리즘영향이없는상태로감소되어, 복시와같은부적절한시각정보는낙상의위험을크게증가시킬것으로예상했던저자들의예상과는상반된결과를보였다. Bronstein과 Buckwell [22] 은자세조절에있어정상적인양안시에의한시각정보는동적상태에서더욱의존된다고하였고, Isotalo 등 [23] 은프리즘영향에의한정적자세조절의방해는근육의긴장에미치는영향때문으로설명하였다. 따라서본연구에서복시를유발하여양안단일시가파괴되는순간, 기존에개입되었던융합성이향운동도더이상요구되지않게됨에따라과도한외안근의긴장에의한자세조절기전의교란도자연적으로제거된결과로생각된다. 더불어정상적인안위와외안근고유수용감각을가진대상자에서복시와같은수용할수없는비정상적인시각정보가일시적으로발생하더라도자세안정성을유지하는다른감각정보 ( 특히, 전정-소뇌로정보 ; vestibulo-cerebellar input) 가강화되는보상기전이작동된것 [24] 도가능한원인으로판단된다. 2. 수평이향운동량의크기에따른낙상지수 (FI) 값의차이 Fig. 4와 5에서는 Scheiman과 Wick의선행문헌 [13] 에제시된이향운동량의평균기댓값들을참고하여원거리융합성개산력의분리점을 10Δ, 융합성폭주력의경우 20Δ을기준으로구분하여 FI값의차이를보이는지알아보았다. 연구결과, 수평이향운동량에따른 FI값의변화는융합성폭주및개산모두에서현저한차이를보이지않았다 Fig. 4. Comparison of fall risk index depending on break point amplitude of fusional vergence measured by BI prism. Fig. 5. Comparison of fall risk index depending on break point amplitude of fusional vergence measured by BO prism. (p>0.05). 하지만융합성폭주의경우, 분리점이 20Δ 이하인대상자가모든검사조건에서낙상의위험이높은경향을보이고있으며, 특히 BO 4Δ과 8Δ에의해융합성폭주력이소진될때그경향은더욱뚜렷하였다. 이향운동신호의질이떨어지면내부고유감각피드백기전이불량해져자세조절을방해하는것으로알려져있다. [25] 이러한경우시각정보외자세안정성을조절하는다른관련감각기관 ( 전정, 체성정보 / 소뇌정보처리 ) 에서의보상기전또한불완전해지게된다. [25] Anoh-Tanon 등 [26] 은이향운동량의결핍은주시안정성을저하시키는원인으로작용하여어지러움과더불어자세불균형을야기시킨다고하였다. 앞서설명했듯이개산과비교해폭주에관여하는세포수가훨씬많을뿐만아니라, [27] 신경적활성정도도폭주자극시월등히높기때문에이향운동량에따른경향또한융합성폭주가개입될때더욱뚜렷하게나타난것으로추측된다. 정상적인융합능력을발휘하는대상자로한본연구결과에서통계적인뒷받침은불충분하나, 이러한경향성을통해개개인의융합성폭주의분리점측정은자세조절능력의질적수준을평가하는간접적인척도로사용될수있는가능성을예측해볼수있다. 하지만이러한연구결과는원거리와정적균형상태에서국한된다는제한점이있으므로추후폭주부족및융합버전스기능이상과같은비사시성양안시이상자와상대적으로폭주능력이감소되는노령층등다양한실험대상군과동적자세상태에서의추가적인분석이필요할것으로생각된다. 정리하면, 정상적인양안단일시가발휘되더라도융합성폭주와수직이향운동이개입될때, 복시와같은비정상적인시각상태에서보다낙상지수는더욱증가되었다. 본연구를통해정적자세에서낙상의위험은양안시가파괴된시각상태에서보다양안단일시를유지하려는이향운동자
The Influence of Binocular Single Vision Intervened Fusional Vergence and Diplopia on The Risk of Falling 447 극에따른외안근의부담이발생될때더욱부정적인영향을미치는요인으로분석되었다. 반면, 각이향운동방향에서융합이파괴된복시상태에서는오히려낙상위험이감소하였는데이런원인은부적절한시각정보의입력이균형을담당하는다른감각기관의보상작용을강화시킨결과로추측되었다. 낙상사고는국민의건강을위협하여삶의질을저하시키고, 의료비증가에따른막대한사회경제적비용도발생시킬수있으므로다양한전문분야에서낙상예방을위한다각적인노력이요구되는실정이다. 따라서불필요한수직및융합성폭주를유발시키는조제가공과정중의오류는반드시피해야하며, 수직사위를교정하면자세안정성을향상시킬수있다는점을고려하여, [20] 문진을통한선택적인프리즘처방은안경광학영역에서낙상사고예방에기여할수있는유용한접근법으로사료된다. 결 론 본연구에서는양안단일시를유지하기위한융합성이향운동이발생되거나양안단일시가파괴된복시와같은시각상태가정적자세에서낙상위험을증가시키는요인으로작용하는지알아보았다. 융합성폭주와수직이향운동의개입으로양안단일시가유지되더라도낙상지수는프리즘영향이없는상태와비교해현저한증가를보였다. 결론적으로낙상위험의영향은양안시가파괴된시각상태에서보다양안단일시를유지하려는이향운동이자극되면서발생하는외안근의부담이안정적인자세조절을더욱방해하여낙상위험을증가시키는요인으로분석되었다. 그러므로임상안광학영역에서는사위를유발시키지않는정확한조제가공과융합성이향운동의부담을줄여주는선택적인프리즘처방을통해낙상사고를예방하는데기여할수있을것으로기대된다. 감사의글 2017년도강원대학교대학회계학술연구조성비로연구하였음. REFERENCES [1] Lamb SE, Jørstad-stein EC, Hauer K, Becker C. Development of a common outcome data set for fall injury prevention trials: the prevention of falls network europe consensus. J Am Geriatr Soc. 2005;53(9):1618-1622. [2] MOHW(Ministry of Health and Welfare, Korea). Imformation: survey of older people in 2014, 2015. http:// www.mohw.go.kr/react/jb/sjb030301vw.jsp?par_menu _ID=03&MENU_ID=032901&CONT_SEQ=337302&page =1(8 April 2015). [3] Tinetti ME. Clinical practice. Preventing falls in elderly persons. N Engl J Med. 2003;348(1):42-49. [4] Cumming RG, Salkeld G, Thomas M, Szonyi G. Prospective study of the impact of fear of falling on activities of daily living, SF-36 scores, and nursing home admission. J Gerontol A Biol Sci Med Sci. 2000;55(5):M299-M305. [5] Ambrose AF, Paul G, Hausdorff JM. Risk factors for falls among older adults: a review of the literature. Maturitas. 2013;75(1):51-61. [6] Langley FA, Mackintosh SF. Functional balance assessment of older community dwelling adults: a systematic review of the literature. Internet J Allied Health Sci Pract. 2007;5(4):1-11. [7] De Boer MR, Pluijm SM, Lips P, Moll AC, Völker-Dieben HJ, Deeg DJ et al. Different aspects of visual impairment as risk factors for falls and fractures in older men and women. J Bone Miner Res. 2004;19(9):1539-47. [8] Nevitt MC, Cummings SR, Kidd S, Black D. Risk factors for recurrent nonsyncopal falls. A prospective study. JAMA 1989;261(18):2663-2668. [9] Kim SY, Moon BY, Cho HG. Changes of body balance on static posture according to types of induced ametropia. J Korean Ophthalmic Opt Soc. 2014;19(2):239-246. [10] Kim SY, Moon BY, Cho HG. Body balance under ametropic conditions induced by spherical lenses in an upright position. J Phys Ther Sci. 2015;27(3):615-618. [11] Glasauer S, Schneider E, Jahn K, Strupp M, Brandt T. How the eyes move the body. Neurology. 2005;65(8): 1291-1293. [12] Kim SY, Moon BY, Cho HG. Smooth-pursuit eye movements without head movement disrupt the static body balance. J Phys Ther Sci. 2016;28(4):1335-1338. [13] Scheiman M, Wick B. Clinical management of binocular vision: heterophoric, accommodative, and eye movement disorders, 4th Ed. Philadelphia: Lippincott Williams & Wilkins, 2014;8. [14] Park CS, Kang KY. Effect of visual biofeedback simulation training for balance in patients with incomplete spinal cord injury. J of Korea Contents Association. 2011; 11(11):194-203. [15] Chang KY, Woo HS. Influence of fall-preventive occupational therapy applied to elderly in the community upon balance ability. J of Korea Contents Association. 2010; 10(3):232-240. [16] Chang WH. Common disorders causing balance problems. Brain Neurorehabil. 2013;6(2):54-57. [17] Ivanenko YP, Grasso R, Lacquaniti F. Neck muscle vibration makes walking humans accelerate in the direction of gaze. J Physiol. 2000;525(Pt 3):803-814. [18] Roll JP, Vedel JP, Roll R. Eye, head and skeletal muscle spindle feedback in the elaboration of body references.
448 Sang-Yeob Kim, Kwang-Keun Oh, Hyeong-Su Kim, Dong Hoan Kim, Byeong-Yeon Moon, Dong-Sik Yu and Hyun Gug Cho Prog Brain Res. 1989;80:113-123. [19] Kapoula Z, Lê TT. Effects of distance and gaze position on postural stability in young and old subjects. Exp Brain Res. 2006;173(3):438-445. [20] Matheron E, Kapoula Z. Vertical phoria and postural control in upright stance in healthy young subjects. Clinical Neurophysiol. 2008;119(10):2314-2320. [21] Bronstein AM. Visual vertigo syndrome: clinical and posturography findings. J Neurol Neurosurg Psychiatry. 1995; 59(5):472-476. [22] Bronstein AM, Buckwell D. Automatic control of postural sway by visual motion parallax. Exp Brain Res. 1997;113(2):243-248. [23] Isotalo E, Kapoula Z, Feret PH, Gauchon K, Zamfirescu F, Gagey PM. Monocular versus binocular vision in postural control. Auris Nasus Larynx. 2004;31(1):11-17. [24] Matsuo T, Yamasaki H, Yasuhara H, Hasebe K. Postural stability changes during large vertical diplopia induced by prism wear in normal subjects. Acta Med Okayama. 2013;67(3):177-183. [25] Bucci MP, Lê TT, Wiener-Vacher S, Brémond-Gignac D, Bouet A, Kapoula Z. Poor postural stability in children with vertigo and vergence abnormalities. Invest Ophthalmol Vis Sci. 2009;50(10):4678-4684. [26] Anoh-Tanon MJ, Bremond-Gignac D, Wiener-Vacher SR. Vertigo is an underestimated symptom of ocular disorders: dizzy children do not always need MRI. Pediatr Neurol. 2002;23(1):49-53. [27] Benjamin WJ. Borish's Clinical Refraction, 2nd Ed. St. Louis: Butterworth-Heinemann, 2006;165-191. 융합이향운동이개입된양안단일시및복시상태가낙상위험에미치는영향 김상엽 *, 오광근, 김형수, 김동환 1, 문병연, 유동식, 조현국 강원대학교안경광학과, 삼척 25949 1 강릉영동대학교물리치료과, 강릉 25521 투고일 (2017 년 10 월 23 일 ), 수정일 (2017 년 11 월 13 일 ), 게재확정일 (2017 년 11 월 16 일 ) 목적 : 융합이향운동이개입된양안단일시및복시와같은시각상태가정적자세에서낙상의위험에미치는영향을알아보았다. 방법 : 평균나이 23.79±2.81 세의 42 명을대상으로하였다. 융합성폭주및융합성개산이개입된양안단일시상태를유발하기위해완전교정상태에서 4Δ 과 8Δ 의 BO BI 프리즘을각각부가하였고, 수직이향운동을유발하기위해우안 -BU 1Δ/ 좌안 -BD 1Δ 을부가하였다. 각이향운동방향에서의복시유발을위해대상자마다복시가발생하는최소프리즘양을부가하였다. TETRAX biofeedback system 을이용하여각검사조건에서낙상지수를측정한후프리즘영향이없는상태와비교분석하였고, 수평이향운동량의분리점의양에따른차이도알아보았다. 결과 : 양안단일시를유지하기위해융합성폭주와수직융합이향운동이개입될때낙상지수는현저하게증가하였고, 복시상태에서는프리즘의영향이없었던상태로감소하였다. BO 분리점의양이적은그룹에서낙상지수는더높은경향을보였다. 결론 : 양안단일시가유지되더라도융합성폭주와수직이향운동이개입된시각상태가복시상태보다낙상의위험을더욱증가시키는요인으로분석되었다. 주제어 : 융합이향운동, 수직이향운동, 양안단일시, 복시, 낙상지수