The Effect of Eye Fixation Control Method on Visual Field Testing Jihyoung Lee 1, Baekhee Lee 1, Yeona Kim 1, Jaheon Kang 2, Heecheon You 1 1 Department of Industrial and Management Engineering, POSTECH, Pohang, 790-784 2 Kyung Hee University International Medical Service, Seoul, 134-727 ABSTRACT Objective: The aim of the study is to examine an optimal eye fixation control method that can be employed to a PC-based visual field testing system. Background: The existing perimeters have disadvantages in terms of size and excessive functionality. Method: Twenty people in their 20s to 70s without glaucoma participated in the study. The combinations of two types of central target form (dot and number) and two conditions of sound presence (on and off) were evaluated in terms of visual field testing performance and subjective satisfaction. The effects of gender, age, eye, central target form, and sound presence were analyzed in terms of fixation error rate, the number of detected targets, the number of missing targets, and subjective satisfaction (7-point Likert scale). Results: The average number of detected targets was 53 out of 55. The lowest fixation error rate (5.0%) was found when central target form = dot and sound = off, while the highest subjective satisfaction (5.7) when central target form = dot and sound = on. A majority of missing targets (72% in the right eye; 79% in the left eye) occurred near the blind spots. Conclusion: Preferred features of eye fixation control method were identified from the experiment, but still a better alternative needs to be explored for effective visual field testing for diagnosis of glaucoma. Application: The findings of the present study can solve as a reference to explore a better eye fixation control method for a PC-based visual field testing system which could be eco-friendly in terms of energy and size than those of existing perimeters. Keywords: Visual field test, Eye fixation, Glaucoma 1. Introduction 다양한안과질환중현재까지치료방법이없는녹내장은조기진단이매우중요한질환이다. 녹내장 (glaucoma) 이란시신경이위축되는형태를띠면서망막신경총세포를포함하는시신경에생기는질환으로시야장애를동반하는안과질환이다 (Mozaffarieh, 2008). 녹내장은전세계에서두번째로많은실명원인질환일뿐만아니라녹내장환자의수는빠르게증가하는추세로보고되고있다 (Kingman S., 2004). 그러나녹내장은발병초기에증상이거의나타나지않아, 지속적으로녹내장을진단하는것이최선의예방책으로알려져있다 ( 국민건강보험공단, 2011). 녹내장은환자에따라서시야손상이진행되는속도와정도가다르기때문에개인별로적합한녹내장진단과치료가요구되는질환이다 (Nam et al., 2009; Cho et al., 2010). 맞춤의료 (personalized medicine) 는각종질환의치료및예방차원에서개인에게적합한진단과치료법에대해자율 성을부여한다 (Lee et al., 2010). 예를들면, 동일한양의흡연을한사람들은개인의유전적정보차이에따라폐암에걸려사망하거나건강하게잘살기도한다. 녹내장역시환자별로진행속도나약물치료에대한반응이다르기때문에환자에맞는검사가필요하다. 녹내장을검사할수있는기존시야검사장비 (perimeter) 들은휴대성과가격측면의한계와함께소비자의수요를과잉충족하고있다. 기존시야검사장비들은큰규격과상당한무게 ( 예 : 600 580 510 mm, 40 kg; HFA II-i Series, Carl Zeiss, Inc, USA) 때문에시야검사장비설치를위한일정이상의공간이필요할뿐만아니라, 시야검사를위해빛의차단이고려된위치에시야검사장비가한번설치되면이동하는것이쉽지않다. 또한, 기존시야검사장비들은상당히고가이기때문에보건소나개인안과에서사용할수있는경제성과효율성이고려된시야검사장비의개발이필요하다. 기존시야검사장비들은시야검사에서중요한시선고정 (eye fixation) 방법이고려되지않아인간공학적인개선
이필요하다. 시야검사는검사자가시선을중심시표에고정시킨상태에서다양한 pattern의중심시야또는주변시야의범위를검사하는방식이다 (Dersu et al., 2006). 시야검사간검사자의시선이이동하게되면, 정확한시야 ( 예 : 중심시야는중심시표기준 30 이내의영역 ) 가검사될수없다. 따라서, 시야검사자가능동적으로시선을고정하도록유도할수있는시야검사방법이필요하다. 본연구는 PC 기반시야검사시스템의유효성을검증하고시야검사간검사자의시선고정을위한최적의방안을탐색한다. 첫째, 본연구는정상인 14명을대상으로중심시야 (central vision) 내의모든시표 (target) 의확인이여부를검증한다. 둘째, 본연구는최적의시선고정방법을파악하기위하여 4가지시선고정 (eye fixation) 방법에따른시야검사성능및주관적만족도를분석한다. 검사자가 monitor 화면에제시되는시표의확인여부를입력하는데사용되었다. 셋째, portable visor는시야검사중외부에서들어오는빛을차단하고시야검사자의집중력을높이는데사용되었다. 마지막으로, 이마를지지하는부분과턱을지지하는부분으로구성된 face support는시야검사실험에서시야검사자가모니터에제시되는시표를확인하는동안시야검사자의안면움직임을최소화하고, 턱을고정시켜정확하고편안한시야검사를수행하는데이용되었다. 2. Method 2.1 Participants 본연구에서는교정시력이 0.8 이상이며시야장애가없는정상인 20명 ( 남성 10명, 여성 10명 ) 을대상으로수행되었다. 본연구에서측정된실험참여자의연령은남성 53.2 ± 13.6세, 여성 42.0 ± 12.8세로파악되었다. 본연구의실험참여자는강동경희대학교병원녹내장검사를받은인원 (2008.02 ~ 2010.04) 의비율을고려하여 50대와 60대실험참여자수의비율을전체의 60% 로지정된 20명 ( 남성 10명, 여성 10명 ) 으로구성되었다. Table 1. Number of participants Age group 20s 30s 40s 50s 60s 70s Total Gender Male 1 1 1 3 3 1 10 Female 1 1 1 3 3 1 10 Total 2 2 2 6 6 2 20 Figure 1. Visual field testing system - hardware 2.2.2 Software 본연구에서사용된시야검사시스템은 Humphrey visual field (HVF) perimeter의 24-2 threshold test 방법을기반으로중심시야를진단할수있도록개발되었다 (Figure 2). 24-2 threshold test 방법 (Paolo, 2006; Choi et al., 2009; Giuffré, 2009; Namoto et al., 2009; Fan et al., 2010; Kogure et al., 2006) 은중심시표로부터상하 24, 좌우 30 내영역에서 57개 ( 단안의경우 : 중심시표 1개, 주변시표 55개, 맹점시표 1개 ) 의시표로구성되어 HVF perimeter를사용하는전문안과의료기관에서주로사용하는시야검사방법중하나이다. 30º 3º Central Target 2.2 Experimental equipment 24º Right eye blind spot 2.2.1 Hardware 6º 본연구의 PC기반시야진단시스템은 PC monitor, keypad, portable visor, 그리고 face support로구성된다 (Figure 1). 첫째, PC monitor(19 inch, Flatron L1940 plus, LG electronics; pixel pitch = 0.294 mm) 는시야검사자의시야영역을측정하기위한시표를제시하는데사용되었다. 둘째, keypad는시야 Figure 2. Visual field testing system right eye
2.3 Experimental conditions 본연구는시야검사간중심시표에제시되는시표의형태와시표가제시될때소리제공여부를조합하여 4가지시선고정 (eye fixation) 방법고안하였다 (Table 2). 시선고정방법은기존시야진단시스템에서사용되는 dot 방법과본연구에서고안된숫자를제시하는방법으로분류된다. 소리제공방법은하나의시표가제시될때마다알림음을제공한다. 예를들면, C1은중심시표가 dot 형태로제시되고, 시표가제시될때마다알림음을들려주는조건을나타낸다. Table 2. Experimental conditions C1 C2 C3 C4 Fixation type* Dot Dot Number Number (central target) Sound On Off On Off *C is abbreviation of condition **number: present 1 or 2 randomly 2.4 Experimental procedure 시야검사실험은 figure 3에나타낸 4단계절차에따라진행되었다. 첫번째단계에서는실험참여자가실험동의서작성및실험진행자로부터충분한설명을제공받았다. 두번째단계에서는실험참여의안면부를 face support에고정한상태에서단안의시선과중심시표가일직선이되도록위치시키고맹점 (blind spot) 이보이지않게되는시야검사거리를결정하였다. 세번째단계에서는 4가지조건 (C1 ~ C4) 의시선고정방법이무작위로수행되었다. 각조건간휴식시간은 1분이제공되었다. 마지막으로, 각조건의실험종료후에주관적만족도 (7점척도 ) 가평가되었다. 한쪽단안에대한검사종료후에는 5분의휴식을제공하고반대쪽단안에대한검사가수행되었다. 시야검사실험은연령에따른반응시간을고려하여시표제시간격을 50대미만의경우 1.5초, 50대이상의경우 2 초가적용되어수행되었다. 시야검사실험의시선고정오류율 (eye fixation error rate, %) 은무작위로제시되는 5번의맹점시표수대비확인된맹점시표수의비율을나타낸다. HVF perimeter에서는시선고정오류율이 33% 이상일경우중심시표에시야검사자의시선이고정되지않은것으로간주한다 (Dersu et al., 2006). 본연구에서는 HVF perimeter의시선고정오류율을반영하여 40% 를초과할경우재실험을수행하였다. Figure 3. Experimental procedure 3. Results 3.1 Number of confirmed targets 실험참여자가확인한시표의비율은평균 96%(55개중 53개 ) 로나타났다 (figure 5). 각조건별로확인된시표의수는 C1조건 (dot/sound on) 에서 53.2개, C2조건 (dot/sound off) 에서 53.0개, C3조건 (number/sound on) 에서 52.8개, 그리고 C4 조건 (number/sound off) 에서 52.7개로나타났으며, 통계적차이가유의하지않은것으로분석되었다. Figure 5. Number of confirmed targets (mean ± SE) 3.2 Eye fixation error rate (%) 시선고정오류율은 C2조건에서 5% 로가장낮게나타났다 (figure 6). C4조건에서의시선고정오류율은 10.7% 로 C2조건에비해약 2.1배높게나타났으며, C2조건과통계적으로유의한차이를보였다. C1조건과 C3조건 ( 알림음제공조건 ) 에서의시선고정오류율은각각 9.3% 와 8.6% 로나타났으나, C2조건과통계적으로유의한차이를보이지않았다.
Eye fixation error rate (%) 16.0 14.0 12.0 10.0 8.0 6.0 4.0 2.0 0.0 C1 C2 C3 C4 * Figure 6. Eye fixation error rate (mean ± SE; *α < 0.05) 3.3 Subjective evaluation Figure 8. Visual field testing system target location 주관적만족도 (7점척도 ) 는 C1조건 (dot/sound on) 에서평균 5.7점으로가장높게평가되었다 (figure 7). C1조건의주관적만족도는 C2조건 (4.9점), C4조건 (4.7점) 보다유의하게높은것으로나타났다. C3조건의주관적만족도 (5.4점) 는 C4조건보다유의하게높은것으로분석되었다. 즉, 알림음이제공된시야고정방식이시야검사자에게더선호되는것으로확인되었다. * Subjective satisfaction 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 * * C1 C2 C3 C4 Figure 7. Subjective Satisfaction (mean ± SE; *α < 0.05) 3.4 Number of missing targets 시야검사자가가장확인하지못한시표는가장맹점과근접한우안검사시 36번 (43%), 좌안검사시 31번 (36%) 시표인것으로나타났다 (Figure 8). 그다음으로확인하지못한시표는우안검사시 37번 (6%), 좌안검사시 30번 (7%) 인것으로나타나역시나맹점과매우근접한시표로분석되었다. 4. Discussion 본연구는현안과에서사용되는시야검사방법인 24-2 threshold test 방법을 PC기반의시야진단시스템에구현하여정상인을대상으로다양한조건의시선고정방식의효과를파악하였다. 시야검사실험을수행한결과, 정상인 20명이확인한시표의수는중심시야 ( 시선의중심으로부터 30 반경 ) 내의 55개시표중 53개 (96%) 로확인되어평균 2개의시표를보지못한것으로분석되었다. 실험참여자가확인하지못한시표들의위치와빈도를분석한결과, 맹점과가장근접한 31번 ( 좌안 ), 36번 ( 우안 ) 시표에서상대빈도가각각 36%, 43% 로가장높게나타났다. 그이유는좌, 우안의맹점시표와 31번, 36번시표와의거리가매우가까운거리에위치 ( 시야각 1 이내 ) 하고있어실험참여자에게맹점과같이인식되었을가능성이높은것으로추정된다. 또다른이유로는일부실험참여자들중시야검사실험에집중하지못한실험참여자들의시야검사결과가함께분석되었기때문이다. 본연구는시야고정방식으로 central target form을 number로제공하여기존시야고정방식과 (dot) 시야검사의정확성을비교분석하였다. 그결과, C2조건 (central target form = dot/sound = off) 이다른조건들에비해시선고정오류율이 1.7 ~ 2.1배정도높게나타났다. 이는시각 (central target) 과청각 (sound) 적자극이동시에제공되어중심시표에시선을고정하는집중력을분산시킨것으로추정된다. 본연구는네가지시야고정방식에따른주관적만족도를분석한결과, C1조건 (dot/sound on) 이가장선호되는시야고정방식으로분석되었다. 선호되는 central target
form으로 dot이선호된것은실험참여자들이간단한작업을원하는경향성이반영된것으로추정되며, sound를제공하는경우가선호된것은실험참여자들이소리를들음으로써다음시표를대비할수있기때문으로사료된다. 본연구의 PC기반시야진단시스템의시선고정방식은추후녹내장환자를대상으로유효성이검증될필요가있다. 검증된 PC기반의시야진단시스템은보건소및지역의료기관에많은진단기회를제공함으로써잠재적녹내장환자의조기진단, 의료진단시스템의질적향상, 맞춤의료시스템구축에기여할것으로기대된다. Acknowledgements 이논문은환경부의에코디자인특성화대학원전문인력양성사업의지원으로수행되었습니다 References Cho, J. W., Nam, Y. P., Kim, D. Y., Kang, S. Y., Sung, K. R., Kook M. S., Clinical Validation of Visual Field Index., J Korean Ophthalmol Soc., 51(1), 49-54, 2010. Choi, J. A., Lee, N. Y., Lee, and Park, C. K., Interpretation of the Humphrey Matrix 24-2 Test in the Diagnosis of Preperimetric Glaucoma, Jpn J Ophthalmol, 53, 24 30, 2009 Dersu, I., Wiggins, M. N., Luther, A., Harper, R. and Chacko, J., Understanding Visual Fields, Part I: Goldmann Perimetry, Journal of Ophathalmic Medical Technology, 2, 1-10, 2006. Fan, X., Wu, L. L., Ma, Z. Z., Xiao, G. G. and Liu, F., Usefulness of Frequency-Doubling Technology for Perimetrically Normal Eyes of Open-Angle Glaucoma Patients with Unilateral Field Loss, BS Ophthalmology, 117 (8), 1530-1537, 2010. Giuffré, I., Frequency Doubling Technology vs. Standard Automated Perimetry in Ocular Hypertensive Patients, The Open Ophthalmology Journal, 3, 6-9, 2009. Kingman S. Glaucoma is second leading cause of blindness globally, Bull World Health Organ, 82, 887-888, 2004. Kogure, S., Toda, Y., and Tsukahara, S. Prediction of future scotoma on conventional automated static perimetry using frequency doubling technology perimetry, Br J Ophthalmol, 90, 347 352, 2006. Mozaffarieh, M., Grieshaber, M. C., Flammer, J., Oxygen and blood flow: players in the pathogenesis of glaucoma, Molecular Vision, 31, 224-233, 2008. Lee, K. M., Hwang, K. S., Kim, W., J., A Data Cluster Specialization-based Patient Class Management Strategy for Personalized Medicine, Proceedings of KIIS Fall Conference, 20(2), 323-324, 2010. Nam, Y., Kang, S. Y., Park, S. B., Sung, K. R., Kook M. S., Performance of Humphrey Matrix Frequency Doubling Technology Perimetry and Standard Automated Perimetry Global Indices, J Korean Ophthalmol Soc., 50(11), 1680-1685, 2009. Nomoto, H., Matsumoto, C., Takada, S., Hashimoto, S., Arimura, E., Sachiko Okuyama, S. and Shimomura, Y., Detectability of Glaucomatous Changes Using SAP, FDT, Flicker Perimetry, and OCT, J Glaucoma, 18(3), 165 171, 2009. Paolo Brusini, Frequency Doubling Technology Staging System 2. J Glaucoma, 15, 315 320, 2006. Kuminilbo. 녹내장환자 40만명 7년간 2배증가. Retrieved April 18, 2011 from http://news.kukinews.com/article/view.asp?page=1&gcode= kmi&arcid=1303116726&cp=nv. Author listings Jihyoung Lee: iwoneye@postech.ac.kr Highest degree: M.S., Department of Life Science, Dongguk Univ., 2010 Position title: M.S., Department of Industrial Engineering, POSTECH Areas of interest: Ergonomic Product Design & Development, Digital Human Modeling & Simulation, Ergonomic Interface System for the Disabled Person Baekhee Lee: x200won@postech.ac.kr Highest degree: M.S., Department of Industrial Engineering, POSTECH Position title: Ph.D., Department of Industrial Engineering, POSTECH Areas of interest: Ergonomic Product Design & Development, Digital Human Modeling & Simulation, Vehicle Ergonomics Yeona Kim: rmaksmf@postech.ac.kr Position title: B.S., Department of Industrial Engineering, POSTECH Areas of interest: Ergonomic Product Design & Development, Vehicle Ergonomics, User interface design & evaluation Jaheon Kang: kjh0614@khu.ac.kr Highest degree: PhD Medical college of Kyung Hee University Position title: Department of Ophthalmology, Kyung Hee University Hospital at Gangdong
Areas of interest: glaucoma Heecheon You: hcyou@postech.ac.kr Highest degree: Ph.D., Industrial Engineering, Pennsylvania State University Position title: Associate Professor, Department of Industrial & Management Engineering, POSTECH Areas of interest: Ergonomic product design & development, User interface design & evaluation, Digital human modeling & simulation, Human performance & workload assessment, Work-related musculoskeletal disorders (WMSDs) prevention, Usability testing