대한안과학회지 2014 년제 55 권제 12 호 J Korean Ophthalmol Soc 2014;55(12):1758-1764 pissn: 0378-6471 eissn: 2092-9374 http://dx.doi.org/10.3341/jkos.2014.55.12.1758 Original Article 두가지장비를이용한각막곡률및각막고위수차의비교 Comparison of Keratometry and Corneal Higher Order Aberrations between Videokeratoscope and Scheimpflug Camera 신지영 1 이민영 2 정소향 1 Ji Young Shin, MD 1, Min Young Lee, MD 2, So Hyang Chung, MD, PhD 1 가톨릭대학교의과대학서울성모병원안과및시과학교실 1, 이수안과의원 2 Department of Ophthalmology and Visual Science, Seoul St. Mary s Hospital, The Catholic University of Korea College of Medicine¹, Seoul, Korea ISU Eye Clinic², Seoul, Korea Purpose: To investigate the correlations of keratometry and corneal high order aberrations (HOAs) between the Keratron videokeratoscope and the HR Scheimpflug camera. Methods: From December 2012 to February 2013, keratometry and corneal HOAs were determined using the Keratron videokeratoscope and HR Scheimpflug camera in 23 healthy individuals (46 eyes). Results: Average keratometry showed high correlation with 95% confidence interval -0.155 ± 0.37 between the Keratron and HR. When comparing HOAs of the Keratron and total corneal HOAs of HR, total root-meansquare (RMS), and spherical aberration were positively correlated between the 2 devices (r = 0.67, p < 0.001 and r = 0.74, p < 0.001, respectively). When comparing HOAs of Keratron and anterior corneal HOAs of HR, total RMS, spherical aberration and coma were positively correlated between the 2 devices (r = 0.62, p < 0.001, r = 0.81, p < 0.001, and r = 0.52, p = 0.047, respectively). Conclusions: Although the 2 devices are based upon different principles, the Keratron videokeratoscope and HR Scheimpflug camera showed positive correlations in keratometry, total RMS, spherical aberration, and coma. Both devices may be useful for clinical applications. J Korean Ophthalmol Soc 2014;55(12):1758-1764 Key Words: Higher order aberrations, Keratometry, Keratron videokeratoscope, HR Scheimpflug camera, Spherical aberration Received: 2014. 7. 5. Revised: 2014. 8. 22. Accepted: 2014. 11. 5. Address reprint requests to So Hyang Chung, MD, PhD Department of Ophthalmology, College of Medicine, The Catholic University of Korea, Seoul St. Mary s Hospital, #222 Banpo-daero, Seocho-gu, Seoul 137-701, Korea Tel: 82-2-2258-1188, Fax: 82-2-599-7405 E-mail: chungsh@catholic.ac.kr * This study was presented as a narration at the 109th Annual Meeting of the Korean Ophthalmological Society 2013. * This work was supported by a grant of the Korea Health Technology R&D Project, Ministry of Health & Welfare, Korea (HI13C0016). 각막의고위수차측정은불규칙난시, 원추각막등의진단뿐아니라백내장수술시비구면인공수정체의선택및맞춤형굴절교정술등에유용하게사용되고있다. 원추각막의진단및진행경과판정에코마수차가사용되고있고, 1,2 환자의각막구면수차를이용하여적절한비구면인공수정체를선택하여수술후시력의질및시기능향상을가져왔으며, 3 각막고위수차를이용한맞춤형굴절교정술이고식적인방법보다좋은시력및시기능을보인다는보고도있었다. 4,5 각막의고위수차는각막지형도의 elevation map을이용하여산출되며 placido-disc를이용한각막지형도와샤임플 c2014 The Korean Ophthalmological Society This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 1758
- 신지영외 : 두장비의각막곡률및각막고위수차비교 - 러그카메라 (Scheimpflug camera) 를이용한각막지형도기계에서수치를얻을수있다. Keratron (Optikon, Italy) 는 28개의 placido ring을 base로하는 videokeratoscope로각막전면의 90% 를반영하는 elevation map을이용하여 Zernike polynomial에따라안구의수차를구하는기기로써슈빈트 (Schwind) 사의아마리스와굴절교정수술시행시연동하여쓰인다. 6 HR (Oculus Inc., Germany) 은 360 로회전하는샤임플러그카메라 (Scheimpflug camera) 를이용하여각막전후면의 elevation map을구하게되며이를통해각막전체및전후면의고위수차를따로구할수있으며, 그재현성역시입증된바있다. 7-11 각막고위수차계를임상에서상용하기위해서는기계의정확성과재현성에대한검증이필요하며 Keratron 의전안부계측의정확성및임상적유용성에대해서는아직까지국내에서보고된바가없었다. 따라서본연구에서는서로다른원리에기반한측정방식을갖는 Keratron 와 HR에서각막곡률과각막고위수차값을비교하고 Keratron 의계측치의상관관계및신뢰도를확인하고자한다. 가눌리지않도록주의하며검사를시행하였다. 한검사자가동일검사를 3회시행하여평균값을기준으로하였다. Keratron videokeratoscope가각막지형도를바탕으로각막전면의 90% 를반영하는 elevation map을이용하여 Zernike polynomial에따라안구의수차를구하는기기이므로 Keratron 의각막고위수차값을 HR의각막총고위수차값및각막전면고위수차값과각각비교분석하였다. 통계학적분석방법으로는 SPSS 18.0 version 18.0 (SPSS Inc., Chicago, IL) 프로그램을사용하여 p 0.05를유의한차이라정의하였다. 급내상관계수 (Interclass correlation coefficient) 를구하여각막곡률과각막고위수차값의상관관계를분석하였고, Bland-Altman plot 분석을사용하여 95% 유의수준을확인하였다. Keratron 의각막고위수차값은 HR의각막전면고위수차및각막총고위수차와비교하였다. 또한 Paired t-test를시행하여결과값간의유의한차이가있는지확인하였다. 결과 대상과방법 본연구는 2012년 12월에서 2013년 2월사이에본원에서근시교정술을받기위해내원한환자를대상으로구면굴절이상도가 -6.00D 이하, 원주굴절이상도는 -3.00D 이하이고, 최대교정시력은 1.0 이상인환자를대상으로하였다. 근시및난시를제외하고는다른안과적질환을가지고있지않으며, 전신질환및안과적수술력, 외상력, 각막질환의과거력이없는환자들중검사전에동의를한 23명 46안을대상으로하였다. 눈물막파괴시간이 10초이하의건성안이있는환자는제외하였고측정시협조가안되어검사시간이길어지거나검사조건에영향을미칠수있는환자도연구에서제외하였다. 본연구는본원임상연구심의위원회 (Institutional Review Board) 승인하에진행되었다 (KC14RISI0578). 동일한한명의검사자에의해같은날연속으로 Keratron 와 HR을이용하여각막지형도검사를시행하고그측정값을비교하였다. 각막고위수차는그값이매우작고역동성을가지고있어서같은대상을동일한검사기기로측정하여도측정시의눈물막 (Tear Film) 상태나시축 (Visual Axis) 의정렬상태등의조건에따른차이가발생할수있다. 12 따라서 Keratron 와 HR로검사시측정오차를최소한으로줄이기위하여숙련된검사자 1명에게이점을숙지시켰으며, 검사도중환자가눈을깜박이거나움직이지않도록주의하고검사자에의해안구 본연구에포함된 23명 46안환자중남자는 8명여자는 15명이었으며, 평균나이는 24.4 ± 4.24세였으며, logmar 나안시력은 0.16 ± 0.08, logmar 최대교정시력은 0.92 ± 0.09였다 (Table 1). Keratron 의평균각막곡률 (Average Keratometry) 과 HR로측정한전면의평균각막곡률은각각 43.39 ± 1.30D와 43.55 ± 1.32D였으며, 두기기사이에통계학적으로유의한상관관계를보였으며 (r=0.88, p<0.001), 수치간에통계학적으로유의한차이를보이지않았다 (p=0.122). 가파른축의각막곡률 (steep keratometry) 및편평한축의각막곡률 (flat keratometry) 역시각각통계학적으로유의한상관관계를보였으며 (steep K r=0.89, p=0.006; flat K r=0.86, p=0.012), 수치간에통계학적으로유의한차이를보이지않았다 (steep K p=0.155; flat K p=0.094). Bland-Altman plot을시행한결과, 두기기간의변동폭 (95% CI) 은 -0.155 ± 0.37D로아주우수하여두기기간의 Table 1. Demographics of 23 patients (M:F = 8:15) Values Age (years) 24.4 ± 4.24 UCVA (log MAR) 0.16 ± 0.08 BCVA (log MAR) 0.92 ± 0.09 Sphere (diopter) -3.76 ± 1.54 Cylinder (diopter) -1.48 ± 0.86 Values are presented as mean ± SD. UCVA = uncorrected visual acuity; BCVA = best corrected visual acuity. 1759
- 대한안과학회지 2014 년제 55 권제 12 호 - Table 2. The comparison of cornea higher order aberrations (HOAs) between the Keratron videokeratoscopy and HR Scheimpflug Camera (corneal HOAs) (corneal HOAs) Total RMS 0.41 ± 0.06 0.37 ± 0.05 0.054 Spherical aberration 0.24 ± 0.07 0.22 ± 0.08 0.061 Coma 0.20 ± 0.07 0.18 ± 0.05 0.005 Trefoil 0.16 ± 0.01 0.10 ± 0.01 <0.001 (corneal HOAs) (anterior corneal HOAs) Total RMS 0.41 ± 0.06 0.40 ± 0.07 0.31 Spherical aberration 0.26 ± 0.06 0.27 ± 0.08 0.153 Coma 0.20 ± 0.07 0.20 ± 0.07 0.173 Trefoil 0.18 ± 0.06 0.10 ± 0.01 <0.001 Values are presented as mean ± SD. RMS = root-mean-square. Table 3. The correlation of cornea higher order aberrations (HOAs) between the Keratron videokeratoscopy and HR Scheimpflug Camera Correlation Differences (corneal HOAs) (corneal HOAs) coefficient Total RMS 0.41 ± 0.06 0.37 ± 0.05 0.04 ± 0.05 0.67 <0.001 Spherical aberration 0.24 ± 0.07 0.22 ± 0.08 0.02 ± 0.05 0.74 <0.001 Coma 0.20 ± 0.07 0.18 ± 0.05 0.03 ± 0.09 0.32 0.189 Trefoil 0.16 ± 0.01 0.10 ± 0.01 0.07 ± 0.06 0.45 0.105 Correlation Differences (corneal HOAs) (anterior corneal HOAs) coefficient Total RMS 0.41 ± 0.06 0.40 ± 0.07 0.01 ± 0.06 0.62 <0.001 Spherical aberration 0.26 ± 0.06 0.27 ± 0.08 0.03 ± 0.05 0.81 <0.001 Coma 0.20 ± 0.07 0.20 ± 0.07 0.02 ± 0.09 0.52 0.047 Trefoil 0.18 ± 0.06 0.10 ± 0.01 0.07 ± 0.07 0.43 0.094 Values are presented as mean ± SD. RMS = root-mean-square. Figure 1. The comparison of average keratometry (K) between the Keratron videokeratoscopy and HR Scheimpflug Camera. The solid line represents ±0.37 standard deviation confidence interval (CI) (i.e. 95% of the points should fall within these lines). 일치도가높음을확인할수있었다 (Fig. 1). 각막중심 6 mm에서 Keratron 의각막고위수차값과 HR의각막총고위수차값을비교하였을때총 root-mean-square (RMS) 및구면수차는통계적으로유의한차이를보이지않았으나 (p>0.05) 코마수차는통계적으로는유의한차이를보였다 (p=0.005). Keratron 의각막고위수차값과 HR의각막전면고위수차값을비교하였을때에는총 RMS, 구면수차및코마수차에서두기기간에통계적으로유의한차이를보이지않았다 (p>0.05). 트레포일수차는 Keratron 의값이 HR의각막전체및각막전면트레포일수차보다통계적으로유의하게높은값을보였다 (p<0.001) (Table 2). Keratron 의각막고위수차값과 HR의각막전체고위수차값과의상관관계를분석한결과총 RMS는두기기의계측치간에통계적으로유의한상관관계를나타내었으며 (r=0.67, p<0.001), Bland-Altman plot을시행한결과, 두기기간의변동폭 (95% CI) 은 0.04 ± 0.05D로두기기간의일치도가높음을확인할수있었다. 구면수차도두기기의계측치간에통계학적으로유의한상관관계를 1760
- 신지영외 : 두장비의각막곡률및각막고위수차비교 - Figure 2. The correlation between corneal higher order aberrations (HOAs) of the Keratron videokeratoscopy and total corneal HOAs of HR Scheimpflug Camera. RMS = root-mean-square; SA = spherical aberration. 나타내었으며 (r=0.74, p<0.001), Bland-Altmann 결과분석시두기기간의변동폭 (95% CI) 은 0.02 ± 0.05D 로두기기간의일치도가높음을확인할수있었다. 그러나코마수차 (Coma) 와트레포일수차 (Trefoil) 는 Keratron 와 HR의계측치간에유의한상관관계를보이지않았다 ( 코마수차 r=0.32, p=0.189; 트레포일수차 r=0.45, p=0.105) (Fig. 2, Table 3). Keratron 의각막고위수차값과 HR의각막전면고위수차값과의상관관계를분석한결과, 각막중심 6 mm에서총 RMS 및구면수차는두기기의계측치간에통계학적으로유의한상관관계를나타내었다 (RMS r=0.62, p<0.001; 구면수차 r=0.81, p<0.001). 그러나각막전체고위수차와달리 HR의각막전면고위수차분석에서는코마수차도두기기간에통계학적으로유의한상관관계를나타내었으며 (r=0.52, p=0.047), 트레포일수차는두기기간에유의한상관관계를보이지않았다 (r=0.45, p=0.105) (Fig. 3, Table 3). 고찰 각막의고위수차측정은원추각막, 주변부각막변성등의 각막질환뿐아니라노화로인한비정상적인시기능도측정할수있고, 각막고위수차를이용한맞춤형굴절교정술이고식적인방법보다좋은결과를가져옴으로써임상적으로유용하게사용되고있다. 또한백내장수술시환자의각막구면수차를이용하여비구면인공수정체를선택하게되면서각막구면수차를측정할수있는기계에관심이집중되었다. 현재까지상용화된각막고위수차측정기계로는 Keratron, 6 Irx3 (Orsay, France), 13 itrace (Tracey Technologies, Houston, TX), 14 OPD-Scan (Nidek, Gamagori, Japan), 15 HR, Gallilei (Ziemer Ophthalmic Systems AG, Zurich, Switzerland) 16 등이있다. 각막곡률값을비교하였을때 Keratron 의중심평균각막곡률과 HR의중심평균각막곡률은높은일치도를보였다. 두기계를비교한한연구에서중심부의가장편평한각막곡률은두기계간차이가없었으나가장가파른각막곡률은차이가있다고보고하였다. 17 이에대해 Keratron 는 Placido-disk imaging 을사용하여반사된 image에의존해서값을산출하고중심주변부각막으로부터중심각막곡률을추론해내지만샤임플러그카메라는광학적 cross-section을사용하여중심각막의 0.33 mm을직접 1761
- 대한안과학회지 2014 년제 55 권제 12 호 - Figure 3. The correlation between corneal higher order aberrations (HOAs) of Keratron videokeratoscopy and anterior corneal HOAs of HR Scheimpflug Camera. RMS = root-mean-square; SA = spherical aberration. 측정하기때문인것으로추정되고있다. 18 그러나본연구에서가파른각막곡률과편평한각막곡률의평균치에는두기계간차이가없었기때문에임상적용시각막곡률치는두기계간의값을교환하여적용해볼수있을것이다. 각막고위수차값을비교하기위하여각막중심 6 mm에서 Keratron 의각막고위수차값과 HR의각막전체고위수차값을비교하였을때총 root-mean-square (RMS) 및구면수차는두기계에서높은상관관계및일치도를보였다. Keratron 가각막지형도를바탕으로각막전면의 90% 까지반영하는 elevation map을이용하여 Zernike polynomial 에따라안구의수차를구하는기기이므로 Keratron 의각막고위수차값을 HR의각막전면고위수차값과비교분석한결과총 RMS 및구면수차에서두기계에서높은상관관계및일치도를보였다. 또한코마수차에서도상관계수가높지는않았으나통계학적으로유의한상관관계를나타내었다. 그러나트레포일수차는 Keratron 값이 HR의각막전체값과각막전면값모두보다통계적으로유의하게높고두기기의계측치간에상관관계를보이지않았다. 두기계의각막의총 RMS는높은상관관계를보였으므 로각막후면이고려되지않았다고할지라도 Keratron 에근거해서시행하는근시교정술은각막고위수차를효과적으로교정하여시력의질향상을가져올수있을것으로생각해볼수있다. 백내장수술전각막의구면수차에근거해서비구면인공수정체를선택할때에도각막후면이고려되지않은 Keratron 의구면수차도 HR의각막전체구면수차와높은일치도를보였으므로유용하게사용될수있다. 두기계간코마수차와트레포일수차의값이일치하지않은것은두기계의측정범위및원리가다른것으로추정해볼수있다. 코마수차에서 Keratron 의코마수차와 HR의각막전면코마수차와는상관관계를보였으나각막전체코마수차와는일치하지않은것은각막전체코마수차에각막후면이기여하는바가큰것을의미한다. 초기원추각막의진단에수직코마수차 (vertical coma) 와각막후면상승 (posterior corneal elevation) 이지표로사용될수있음이보고되었으므로 19,20 원추각막의진단에는각막후면을반영할수있는 HR이더유용할것이다. 트레포일수차는각막의주변부의각도에따른기복을주로반영하여나타나므로 Placido-disc imaging 을바탕으로 ele- 1762
- 신지영외 : 두장비의각막곡률및각막고위수차비교 - vation map 을이용하여고위수차를구하는 Keratron 의산출방식과광학적 cross-section을사용하여각막전후면의 elevation map을이용하여고위수차를구하는 HR의산출방식이각막주변부에서는일치도가떨어지는것으로추정해볼수있다. 본연구에서는모든개별각막고위수차값을비교하지않은것이제한점이나총 RMS 값에근거하여굴절교정수술을시행하고, 백내장수술시각막구면수차를근거로비구면인공수정체를선택하며, 각막의코마수차가원추각막의진단및진행을판단하는데도움을줄수있기때문에측정원리가다른두기계에서임상적으로중요한각막고위수차를비교하였다. 비록대상자수가 46안으로많지는않지만각막고위수차에영향을줄수있는고령, 고도근시, 난시, 각막질환환자, 건성안환자및협조가안되는환자를모두제외하고한명의검사자가세번측정하여평균값을산출하여비교하였으므로검사의정확도에대한신뢰도는확보되었다고볼수있다. 모든기계를다보유할수없는현실속에서서로다른원리에입각한 Keratron 와 HR 계측치중평균각막곡률값과각막고위수차중총 RMS, 구면수차및 HR의각막전면코마수차는두기계의측정치를상호교환하여임상적용할수있을것으로생각한다. REFERENCES 1) Bühren J, Kook D, Yoon G, Kohnen T. Detection of subclinical keratoconus by using corneal anterior and posterior surface aberrations and thickness spatial profiles. Invest Ophthalmol Vis Sci 2010;51:3424-32. 2) Jafri B, Li X, Yang H, Rabinowitz YS. Higher order wavefront aberrations and topography in early and suspected keratoconus. J Refract Surg 2007;23:774-81. 3) Kim HS, Kim SW, Ha BJ, et al. Ocular aberrations and contrast sensitivity in eyes implanted with aspheric and spherical intraocular lenses. J Korean Ophthalmol Soc 2008;49:1256-62. 4) Lee SM, Lee MJ, Kim MK, et al. Comparison of changes in higher-order aberrations between conventional and wavefront-guided LASEK. J Korean Ophthalmol Soc 2007;48:1028-35. 5) Kim SI, Oh JJ, Oh TH, et al. Higher-order aberrations and visual acuity with wavefront-guided and wavefront-optimized ablation in laser keratorefractive surgery. J Korean Ophthalmol Soc 2014;55:480-5. 6) Tripoli NK, Cohen KL, Holmgren DE, Coggins JM. Assessment of radial aspheres by the Arc-step algorithm as implemented by the Keratron keratoscope. Am J Ophthalmol 1995;120:658-64. 7) Buehl W, Stojanac D, Sacu S, et al. Comparison of three methods of measuring corneal thickness and anterior chamber depth. Am J Ophthalmol 2006;141:7-12. 8) Lackner B, Schmidinger G, Pieh S, et al. Repeatability and reproducibility of central corneal thickness measurement with, Orbscan, and ultrasound. Optom Vis Sci 2005;82:892-9. 9) Lackner B, Schmidinger G, Skorpik C. Validity and repeatability of anterior chamber depth measurements with and Orbscan. Optom Vis Sci 2005;82:858-61. 10) O'Donnell C, Maldonado-Codina C. Agreement and repeatability of central thickness measurement in normal corneas using ultrasound pachymetry and the OCULUS. Cornea 2005;24: 920-4. 11) Barkana Y, Gerber Y, Elbaz U, et al. Central corneal thickness measurement with the Scheimpflug system, optical lowcoherence reflectometry pachymeter, and ultrasound pachymetry. J Cataract Refract Surg 2005;31:1729-35. 12) Miranda MA, O'Donnell C, Radhakrishnan H. Repeatability of corneal and ocular aberration measurements and changes in aberrations over one week. Clin Exp Optom 2009;92:253-66. 13) Visser N, Berendschot TT, Verbakel F, et al. Evaluation of the comparability and repeatability of four wavefront aberrometers. Invest Ophthalmol Vis Sci 2011;52:1302-11. 14) Alpins NA. A new method of analyzing vectors for changes in astigmatism. J Cataract Refract Surg 1993;19:524-33. 15) MacRae S, Fujieda M. Slit skiascopic-guided ablation using the Nidek laser. J Refract Surg 2000;16:S576-80. 16) Savini G, Carbonelli M, Barboni P, Hoffer KJ. Repeatability of automatic measurements performed by a dual Scheimpflug analyzer in unoperated and post-refractive surgery eyes. J Cataract Refract Surg 2011;37:302-9. 17) Kawamorita T, Nakayama N, Uozato H. Repeatability and reproducibility of corneal curvature measurements using the and Keratron topography systems. J Refract Surg 2009;25:539-44. 18) Tripoli NK, Cohen KL, Holmgren DE, Coggins JM. Assessment of radial aspheres by the Arc-step algorithm as implemented by the Keratron keratoscope. Am J Ophthalmol 1995;120:658-64. 19) Piñero DP, Nieto JC, Lopez-Miguel A. Characterization of corneal structure in keratoconus. J Cataract Refract Surg 2012;38:2167-83. 20) Bühren J, Kühne C, Kohnen T. Defining subclinical keratoconus using corneal first-surface higher-order aberrations. Am J Ophthalmol 2007;143:381-9. 1763
- 대한안과학회지 2014 년제 55 권제 12 호 - = 국문초록 = 두가지장비를이용한각막곡률및각막고위수차의비교 목적 : Keratron videokeratoscope 와 Scheimpflug Camera 의각막곡률과각막고위수차를비교하고상관관계를알아보고자하였다. 대상과방법 : 2012 년 12 월부터 2013 년 2 월까지건강한성인 23 명 (46 안 ) 을대상으로 Keratron videokeratoscope 와 HR Scheimpflug Camera 를이용하여각막곡률과각막고위수차를측정하고비교하였다. 결과 : Keratron 와 HR 을사용하여측정한각막곡률은 95% confidence interval -0.155 ± 0.37 로높은수준의상관관계를보였다. Keratron 와 HR 간에각막총고위수차의상관분석에서총 Root-mean-square (RMS) 및구면수차는통계학적으로유의한상관관계를나타내었다 (r=0.67, p<0.001, r=0.74, p<0.001). Keratron 의각막고위수차와 HR 의각막전면고위수차의상관분석에서는총 RMS, 구면수차및코마수차에서통계학적으로유의한상관관계를나타내었다 (r=0.62, p<0.001, r=0.81, p<0.001, r=0.52, p=0.047). 결론 : 다른원리를사용하는 Keratron 와 HR 의두기기의각막곡률값과임상적으로중요한총 RMS, 구면수차및코마수차에서유의한상관관계를나타내어서두장비모두임상적으로유용하게사용될수있다. < 대한안과학회지 2014;55(12):1758-1764> 1764