디지털 PLL을 이용한 clock 발생용 회로에 관한 연구

학위논문(석사) --서울대학교 대학원 :전기. 컴퓨터공학부,2007.Maste

푸리에 도메인 (Fourier-domain) 방식 빛간섭 단층촬영을 이용한 두 종류의 펨토초레이 저와 미세각막절개도에 의해 만들어진 라식(LASIK) 절편의 형태학적 비교

의학과/석사[한글]목적 : 푸리에도메인 방식 전안부 빛간섭단층촬영을 통해, 두 종류의 서로 다른 펨토초레이저를 이용하여 제작된 라식 절편과 미세각막절개도를 사용한 경우의 각막 절편의 두께와 변연부 절단각을 비교하고자 하였다.방법 : 펨토초레이저 및 미세각막절개도를 이용하여 라식 수술을 시행받은 환자를 대상으로, 각막 절편 제작에 사용한 도구에 따라 IntraLase (AMO Inc., Santa Ana, CA, USA) 군 30명 (60안), Femto-LDV (Ziemer, Port, Switzerland) 군 32명 (64안), 미세각막절개도군 26명 (52안)으로 구분하여 술 후 2개월째에 나안시력, 굴절검사를 시행하였고, RTVue (Optovue Inc., Fremont, CA, USA) 를 이용하여 총 14 지점에서 절편의 두께를 측정하였으며 4 방향에서 절편의 변연부 절단각을 측정하였다. 형태학적 분석은 네 가지 측면에서 이루어졌다. 각막 절편의 평균 두께를 통해 절편의 형태를 비교하였고, 의도한 절편 두께와 측정값과의 차이를 절편 제작의 예측도로 정의하여 평가하였다. 각막 절편의 균일성을 평가하기 위해 모든 측정 위치 사이에서의 통계학적 연관성을 분석하는 동시에 각각의 각막 절편에서 중심부와 주변부의 두께 차이를 비교하였다. 마지막으로 절편 변연부의 절단각을 비교하였다. 결과 : 두 종류의 펨토초레이저를 이용하여 만든 각막 절편이 미세각막절개도로 제작한 절편에 비해 비교적 고른 형태를 나타내었다. 절편 두께의 예측도는 Femto-LDV 군에서 다른 두 군에 비해 적었다 (p<0.001). 각 측정 지점 사이의 통계적 연관성 및 각막 중심부와 주변부 두께의 차이는 IntraLase 군에서 가장 적었다 (p<0.001). 절편 변연부 절단각은 IntraLase 군이 다른 두 군에 비해 유의하게 적었던 반면 (p<0.001), Femto-LDV 군과 미세각막절개도군 사이에서는 차이를 보이지 않았다. 결론 : 펨토초레이저를 이용하여 제작한 라식 절편은 비교적 균일한 두께와 형태를 가지며, 미세각막절개도는 중심부에서 훌륭한 예측도를 보인 반면 주변부와는 차이를 보였다. 또한 두 종류의 펨토초레이저 사이에도 형태학적 차이가 존재하였으므로, 라식 절편의 제작 시에는 이러한 제작 도구의 특징을 세심하게 고려해야 할 것이다. [영문]Purpose : To evaluate thickness and side cut angle of LASIK flap made by two different types of femtosecond laser system and a microkeratome using Fourier-domain optical coherent tomography (FD-OCT).Methods : One hundred and sixty six eyes (83 patients) which had underwent LASIK surgery were allocated to 3 groups according to the method for flap creation. Fifty eyes (25 patients) were subject to the IntraLase group, 64 eyes (32 patients) to the Femto-LDV group, and 52 eyes (26 patients) to the microkeratome group. Fourteen measuring points of the flap thickness and four directions of incision angle at the margin were measured with the RTVue FD-OCT system (Optovue Inc., Fremont, CA, USA) at 2 months postoperatively. Morphologic analysis was performed in four aspects. Flap configuration was evaluated with mean flap thickness at each measuring point. Predictability was defined as the disparity between measured and intended thickness. And regularity of flap thickness was analyzed by identifying statistical interactions between measuring points in each flap. Differences between peripheral and central flap thickness also were evaluated as regularity index. Side cut angles at the flap margin were compared.Results : Two femtosecond laser groups presented with relatively even configuration of flap in comparison to microkeratome group. Femto-LDV group showed better predictability comparing to other groups (p<0.001). Statistical interactions between measuring points and differences between peripheral and central flap thickness were the least in the IntraLase group (p<0.001). Side cut angles at the flap margin were more acute and close to a right angle in IntraLase group at four directions (p<0.001). But there was no significant difference between Femto-LDV and microkeratome group.Conclusion : Flap made with femtosecond laser systems showed even configuration and better regularity in thickness. Microkeratome made predictable flap thickness in central area, but there is disparity between central and peripheral areas. Between two different femtosecond laser systems, there also are morphological differences. Because each method has different character depending on its own mechanism, it is important to consider these differences in flap creation.ope

Comparison of laser in situ keratomileusis flaps created by 3 femtosecond lasers and a microkeratome

PURPOSE: To evaluate the thickness and side-cut angle of laser in situ keratomileusis (LASIK) flaps created by 1 of 3 femtosecond lasers or a microkeratome using Fourier-domain optical coherence tomography (OCT). SETTING: Department of Ophthalmology, Institute of Vision Research, Yonsei University College of Medicine, Seoul, Korea. DESIGN: Comparative case series. METHODS: Flap creation for bilateral LASIK was performed using an IntraLase (femtosecond group 1), VisuMax (femtosecond group 2), or Femto LDV (femtosecond group 3) femtosecond laser or an M2 microkeratome. Flap thickness was determined at 14 points. The side-cut angle was measured in 4 directions at the margin interface. Measurements were taken 2 months postoperatively using an RTVue Fourier-domain OCT device and integrated software. RESULTS: Femtosecond group 1 comprised 50 eyes; femtosecond group 2, 40 eyes; femtosecond group 3, 64 eyes; and the microkeratome group, 52 eyes. Eyes in femtosecond groups 1 and 2 had relatively even flap configuration. Flaps in femtosecond group 3 and the microkeratome group had a meniscus shape. Flaps in femtosecond group 1 had the least difference between the mean peripheral and the central flap thickness (P<.001). The greatest flap thickness predictability (measured versus intended thickness) was in femtosecond group 3 (P<.001). Flaps in femtosecond group 1 had a side-cut angle closest to 90 degrees (P<.001). CONCLUSIONS: Flap morphology differed according to the system used. The 3 femtosecond laser systems appeared to be superior to the microkeratome system generally. The 3 femtosecond laser systems also produced different flap configurations depending on their individual mechanisms.ope

Efficacy of sodium hyaluronate and carboxymethylcellulose in treating mild to moderate dry eye disease

PURPOSE: We compared the efficacy and safety of sodium hyaluronate (SH) and carboxymethylcellulose (CMC) in treating mild to moderate dry eye. METHODS: Sixty-seven patients with mild to moderate dry eye were enrolled in this prospective, randomized, blinded study. They were treated 6 times a day with preservative-free unit dose formula eyedrops containing 0.1% SH or 0.5% CMC for 8 weeks. Corneal and conjunctival staining with fluorescein, tear film breakup time, subjective symptoms, and adverse reactions were assessed at baseline, 4 weeks, and 8 weeks after treatment initiation. RESULTS: Thirty-two patients were randomly assigned to the SH group and 33 were randomly assigned to the CMC group. Both the SH and CMC groups showed statistically significant improvements in corneal and conjunctival staining sum scores, tear film breakup time, and dry eye symptom score at 4 and 8 weeks after treatment initiation. However, there were no statistically significant differences in any of the indices between the 2 treatment groups. There were no significant adverse reactions observed during follow-up. CONCLUSIONS: The efficacies of SH and CMC were equivalent in treating mild to moderate dry eye. SH and CMC preservative-free artificial tear formulations appropriately manage dry eye sign and symptoms and show safety and efficacy when frequently administered in a unit dose formulaope

Comparison of higher order aberrations after implantable Collamer Lens implantation and wavefront-guided LASEK in high myopia

PURPOSE: To compare changes in ocular higher order aberrations (HOAs) after Visian Implantable Collamer Lens (ICL, STAAR Surgical Co) implantation and wavefront-guided laser epithelial keratomileusis (WFG-LASEK) to correct high myopia. METHODS: This prospective case series comprised 30 eyes (18 patients) that underwent ICL implantation (ICL group) and 33 eyes (18 patients) that underwent WFG-LASEK (WFG-LASEK group). All eyes had spherical equivalent of -6.00 to -9.00 diopters. Entire ocular, internal optic, and corneal HOAs were measured before surgery and 3 months after surgery using a laser ray tracing aberrometer. Contrast sensitivity testing was performed in 10 eyes from each group at a photopic light level of 85 cd/m(2) and a mesopic level of 3 cd/m(2) 3 months after surgery. RESULTS: In the ICL group, HOAs changed for the entire ocular trefoil-y, spherical aberration, internal optic spherical aberration, and corneal trefoil-y. In the WFG-LASEK group, increased HOAs were observed for total HOAs, entire ocular and corneal spherical aberration, secondary astigmatism, and tetrafoil. The ICL group had lower induced aberration values of entire ocular and corneal HOAs compared with the WFG-LASEK group. No significant differences in contrast sensitivity values between groups at the photopic level were noted; however, contrast sensitivity values were significantly lower for 3 (P=.01) and 6 cycles per degree (P<.001) in the WFG-LASEK group at the mesopic level. At the mesopic level, total HOAs, trefoil-y, spherical aberration, and secondary astigmatism were higher in the WFG-LASEK group. CONCLUSIONS: Implantable Collamer Lens implantation induced fewer ocular and corneal HOAs and resulted in better contrast sensitivity at mesopic levels than WFG-LASEK in eyes with high myopia.ope

Comparison of the Refractive Error Measurement Using Different Methods in Wavefront-Guided LASEK

PURPOSE: To predict the accuracy of preoperative refractive error measurement methods in wavefront-guided laser-assisted subepithelial keratectomy (LASEK) surgery and to formulate a nomogram for satisfactory surgical results. METHODS: The medical records of 30 patients (57 eyes) who had undergone wavefront-guided LASEK were reviewed. The ideal surgical ablation amount was defined as the sum of the real surgical ablation amount and the remaining refractive errors. Comparison between the ideal surgical ablation amount and preoperative refractive errors was made using autorefraction, manifest refraction, cycloplegic refraction, postcycloplegic refraction, wavescan, and iTrace aberrometer measurements. RESULTS: The refractive errors measured by the postcycloplegic refraction showed the closest relation with the ideal surgical amount, and the nomogram based on this refraction correlated statistically significantly with the ideal surgical ablation amount. The refractive error using the wavescan also showed more accurate refractive measurements than the autorefractor and iTrace aberrometer. CONCLUSIONS: Accurate manifest refraction immediately before surgery is the most important in determining the ablation amount. Additionally, the refractive errors measured with the wavescan, which is an aberrometer used for wavefront-guided LASEK, showed a minimal amount of errors. After reviewing the results, the nomogram based on these 2 methods can be concluded to possibly contribute to an increase in the accuracy of surgeryope

Comparison of Measurement of Anterior Segment Parameters Between Scheimpflug Camera and Ultrasound Biomicroscopy

Purpose: To evaluate the clinical reliability of PentacamⓇ by comparing anterior chamber parameters measured by Oculus Pentacam system (Oculus Inc., Germany) and Hi-scan ultrasound biomicroscopy (OPTIKON 2000, Rome, Italy) in primary angle closure (PAC) and normal patients. Methods: A prospective study was performed from June 2006 to January 2007. Fifty-one eyes in 26 primary angle-closure patients and 39 eyes in 20 normal control patients, for a total of 90 eyes of 46 patients were recruited from glaucoma out-patient clinics. The correlation and agreement of both measurements of anterior chamber depth and anterior chamber angle measured by UBM and PentacamⓇ were calculated. Sensitivity and specificity of each tool were also compared and the diagnostic value of angle closure was examined. Results: Anterior chamber depth measured by UBM and PentacamⓇ showed strong correlation in the normal control group (r=0.821) and PAC group (r=0.957). Anterior chamber angle showed moderate correlation in the normal control group (r=0.523) and PAC group (r=0.456) while good agreement was also observed. In diagnosing angle closure, anterior chamber measurements appear similar in UBM and PentacamⓇ using the ROC curve (AUC of UBM, 0.942; AUC of PentacamⓇ, 0.931). Conclusions: PentacamⓇ shows high to moderate correlation of anterior chamber measurements and good agreement compared with UBM. PentacamⓇ shows similar ability in diagnosing angle closure compared with UBM and thus is expected to be a good tool in diagnosing angle closureope

Early Glaucoma Detection Using the Humphrey Matrix Perimeter, GDx VCC, Stratus OCT, and Retinal Nerve Fiber Layer Photography

PURPOSE: To compare the effectiveness of Humphrey Matrix perimetry, GDx VCC, Stratus OCT, and retinal nerve fiber layer (RNFL) photography using the Heidelberg Retina Angiograph 1 (HRA1) for early glaucoma detection. DESIGN: Cross-sectional comparative study. PARTICIPANTS: Seventy-two primary open-angle glaucoma patients with early-stage visual field defects and 48 healthy controls were included. METHODS: Measurements using Humphrey Matrix perimetry, GDx VCC, Stratus OCT, and RNFL photography using HRA1, as well as standard automated perimetry, were obtained. We constructed receiver operating characteristic (ROC) curves for all available parameters and calculated the area under the ROC curves (AUC) to seek the best discriminating parameter of each test. Subsequently, the ROC curves were calculated for the combinations of the best discriminating parameters of each test to seek the most effective combination for early glaucoma detection. MAIN OUTCOME MEASURE: The AUC for various parameters of Humphrey Matrix perimetry, GDx VCC, Stratus OCT, and RNFL photography using HRA1. RESULTS: The AUCs of Humphrey Matrix perimetry, GDx VCC, Stratus OCT, and RNFL photography using HRA1 with the best discriminating parameter were 0.990, 0.906, 0.794, and 0.751, respectively. The AUC of the following best combination was 0.972, more than 5 points depressed below the level of 5% on the pattern deviation plot from Humphrey Matrix perimetry, and the nerve fiber indicator was larger than 20 from GDx VCC. CONCLUSIONS: The AUC of the Humphrey Matrix perimetry was greater than that of the GDx VCC, Stratus OCT, and RNFL photography using HRA1.ope