Application of anterior segment optical coherence tomography in glaucoma

Optical coherence tomography (OCT) is a cross-sectional, three-dimensional, high-resolution imaging modality that uses low coherence interferometry to achieve axial resolution in the range of 3–20 μm. Two OCT platforms have been developed: time domain (TD-OCT) and spectral (or Fourier) domain (SD/FD-OCT). Visante anterior segment OCT (Carl Zeiss Meditec) is a TD-OCT widely used for anterior segment imaging. The SD-OCT systems with both posterior and anterior segment imaging capabilities include the RTVue, iVue (Optovue), the Cirrus (Carl Zeiss Meditec), and the Spectralis (Heidelberg Engineering, Inc.). Each of the SD-OCTs has a wavelength in the range of 820–879 nm. Anterior segment OCT is a non-contact method providing high resolution tomographic cross-sectional imaging of anterior segment structures. Anterior segment OCT provides qualitative and quantitative assessment of the anterior segment structures important to the pathogenesis and the anatomical variations of glaucoma, and the approach to and success of treatment. We summarize the clinical applications of anterior segment OCT in glaucoma.     

眼前节相干光断层扫描技术的临床应用进展

近年来,相干光断层扫描(OCT)技术在眼前节疾病诊治中的应用飞速发展.由于OCT的分辨率更高、成像效果更好且为无创的非接触测量,所以它在前房参数测量、角膜地形测量及房角测量等方面具有明显的优势.高速、高分辨率的傅立叶OCT技术与传统的时域OCT技术相辅相成,推动和发展OCT在眼科临床中的应用.本文介绍了眼前节OCT的成像原理,结合相应的临床应用展示了OCT在眼前节疾病发病机制研究及诊疗中的价值与局限,并对OCT技术未来的发展进行展望.     

Anterior Segment Optical Coherence Tomography

Optical coherence tomography (OCT) is a non-contact optical signal acquisition and processing device that provides magnified, high resolution cross-sectional images of ocular tissues. Development of anterior segment OCT (AS-OCT) offers the benefits of fine resolution and noninvasive examination to investigation of anterior segment anatomy to the depth of the iris plane. This imaging device has been utilized for investigation into a myriad of corneal and anterior segment disease. Recent technological advances toward three-dimensional visualization broaden the scope of AS-OCT in ophthalmologic evaluation. The AS-OCT is a valuable imaging tool whose use in research and clinical practice will continue to expand our knowledge and management of various ophthalmic conditions.     

Anterior segment optical coherence tomography

Optical coherence tomography (OCT) is a non-contact optical signal acquisition and processing device that provides magnified, high resolution cross-sectional images of ocular tissues. Development of anterior segment OCT (AS-OCT) offers the benefits of fine resolution and noninvasive examination to investigation of anterior segment anatomy to the depth of the iris plane. This imaging device has been utilized for investigation into a myriad of corneal and anterior segment disease. Recent technological advances toward three-dimensional visualization broaden the scope of AS-OCT in ophthalmologic evaluation. The AS-OCT is a valuable imaging tool whose use in research and clinical practice will continue to expand our knowledge and management of various ophthalmic conditions.     

1310 nm傅里叶域眼前节OCT的成像特点及与其他两种OCT的对比分析

目的 探讨1310 nm傅里叶域实时眼前节光学相干断层扫描(OCT)的成像特点及与RTV-ue100 OCT,Visante OCT对眼前节重要结构的成像能力的对比.方法 横断面研究.选择受试者6例(12眼,24个方位),运用1310 nm傅里叶域实时眼前节OCT,RTV-ue100 OCT与Visante OCT进行房角成像,对巩膜突、Schlemm's管、房角隐窝及Schwalbe线进行定义,测量前房角角度(TIA500)、500 μm前房角开放距离(AOD500)、500 μm小梁虹膜面积(TISA500)、Schlemn's管长径以及面积.运用Fisher's确切概率法对比3台仪器对房角重要结构的定义能力,并采用独立样本t检验研究三者生物学测量结果的差异.结果 傅里叶域实时眼前节OCT可在8眼(67％)13方位(54％)、12眼(100％)22方位(92％)、12 眼(100％)24方位(100％)及6眼(50％)9方位(38％)分别定义巩膜突、Schlemm's管、房角隐窝及Schwalbe线.RTV-ue100 OCT可于8眼(67％)8方位(33％)定义Schlemm's管,10眼(83％)19方位(79％)定义Schwalbe线,不能定义巩膜突与房角隐窝.Visante OCT于12眼(100％)21方位(88％)定义巩膜突,12眼(100％)24方位(100％)定义房角隐窝,不能定义Schlemm's管与Schwalbe线.3种OCT对巩膜突、Schlemm's管、房角隐窝、Schwalbe线定义能力差异有统计学意义(F=24.30、25.20、28.22、17.10,P＜0.01).傅里叶域实时眼前节OCT与Visante OCT测量TIA500、AOD500、TISA500的差异无统计学意义.傅里叶域实时眼前节OCT与RTV-ue100 OCT测量Schlemm's管面积、长径差异无统计学意义.结论 三种OCT都实现了前房角的清晰成像,显示角膜、巩膜、结膜以及巩膜突、Schlemm's管与Schwalbe线等房角结构.RTV-ue OCT和傅里叶域实时眼前节OCT的图像分辨率较高,能够显示Schlemm’s管与Schwalbe线等细微结构;Visante OCT和傅里叶域实时眼前节OCT深层结构检测能力强,各设备所得生物学参数无明显差异.     

1310 nm傅里叶域眼前节OCT的成像特点及与其他两种OCT的对比分析

目的 探讨1310 nm傅里叶域实时眼前节光学相干断层扫描(OCT)的成像特点及与RTV-ue100 OCT,Visante OCT对眼前节重要结构的成像能力的对比.方法 横断面研究.选择受试者6例(12眼,24个方位),运用1310 nm傅里叶域实时眼前节OCT,RTV-ue100 OCT与Visante OCT进行房角成像,对巩膜突、Schlemm's管、房角隐窝及Schwalbe线进行定义,测量前房角角度(TIA500)、500 μm前房角开放距离(AOD500)、500 μm小梁虹膜面积(TISA500)、Schlemn's管长径以及面积.运用Fisher's确切概率法对比3台仪器对房角重要结构的定义能力,并采用独立样本t检验研究三者生物学测量结果的差异.结果 傅里叶域实时眼前节OCT可在8眼(67％)13方位(54％)、12眼(100％)22方位(92％)、12 眼(100％)24方位(100％)及6眼(50％)9方位(38％)分别定义巩膜突、Schlemm's管、房角隐窝及Schwalbe线.RTV-ue100 OCT可于8眼(67％)8方位(33％)定义Schlemm's管,10眼(83％)19方位(79％)定义Schwalbe线,不能定义巩膜突与房角隐窝.Visante OCT于12眼(100％)21方位(88％)定义巩膜突,12眼(100％)24方位(100％)定义房角隐窝,不能定义Schlemm's管与Schwalbe线.3种OCT对巩膜突、Schlemm's管、房角隐窝、Schwalbe线定义能力差异有统计学意义(F=24.30、25.20、28.22、17.10,P＜0.01).傅里叶域实时眼前节OCT与Visante OCT测量TIA500、AOD500、TISA500的差异无统计学意义.傅里叶域实时眼前节OCT与RTV-ue100 OCT测量Schlemm's管面积、长径差异无统计学意义.结论 三种OCT都实现了前房角的清晰成像,显示角膜、巩膜、结膜以及巩膜突、Schlemm's管与Schwalbe线等房角结构.RTV-ue OCT和傅里叶域实时眼前节OCT的图像分辨率较高,能够显示Schlemm’s管与Schwalbe线等细微结构;Visante OCT和傅里叶域实时眼前节OCT深层结构检测能力强,各设备所得生物学参数无明显差异.     

Imaging of the anterior eye chamber with optical coherence tomography

BACKGROUND: Optical coherence tomography (OCT) represents a high-resolution diagnostic method which can be used to precisely image the anterior eye segment. Further developments in scanning technology and data evaluation allowed to visualize the entire anterior eye segment in one image, and the purpose of this study was to clinically evaluate this new system. PATIENTS AND METHODS: The studied OCT system was adapted to a slit-lamp and allowed us to image the anterior segment with an axial resolution of 10 microm at a scanning rate of 200 Hz with a depth of 7 mm and a maximal width of 15 mm. In selected cases the clinical value of anterior segment OCT was assessed. The reproducibility and level of agreement of anterior chamber depth measurements were assessed during the preoperative examination in 49 cataract surgery patients and compared to ultrasound (US) biometry (10 MHz). RESULTS: The studied anterior segment OCT allowed the cross-sectional imaging of the entire anterior eye segment. Changes of the anterior chamber before and after cataract surgery or surgical iridectomy were visualised. Furthermore, the findings of the anterior chamber after implantation of an iris-fixated intraocular lens (IOL) and an iris prosthetic system could be assessed. The reproducibility of the anterior chamber depth measurement was +/- 22 microm (OCT) and +/- 76 microm (US). The mean difference between optical and acoustic values was 1 microm (0.03 % p = 0.921) and the limits of agreement (95 % confidence interval) were 260 microm (8.58 %). CONCLUSIONS: The anterior segment OCT proved to be a helpful diagnostic method. The cross-sectional visualisation of the entire anterior chamber allowed us to assess important values for the implantation of iris-fixated IOL and other changes after surgical procedures. The resolution and reproducibility were higher than for conventional ultrasound biometry.     

Slit-lamp-adapted optical coherence tomography of the anterior segment

· Purpose: To evaluate the diagnostic potential of a slit-lamp-adapted optical coherence tomography (OCT) system as an in vivo imaging device for routine clinical examination of the anterior segment of the eye. · Patients and methods: In a pilot study, healthy volunteers and patients with different pathologies of the anterior segment were examined with a slit-lamp-adapted OCT system using 100–200 axial scans with 100-Hz line-scan frequency. The scan length is variable up to 7 mm, and the axial depth is 1.5 mm in tissue. · Results: The slit-lamp-adapted OCT system allowed direct biomicroscopic imaging of the measured area. Anatomic structures and morphological changes anterior to the attenuating iris pigment epithelium could be visualized with high accuracy. Biometric analyses of the cornea, the chamber angle, the iris and secondary cataract were possible. Complete demonstration of the chamber angle was difficult due to the backscattering properties of the anterior part of the sclera and the consequent shadowing of the most peripheral part of the iris. · Conclusions: Slit-lamp-adapted OCT is a useful diagnostic tool which allows in vivo microscopic cross-sectional imaging of the anterior segment and precise measurement of ocular structures. Received: 11 February 1999 Revised version received: 28 April 1999 Accepted: 17 May 1999     

Anterior segment optical coherence tomography

Optical coherence tomography (OCT) provides non-contact, rapid in vivo imaging of ocular structures, and has become a key part of evaluating the anterior segment of the eye. Over the years, improvements to technology have increased the speed of capture and resolution of images, leading to the increasing impact of anterior segment OCT imaging on clinical practice. In this review, we summarize the historical development of anterior segment OCT, and provide an update on the research and clinical applications of imaging the ocular surface, cornea, anterior chamber structures, aqueous outflow system, and most recently anterior segment vessels. We also describe advancements in anterior segment OCT technology that have improved understanding with greater detail, such as tear film in dry eye disease evaluation, intra-operative real-time imaging for anterior segment surgery, and aqueous outflow with angle assessment for glaucoma. Improvements to image processing and software have also improved the ease and utility of interpreting anterior segment OCT images in everyday clinical practice. Future developments include refinement of assessing vascular networks for the anterior segment, in vivo ultra-high resolution anterior segment optical coherence tomography with histology-like detail, en-face image with 3-dimensional reconstruction as well as functional extensions of the technique.     

OCT3 exploration of anterior segment

PURPOSE: Posterior pole imaging with OCT3 provides macular scans with a very high resolution. Use of OCT1 has already been described for anterior segment imaging. This work presents the advantages of OCT3 in anterior segment imaging compared to UBM (50 MHz) and 20-MHz ultrasound imaging with long focal distance (patent pending PCT/FR98/02788). MATERIAL: and methods: We used an OCT3 unit dedicated to the posterior pole. By defocusing the laser beam we obtained high-resolution scans of the cornea, angle, lens and IOLs. Fifty-seven eyes (35 patients) were imaged by OCT3 and high-resolution ultrasound in cases of corneal dystrophy, corneal transplant, LASIK, narrow angle, iris bowing, etc. RESULTS: In all cases OCT3 provided high-resolution information with a limit of penetration at the posterior part of the iris. This limitation was not observed with ultrasound imaging. Nevertheless, OCT3 is a useful tool for corneal imaging in cases of opacities limiting biomicroscope imaging. OCT3 corneal scans at high resolution make it possible to identify the corneal interface in lamellar transplants or LASIK. With a narrow angle, a dynamic test of angle closure can be done. With iris bowing, OCT3 can differentiate iris cysts and iris tumors. Anterior chamber IOLs can be imaged with their relationships to anterior segment structures. CONCLUSION: OCT3 provides non-contact anterior segment imaging with high resolution but with a limit of penetration given by posterior part of the iris.     

Recent advances in ophthalmic anterior segment imaging: a new era for ophthalmic diagnosis?

Anterior segment imaging is a rapidly advancing field of ophthalmology. New imaging modalities, such as rotating Scheimpflug imaging (Pentacam-Scheimpflug) and anterior segment optical coherence tomography (Visante OCT and Slit-Lamp OCT), have recently become commercially available. These new modalities supplement the more established imaging devices of Orbscan scanning slit topography and ultrasound biomicroscopy (UBM). All devices promise quantitative information and qualitative imaging of the cornea and anterior chamber. They provide a quantitative angle estimation by calculating the angle between the iris surface and the posterior corneal surface. Direct angle visualisation is possible with the OCT devices and UBM; they provide images of the scleral spur, ciliary body, ciliary sulcus and even canal of Schlemm in some eyes. Pentacam-Scheimpflug can measure net corneal power, a feature particularly useful for cataract patients having undergone previous corneal surgery. Anterior segment OCT can measure corneal flap depth following LASIK and anterior chamber width prior to phakic intraocular lens implantation. The arrival of the new imaging devices may herald the dawn of a new era for ophthalmic diagnosis, particularly in view of the ease and non-contact nature of examination.     

Anterior segment optical coherence tomography: its application in clinical practice and experimental models of disease

Optical coherence tomography (OCT) provides non‐invasive, high‐resolution in vivo imaging of the ocular surface and anterior segment. Over the years, it has become an essential tool for evaluating the anterior segment of the eye to monitor ocular development and ocular pathologies in both the clinical and research fields of ophthalmology and optometry. In this review, the clinical applications relating to the use of anterior segment OCT for imaging and quantifying normal and pathological features of the ocular surface, cornea, anterior chamber, and aqueous outflow system are summarised in a range of human ocular diseases. Applications of anterior segment OCT technology that have improved imaging and quantitation of ocular inflammation in experimental animal models of ocular diseases, such as anterior uveitis, microbial keratitis and glaucoma, are also described. The capacity to longitudinally evaluate anterior segment anatomical changes during development, and inflammation facilitates the understanding of the dynamics of tissue responses, and further enhances the intra‐operative in vivo imaging during procedures, such as corneal transplantation and drug delivery. Future developments including in vivo ultrahigh‐resolution anterior segment OCT, automated analyses of anterior segment OCT images and functional extensions of the technique, may revolutionise the clinical evaluation of anterior segment, corneal and ocular surface diseases.     

Corneal imaging with anterior segment optical coherence tomography for lamellar keratoplasty procedures

PURPOSE: To assess and describe the uses of anterior segment optical coherence tomography (OCT) in the evaluation of the cornea before and after lamellar corneal transplantation procedures. DESIGN: Prospective, noncomparative, observational case series. METHODS: Seven eyes of seven patients undergoing anterior and posterior lamellar corneal transplantation procedures at the Singapore National Eye Centre were included in the study. High-resolution anterior segment OCT scans of the cornea and anterior segment were performed both before and after lamellar transplantation procedures on the cornea with the Visante anterior segment OCT system (Visante OCT; Carl Zeiss Meditec, Inc, Dublin, California, USA), and the imaging findings were correlated with the clinical picture. Measurements of lamella thickness were performed with the software provided. RESULTS: Anterior segment OCT images were able to provide valuable information on donor apposition, Descemet membrane detachment after deep anterior lamellar keratoplasty (DALK), posterior lamellar dislocation, primary graft failure, and anterior chamber crowding with consequent chamber angle encroachment and pupillary block after Descemet stripping automated endothelial keratoplasty (DSAEK). CONCLUSIONS: Anterior segment OCT is a valuable imaging tool for assessing the feasibility of lamellar transplantation surgery in the diseased cornea and in the management of surgical complications after such procedures.     

Intraocular lens-capsular bag imaging with ultrahigh-resolution optical coherence tomography Pseudophakic human autopsy eyes

PURPOSE: To compare in vitro ultrahigh-resolution optical coherence tomography (UHR OCT) cross-sectional images of the pseudophakic human autopsy eye with histology to evaluate the potential of this imaging technique for enhanced visualization of the anterior segment, especially the capsular bag, intraocular lens (IOL), and posterior capsule opacification (PCO) formation after cataract surgery. SETTING: Department of Medical Physics and Department of Ophthalmology, University of Vienna, Vienna, Austria, and Department of Oral and Maxillofacial Surgery Institute of Dentistry, University of Turku, Turku, Finland. METHODS: Ultrahigh-resolution OCT images were acquired from 7 pseudophakic human autopsy eyes using 1.4 microm axial x 3.0 microm transverse resolution. The axial resolution with UHR OCT is 1.4 microm compared to 10.0 microm with the commercially available OCT. Plastic-embedded histologic sections were obtained in precise alignment with the OCT tomograms. RESULTS: Ultrahigh-resolution OCT cross-sectional tomograms corresponded to the histologic sections. With the wavelength used (800 nm), the anterior and posterior capsules, area of lens epithelial cell growth and extracellular matrix proliferation, and IOL could be clearly visualized. The extent of capsular bag adhesion to the IOL could be detected, as well as the amount of PCO formation. CONCLUSIONS: The improved resolution makes UHR OCT a powerful tool in anterior segment imaging and evaluation of the capacity of IOL materials and models to induce capsular bag adhesion. Ultrahigh-resolution OCT may also help in determining the area of origin of PCO after cataract surgery.     

Anterior segment optical coherence tomography in glaucoma

In recent years, the rapid development of diagnostic optic devices has generated optical coherence tomography (OCT) as a new, non-invasive diagnostic method. With technical progress of the infrared spectrum at 1,310 nm, OCT of the anterior segment also became feasible. With anterior segment OCT different examinations which so far were ruled out by ultrasound in contact manner could be executed in a non-contact technique: pachymetry, goniometry, illustration of iris and lens configuration as well as postoperative results after different glaucoma surgeries such as trabeculectomy, deep sclerectomy and glaucoma drainage devices. Additionally, anterior segment OCT provides an imaging device for experimental approaches in glaucoma. Today two commercially available units are available: SL OCT (Heidelberg Engineering, Heidelberg, Germany) und Visante(R) OCT (Zeiss Meditec, Jena, Germany). For all applications OCT delivered a high inter- and intraobserver reproducibility, is equal to ultrasound in accuracy and involves a higher patient comfort. Within the different applications, a direct comparison with ultrasound technique reveals minor differences depending on the device type. Therefore, it is advised to indicate the device type with all measurements. OCT enables precise, two-dimensional, non-contact imaging of the anterior segment in high resolution. For glaucomatous diseases, anterior segment OCT enlarges and enriches the armamentarium of glaucoma diagnostics and postoperative care of current modern glaucoma surgery.     

Imaging through opaque corneas using anterior segment optical coherence tomography.

BACKGROUND AND OBJECTIVE: To investigate the capability of the prototype AC Cornea OCT (Ophthalmic Technologies Inc., Toronto, Ontario, Canada) for imaging eyes with opaque corneas. PATIENTS AND METHODS: More than 50 eyes of patients were included in the study. RESULTS: The density of opacification influenced the ability of OCT to reveal anterior segment details. Imaging was limited by shadows cast by abnormal pigmentation or vascularity within the cornea. However, the system's unique coronal perspective capability was helpful in revealing occult spatial relationships. CONCLUSIONS: The AC Cornea OCT is valuable for examining eyes with opaque corneas and provides cross-sectional and coronal views helpful in formulating specific management strategies.     

Optical coherence tomography: a new tool for glaucoma diagnosis

Optical coherence tomography (OCT) is a novel technique that allows cross-sectional imaging of the anterior and posterior eye. OCT has a resolution of approximately 10 microns, with extremely high sensitivity (approximately 10(-10) of incident light). OCT is analogous to computed tomography, which uses x-rays, magnetic resonance imaging, which uses spin resonance, or B-scan ultrasound, which uses sound waves, but OCT uses only light to derive its image. OCT is a noncontact, noninvasive system by which retinal substructure may be analyzed in vivo. OCT is useful in the evaluation of retinal pathologies and glaucoma. In retinal disease, entities such as macular holes, macular edema, central serous chorioretinopathy, retinal vascular occlusion and other factors have been examined. Separation between the posterior vitreous and retina, or lack thereof, are seen and quantitated. In glaucoma, retinal nerve fiber layer (NFL) thickness is measured at standardized locations around the optic nerve head. A circular scan produces a cylindrical cross-section of the retina, from which the NFL can be analyzed. In addition, radial scans through the optic nerve head are used to evaluate cupping and juxtapapillary NFL thickness. OCT, a new imaging technology by which the anterior and posterior segment are seen in cross-section, may permit the early diagnosis of glaucoma, and the early detection of glaucomatous progression.     

几种新型眼前节影像技术及临床应用

以眼前节光学相干断层扫描（OCT）、Scheimpflug技术、高分辨率磁共振成像及裂隙扫描等为代表的眼前节影像技术提供了房角的各种参数,可测量角膜前后表面的曲率和前房内径,计算出角膜的屈光度,在准分子激光角膜原位磨镶术（LASIK）术后能够测量角膜瓣厚度,甚至可用于调节功能及老视的研究,极大地提高了诊疗水平。就几种新型眼前节影像技术的研究进展及其临床应用进行综述。     

光学相干断层成像术及其在眼科中的应用

光学相干断层成像术(OCT)是近几年始用于临床的新型影象诊断技术。与超声成像等技术不同,它利用光波在生物组织的传播特性并检测反射光的时程延迟,构成组织横断面图象,以观察其微细结构并进行定量分析,纵向分辨力可高达10μm,并具有非接触性、非侵害性等特点。在眼科,它不仅能够对眼前节的结构进行成像,还可以对视网膜各层次结构进行清晰的显像,为多种眼内疾病、特别是青光眼的早期诊断和研究提供了一种新的有效途径。眼科学报1998;14:116—120。     

Ultra High-Resolution Anterior Segment Optical Coherence Tomography in the Diagnosis and Management of Ocular Surface Squamous Neoplasia

The development of optical coherence tomography (OCT) technology has helped to usher in a new era of in vivo diagnostic imaging of the eye. The utilization of OCT for imaging of the anterior segment and ocular surface has evolved from time-domain devices to spectral-domain devices with greater penetrance and resolution, providing novel images of anterior segment pathology to assist in diagnosis and management of disease. Ocular surface squamous neoplasia (OSSN) is one such pathology that has proven demonstrable by certain anterior segment OCT machines, specifically the newer devices capable of performing ultra high-resolution OCT (UHR-OCT). Distinctive features of OSSN on high resolution OCT allow for diagnosis and differentiation from other ocular surface pathologies. Subtle findings on these images help to characterize the OSSN lesions beyond what is apparent with the clinical examination, providing guidance for clinical management. The purpose of this review is to examine the published literature on the utilization of UHR-OCT for the diagnosis and management of OSSN, as well as to report novel uses of this technology and potential directions for its future development.