Anterior segment imaging in glaucoma: An updated review

Anterior segment imaging allows for an objective method of visualizing the anterior segment angle. Two of the most commonly used devices for anterior segment imaging include the anterior segment optical coherence tomography (AS-OCT) and the ultrasound biomicroscopy (UBM). AS-OCT technology has several types, including time-domain, swept-source, and spectral-domain-based configurations. We performed a literature search on PubMed for articles containing the text “anterior segment OCT,” “ultrasound biomicroscopy,” and “anterior segment imaging” since 2004, with some pertinent references before 2004 included for completeness. This review compares the advantages and disadvantages of AS-OCT and UBM, and summarizes the most recent literature regarding the importance of these devices in glaucoma diagnosis and management. These devices not only aid in visualization of the angle, but also have important postsurgical applications in bleb and tube imaging.     

Practical Applications of Anterior Segment Optical Coherence Tomography Imaging Following Corneal Surgery

Anterior segment optical coherence tomography (AS-OCT) has recently emerged as an important modality for imaging of the cornea. Since its introduction less than a decade ago, it has been clinically used for the diagnosis and management of an expanding number of corneal conditions. In this review, we will discuss the applications of anterior segment optical coherence tomography after corneal surgery, focusing on penetrating and lamellar keratoplasty, keratoprosthesis, intracorneal ring segments, collagen cross-linking and refractive surgery. Anterior segment optical coherence tomography is useful in evaluating outcomes, detecting adverse events, determining prognosis, guiding management decisions, and surgical planning.     

光学相干断层扫描技术在眼前节结构应用的新进展

光学相干断层扫描技术（OCT）是一种利用光的干涉原理来成像眼部结构的方法,最初用于眼后节的测量和检查,但随着OCT技术的进展,目前已广泛用于眼前节各组织的测量和检查.眼前节光学相干断层扫描技术（AS-OCT）可将角膜、前房、瞳孔、虹膜等眼前节组织结构显示于一张图像上,并可用于准分子激光角膜原位磨镶术术后角膜前后表面情况和角膜曲率的测定,青光眼患者房角、虹膜、睫状体的观察,抗青光眼术后功能性滤过泡的动态变化以及眼外伤患者的眼前节组织结构变化等.AS-OCT检测具有非接触、分辨率高、检测快捷、可定量分析等特点,因此是眼前节组织的检测的有力工具.就AS-OCT技术在眼科的临床应用、优缺点及展望进行综述.     

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.     

Multimodal Imaging in Anterior Uveitis

Anterior uveitis is the most common group of uveitis worldwide, with a diverse spectrum ranging from autoimmune and infectious to masquerade etiologies. Elucidation of the underlying etiology may be challenging, but it remains important, especially for recurrent uveitis. Multimodal imaging has improved our understanding and management of many posterior uveitis and panuveitis. Similarly, a wide variety of anterior segment ophthalmic imaging techniques are available to allow the monitoring of the structural changes that may develop during anterior uveitis. These include anterior segment photography, specular microscopy, in vivo confocal microscopy, anterior segment optical coherence tomography (AS-OCT), ultrasound biomicroscopy (UBM), laser flare photometry, and less commonly used techniques such as anterior segment fluorescein and indocyanine green angiography, iris autofluorescence, and infrared imaging. This review recapitulates the past and recent application of these ophthalmic imaging modalities to the diagnosis and management of anterior uveitis.     

Identification and localization of multiple intrastromal foreign bodies with anterior segment optical coherence tomography and ocular Pentacam

To report the clinical aspects and the imaging of a patient with intrastromal glass foreign bodies after a road traffic accident using both anterior segment optical coherence tomography (OCT) and ocular Pentacam. A detailed case report was made of the use of anterior segment OCT (AS-OCT) and ocular Pentacam to evaluate intrastromal foreign bodies. AS-OCT and Pentacam were valuable non-invasive tools in identification, localization and monitoring patients with intrastromal foreign bodies. This report demonstrates that AS-OCT and ocular Pentacam are effective and necessary procedures for both the diagnosis and follow-up of intracorneal foreign bodies.     

光相干断层扫描技术在眼表鳞状上皮瘤诊疗中的应用及展望

眼前节光相干断层扫描技术(AS-OCT)作为一种无创性检查手段,具有检测肿瘤性上皮病变的巨大潜力。依据AS-OCT上的特征性表现,可在多种眼表疾病中检测出眼表鳞状上皮瘤(OSSN)的存在,其诊断效果堪比病理组织活检。随着技术的发展,AS-OCT成像模式已从时域OCT发展到具有更高外显率和分辨率的频域OCT,其呈现的高质...     

Comparison of anterior segment optical coherence tomography and ultrasound biomicroscopy for assessment of the anterior segment

PURPOSE: To compare anterior segment parameters using quantitative imaging by anterior segment optical coherence tomography (AS-OCT) and ultrasound biomicroscopy (UBM). SETTING: Tertiary-care glaucoma research center. METHODS: Sixty-three eyes of 63 subjects had anterior segment evaluation by AS-OCT (Visante-Zeiss) and UBM (Paradigm). Central corneal thickness (CCT), anterior chamber depth (ACD) (measured from the central corneal endothelium to the anterior lens capsule), and the peripheral iridocorneal angles (temporal and nasal) were assessed and compared. RESULTS: There was an excellent correlation between AS-OCT and UBM measurements for the nasal angle (r = 0.84; P<.0001), temporal angle (r = 0.86; P<.0001), ACD (r = 0.97; P<.0001), and CCT (r = 0.91; P<.0001). There was no significant difference (paired t test) between the mean ACD, CCT, and angle parameters measured by AS-OCT or UBM. The mean values of the parameters measured by AS-OCT and UBM were, respectively, as follows: nasal angle, 26.25 degrees +/- 11.0 (SD) and 28.27 +/- 11.3 degrees (P = .3); temporal angle, 25.1 +/- 11.4 degrees and 28.3 +/- 13.5 degrees (P = .15); ACD, 2.85 +/- 0.5 mm and 2.78 +/- 0.5 mm (P = .2); and CCT, 512 +/- 46 microm and 502 +/- 46 microm (P = .25). The AS-OCT images showed sharper definition of the scleral spur than the UBM images. CONCLUSION: Anterior segment optical coherence tomography and UBM can both be used for anterior segment measurements and yielded comparable results.     

三种仪器对近视患者眼前节生物学参数测量的比较

背景 近视屈光手术的开展需要我们对患者眼前节的数据进行精确测量和评估.目前临床上有多种仪器和方法可以对患者的眼前节进行生物学测量,但是哪种方法更为精确和方便,仍需进一步探讨.目的 比较眼前节光学相干断层扫描（AS-OCT）、OrbscanⅡ、超声生物测厚仪对近视患者眼前节参数的测量结果.方法 回顾性分析2011年11月至2012年5月于浙江大学医学院附属第二医院眼科中心就诊的拟行角膜屈光手术的近视患者70例140眼,受检者等效球镜度为-0.75 ～-10.25 D.分别用AS-OCT、OrbscanⅡ和超声角膜测厚仪测量角膜中央厚度（CCT）,用AS-OCT测量前房深度（ACD）和前房角间距（ATA）,用OrbscanⅡ测量ACD和角膜白到白距离（WTW）,对3种测量仪器的测量结果进行比较. 结果 AS-OCT、超声角膜测厚仪和OrbscanⅡ测量的平均CCT值分别为（516.57±30.25）、（523.68±31.87）和（514.69±38.40） μm,3种测量仪器间测量结果的总体比较差异无统计学意义（F=2.775,P=0.063）.根据超声角膜测厚仪所测的CCT结果将受检者分为＜500μm组、500 ～ 569 μm组和≥570 μm组,＜500 μm组受检者以超声角膜测厚仪测量的CCT值最高,OrbscanⅡ测量值最低,用3种方法测量的CCT值差异有统计学意义（F=22.236,P=0.000）;AS-OCT和超声角膜测厚仪的测量值间差异无统计学意义（P＞0.05）.500～569 μm组受检者用3种仪器测量的CCT值总体比较差异无统计学意义（F=3.011,P=0.051）.≥570 μm组受检者用超声角膜测厚仪测量的CCT最高,AS-OCT测量值最低,3种仪器的测量值总体比较差异有统计学意义（F=4.133,P=0.021）,超声角膜测厚仪与Orbscan Ⅱ测量的CCT值差异无统计学意义（P＞0.05）.AS-OCT和OrbscanⅡ测量的ACD值分别为（3.83±0.21）mm和（3.75±0.21）mm,二者差异有统计学意义（t=-8.520,P=0.000）;AS-OCT测量的ATA为（12.43±0.74） mm,OrbscanⅡ测量的WTW为（11.42±0.33） m     

Diagnosis of residual Descemet's membrane after Descemet's stripping endothelial keratoplasty with anterior segment optical coherence tomography

We present a patient with residual Descemet's membrane diagnosed by anterior segment optical coherence tomography (AS-OCT) after Descemet's stripping endothelial keratoplasty (DSEK). Postoperatively, persistent partial corneal edema and interface fluid without dislocation of the donor button were observed. No improvement of interface fluid was found during the follow-up period. A primary donor graft failure was diagnosed within 4 months, and the patient was regrafted with penetrating keratoplasty. Pathology examination of the specimen revealed the presence of residual Descemet's membrane in the recipient corneal button, confirmed using AS-OCT imaging. This case report demonstrates that inadequate Descemet's stripping in the recipient button could be a potential cause of DSEK failure; AS-OCT is a useful and noninvasive instrument for diagnosing and monitoring this post-DSEK complication.     

Applications of optical coherence tomography in the anterior segment

Optical coherence tomography provides high-resolution images of the anterior segment (AS-OCT). When used as a measuring tool, corneal thickness, anterior and posterior chamber depths, anterior chamber diameter and chamber angle configuration are defined reproducibly. In terms of an optical biopsy by cellular imaging, tissue infiltration, deformation and deposits can be analysed microstructurally. A comparison of pre- and post-operative, as well as long-term follow-up of pathological findings are possible. Examination with AS-OCT is a no-contact procedure, and is well tolerated by the patient. The following instruments were used: Visante-OCT and Cirrus HD-OCT (Carl Zeiss Meditec GmbH, Germany) and SS100 CASIA (Tomey Europe, Erlangen).     

Anterior Segment Imaging and the Intraocular Pressure Lowering Effect of Cataract Surgery for Open and Narrow Angle Glaucoma

Anterior segment imaging modalities including anterior segment optical coherence tomography (AS-OCT) and ultrasound biomicroscopy (UBM) are increasingly widespread, and can quantify several parameters of the anterior segment, such as anterior chamber depth and angle anatomy. These parameters are important to assess, particularly in patients with forms of narrow angle glaucoma. In many cases of open and narrow angle glaucoma, cataract extraction has been shown to result in favorable modification of these parameters, and a lasting decrease in intraocular pressure. Anterior segment imaging has the ability to enable the development of predictive models regarding the potential intraocular pressure lowering effect of cataract extraction in a given individual.     

根据超声生物显微镜和眼前节OCT图像对房角关闭机制进行分型的一致性研究

背景 房角关闭是引起原发性房角关闭性疾病(PACD)的病理基础,了解不同类型的房角关闭机制对于PACD的危险因素评估、预防及诊治有重要意义.临床多采用超声生物显微镜(UBM)对房角关闭机制进行分型,但该检查为接触性,在使用中具有一定的局限性.眼前节OCT(AS-OCT)是一种非接触性的眼前节成像方法,能够对房角结构进行定性和定量评估. 目的 探讨根据UBM图像和AS-OCT图像对中国PACD患者房角关闭机制进行分型的一致性.方法 采用横断面研究.纳入2013年9-10月在北京同仁医院就诊并接受UBM和AS-OCT检查的PACD患者.UBM检查采集每眼上方、下方、鼻侧和颞侧4个方位的眼前节图像,AS-OCT检查采取四线扫描模式(包括0°～ 180°、45°～225°、90°～ 270°和135°～315°)对眼前节进行成像.根据UBM图像和AS-OCT图像分别进行房角关闭机制分型,并分为瞳孔阻滞型、睫状体前位型和周边虹膜肥厚型.每例受检眼的4张UBM图像及4张AS-OCT图像中分别至少2张显示相同的房角关闭机制分型作为该眼的UBM及AS-OCT分型.纳入符合标准的患眼,若双眼均符合标准则纳入右眼.用Kappa系数评估AS-OCT和UBM 2种方法对房角关闭机制分型结果的一致性.结果 最终纳入PACD患者40例40眼,其中右眼27眼,左眼13眼.根据UBM图像及房角关闭机制的分型标准,瞳孔阻滞型12眼,占30.0％;睫状体前位型23眼,占57.5％;周边虹膜肥厚型5眼,占12.5％.根据AS-OCT图像及房角关闭机制的分型标准,瞳孔阻滞型为12眼,占30.0％.睫状体前位型21眼,占52.5％;周边虹膜肥厚型7眼,占17.5％.两种房角关闭机制分型方法间的Kappa值为0.872,即高度一致. 结论 成功建立了根据AS-OCT图像对中国PACD患者房角关闭机制分型的标准,根据AS-OCT图像和UBM图像对房角关闭机制进行分型的判断结果高度一致.     

Anterior Segment Optical Coherence Tomography: Assisted Topographic Corneal Epithelial Thickness Distribution Imaging of a Keratoconus Patient

Purpose

To evaluate safety, efficacy and ease of measurement of epithelial thickness in a keratoconic patient based on anterior segment optical coherence tomography (AS-OCT).

Methods

A 25-year-old male patient, previously diagnosed with keratoconus, with highly asymmetric manifestation among the two eyes, was subjected to AS-OCT corneal epithelial imaging. We investigated epithelial thickness and epithelial topographic thickness distribution.

Results

Mean epithelial thickness was 51.97 ± 0.70 for the less affected right eye (OD), and 55.65 ± 1.22 for the more affected left eye (OS). Topographic epithelial thickness variability for the OD was 1.53 ± 0.21 μm, while for the OS it was 9.80 ± 0.41 μm.

Conclusions

This case further supports our previous findings with high-frequency ultrasound measurements of the increase in overall epithelial thickness in keratoconic eyes in comparison with normal eyes. AS-OCT further offers ease of use and possibly higher predictability of measurement. This case report, based on AS-OCT imaging, verifies increased overall epithelial thickness in keratoconic eyes, as introduced by a previous study [Kanellopoulos et al.: Clin Ophthalmol 2012;6:789–800], based on high-frequency scanning ultrasound biomicroscopy imaging.Key words: Anterior segment optical coherence tomography, Keratoconus, Epithelial imaging, Pentacam HR     

Imaging of the Sclera in Patients with Scleritis and Episcleritis using Anterior Segment Optical Coherence Tomography

Purpose: To evaluate the sclera and episclera in patients with scleritis and episcleritis using anterior segment optical coherence tomography (AS-OCT).

Methods: Cross-sectional prospective case series of 11 consecutive patients with episcleral or scleral inflammatory disease located anterior to the equator. The thickness of the ocular wall (sclera and the episclera) was measured using AS-OCT and compared to the contralateral healthy eye.

Results: Eleven patients with a mean age of 49.5 years presented with symptomatic scleritis or episcleritis. The mean thickness of the ocular wall in the affected eye was 982?±?56?μm compared to 790?±?23?μm (p?Conclusion: Enhanced-depth AS-OCT may be a useful tool for imaging scleritis or episcleritis and may serve to monitor therapeutic success in these patients.     

Meridional differences in internal dimensions of the anterior segment in human eyes evaluated with 2 imaging systems

PURPOSE: To evaluate meridional differences in angle-to-angle (A-A) and sulcus-to-sulcus (S-S) dimensions in human eyes using very high frequency ultrasound (VHF US) and anterior segment optical coherence tomography (AS-OCT). SETTING: John A. Moran Eye Center, University of Utah, USA; Berlin Eye Research Institute, Germany; Quattroelle Centri Oftalmochirurgici, Italy. METHODS: Human autopsy eyes were fixated to special eye holders and had anterior segment scanning using 50 MHz ultrasound (Artemis, Ultralink) (20 eyes) and AS-OCT (SL-OCT, Heidelberg Engineering) (24 eyes). Seventy-three eyes (58 patients) also had anterior segment scanning using the same systems (Artemis, 50 eyes; SL-OCT, 23 eyes). Four meridians were evaluated in each eye. The A-A dimensions were measured by VHF US and AS-OCT. The S-S dimensions were also measured by VHF US. Statistical analyses were done with the Huynh-Feldt test. RESULTS: In the autopsy-eye study, the differences in A-A and S-S dimensions between the 4 meridians in eyes analyzed with VHF US were statistically significant (P=.002 and P=.009, respectively). The differences in A-A dimensions in eyes analyzed with the AS-OCT were also significant (P=.005). The same findings were observed in the clinical study (VHF US, P=.001 for A-A and P<.001 for S-S; AS-OCT, P<.001 for A-A). CONCLUSIONS: This study suggests that the internal geometry of the anterior segment of human eyes does not constitute a circle. This may have significant relevance for the accurate sizing of phakic intraocular lenses.     

Comparative study of anterior segment measurement with Pentacam and anterior segment optical coherence tomography

Objective: To evaluate the repeatability of central corneal thickness (CCT), anterior chamber volume (ACV), and central anterior chamber depth (CACD) measurements obtained using a Pentacam rotating Scheimpflug camera, and to examine their agreement with measurements obtained using an anterior segment optical coherence tomography (AS-OCT) imaging system.Design: Observational cross-sectional study.Participants: Fifty eyes from 50 healthy subjects were recruited.Methods: CCT, CACD, and ACV were measured. Subjects were re-examined twice within a week of the first measurements. Intrasession and intersession within-subject SD (S_w), precision (1.96 × S_w), coefficient of variation (CV_w: 100 × S_w/ overall mean), and intraclass correlation coefficient (ICC) were calculated to evaluate repeatability and reproducibility. Bland-Altman plots were used to assess agreements between Pentacam and AS-OCT measurements.Results: For intrasession repeatability, CVwand ICC values were 0.78 and 0.98 for CCT, 0.92 and 0.99 for CACD, and 3.52 and 0.98 for ACV, respectively. For intersession repeatability, CV_w and ICC values were 1.19 and 0.96 for CCT, 1.25 and 0.99 for CACD, and 3.96 and 0.96 for ACV, respectively. The AS-OCT CCT measurement (519.23 [SD 34.37] μm) was 18.53 μm less than the Pentacam measurement (537.76 [SD 31.84] μm). The Pentacam CACD measurement (3.03 [SD 0.32] mm) was 0.08 less than the AS-OCT measurement (3.11 [SD 0.31] mm). The Pentacam ACV measurement (165.56 [SD 34.86] μL) was 14.21 μL less than the AS-OCT measurement (179.77 [SD 34.57] μL).Conclusions: Although the Pentacam measurements of the anterior segment parameters were reliable, their agreement with the AS-OCT measurements was not sufficient.     

原发性闭角型青光眼早期干预后眼前段结构改变定量研究

目的 应用光学成像系统一前段OCT(Anterior Segment Optical Coherence Tomographv.AS-OCT)量化评价原发性闭角犁青光眼患者(Primary Angle Closure Glaucoma,PACG)早期干预后眼前段结构的改变.方法 对确诊的早期PACG患者36例(60只眼)予以激光周边虹膜切开术(Laser Peripheral Iri-dotomy,LPI)进行早期干预;采用AS-OCT量化评价干预后眼前段结构的改变.对视力、眼压、房角开放情况及眼前段结构包括AOD500(巩膜突前500μm的房角开放距离)、前房轴深、晶状体厚度等进行观察,随访时间3个月.结果 术后视力无明显变化,术后眼压较术前下降,差异有统计学意义(t=3.506,P<0.01).术后房角增宽,AOD500增加,差异有统计学意义(t=-8.34,P<0.01),术后前房轴深加深,差异有统计学意义,(t-2.909,P<0.01),术后晶状体厚度增加,差异有统计学意义(t-3.701,P<0.01 o结论AS-OCT的精确定量能够发现LPI术后眼前段结构的细微改变,是研究原发性闭角型青光眼早期于预的有力辅助工具.     

Comparison of anterior segment optical coherence tomography findings in acanthamoeba keratitis and herpetic epithelial keratitis

This study is to investigate the characteristic features of Acanthamoeba keratitis (AK) that differentiating it from herpetic epithelial keratitis (HEK) using anterior segment optical coherence tomography (AS-OCT). Medical records of three eyes of each AK and herpetic keratitis who had AS-OCT examination were reviewed in this study. Slit-lamp biomicroscopy and AS-OCT was performed on the initial visit and on every follow-up visits in all patients. In all three AK cases, reflective bands in the corneal stroma that correspond to the area of radial keratoneuritis were observed. The depth of the reflective bands varied in each case. After AK treatment, slit-lamp biomicroscopy confirmed that radial keratoneuritis had resolved and AS-OCT confirmed that reflective bands in the corneal stroma had also disappeared in all patients. Unlike the AS-OCT results found in AK, highly reflective HEK lesions were observed only in the subepithelial area, not in the stroma. AS-OCT seems to be helpful analyzing the specific depth of the lesion which enables to distinguish AK from HEK.