Anterior-segment imaging for assessment of glaucoma

A Deep Learning Model for Automatically Quantifying the Anterior Segment in Ultrasound Biomicroscopy Images of Implantable Collamer Lens Candidates

OBJECTIVE

This study aimed to develop and evaluate a deep learning-based model that could automatically measure anterior segment (AS) parameters on preoperative ultrasound biomicroscopy (UBM) images of implantable Collamer lens (ICL) surgery candidates.

METHODS

A total of 1164 panoramic UBM images were preoperatively obtained from 321 patients who received ICL surgery in the Eye Center of Renmin Hospital of Wuhan University (Wuhan, China) to develop an imaging database. First, the UNet++ network was utilized to segment AS tissues automatically, such as corneal lens and iris. In addition, image processing techniques and geometric localization algorithms were developed to automatically identify the anatomical landmarks (ALs) of pupil diameter (PD), anterior chamber depth (ACD), angle-to-angle distance (ATA), and sulcus-to-sulcus distance (STS). Based on the results of the latter two processes, PD, ACD, ATA, and STS can be measured. Meanwhile, an external dataset of 294 images from Huangshi Aier Eye Hospital was employed to further assess the model's performance in other center. Lastly, a subset of 100 random images from the external test set was chosen to compare the performance of the model with senior experts.

RESULTS

Whether in the internal test dataset or external test dataset, using manual labeling as the reference standard, the models achieved a mean Dice coefficient exceeding 0.880. Additionally, the intra-class correlation coefficients (ICCs) of ALs' coordinates were all greater than 0.947, and the percentage of Euclidean distance distribution of ALs within 250 μm was over 95.24%.While the ICCs for PD, ACD, ATA, and STS were greater than 0.957, furthermore, the average relative error (ARE) of PD, ACD, ATA, and STS were below 2.41%. In terms of human versus machine performance, the ICCs between the measurements performed by the model and those by senior experts were all greater than 0.931.

CONCLUSION

A deep learning-based model could measure AS parameters using UBM images of ICL candidates, and exhibited a performance similar to that of a senior ophthalmologist.

Microsurgery Robots: Applications, Design, and Development

Microsurgical techniques have been widely utilized in various surgical specialties, such as ophthalmology, neurosurgery, and otolaryngology, which require intricate and precise surgical tool manipulation on a small scale. In microsurgery, operations on delicate vessels or tissues require high standards in surgeons' skills. This exceptionally high requirement in skills leads to a steep learning curve and lengthy training before the surgeons can perform microsurgical procedures with quality outcomes. The microsurgery robot (MSR), which can improve surgeons' operation skills through various functions, has received extensive research attention in the past three decades. There have been many review papers summarizing the research on MSR for specific surgical specialties. However, an in-depth review of the relevant technologies used in MSR systems is limited in the literature. This review details the technical challenges in microsurgery, and systematically summarizes the key technologies in MSR with a developmental perspective from the basic structural mechanism design, to the perception and human-machine interaction methods, and further to the ability in achieving a certain level of autonomy. By presenting and comparing the methods and technologies in this cutting-edge research, this paper aims to provide readers with a comprehensive understanding of the current state of MSR research and identify potential directions for future development in MSR.

Corneal optical density: Structural basis, measurements, influencing factors, and roles in refractive surgery

The cornea is the main refractive medium of the human eye, and its clarity is critical to visual acuity. Corneal optical density (COD) is an important index to describe corneal transparency. Intact corneal epithelial and endothelial cells, regular arrangement of collagen fibers in the stroma, and normal substance metabolism are all integral for the cornea to maintain its transparency. In the last two decades, the Pentacam Scheimpflug imaging system has emerged as a breakthrough for the measurement of COD (also called corneal densitometry). It has been found that a wide variety of factors such as age, refractive status, and corneal diseases can affect COD. Different corneal refractive surgery methods also change COD in different corneal regions and layers and affect visual acuity following the surgery. Thus, COD has gradually become a significant indicator to evaluate corneal health, one on which the attention of clinicians has been increasingly focused.

[The effect of phacoemulsification of age-related cataract on intraocular pressure and iridocorneal angle parameters in primary open-angle glaucoma]

Cataract phacoemulsification with intraocular lens implantation significantly affects the morphology of the anterior chamber angle (ACA) and contributes to a reduction of intraocular pressure (IOP).

PURPOSE

This study investigates the changes in anterior chamber angle configuration and IOP level before and after cataract surgery in primary open-angle glaucoma (POAG) eyes, and assesses its possible relationship with the axial length of the eye.

MATERIAL AND METHODS

The study included 38 patients with immature senile cataract and compensated unoperated stage I-II POAG. Patients underwent anterior segment optical coherence tomography (AS-OCT) with measurement of the angle opening distance (AOD750) and trabecular-iris space area (TISA750) before and six weeks after the surgery, as well as axial length and corneal-compensated IOP (IOPcc).

RESULTS

After the surgery 92.11% of patients showed a decrease in IOPcc an average of 1.84±1.95 mm Hg (by 12.33±10.21% of the baseline); the maximum decrease in the IOPcc level was 8.35 mm Hg (by 40.97% of the baseline). AS-OCT data indicates that cataract phacoemulsification causes an increase in anterior chamber angle width: AOD750 increased from 0.510±0.175 to 0.771±0.156 mm, and TISA750 increased from 0.266±0.090 to 0.494±0.096 mm2. The strongest correlations were found between the axial length, postoperative TISA750 increase (Δ%TISA750) and postoperative IOPcc reduction (Δ% IOPcc). Postoperatively, specific changes could be observed in the trabecular meshwork in 28.95% of cases in the form of elongation and strain of the membrane.

CONCLUSIONS

Cataract extraction contributes to a significant reduction in IOP due to anterior chamber angle expansion, trabecular meshwork stretching, and improved aqueous outflow.

Comparison of corneal, endothelial, and anterior segment parameters in eyes with and without pigment dispersion

BACKGROUND

To evaluate the differences of central corneal thickness (CCT), corneal endothelial cell morphology, and biometric parameters of the anterior chamber and iridocorneal angle in pigment dispersion syndrome (PDS), pigmentary glaucoma (PG), primary open-angle glaucoma (POAG), and healthy group.

METHODS

Twenty- three eyes in the PDS group, 39 eyes in the PG group, 33 eyes in the POAG group, and 45 eyes in the healthy control group were included in this cross-sectional retrospective study. Corneal endothelial cell density, the coefficient of variation in the cell area, hexagonality, and central corneal thickness (CCT) were obtained by specular microscopy (CEM 530, NIDEK, Japan). Anterior chamber depth (ACD), iridocorneal angle parameters and CCT were measured by anterior segment optical coherence tomography (AS-OCT) (Visante OCT, Carl Zeiss AG, Germany).

RESULTS

The mean CCT via specular microscopy (SM-CCT) was measured at the thinnest value in the PG group (531.20 ± 34.91 µm) and the thickest in the control group (569.13 ± 37.52 µm). CV value was higher in PG (34.65 ± 6.84) and POAG group (34.27 ± 9.93) and lower in control group (28.82 ± 5.18) (p = 0,005). The mean AS-OCT-CCT was the thinnest in the PG group (513.61 ± 39.94 µm), and the thickest in the control group (547.04 ± 36.72 µm) (p = 0.001). All parameters of the iridocorneal angle were larger in the PDS and PG groups (p < 0.001). In the correlation analysis of the glaucomatous eyes, a negative correlation between the C/D ratio and SM-CCT and AS-OCT-CCT (p = 0.037, p = 0.017, respectively) and a positive correlation between the pRNFL thickness and AS-OCT- CCT (p = 0.002).

CONCLUSION

CCT values obtained with both SM and AS-OCT were found to be significantly thinner in PG cases. CV, which is the measure of polymegatism, was found to be significantly higher in PG cases.

Encircling Scleral Buckling Surgery for Severe Hypotony with Ciliary Body Detachment on Anterior Segment Swept-Source Optical Coherence Tomography: A Case Series

This study aimed to evaluate the usefulness of an encircling scleral buckling procedure to manage severe hypotony secondary to proliferative vitreoretinopathy (PVR)-induced retinal detachment. This retrospective study included six eyes of six patients (five women and one man) with hypotony (intraocular pressure [IOP] ≤ 6 mmHg) after multiple reattachment surgeries for PVR-induced retinal detachment. In patients with failure of hypotony resolution after conservative treatment (dexamethasone drops five times daily), 360° scleral buckling was performed under periocular anesthesia. The light perception was evaluated immediately postoperatively. The anatomic parameters were evaluated pre- and postoperatively observed on anterior segment swept-source optical coherence tomography. Ciliary body detachment (CBD) secondary to advanced cyclitic membranes associated with PVR grades C and D was detected in all eyes with hypotony. The mean IOP increased in all eyes (4.83 mmHg preoperatively vs. 10.17 mmHg postoperatively, p = 0.006), with subsequent improvement in best-corrected visual acuity (1.91 logMAR preoperatively vs. 1.50 logMAR postoperatively, p = 0.034). However, no eye showed any significant changes in CBD postoperatively. Scleral buckling surgery might be useful to increase IOP in eyes with persistent severe hypotonia secondary to PVR-induced CBD. Further studies are needed to improve outcomes in eyes with severe PVR-induced retinal detachment.

Automatic Localization of the Scleral Spur Using Deep Learning and Ultrasound Biomicroscopy

Purpose

The purpose of this study was to develop a convolutional neural network (CNN) for automated localization of the scleral spur in ultrasound biomicroscopy (UBM) images of open-angle eyes.

Methods

UBM images were acquired, and one glaucoma specialist provided reference coordinates of scleral spur locations in all images. A CNN model based on the EfficientNetB3 architecture was developed to detect the scleral spur in each image. The prediction errors and Euclidean distance were used to evaluate localization performance of the CNN model. Trabecular-iris angle 500 (TIA500) and angle-opening distance 500 (AOD500) were measured and analyzed using the scleral spur locations provided by the specialist and predicted by the CNN model.

Results

The CNN was developed using a training dataset of 2328 images and tested using an independent dataset of 258 images. The mean absolute prediction errors of CNN model were 48.06 ± 45.40 µm for X-coordinates and 30.84 ± 27.03 µm for Y-coordinates. The mean absolute intraobserver variability was 47.80 ± 44.45 µm for X-coordinates and 29.50 ± 25.77 µm for Y-coordinates. The mean Euclidean distance of the CNN was 60.41 ± 49.02 µm and the intraobserver mean Euclidean distance was 59.78 ± 47.12 µm. The mean absolute error in TIA500 was 1.26 ± 1.38 degrees for all test images and in AOD500 was 0.039 ± 0.051 mm.

Conclusions

A CNN can detect the scleral spur on UBM images of open-angle eyes with performance similar to that of a glaucoma specialist.

Translational Relevance

Deep learning algorithms for automating scleral spur localization would facilitate the quantitative assessment of the opening of the angle and the risk in angle closure.

Iridocorneal angle assessment of companion rabbits using gonioscopy, spectral-domain optical coherence tomography (Optovue iVue® ), high-resolution ultrasound, and Pentacam® HR imaging

OBJECTIVE

Iridocorneal angle (ICA) narrowing is a known risk factor for primary glaucoma in multiple species, but has not been described in companion rabbits. This study aimed to develop an ICA grading scheme for companion rabbits to enable early glaucoma predisposition diagnosis.

ANIMALS STUDIED

Twenty healthy rabbits of varying breeds and ages.

PROCEDURES

Rabbits received complete ophthalmic examinations, including gonioscopy, and imaging of the ICA using spectral-domain optical coherence tomography (SD-OCT), Scheimpflug imaging (Pentacam^® HR), and high-resolution ultrasound (HRUS). Angle opening distance (AOD) and angle recess area (ARA) of the ICA were measured and assessed for agreement using a Bland-Altman analysis. A five-stage gonioscopy grading scheme was created, and Spearman-rank test assessed for correlation between gonioscopy grades and ICA measurements. Differences among age and sex were analyzed with a nonparametric ANOVA and Wilcoxon rank-sum test, respectively.

RESULTS

Analysis revealed AOD medians of 0.28mm for SD-OCT [95% CI: 0.24-0.31], 0.20mm for Pentacam^® HR [95% CI: 0.18-0.21], and 0.25mm for HRUS [95% CI: 0.22-0.28]. The median ARA was 0.14mm² for SD-OCT [95% CI: 0.117-0.163], 0.09mm² for Pentacam^® HR [95% CI: 0.082-0.100], and 0.06mm² for HRUS [95% CI: 0.046-0.054]. The association between gonioscopy grade and SD-OCT ARA was significant (P < 0.05), and there was a significant difference (P < 0.001) between imaging modalities for both ARA and AOD.

CONCLUSIONS

Gonioscopy grade correlated well with SD-OCT ARA. Therefore, SD-OCT is recommended as a noncontact method for evaluating companion rabbit ICA. Each imaging device should not be used interchangeably for ICA evaluation.

Anterior Segment Imaging for Angle Closure

PURPOSE

To summarize the role of anterior segment imaging (AS-imaging) in angle closure diagnosis and management, and the possible advantages over the current standard of gonioscopy.

DESIGN

Literature review and perspective.

METHODS

Review of the pertinent publications with interpretation and perspective in relation to the use of AS-imaging in angle closure assessment focusing on anterior segment optical coherence tomography and ultrasound biomicroscopy.

RESULTS

Several limitations have been encountered with the reference standard of gonioscopy for angle assessment. AS-imaging has been shown to have performance in angle closure detection compared to gonioscopy. Also, imaging has greater reproducibility and serves as better documentation for long-term follow-up than conventional gonioscopy. The qualitative and quantitative information obtained from AS-imaging enables better understanding of the underlying mechanisms of angle closure and provides useful parameters for risk assessment and possible prediction of the response to laser and surgical intervention. The latest technologies-including 3-dimensional imaging-have allowed for the assessment of the angle that simulates the gonioscopic view. These advantages suggest that AS-imaging has a potential to be a reference standard for the diagnosis and monitoring of angle closure disease in the future.

CONCLUSIONS

Although gonioscopy remains the primary method of angle assessment, AS-imaging has an increasing role in angle closure screening and management. The test should be integrated into clinical practice as an adjunctive tool for angle assessment. It is arguable that AS-imaging should be considered first-line screening for patients at risk for angle closure.

Semiautomatic procedure to assess changes in the eye accommodative system

PURPOSE

The aim of this pilot study was to evaluate a new semiautomatic procedure to assess in vivo changes in the crystalline lens and ciliary muscle during accommodation.

METHODS

A total of 14 subjects were divided into two groups, young (aged between 20 and 25 years) and adult (aged between 35 and 40 years), and measured with an anterior segment optical coherence tomography. A semiautomatic procedure was implemented to measure the central lens thickness (CLT), anterior lens radius (ALR) and the ciliary muscle area (CMA) for the unaccommodated eye and for a vergence of - 3.00 D.

RESULTS

The CLT increase for each population group was smaller than 5%, and the dispersion of each group was similar between them. Contrariwise, the reduction in the ALR was about 30% for both groups, although the young one showed the largest variability. The CMA increase was smaller than 30% for both groups, and the dispersion was similar between them. For each metric, differences between both groups were not statistically significant.

CONCLUSIONS

The semiautomatic procedure seems to be useful for the in vivo analysis of the accommodative system. Additionally, the results obtained showed that changes in the CLT were much smaller compared to those obtained for the ALR or CMA.

Iris cysts: A comprehensive review on diagnosis and treatment

Iris cysts, both primary and secondary, are a diagnostic and treatment challenge. Primary cysts arise either from the iris pigment epithelium or the iris stroma. Posterior pigment epithelial cysts are subdivided according to their location as central, midzonal, and peripheral. Iris stromal cysts are classified either as congenital or acquired. Free-floating cysts are usually dislodged pigment epithelial cysts. Secondary cysts are classified according to the underlying cause as implantation cysts, drug-induced, uveitic, tumor-induced, parasitic, or as cysts associated with systemic disorders. Differential diagnosis is based on the clinical presentation and imaging. Ultrasound biomicroscopy is the gold standard for the imaging of iris cysts, combining excellent resolution with sufficient tissue penetration. Treatment of iris cysts depends largely on whether they become symptomatic or not. Symptoms include obstruction of the visual axis, corneal decompensation, secondary uveitis, and secondary glaucoma. Treatment options cover a range from simple observation to fine-needle aspiration (with or without intracystic injection of absolute alcohol or antimitotic agents), laser (argon, Nd:YAG), or surgical excision. In the past, the prevailing notion was that of a radical surgical intervention in the form of iridectomy or iridocyclectomy. Given the high rate of recurrence, a stepwise conservative approach is currently favored by most clinicians.

Ageing and ocular surface immunity

Foreword

It gives me pleasure to introduce the 4th edition of the EGS Guidelines. The Third edition proved to be extremely successful, being translated into 7 languages with over 70000 copies being distributed across Europe; it has been downloadable, free, as a pdf file for the past 4 years. As one of the main objectives of the European Glaucoma Society has been to both educate and standardize glaucoma practice within the EU, these guidelines were structured so as to play their part.

Glaucoma is a living specialty, with new ideas on causation, mechanisms and treatments constantly appearing. As a number of years have passed since the publication of the last edition, changes in some if not all of these ideas would be expected.

For this new edition of the guidelines a number of editorial teams were created, each with responsibility for an area within the specialty; updating where necessary, introducing new diagrams and Flowcharts and ensuring that references were up to date. Each team had writers previously involved with the last edition as well as newer and younger members being co-opted.

As soon as specific sections were completed they had further editorial comment to ensure cross referencing and style continuity with other sections.

Overall guidance was the responsibility of Anders Heijl and Carlo Traverso. Tribute must be made to the Task Force whose efforts made the timely publication of the new edition possible.

Roger Hitchings

Chairman of the EGS Foundation

www.eugs.org

The Guidelines Writers and Contributors 

Augusto Azuara Blanco

Luca Bagnasco

Alessandro Bagnis

Keith Barton

Christoph Baudouin

Boel Bengtsson

Alain Bron

Francesca Cordeiro

Barbara Cvenkel

Philippe Denis

Christoph Faschinger

Panayiota Founti

Stefano Gandolfi

David Garway Heath

Francisco Goni

Franz Grehn

Anders Heijl

Roger Hitchings

Gabor Hollo

Tony Hommer

Michele Iester

Jost Jonas

Yves Lachkar

Giorgio Marchini

Frances Meier Gibbons

Stefano Miglior

Marta Misiuk-Hojo

Maria Musolino

Jean Philippe Nordmann

Norbert Pfeiffer

Luis Abegao Pinto

Luca Rossetti

John Salmon

Leo Schmetterer

Riccardo Scotto

Tarek Shaarawy

Ingeborg Stalmans

Gordana Sunaric Megevand

Ernst Tamm

John Thygesen

Fotis Topouzis

Carlo Enrico Traverso

Anja Tuulonen

Ananth Viswanathan

Thierry Zeyen

The Guidelines Task Force 

Luca Bagnasco

Anders Heijl

Carlo Enrico Traverso

Augusto Azuara Blanco

Alessandro Bagnis

David Garway Heath

Michele Iester

Yves Lachkar

Ingeborg Stalmans

Gordana Sunaric Mégevand

Fotis Topouzis

Anja Tuulonen

Ananth Viswanathan

The EGS Executive Committee 

Carlo Enrico Traverso (President)

Anja Tuulonen (Vice President)

Roger Hitchings (Past President)

Anton Hommer (Treasurer)

Barbara Cvenkel

Julian Garcia Feijoo

David Garway Heath

Norbert Pfeiffer

Ingeborg Stalmans

The Board of the European Glaucoma Society Foundation 

Roger Hitchings (Chair)

Carlo E. Traverso (Vice Chair)

Franz Grehn

Anders Heijl

John Thygesen

Fotis Topouzis

Thierry Zeyen

The EGS Committees 

CME and Certification 

Gordana Sunaric Mégevand (Chair)

Carlo Enrico Traverso (Co-chair)

Delivery of Care 

Anton Hommer (Chair)

EU Action 

Thierry Zeyen (Chair)

Carlo E. Traverso (Co-chair)

Education 

John Thygesen (Chair)

Fotis Topouzis (Co-chair)

Glaucogene 

Ananth Viswanathan (Chair)

Fotis Topouzis (Co-chair)

Industry Liaison 

Roger Hitchings (Chair)

Information Technology 

Ingeborg Stalmans (Chair)

Carlo E. Traverso (Co-chair)

National Society Liaison 

Anders Heijl (Chair)

Program Planning 

Fotis Topouzis (Chair)

Ingeborg Stalmans (Co-chair)

Quality and Outcomes 

Anja Tuulonen (Chair)

Augusto Azuara Blanco (Co-chair)

Scientific 

Franz Grehn (Chair)

David Garway Heath (Co-chair)

Evaluation of immersion 20 MHz B-scan ultrasonography in observing lens in the alkali burn eyes

AIM

To evaluate the accuracy of 20 MHz immersion B-scan ultrasonography in observing lens and to investigate the value of this noninvasive preoperative diagnosis method in alkali burn eyes.

METHODS

It was a comparative study. Fifty-six cases (56 eyes) of alkali burn eyes were examined by ultrasound biomicroscopy (UBM) and immersion 20 MHz B-scan ultrasonography from June 2011 to April 2013, the images were analyzed, and the ultrasonographic diagnosis compared with the operation results.

RESULTS

In 56 alkali burn eyes examined by UBM, the lens were not detected in 16 eyes; the IOL could be detected in 2 eyes; the anterior lens capsule surface or/and the front lens could be detected in 18 eyes, and lens opacification in 3 eyes of them; suspected abnormal lens were detected in the other 20 eyes. In all the same eyes examined by immersion 20 MHz B-scan ultrasonography, the lens were not detected in 16 eyes; the IOL could be detected in 2 eyes; 24 abnormal lens (opacity, lens expansion, shrinkage) and 14 normal lens were found. Compared with the intraoperative findings, the diagnostic accordance rate of the immersion 20 MHz B-scan appearance of lens was 100% (56/56), which was significantly higher than examined by UBM 57.14% (32/56) (χ(2)=30.55, P=0.0000).

CONCLUSION

Immersion 20 MHz B-scan ultrasonography can observe the lens accurately in alkali burn eyes. It has important clinical value to combine with UBM in eyes of alkali burn.

Anterior chamber angle evaluation with ultrasound biomicroscopy and optical coherence tomography in eyes implanted with a Crystalens

This study employs optical coherence tomography (OCT) and ultrasound biomicroscopy (UBM) imaging as well as optical aberrometry to examine correlations between the anterior chamber angle aperture and visual acuity for near vision as well as coma along the horizontal and vertical axes in eyes implanted with an accommodative intraocular lens (Crystalens). A retrospective comparative consecutive case series of 22 eyes of 11 patients (5 males) uneventfully implanted with a Crystalens. Eyes with signs of posterior capsular opacification were excluded. All eyes were examined with 40 MHz UBM (Ellex Eyecubed) and spectral-domain OCT (Zeiss Visante). The angle aperture along the horizontal and vertical meridians was recorded based on the software of the systems. The coma root mean square (RMS) scores for the horizontal and vertical meridians were also recorded with the iTrace aberrometer. The anterior chamber angle was significantly wider along the horizontal axis compared with the vertical axis by UBM (46.37° and 44.20°, respectively) and by OCT (46.79° and 43.58°, respectively) (p = 0.02 in both cases, paired-samples t test). The correlations between the logMAR-converted Jaeger near vision score and the horizontal or vertical angle apertures was not statistically significant. Horizontal coma RMS was significantly inversely correlated with the horizontal angle aperture (r = -0.45, p = 0.03 and r = -0.39, p = 0.04 by OCT and UBM, respectively). Measurement of the horizontal angle aperture by the modalities used may represent an anatomical and clinical predictor of the optical aberrations induced by the Crystalens.

Width of anterior chamber angle determined by OCT, and correlation to refraction and age in a German working population: the MIPH Eye&Health Study

BACKGROUND

Optical coherence tomography (OCT) of the anterior segment allows quantitative analysis of the geometry of the chamber angle. We performed bilateral spectral-domain OCT measurements in healthy, emmetropic, hyperopic, and myopic subjects to establish correlations between the width of the angle, the refraction, and intraocular pressure of the test persons.

METHODS

Out of 4,617 eyes (2,309 subjects), those with refractive errors of < -4 or > +3 diopters were identified by objective refraction measurement (KR-8800 Kerato-Refractometer, Topcon Inc., Japan) and examined using the anterior segment mode of a spectral-domain 3D OCT-2000 (Topcon Inc., Japan). Non-contact tonometry was performed (CT-80, Topcon Inc., Japan). One hundred and eight eyes of 54 emmetropic subjects (± 0.5 dpt) served as reference group. Previous ocular surgery was exclusion criterion in all groups. Width of the chamber angle was determined using semi-automated software tools and statistical analysis of the data (Pearson correlation, ANOVA with post-hoc test and Bonferroni correction, regression analysis) was performed using SPSS software (SPSS 19.0, Chicago, IL, USA).

RESULTS

Six hundred and sixty-eight eyes of 398 persons (292 male, 96 female) were included in the study. Mean hyperopic refraction was +4.24 (+3  to +7.75) dpt, mean myopic refraction was -5.86 (-4 to -11.75) dpt. Valid chamber angle OCT measurements could be obtained from 50 (69.4 %) hyperopic and 400 (71.4 %) myopic eyes meeting the inclusion criteria. The mean width of the chamber angle was determined as 31.8° (range: 13.5 to 45.6, SD 7.49) in the hyperopic group, 40.8° (range: 19.3 to 66.0, SD 8.1) in the myopic group, and 36.3° (range: 21.1 to 51.8, SD 6.8) in the emmetropic reference group. Correlation was highly significant (p > 0.001) between refractive error and the aperture of the chamber angle as measured from OCT. The association of the intraocular pressure and the refraction was also highly significant (p > 0.001) for the three groups.

CONCLUSION

The spectral-domain OCT yielded measurements that could be used for digital analysis of the chamber angle geometry. Our results highlight the correlation between refraction and aperture of the angle in hyperopia and myopia as determined by the 3D OCT-2000: hyperopia is associated with a narrower chamber angle, myopia with a wider aperture of the angle.

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.

Ultrasound biomicroscopic evaluation of anterior segment cysts as a risk factor for ocular hypertension and closure angle glaucoma

AIM

To investigate the relationship between the ultrasound biomicroscopic (UBM) features of anterior-segment cysts (ASCs) and increased intraocular pressure (IOP) as a risk factor for closed-angle glaucoma (CAG).

METHODS

Totally 24 eyes with recently diagnosed ASCs were divided into two groups. First group with ASC and ocular normotension (n=13), second group with ASC and ocular hypertension (n=11). An ophthalmologic examination, including tonometry, slit-lamp biomicroscopy (SLBM), gonioscopy, fundoscopy, pentacam, and UBM, was performed. The features of the ASCs were compared with the IOP.

RESULTS

ASCs were accurately diagnosed and delineated in 24 eyes using UBM. IOP was elevated in those ASCs with a secondary aetiology (P=0.027), iridociliary location (P=0.006), deformed shape (P=0.013), increased size (P=0.001) and elongated pupillary aperture (P=0.009). However, the count (P=0.343) of ASCs, anterior chamber depth (ACD; P=0.22) and axial lenght (AL; P=0.31) were not associated with ocular hypertension. Correlations were found between the IOP and ASC size (r=-0.712; P=0.003), anterior chamber angle (ACA; r=-0.985; P<0.001), angle opening area (AOA; r=0.885; P<0.001), angulation of iris (r=-0.776, P<0.001), and affected iris quadrant (r =-0.655, P=0.002).

CONCLUSION

Ocular hypertension in some eyes with ASC might be associated with various mechanisms, including secondary aetiology, iridociliary location, deformed shape, increased size and elongated pupill, which can be determined by UBM.

Anterior segment imaging in glaucoma

Anterior segment imaging allows objective assessment of the anterior segment of the eye, particularly the anterior chamber angle. Both qualitative and quantitative analyses are possible and aid in detecting and managing closed-angle and open-angle mechanisms in various forms of glaucoma. This review focuses primarily on anterior segment optical coherence tomography and ultrasound biomicroscopy, with emphasis on principles of technology, commercially available devices, and clinical applications in glaucoma with potential advantages and disadvantages of each technology.

Pentacam anterior chamber parameters in young and middle-aged Chinese

BACKGROUND

The aim was to compare the anterior segment of two groups of Chinese using the Pentacam system.

METHODS

Fifty young (median age 21 years) and 50 middle-aged (median age 46 years) subjects with equal numbers of males and females had their axial length measured with the IOL Master. Their axial anterior chamber depth, anterior chamber volume and temporal and nasal anterior chamber angles were measured using the Pentacam and comparisons were made between the two groups.

RESULTS

Both groups shared similar axial lengths (unpaired t-test: p = 0.37) but young subjects had significantly deeper anterior chamber by 11 per cent (3.60 ± 0.40 mm) compared with middle-aged subjects (3.24 ± 0.34 mm) (analysis of variance: p < 0.001). The anterior chamber volume was significantly greater in young subjects by 24 per cent (200.12 ± 35.59 mm(3)) than the middle-aged subjects (161.03 ± 37.79 mm(3)). The associations of anterior chamber depth and anterior chamber volume with axial length were significant (R(2) from 0.16 to 0.50) and similar in both groups. Young subjects had wider anterior chamber angles (mean differences: 4.60° and 6.07° at temporal and nasal, respectively) than middle-aged subjects. Among middle-aged subjects, females had significantly shorter axial length but anterior chamber depths were similar between the two sexes. Females had significantly smaller anterior chamber volumes.

CONCLUSIONS

Middle-aged subjects had more crowded anterior chambers than young subjects with similar axial lengths. Anterior chamber volume may be a more sensitive parameter to reveal this difference than a linear measurement of the anterior chamber depth.

Changing trends of imaging in angle closure evaluation

Primary angle closure glaucoma (PACG) is a significant cause of visual disability worldwide. It predominantly affects the Eastern and South Asian population of the world. Early detection of anatomically narrow angles is important, and the subsequent prevention of visual loss from PACG depends on an accurate assessment of the anterior chamber angle (ACA). Gonioscopy has given way to modern day imaging technologies such as ultrasound biomicroscopy (UBM) and more recently, anterior segment optical coherence tomography (AS-OCT). Ultrasound biomicroscopy provides objective, high-resolution images of anterior segment anatomy, including the cornea, iris, anterior chamber, anterior chamber angle, and ciliary body. Optical coherence tomography (OCT) is a noncontact optical signal acquisition and processing device that provides magnified, high-resolution cross-sectional images of ocular tissues. Recent technological advances towards three-dimensional visualization broadened the scope of AS-OCT in ophthalmologic evaluation. Optical coherence tomography systems use low-coherence, near-infrared light to provide detailed images of anterior segment structures at resolutions exceeding that of UBM. This paper summarizes the clinical application of UBM and OCT for assessment of anterior segment in glaucoma.

Gender differences in iridocorneal angle morphology: a potential explanation for the female predisposition to primary angle closure glaucoma in dogs

OBJECTIVE

Female dogs have approximately twice the risk of males for developing primary angle closure glaucoma (PACG). The cause of this gender difference is unknown, but one theory proposes that the gender differences in iridocorneal angle morphology are involved in this risk differential.

PROCEDURES

Fifty beagles (25 males, 25 females) were included into this study and had normal baseline ophthalmic examinations. Normal dogs were selected so as to avoid any potentially confounding influence of goniodysgenesis. Standardized 20-MHz high-resolution ultrasound images of the iridocorneal angle were acquired from one eye of each dog with the scan plane perpendicular to the limbus in the superior temporal quadrant. Images were imported into ImageJ, and the angle opening distance (AOD) and angle recess area (ARA) were measured by a masked observer, and the analysis of variance method was used to compare differences.

RESULTS

The mean (±SD) AOD was significantly smaller for female dogs (0.847 ± 0.241 mm) vs. male dogs (1.058 ± 0.322 mm) P-value = 0.012. The mean (± SD) ARA tended to be smaller for female dogs (0.584 ± 0.278 mm) vs. male dogs (0.748 ± 0.385 mm), but this difference was not significant (P-value = 0.092).

CONCLUSIONS

Female dogs have a significantly smaller AOD vs. males. This difference may render the female iridocorneal angle more susceptible to closure and may partially explain the 2:1 female/male predisposition to PACG. Further studies using goniodysgenic dogs are warranted.