Anterior chamber depth in plateau iris syndrome and pupillary block as measured by ultrasound biomicroscopy

Imaging of the Ciliary Body: A Major Review

PURPOSE

We conducted a systematic search of literature to understand the various methods of imaging of the ciliary body.

METHODS

PubMed, Science Direct, Cochrane Library and Google Scholar were searched comprehensively and systematically to find studies related to the various modalities of ciliary body imaging.

RESULTS

The various ciliary body parameters that have been described are Ciliary body thickness, Ciliary body length, ciliary muscle thickness, ciliary process length, ciliary muscle length, ciliary muscle anterior length, trabecular ciliary process distance and Iris ciliary process distance. The various angles which have been measured, which mostly have a significance in Primary angle closure glaucoma (PACG) are Iris ciliary angle, Trabecular ciliary angle, scleral ciliary process angle. Various authors have defined them in various ways with subtle differences. Plateau iris and PACG mechanisms, not forgetting malignant glaucoma are better understood with imaging of the ciliary body using the ultrasound biomicroscopy (UBM). The anterior segment optical coherence tomography (ASOCT) imaging of the ciliary body has been described albeit with its own disadvantages. A few other fields dependant on the importance of ciliary body imaging are intravitreal injections, pars plana vitrectomy, measurements for implantable collamer lens (ICL) and of utmost importance, the differentiating features of ciliary body masses.

CONCLUSION

The UBM is still preferred over the ASOCT for imaging of the ciliary body. A lot of lacunae of knowledge still exists and consensus has to be reached on defining all the parameters universally. Future studies will be able to shed more light on the role of the ciliary body in the many ocular disorders mentioned in this review.

Comparison of Anterior Chamber Depth with Posture Change Between Primary and lens-induced Angle Closure Glaucomas

Purpose: To compare the changes in central anterior chamber depth between supine and sitting positions using an ultrasound biomicroscope among acute angle closure glaucoma, lens-induced angle closure glaucoma, and normal groups.Methods: This study included 18, 13, and 29 individuals with acute angle closure glaucoma, lens-induced angle closure glaucoma, and control, respectively. The central anterior chamber depth, trabecular iris angle, corneal curvature, and axial length were measured in the sitting and supine positions.Results: The central anterior chamber depth in the supine and sitting positions were 1.61 ± 0.47 mm and 1.55 ± 0.46 mm in the acute angle closure glaucoma, which were significantly smaller than those in the normal group (2.48 ± 0.49 mm and 2.47 ± 0.50 mm) (p = 0.01 and p = 0.009, respectively). In lens-induced angle closure glaucoma, the central anterior chamber depth in the supine and sitting positions were 1.65 ± 0.84 mm and 1.52 ± 0.82 mm, respectively, which were significantly smaller than those in the normal group (p < 0.001 for both). The absolute change in central anterior chamber depth with posture alteration was significantly larger in both acute angle closure glaucoma (0.15 ± 0.09 mm) and lens-induced angle closure glaucoma (0.25 ± 0.11 mm) than in the normal control (0.09 ± 0.08 mm) (p = 0.011, p < 0.001, respectively). The largest amount of change was shown in the lens-induced angle closure glaucoma (p = 0.012). The absolute change in anterior chamber angle with posture change wa not significantly different between the groups (p = 0.165).Conclusions: Compared to the control group, the central anterior chamber depth was smaller in both glaucoma groups. The absolute change in the anterior chamber depth with posture was significantly larger in the lens-induced angle closure glaucoma than in acute angle closure glaucoma.

Smartphone-Acquired Image Photogrammetry for Detection of Shallow Anterior Chamber

Purpose

This study aimed to explore the role of smartphone imaging of the eye using two perspectives — anterior and temporal — in the detection of a shallow anterior chamber (AC). The AC depth (ACD) of an eye can be used as a surrogate marker for identification of eyes at risk of developing angle-closure disease.

Methods

A prospective observational study was conducted at a university teaching hospital in South India. Each eye was photographed with a smartphone using the two perspectives, followed by quantitative measurement of ACD using optical biometry. The percentage of nasal iris illuminated was measured from the image acquired using the flashlight method (anterior perspective), whereas pupil position relative to the cornea was measured from the image acquired using the temporal perpendicular method (temporal perspective). The receiver-operating characteristic curve and area under the curve (AUC) were studied for both perspectives independently for overall predictive accuracy in detection of shallow AC (ACD <2.7 mm, obtained by IOL Master).

Results

A total of 275 eyes were examined, of which 77 (28%) had an ACD <2.7 mm. The accuracy of detection of shallow AC was found to be 95.2% for both perspectives when used alone or in combination. AUC of the anterior perspective was 0.99 (95% CI 0.982–0.997). The AUC for the temporal perspective was 0.993 (95% CI 0.988–0.999).

Conclusion

Smartphone-acquired image photogrammetry of an eye with anterior and temporal perspectives independently and in combination provided accuracy nearing 95% in the detection of shallow AC (ACD <2.7 mm).

Registration

This trial was registered with the Clinical Trial Registry of India (CTRI/2018/09/015867, September 28, 2018).

Using Anterior Segment Optical Coherence Tomography (ASOCT) Parameters to Determine Pupillary Block Versus Plateau Iris Configuration

PRéCIS:: The potential parameters for differentiating pupillary block (PB) from plateau iris configuration (PIC) on anterior segment optical coherence tomography (ASOCT) are lens/pupil size parameters and angles. Further study is needed to determine a landmark peripheral to the centroid of the iris.

PURPOSE

Investigate anterior segment parameters to distinguish between 2 mechanisms of angle closure, PB and PIC, using swept-source Fourier domain ASOCT.

PATIENTS AND METHODS

Retrospective ASOCT images from narrow angle eyes were reviewed. PIC was defined either by ultrasound biomicroscopy and/or clinically when an iridoplasty was performed. Images were read by a masked reader using Anterior Chamber Analysis and Interpretation software to identify scleral spur landmarks and calculate anterior chamber, peripheral angle, iris size, iris shape, and lens/pupil size parameters. ASOCT parameters were summarized and compared using the 2-sample t test. Thresholds and area under receiver operating characteristic curve were calculated using logistic regression analysis.

RESULTS

One hundred eyes (66 PB and 34 PIC) of 100 participants were reviewed. Of all ASOCT parameters, iris length in each quadrant, pupil arc, lens/pupil parameters (pupil arc, lens vault, and pupil diameter), all pupillary margin-center point-scleral spur landmark (PM-C-SSL) parameters, and all except superior central iris vault parameters were significantly different between PB and PIC. On threshold evaluation, lens/pupil parameters had the greatest area under receiver operating characteristic curve values (0.77 to 0.80), followed by PM-C-SSL angles (0.71 to 0.75).

CONCLUSIONS

We propose that the pupil size parameters and PM-C-SSL angle are the most reliable novel ASOCT parameters to distinguish between PB and PIC eyes. These parameters do not rely on the visibility of the posterior iris surface, which is difficult to identify with ASOCT, but may be ambient lighting dependent.

The Iris Thickness in a Healthy Saudi Population

Purpose

Iris thickness (IT), a known risk factor for angle closure glaucoma, has not been evaluated in the normal Saudi population.

Methods

Quantitative information on IT was evaluated in healthy Saudi eyes using anterior segment optical coherence tomography (ASOCT). IT and iris volume was measured with the room ‘light on’ (LON) and ‘light off’ (LOFF) using Image J software. IT in the nasal and temporal iris was measured at 500 µm (IT500) and 750 µm (IT750) from the scleral spur (SS). Differences in IT measurements by age, gender and type of refractive error were evaluated.

Results

We included 100 eyes of 50 healthy adult Saudis without ocular disease other than refractive errors. The mean age of 56 males and 44 females in the study group was 41.7 ± 14.5 years. The refractive status was as follows: emmetropia (35 eyes), mild/moderate myopia (33 eyes), high myopia (17 eyes) and hyperopia (15 eyes). The IT750 with LON was significantly more than IT500 both nasally (P = 0.03) and temporally (P < 0.001). The difference in IT750 and IT500 with LOFF was significantly more nasally (P = 0.03), temporally (P = 0.02), and with LON nasally (P = 0.005). IT was thicker in males when compared to females and variation of IT by refractive error was significant but not by age. The mean pupil diameter and anterior chamber depth decreased with age (P < 0.001). Anterior chamber width was not affected by age or illumination.

Conclusion

The baseline iris thickness in the Saudi eyes could be used to compare iris thickness in eyes with angle closure glaucoma among the Arab population.

Size Matters for Interplicata Diameter: A Case-Control Study of Plateau Iris

PURPOSE

Ultrasound biomicroscopy (UBM) has been used to characterize anterior segment dimensions in plateau iris configuration (PIC), but transverse measurements between the recesses of the ciliary sulcus (sulcus-to-sulcus diameter [STSD]) and the ciliary body processes (interplicata diameter [IPD]) have not been reported. We measured STSD and IPD and compared these among eyes with PIC, primary angle closure (PAC), and control eyes with open angles.

DESIGN

Retrospective, cross-sectional clinical study.

PARTICIPANTS

Sixty-nine participants, 37 PIC, 13 PAC, and 19 controls.

METHODS

We searched our clinical UBM database for PAC and PIC cases. Controls were assembled by reviewing images obtained for surveillance of ocular surface lesions. Anterior segment measurements were performed using the UBM digital caliper tool. Robust-fit ANOVA identified among-group differences. Pairwise t tests were used to test the significance of between-group differences.

MAIN OUTCOME MEASURES

Anterior chamber depth (ACD), angle opening distance (AOD), ciliary body area and thickness, iris area, horizontal and vertical STSD, and horizontal and vertical IPD.

RESULTS

Fifty-five left eyes were analyzed (30 PIC, 10 PAC, and 15 controls). ACD was smaller in PAC than in PIC and control eyes (P < 0.05 for PIC vs. PAC; P < 0.01 for control vs. PAC). Mean AOD was smaller in PIC than controls (P < 0.05) and smaller in PAC than PIC (P < 0.001). Vertical STSD was smaller in both PAC and PIC than controls (P = 0.04 for PIC vs. control; P < 0.01 for PAC vs. control). Horizontal STSD was smaller in PIC than controls (P = 0.02). Vertical IPD was smaller in PIC than controls (P = 0.04) and smaller in PAC than PIC eyes (P = 0.02). Horizontal IPD was smaller in PIC and PAC than controls (P = 0.03 for PIC vs. control; P < 0.01 for PAC vs. control).

CONCLUSIONS

STSD and IPD are narrower in PIC and PAC than in healthy eyes. Further studies that examine the ratio of white-to-white cornea diameter to the IPD may provide a mechanism for reported cases of in-the-bag uveitis-glaucoma-hyphema syndrome in PIC.

Measurement of the depths at different regions of the anterior chamber in healthy Chinese adults

AIM

To measure the depths of different regions of the anterior chamber (AC) in healthy Chinese adults, and to explore possible correlations with age or gender.

METHODS

The AC was imaged by swept-source optical coherence tomography in healthy Chinese adults. The horizontal scan of the right eye was used to measure the anterior chamber depth (ACD) at 199 points.

RESULTS

A total of 309 images from 309 subjects were analyzed. The ACD values at nearly all locations were negatively correlated with age (all P<0.05), except for ACD1, 2, 198, and 199 (correspond to the iris roots). The mean annual decrease 0.013±0.005 mm/y for all ACDs combined, 0.008±0.004 mm/y for the peripheral region, 0.017±0.003 mm/y for the middle peripheral region, and 0.014±0.001 mm/y for the central region. The mean annual decrease was significantly different among these three regions (P<0.001). The ACD was greater in males than in females (P<0.05). The mean difference in ACD between males and females was 0.081±0.025 mm.

CONCLUSION

This study showed that optical coherence tomography can be used to measure the ACD of different regions of the AC. We found reductions in ACD with age, although the reduction varied among different points, in healthy Chinese adults.

Argon Laser Iridoplasty For Plateau Iris Syndrome: Long-Term Outcomes of 48 Eyes

PRECIS

Argon laser peripheral iridoplasty (ALPI) was performed on 48 eyes with plateau iris syndrome (PIS). Indentation gonioscopy was used to monitor the opening of the iridocorneal angle. Mean intraocular pressure (IOP) at 5 years decreased from 15.9 to 14.4 mm Hg. None of the eyes required trabeculectomy.

PURPOSE

The purpose of this article was to report the long-term outcomes of ALPI for PIS.

MATERIALS AND METHODS

A retrospective chart review was performed on all patients with PIS treated with ALPI from 2001 to 2012. The study included 48 eyes from 28 patients with PIS after peripheral iridotomy, with a follow-up of at least 5 years. Patients with advanced glaucoma requiring initial surgical treatment (pathologic discs and IOP above the target IOP despite medical treatment) were excluded. The primary outcomes were the effect on the number of IOP medications, and the need for complementary selective laser trabeculoplasty (SLT) or surgery (trabeculectomy and/or phacoemulsification). Secondary outcomes were optic nerve head changes and adverse events.

RESULTS

The mean IOP statistically decreased after ALPI (15.91±2.62 vs. 14.35±2.18 mm Hg, P>0.001). The mean number of IOP-lowering medications statistically increased after ALPI (0.81±0.94 vs. 1.2±1.04, P>0.001). Mean follow-up was 92.4±26.5 months. At the end of the follow-up, 12 (25%) eyes had no medications, 20 (42%) had 1 medication, 11 (23%) had 2 medications, 3 (6%) had 3 medications, and 2 (4%) had 4. Ten (21%) eyes underwent SLT, 6 (10%) underwent phacoemulsification, and no trabeculectomy was necessary during follow-up. The change in cup to disc ratio from pre-ALPI to latest follow-up was not statistically significant, and no adverse events were reported.

CONCLUSIONS

ALPI is relatively effective and safe to prevent angle-closure glaucoma and avoid trabeculectomy in patients with PIS. This procedure often helps to control IOP, although SLT and additional medical treatments are frequently necessary to maintain the target IOP.

Qualitative and quantitative evaluation of acute angle-closure mechanisms

BACKGROUND

To evaluate ocular biometric parameters in different subtypes of acute angle closure and compared to fellow eyes of AAC and PACS eyes.

METHODS

This is a retrospective chart review study. A total of 167 eyes (96 patients) consisting of 71 AAC eyes, 71 fellow eyes of AAC, and 25 PACS eyes were recruited. All patients underwent ocular examination and biometry. The mechanism of AAC was confirmed by ultrasound biomicroscopy. We then subdivided AAC eyes into four subgroups: crowded-angle (CR), lens subluxation (LS) pupillary block (PB), and plateau iris syndrome (PL). Outcome variables included anterior chamber depth (ACD), lens thickness (LT), vitreal length (VL), axial length (AL), lens position and relative lens position (LP and RLP, respectively), and lens axial length factor (LAF).

RESULTS

Among the three groups, ACD was shallower in AAC eyes than fellow eyes of AAC and PACS eyes (p < 0.01 for both) and AAC eyes demonstrated a lesser LP and RLP. The LT, VL, AL, and LAF were not significantly different among the three groups. Among the four subgroups, LS displayed the most shallow ACD (p = 0.01). The lens position in PL was greater than in CR and LS (p < 0.05 and <0.01, respectively).

CONCLUSIONS

AAC eyes had a more anterior lens position than fellow eyes and PACS eyes, though lens thickness did not differ among the groups. As such, an anterior lens position may offer more sensitive prognostication regarding future development of AAC compared to lens thickness.

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.

Comparison of Anterior Chamber Parameters in Patients With Plateau Iris Configuration and Pupillary Block Using ASOCT

PURPOSE

To quantitatively analyze the anterior chamber parameters in patients with pupillary block (PB) and plateau iris configuration (PIC) using anterior segment optical coherence tomography (ASOCT).

PATIENTS AND METHODS

In this cross-sectional study, nonglaucomatous subjects consecutively recruited and a total of 212 eyes divided into 3 groups of PIC (31 eyes), PB (60 eyes), and open angles (121 eyes) based on gonioscopic and ultrasound biomicroscopy findings. All patients underwent ASOCT imaging and A-scan biometry of both eyes. Anterior chamber depth (ACD), anterior chamber area (ACA), iris thickness (IT), iris curvature, lens vault (LV), anterior vault, and angle parameters including angle opening distance, and trabecular iris space area were measured in qualified images using the Zhongshan Angle Assessment Program, and compared using linear mixed model. The data from 1 eye of each subject were used for final analysis.

RESULTS

Mean age was 64.5±12.1, 64.8±10.5, and 62.3±9.2 years for PB, PIC, and open angle eyes, respectively (P=0.26). There was no significant difference in angle parameters (angle opening distance and trabecular iris space area at 250, 500, and 750 µm from sclera spur), anterior segment parameters (ACD and ACA), iris area, iris curvature, and LV between PB and PIC groups. PIC eyes had greater IT at 750 µm from sclera spur than the PB group (P=0.05). Normal eyes had greater ACD, ACA, and anterior chamber width, and angle parameters and lesser LV and iris curvature than the other 2 groups.

CONCLUSIONS

ASOCT parameters are not significantly different between PB and PIC eyes. PIC eyes may have greater IT at its base.

Endoscopic Cycloplasty (ECPL) and Lens Extraction in the Treatment of Severe Plateau Iris Syndrome

PURPOSE

To describe the anatomic and clinical results of the treatment of severe plateau iris syndrome with lens extraction and endoscopic cycloplasty (ECPL). A secondary aim was to describe 4 novel ultrasound biomicroscopy (UBM) measurements for plateau iris syndrome.

DESIGN

Prospective case series with UBM evaluation.

METHODS

Included were 12 eyes of 6 patients with plateau iris refractory to laser iridotomy and iridoplasty, miotic and other glaucoma medical treatment, with appositional angle closure in at least 3 quadrants. Treatment consisted of lens extraction and ECPL, an endoscopic diode laser treatment of the ciliary processes in the superior, nasal, and inferior quadrants. UBM measurements were taken in all quadrants before and after surgery. The untreated temporal quadrants were used as controls. Measurement parameters included: anterior chamber depth (ACD), angle opening distance (AOD 500), trabecular ciliary process distance (TCPD), iris ciliary process distance (ICPD), iris depth (ID), iridocorneal angle (ICA), and sulcus angle (SA). Four novel measurements included: ciliary process thickness (CPT), ciliary process width (CPW), ciliary process area (CPA), and iris ciliary process contact length (ICPCL). Visual acuity, intraocular pressure, glaucoma medications, and complications were also followed.

RESULTS

The ACD, AOD 500, and ICA all increased significantly (P<0.001). ICPD, CPT, CPW, CPA, and ICPL all decreased significantly (P<0.01). Parameters remaining unchanged were: TCPD, ID, and SA. The untreated quadrants showed similar measurements to the preoperative measurements. There were no serious complications noted.

DISCUSSION

Treating the ciliary processes with diode laser using an endoscopic approach (ECPL) and lens extraction, results in opening of the anterior chamber angle and shrinkage of the ciliary processes in the treated areas. This effect seems to be primarily a result of the laser treatment in combination rather than the lens extraction alone. This effectively reverses the anatomic cause and angle closure of plateau iris syndrome.

Is being female a risk factor for shallow anterior chamber? The associations between anterior chamber depth and age, sex, and body height

Aim of Study:

To analyze the association between anterior chamber depth (ACD) and age, sex, and body height (BH).

Materials and Methods:

One thousand four hundred eighty eyes of 1480 adults 40 years of age and older receiving preoperative evaluation for cataract surgery were recruited consecutively from June 1, 2006, to December 31, 2010. ACD was measured with the Zeiss IOLMaster. Univariate and multivariate linear regression models were used to analyze the correlations, and receiving operator characteristic (ROC) curves and the area under the curve (AUC) were used for evaluating the predictability of an ACD less than 2.70 mm.

Results:

ACD was negatively correlated with age and positively correlated with BH in both univariate and multivariate regression analysis (P < 0.001). Sex was associated with ACD in univariate analysis, but not after adjustment with age and BH. In predicting an ACD less than 2.70 mm, the AUCs of ROC curves for ‘age and sex’, ‘age and BH’, and ‘age, sex, and BH’ were 0.687, 0.689, and 0.689, respectively.

Conclusion:

Age and BH were independent associating factors of ACD; however, sex was not. Older people and shorter ones likely had shallower ACD, and therefore were predisposed to Primary angle closure glaucoma (PACG). The predictability of ACD by age and BH solely was low, and adding sex did not increase it.

Plateau iris in Japanese patients with primary angle closure and primary angle closure glaucoma

Purpose

To determine the prevalence of plateau iris in Japanese patients with primary angle closure (PAC) and primary angle closure glaucoma (PACG) and analyze the biometric parameters in patients with plateau iris using ultrasound biomicroscopy (UBM).

Methods

In this cross-sectional observational study, subjects aged >50 years with PAC and PACG who had previously undergone a patent laser peripheral iridotomy underwent UBM in one eye. UBM images were qualitatively analyzed using standardized criteria. Plateau iris in a quadrant was defined by anteriorly directed ciliary body, absent ciliary sulcus, steep iris root from its point of insertion followed by a downward angulation, flat iris plane, and irido-angle contact. At least two quadrants had to fulfill these UBM criteria for an eye to be classified as having plateau iris. A-scan biometry was used to measure anterior segment parameters.

Results

Ninety-one subjects with PAC (58 subjects) or PACG (33 subjects) and 68 normal controls were recruited. The mean (standard deviation) ages of PAC and PACG patients and normal controls were 73.5 (6.2) and 72.6 (7.3), respectively. Based on UBM criteria, plateau iris was found in 16 eyes (17.6%) of 91 eyes. In these 16 eyes, quadrant-wise analysis showed ten eyes (62.5%) had plateau iris in two quadrants; four eyes (25%) had plateau iris in three quadrants; and two eyes (12.5%) had plateau iris in four quadrants. Anterior chamber depth, lens thickness, axial length, lens position, and relative lens position were not statistically significant between the group having plateau iris and that not having plateau iris, respectively.

Conclusion

Approximately 20% of Japanese subjects with PAC and PACG with a patent laser peripheral iridotomy were found to have plateau iris on UBM. No morphological difference was noted in the anterior segment of the eye between those with or without plateau iris.

Enhancing the early differential diagnosis of plateau iris and pupillary block using a-scan ultrasonography

Purpose

To distinguish the frequently misdiagnosed plateau iris eyes from pupillary block group and normal group, we compared the ocular biometrical parameters of them by A-scan ultrasongraphy.

Methods

In total, we retrospectively reviewed general characteristics and ocular findings including ocular biometric measurements of 71 normal, 39 plateau iris, and 83 pupillary block eyes.

Results

The normal controls, plateau iris group and pupillary block group were significantly different in age, but not in gender. The anterior chamber depth tended to decrease and the lens thickness tended to increase from normal to plateau iris to pupillary block eyes. Compared to those of plateau iris group, the pupillary block group had significantly shallower anterior chamber depth (2.90mm vs. 2.33mm; p<0.001), thicker lens (4.77mm vs. 5.11mm; p<0.001), shorter axial length (23.16mm vs. 22.63mm; p<0.001), smaller relative lens position (2.28 vs. 2.16; p<0.001) and larger lens/axial length factor (2.06 vs. 2.26; p<0.001). However, when comparing plateau iris and normal eyes, only axial length and lens/axial length factor were significantly different (23.16 vs. 23.54; p<0.05 and 2.06 vs. 1.96; p<0.05).

Conclusions

Measured by A-scan ultrasonography, the ocular biometrics of plateau iris were significantly different from those of pupillary block eyes. However, our A-scan ultrasongraphy generally found no significant biometric differences between plateau iris and normal eyes. These findings suggest that while A-scan ultrasonography might be used as a practical tool for differentiating plateau iris and papillary block eyes, a more meticulous gonioscopy and other assessments may be necessary to distinguish plateau iris from normal eyes.

Anterior-segment imaging for assessment of glaucoma

This article summarizes the physics, technology and clinical application of ultrasound biomicroscopy (UBM) and optical coherence tomography (OCT) for assessment of the anterior segment in glaucoma. UBM systems use frequencies ranging from approximately 35 to 80 MHz, as compared with typical 10-MHz systems used for general-purpose ophthalmic imaging. OCT systems use low-coherence, near-infrared light to provide detailed images of anterior segment structures at resolutions exceeding that of UBM. Both technologies allow visualization of the iridocorneal angle and, thus, can contribute to the diagnosis and management of glaucoma. OCT systems are advantageous, being noncontact proceedures and providing finer resolution than UBM, but UBM systems are superior for the visualization of retroiridal structures, including the ciliary body, posterior chamber and zonules, which can provide crucial diagnostic information for the assessment of glaucoma.

Peripheral laser iridoplasty opens angle in plateau iris by thinning the cross-sectional tissues

Plateau iris syndrome has been described as persistent angle narrowing or occlusion with intraocular pressure elevation after peripheral iridotomy due to the abnormal plateau iris configuration. Argon laser peripheral iridoplasty (ALPI) is an effective adjunct procedure to treat plateau iris syndrome. Classic theory suggests that the laser causes the contraction of the far peripheral iris stroma, “pulls” the iris away from the angle, and relieves the iris-angle apposition. We report a case of plateau iris syndrome that was successfully treated with ALPI. Spectral domain optical coherence tomography confirmed the angle was open at areas with laser treatment but remained appositionally closed at untreated areas. Further analysis suggested significant cross-sectional thinning of the iris at laser-treated areas in comparison with untreated areas. The findings indicate that APLI opens the angle, not only by contracting the iris stroma, but also by thinning the iris tissue at the crowded angle. This is consistent with the ALPI technique to aim at the iris as far peripheral as possible. This case also suggests that spectral domain optical coherence tomography is a useful adjunct imaging tool to gonioscopy in assessing the angle condition.

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.

Association between baseline angle width and induced angle opening following prophylactic laser peripheral iridotomy

PURPOSE

To evaluate the association between baseline angle width and laser peripheral iridotomy (LPI)-induced opening of the anterior chamber angle.

METHODS

Anterior segment optical coherence tomography images captured before and after LPI were analyzed to determine the angle opening distance at 250 μm (AOD250), 500 μm (AOD500), and 750 μm (AOD750) from the scleral spur; trabecular-iris space area at 500 μm (TISA500) and 750 μm (TISA750) from the scleral spur; angle recess area at 750 μm (ARA750) from the scleral spur; and trabecular-iris angle (TIA). Differences in preoperative and postoperative measurements for the anterior chamber angle width parameters were compared by paired Student's t-tests. Univariate and linear mixed-effects regression models were used to examine the association between baseline and LPI-induced opening of anterior chamber angle width parameters.

RESULTS

Eighty-four eyes of 52 primary angle closure suspects were included in the analysis. AOD250, AOD500, AOD750, TISA500, TISA750, ARA750, and TIA significantly increased following LPI by paired Student's t-tests (all P < 0.0001). Lower baseline measurements were significantly associated with greater postoperative opening in all anterior chamber angle width parameters in both univariate and linear mixed-effects regression analyses (all P < 0.05).

CONCLUSIONS

Our results showed significant opening of the anterior chamber angle width after LPI and demonstrated an inverse association between baseline and LPI-induced opening of the anterior chamber angle width, such that eyes with a more crowded anterior chamber angle undergoing LPI had a greater magnitude of increase in anterior chamber angle width after the procedure.

Anterior Segment Optical Coherence Tomography and its Clinical Applications in Glaucoma

Anterior segment optical coherence tomography (ASOCT) is an imaging modality that provides both quantitative and qualitative information on the cornea, anterior chamber angle, iris and crystalline lens. ASOCT shows excellent repeatability and reproducibility for the measurement of corneal thickness, anterior chamber angle and anterior chamber depth. With realtime video recording, ASOCT can also effectively capture the dynamic changes of the iris and lens in response to light and eye accommodation. With this additional information, physiological and pathological changes of the anterior segment structures are now better understood. This article aims to provide an overview of the current applications of ASOCT in glaucoma.

HOW TO CITE THIS ARTICLE

Li H, Jhanji V, Dorairaj S, Liu A, Lam DSC, Leung CK. Anterior Segment Optical Coherence Tomography and its Clinical Applications in Glaucoma. J Current Glau Prac 2012;6(2):68-74.

The posterior location of the dilator muscle induces anterior iris bowing during dilation, even in the absence of pupillary block

PURPOSE

To examine the effect of the posterior location of the dilator on iris anterior curvature during dilation.

METHODS

An in vivo human study, an ex vivo porcine experiment, and an in silico computational model were performed in parallel. Iris anterior curvature was measured in vivo before and after dilation by time-domain slit lamp optical coherence tomography (SL-OCT). All patients (n = 7) had undergone laser peripheral iridotomy to eliminate any pupillary block due to primary angle-closure glaucoma. In the ex vivo experiments, isolated porcine irides (n = 30) were secured at the periphery and immersed in an oxygenated Krebs-Ringer buffer. Dilation was induced pharmaceutically by the addition of 2.5% phenylephrine and 1% tropicamide. An in-house optical coherence tomography (OCT) system was used to obtain iris images before and after dilation. A finite element model was also developed based on typical geometry of the iris from the initial OCT image. The iris was modeled as a neo-Hookean solid, and the active muscle component was applied only to the region specified as the dilator.

RESULTS

An increase in curvature and a decrease in chord length after dilation were observed in both experiments. In both the in vivo and ex vivo experiments, the curvature-to-chord length ratio increased significantly during dilation. Computer simulations agreed well with the experimental results only when the proper anatomic position of dilator was used.

CONCLUSIONS

The posterior location of the dilator contributes to the anterior iris bowing via a nonpupillary block dependent mechanism.

Quantitative iris parameters and association with narrow angles

PURPOSE

To investigate the relationship between quantitative iris parameters (iris curvature [I-Curv], iris area [I-Area], and iris thickness) and the presence of narrow angles.

DESIGN

Cross-sectional, community-based study.

PARTICIPANTS

We recruited 2047 subjects >50 years old without ophthalmic symptoms from a community clinic in Singapore.

METHODS

All subjects underwent gonioscopy and anterior segment optical coherence tomography (AS-OCT) under dark conditions. An eye was considered to have narrow angles if the posterior pigmented trabecular meshwork was not visible for >/=180 degrees on nonindentation gonioscopy with the eye in the primary position. Customized software was used on horizontal AS-OCT scans to measure I-Curv, I-Area, and iris thickness 750 mum (IT750) and 2000 mum (IT2000) from the scleral spur. The average of both temporal and nasal measured values of the right eye was used for analysis.

MAIN OUTCOME MEASURES

The association between iris parameters and narrow angles on gonioscopy.

RESULTS

Iris parameters from 1465 eyes (71.6%) were available for analysis. Of these, 315 subjects (21.5%) had narrow angles. The mean I-Curv (0.366 vs 0.259 mm; P<0.020), IT750 (0.476 vs 0.453 mm; P<0.001), and IT2000 (0.491 vs 0.482 mm; P = 0.010) were greater in persons with than without narrow angles. After adjusting for age, gender, anterior chamber depth, axial length, and pupil size, the greater I-Curv, I-Area, IT750, and IT2000 were significantly associated with narrow angles (odds ratio [OR] 2.5 and 95% confidence interval [CI], 1.3-5.1; OR, 2.7 and 95% CI, 1.6-4.8; OR, 2.6 and 95% CI, 1.6-4.1; OR, 2.7 and 95% CI, 1.5-4.7, comparing 4th with 1st quartile for each parameter, respectively). In stratified analysis, women and subjects aged >/=60 years had stronger associations for most iris parameters with narrow angles than men and younger subjects.

CONCLUSIONS

Quantitative iris parameters (I-Curv, I-Area, and iris thickness) are independently associated with narrow angles, particularly in women and older subjects. These data provide further insights into the pathogenesis of angle closure in Singaporeans.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found after the references.

High-resolution ultrasound imaging of the eye - a review

This report summarizes the physics, technology and clinical application of ultrasound biomicroscopy (UBM) of the eye, in which frequencies of 35 MHz and above provide over a threefold improvement in resolution compared with conventional ophthalmic ultrasound systems. UBM allows imaging of anatomy and pathology involving the anterior segment, including regions obscured by overlying optically opaque anatomic or pathologic structures. UBM provides diagnostically significant information in conditions such as glaucoma, cysts and neoplasms, trauma and foreign bodies. UBM also can provide crucial biometric information regarding anterior segment structures, including the cornea and its constituent layers and the anterior and posterior chambers. Although UBM has now been in use for over 15 years, new technologies, including transducer arrays, pulse encoding and combination of ultrasound with light, offer the potential for significant advances in high-resolution diagnostic imaging of the eye.

Argon laser peripheral iridoplasty for plateau iris associated with iridociliary cysts: a case report

Introduction

Plateau iris is recognised as an important cause of primary angle closure glaucoma. The management of this condition generally comprises laser peripheral iridotomy and iridoplasty, to remove any component of relative pupillary block and to widen the iridotrabecular drainage angle respectively. However, plateau iris may be associated with multiple iris cysts at the iridociliary junction, which then presents diagnostic and management problems.

Case presentation

We present a fifty-three year old Caucasian gentleman with plateau iris associated with peripheral iris cysts, in which the iridotrabecular angle did not widen despite having had both laser peripheral iridotomy and iridoplasty. The patient has remained asymptomatic over 12 months, and is under close follow-up to monitor for signs of glaucoma.

Conclusion

Plateau iris with iridociliary cysts can be difficult to diagnose and manage. Ultrasound biomicroscopy should be performed on patients with appositional iridotrabecular angle closure on gonioscopy, especially if the angle closure is not relieved with either laser peripheral iridotomy or iridoplasty. Question marks can be raised as to the benefit of laser iridotomy when plateau iris without pupillary block has already been conclusively diagnosed on ultrasound biomicroscopy.

Prevalence of Plateau Iris in Primary Angle Closure Suspects

PURPOSE

To determine the prevalence of plateau iris in a cohort of primary angle closure suspects (PACSs) using ultrasound biomicroscopy (UBM).

DESIGN

Cross-sectional observational study.

PARTICIPANTS

Subjects over the age of 50 years diagnosed as PACSs.

INTERVENTION

Subjects were randomized to undergo laser peripheral iridotomy (LPI) in one eye. Ultrasound biomicroscopy was performed before and a week after LPI.

MAIN OUTCOME MEASURES

Ultrasound biomicroscopy images were qualitatively assessed using standardized criteria. Plateau iris was defined in a quadrant by the presence of an anteriorly directed ciliary body, an absent ciliary sulcus, a steep iris root from its point of insertion followed by a downward angulation from the corneoscleral wall, presence of a central flat iris plane, and irido-angle contact. At least 2 quadrants had to fulfil the above criteria for an eye to be defined as plateau iris.

RESULTS

Two hundred five subjects were enrolled; UBM images of 167 subjects were available for analysis. Plateau iris was found in 54 of 167 (32.3%) PACS eyes after LPI. Quadrantwise analysis showed that 44 of 167 (26.3%) eyes had plateau iris in 1 quadrant, 36 (21.5%) in 2 quadrants, 16 (9.5%) in 3 quadrants, and 2 (1.2%) in all 4 quadrants. Plateau iris was most commonly observed in the superior and inferior quadrants.

CONCLUSIONS

Using standardized UBM criteria, plateau iris was found in about a third of PACS eyes after LPI. Prospective longitudinal studies are required to determine the clinical significance of this finding for the management of PACSs.

Prevalence of plateau iris syndrome in young patients with recurrent angle closure

BACKGROUND

To assess and describe the prevalence and clinical features associated with plateau iris syndrome (PIS) in young individuals with recurrent angle closure despite initial therapy.

METHODS

Chart review of 137 relatively young individuals (aged < 60 years) with symptoms of angle closure between 1995 and 2005. A follow-up period of 36 months after initial presentation was retrospectively analysed. Seventy-six patients with recurrent angle closure symptoms were clinically reviewed using gonioscopy and ultrasound biomicroscopy.

RESULTS

Based on chart analysis, 30 of 137 individuals were diagnosed with PIS (22%). After clinical review, 34 additional patients suffered from PIS as the underlying cause for persistent angle closure symptoms. The prevalence of PIS in our patient population with recurrent angle closure symptoms in spite of initial iridotomy or iridectomy was 54%.

CONCLUSION

Among angle closure in young individuals, PIS is not uncommon. The causative mechanism of PIS in young individuals is peripheral iris block, rather than pupillary block which is more often prevalent in older patients. For proper diagnosis and therapy, ultrasound biomicroscopy and gonioscopy should be performed on every young individual with angle closure symptoms.

Migraine and anisocoria

A 42-year-old woman presents with headache and anisocoria. Gonioscopy suggested narrow angles. Ultrasound biomicroscopy confirmed the diagnosis. The patient underwent bilateral peripheral iridotomies with resolution of her symptoms. The differential diagnosis of headache and anisocoria are reviewed. Plateau iris syndrome and subacute angle closure are discussed.

[Applications of noninvasive high-resolution ultrasound imaging in ophthalmology]

While ultrasonography has been applied to eye examination since the beginning of medical applications of ultrasound, the use of high frequencies is relatively recent in this context. Recent developments since the 1990s have made devices available that are well suited for examining the anterior segment as well as the posterior pole, providing precise data for corneal lesions, iris, chamber angle, and ciliary body abnormalities, and lesions of the papilla and macula.

High prevalence of plateau iris configuration in family members of patients with plateau iris syndrome

PURPOSE

The purpose of the study was to ascertain the prevalence of plateau iris syndrome in the first-degree relatives of those patients affected with plateau iris syndrome.

METHODS

All patients seen with plateau iris syndrome over a 5-year period were identified. These patients were approached for participation and first-degree family members above 18 years of age were screened. All people identified with plateau iris configuration underwent ultrasound biomicroscopy to document and confirm the angle configuration and subsequent gonioscopy after laser iridotomies.

RESULTS

Sixteen patients were identified; 3 refused to participate, 2 were unable to be contacted, and 1 withdrew after initially consenting to participate. In this case, the patient agreed to participate, but all her living first-degree family members refused to be screened. Among the 10 patients whose living first-degree relatives were screened, we found 5 families with at least 1 additional first-degree family member having plateau iris syndrome.

CONCLUSIONS

Some families have more than 1 member with plateau iris syndrome. The pattern of inheritance resembles an autosomal dominant pattern with incomplete penetrance.

Evaluation and management of plateau iris syndrome: case report and review

BACKGROUND

This article documents a case of plateau iris syndrome and provides a review of the current concepts regarding the pathogenesis, diagnosis, and management of this condition.

CASE REPORT

A patient who had patent peripheral iridotomies O.D. and O.S. to treat previous episodes of acute angle closure came to clinic with unilaterally elevated intraocular pressures, narrow anterior chamber angles, and a flat iris configuration. The patient was diagnosed with plateau iris syndrome.

CONCLUSIONS

The clinician must be aware of, and be able to distinguish, the clinical signs that are characteristic of plateau iris syndrome. An understanding of the mechanisms involved in the development of this type of primary angle closure may facilitate its appropriate diagnosis and management.

Phacoemulsification and Goniosynechialysis in the Management of Unresponsive Primary Angle Closure

PURPOSE

To evaluate the effectiveness of phacoemulsification and goniosynechialysis (PEGS) in managing acute and subacute primary angle closure unresponsive to conventional therapy.

MATERIALS AND METHODS

Retrospective series of patients of six glaucoma-trained surgeons with primary angle closure that did not respond to medical management, Nd:YAG laser peripheral iridotomy, or argon laser peripheral iridoplasty.

RESULTS

A total of twenty-one patients with an average age of 65.6 years were included. Underlying mechanism of angle closure included pupillary block (n = 18) and plateau iris (n = 3). Average intraocular pressure (IOP) immediately prior to PEGS was 40.7 mm Hg, and mean follow-up time after PEGS was 11.7 months. PEGS decreased mean IOP by 25 mm Hg (62%), and mean number of medications from 3.8 pre-surgery to 1.7 post-surgery (55%). Mean LogMar visual acuity improved after PEGS, from 0.64 to 0.44 (Paired t test t = 4.120 P = 0.001). Subsequent trabeculectomy was necessary in one case (5%).

CONCLUSIONS

Phacoemulsification with goniosynechialysis may be an effective treatment option for primary angle closure unresponsive to conventional therapy.