Morphological changes of the anterior segment after laser peripheral iridotomy in primary angle closure

Comparison of intraocular pressure and anterior segment parameters in subjects with asymmetrical primary angle closure disease

BACKGROUND

To compare intraocular pressure (IOP) and anterior segment parameters between eyes with unilateral primary angle closure glaucoma (PACG) and their fellow eyes with primary angle closure (PAC) or primary angle closure suspect (PACS).

METHODS

Subjects underwent anterior segment imaging using 360-degree swept-source optical coherence tomography (SS-OCT, CASIA Tomey, Nagoya, Japan) and ocular investigations including gonioscopy and IOP measurement. Each SS-OCT scan (divided into 8 frames, 22.5 degrees apart) was analysed and an average was obtained for the following anterior segment parameters: iridotrabecular contact (ITC), angle opening distance (AOD750), iris thickness and curvature, anterior chamber width, depth and area (ACW, ACD and ACA) and lens vault (LV).

RESULTS

Among 132 unilateral PACG subjects (mean age: 62.91 ± 7.2 years; 59.1% male), eyes with PACG had significantly higher presenting IOP (24.81 ± 0.94 vs. 18.43 ± 0.57 mmHg, p < 0.001), smaller gonioscopic Shaffer grade (2.07 ± 0.07 vs. 2.31 ± 0.07, p < 0.001) and a greater extent of peripheral anterior synechiae (PAS, 1.21 ± 0.21 vs. 0.54 ± 0.16 clock hours, p = 0.001). PACG eyes also exhibited increased ITC, ITC area, greater LV and smaller AOD750, ACD and ACA (all p < 0.05). Using the forward stepwise regression model, an increase in 1 mmHg in presenting IOP before laser peripheral iridotomy (LPI) increases the odds of having PACG by 9% (95% confidence interval 5%-14%).

CONCLUSIONS

PACG eyes have higher presenting IOP, smaller anterior segment parameters, greater extent of PAS, and larger LV compared to their fellow eyes with angle closure. Narrower anterior chamber dimensions and higher presenting IOP before LPI may increase risk of chronic elevated IOP and glaucomatous optic neuropathy after LPI.

Comparison of intraocular lens power calculation formulas in patients with a history of acute primary angle-closure attack

BACKGROUND

To compare the accuracy of nine intraocular lens (IOL) power calculation formulas, including three traditional formulas (SRK/T, Haigis, and Hoffer Q) and six new-generation formulas (Barrett Universal II [BUII], Hill-Radial Basis Function [RBF] 3.0, Kane, Emmetropia verifying optical [EVO], Ladas Super, and Pearl-DGS) in patients who underwent cataract surgery after acute primary angle closure (APAC).

METHODS

In this retrospective cross-sectional study, 44 eyes of 44 patients (APAC) and 60 eyes of 60 patients (control) were included. We compared the mean absolute error, median absolute error (MedAE), and prediction error after surgery. Subgroup analyses were performed on whether axial length (AL) or preoperative laser peripheral iridotomy affected the postoperative refractive outcomes.

RESULTS

In the APAC group, all formulas showed higher MedAE and more myopic shift than the control group (all P < 0.05). In APAC eyes with AL ≥ 22 mm, there were no differences in MedAEs according to the IOL formulas; however, in APAC eyes with AL < 22 mm, Haigis (0.49 D) showed lower MedAE than SRK/T (0.82 D) (P = 0.036) and Hill-RBF 3.0 (0.54 D) showed lower MedAE than SRK/T (0.82 D), Hoffer Q (0.75 D) or Kane (0.83 D) (P = 0.045, 0.036 and 0.027, respectively). Pearl-DGS (0.63 D) showed lower MedAE than Hoffer Q (0.75 D) and Kane (0.83 D) (P = 0.045 and 0.036, respectively). Haigis and Hill-RBF 3.0 showed the highest percentage (46.7%) of eyes with PE within ± 0.5 D in APAC eyes with AL < 22 mm. Iridectomized eyes did not show superior precision than the non-iridotomized eyes in the APAC group.

CONCLUSIONS

Refractive errors in the APAC group were more myopic than those in the control group. Haigis and Hill-RBF 3.0 showed high precision in the eyes with AL < 22 mm in the APAC group.

Automated iris volume analysis and trabecular meshwork length using anterior segment optical coherence tomography - Application in pseudoexfoliation and pseudoexfoliation glaucoma

Purpose:

The aim of this study was to evaluate differences in the iris and angle parameters in psuedoexfoliation syndrome (PXF) and pseudoexfoliation glaucoma (PXG) using anterior segment optical coherence tomography (ASOCT).

Methods:

Patients with PXF or PXG were compared using ASOCT with primary open-angle glaucoma POAG eyes as controls in this noninterventional comparative study conducted at a tertiary eye care center in East India. All angle parameters, TM length, and iris thickness were analyzed from the enhanced depth imaging (EDI) single scans obtained. Quadrant scans were used for the calculation of iris volume using a custom-built in-house software. In particular, the software performs multiple operations including edge detection, connected components, and thresholding to localize and segment the iris. Differences in the iris volume/thickness and TM length in PXF and PXG with POAG were analyzed.

Results:

A total of 225 eyes were included, which included 75 PXG and 98 PXF cases and 52 POAG with a mean age of 67 ± 9.7 years at presentation. The algorithm repeatability and reproducibility was also established with correlation coefficients more than 99% which was substantiated with Bland-Altman plots. The iris volume (calculated in 197 images of 225 eyes) did not differ significantly in PXF and PXG eyes, although both had significantly greater volume compared to POAG eyes. The iris volume or other angle parameters including TM length did not correlate with clinical variables such as IOP, age, or visual field indices.

Conclusion:

Iris parameters or TM length do not explain pathogenesis of glaucoma in pseudoexfoliation.

Impact of laser iridotomy on headache symptoms in angle-closure subjects

BACKGROUND

Migraine symptoms are frequently referred by glaucoma patients. Although most studies analyze headache in the acute setting of angle closure, many patients with chronic occludable angles also complain of headaches. The aim of this study was to determine the impact of laser peripheral iridotomy (LPI) on the magnitude and frequency of headache symptoms in patients with occludable angles.

METHODS

Prospective cohort study. Patients with indication for prophylactic LPI due to occludable iridocorneal angle were included. Headache symptoms were assessed before and at least 4 weeks after LPI using the Headache Impact Test-6 (HIT-6) questionnaire. A HIT-6 score of ≥ 50 points was labeled as a clinically significant headache.

RESULTS

Thirty-one subjects were included. Prophylactic LPI was performed in 60 eyes, as 2 patients were pseudophakic in the fellow eye. Baseline HIT-6 score was 59.9 ± 11.8, with over three quarters of these patients scoring higher than 50 points (n = 24). A statistically significant reduction in HIT-6 score was found after LPI treatment (45.4 ± 7.7, p < 0.01). Sub-analysis within the clinically symptomatic subjects disclosed a significant improvement after treatment in this group (baseline, 65.3 ± 6.2 vs post-LPI 46.2 ± 8.3, p < 0.01), with a high baseline HIT-6 score being predictive of a symptomatic improvement after LPI (χ²(8) = 15.3, p = 0.001). This is mimicked from the patient's perspective, as the two subjective questions after LPI, concerning pain intensity and frequency, report that 79.2% had a statistically significant improvement of the headaches.

CONCLUSIONS

Within our sample, the majority of patients with occludable angles had clinically relevant headaches. LPI provided symptomatic relief in the majority of those patients with high HIT-6 scores. Further studies are needed to explore the relationships between headache and angle anatomy.

Low iris and anterior chamber volume is associated with deepening after laser peripheral iridotomy in primary angle closure suspects

PURPOSE

To evaluate the association between baseline ocular variables and the widening of the anterior chamber angle by laser peripheral iridotomy (LPI) in primary angle closure suspects (PACS) using a new Fourier-domain swept-source anterior segment optical coherence tomography (FD-ASOCT).

METHOD

Sixty-six PACS eyes of 41 individuals were enrolled in this prospective interventional case series. An FD-ASOCT (Casia SS-1000 OCT; Tomey, Nagoya, Japan) was used to measure biometric baseline variables and at 1 month after the LPI. Paired t test was used to compare the difference between pre-and post-LPI measurements. Multivariate regression analysis was used to test for an association between baseline iris thickness and volume, anterior chamber depth and volume, and lens vault with a widening of the angle after an LPI. Changes in trabecular iris space area and angle opening distance after the LPI were main outcome measures.

RESULTS

The mean age of participants was 58.6 ± 8.7 years, 68.2% of whom were female. The angle opening distance, recess area, and trabecular iris surface area at 500 μm increased by 48 to 73% (all P < 0.001). Lens vault and iris volume did not change. A low anterior chamber volume and low iris volume were associated with angle greater deepening by LPI.

CONCLUSION

Eyes with a shallow anterior chamber and thinner irises are more likely to experience angle opening from an LPI.

Pupillary responses to light are not affected by narrow irido-corneal angles

Chromatic pupillometry is an emerging method for evaluating ocular health that relies upon the differential stimulation of rods, cones, and intrinsically photosensitive retinal ganglion cells (ipRGCs). Although it has been investigated in conditions affecting the outer or inner retina, there is a paucity of studies in conditions where the anterior chamber of the eye is affected. Primary angle closure suspects (PACS) are defined as eyes with narrow anterior chamber angles and intact retina. PACS patients are at risk of developing primary angle closure glaucoma and are prophylactically treated by performing laser peripheral iridotomy (LPI). Here we evaluated pupillary responses to monchromatic lights in 18 PACS before and after LPI, and compared the results with those of 36 age-matched controls who had gonioscopically open angles. Dose response curves for pupillary constriction were similar between PACS patients and controls (p = 0.98 for blue and 0.90 for red light) and within subjects pre- and post-LPI (p = 0.58 for blue and 0.20 for red light). Baseline-adjusted pupillary constriction responses to blue and red lights were similar in controls and PACS, and not altered after LPI. Our findings suggest that narrow irido-corneal angles and LPI do not influence pupillary responses in PACS.

Changes in ocular biometry and anterior chamber parameters after pharmacologic mydriasis and peripheral iridotomy in primary angle closure suspects

PURPOSE

The aim of this study was to evaluate the effects of pharmacologic mydriasis and Peripheral Iridotomy (PI) on ocular biometry and anterior chamber parameters in primary angle closure suspects.

METHODS

In this prospective interventional case series, 21 primary angle closure suspects were enrolled. Intraocular pressure, refraction, ocular biometry (Lenstar, LS900), and anterior chamber parameters (Pentacam HR) were measured at four occasions: before PI (before and after mydriasis with phenylephrine) and two weeks after PI (before and after mydriasis). The study was conducted on both eyes and only one eye per patient, in random, was included in the analysis.

RESULTS

The mean age of the participants was 60±7 years and 17 (81%) were female. There were no significant differences in intraocular pressure, refraction, keratometry, biometric and anterior chamber parameters between groups, except for anterior chamber volume, which showed increments with PI and mydriasis. The corresponding values for anterior chamber volume were as follows: 88.2±13.7mm(3) before PI, undilated; 106.3±18.8 before PI, dilated; 99.0±14.6 after PI, undilated, and 107.4±16.5 after PI, dilated (P<0.001).

CONCLUSIONS

This study showed no change in the ocular biometric and anterior chamber parameters including iridocorneal angle after PI and/or pharmacologic mydriasis except for increments in anterior chamber volume. This factor has the potential to be used as a numerical proxy for iris position in evaluating and monitoring patients with primary angle closure suspects after PI.

Subsequent Receipt of Interventions for Glaucoma Among a Nationwide Sample of Patients Who Underwent Laser Peripheral Iridotomy

PURPOSE

To evaluate use of medical, laser, or incisional surgical interventions for glaucoma after laser peripheral iridotomy (LPI).

DESIGN

Retrospective longitudinal cohort study.

METHODS

All enrollees aged ≥21 years in a US managed-care network who underwent bilateral LPIs in 2001-2011 were identified. The mean numbers of pre- and post-LPI glaucoma medication classes prescribed and the proportion of enrollees requiring cataract or glaucoma surgery within 2 years after the LPIs were determined. Multivariable logistic regression assessed factors associated with enrollees' prescription of ≥1 glaucoma medication class after bilateral LPIs.

RESULTS

Of the 1660 patients undergoing bilateral LPIs, 1280 (77.1%) had no pre- or post-LPI prescriptions for any glaucoma medication class. Of the remaining patients, 251 (66.1%) required more glaucoma medication classes after than before the procedures, whereas 44 (11.6%) used fewer after the procedures; 85 (22.4%) were prescribed the same number before and after the LPIs. A total of 167 patients (10.1%) underwent cataract surgery and 79 (4.8%) received glaucoma surgery over the 2-year follow-up. Black patients had a 130% increased odds for glaucoma medication-class prescriptions after bilateral LPIs, compared with white patients (P = .02). The odds of post-LPI glaucoma medication use increased by 21% for every additional 5 years of age (P < .0001).

CONCLUSION

Most patients undergoing bilateral LPIs received no pre- or post-LPI glaucoma medication-class prescriptions and had no cataract or additional glaucoma surgery within 2 years after LPIs. Clinicians should alert black or older patients and those already taking glaucoma medications before the procedure of their higher odds of requiring medications afterward.

Baseline Anterior Segment Parameters Associated with the Long-term Outcome of Laser Peripheral Iridotomy

PURPOSE

To investigate the baseline anterior segment (AS) parameters determined by AS optical coherence tomography (AS OCT) in the prediction of long-term outcome of laser peripheral iridotomy (LPI) in primary angle closure suspect (PACS) eyes Methods: Participants were imaged at pre-LPI and at 2 weeks and 3 years post-LPI using AS OCT. Based on these images, anterior chamber depth (ACD), iris curvature (IC), anterior chamber width (ACW), iris thickness at 750 µm from the scleral spur (IT750), lens vault (LV), and iris area (IA) were estimated using the Image J software (version 1.46). Proportional change (%) in angle opening distance at 750 µm from the scleral spur (AOD750) was used as an outcome measure for LPI. Univariate and multivariate regression analyses were performed to evaluate baseline AS parameters associated with changes in AOD750.

RESULTS

A total of 39 PACS eyes were included. At 2 weeks post-LPI, thinner IT750 (p = 0.006) and less AOD750 (p < 0.001) at baseline were related to a greater AOD750 change. When assessed at 3 years post-LPI, thinner IT750 (p = 0.039) and less AOD750 (p = 0.003) at baseline were associated with a greater AOD750 change.

CONCLUSIONS

Thin peripheral iris and less AOD750 at baseline were associated with greater changes in longitudinal assessment after LPI. PACS eyes with thick peripheral iris at baseline showed less AOD750 change at both early and late follow up after LPI; therefore, such eyes should be followed with caution despite successful LPI.

Peripheral iris thickness and association with iridotrabecular contact after laser peripheral iridotomy in patients with primary angle-closure and primary angle-closure glaucoma

Purpose

To investigate the relation between the quantitative iris parameters and iridotrabecular contact (ITC) in patients with primary angle-closure (PAC) and PAC glaucoma (PACG).

Materials and methods

PAC and PACG with laser peripheral iridotomy were recruited prospectively. Anterior-segment optical coherence tomography (ASOCT) was performed under light and dark conditions, and scans were taken along the vertical and horizontal axes. Iris thickness at 500 μm (IT500) and 750 μm (IT750) from the scleral spur, maximal iris thickness (MIT), and cross sections of the iris area (I-Area) were measured by using software. ITC was defined by the ASOCT as the contact between the peripheral iris and angle wall anterior to the scleral spur. The ITC⁺ and ITC⁻ groups were defined as eyes that had ITC in two or more quadrants and in no or one quadrant, respectively.

Results

A total of 79 eyes of 60 patients (consisting of 48 PAC and 31 PACG) were recruited. The prevalence of superior, inferior, temporal, and nasal ITC was 44 eyes (55.7%), 48 eyes (60.8%), 18 eyes (22.8%), and 16 eyes (20.2%), respectively. These iris parameters of the inferior quadrant, which had the highest prevalence of all the quadrants, were used for the analysis. After adjusting for age, sex, pupil size, and central anterior chamber depth, mean values of IT500 and IT750 were significantly greater in the ITC⁺ group than the ITC⁻ group (P<0.05). Multivariate-adjusted odds ratios of parameters for the ITC⁺ group compared with the ITC⁻ group were: IT500, 1.9 (P=0.029); IT750, 2.0 (P=0.011), MIT, 1.4 (P=0.244), and I-Area, 0.97 (P=0.406), respectively, per 0.1-unit increase.

Conclusion

Peripheral iris thickness is associated with ITC in patients with angle closure.

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.

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.

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.

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.

Repeatability and reproducibility of anterior chamber volume measurements using 3-dimensional corneal and anterior segment optical coherence tomography

PURPOSE

To evaluate the repeatability and reproducibility of anterior chamber volume (ACV) measurements using swept-source 3-dimensional corneal and anterior segment optical coherence tomography (CAS-OCT) and dual Scheimpflug imaging.

SETTING

Department of Ophthalmology, Institute of Clinical Medicine, University of Tsukuba, Ibaraki, Japan.

DESIGN

Nonrandomized clinical trial.

METHODS

Measurements were taken in normal eyes (subject group) and in eyes with primary angle closure (PAC) (patient group). In the subject group, the entire ACV and the central 8.0 mm diameter ACV were measured using CAS-OCT and dual Scheimpflug imaging. In the patient group, the entire ACV and 8.0 mm ACV were measured using CAS-OCT. The coefficient of variation and intraclass correlation coefficient (ICC) were calculated to evaluate repeatability and reproducibility, and the correlation between the 2 devices was assessed.

RESULTS

In the subject group, the mean 8.0 mm ACV was 110.14 mm(3) ± 12.57 (SD) using CAS-OCT and 114.51 ± 14.69 mm(3) using Scheimpflug imaging; there was a significant linear correlation (r = 0.878, P < .0001). The mean entire ACV on CAS-OCT was 165.15 ± 29.29 mm(3). The ICCs of the 8.0 mm and entire ACV measurements were greater than 0.94. The coefficients of repeatability and reproducibility of the 8.0 mm ACV and entire ACV measurements were less than 5%. In the patient group, the 8.0 mm and entire ACV measurements showed good reproducibility and repeatability.

CONCLUSIONS

The CAS-OCT method allowed noninvasive measurement of the entire ACV with sufficient repeatability and reproducibility. The 8.0 mm ACV measurements with CAS-OCT and Scheimpflug imaging were comparable.

High prevalence of narrow angles among Chinese-American glaucoma and glaucoma suspect patients

PURPOSE

To evaluate the prevalence of gonioscopically narrow angles in a Chinese-American population with glaucoma or glaucoma suspicion.

PATIENTS AND METHODS

Charts from all Chinese-American patients seen in a comprehensive ophthalmology clinic in the Chinatown district of San Francisco in 2002 were reviewed. One eye from each patient with glaucoma or glaucoma suspicion that met inclusion criteria was included (n=108). Data were collected for sex, age, race (self-declared), refraction (spherical equivalent), intraocular pressure, gonioscopy, and vertical cup-to-disk ratio.

RESULTS

Sixty percent (n=65) of Chinese-American eyes with glaucoma or glaucoma suspicion had gonioscopically narrow angles (Shaffer grade < or = 2 in 3 or more quadrants). Those with narrow angles were significantly older (P=0.004) than their open angle counterparts, but the 2 groups did not differ in terms of sex, refraction, intraocular pressure, or cup-to-disk ratio (all, P > or = 0.071). In a multivariate model including age, sex, and refraction as predictors of angle grade (open or narrow), only age was a significant predictor of angle grade (P=0.004).

CONCLUSIONS

A large proportion of Chinese-Americans in our study population with glaucoma or glaucoma suspicion had gonioscopically narrow angles. In multivariate analysis, patients with narrow angles were older than those with open angles but did not differ from them in terms of sex or refraction. Continued evaluation of angle closure glaucoma risk among Chinese-Americans is needed.