Update on the usefulness of optical coherence tomography in assessing the iridocorneal angle

The iridocorneal angle, due to its implications in the physiopathology of aqueous humour drainage, is a fundamental structure of the anterior chamber. Anterior segment optical coherence tomography is a rapid and non-invasive technique that obtains images in vivo. The high resolution allows it to analyse the normal anatomy of the angle, any alterations, and the changes that occur after different therapeutic interventions. Anterior segment optical coherence tomography technology has evolved to provide images that allow the identification and quantification of the angular structures in healthy subjects and in glaucoma patients, and especially the trabecular meshwork and the Schlemm's canal. It also enables the angle width to be quantified, with some objective parameters that have been standardised in recent years, such as the trabecular-iris angle, the angle opening distance, and the trabecular-iris area. This technique has multiple uses in the study of the different mechanisms of angle closure, the evaluation of changes after a laser peripheral iridotomy or iridoplasty after cataract surgery, as well as after the implantation of phakic lenses.

The change of anterior segment parameters after cataract surgery in normal-tension glaucoma

AIM

To investigate the change of anterior chamber angle morphology and intraocular pressure (IOP) reduction after cataract surgery in patients with normal-tension glaucoma (NTG) using swept-source optical coherence tomography (SS-OCT).

METHODS

This prospective, comparative, observational study recruited patients into two groups. Group 1 was the control group including normal subjects except those with cataracts (cataract group, n=67 eyes of 67 patients), and group 2 was NTG group including patients who were diagnosed with NTG and cataracts (n=43 eyes of 43 patients), which were treated with phacoemulsification and intraocular lens implantation. Before surgery, and at postoperative 1 and 6mo, anterior chamber angles were evaluated by SS-OCT under dark conditions using three-dimensional angle analysis scan protocol. Angle opening distance (AOD), angle recess area (ARA), and trabecular-iris surface area (TISA) at four quadrants (temporal, nasal, superior, and inferior) were calculated automatically by SS-OCT, after the observer marked scleral spurs.

RESULTS

A total of 106 patients (54 males and 52 females) were enrolled in the study. Angle parameters, AOD, ARA, and TISA were increased after surgery in both groups. However, changes of angle parameters were only significant in group 2. In group 2, preoperative IOP was 13.2±2.9 mm Hg, and postoperative IOP at 1 and 6mo were 10.5±3.0 and 10.7±2.8 mm Hg, respectively. In group 1, preoperative IOP was 12.4±2.8 mm Hg, and postoperative IOP at 1 and 6mo were 11.6±2.5 and 12.0±2.8 mm Hg, respectively. After cataract surgery, angle parameters changed significantly while IOP significantly reduced and was maintained in group 2 (P<0.001). The changes in angle parameters (ΔAOD500, ΔTISA500 at temporal; ΔAOD500, ΔARA500 at nasal) were linearly correlated with postoperative IOP changes.

CONCLUSION

Cataract surgery may have improved anterior chamber angle parameters and decreased IOP in NTG patients.

Correlations between Preoperative Angle Parameters and Postoperative Unpredicted Refractive Errors after Cataract Surgery in Open Angle Glaucoma (AOD 500)

PURPOSE

To assess the accuracy of intraocular lens (IOL) power prediction for cataract surgery with open angle glaucoma (OAG) and to identify preoperative angle parameters correlated with postoperative unpredicted refractive errors.

MATERIALS AND METHODS

This study comprised 45 eyes from 45 OAG subjects and 63 eyes from 63 non-glaucomatous cataract subjects (controls). We investigated differences in preoperative predicted refractive errors and postoperative refractive errors for each group. Preoperative predicted refractive errors were obtained by biometry (IOL-master) and compared to postoperative refractive errors measured by auto-refractometer 2 months postoperatively. Anterior angle parameters were determined using swept source optical coherence tomography. We investigated correlations between preoperative angle parameters [angle open distance (AOD); trabecular iris surface area (TISA); angle recess area (ARA); trabecular iris angle (TIA)] and postoperative unpredicted refractive errors.

RESULTS

In patients with OAG, significant differences were noted between preoperative predicted and postoperative real refractive errors, with more myopia than predicted. No significant differences were recorded in controls. Angle parameters (AOD, ARA, TISA, and TIA) at the superior and inferior quadrant were significantly correlated with differences between predicted and postoperative refractive errors in OAG patients (-0.321 to -0.408, p<0.05). Superior quadrant AOD 500 was significantly correlated with postoperative refractive differences in multivariate linear regression analysis (β=-2.925, R²=0.404).

CONCLUSION

Clinically unpredicted refractive errors after cataract surgery were more common in OAG than in controls. Certain preoperative angle parameters, especially AOD 500 at the superior quadrant, were significantly correlated with these unpredicted errors.

Predictors of intraocular pressure change after phacoemulsification in patients with pseudoexfoliation syndrome

AIM

To evaluate anterior chamber biometric factors and intraoperative metrics associated with the intraocular pressure (IOP) reduction after phacoemulsification in non-glaucomatous pseudoexfoliative syndrome (PXS) eyes.

METHOD

Thirty-three patients were enrolled in this prospective interventional study. Images were excluded if they had poor quality, poor perpendicularity or inability to locate sclera spurs. Anterior chamber depth (ACD), anterior chamber area (ACA), iris thickness, iris area, iris curvature, lens vault, angle opening distance (AOD500, AOD750) and trabecular iris space area (TISA500, TISA750) were measured in qualified images using the Zhongshan Angle Assessment Program and compared preoperatively and 3 months postoperatively. Cumulative dissipated energy (CDE), aspiration time and infusion fluid usage during cataract surgery were obtained from the phacoemulsification machine's metrics record. Postoperative IOP change was compared with these anatomical and intraoperative metric parameters.

RESULTS

Mean IOP was 18.1±3.4 mm Hg preoperatively and decreased by 3.3 mm Hg (18%) to 14.8±3.6 mm Hg at 3 months postoperatively (p<0.001). All angle parameters, ACD and ACA increased significantly postoperatively (p<0.001 for all) and iris curvature decreased (p<0.001). In univariate analysis, preoperative IOP (B=-0.668, p=0.002), infusion fluid usage (B=-0.040, p=0.04) and aspiration time (B=-0.045, p=0.003) were negatively associated with IOP decrease after phacoemulsification. Changes in IOP did not demonstrate significant associations with CDE measurements or anterior segment optical coherence tomography measurements, including preoperative angle, iris or anterior segment parameters. In the final multivariate regression model, preoperative IOP (B=-0.668, p=0.002) and infusion fluid usage (B=-0.041, p=0.04) were significantly associated with IOP drop and together can predict 45.1% (p=0.002) of the variability in IOP change.

CONCLUSIONS

Non-glaucomatous patients with PXS experience moderate IOP reduction following phacoemulsification, and this effect is correlated with preoperative IOP, aspiration time and infusion fluid used intraoperatively.

Intraocular Pressure Reduction after Phacoemulsification versus Manual Small-Incision Cataract Surgery: A Randomized Controlled Trial

PURPOSE

To compare reduction in intraocular pressure (IOP) and change in anterior chamber angle configuration between eyes undergoing phacoemulsification versus those undergoing manual small-incision cataract surgery (MSICS).

DESIGN

Prospective, randomized, double-masked, parallel assignment clinical trial.

PARTICIPANTS

Five hundred eyes of 500 participants 40 to 70 years of age with normal IOP, gonioscopically open angles, and age-related cataract.

METHODS

Eyes underwent phacoemulsification or MSICS after a 1:1 randomization and allocation code. Best-corrected vision, IOP, comprehensive slit-lamp evaluation, and anterior segment (AS) optical coherence tomography (OCT) were performed at baseline and at 1, 3, and 6 months follow-up.

MAIN OUTCOME MEASURES

Change in IOP (ΔIOP) and AS OCT parameters between baseline and 6 months after surgery.

RESULTS

Six months, similar IOP reduction was observed in eyes undergoing phacoemulsification (ΔIOP = 2.7±2.9 mmHg) and MSICS (ΔIOP = 2.6±2.6 mmHg; P = 0.70). Widening of the angle opening distance (AOD) 500 μm from the scleral spur (median ΔAOD500 = 103 μm; interquartile range = 39-179 μm) was also similar in both groups (P = 0.28). Multivariate linear regression analysis showed that eyes with higher baseline IOP experienced significantly greater reduction in IOP at 6 months (ΔIOP = 0.46-mmHg reduction for every 1-mmHg increment in baseline IOP; 95% confidence interval [CI], 0.4-0.5 mmHg; P < 0.001). After adjusting for covariates, the magnitude of widening of AOD500 was not associated significantly with reduction in IOP (1.33-mmHg reduction for every 1-mm increment in AOD500; P = 0.07). Baseline AOD500 (β = -0.60-mm change/1-mm increment of baseline AOD; 95% CI, -0.67 to -0.53 mm) and anterior chamber depth (β = 0.07-mm change/1-mm increment of baseline anterior chamber depth; 95% CI, 0.04-0.1 mm) were significant predictors of AOD500 widening at 6 months.

CONCLUSIONS

Both phacoemulsification and MSICS led to significant and similar IOP reductions 6 months after surgery, and both surgeries produced similar changes in anterior chamber and angle parameters. Higher baseline IOP was associated with greater IOP reduction; IOP reduction also can be attributed partly to changes in angle and anterior chamber configuration, although these parameters were unable to predict significantly predict IOP drop at 6 months.

Therapeutic ultrasound for glaucoma: clinical use of a low-frequency low-power ultrasound device for lowering intraocular pressure

BACKGROUND

This is a first-in-human study to determine the efficacy and tolerability of a new method of treating glaucoma using a low-power, low-frequency, focused therapeutic ultrasound for glaucoma (TUG) device designed to trigger an inflammatory reaction in the anterior chamber angle and trabecular meshwork to enhance outflow. The use of the device is anticipated for mild or moderate open-angle glaucoma as an enhancement to outflow.

METHODS

In a two-branch clinical trial, a total of 26 primary open-angle glaucoma patients underwent a procedure consisting of the external application of the TUG device. In branch 1, nine of these patients were naïve to pharmaceutical treatment or had been off of medication for over 6 months. In branch 2, 17 patients were treated after a medication washout period. All patients in the study were followed for 12 months.

RESULTS

In branch 1, there was a decrease in intraocular pressure averaging over 20% lasting at least a year in 74% of the eyes with non-normotensive open-angle glaucoma. In branch 2, an average of two visits while on medication provided the comparison intraocular pressure (IOP) to the effect of the TUG treatment after washout. It was seen that the intraocular pressure over the year post-treatment was equal to or better than the pharmaceutical control in close to 80% of measurements.

CONCLUSION

A novel device for lowering intraocular pressure is described with a potential for adding to our armamentarium for treating glaucoma. This is a small cohort study which indicates beneficial trends.

TRIAL REGISTRATION NUMBER

The study was a registered clinical trial, #ISRCTN50904302.

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.

There is insufficient evidence to recommend lens extraction as a treatment for primary open-angle glaucoma: an evidence-based perspective

Cataract extraction in primary open-angle glaucoma has not been thought to provide a clinically useful or predictable decrease in IOP. This concept has now been challenged, with the opposite belief being promulgated: namely, that lens exchange should be considered as treatment for glaucoma. This revelation could bring a significant change in the glaucoma treatment paradigm. There are no randomised controlled trials to guide the role of lens extraction in primary open-angle glaucoma. The available evidence suggests at most a modest reduction in IOP from cataract extraction - greater in the presence of pseudoexfoliation - which is likely to be of marginal benefit, and only in milder forms of open-angle glaucoma. There is currently no evidence of any quality to suggest that lens extraction routinely represents a clinically useful treatment for primary open-angle glaucoma.