Ultrasound biomicroscopic measurement of development of anterior chamber angle

The correlation of anterior segment structures in primary congenital glaucoma by ultrasound biomicroscopy with disease severity and surgical outcomes

PURPOSE

To evaluate the anterior segment structures using ultrasound biomicroscopy (UBM) in primary congenital glaucoma (PCG) and explore their correlation with disease severity and surgical outcomes.

METHODS

Clinical information of PCG patients who underwent UBM prior to their first glaucoma surgeries from September 2014 to March 2021 were reviewed. The study included 214 UBM images of 154 PCG eyes and 60 fellow unaffected eyes. Anterior segment characteristics were analyzed. UBM parameters, including the iris thickness (IT) at variant distances from the pupil edge and iris root, anterior chamber depth (ACD), and pupil diameter (PD), were compared between two groups and their relationship with clinical factors and surgical outcomes were analyzed in PCG eyes.

RESULTS

PCG eyes had unclear scleral spur, thin iris, wide anterior chamber angle, deep anterior chamber, rarefied ciliary body, elongated ciliary processes, and abnormal anterior iris insertion. ITs were thinner, ACD was deeper, and PD was larger in PCG eyes than fellow unaffected eyes (all P < 0.001). In PCG eyes, thinner ITs correlated with bilateral involvement and earlier age at presentation, and larger PD correlated with earlier age at presentation (P = 0.030) and higher intraocular pressure (P < 0.001). Thinner IT2 (P = 0.046) and larger PD (P = 0.049) were identified as risk factors for surgical failure.

CONCLUSION

UBM is a powerful technique to exam anterior segment structures in PCG. The anatomical features are associated with disease severity and surgical outcomes, providing essential clinical insights.

Primary congenital glaucoma: An iridotrabeculodysgenesis?

PURPOSE

To analyze primary congenital glaucoma (PCG) anterior chamber and angle anomalies over 360° as possible biomarkers of severity and prognosis.

METHODS

A cross-sectional observational study was conducted analyzing anterior segment anomalies of PCG patients over 4 years of age who underwent trabeculectomy combined with trabeculotomy and age-matched controls using anterior segment optical coherence tomography (ASOCT), CASIA-2. Anterior iridotrabecular adhesions or anterior iris insertion was identified and quantified from the scleral spur using the iridotrabecular contact (ITC) index parameter as a surrogate.

RESULTS

There was a variable but significantly increased anterior iridotrabecular adhesion on ITC index, ITC area, corneal volume, anterior chamber volume, iris volume, anterior chamber depth, and small/absent trabecular meshwork in PCG eyes compared to control eyes. In PCG eyes, anterior iridotrabecular adhesion had a positive correlation with pre-operative central corneal thickness (CCT) (r = 0.53, P = 0.02), review iris thickness (r = 0.4, P = 0.04), and ITC area (r = 0.85, P < 0.001). Review iris thickness had a negative correlation with pre-operative vertical cup-disc ratio (r = -0.51, P = 0.008). Iris hypoplasia with fewer or absent folds, collarette, pupillary ruff, and pupillary ruff to collarette distance was significantly different from controls.

CONCLUSION

ASOCT in PCG eyes has shown that they have variable anterior iridotrabecular tissue adhesions, anomalous tissue/membranes in the angle, and iris hypoplasia correlating with pre-operative cup-disc ratio. These features could be used as gonioscopic and clinical biomarkers to assess the severity and prognosis of the disease. The presence of abnormal iris morphology and iridotrabecular tissue anomalies in PCG suggests that it is more than just isolated trabeculodysgenesis and is probably best considered as part of the anterior segment dysgenesis spectrum.

Refractive development I: Biometric changes during emmetropisation

PURPOSE

Although there are many reports on ocular growth, these data are often fragmented into separate parameters or for limited age ranges. This work intends to create an overview of normal eye growth (i.e., in absence of myopisation) for the period before birth until 18 years of age.

METHODS

The data for this analysis were taken from a search of six literature databases using keywords such as "[Parameter] & [age group]", with [Parameter] the ocular parameter under study and [age group] an indication of age. This yielded 34,409 references that, after screening of title, abstract and text, left 294 references with usable data. Where possible, additional parameters were calculated, such as the Bennett crystalline lens power, whole eye power and axial power.

RESULTS

There were 3422 average values for 17 parameters, calculated over a combined total of 679,398 individually measured or calculated values. The age-related change in refractive error was best fitted by a sum of four exponentials (r²  = 0.58), while all other biometric parameters could be fitted well by a sum of two exponentials and a linear term ('bi-exponential function'; r² range: 0.64-0.99). The first exponential of the bi-exponential fits typically reached 95% of its end value before 18 months, suggesting that these reached genetically pre-programmed passive growth. The second exponentials reached this point between 4 years of age for the anterior curvature and well past adulthood for most lenticular dimensions, suggesting that this part represents the active control underlying emmetropisation. The ocular components each have different growth rates, but growth rate changes occur simultaneously at first and then act independently after birth.

CONCLUSIONS

Most biometric parameters grow according to a bi-exponential pattern associated with passive and actively modulated eye growth. This may form an interesting reference to understand myopisation.

Distribution of anterior chamber angle measurements in South African young adults: an optical coherence tomography study

PURPOSE

Assessment of anterior chamber angle (ACA) variables is important to screen, diagnose and monitor ocular anomalies. Even though data on ACA variables, such as angle-opening distance taken at 500 µm (AOD500) and trabecular-iris angle (TIA), are available in the literature, limited information is available about these variables in African sub-populations. The purpose of this study is to describe the distribution of ACA measurements (AOD500 and TIA) in a South African young adult population.

METHODS

In this cross-sectional study, 700 young adults were recruited from a university student population using two-stage random sampling. The Optovue iVue 100 optical coherence tomographer was used to measure the ACA variables. The distribution of the AOD500 and TIA measurements was analysed using descriptive and inferential statistics. Data from only the right eyes were analysed because the ACA measurements in the two eyes showed high levels of interocular symmetry.

RESULTS

The measurements for the nasal and temporal ACAs were asymmetrically distributed (p < 0.001). The median AOD500 measurements in the nasal and temporal angles were 539 µm and 542 µm, respectively. The median TIA measurements were similar (~ 36°) in the two horizontal angles. The temporal ACA measurements were slightly higher than the nasal ACA measurements. Females had higher median ACA measurements than males (p ≥ 0.029).

CONCLUSION

The ACA measurements in South African young adults resemble non-Gaussian curves. The ACA measurements are different from that reported in other sub-populations worldwide and most participants had ACA measurements associated with non-occludable ACAs.

Anterior Chamber Measurements in Healthy Children: A Cross-Sectional Study Using Optical Coherence Tomography

Purpose

To establish anterior chamber measurements in children and investigate the influence of demographic factors on anterior chamber development.

Methods

Handheld optical coherence tomography was used to scan the anterior chamber of participants' eyes, without sedation. ImageJ was used to generate quantitative anterior chamber measurements, including central corneal thickness (CCT), anterior chamber width, trabecular meshwork length (TML), Schwalbe's line-angle opening distance (SL-AOD), and trabecular iris surface area (SL-TISA). The average anterior chamber measurements per age group, with 95% prediction intervals, were estimated using fractional polynomial modeling. Mixed regression models were used to evaluate the influence of age, gender, eye, angle, and refractive error variation on anterior chamber measurements.

Results

Scans from 223 healthy children (2 days to 15 years of age) and 59 adults (16 to 47 years of age) were included. The anterior chamber width, TML, Schwalbe's line-angle opening distance, and Schwalbe's line-trabecular iris surface area significantly increased, whereas CCT decreased with aging (all P < 0.001). The anterior chamber has a rapid phase of development during the first 18 months of age and reaches maturity by the age of 5 years. Girls have significantly smaller anterior chambers compared with boys (all P < 0.001). There was no difference between right and left eye development (all P > 0.05). The temporal TML development was significantly greater than the nasal TML (P < 0.05). CCT development was negatively correlated with refractive power.

Conclusions

This novel, non-invasive study describes the postnatal development of anterior chamber in newborn children.

Translational Relevance

Our established quantitative measurements have potential clinical use in understanding anterior segment diseases.

A systematic review of ultrasound biomicroscopy use in pediatric ophthalmology

Ultrasound biomicroscopy (UBM) is the only available option for noninvasive, high-resolution imaging of the intricate iridociliary complex, and for anterior segment imaging with corneal haze or opacity. While these unique features render UBM essential for specific types of trauma, congenital anomalies, and anterior segment tumors, UBM imaging has found clinical utility in a broad spectrum of diseases for structural assessments not limited to the anterior intraocular anatomy, but also for eyelid and orbit anatomy. This imaging tool has a very specific niche in the pediatric population where anterior segment disease can be accompanied by corneal opacity or clouding, and anomalies posterior to the iris may be present. Pediatric patients present additional diagnostic challenges. They are often unable to offer detailed histories or fully cooperate with examination, thus amplifying the need for high-resolution imaging. This purpose of this systematic review is to identify and synthesize the body of literature involving use of UBM to describe, evaluate, diagnose, or optimize treatment of pediatric ocular disease. The collated peer-reviewed research details the utility of this imaging modality, clarifies the structures and diseases most relevant for this tool, and describes quantitative and qualitative features of UBM imaging among pediatric subjects. This summary will include information about the specific applications available to enhance clinical care for pediatric eye disease.

Disease-related and age-related changes of anterior chamber angle structures in patients with primary congenital glaucoma: An in vivo high-frequency ultrasound biomicroscopy-based study

OBJECTIVES

To provide in vivo measurements of anterior chamber angle structures and their relationship with age as evaluated by high-frequency ultrasound biomicroscopy (UBM) in patients with primary congenital glaucoma (PCG).

METHODS

High-frequency UBM was done for 51 PCG eyes from 40 patients (aged from 3 to 96 months) and 11 unaffected contralateral eyes. Parameters, including the proportion of observable abnormal tissue membrane and Schlemm's canal, the largest cross-sectional area (CSA) of Schlemm's canal (SC), SC meridional diameter, trabecular-iris angle (TIA), trabecular meshwork (TM) thickness, iris thickness, ciliary process length, and corneal limbus thickness were compared between the two groups and their relationship with age was explored in PCG eyes.

RESULTS

Abnormal tissue membrane was detected in 27.5% of PCG eyes and none in unaffected eyes. SC was observed in 73.1% of PGC eyes compared to 100% in unaffected eyes (P<0.001). The largest CSA of SC, SC meridional diameter, iris thickness, and corneal limbus thickness were all significantly smaller in PCG eyes compared to unaffected eyes (all P<0.05). TIA and ciliary process length in unaffected eyes were smaller than PCG eyes (both P<0.05). The largest CSA of SC, TM thickness, iris thickness, and ciliary process length were all significantly correlated to age in PCG eyes (P<0.05).

CONCLUSIONS

The anatomical information evaluated by high-frequency UBM may provide glaucoma specialists a useful tool to aid in understanding the dysgenesis and changes with age of anterior chamber angle in PCG.

Correlation Between Trabeculodysgenesis Assessed by Ultrasound Biomicroscopy and Surgical Outcomes in Primary Congenital Glaucoma

PURPOSE

To evaluate ultrasound biomicroscopy (UBM) characteristics of trabeculodysgenesis and explore its correlation with the outcomes of microcatheter-assisted trabeculotomy (MAT) in eyes with primary congenital glaucoma (PCG).

DESIGN

A prospective, interventional case series.

METHODS

Patients with newly diagnosed PCG were consecutively recruited, and subsequently MAT was tried as their first glaucoma surgery. All participants underwent UBM prior to surgery. The trabeculodysgenesis was classified into 3 types according to the severity of the anterior insertion of iris and ciliary processes (type 1, severe trabeculodysgenesis; type 2, moderate trabeculodysgenesis; type 3, mild trabeculodysgenesis). Surgical success was defined as a postoperative intraocular pressure of ≤ 21 mm Hg with at least a 30% reduction from preoperative intraocular pressure without additional medical or surgical therapy, and with decreased corneal edema, stabilized corneal diameter, and no additional optic nerve damage for at least 6 months after surgery.

RESULTS

MAT was tried on 49 eyes with PCG (33 patients) as the first glaucoma surgery. The ratios of the type of trabeculodysgenesis (type 1: type 2: type 3) were 1:1:1.7 among eyes. In multivariate analysis, age (at the time of operation) (P < .001) and sex (P = .002) were factors associated with the type of trabeculodysgenesis. At 24-month follow-up, type 1 achieved a 57.1% surgical success rate, type 2 achieved 70.5%, and type 3 achieved 95.5% (P = .022). Severe trabeculodysgenesis (P = .014), as well as poorer corneal transparency (P = .037), was associated with worse surgical outcome.

CONCLUSIONS

UBM grading of trabeculodysgenesis in PCG is helpful for MAT prognosis. Combined with preoperative corneal opacity score, it may be used to predict the outcome of MAT surgery.

Anterior segment ultrasound biomicroscopy image analysis using ImageJ software: Intra-observer repeatability and inter-observer agreement

PURPOSE

In this novel study, we demonstrate a standardized imaging and measurement protocol of anterior segment (AS) structures with reliability analysis using ultrasound biomicroscopy (UBM) and ImageJ software.

METHODS

Ten pediatric and young adult patients undergoing examination under anesthesia for AS pathology were imaged using UBM. Four trained observers analyzed 20 images using ImageJ. Forty-five structural parameters were measured. Those that relied on the trabecular-iris angle (TIA) as a reference landmark were labeled TIA-dependent (TD) and all others were labeled non-TIA dependent (NTD). Intra-observer repeatability (IOR) and inter-observer agreement (IOA) of measurements were determined using coefficient of variation (CV) and intra-class correlation (ICC) followed by assessment of Bland-Altman plots (BAP) for each pair of observers, respectively.

RESULTS

For NTD parameters, non-ciliary body (CB) related measurements showed CV range 0.60-16.22% and ICC range 0.84-0.89, whereas CB-related parameters showed CV range 2.86-23.40% and ICC range 0.29-0.92. For TD parameters, parameters < 2 degrees removed from reference showed CV range 0.02-5.40% and ICC range 0.89-1.00, whereas parameters > 1 degree removed showed CV range 0.63-27.44% and ICC range 0.22-1.00. No systematic proportional bias was detected by BAPs.

CONCLUSIONS

Preplaced landmarks yielded good IOR and IOA in quantitative assessment of AS structures that were NTD and non-CB-related or less removed from the reference. CB-related NTD measurements varied greatly in IOR and IOA, indicating protocol modifications or CB qualitative assessments needed to improve accuracy. Variability in TD measurements increased the further removed from the reference, which supports implementation of a reliable reference landmark to minimize variation.

Ultrasound biomicroscopy measurement of Schlemm's canal in pediatric patients with and without glaucoma

PURPOSE

To compare the diameter of Schlemm's canal in children with and without congenital glaucoma as measured in vivo by means of ultrasound biomicroscopy.

METHODS

In this prospective single-center study of pediatric subjects (<18 years of age) the diameter of Schlemm's canal in nonglaucomatous and glaucomatous eyes was compared. An 80 MHz iUltrasound probe (iScience Interventional Inc, Menlo Park, CA) placed near the limbus was used to identify and measure the canal's diameter with special attention to the anterior segment anatomy (especially in subjects with congenital glaucoma).

RESULTS

A total of 20 subjects were included; mean age of subjects without glaucoma was 6.6 ± 6.65 years; of those with glaucoma, 9.4 ± 11.80 months. The mean canal diameter in nonglaucomatous eyes was 142 ± 33.2 μm (range, 90-196 μm); in glaucomatous eyes, 64.9 ± 10.90 μm (P = 0.007). Schlemm's canal could not be identified in 50% of patients with congenital glaucoma. There was a trend toward smaller canal diameter in subjects with no glaucoma <2 years old. Mean canal diameter in nonglaucomatous eyes was 103 ± 8 μm (range, 90-115 μm) in subjects <2 years of age and 161 ± 20 μm (range, 110-196 μm) in subjects >2 years of age (P = 0.0012).

CONCLUSIONS

In our pediatric study cohort the diameter of Schlemm's canal varied by age and presence of glaucoma.

Congenital narrow-angle glaucoma and iris nevi in a neonate with epidermal nevus syndrome

Epidermal nevus syndrome (ENS) is a neurocutaneous disorder characterized by epidermal hamartomas and abnormalities of the brain, eye, and other systems. We report the occurrence of congenital angle closure glaucoma in a patient with epidermal nevus syndrome. Intraoperative use of ultrasound biomicroscopy was essential in making the diagnosis.

Viscocanalostomy versus trabeculotomy ab externo in primary congenital glaucoma: 1-year follow-up of a prospective controlled pilot study

AIM

To study the effectiveness of viscocanalostomy in patients with primary congenital glaucoma of the isolated trabecular dysgenesis category and compare it with trabeculotomy ab externo.

METHODS

Eight patients with bilateral primary congenital glaucoma were enrolled in the study. After establishing the diagnosis, the more severely affected eye was randomly selected to undergo either trabeculotomy ab externo or viscocanalostomy, whereas the second eye underwent the other surgery 2 weeks after the first. The patients were examined on day 1, week 1, week 4 and thereafter every 4 weeks. Intraocular pressure (IOP) and corneal diameter measurements were obtained at week 1, month 6 and at the last reported follow-up. The paired-sample's Student's t test was applied for statistical analysis.

RESULTS

The mean (standard deviation (SD)) follow-up period was 12.5 (1.86) months. Preoperative IOP of eyes undergoing trabeculotomy (34.0 (2.6) mm Hg) and that of eyes undergoing viscocanalostomy (32.3 (4.1) mm Hg) showed no significant difference (p>0.1). A drop in IOP was noted in both groups at week 1, month 6 and at the last follow-up visit (p<0.001). Similarly, a decrease in the postoperative vertical and horizontal corneal diameters was noted in the two study groups.

CONCLUSION

Viscocanalostomy proved to be as effective as trabeculotomy ab externo in lowering IOP. Moreover, it is likely to be a good surgical alternative with a higher long-term success rate in eyes with more aggressive disease.

Anterior segment imaging: ultrasound biomicroscopy

Ultrasound biomicroscopy technology has become an indispensable tool in qualitative and quantitative assessment of the anterior segment. Advances in soft-ware design and algorithms will improve theoretical understanding of the pathophysiology of anterior segment disorders. Future applications of quantitative techniques will yield important information regarding mechanisms of angle closure, improving understanding of the dynamic functions of the iris,accommodation, presbyopia, and other aspects of anterior segment physiology and pathophysiology.

Quantitative assessment of the anterior segment using ultrasound biomicroscopy

The development of ocular imaging devices has progressed rapidly during the past 10 years. Ultrasound biomicroscopy has revolutionized the evaluation of the anterior segment of the eye. The qualitative information gathered using this technology has contributed to our understanding of the pathophysiology of angle-closure glaucoma, pigmentary glaucoma, and a variety of other anterior segment disorders. However, the area of quantitative analysis of ultrasound biomicroscopic images remains largely to be developed. This review describes the role of ultrasound biomicroscopy in the measurement of the anatomic structures and their configurations within the anterior segment. Included are previously published and established methods as well as methods in their early stages of development. Application of quantitative image analysis techniques should yield significant information about mechanisms of appositional angle closure, dynamic functions of the iris, accommodation, and presbyopia.