Ultrasound biomicroscopy. II. Intraobserver and interobserver reproducibility of measurements

Evaluation of intra- and interobserver reliability and image reproducibility to assess usefulness of high-resolution ultrasonography for measurement of anterior segment structures of canine eyes

OBJECTIVE

To evaluate the usefulness of high-resolution ultrasonography (HRUS) for measurements of anterior segment structures in canine eyes.

ANIMALS

4 clinically normal Beagles.

PROCEDURE

Images were obtained from 8 eyes with a handheld 20-MHz transducer. Eleven anterior segment structures on each image were measured 5 times by 2 independent observers. Coefficients of variation (CVs) for measurements were used to assess intraobserver reliability. Interobserver reliability was assessed by comparing measurements obtained by the 2 observers from the same images. Five images were sequentially obtained from 2 locations (ie, superior and temporal) to evaluate image reproducibility. Anterior segment structures were measured once on each image; image reproducibility was assessed by use of the CV for each parameter measured. Imaging location was assessed by comparison of CV for measurements from each location.

RESULTS

CVs were < 10% for observer A for all measurements except the ciliary cleft area (11.63%). The CVs were > 10% for observer B for measurements of the angle recess area (18.51%) and ciliary cleft width (17.44%) and area (16.01%). Significant differences in measurements between observers were found for 5 of 11 anterior segment structures. Imaging the superior aspect of the globe provided the most reproducible images, although image reproducibility was still somewhat variable, with the highest and lowest CVs for measurements of 33.01% and 11.32%, respectively, in the superior position.

CONCLUSIONS AND CLINICAL RELEVANCE

High-resolution ultrasound images can be used to reliably measure various anterior segment structures. Clinically relevant findings in the anterior segment of canine eyes may be detectable by use of HRUS.

Angle closure: classification, concepts, and the role of ultrasound biomicroscopy in diagnosis and treatment

The angle closure glaucomas are a diverse group of disorders characterized by mechanical blockage of the trabecular meshwork by the peripheral iris leading to elevated intraocular pressure and glaucoma. Understanding the pathophysiologic mechanisms underlying these disorders is essential for both diagnosis and management. This review covers the anatomy, etiology, classification, and therapy of the various angle closure glaucomas and the role that ultrasound biomicroscopy has played in helping us understand these diseases.

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.

Ultrasound biomicroscopic study of anterior segment changes after phacoemulsification and foldable intraocular lens implantation

PURPOSE

To report quantitative changes in the anterior segment configuration after clear corneal incision phacoemulsification and foldable intraocular lens (IOL) implantation by means of ultrasound biomicroscopy (UBM).

DESIGN

Prospective, nonrandomized, comparative (self-controlled) trial.

PARTICIPANTS

Twenty-one eyes of 19 patients with senile or presenile cataracts and no other ocular illness.

METHODS

Patients were examined with UBM before and 1 and 3 months after surgery. At each UBM examination, axial images of the anterior chamber and radial sections of the angle at the superior, lateral, inferior, and medial quadrants were obtained.

MAIN OUTCOME MEASURES

Central anterior chamber depth (ACD), iris-lens contact distance, iris-lens angle (ILA), angle opening distance at points 250 (AOD250) and 500 microm (AOD500) from the scleral spur, trabecular-iris angle (TIA), iris thickness 500 microm from the scleral spur (IT), trabecular-ciliary process distance (TCPD), iris-ciliary process distance (ICPD), iris-zonule distance, iris-sclera angle (ISA), and ciliary process-sclera angle (CPSA). After surgery, central anterior chamber depth was also measured from the cornea to the IOL (ACD) and from the cornea to the pupillary plane (ACD2). Each variable was measured twice in different days by the same observer.

RESULTS

The variables IT, TCPD, ICPD, IZD, and CPSA did not significantly change after surgery (P > 0.01). Central anterior chamber depth increased approximately 30% after surgery (approximately 850 microm; P < 0.001), by both measurement methods used (ACD x ACD and ACD x ACD2). Anterior chamber angle significantly increased, by approximately 50% of the initial value, by the three measurement methods used: AOD250 (P <or= 0.002), AOD500 (P < 0.001), and TIA (P <or= 0.003). The ISA increased by approximately 10 degrees (30%) after surgery (P < 0.001). The ILCD and ILA did not exist after surgery, except in two eyes.

CONCLUSIONS

After phacoemulsification and foldable IOL implantation, UBM revealed that the iris diaphragm shifted backward, deepening the anterior chamber by approximately 850 microm and widening its angle by approximately 10 degrees. These findings may be of clinical significance in eyes with angle-closure glaucoma or with occludable angles.

Comparison of central corneal thickness measurements by specular microscopy, ultrasound pachymetry, and ultrasound biomicroscopy

PURPOSE

To compare the reproducibility and mean values of central corneal thickness (CCT) obtained by specular microscopy, ultrasound pachymetry, and ultrasound biomicroscopy (UBM).

SETTING

Department of Ophthalmology, University of Toronto, Toronto, Ontario, Canada.

METHODS

Thirty-one healthy volunteers were recruited for a sample size of 62 eyes. All subjects had pachymetric measurements by specular microscopy, ultrasound pachymetry, and UBM. Three separate measurements meeting criteria for centrality and perpendicularity were recorded for each eye.

RESULTS

The mean CCT by specular microscopy was 572 microm (95% confidence interval (CI), 566-578 microm), which was significantly greater than 550 microm (95% CI, 545-556 microm) (P<.001) and 555 microm (95% CI, 550-560 microm) (P<.001) by ultrasound pachymetry and UBM, respectively. The mean standard deviation (SD) of repeated measurements by specular microscopy was 7.82 microm, which was significantly greater than the mean SDs of 4.14 microm (P<.001) and 3.90 microm (P<.001) by ultrasound pachymetry and UBM, respectively. There was no statistically significant difference between the mean SDs by ultrasound pachymetry and UBM (P=.156).

CONCLUSIONS

Although the CCT measurements by specular microscopy were significantly less reproducible than those by ultrasound pachymetry and UBM, the error levels were clinically acceptable. Both ultrasound pachymetry and UBM produced similar CCT measurements, which were significantly less than those generated by specular microscopy. One should be aware of the advantages and limitations of each machine and of possible differences in the CCT measurements by optical and ultrasound pachymetry.

Reliability of Corneal Thickness and Endothelial Cell Density Measures

PURPOSE

We evaluated the reliability and agreement between the Orbscan, an ultrasonic pachymeter (Humphrey 855), and the Konan SP 9000-LC in terms of central corneal thickness. The Konan was also used to study the reliability and agreement between endothelial cell density measures.

METHODS

Twenty-five normal subjects were examined on two occasions (mean separation = 9 +/- 5 days) by a single examiner using all three instruments for central corneal pachymetry. The Konan Center Method and a manual counting method were performed by two examiners to determine endothelial cell density. Reliability and agreement were assessed by calculating the 95% limits of agreement (LoA) and intraclass correlation coefficients (ICC).

RESULTS

For corneal pachymetry test-retest reliability, the 95% limits of agreement were -20 to +17 microm for the ultrasound, -27 to +22 microm for the Konan, and -13 to +13 microm for the Orbscan. There was fair-to-good agreement between the pachymeters (intraclass correlation coefficients range = 0.85 to 0.92). For endothelial cell density test-retest reliability, the 95% limits of agreement for the Konan Center Method was -498 to +530, and -482 to +333 cells/mm2 for examiners 1 and 2, respectively. The test-retest 95% limits of agreement for the manual overlaid grid method was -355 to +355, and -535 to +670 cells/mm2 for examiners 1 and 2, respectively.

CONCLUSIONS

The reliability and agreement of the Orbscan and Konan corneal pachymeters was good, although the reliability of the Konan for estimating endothelial cell density was fair, at best.

The efficacy of latanoprost is independent of the width of the ciliary body face

PURPOSE

To assess the relation between the intraocular pressure-lowering efficacy of latanoprost 0.005% and the area of the ciliary body face exposed to the anterior chamber as assessed by ultrasound biomicroscopy.

PATIENTS AND METHODS

Untreated, latanoprost-naive patients with ocular hypertension or open-angle glaucoma were enrolled in this prospective clinical trial. A radial, perpendicular ultrasound biomicroscopy image at the 6-o'clock position detailing Schwalbe line, scleral spur, and iris insertion was obtained. The distances between these structures were then measured and their relations to the intraocular pressure-lowering effect of latanoprost at 1, 2, 3, and 6 months were analyzed.

RESULTS

Fifty-four eyes (54 patients) were enrolled. The mean age of participants was 60.2 +/- 13.9 years, and mean pretreatment intraocular pressure was 26.4 +/- 3.8 mm Hg. The mean intraocular pressure reduction from baseline was 7.1 mm Hg (26.9%), 7.3 (27.7%), 7.8 (29.5%), and 7.7 (29.2%) at 1, 2, 3 and 6 months, respectively. The mean distance between the scleral spur and the iris insertion was 0.14 +/- 0.08 mm (range, 0.04-0.33 mm). There was a significant correlation between intraocular pressure reduction at 1 month and trabecular meshwork height, suggesting that intraocular pressure reduction was associated with increasing trabecular meshwork height (P < 0.05). No other correlation could be found regarding intraocular pressure reduction.

CONCLUSION

Although latanoprost lowers intraocular pressure by enhancing uveoscleral outflow, its efficacy is independent of the height of the ciliary face.

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.