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ORIGINAL ARTICLE
Year : 2006  |  Volume : 54  |  Issue : 3  |  Page : 159-163

Evaluation of the anterior chamber angle in Asian Indian eyes by ultrasound biomicroscopy and gonioscopy


Department of Ophthalmology, Postgraduate Institute of Medical Education and Research, Chandigarh - 160 012, India

Correspondence Address:
Sushmita Kaushik
Department of Ophthalmology, Postgraduate Institute of Medical Education and Research, Chandigarh - 160 012
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0301-4738.27065

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  Abstract 

Purpose: To compare the ultrasound biomicroscopic measurement of the anterior chamber angle in Asian Indian eyes, with the angle width estimated by gonioscopy.
Materials and Methods:
Participants: Patients with open and closed angles attending a glaucoma clinic were recruited for the study.
Observation Procedures:
Temporal quadrants of the angles of patients were categorized by gonioscopy as Grade 0 to Grade 4, using Shaffer's classification. These angles were quantified by ultrasound biomicroscopy (UBM) using the following biometric characteristics: Angle opening distance at 250 µ (AOD 250) and 500 µ (AOD 500) from the scleral spur and trabecular meshwork-ciliary process distance (TCPD). The angles were further segregated as "narrow angles" (Schaffer's Grade 2 or less) and "open angles" (Schaffer's Grade 3 and 4).
Main Outcome Measures:
The UBM measurements were computed in each case and analyzed in relation to the gonioscopic angle evaluation.
Results:
One hundred and sixty three eyes of 163 patients were analyzed. One hundred and six eyes had "narrow angles" and 57 eyes had "open angles" on gonioscopy. There was a significant difference among the mean UBM measurements of each angle grade estimated by gonioscopy ( P < 0.001). The Pearson correlation coefficient between all UBM parameters and gonioscopy grades was significant at the 0.01 level. The mean AOD 250, AOD 500 and TCPD in narrow angles were 58±49 µ, 102±84 µ and 653±124 respectively, while it was 176±47 µ, 291±62 µ and 883±94 µ in eyes with open angles ( P < 0.001) respectively.
Conclusions:
The angle width estimated by gonioscopy correlated significantly with the angle dimensions measured by UBM. Gonioscopy, though a subjective test, is a reliable method for estimation of the angle width.

Keywords: Angles, gonioscopy, ultrasound biomicroscopy.


How to cite this article:
Kaushik S, Jain R, Pandav SS, Gupta A. Evaluation of the anterior chamber angle in Asian Indian eyes by ultrasound biomicroscopy and gonioscopy. Indian J Ophthalmol 2006;54:159-63

How to cite this URL:
Kaushik S, Jain R, Pandav SS, Gupta A. Evaluation of the anterior chamber angle in Asian Indian eyes by ultrasound biomicroscopy and gonioscopy. Indian J Ophthalmol [serial online] 2006 [cited 2020 Feb 19];54:159-63. Available from: http://www.ijo.in/text.asp?2006/54/3/159/27065



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Recent literature on primary angle closure glaucoma (PACG) has renewed interest in this entity as a major cause of blindness worldwide.[1] Gonioscopy has been the mainstay of diagnosing narrow or occludable angles. However, the technique is limited by its inability to measure anterior segment structures in the far periphery of the angle. The angle opening in degrees is difficult to define, because of anatomic variations in angle and iris configuration. Being a subjective evaluation, gonioscopy is also limited by inter-observer variation in the angle assessment and diagnosis.

The advent of the ultrasound biomicroscope (UBM) has made high resolution imaging of the anterior segment possible,[2],[3] permitting reproducible imaging of the cross-sectional anterior chamber angle anatomy. Pavlin et al .[3] have described and quantified values for the anterior segment anatomy in normal and glaucomatous Caucasian eyes. The aim of the study was to correlate the angles assessed and categorized by gonioscopy, with the quantified value of angles by the UBM, in Indian eyes.


  Materials and Methods Top


The study was carried out at a tertiary care referral institute. Patients with open and narrow angles were recruited from the Glaucoma Clinic of the Ophthalmology Department, Postgraduate Institute of Medical Education and Research, Chandigarh, India. Those with open angles were either ocular hypertensives or had primary open angle glaucoma. Those with narrow angles were of the entire spectrum of primary angle closure such as primary angle closure suspects (PACS), primary angle closure (PAC) and PACG. Patients with prior history of laser treatment, intraocular surgery, blunt ocular trauma, secondary glaucoma or those on Pilocarpine drops, were excluded from the study.

Informed consent was obtained from all participants and the study was accorded ethical clearance by the institute ethics committee. The study adhered to the principles of the Declaration of Helsinki.

All patients underwent baseline evaluation including best corrected visual acuity (BCVA), intraocular pressure (IOP), clinical assessment of central and peripheral anterior chamber depth, gonioscopy and stereoscopic optic nerve head evaluation by slit lamp biomicroscopy.

For the sake of uniformity, the gonioscopy findings and UBM measurements of the temporal quadrants of all angles were analyzed.

Gonioscopy

Gonioscopy was performed in a semi-darkened room with minimum-possible slit lamp illumination, using a Sussman four-mirror goniolens. Care was taken to ensure that the slit-lamp beam did not fall across the pupil, so that there was no artificial opening of the angle. The angles were graded numerically according to Schaffer's[4] classification.

UBM

All examinations of this study were performed with the UBM Model 840, Paradigm Medical Industries Inc, with a 50 MHz transducer probe. The image has a lateral and axial physical resolution of approximately 50 µ and 25 µ respectively and a penetration depth of 4-5 mm.[2] After instilling 4% lignocaine drops in the eye, a plastic eyecup was used to gently part the lids and retain a layer of 2% methylcellulose coupling agent with care, so as not to exert pressure on the globe. Scanning was performed in standard lighting conditions for all patients, which was a semi-darkened room similar to that where the gonioscopy was performed. The patient was in the supine position and the probe was manually moved perpendicular to the structure to be scanned. Fixation and accommodation was held constant by having the patient fixate with the fellow eye on a target on the ceiling.

The ciliary body and sclera can be readily differentiated on the UBM, owing to their different echogenic properties. The scleral spur was identified as the anterior-most point of the demarcation line between the ciliary body and sclera, visualized on a longitudinal scan across the limbus.

The operator performing the UBM was masked to the gonioscopic finding of the patients. The following parameters of angles in the temporal quadrant were obtained using a special caliper included in the instrument software package and manipulated by the examiner [Figure - 1].

1. The angle-opening-distance (AOD): This was defined as the distance from the corneal endothelium to the anterior iris, perpendicular to a line drawn along the trabecular meshwork (TM), at a given distance from the scleral spur. This was measured at 250 µ (AOD 250), which would consistently fall on the trabecular meshwork and 500 µ (AOD 500) from the scleral spur, which would measure the angle opening anterior to the trabecular meshwork.

2. The Trabecular-ciliary process distance (TCPD): This was measured from a point on the trabecular meshwork, 500µ anterior to the scleral spur, extended perpendicularly through the iris to the ciliary process. The TCPD defines the port through which the iris must traverse and has implications as to the potential maximal angle opening.

The AOD 250, AOD 500 and TCPD were noted in each case. Three standard axial scans were obtained at the temporal quadrant and the mean values of the three readings were computed in each case. The UBM measurements were compared with the gonioscopy findings and were statistically analyzed using SPSS® Version 10.0 for Windows (SPSS Inc, Chicago, IL). The Independent Samples t-test assuming unequal variance was used to compare mean values of UBM parameters among angles categorized as Grade 0 to Grade 4 by gonioscopy. The Pearson Correlation was used to analyze the relation between the gonioscopic estimation of the angle width and the UBM quantification of the same angle grade. Results were considered significant at a P -value less than 0.05.


  Results Top


163 eyes of 163 consecutive patients meeting the eligibility criteria were included for analysis. There were 92 women and 71men. Patient demography is presented in [Table - 1]. In the narrow angle group, the mean age of women was less than men, but the difference did not reach statistical significance. The temporal angles of 34 eyes were categorized by gonioscopy as Grade 0, 38 angles were Grade 1, 34 angles were Grade 2, 42 angles were Grade 3 and 15 eyes had Grade 4 angles. Angles graded as 2 or less were grouped as "narrow angles" (106 eyes; [Figure - 2]) and Grade 3 and Grade 4 angles were grouped together as "open angles" (57 eyes; [Figure - 3]). The mean refractive error (spherical equivalent) of the narrow angle group was + 0.6 ± 0.6 D, while it was - 0.21 ± 1.35 D in the open angle group.

The mean UBM parameters between the two groups differed significantly [Table - 1].

The mean UBM values of the AOD 250, AOD 500 and TCPD compared to the gonioscopy grading, is depicted in [Table - 2] and [Figure - 4]. UBM measurements in relation to the gonioscopic estimation of the angle width were determined by the Pearson Correlation test. The correlation coefficient of AOD 250, AOD 500 and TCPD versus the gonioscopic angle grading was 0.917, 0.907 and 0.744 respectively, which was significant at the 0.01 level.

The UBM measurements in all groups were compared to each other using the Independent Samples t-test, assuming that variances were not equal. The statistical analyses are tabulated in [Table - 3]. All three UBM parameters differed significantly among all angle grades estimated by gonioscopy.


  Discussion Top


Gonioscopy remains the mainstay of diagnosing narrow angles. The Shaffer[4] grading system is commonly used to assess the risk of angle closure. The approximate angle is recorded in degrees and grade 2 is considered the cut-off between open and narrow angles.[5] However, being a subjective examination, it provides only an estimation of the angle width, which is a qualitative assessment.[6] There has also been disagreement between glaucoma subspecialists, as to the grading of the angle and its occludability.[7] Recognizing these fallacies, Congdon et al .[8] designed a system of biometric gonioscopy in an attempt to improve the inter-observer reliability and to more clearly define the screening cut-off criteria for the angle.

The UBM has enabled clinicians to quantitatively assess the iris curvature and degree of angle opening, since it images a cross-section of angle structures similar to that of a low power microscope section. One can determine the state of closure of the entire angle, even when it cannot be visualized by gonioscopy.

The general configuration of the iris in normal patients is planar or has a gentle anterior convexity.[9] A relative pupillary block results in an anteriorly bowed iris, with a corresponding decrease in angle opening. The AOD 250 is a measure of the angle opening at the level of the posterior trabecular meshwork, while the AOD 500 is a measure of the angle opening at the level of the anterior Schwalbe's line. The AOD measured by the UBM may thus reflect the amount of relative pupillary block in eyes with narrow angles.[10]

The TCPD, as reported by Pavlin et al .,[3] is a particularly important parameter, since it defines the space available for the iris between the trabecular meshwork and ciliary process and is a typical feature in an individual eye. The TCPD is the sum of three segments: the angle opening 500 µ from the scleral spur; the thickness of the iris at that point and the width of the ciliary sulcus. An anteriorly placed ciliary process or a thick iris can reduce the peripheral anterior chamber depth and make it susceptible to occlusion.

There are two published reports of UBM measurements in Indian eyes. In the study by Garudadri et al .,[11] the method of estimating the AOD 500 and TCPD was different from the one described by Pavlin et al .[3] and used in the present study and is therefore not comparable. Narayanaswamy et al .[12] found a tendency to overestimate the angle width by gonioscopy compared to the UBM.

In our study, UBM measurements were significantly correlated with the gonioscopic assessment of the angle width. All UBM parameters differed significantly among the different grades of angles categorized by gonioscopy. This indicates that gonioscopy, despite being a subjective evaluation, appears to provide accurate information with regard to the angle width estimation.

Angle closure is now being recognized as a major problem in India. The Andhra Pradesh eye disease study[13] reported that 2.21% of the population > 40. 0 years, had occludable angles at risk of angle closure and 1.08% had manifest PACG, a large proportion of whom were undiagnosed and untreated. In the Vellore eye study,[14] manifest PACG was as high as 4.3%. Since visual loss resulting from PACG is potentially preventable if peripheral iridotomy is performed at an early stage, strategies for the early detection of PAC could reduce the risk of blindness resulting from PACG.

Inspite of the advent of the UBM for quantitative estimation of the anterior chamber angle, gonioscopy remains the reference standard for differentiating appositional from synechial angle closure and quantifying the extent of peripheral anterior synechiae, in addition to characterizing the anatomic appearance of the anterior chamber angle. It is appropriate for use in Asian countries, where the prevalence of angle closure glaucoma is highest and access to quantitative methods like the UBM is limited. Widespread and mandatory use of gonioscopy would probably help towards reducing the morbidity from PACG by earlier detection and timely management of occludable angles. Gonioscopy appears to be equally effective in grading the anterior chamber angle as compared to UBM grading in Asian Indian eyes[15].

 
  References Top

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Quigley HA. Number of people with glaucoma worldwide. Br J Ophthalmol 1996;80:389-93.  Back to cited text no. 1
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Pavlin CJ, Harasiewicz K, Sherar MD, Foster S. Clinical use of Ultrasound Biomicroscopy. Ophthalmol 1991;98:287-95.  Back to cited text no. 2
    
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Pavlin CJ, Harasiewicz K, Eng P, Foster FS. Ultrasound biomicroscopy of anterior segment in normal and glaucomatous eyes. Am J Ophthalmol 1992; 113:381-9.  Back to cited text no. 3
    
4.
Shaffer RN. Gonioscopy, Ophthalmoscopy and Perimetry. Trans Am Acad Ophthalmol Otolaryngol 1960;64:112-6  Back to cited text no. 4
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Hoskins HD, Kass MA. Becker-Shaffer's diagnosis and therapy of the Glaucomas 6th Ed, Mosby; St. Louis: 1989. p. 106-16.  Back to cited text no. 5
    
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Ishikawa H, Esaki K, Liebmann JM, Uji Y, Ritch R. Ultrasound Biomicroscopy dark room provocative testing: A quantitative method for estimating anterior chamber width. Jpn J Ophthalmol 1999;43:536-34.  Back to cited text no. 6
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Wilensky J. Gonioscopy. Invest Ophthalmol Vis Sci 1978;17:144.  Back to cited text no. 7
    
8.
Congdon NG, Spaeth GL, Augsburger J, Klancnik J Jr, Patel K, Hunter DG. A proposed simple method for measurement in the anterior chamber angle: Biometric gonioscopy. Ophthalmology 1999;106:2161-7.  Back to cited text no. 8
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Pavlin CJ, Harasiewicz K, Foster FS. An Ultrasound Biomicroscopic dark-room provocative test. Ophthal Surg 1995;26:253-5.  Back to cited text no. 9
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Lowe RF. Etiology of the anatomical basis for primary angle-closure glaucoma. Biometric comparisons between normal eye sand eyes with primary angle-closure glaucoma. Br J Ophthalmol 1970; 54:161-9.  Back to cited text no. 10
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Garudadri CS, Chelerkar V, Nutheti R. An ultrasound biomicroscopic study of the anterior segment in Indian eyes with primary angle-closure glaucoma. J Glaucoma 2002;11:502-7.  Back to cited text no. 11
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Narayanaswamy A, Vijaya L, Shantha B, Baskaran M, Sathidevi AV, Baluswamy S. Anterior chamber angle assessment using gonioscopy and ultrasound biomicroscopy. Jpn J Ophthalmol 2004;48:44-9.  Back to cited text no. 12
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Dandona L, Dandona R, Mandal P, Srinivas M, John RK, McCarty CA, et al . Angle-closure glaucoma in an urban population in southern India. The Andhra Pradesh eye disease study. Ophthalmology 2000;107:1710-6.  Back to cited text no. 13
    
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Jacob A, Thomas R, Koshi SP, Braganza A, Muliyil J. Prevalence of primary glaucoma in an urban south Indian population. Indian J Ophthalmol 1998;46:81-6.   Back to cited text no. 14
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Marchini G, Pagliarusco A, Toscano A, Tosi R, Brunelli C, Bonomi L. Ultrasound Biomicroscopic and conventional ultrasonographic study of ocular dimensions in primary angle-closure glaucoma. Ophthalmology 1998;105:2091-8.   Back to cited text no. 15
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    Figures

  [Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4]
 
 
    Tables

  [Table - 1], [Table - 2], [Table - 3], [Table - 4]


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