Agreement Between Gonioscopy and Ultrasound Biomicroscopy in Detecting Iridotrabecular Apposition

Objective  To assess the agreement between findings obtained at dark-room gonioscopy and ultrasound biomicroscopy (UBM) in the diagnosis of iridotrabecular apposition in light and dark conditions.

Methods  We enrolled patients with appositional angle closure at dark-room gonioscopy performed using a 1-mm slitlamp beam that did not cross the pupil. Ultrasound biomicroscopic images were acquired in normal room light and subsequently with all room lights off. Images were evaluated for the presence or absence of iris-cornea contact. The angle opening distance at 500 μm was calculated.

Results  Iridotrabecular apposition in at least 1 angle quadrant was demonstrated in all 18 eyes at dark-room gonioscopy, 17 eyes (94%) at dark-room UBM, and only 10 eyes (56%) at UBM in room light. Of 18 superior angles that were appositionally closed at dark-room gonioscopy, apposition was demonstrated on UBM images in 16 (89%) in a dark room but only 6 (33%) in room light. Angle opening distance was less during dark-room gonioscopy in all but the nasal quadrant.

Conclusion  We found high agreement between gonioscopy and UBM when both are performed in a completely dark room. Our findings support the recommendation that, in routine clinical practice, gonioscopy be performed in a dark room to avoid misdiagnosis of treatable iridotrabecular apposition.

Primary angle-closure glaucoma, a leading cause of blindness worldwide, is potentially preventable if diagnosed before irreversible damage has occurred to the optic nerve or trabecular meshwork. Iridotrabecular apposition can be eliminated using laser peripheral iridotomy and, when necessary, argon laser peripheral iridoplasty.¹ The diagnosis of angle closure requires accurate interpretation of gonioscopic findings. However, gonioscopy is not performed often enough and, when it is, is often not performed accurately, with the correct gonioprism, or under proper lighting conditions.

To emphasize the importance of accurate diagnosis of angle closure in routine clinical practice, we have repeatedly described our technique for indentation gonioscopy, emphasizing that it be performed in a completely dark room using a lens with a smaller diameter than the cornea.^2-5 Miosis resulting from ambient light or slitlamp illumination entering the pupil may open the angle, preventing the observation of iridotrabecular apposition that occurs in the dark. This phenomenon is difficult to demonstrate convincingly, owing to the subjective and semiquantitative nature of gonioscopy. Ultrasound biomicroscopy (UBM) enables objective, quantitative examination of angle anatomy.^6,7 Using ultrasound rather than light waves, UBM provides measurements, in both light and dark, that are unaffected by the measurement process. Several studies have shown that an open angle can narrow or even close when room lights are extinguished.^2,4,8-13

Despite constant admonitions, gonioscopy is usually performed under bright room light conditions or with a bright slitlamp beam, and it is often not emphasized in teaching gonioscopy that findings can differ substantially in light and dark. For example, recent instructional material published by the American Academy of Ophthalmology^14,15 neither recommends nor considers the implications of lighting conditions during gonioscopy.

To our knowledge, previous studies have not addressed the concurrence of dark-room gonioscopy and UBM in light and dark conditions in diagnosing iridotrabecular apposition. Assessment of this relationship was the primary purpose of the present study. We sought specifically to estimate the chance of missing a diagnosis of iridotrabecular apposition when gonioscopy is performed in light vs dark-room conditions.

The study protocol was approved by the Institutional Review Board for Human Research of the New York Eye and Ear Infirmary, New York, and informed consent was obtained from all participants. Consecutive participants underwent a complete eye examination including slitlamp biomicroscopy and intraocular pressure measurement. Dark-room gonioscopy was then performed by a single examiner (R.R.) in a completely dark room with the patient sitting, using a 4-mirror Zeiss-type gonioprism and a 1-mm light beam. The light beam did not cross the pupillary border; thus, a miotic response was avoided. When a convex iris prevented observation of the angle, the patient was requested to look in the direction of the mirror, thereby bringing the angle into view. If the posterior pigmented meshwork was not seen, corneal indentation was performed with the gonioprism. If the angle widened to expose the pigmented meshwork or more posterior landmarks, appositional angle closure was diagnosed and the patient was enrolled in the study. This was repeated for each of the superior, inferior, nasal, and temporal angle quadrants. If indentation did not bring about widening of a closed angle, synechial angle closure was diagnosed and the patient was excluded. Also excluded were patients with a history of trauma or use of any topical or systemic medication affecting the drainage angle configuration, patients with iridociliary cysts or uveitis, and patients who had undergone previous incisional or laser surgery. If both eyes in the same patient were eligible, 1 eye was randomly selected for inclusion in the study.

Enrolled patients underwent imaging with an ultrasound biomicroscope (model P40; Paradigm Medical Industries Inc, Salt Lake City, Utah), performed by a single observer (S.K.D.), with the patient in the supine position, using an immersion technique and a 50-MHz transducer that provides 4 to 5 mm of tissue penetration and 50-μm resolution. Radial perpendicular images at the corneoscleral junction were acquired at the superior, inferior, nasal, and temporal quadrants, with special care to avoid compression of the angle by the eyecup. Examination was first performed in normal, constant room lighting and again approximately 1 minute after turning all room lights off. Variation in accommodation was minimized by fixation of the fellow eye on a standard target fixed on the ceiling. Because UBM enables placement of the plane of section through a ciliary process or through the ciliary valley between the processes, radial scans were obtained through a typical ciliary process to show its relationship to the posterior iris.

Images were transferred to a computer and analyzed using commercially available software (UBM Pro 2000 for Windows; Paradigm Medical Industries Inc) as previously described.^8,16 The angle opening distance (AOD500; the distance from the corneal endothelium to the anterior iris, perpendicular to a line drawn along the trabecular meshwork, 500 μm anterior to the scleral spur along the trabecular meshwork) was computed automatically by the software after the operator marked the point of the scleral spur. The mean of 3 measurements was used for the study. The UBM images were also subjectively evaluated for the presence or absence of contact between the peripheral iris and cornea, that is, appositional angle closure. If this was present, AOD500 was considered to have a value of zero.

The mechanism of angle closure was diagnosed as either mainly pupillary block or plateau iris configuration. Pupillary block was diagnosed if, at both gonioscopy and UBM, there was characteristic iris convexity and if the peripheral iris was easily displaced from corneal apposition with slight pressure during indentation gonioscopy. Plateau iris configuration was diagnosed when there was a double-hump sign at indentation gonioscopy and if there was the characteristic configuration of large anteriorly positioned ciliary processes obliterating the ciliary sulcus on UBM images.^1,17 The diagnosis of an anteriorly positioned ciliary process was made on the basis of clinical judgment by subjective interpretation of the UBM images, and the absence of ciliary sulcus was established if the ciliary process was apposed to the posterior peripheral iris. All UBM images were assessed by an observer (S.K.D.) masked to both the gonioscopic findings and the diagnosis of angle closure and its mechanism.

We calculated percent agreement in diagnosing appositional angle closure between dark-room gonioscopy and UBM in light and dark. The t test was used to compare AOD500 values in each angle quadrant measured in light and dark with Microsoft Office Excel 2003 software (Microsoft Corp, Redmond, Washington).

Eighteen patients (6 men and 12 women) aged 45 to 82 years (mean ± SD, 61.0 ± 10.4 years) were enrolled. Sixteen patients were white, 1 was African American, and 1 was Hispanic. Eleven right eyes and 7 left eyes were studied. Mean ± SD spherical equivalent refraction was 1.6 ± 1.7 diopters (D) (range, −2.50 to +5.25 D). Mean ± SD intraocular pressure was 17.7 ± 2.4 mm Hg (range, 12-21 mm Hg). Nine eyes (50%) had plateau iris configuration, and 9 eyes had mainly pupillary block.

Demographic, gonioscopic, and UBM data for each participant are given in Table 1, the rate of iridotrabecular apposition diagnosed with each of the 3 methods in Table 2, and percent agreement between the 3 methods in Table 3. Rates of apposition were nearly identical at dark-room gonioscopy and dark-room UBM, and much less frequent at UBM in lighted room conditions. Of 18 superior angles that were appositionally closed at dark-room gonioscopy, apposition was demonstrated on UBM images in 16 (89%) in dark conditions but in only 6 (33%) in normal room light. Iridotrabecular apposition in at least 1 angle quadrant was demonstrated in all 18 eyes at dark-room gonioscopy, in 17 eyes (94%) at dark-room UBM, and in only 10 eyes (56%) at UBM in room light. Sample UBM images in light and dark (of the superior angle of eye No. 6) are shown in the Figure.

Table 4 gives mean AOD500 values for the 4 angle quadrants, first for all eyes including those with zero value indicating apposition, then for only angle segments without apposition, that is, excluding all zero values.

It is generally accepted that laser peripheral iridotomy and, when necessary, argon laser peripheral iridoplasty may prevent the development or progression of trabeculardamage; that is, they prevent the progression from appositional angle closure to chronic angle closure with elevated intraocular pressure, glaucomatous optic neuropathy, andvisual field loss. However, ophthalmologists are often not confident that an angle is narrow or occludable enough to necessitate surgical intervention. Even when the definition ofoccludable angle is clear linguistically but anatomically arbitrary, for example, as a posterior trabecular meshwork [that] can be seen for less than 90° of the anglecircumference,¹⁸ chronic angle closure may be substantially underdiagnosed. As we have previously stated,⁴the gonioscopic visualization of spontaneous, reversible iridotrabecular apposition is a definite, unequivocal indication for laser peripheral iridotomy. Hence, it is important to perform gonioscopy, and in a manner that will maximize its yield. Imaging techniques such as UBM and anterior segment optical coherence tomography that provide more objective assessment of the iridocorneal angle are not yet replacements for gonioscopy in routine clinical practice.

Our results demonstrate that iridotrabecular apposition can be diagnosed with a great degree of agreement at gonioscopy and UBM performed in a dark room. However, if UBM is performed incorrectly in room light, apposition will not be observed in a substantial number of cases. Whereas iridotrabecular apposition in at least 1 quadrant was diagnosed in all eyes at dark-room gonioscopy, only about half the eyes examined (56%) showed apposition at UBM in room light. If we extrapolate these findings to clinical practice, gonioscopy performed in room light is likely to miss many eyes with angle closure.

It can be argued that lighted room UBM findings cannot be simply extrapolated to lighted room gonioscopic findings, primarily because UBM is performed with the patient in the supine position, whereas the patient is sitting during gonioscopy. However, considering the high agreement observed between the 2 techniques when performed in a dark room, a similarly high concordance should exist under room light conditions. Comparison of these 2 examination methods may be carried out in future studies with the patient in the same body position, for example, using a handheld slitlamp and goniolens with the patient in the supine position.

Agreement in the diagnosis of apposition between expert gonioscopy and UBM has not been well studied previously. In one study, Spaeth et al¹⁹ correlated gonioscopic and UBM findings in 22 eyes with varied angle widths. Their data showed that gonioscopy identified iridotrabecular apposition in 6 eyes and, in 4 of these eyes, apposition was also determined at UBM. In 2 other eyes, UBM showed iridocorneal contact anterior to the meshwork, whereas gonioscopy showed a visible trabecular meshwork. However, in this study there is no mention of lighting conditions during either gonioscopy or UBM.

The results of our study add to previous literature that reports the importance of room light conditions during imaging of the angle. Sakuma et al²⁰ studied 46 eyes with narrow angles defined as grade 2 or lower by Shaeffer's classification (scale of 0-4) and with peripheral anterior synechia 50% or less of the angle circumference. Dark-room UBM demonstrated appositional angle closure in a high percentage (87%) of these eyes, and this finding did not correlate with the presence of peripheral anterior synechia. Pavlin et al¹¹ used UBM to image 8 eyes with narrow angles in both light and dark-room conditions. They reported that, in the dark, all eyes showed iris thickening and shortening, increased anterior convexity of the iris, and varying degrees of angle narrowing. Narrowing in the dark to the point of iridotrabecular apposition was reported in 1 eye, and this was relieved by iridotomy. Ishikawa et al⁸ performed UBM in both light and dark-room conditions in 178 eyes with clinically narrow angles defined as Shaffer grade 1 or 2. Under light conditions, all eyes had open angles, whereas in the dark, 55.6% of eyes exhibited iridotrabecular apposition.

Woo et al¹³ examined 24 eyes with clinically narrow angles and pupillary block configuration at UBM. The AOD500 (mean for 4 quadrants) decreased significantly, from 185.6 ± 26 μm in the light to 96.6 ± 18 μm in the dark. The authors attributed this finding to the combination of increased iris thickening and increased anterior iris bowing. They did not report on iridotrabecular apposition either clinically or at UBM. Gazzard et al⁹ imaged the inferior, nasal, and temporal quadrants of the untreated eyes in 54 Asian patients whose fellow eyes exhibited acute angle closure. Again, mean AOD500 decreased significantly, from 75.3 ± 62.0 μm in the light to 46.4 ± 51.6 μm in the dark. The rate of iridotrabecular apposition in light and dark was not reported. Pavlin and Foster¹² reported 10 eyes with persistent narrow angles after patent peripheral Nd:YAG laser iridotomy and ciliary body configuration characteristic of plateau iris at UBM. Only the inferior angle was studied. Mean AOD500 decreased significantly, from 113.6 ± 34 μm in the light to 22.6 ± 34 μm in the dark. Iridotrabecular apposition (AOD of zero) was observed in 6 eyes in the dark and no eyes in the light.

Gazzard et al¹⁰ provided clear visual demonstration of the dynamic nature of angle anatomy and closure. In a UBM videograph of a 70-year-old Chinese woman, they showed that in light conditions of direct torch illumination into the contralateral eye, the angle is wide open. In the dark, a pronounced increase in iris convexity accompanied limited pupillary dilation, resulting in appositional closure anterior to the Schwalbe line. The authors comment that the angle would be graded open at gonioscopy under photopic conditions, yet it clearly closes in near darkness.

In our study, the mean AOD500 in light and dark was substantially different in the superior, inferior, and temporal angle quadrants. However, when only the open-angle segments were compared, there was no substantial difference between mean AOD500 in light and dark conditions. This may be partially attributable to the small sample size, most notably in the case of the superior angle, where there were only 2 open angles in the dark.

Our study findings support our previous recommendation that, in routine clinical practice, gonioscopy should be performed in a completely dark room. This may require some minor changes in the working environment of some ophthalmologists, such as the relocation of a light switch to within reach of the slitlamp or linkage of the 2 so that room lights are automatically turned off when the slitlamp is turned on.

In conclusion, gonioscopy must be performed in a dark room with the least amount of slitlamp illumination that still allows visualization of the angle structures. We believe investigations of angle-closure glaucoma should adhere to these requirements and report the type of gonioprism used, the method of indentation, the lighting conditions, and the status of appositional or synechial iridotrabecular contact.

Correspondence: Robert Ritch, MD, Glaucoma Service, Einhorn Clinical Research Center, New York Eye and Ear Infirmary, 310 E 14th St, New York, NY 10003 (ritchmd@earthlink.net).

Submitted for Publication: December 9, 2006; final revision received February 19, 2007; accepted February 21, 2007.

Author Contribution: Dr Barkana had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Financial Disclosure: None reported.

Funding/Support: This study was supported in part by the Joseph and Marilyn Rosen Research fund of the New York Glaucoma Research Institute.