Assessment of anterior chamber angle

1. Sujay Chauhan
ASSESSMENT OF
ANTERIOR CHAMBER ANGLE

2. INDICATIONS FOR ASSESSMENT OF
ANTERIOR CHAMBER ANGLE
All patients on the first visit

3. • Glaucoma suspects
• Open angle glaucoma
• Ocular hypertension
• Angle closure post-iridotomy
• Retinal vein occlusion
• Blunt trauma
Indications

4. METHODS FOR ASSESSMENT OF
ANTERIOR CHAMBER ANGLE

5. SUBJECTIVE ASSESSMENT
• Oblique flashlight test
• Van Herrick’s technique
• Gonioscopy

6. OBLIQUE FLASHLIGHT TEST

7. GRADE I GRADE II GRADE III GRADE IV
< 1/3
illuminated
1/3-2/3
illuminated
>2/3
illuminated
Fully
illuminated
Oblique flashlight test

8. • Good inter-observer agreement (p = 0.04)
• Good reproducibility (weighted kappa value = 0.74)
• Sensitivity: 75-97%
• Specificity: 67-99.4%
• Gracitelli et al. Ability of non-ophthalmologist doctors to detect eyes with occludable angles using the
flashlight test. Int Ophthalmol. 2014 Jun;34(3):557-561
• Congdon NG et al. Screening techniques for angle-closure glaucoma in rural Taiwan. Acta Ophthalmol
Scand 1996;74:113–119
• He M et al. Angle-closure glaucoma in East Asian and European people. Different diseases? Eye
2006;20:3–12
• Thomas R et al. The flashlight test and van Herick’s test are poor predictors for occludable angles.
Aust N Z J Ophthalmol 1996;24:251–256
• Vargas E, Drance SM Anterior chamber depth in angle-closure glaucoma. Clinical methods of depth
determination in people with and without the disease. Arch Ophthalmol 1973;90:438–439
Oblique flashlight test

9. • Simple
• No sophisticated equipment required
Advantages
Oblique flashlight test

10. • Lack of standardization
• Arbitrary cut-offs
Limitations
Oblique flashlight test

11. LIMBALANTERIOR CHAMBER DEPTH
AND
VAN HERRICK’S TECHNIQUE

12. 5% 15% 25%
40% 75% >100%
Limbal Chamber Depth as a Fraction of Corneal Thickness
LCD & VH

13. All Occludable Angles PAC PACG
LCD VH Sensitivity Specificity Sensitivity Specificity Sensitivity Specificity
0% NA 17.8% 99.6% 29.3% 99.2% 52.2% 98.9%
≥5% NA 60.5% 96.1% 70.7% 93.7% 91.3% 92.6%
≥15% 1 83.7% 85.7% 84.5% 82.4% 91.3% 81.1%
≥25% 2 99.2% 65.5% 100% 62.4% 100% 61.1%
≥40% 3 100% 40.3% 100% 38.3% 100% 37.5%
Performance Indices of Limbal Chamber Depth Estimation in
Detection of Gonioscopically Occludable Angles, PAC and PACG
Foster PJ et al. Detection of gonioscopically occludable angles and primary angle closure glaucoma by
estimation of limbal chamber depth in Asians: modified grading scheme. Br J Ophthalmol.
2000;84:186-192.
LCD & VH

14. • Good interobserver agreement (weighted kappa value = 0.73-0.76)
• High intraobserver repeatability
• Sensitivity = 99%
• Thomas R et al. The flashlight test and van Herick’s test are poor predictors for occludable angles.
Aust N Z J Ophthalmol 1996;24:251–256
• Foster PJ et al. Detection of gonioscopically occludable angles and primary angle closure glaucoma
by estimation of limbal chamber depth in Asians: modified grading scheme. Br J Ophthalmol
2000;84:186–192
• Cockburn DM. Slitlamp estimate of anterior chamber depth as a predictor of the gonioscopic
visibility of angle structures. Am J Optom Physiol Opt 1982;59:904–908
LCD & VH

15. Advantages
• Quick
• Non-invasive
• No auxiliary equipment
LCD & VH

16. • Subjective
• Overestimation of angle depth (if slit beam moved too far on to
the cornea, nasal limbus)
• Little or no information regarding angle morphology
• Affected by corneal degenerations such as arcus senilis
• Horizontal quadrants only
Limitations
LCD & VH

17. GONIOSCOPY
• Indirect gonioscopy – most common, reference standard
• Grading of anterior chamber angle depth
• Iris configuration
• Insertion of iris root
• Peripheral anterior synechiae
• Pigment deposition
• Neovascularisation
• Uveitis (nodules)
• Blunt trauma (angle recession, cyclodialysis cleft)

18. High interobserver agreement (kappa value = 0.62-0.82)
• Foster PJ et al. Detection of gonioscopically occludable angles and primary angle closure glaucoma by
estimation of limbal chamber depth in Asians: modified grading scheme. Br J Ophthalmol
2000;84:186–192
• Jacob JT et al. Evaluation of interobserver agreement in gonioscopy. Kerala J Ophthalmol.
2008;XX:253–255
• Lavanya R et al. Screening for narrow angles in the Singapore population: evaluation of new
noncontact screening methods. Ophthalmology 2008:115:1720–1727
• Thomas R et al. The flashlight test and van Herick’s test are poor predictors for occludable angles. Aust
N Z J Ophthalmol. 1996;24:251–256
Gonioscopy

19. Advantages
• Easily and quickly performed
• Not expensive
Gonioscopy

20. • Invasive
• Subjective, requires skill and experience
• Variables – inadvertent pressure on cornea, light exposure onto
pupil, patient cooperation, type of lens used, direction of gaze
• Does not provide quantitative evaluation of the angle
• Can not visualize structures posterior to iris
Limitations
Gonioscopy

21. OBJECTIVE MEASURES
• Ultrasound biomicroscopy (UBM)
• Anterior segment optical coherence tomography (AS-OCT)
Gonioscopy

22. ULTRASOUND BIOMICROSCOPY (UBM)

23. • Two-dimensional high-resolution gray-scale images of ocular
structures anterior to pars plana
• Quantitative and qualitative evaluation
• Principle similar to that of B-scan (10 MHz)
• Frequency – 50 MHz – More frequency – less penetration (5 mm)
and more resolution
UBM

24. Interpretation of anterior chamber angle configuration is
dependent on determining the location of scleral spur (inward
protrusion of sclera)
UBM

25. Kong X, Foster PJ, Huang Q et al. Appositional Closure Identified by Ultrasound Biomicroscopy in
Population-Based Primary Angle-Closure Glaucoma Suspects: The Liwan Eye Study. Glaucoma.
2011;52:7.
No ITC
High ITC
(S type)
High ITC
(B type)
Low ITC
UBM

26. • Angle opening distance (AOD500): Length of a perpendicular
from TM to iris at a point 500 µm from SS
• Trabecular-iris angle (Ø1): Apex in the iris sulcus and arms
passing through the point 500 µm from SS and the point
perpendicularly opposite on the iris
UBM

27. AOD500 :
• Sensitivity = 82%
• Specificity = 96%
Trabecular iris angle:
• Sensitivity = 83%
• Specificity = 93%
Henzan, IM et al. Comparison of Ultrasound Biomicroscopic Configurations Among Primary Angle
Closure, Its Suspects, and Nonoccludable Angles: The Kumejima Study. Am J Ophthalmol.
2011;151(6):1065-1073
UBM

28. Advantages
• High resolution of 50 µm at a frequency of 50 MHz
• Cross-sections of angle can be captured without lighting –
changes in iris shape with or without light can be ascertained
• Independent of corneal opacity
• Dynamic changes can be recorded
• Images can be automatically quantified
UBM

29. Assessment of areas not possible by gonioscopy:
• Ciliary body
• Inside the iris
• Posterior chamber
• Inside filtering blebs
• Outflow tract for aqueous humour inside sclera
UBM

30. Limitations
• Supine position – iris diaphragm falls back – angle opens
• Only 1 quadrant can be imaged at a time
• Angle region measured is located subjectively as superior, nasal,
inferior and temporal
• Skilled examiner
• Longer image acquisition time
• Use of anaesthesia
• Contact with the eye using a cup with a coupling medium or a
probe – corneal abrasion, infection
UBM

31. Can not detect:
• Pigmentation in the angle
• Inflammatory exudate in the angle
• Neovascularization in the angle
UBM

32. ANTERIOR SEGMENT OPTICAL
COHERENCE TOMOGRAPHY (AS-OCT)

33. POSTERIOR SEGMENT OCT ANTERIOR SEGMENT OCT
830 nm 1310 nm
Unable to penetrate sclera Penetrates sclera and iris
More time for image acquisition Reduced time
Compromised image quality Reduced motion artefacts – better
image quality
AS-OCT

34. • Low coherence interferometry to obtain cross-sectional images of
the ocular structures
• Similar to UBM, interpretation of anterior chamber angle
configuration is dependent on determining the location of scleral
spur
AS-OCT

35. Angle closure in more than one quadrant was detected by:
• AS-OCT in 71% of patients
• Gonioscopy in 49.5% of patients
When performed in dark conditions,
AS-OCT identified angle closure in:
• 98% of subjects found to have angle closure on gonioscopy
• 44.6% of subjects found to have open angles on gonioscopy
Specificity of AS-OCT to detect angle closure: 55.4%
Nolan et al. Detection of primary angle closure using anterior segment optical coherence tomography in
Asian eyes. Ophthalmology. 2007 Jan;114(1):33-39.
AS-OCT

36. Intraobserver variability = 9.4% to 12.5%
Interobserver variability = 10.7%
High reproducibility: 0.875-0.942
Tan AN et al. Reproducibility of anterior chamber angle measurements with anterior segment optical
coherence tomography. Invest Ophthalmol Vis Sci, 52(5), 2095-2099
AS-OCT

37. AS-OCT scanning protocol Sensitivity Specificity
Nasal-temporal quadrants 47% 88%
Inferior quadrant 84% 69%
Superior-inferior quadrants 92% 54%
Khor WB et al. Evaluation of scanning protocols for imaging the anterior chamber angle with anterior
segment-optical coherence tomography. J Glaucoma. 2010 Aug;19(6):365-368.
AS-OCT

38. Advantages
• Higher resolution than UBM (18 µm vs 25 µm)
• Non-contact method
• All 4 quadrants are imaged at once
• Entire cross-section of anterior segment is imaged into one frame
– permits assessment and documentation of iris profile and its
relationship to other anatomical parameters of eye
• Patient in sitting position – no alteration in anterior chamber
depth
• Does not require a skilled operator
AS-OCT

39. Limitations
• Infrared light blocked by iris pigment – precludes assessment of
structures located behind iris
• Degradation of light by sclera – ciliary body not imaged fully
• Can not obtain clear images through opaque media
• Obstruction by eyelids – difficulty in imaging superior and
inferior angles
AS-OCT

40. OCT and UBM had similar
• mean values of angle opening distance, angle recess area and
trabecular-iris space area
• reproducibility, and
• sensitivity-specificity profiles
in identifying eyes with narrow angles
Radhakrishnan S et al. Comparision of optical coherence tomography and ultrasound biomicroscopy for
detection of narrow anterior chamber angles. Arch Ophthalmol. 2005 Aug:123(8):1053-1059.
AS-OCT

41. CONCLUSION
• UBM and AS-OCT provide real-time cross-sectional images of
anterior chamber angle – accuracy and reproducibility yet to be
proved
• Gonioscopy – continues to remain essential for glaucoma
evaluation and management