ITC End Point marked as `+` (a) First image of eye with closed angle

Comparison Of Diagnostic Performance Of Iris-trabecular
Contact Index With Multiple Slices On Swept Source
Anterior Segment Optical Coherence Tomography
Super Speciality Eye Hospital &
Post Graduate Institute of Ophthalmology
Imaging - Glaucoma
Sujatha Kadambi, Rajesh SasiKumar, Jayasree Venugopal, Sathi Devi, Ramgopal Balu, Dhanraj Rao, Narendra Puttiah
Glaucoma Services, Narayana Nethralaya, Bangalore, India
Background
WGCSUB-1670
ITC Analysis Screen in an Open Angle
Time domain and spectral domain optical coherence tomography (OCT) devices
currently allow only limited cross sectional imaging which is not representative of
the circumferential anterior chamber angle configuration.
The swept source OCT (SSOCT) allows 128 cross sections, there by providing a
‘gonioscopic’ view.
In built software in the SSOCT (Casia 1000, Tomey, Nagoya, Japan) provides the
extent of iris-trabecular contact as an index (ITC index).
Purpose
To determine diagnostic performance of iris-trabecular contact index (ITC) using
multiple slices (4, 8, 16, and 32) on the SSOCT.
To compare the results with gonioscopy.
Materials and Methods
Prospective Observational Study
Results
Inclusion Criteria
Exclusion Criteria
• 30-80 years
• Corneal pathology
• Phakic patients
• Uveitis
• Narrow angle without PAS or open
• Ocular procedures except
angle
peripheral iridotomy
56 eyes (56 subjects) were enrolled, one was excluded due to poor image quality.
On gonioscopy 41 subjects had angle closure; none had peripheral anterior
synechiae.
ITC index with 4, 8, 16, and 32 slices were comparable [66.28%, 66.56%, 67.16%, and
66.51%] (p>0.05).
All patients underwent detailed ophthalmic evaluation including gonioscopy and
angle imaging with SSOCT.
A single observer masked to gonioscopic findings marked 4, 8, 16 and 32 slices for
determining the ITC index with the built-in software.
Area under receiver operating characteristic curve (AUC) analysis was done for
detecting closed angles using ITC index in comparison with gonioscopy.
The AUC for detection of angle closure using ITC index was highest with 32 slices
[0.82 (95% C.I., 0.69-0.91)].
ITC index >50% has a sensitivity of 90.2% and specificity of 78.5% for angle closure.
No statistical difference using lesser number of scans.
ITC index
N
Open:Closed
(Gonioscopy)
AUC (95%CI)
Youden’s
index
ITC4
45
12:33
0.777
(0.628,0.887)
>60
75.8
83.3
ITC8
55
14:41
0.675
(0.675,0.899)
>56
82.9
78.6
ITC16
55
14:41
0.814
(0.686,0.906)
>51
90.2
78.6
ITC32
55
14:41
0.820
(0.693,0.960)
>48
90.2
78.6
Comparision of closed and open angle
Sensitivity Specificity
(%)
(%)
Closed
SS - Scleral Spur marked as ‘x’ EP - ITC End Point marked as ‘+’
Open
Discussion
ITC index was comparable across the different slice numbers analysed.
Higher number of slices gives better ‘gonioscopic’ picture of angle configuration.
In clinically closed angles, average ITC index was more than 73.5%.
In open angles, average ITC index was less than 46.33% which decreased with the
increase in number of slices analysed.
A cut off ITC index of 50% to categorize angles as either closed or open showed good
sensitivity of more than 90% and reasonable specificity of 78%.
(a) First image of eye with closed angle, SS is posterior to EP
(b) Second image of eye with open angle, SS is anterior to EP
This disparity could be because of the difference in definition of ‘closed angles’
between gonioscopy and ASOCT; gonioscopy takes pigmented trabecular
meshwork as the landmark where as it is the scleral spur in ASOCT images.
ASOCT tends to overestimate ‘closed angles’ and hence might have a high sensitivity
and average specificity.
ITC Analysis Screen in Closed Angle
Limitations of our study
Small sample size
Closed angles are oversampled ,thereby sensitivity is overestimated
Invisible range was not considered
Conclusion
The ITC index showed good diagnostic performance across different frame rates.
Analyzing more slices might provide a gonioscopic view of the angle.
Analysis of 16 slices appears to be as effective as analyzing 32 slices
References
Bhaskaran M et al. Assessment of circumferential angle-closure by the iristrabecular contact index with swept source optical coherence tomography,
Ophthalmology 2013;120:2226-31.
The red oval on left upper end denotes the number of slices included in
calculating ITC index. Blue square shows the ITC chart.
The blue shaded portion represents iris-trabecular contact in extent and
distribution.
The red box is the ITC Result table; ITC Index and Invisible Range are given.
The dotted red box shows the ITC graph; y axis- ITC, x-axis- degree of angle.
Financial interest - Nil
Mishima K et al. Iridotrabecular Contact Observed Using Anterior Segment ThreeDimensional OCT in Eyes With a Shallow Peripheral Anterior Chamber. Invest
Ophthalmol vis Sci 2013;54:4628–35.
Radhakrishnan S et al. Optical Coherence Tomography Imaging of the Anterior
Chamber Angle. Ophthalmol Clin north Am 2005;18:375-81.
Sakata et al. Comparison of gonioscopy and anterior segment optical coherence
tomography in detecting different quadrants of the anterior chamber angle.
Ophthalmology 2008;115:769-74.
Conflict of interest - Nil
Support - Nil