1. Anterior segment Scheimpflug imaging for screening angle closure diseases
Andrew Winegarner1,, Atsuya Miki1, Miho Kumoi1, Yuchiro Ishida1, Taku Wakabayashi1, Shinichi Usui1, Kenji Matsushita1, Kohji Nishida1
1Department of Ophthalmology Osaka University Graduate School of Medicine
Introduction
Results
PACG affects approximately 0.75% of all adult Asians with rates doubling every decade, and affects 0.4% of all European-descent adults over the age of 40
Gonioscopic examination is the gold standard for the diagnosis of PACG. However, it requires a highly-trained ophthalmologist, direct contact with the eyeball, and results are not easily reproducible by unskilled examiners.
Anterior segment Scheimpflug imaging offers a noninvasive means to quantitatively assess anterior chamber parameters in an automated and standardized manner.
Technicians would require minimal training and be able to screen and refer suspected cases of PACG to an ophthalmologist for proper diagnosis.
Normative data on anterior chamber parameters such as depth, volume, and angle have been generated from two previous studies and included in the Pentacam Scheimpflug imaging device.
Patient’s individual data may be analyzed against the normative data directly on the device.
We have used the normative data as screening tool on our own patient population to both further validate the normative data, and test the feasibility of establishing a screening protocol.
We generated our own normative data for comparison with previous normative data. 2
Representative control case for Scheimpflug imaging data page
Representative patient case for Scheimpflug imaging data page
Normative Data Screen
Methods & Materials
88 consecutive patients with gonioscopy-diagnosed angle closure diseases (PACS, PAC, and PACG) and Scheimpflug imaging data were retroactively surveyed.
35 healthy control subjects were analyzed via Scheimpflug imaging for comparison.
The analyzing software of the Pentacam Scheimpflug imaging device provides threshold values (standard deviations) based on the normative data.
We used 1 SD from the normative mean values (depth ≤ 2.37mm, volume ≤ 111 mm2, and angle ≤ 31degrees) as cut-off points for delineating between angle closure disease and those not at risk for PACG.
The raw data from the present study was analyzed via ROC curves in order to generate new cut-off values to compare with previous studies’ sensitivity and specificity.
Exclusion criteria included intraocular diseases such as a history of intraocular surgery, history of laser iridotomy, secondary glaucoma, and being over the age of 90 and under the age of 40. Cataract and epiretinal membrane cases were not excluded.
Variables of age, axial length, spherical equivalent, ACD, ACV, and ACA were compared, with P-value less than 0.05 considered significant.
ROC Curves
TABLE 1. Clinical characteristics
Total
Angle Closure
Control
P Value
Eyes / Subjects
122 / 122
87 / 87
35 / 35
Age, years (range)
72.1 ± 7.7 (49 – 87)
72.3 ± 7.7 (49 – 87)
71.6 ± 8 (56–87)
0.6403
Gender, female / male
80 / 42
62 / 25
18 / 17
0.037
Eye, right / left
64 /58
50 / 37
14 / 21
0.081
Axial Length, mm (range)
23.1 ± 1.5 (20.5 – 27.8)
22.5 ± 0.8 (20.5 – 24.4)
24.7 ± 1.6 (20.8 – 27.8)
<0.001
Spherical equivalent refraction (range)
-0.2 ± 3.1 (-10.6 – 5)
0.9 ± 1.9 (-5.4 – 5)
-2.8 ± 4 (-10.6 – 4.4)
Anterior chamber depth, mm (range)
2.12 ± 0.61 (1.26 – 3.97)
1.8 ± 0.27 (1.26 – 2.51)
2.92 ± 0.47 (1.97 – 3.97)
Anterior chamber volume, mm2 (range)
88.8 ± 45.6 (29 – 244)
65.1 ± 17.3 (29 – 122)
147.7 ± 40.2 (75 – 244)
Anterior chamber angle, degree (range)
25.0 ± 7.8 (9.2 – 45.7)
21.6 ± 5.7 (9.2 – 34.2)
33.7 ± 5.4 (20.8 – 45.7)
Depth
Volume
 Table 2.
Sensitivity and Specificity
Sensitivity with
1 SD normative
Specificity with
ROC analysis
Depth
97.7%
91.4%
95.4%
94.3%
Volume
98.9%
71.4%
Angle
88.5%
85.7%
Angle
Conclusions
Previous studies’ normative data have been incorporated into the Pentacam Scheimpflug image analyzing software, so the technician may easily determine whether the values of the examined eyes fall within the normal limits (Fig. 1c).
Technicians may noninvasively screen for angle closures with automated and standardized Scheimpflug imaging, which takes under 5 minutes per patient.
Positive screens may be referred to an ophthalmologist for proper diagnosis via gonioscopy.
In conclusion, our study clarified the excellent discriminative performance of the anterior segment Scheimpflug imaging parameters for angle closure diseases. Using the integrated thresholds generated from previous studies’ normative data, we accurately discriminated angle closure diseases from normal subjects. Our study confirmed the relevance of using these threshold values as screening tools in a large patient population, distinct from the one used in the normative data’s creation. Additionally, cut-off points generated from our own raw data yielded even better sensitivity and specificity. Our data strongly support the use of Scheimpflug imaging for screening angle closure diseases.
References
Study was undertaken to assess the discriminative power of anterior chamber parameters obtained with the anterior segment Scheimpflug imaging in screening angle closure diseases.
Using 1 SD from the mean anterior chamber depth in normative data, angle closure patients were screened with a 97.7% sensitivity, and a 91.4% specificity.
This study provides a larger population of patients with angle closure diseases than previous studies using anterior segment Scheimpflug imaging.
It is the first study to validate the incorporated normative data with a separate patient population.
Study’s limitation is all patients were taken from a university hospital setting, but we still believe these numbers to sufficient for screening purposes, especially given that the cut-off points used were not generated from the population being screened, excluding the possibility of an over-fitting.
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