**4. Scanning peripheral anterior chamber depth analyzer**

The scanning peripheral anterior chamber depth analyzer (SPAC) is a non-invasive device that objectively and quantitatively assesses the anterior ocular segment by employing the Scheimp‐ flug camera principle [18]. The light from the slit lamp is in the visible spectrum and is projected from the temporal side at an angle of 60° from the optical axis. A camera records cross sectional slit images from the anterior cornea to the anterior iris, and does not rotate as Pentacam-Scheimpflug. The SPAC measures the peripheral ACD and converts the measurements into numerical and categorical grades by comparison with a normative database. SPAC quantita‐ tively measures ACD in a noncontact fashion from the optical axis to the limbus in approxi‐ mately 0.66 second and takes 21 consecutive slit-lamp images at 0.4 mm intervals. SPAC measurements ranged from 1 to 12, with 1 representing the shallowest anterior chamber. SPAC is equipped with an autofocusing system and a program for the detection of eyes with narrow angle, and usually completes measurement within 15 seconds for a pair of eyes by pressing

the start button. The SPAC also reports 3 categorical grades for risk of angle closure: S (for "suspect angle closure"*,* if there were ≥4 measured points exceeding the 95% confidence interval [CI]), P (for "potential angle closure", if there were ≥4 points exceeding the 72% CI), and no suffix (for "normal") [18]. It has been previously reported that the results of peripheral anterior chamber measurement by SPAC were well correlated with those by the van Herick technique as well as Shaffer's grading system and the ultrasound biomicroscope [19].

and usually completes measurement within 15 seconds for a pair of eyes by pressing the

start button. The SPAC also reports 3 categorical grades for risk of angle closure: S (for

"suspect angle closure"*,* if there were ≥4 measured points exceeding the 95%

confidence interval [CI]), P (for "potential angle closure", if there were ≥4 points

It has been previously reported that the results of peripheral anterior chamber measurement by SPAC were well correlated with those by the van Herick technique as well as Shaffer's grading system and the ultrasound biomicroscope [19]. Pentacam-Scheimpflug (rotating scheimpflug imaging) uses the Scheimpflug principle in order to obtain images of the anterior segment [10]. It has a rotating Scheimpflug

Pentacam-Scheimpflug (rotating scheimpflug imaging) uses the Scheimpflug principle in order to obtain images of the anterior segment [10]. It has a rotating Scheimpflug camera that takes up to 50 slit images of the anterior segment in less than 2 seconds [20]. Soft‐ ware is then used to construct a three‐dimensional image. It calculates data for corneal topography (anterior and posterior corneal surface) and thickness, anterior chamber depth (ACD), lens opacification and lens thickness. It also provides data on corneal wavefront of the anterior and posterior corneal surface using Zernike polynomials. Com‐ pared with SPAC, Pentacam is highly expensive. camera that takes up to 50 slit images of the anterior segment in less than 2 seconds [20]. Software is then used to construct a three‐dimensional image. It calculates data for corneal topography (anterior and posterior corneal surface) and thickness, anterior chamber depth (ACD), lens opacification and lens thickness. It also provides data on corneal wavefront of the anterior and posterior corneal surface using Zernike **Fig.1. Definitions of the parameters from the scanning peripheral anterior chamber depth analyzer (SPAC) measurements. a.** SPAC automatically calculates

central anterior chamber depth (ACD, red line) and the most peripheral SPAC-derived anterior chamber depth values (yellow kine) 5.6 mm apart from the anterior pole of

polynomials. Compared with SPAC, Pentacam is highly expensive.

the lens. **b.** Printout of the result of SPAC measurement.

*line) along the visual axis. SD5.6 (yellow line) means peripheral anterior chamber depth at 5.6 mm apart from the anterior pole of the lens. b. Printout of the results of SPAC measurement. The radius of curvature, the corneal thickness, and the anterior*  **Figure 3.** The SPAC automatically calculates central anterior chamber depths (ACD, red line) along the visual axis. SD5.6 (yellow line) means peripheral anterior chamber depth at 5.6 mm apart from the anterior pole of the lens. b. Printout of the results of SPAC measurement. The radius of curvature, the corneal thickness, and the anterior chamber depth are displayed. The SPAC anterior chamber depth value (corneal epithelium to anterior lens) was calculated by summing the corneal thickness and true anterior chamber depth measurements.

*Fig. 3a. The SPAC automatically calculates central anterior chamber depths (ACD, red* 

8

**5. Application of anterior chamber imaging instruments for glaucoma**

at risk of angle closure glaucoma [22].

**6. Research course** 

**7. Method used** 

**6. Research course**

**8. Participants** 

**7. Method used**

ular, women.

**9. Screening examination** 

**10. Definitive examination** 

measured three times, and the mean value was adopted.

Figure 4. Flow chart for the detection and diagnosis of the narrow anterior chamber.

**Figure 4.** Flow chart for the detection and diagnosis of the narrow anterior chamber.

Slit-lamp examination •≤ van Herick grade 2

underwent glaucoma screening. All of the participants were ethnically Japanese.

participants gave written informed consent for this research prior to their participation.

Cross-sectional, observational, community-based study.

Cross-sectional, observational, community-based study.

[22].

ACD

measurement •SPAC

The ideal community-based screening test should be clinician-independent, quick, and noninvasive, and have high sensitivity and specificity. SPAC has an advanatage of de‐ tecting eyes at risk of ACG by non-physicians in public health screening [20]. When us‐ ing gonioscopy as the gold standard [8,10], the performance of SPAC combined grade (P or S and/or ≤ grade 5) gave a sensitivity and specificity of 93.0% and 70.8%, respectively [19]. With sequential testing using both SPAC and van Herick, the specificity and sensi‐ tivity improves to 94.4% and 87.0%, respectively [21, 22]. Therefore, the SPAC examina‐ tion in conjunction with the van Herick method is considered as a choice of the first-line screening tests for angle closure following precise examination by OCT, UBM, or gonio‐ scopy (Fig. 4). Kashiwagi et al. [23] proposed the protocol of detecting angle closure glaucoma using SPAC in public health examination. Their protocol consisted of 2 phases: primary screening using SPAC measurements of ACD by nonphysicians and definitive examination by glaucoma specialists (Fig. 4), and was revealed useful for detecting eyes

Screening for Narrow Angles in the Japanese Population Using Scanning Peripheral Anterior Chamber Depth Analyzer

sensitivity improves to 94.4% and 87.0%, respectively [21, 22]. Therefore, the SPAC examination in conjunction with the van Herick method is considered as a choice of the first-line screening tests for angle closure following precise examination by OCT, UBM, or gonioscopy (Fig. 4). Kashiwagi et al. [23] proposed the protocol of detecting angle closure glaucoma using SPAC in public health examination. Their protocol consisted of 2 phases: primary screening using SPAC measurements of ACD by nonphysicians and definitive examination by glaucoma specialists (Fig. 4), and was revealed useful for detecting eyes at risk of angle closure glaucoma

Difinitive diagnosis

http://dx.doi.org/10.5772/54556

257

•AS-OCT •UBM •Gonioscopy

To investigate the frequency of eyes with a shallow anterior chamber at risk, the SPAC was used in subjects visiting a health screening center. In addition, the influences of age and sex on the distribution of central and peripheral ACD were also examined. Indeed, a productive approach would be to target high-risk groups, such as the elderly, far- sighted, and in particular, women.

This was a cross-sectional study in an institutional setting [24]. Subjects older than 30 years were recruited at an annual community health checkup project held in the city of Akita (with a population of 325,537), the capital of Akita Prefecture, Japan. A total of 1,173 subjects participated in the comprehensive examinations from September 10, 2007 to October 26, 2007. Of these, 710 individuals

This study was performed after the approval by the Ethical Committee of Akita Prefecture Health Care Foundation. All study procedures adhered to the principles outlined in the Declaration of Helsinki for research involving human subjects, and all

Exclusion criteria were (1) eyes with previous ocular surgery, trauma, or significant ocular disease; (2) eyes with any inborn

The initial non-contact ocular examination was conducted by trained non-ophthalmologists and included measurement of refraction and keratometry (Topcon KR-8100PA, Tokyo, Japan), IOP by noncontact pneumotonometry (Topcon CT-90A, Tokyo, Japan), angle width (Scanning Peripheral Anterior Chamber Analyzer, Takagi Seiko, Nagano, Japan), non-mydriatic optic disc photography by stereoscopic fundus camera (30o angle, 3-DX/NM, Nidek, Gamagori, Japan), and confocal laser scanning tomography (Heidelberg Retina Tomograph II, software version 3.0, Heidelberg Instruments, Heidelberg, Germany). IOP was

When at least 1 finding suggested the presence of glaucoma, the subjects were recruited for definitive examination (Table 1). A definitive examination was performed when a subject was suspected to have glaucoma based upon the findings of the initial noncontact ocular examination. The definitive examination consisted of the following procedures: slit-lamp biomicroscopy, Goldmann applanation tonometry, gonioscopy, and optic nerve head evaluation using a Goldmann three-mirror lens (Haag-Streit International, Koeniz, Switzerland) and a visual field test with the Humphrey Field Analyzer II 24-2 SITA Standard Program (Carl Zeiss Meditec Inc, Dublin, CA, USA). Diagnosis of glaucoma was made based on optic disc appearance, including cup-to-disc ratio, rim width, nerve fiber layer defect, the visual field test, and the clinical records that were obtained through screening and definitive examinations. When present or suspected, glaucoma was categorized based upon the criteria of previous population studies (Table

aberrations, which might affect the morphology of the optic disc (eg, superior segmental optic disc hypoplasia).

To investigate the frequency of eyes with a shallow anterior chamber at risk, the SPAC was used in subjects visiting a health screening center. In addition, the influences of age and sex on the distribution of central and peripheral ACD were also examined. Indeed, a productive approach would be to target high-risk groups, such as the elderly, far- sighted, and in partic‐
