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

Noriko Sato, Makoto Ishikawa, Yu Sawada, Daisuke Jin, Shun Watanabe, Masaya Iwakawa and Takeshi Yoshitomi

Additional information is available at the end of the chapter

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

**1. Introduction**

Primary chronic angle-closure glaucoma (PACG) is a leading cause of blindness, and has particularly high prevalence rate in East Asia [1–3]. The Handan Eye Study [4] reported that the standardized prevalence of PACG is 0.5%, and two thirds of those with PACG were blind in at least one eye. Many cases of PACG are asymptomatic and often present with severe visual field loss at the first visit. The severe visual impairment from PACG is related to the insidious development of the disease. [5]

Primary angle closure suspect (PACS) is characterized by narrow or occludable angles without raised intraocular pressure (IOP) or glaucomatous optic neuropathy. Primary an‐ gle closure (PAC) is the eyes with narrow angles and the appositional closure, peripheral anterior synechiae (PAS) and/or raised IOP but without glaucomatous optic neuropathy. PACG is defined as the case of PAC with glaucomatous optic neuropathy. It has been estimated that 22% of the eyes with PACS progress to PAC and 28.5% progress from PAC to PACG over 5–10 years [6]. Prophylactic laser iridotomy (LI) is the first-line treat‐ ment for narrow angles, and may stop the progression of the angle closure process and prevent development of PACG. However, LI is less effective in controlling IOP if optic nerve damage with PAS has already occurred [7].

Assessment of angle width is essential for the diagnosis and managing angle closure [8–10]. Currently, the golden standard for angle assessment has been indirect visualization by

© 2013 Sato et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

gonioscopy. However, it is limited by its dependency on subjective interpretation and difficulties in manipulation techniques. Ultrasound biomicroscopy (UBM) generates highresolution images of the angle, which can be used in quantitative analysis, and it adds useful information regarding causal mechanisms of angle closure. However, this method also requires trained and experienced technicians and is time consuming. Both gonioscopy and UBM require contact with the globe, and as a result, they can be unpleasant for the patient and can induce artifacts.

the angle. Nevertheless, it may induce changes in the apposition of the iris depending on the

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

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

253

The UBM measurement requires trained and experienced technicians and is time consuming. In addition, UBM require contact with the globe, and as a result, UBM can induce artifacts by inadvertent compression of the globe. Consequently, UBM is not suitable for glaucoma

**Figure 1. (a)** UBM image of the normal anterior segment. This scan demonstrates all anterior segment structures, in‐ cluding anterior lens surface, iris, and ciliary body. In UBM, frequencies of 35-50 MHz and above provide over a three‐ fold improvement in resolution compared with conventional ophthalmic ultrasound systems **(b)**. **b.** Conventional Bmode ultrasound image of the posterior segment. **c and d.** UBM image of the normal **(c)** and the PAC anterior segment **(d)**. Note the shallow anterior chamber depth of the PAC compared with the normal. **e and f.** UBM image of the anterior segment of the PACG patient before **(e)** and after laser iridotomy **(f)**. Note the increase of anterior cham‐ ber depth after laser iridotomy (LI). Arrow indicates the portion of the LI. **g and h.** UBM image of the anterior segment of the PACG patient before **(g)** and after cataract surgery (phacoemulsification and intraocular lens implantation) **(h)**.

Note the increase of anterior chamber depth after cataract surgery.

technique and the lens.

screening examination.

New devices for evaluating the anterior ocular segment in a more objective and quantita‐ tive manner have been introduced. Anterior-segment optical coherence tomography (AS-OCT) is a noninvasive technique allowing the measurement of the anterior ocular structures. A new generation of OCT, swept-source OCT (SS-OCT), has been recently in‐ troduced for the measurement of the anterior ocular segment. The SS-OCT is over ten‐ fold faster than the time-domain OCT and gives a three-dimensional (3D) observation of the anterior ocular segment. The SS-OCT employs 1,310 nmin the nearinfrared light source and its scan rate is 30,000 A scan/s.

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. The SPAC measures the peripheral ACD and converts the measure‐ ments into numerical and categorical grades by comparison with a normative database. The SPAC has been proposed as a clinician-independent screening tool for angle closure.

In the study reported here, we review the advantages and limitations of newer anterior chamber imaging technologies, namely ultrasound biomicroscopy (UBM), anterior segment optical coherence tomography (AS-OCT), and scanning peripheral anterior chamber depth analyzer (SPAC). Additionally, the present study assessed the effectiveness and possibility of the SPAC in the glaucoma screening.
