Pupillary block is the most common mechanism responsible for angle closure [9], but the anatomical configuration which causes a plateau iris may be a more common mechanism than was previously thought. Pupillary block mechanismIn pupillary block, the resistance to aqueous flow from the posterior to anterior chamber is at the level of the pupil, creating a pressure gradient that causes forward bowing of the peripheral iris and closure of the angle [10,11].Aqueous humor flow from the posterior chamber into the anterior chamber is regulated by a differential pressure between the anterior and the posterior chamber. This pressure differential may increase greatly when the dimensions of the iris-lens channels are changed. As this pressure increment increases, the iris becomes more convex and can close angle.Extreme anterior iris-bulging, iris bombé would be expected with pressure differentials of 10-15 mm Hg [12]. The variables that influence the flow through the ''pinch region'' (iris-lens channels) and influence the pressure differential and related iris contour have been studied extensively [12][13][14][15][16].Changes in pupillary size, increased channel length and decreased height, movement of the iris insertion posteriorly or of the lens anteriorly, were associated with an expected increase in the pressure differential. Other variables exist and interact to determine the iris contour, including eye size, especially the dimensions of the anterior segment, lens size and position, iris stroma and iris musculature characteristics, ciliary body anatomy, and physiologic parameters including aqueous humor flow rate, facility of outflow, vitreousaqueous fluid flow, and the effects of accommodation and blinking [9]. AbstractPrimary open angle glaucoma (PACG) is a major cause of blindness especially in Asia. The pathogenesis of this condition has been widely investigated. Traditionally gonioscopy is the method of choice for the esamination of patients considered to be at risk for angle closure, but it is a rather invasive procedure and it is reported to be primarily used by glaucoma specialists. Recently newer ultrasound and optical methods for the evaluation of the anterior chamber angle have been introduced in the clinical practice, with distinct advantages and disadvantages both compared to each other and to gonioscopy. This review will address the pathogenesis of PACG, the use of gonioscopy and will evaluate the newer methods of angle examination.