Final answer:
The iris can block aqueous humor flow in two ways: pupillary block and plateau iris, both of which can lead to increased intraocular pressure and potentially cause glaucoma.
Step-by-step explanation:
The two ways the iris can block aqueous flow are pupillary block and plateau iris. Pupillary block occurs when the flow of aqueous humor between the lens and iris impedes, causing a rise in pressure that pushes the iris forward, eventually obstructing the trabecular meshwork where aqueous humor drains. Plateau iris is a configuration where the ciliary body is positioned in such a way that it pushes the peripheral iris forward, again blocking the trabecular meshwork and interrupting drainage of aqueous humor, potentially leading to glaucoma.