Final answer:
The sclera and iris are typically not the most susceptible parts of the eye to microbial infection. Instead, the conjunctiva is more commonly affected due to its exposure and contact with the environment, despite its normal microbiota which aids in defense against pathogens.
Step-by-step explanation:
The statement that the sclera and iris are the most susceptible parts of the eye to microbial infection is false. In fact, the conjunctiva of the eye is more commonly a site for microbial infections. The sclera, being a protective layer composed mainly of collagen and elastic fibers, and the iris, a smooth muscle controlling light entry into the eye, are not typically the initial sites for infections. Rather, the mucous membranes such as the conjunctiva, which is exposed and in contact with environmental agents, are more prone to microbial invasion despite the presence of normal microbiota that can help defend against pathogens.
The surfaces of the eyeball and inner eyelid, which are mucous membranes called conjunctiva, do contain normal microbiota that provide a barrier to infection. However, when pathogens overcome these defenses, infections like conjunctivitis can occur. Deeper infections of the eye, affecting structures such as the sclera or iris, are less common as these parts have robust structural defenses that make them less susceptible to microbial attack.