Final answer:
Uveitis is the most common systemic manifestation of Scleritis, not conjunctivitis, keratitis, or vasculitis; uveitis involves inflammation of the uveal tract that is often associated with scleritis.
Step-by-step explanation:
The most common systemic manifestation of Scleritis is not conjunctivitis, keratitis, or vasculitis, but rather uveitis. Scleritis, which is defined primarily as an inflammation of the sclera, can have systemic associations, potentially affecting other parts of the eye such as the uvea, leading to uveitis. Uveitis is characterized by inflammation of the uvea, which includes the iris, ciliary body, and choroid. Because scleritis can affect contiguous structures within the eye, the resulting inflammation can spread to the uvea.
Conditions such as conjunctivitis affect the conjunctiva, while keratitis involves the cornea. Though these are also eye-related inflammations, they are not the most common systemic manifestations of scleritis. Vasculitis, a broader term for inflammation of the blood vessels, may be seen in systemic diseases associated with scleritis, but it is not the symptom most directly linked to scleritis itself.
Therefore, the correct answer is 2) Uveitis, which involves the inflammation of uveal tract adjacent to the sclera.