Final answer:
Pilocarpine is commonly injected during surgery to reduce intraocular pressure (IOP) and induce miosis, which is useful in managing eye disorders such as glaucoma.
Step-by-step explanation:
The substance that may be injected during surgery to decrease IOP (intraocular pressure) and to cause miosis is pilocarpine. Pilocarpine is a muscarinic agonist that works primarily on the smooth muscle of the iris to constrict the pupil (miosis), reversing mydriasis. Moreover, it causes the ciliary muscle to contract. This action opens up the trabecular meshwork at the base of the cornea, facilitating the outflow of aqueous humor from the anterior chamber, effectively reducing IOP. This reduction is particularly beneficial in managing glaucoma, where elevated intraocular pressure is a significant concern.