Final answer:
The most frequently used topical anesthetic for preoperative ocular instillation is tetracaine, favored for its effective numbing properties. Lidocaine and novocaine, as sodium channel blockers, prevent the transmission of pain signals, representing the mechanism of action for local anesthetics.
Step-by-step explanation:
The topical anesthetic used most frequently for preoperative ocular instillation is tetracaine. Tetracaine is preferred due to its effective numbing properties which are necessary prior to eye surgeries to reduce discomfort and facilitate the procedure. While lidocaine is a common local anesthetic for various medical procedures, tetracaine is specifically favored for ocular use.
Drugs such as lidocaine and novocaine act as sodium channel blockers, which means they prevent sodium ions from crossing the neuronal membrane. This blocking action is essential for their efficacy as local anesthetics because it interrupts the pain signal transmission along nerves, thereby providing the desired anesthesia.
The historical anesthetic, cocaine, was the first local anesthetic discovered but is not commonly used today because of its potential for abuse and side effects. Instead, alternatives like tetracaine and lidocaine are chosen for their safety and effectiveness.