## Core Concept
β blockers, or beta blockers, are a class of medications that inhibit the action of beta-adrenergic receptors in the body. They are primarily used to treat cardiovascular diseases but can also be used for conditions like glaucoma and, with caution, in patients with asthma. The key consideration in choosing a β blocker is its selectivity for β1 versus β2 receptors, as well as its intrinsic sympathomimetic activity (ISA) and membrane-stabilizing effects.

## Why the Correct Answer is Right
In a patient with asthma and glaucoma, the ideal β blocker would be one that does not exacerbate asthma (by blocking β2 receptors in the lungs) but can still lower intraocular pressure in glaucoma. **Betaxolol** is a β1 selective (cardioselective) β blocker with partial agonist activity. Its β1 selectivity means it is less likely to provoke bronchospasm in asthma patients, making it a safer choice compared to non-selective β blockers.

## Why Each Wrong Option is Incorrect
- **Option A:** Non-selective β blockers like propranolol would block both β1 and β2 receptors, potentially worsening asthma due to unopposed β2 blockade in the bronchial smooth muscle.
- **Option B:** While some β blockers have intrinsic sympathomimetic activity (ISA), this characteristic alone does not specifically address the need for β1 selectivity in a patient with asthma and glaucoma.
- **Option D:** A non-selective β blocker with additional properties might not offer the same safety profile as a β1 selective agent in a patient with asthma.

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that β1 selective blockers like **betaxolol** are preferred in patients with asthma or chronic obstructive pulmonary disease (COPD) who require β blocker therapy, as they are less likely to induce bronchospasm. However, it's crucial to note that even β1 selective blockers should be used with caution and started at a low dose in patients with asthma.

## Correct Answer: C. Betaxolol.