**Core Concept**
Intravitreal injection is a treatment method for various eye diseases, but it carries the risk of drug toxicity to the retina. Macular toxicity refers to damage to the macula, the part of the retina responsible for central vision. Certain drugs can cause macular toxicity when administered intravitreally due to their high concentration and prolonged exposure to the retina.

**Why the Correct Answer is Right**
Gentamicin is an aminoglycoside antibiotic that is commonly used to treat bacterial infections. When administered intravitreally, gentamicin can cause macular toxicity due to its ability to bind to the mitochondrial ribosomes, leading to mitochondrial dysfunction and ultimately, retinal toxicity. This is a well-documented side effect of gentamicin, particularly when used in high concentrations or for prolonged periods.

**Why Each Wrong Option is Incorrect**
**Option B:** Vancomycin is a glycopeptide antibiotic that is not typically associated with macular toxicity when used intravitreally. While vancomycin can cause other side effects, such as retinal detachment or uveitis, macular toxicity is not a well-documented risk.

**Option C:** Dexamethasone is a corticosteroid that is commonly used to treat various eye diseases, including macular edema. While dexamethasone can cause side effects such as cataract formation or glaucoma, macular toxicity is not typically associated with its use.

**Option D:** Ceftazidime is a cephalosporin antibiotic that is not commonly used for intravitreal injection. While ceftazidime can cause side effects such as nephrotoxicity or neurotoxicity, macular toxicity is not a well-documented risk.

**Clinical Pearl / High-Yield Fact**
When administering intravitreal injections, it is essential to weigh the benefits of treatment against the risks of drug toxicity. Aminoglycoside antibiotics, such as gentamicin, should be used with caution and only when absolutely necessary, as they can cause irreversible damage to the retina.

**✓ Correct Answer: A. Gentamycin**