**Core Concept:** Intravitreal injections are procedures where drugs are injected directly into the vitreous humor of the eye for therapeutic purposes, such as anti-vascular endothelial growth factor (anti-VEGF) agents for treating conditions like diabetic retinopathy, retinal vein occlusion, and age-related macular degeneration. These drugs can potentially cause ocular complications, including macular toxicity.

**Why the Correct Answer is Right:** Intravitreal injection of drugs like DEX (dexamethasone) can lead to macular toxicity due to increased intraocular pressure (IOP) and inflammation. Dexamethasone is a potent corticosteroid with anti-inflammatory properties, which can cause an increase in IOP and decrease in ocular perfusion pressure, leading to ischemia and subsequent macular edema.

**Why Each Wrong Option is Incorrect:**

A. **Option C (Lumican):** Lumican is a proteoglycan that is involved in maintaining corneal transparency and wound healing. It is not related to macular toxicity in intravitreal injections.

B. **Option D (Sodium Polystyrene Sulfonate):** Sodium polystyrene sulfonate is a drug used in the treatment of hyperkalemia (elevated potassium levels) and is not associated with macular toxicity in intravitreal injections.

C. **Option A (Dexamethasone):** As explained earlier, dexamethasone can cause macular toxicity due to increased IOP and inflammation.

**Clinical Pearl:** When considering intravitreal injections, clinicians should carefully weigh the potential benefits against the risks, including macular toxicity, and choose the appropriate treatment options for each patient based on their specific condition and medical history. Regular monitoring of IOP and visual acuity is crucial after intravitreal injections to detect any potential complications early and manage them promptly.