**Core Concept**
The best site for intraocular lens (IOL) implantation is a critical decision in cataract surgery, as it affects the postoperative visual outcome and patient satisfaction. The choice of IOL location depends on various factors, including the type of IOL, the patient's corneal curvature, and the presence of any ocular comorbidities.

**Why the Correct Answer is Right**
The scleral fixated IOL is implanted in a position that allows for optimal optical alignment and minimal risk of complications. This type of IOL is typically used in patients with complex ocular conditions, such as high myopia or aphakia. The posterior chamber is the most suitable location for IOL implantation, as it allows for the most natural optical alignment and minimizes the risk of glare and halos.

**Why Each Wrong Option is Incorrect**
* **Option A:** Anterior chamber IOLs are associated with a higher risk of complications, including iris chafing, uveitis, and glaucoma.
* **Option B:** Epithelial downgrowth is a rare complication of anterior chamber IOLs, which can lead to chronic uveitis and vision loss.
* **Option C:** Scleral fixated IOLs are typically used in patients with complex ocular conditions, such as high myopia or aphakia, and are not the best site for routine IOL implantation.

**Clinical Pearl / High-Yield Fact**
In general, the best site for IOL implantation is the posterior chamber, as it allows for the most natural optical alignment and minimizes the risk of complications.

**Correct Answer:** C. Scleral fixated IOL in the posterior chamber.