**Core Concept:** Anterior uveitis is an inflammation of the uvea, which is the middle layer of the eye that contains blood vessels. Posterior segment involvement in uveitis can lead to decrease in vision due to inflammation and damage to the retina, optic nerve, and choroid.

**Why the Correct Answer is Right:** Decrease in vision in anterior uveitis patients can occur due to posterior segment involvement. In this case, the correct answer is **D**. Posterior uveitis refers to inflammation affecting the posterior segment of the eye, including the retina, optic nerve, and choroid. When these structures are inflamed or damaged, it can lead to decrease in vision.

**Why Each Wrong Option is Incorrect:**

A. **Anterior uveitis:** This refers to inflammation affecting the anterior segment of the eye, which includes the cornea, sclera, and iris. Posterior segment involvement is not a typical feature of anterior uveitis, so options A, B, and C are incorrect.

B. **Ischemic optic neuropathy:** This is a type of optic nerve damage caused by reduced blood flow. It can happen in diabetes, but does not directly relate to the inflammation in anterior uveitis, so option B is incorrect.

C. **Retinal detachment:** This is a condition where the retina separates from its blood supply. It is unrelated to anterior uveitis, so option C is incorrect.

E. **Intraocular pressure elevation:** This refers to increased pressure within the eye, which can result in glaucoma. While this may exacerbate pre-existing optic neuropathies, it does not explain the decrease in vision due to posterior segment involvement in anterior uveitis, so option E is incorrect.

**Clinical Pearl:** Posterior segment involvement in uveitis is a critical aspect to consider since it can lead to optic neuropathy, macular edema, and retinal vasculitis, which can result in decreased vision. It is essential for diagnosing and managing uveitis cases to evaluate for posterior segment involvement.