**Core Concept**
Posterior uveitis involves inflammation of the posterior segment of the eye, including the retina and choroid. The symptoms of posterior uveitis are often non-specific and may not directly correlate with the location of the inflammation.

**Why the Correct Answer is Right**
The most common symptom of posterior uveitis is diminished vision. This occurs due to the inflammation affecting the photoreceptors in the retina, leading to impaired vision. The inflammation can also cause retinal edema, which further contributes to decreased vision. Posterior uveitis can also lead to secondary complications such as retinal detachment, which can result in significant visual impairment.

**Why Each Wrong Option is Incorrect**
**Option A:** Pain is a common symptom of anterior uveitis, but it is not typically associated with posterior uveitis. In posterior uveitis, pain is usually absent or mild.
**Option B:** Photophobia is a symptom of anterior uveitis, but it is not a characteristic symptom of posterior uveitis. While some patients with posterior uveitis may experience photophobia, it is not as common as diminished vision.
**Option C:** Lacrimation is not typically associated with posterior uveitis. Lacrimation is often seen in conditions such as conjunctivitis or dry eye, but it is not a common symptom of posterior uveitis.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the symptoms of posterior uveitis can be non-specific, and a thorough ocular examination is necessary to diagnose this condition. A complete ophthalmic examination, including fundus examination and optical coherence tomography (OCT), is crucial for diagnosing posterior uveitis.

**✓ Correct Answer: D. Diminished vision**