Typical field defect observed in anterior ischaemic optic neuropathy is:
**Core Concept**
Anterior ischemic optic neuropathy (AION) is a condition characterized by sudden loss of vision due to ischemia of the optic nerve head. The **optic nerve** is supplied by the **short posterior ciliary arteries**, and ischemia in these arteries can lead to AION. This condition often results in specific visual field defects.
**Why the Correct Answer is Right**
The typical field defect observed in AION is an **altitudinal field defect**, which affects either the upper or lower half of the visual field. This is because the ischemia tends to affect either the upper or lower portion of the optic nerve head, leading to a corresponding loss of vision in the contralateral visual field. The **mechanism** involves infarction of the nerve tissue due to inadequate blood supply.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the typical field defect seen in AION.
**Option B:** Similarly, this option does not match the characteristic visual field loss associated with AION.
**Option D:** This option is also incorrect as it does not correspond to the typical presentation of AION.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that AION often presents with sudden, painless loss of vision, typically in one eye, and is more common in older adults. Recognizing the characteristic **altitudinal field defect** is crucial for diagnosing AION.
**Correct Answer:** D. Altitudinal field defect.