Cherry red spot is seen in all except –
**Core Concept**
The cherry red spot refers to a characteristic fundoscopic finding where the fovea of the retina appears red due to the presence of a high concentration of oxyhemoglobin. This phenomenon occurs in conditions where there is a significant reduction in blood flow to the retina, but the retinal vessels themselves remain patent. The cherry red spot is often associated with conditions that affect the brain or the optic nerve.
**Why the Correct Answer is Right**
The cherry red spot is typically seen in conditions that cause a decrease in cerebral blood flow, such as in carbon monoxide poisoning, cyanide poisoning, and in cases of mitochondrial myopathies. In these conditions, the brain tissue is unable to utilize oxygen properly, leading to a shift in the oxygen-hemoglobin dissociation curve. As a result, the retinal vessels remain patent, but the retina itself becomes ischemic, leading to the characteristic cherry red spot appearance.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it is a condition that typically presents with a pale retina, not a cherry red spot.
* **Option B:** This option is incorrect because it is a condition that typically presents with a retinal hemorrhage, not a cherry red spot.
* **Option C:** This option is incorrect because it is a condition that typically presents with a normal retina, not a cherry red spot.
**Clinical Pearl / High-Yield Fact**
The cherry red spot is a classic sign of carbon monoxide poisoning, and its presence should prompt immediate action to remove the patient from the source of carbon monoxide exposure.
**Correct Answer: D.**