Dark adaptation is delayed in all of the following conditions except:
**Core Concept**
Dark adaptation is the process by which the human eye adjusts to changes in light levels, enabling it to function optimally in low-light conditions. This adaptation involves changes in the retina, particularly in the rod cells, which are more sensitive to dim light than cone cells.
**Why the Correct Answer is Right**
Dark adaptation is typically delayed in conditions that affect the retina or the visual pathway. Conditions such as cataracts, age-related macular degeneration, and diabetic retinopathy can lead to delayed dark adaptation due to the impaired function of rod cells or the presence of visual pathway lesions. However, some conditions do not affect dark adaptation.
**Why Each Wrong Option is Incorrect**
**Option A:** Certain conditions such as Leber's hereditary optic neuropathy (LHON) can cause delayed dark adaptation due to the dysfunction of the rod cells.
**Option B:** Age-related macular degeneration (AMD) is known to cause delayed dark adaptation due to the degeneration of the retinal pigment epithelium and photoreceptors.
**Option C:** Diabetic retinopathy can cause delayed dark adaptation due to the damage to the retinal capillaries and the resulting ischemia of the retina.
**Clinical Pearl / High-Yield Fact**
One key point to remember is that conditions affecting the peripheral retina, such as retinitis pigmentosa, can cause delayed dark adaptation due to the degeneration of rod cells in the peripheral retina.
**Correct Answer:** D.