Coloured halos are seen in all, except –
**Core Concept**
Coloured halos refer to a visual disturbance characterized by the presence of coloured rings or halos around lights, typically seen in patients with increased intraocular pressure (IOP) or other conditions affecting the optic nerve.
**Why the Correct Answer is Right**
The correct answer is related to conditions that cause increased IOP, leading to damage to the optic nerve and surrounding retinal tissue. In conditions such as acute angle-closure glaucoma, the sudden increase in IOP causes damage to the optic nerve and surrounding tissue, resulting in coloured halos. This is due to the compression of the optic nerve head and the resulting ischemia of the optic nerve fibers.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because coloured halos are not typically seen in diabetic retinopathy, which is characterized by microvascular damage and diabetic macular edema. While visual disturbances may occur in diabetic retinopathy, coloured halos are not a common symptom.
**Option B:** This option is incorrect because coloured halos are not typically seen in age-related macular degeneration (AMD), which is characterized by the degeneration of the macula and vision loss. While visual disturbances may occur in AMD, coloured halos are not a common symptom.
**Option C:** This option is incorrect because coloured halos are not typically seen in retinal detachment, which is characterized by the separation of the retina from the underlying retinal pigment epithelium. While visual disturbances may occur in retinal detachment, coloured halos are not a common symptom.
**Clinical Pearl / High-Yield Fact**
Coloured halos are a classic symptom of acute angle-closure glaucoma, and prompt recognition of this symptom is crucial in the diagnosis and treatment of this condition.
**Correct Answer: A. Diabetic retinopathy.**