**Core Concept**
Argon laser is a type of gas laser that emits light in the blue-green spectrum, typically in the range of 488-514 nanometers. It is commonly used in ophthalmology for photocoagulation of retinal tissues and in dermatology for treating vascular lesions.

**Why the Correct Answer is Right**
Argon laser photocoagulation works by selectively targeting and damaging the retinal tissue, leading to the formation of scar tissue and subsequent closure of abnormal blood vessels. This is particularly useful in treating conditions such as diabetic retinopathy and retinal tears. The argon laser's wavelength is well-absorbed by hemoglobin, allowing for precise targeting of vascular lesions in the skin.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because argon laser is indeed used in ophthalmology for photocoagulation of retinal tissues.
**Option B:** This option is incorrect because argon laser is used in dermatology for treating vascular lesions such as port-wine stains and hemangiomas.
**Option C:** This option is incorrect because argon laser is used in retinal detachment surgery to treat retinal tears and holes.

**Clinical Pearl / High-Yield Fact**
It's essential to note that argon laser photocoagulation should be used with caution in patients with certain medical conditions, such as glaucoma or cataracts, as it can exacerbate these conditions.

**Correct Answer:**
I. Argon laser is used in all except: **Photodynamic therapy**.