Okay, so the question is about the type of laser used for iridotomy. Let me start by recalling what iridotomy is. Iridotomy is a surgical procedure where a small hole is made in the iris. This is typically done to treat or prevent angle-closure glaucoma by allowing the aqueous humor to flow more freely, thus reducing intraocular pressure.

Now, the question is about which laser is used. I remember that lasers used in ophthalmology come in different types, like Nd:YAG, Argon, Excimer, CO2, etc. Each has specific uses. For iridotomy, the most common laser is the Nd:YAG (Neodymium-doped Yttrium Aluminum Garnet) laser. I think that's because it's a solid-state laser that can create precise cuts with minimal thermal damage, which is important in delicate eye surgery. The Nd:YAG laser emits infrared light at a wavelength of 1064 nm, which is well-absorbed by the iris tissue, allowing for effective cutting without much damage to surrounding structures.

Let me check the other options. Argon laser is used in trabeculoplasty, not iridotomy. Excimer lasers are used in photorefractive keratectomy (LASIK) for reshaping the cornea. CO2 lasers are used in some dermatological procedures but not in ophthalmology for iridotomy. Diode lasers are used in other areas like retinal photocoagulation but not for iridotomy. So the correct answer should be Nd:YAG.

The clinical pearl here is that Nd:YAG is the go-to laser for creating an iridotomy because of its precision and minimal collateral damage. Remembering the specific wavelengths and their applications is key here. Also, angle-closure glaucoma is an emergency, so knowing the correct laser for quick intervention is crucial.

**Core Concept**
Iridotomy is a laser procedure to create an opening in the iris, typically for angle-closure glaucoma. The **Nd:YAG laser** is the gold standard due to its precision, minimal thermal damage, and ability to create a clean iridectomy. It operates at **1064 nm wavelength**, effectively ablating iris tissue without corneal contact.

**Why the Correct Answer is Right**
The **Nd:YAG laser** is a solid-state laser that emits high-energy infrared light. It is ideal for iridotomy because it can create a small, precise hole in the iris to relieve pupillary block. The laser’s wavelength is highly absorbed by the iris pigment epithelium, allowing controlled tissue vaporization without damaging adjacent structures like the cornea or lens. It is non-contact, rapid, and associated with fewer complications compared to other lasers.

**Why Each Wrong Option is Incorrect**
**Option A:** Argon laser is used for trabeculoplasty or photocoagulation, not iridotomy.
**Option B:** Excimer laser is used for refractive surgeries (e.g., LASIK) due to its ultraviolet wavelength.
**Option C:** CO2 laser is not used in ophthalmology; it’s employed in dermatology for ablative procedures.

**Clinical Pearl / High-Yield Fact**
**Nd:YAG laser** is the only laser approved for iridotomy in angle

✓ Correct Answer: C. Nd: YAG