Refractive Surgery Practice Questions

Q: Which of the following is used for the treatment of Myopia?

Excimer Laser. **Explanation:** **Correct Answer: B. Excimer Laser** The **Excimer laser** (Argon-Fluoride gas, 193 nm wavelength) is the gold standard for corneal refractive surgeries like **LASIK, PRK, and SMILE**. It works via **photoablation**, a process where high-energy ultraviolet light breaks molecular bonds in the corneal stroma without generating heat (cold laser). In myopia, the Excimer laser is used to flatten the central cornea, thereby reducing its refractive power so that light focuses accurately on the retina. **Incorrect Options:** * **A. Nd:YAG Laser (1064 nm):** This is a solid-state laser used for **photodisruption**. Its primary uses in ophthalmology include Posterior Capsulotomy (for PCO) and Peripheral Iridotomy (for Angle-Closure Glaucoma). It is not used for reshaping the cornea. * **C. Carbamazepine:** This is an anticonvulsant and the first-line treatment for **Trigeminal Neuralgia**. It has no role in treating refractive errors. * **D. SSRIs (Selective Serotonin Reuptake Inhibitors):** These are antidepressants. In ophthalmology, they are clinically significant because they can occasionally cause mydriasis and precipitate acute angle-closure glaucoma, but they do not treat myopia. **High-Yield Clinical Pearls for NEET-PG:** 1. **Laser Wavelengths:** Excimer (193 nm), Nd:YAG (1064 nm), Argon (514 nm - used for photocoagulation in diabetic retinopathy). 2. **Femtosecond Laser:** Used in "Bladeless LASIK" to create the corneal flap; it operates at 1053 nm. 3. **Contraindications for LASIK:** Thin cornea (<450-480 μm), Keratoconus, and unstable refractive error. 4. **SMILE (Small Incision Lenticule Extraction):** The newest refractive procedure that uses only a Femtosecond laser, eliminating the need for a corneal flap.

Q: What is the wavelength of laser (in nanometers) used for shaping the cornea in refractive surgery?

193 nm. **Explanation:** The correct answer is **193 nm**. This wavelength belongs to the **Excimer laser** (Argon-Fluoride gas), which is the gold standard for corneal refractive surgeries like LASIK, PRK, and LASEK. **Why 193 nm is correct:** The Excimer laser operates in the far-ultraviolet spectrum. Its primary mechanism is **photoablation** (or photodecomposition). The high-energy 193 nm photons have enough energy to break intermolecular organic bonds in the corneal stroma without generating significant heat. This allows for extremely precise tissue removal (0.25 microns per pulse) without damaging the surrounding transparent corneal tissue, making it ideal for reshaping the cornea to correct refractive errors. **Analysis of Incorrect Options:** * **451 nm:** This falls within the blue light spectrum and is not typically used for therapeutic corneal ablation. * **532 nm (Frequency-doubled Nd:YAG):** This is a green laser used primarily for **retinal photocoagulation** (e.g., in Diabetic Retinopathy) and laser trabeculoplasty in glaucoma. * **1064 nm (Nd:YAG):** This is an infrared laser used for **photodisruption**. It is commonly used for Posterior Capsulotomy (after cataract surgery) and Peripheral Iridotomy. **High-Yield Clinical Pearls for NEET-PG:** * **Femtosecond Laser:** Uses a wavelength of **1053 nm** (near-infrared) and is used for creating the LASIK flap or in SMILE (Small Incision Lenticule Extraction). * **Photoablation vs. Photodisruption:** Remember that Excimer (193 nm) *ablates* (vaporizes), while Nd:YAG (1064 nm) *disrupts* (cuts/blasts) tissue. * **Corneal Thickness:** A minimum residual stromal bed of **250–300 microns** must be maintained after laser ablation to prevent corneal ectasia.

Q: Which of the following is NOT a characteristic of femtolasik?

Flapless lasik. **Explanation:** **Femto-LASIK** (Femtosecond Laser-Assisted In Situ Keratomileusis) is an advanced refractive surgery where a femtosecond laser is used to create a corneal flap instead of a mechanical microkeratome (blade). 1. **Why Option A is correct:** Femto-LASIK is **not** flapless. It still involves the creation and displacement of a corneal flap to allow the excimer laser to reshape the underlying stroma. The term "Flapless" refers to procedures like **SMILE** (Small Incision Lenticule Extraction) or surface ablations like **PRK**. 2. **Why Option B is incorrect:** It is indeed "Bladeless" because the femtosecond laser replaces the traditional oscillating steel blade (microkeratome). 3. **Why Option C is incorrect:** Femto-LASIK is associated with a lower incidence of dry eyes compared to traditional LASIK. This is because the laser allows for a thinner, more predictable flap, which results in less damage to the sub-basal corneal nerve plexus. 4. **Why Option D is incorrect:** Like traditional LASIK, Femto-LASIK requires a minimum residual stromal bed (usually >250-300 microns) to prevent ectasia. Therefore, it cannot be safely performed in patients with very thin corneas. **High-Yield Clinical Pearls for NEET-PG:** * **SMILE:** The true "flapless" and "bladeless" procedure where a lenticule is extracted through a small incision. * **Flap Thickness:** Femtosecond lasers create flaps of approximately 100–110 microns, whereas microkeratomes are less predictable (130–160 microns). * **Complication:** A specific complication of Femto-LASIK is **Transient Light Sensitivity Syndrome (TLSS)**.

Q: Which of the following is a treatment modality for myopia?

LASER Keratomileusis. **Explanation:** **Myopia (Nearsightedness)** occurs when the axial length of the eye is too long or the refractive power of the cornea/lens is too high, causing light rays to focus in front of the retina. Treatment aims to decrease the refractive power of the eye. **Why LASER Keratomileusis is correct:** **LASIK (Laser-Assisted In Situ Keratomileusis)** is the gold standard surgical treatment for myopia. It involves creating a corneal flap and using an **Excimer laser (193 nm)** to ablate the central corneal stroma. By flattening the central cornea, the refractive power is reduced, allowing light to focus accurately on the retina. **Analysis of Incorrect Options:** * **Radial Keratotomy (RK):** While historically used for myopia (making radial incisions to flatten the cornea), it is now **obsolete** due to complications like diurnal vision fluctuation and globe instability. In the context of modern exams, LASIK is the preferred laser-based modality. * **Epikeratophakia:** This involves suturing a donor corneal lenticule onto the surface of the patient's cornea. It was primarily used for **aphakia** or high hyperopia, not standard myopia. * **LASER Keratoplasty:** This refers to corneal transplantation using a laser (like Femtosecond) for incisions. It is a treatment for corneal scarring or keratoconus, not a refractive procedure for simple myopia. **High-Yield Clinical Pearls for NEET-PG:** * **Excimer Laser:** Uses Argon-Fluoride (ArF) gas; wavelength is **193 nm** (Ultraviolet range). * **Prerequisites for LASIK:** Age >18 years, stable refraction for 1 year, and a minimum residual stromal bed thickness of **250 microns** to prevent corneal ectasia. * **SMILE (Small Incision Lenticule Extraction):** The newest "flapless" refractive surgery for myopia using a Femtosecond laser.

Question 1

Absolute contraindication for LASIK is:

Accepted Answer

Central corneal thickness < 480 µm

Answer

Age < 13 years

Answer

Myopia of −4 D

Answer

Stable refraction for 1 year

Question 2

Which of the following is used for the treatment of Myopia?

Accepted Answer

Excimer Laser

Answer

Nd–YAG LASER

Answer

Carbamazepine

Answer

SSRI

Question 3

What is the wavelength of laser (in nanometers) used for shaping the cornea in refractive surgery?

Accepted Answer

193 nm

Answer

451 nm

Answer

532 nm

Answer

1064 nm

Question 4

Which of the following is NOT a characteristic of femtolasik?

Accepted Answer

Flapless lasik

Answer

Bladeless lasik

Answer

Less incidence of dry eyes

Answer

Cannot be done in thinner corneas

Question 5

Which of the following is a treatment modality for myopia?

Accepted Answer

LASER Keratomileusis

Answer

Radial keratotomy

Answer

Epikeratophakia

Answer

LASER Keratoplasty

Refractive Surgery — MCQs

Refractive Surgery — MCQs

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