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.

Q: Which of the following lasers is used for the treatment of myopia?

Excimer Laser. **Explanation:** **1. Why Excimer Laser is Correct:** The **Excimer laser** (Excited Dimer) is the gold standard for refractive surgeries like LASIK, PRK, and LASEK. It utilizes a **193 nm Argon-Fluoride (ArF) gas** mixture to produce ultraviolet light. The underlying mechanism is **photoablation**, where the laser breaks intermolecular bonds in the corneal stroma without generating heat. By precisely reshaping the central cornea (flattening it), the refractive power is reduced, thereby correcting myopia. **2. Why Other Options are Incorrect:** * **Nd:YAG Laser (1064 nm):** This is a solid-state laser used for **photodisruption**. Its primary uses include Posterior Capsulotomy (for PCO) and Peripheral Iridotomy (for Angle Closure Glaucoma). * **Argon Laser (488–514 nm):** This laser works via **photocoagulation**. It is used for retinal procedures like Pan-Retinal Photocoagulation (PRP) in diabetic retinopathy and for treating retinal breaks. * **Harmonium Laser:** This is a distractor and is not a standard laser used in clinical ophthalmology. **3. High-Yield Clinical Pearls for NEET-PG:** * **Femtosecond Laser (1053 nm):** Used for creating the corneal flap in "Bladeless LASIK" and for lenticule extraction in **SMILE** (Small Incision Lenticule Extraction). * **LASIK Contraindications:** Keratoconus (most important), thin corneas (<450-480 μm), and active ocular infections. * **Post-LASIK Complication:** The most common side effect is **Dry Eye**. The most serious (though rare) is **Corneal Ectasia**. * **Wavelength Memory:** Excimer (193 nm), Argon (514 nm), Nd:YAG (1064 nm).

Q: Excimer laser is used in which of the following conditions?

None of the above. ### Explanation The correct answer is **None of the above** because the Excimer laser is primarily used in **refractive surgery** to reshape the cornea, rather than for treating glaucoma, cataracts, or uveitis. #### 1. Why "None of the above" is correct The **Excimer laser** (Argon-Fluoride gas, wavelength **193 nm**) is a "cold" ultraviolet laser. It works through **photoablation**, which breaks intermolecular bonds in the corneal stroma without causing thermal damage to surrounding tissues. Its primary clinical applications include: * **LASIK** (Laser-assisted in situ keratomileusis) * **PRK** (Photorefractive keratectomy) * **PTK** (Phototherapeutic keratectomy) for superficial corneal dystrophies and scars. #### 2. Why other options are incorrect * **Glaucoma:** Lasers used here include the **Argon laser** or **Frequency-doubled Nd:YAG** (for Trabeculoplasty) and the **Nd:YAG laser** (for Peripheral Iridotomy). * **Cataract:** The **Femtosecond laser** is used in FLACS (Femtosecond Laser-Assisted Cataract Surgery) for capsulotomy and lens fragmentation. The **Nd:YAG laser** is used for Posterior Capsulotomy (treating after-cataract). * **Uveitis:** Lasers have no direct role in treating active uveitis, which is managed medically (steroids/cycloplegics). #### 3. High-Yield Clinical Pearls for NEET-PG * **Wavelength:** 193 nm (Far UV spectrum). * **Mechanism:** Photoablation (1 micron of tissue is removed per pulse). * **Nd:YAG Laser (1064 nm):** Used for Posterior Capsulotomy and Iridotomy (Mechanism: Photodisruption). * **Argon Laser (488–514 nm):** Used for Retinal Photocoagulation and Trabeculoplasty (Mechanism: Photocoagulation). * **Femtosecond Laser (1053 nm):** Used for creating LASIK flaps and in cataract surgery (Mechanism: Photodisruption).

Q: What is the main corneal mechanism holding the LASIK flap in place after surgery?

Endothelial pump. In LASIK (Laser-Assisted In Situ Keratomileusis), a flap is created and then repositioned without sutures. The primary mechanism responsible for the immediate adherence and long-term stability of this flap is the **Endothelial Pump**. ### Why the Endothelial Pump is Correct The corneal endothelium contains active Na+/K+ ATPase pumps that constantly move ions (and consequently water) from the corneal stroma into the aqueous humor. This creates a **negative hydrostatic pressure** (suction effect) within the stroma. When the flap is replaced, this "vacuum" effect pulls the flap tightly against the underlying stromal bed, ensuring immediate apposition. ### Why Other Options are Incorrect * **Stromal collagen adhesions:** While a permanent scar (fibrosis) eventually forms at the flap edges, this takes weeks to months. It is not the primary mechanism for immediate adherence. * **Bowman's layer-stromal adhesions:** LASIK involves creating a flap that includes the epithelium, Bowman’s layer, and superficial stroma. Since Bowman’s layer is severed during flap creation, it cannot provide adhesion to the underlying bed. * **Endothelial-Descemet's membrane forces:** These structures are located at the posterior-most aspect of the cornea and do not directly interact with the anterior flap interface. ### High-Yield Clinical Pearls for NEET-PG * **Flap Adhesion:** Immediate adhesion is due to the **endothelial pump**; long-term stability is due to **peripheral epithelial plug** and marginal scarring. * **Interface Fluid Syndrome:** If intraocular pressure (IOP) rises significantly (e.g., steroid-induced), the endothelial pump may be overwhelmed, causing fluid to accumulate under the flap. * **Ectasia Risk:** The "Residual Stromal Bed" (RSB) must be at least **250–300 μm** to prevent post-LASIK ectasia. * **Nerve Damage:** LASIK severs the sub-basal nerve plexus, which is why **dry eye** is the most common post-operative complication.

Q: Radial keratotomy is used as a treatment modality for which of the following conditions?

Low degree myopia. **Explanation:** **Radial Keratotomy (RK)** is a surgical procedure historically used to correct **low-degree myopia** (typically between -1.00 to -4.00 Diopters). **Why Option A is correct:** The procedure involves making deep, non-perforating radial incisions (usually 4 to 8) in the peripheral cornea, sparing the central optical zone. These incisions weaken the corneal periphery, causing it to bulge outward due to intraocular pressure. This peripheral bulging results in a compensatory **flattening of the central cornea**, thereby reducing the refractive power of the eye and correcting nearsightedness. **Why other options are incorrect:** * **B. Progressive non-healing ulcer:** RK is a refractive procedure, not a treatment for infections. In fact, corneal thinning or infection are contraindications for RK. * **C. High astigmatism:** While "Astigmatic Keratotomy" (using transverse or arcuate incisions) exists, RK specifically targets spherical myopia. High astigmatism is better managed with Toric IOLs or LASIK. * **D. High hypermetropia:** RK flattens the cornea, which would worsen farsightedness. Hypermetropia requires central steepening (e.g., Thermal Keratoplasty or LASIK). **High-Yield Clinical Pearls for NEET-PG:** * **The "Coupling Phenomenon":** In RK, as the peripheral cornea bulges, the central cornea flattens. * **Complications:** The most characteristic late complication of RK is **diurnal fluctuation of vision** and **progressive hyperopic shift** (the cornea continues to flatten years after surgery). * **Incision Depth:** Incisions are typically made to 90% of the corneal thickness using a diamond knife. * **Current Status:** RK has largely been replaced by excimer laser procedures (LASIK/PRK) due to better predictability and structural stability.

Q: Intrastromal corneal ring segments (Intacs) are used in all conditions EXCEPT?

Irregular astigmatism. **Explanation:** Intrastromal Corneal Ring Segments (ICRS), commonly known by the brand name **Intacs**, are PMMA (polymethylmethacrylate) micro-inserts placed into the peripheral corneal stroma. Their primary mechanism is to create an "arc-shortening" effect, which flattens the central cornea. **Why "Irregular Astigmatism" is the correct answer:** While Intacs can help regularize a cone in keratoconus, they are **not** indicated for the treatment of generalized irregular astigmatism (especially that caused by corneal scarring or trauma). In fact, the presence of central corneal scarring or severe irregular astigmatism is a **contraindication** for Intacs, as the rings cannot reshape a scarred or non-compliant stromal bed effectively. **Analysis of Incorrect Options:** * **Post-LASIK Keratectasia:** Intacs are a standard treatment to provide structural support and flatten the cornea in cases where the cornea has thinned and bulged following refractive surgery. * **Keratoconus:** This is the most common indication. Intacs are used in mild-to-moderate cases (with clear centers) to flatten the cone, improve visual acuity, and potentially defer the need for a corneal transplant. * **Low Myopia:** Intacs were originally FDA-approved for the correction of low myopia (-1.00 to -3.00 Diopters) in patients with healthy corneas. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** They act as "passive spacers" that flatten the central cornea without removing tissue (unlike LASIK). * **Reversibility:** A key advantage of Intacs is that they are removable and exchangeable. * **Prerequisite:** The central cornea must be **clear** (no scarring) for Intacs to be effective. * **Placement:** They are inserted at approximately **80% depth** of the corneal stroma.

Question 1

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

Accepted Answer

Excimer Laser

Answer

Nd–YAG LASER

Answer

Carbamazepine

Answer

SSRI

Question 2

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 3

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 4

Which of the following is a treatment modality for myopia?

Accepted Answer

LASER Keratomileusis

Answer

Radial keratotomy

Answer

Epikeratophakia

Answer

LASER Keratoplasty

Question 5

Which of the following lasers is used for the treatment of myopia?

Accepted Answer

Excimer Laser

Answer

Nd-YAG LASER

Answer

Harmonium Laser

Answer

Argon Laser

Question 6

Excimer laser is used in which of the following conditions?

Accepted Answer

None of the above

Answer

Glaucoma

Answer

Cataract

Answer

Uveitis

Question 7

What is the main corneal mechanism holding the LASIK flap in place after surgery?

Accepted Answer

Endothelial pump

Answer

Stromal collagen adhesions

Answer

Bowman's layer-stromal adhesions

Answer

Endothelial-Descemet's membrane forces

Question 8

In the surgical procedure LASIK, the shape of the cornea may be flattened. This will result in which of the following?

Accepted Answer

Decreased refraction of light by the cornea

Answer

A decreased amount of light entering through the cornea

Answer

Conversion of the cornea from a "stationary" to an "adjustable" form of refraction

Answer

Maintenance of the lens in a more flattened state

Question 9

Radial keratotomy is used as a treatment modality for which of the following conditions?

Accepted Answer

Low degree myopia

Answer

Progressive non-healing ulcer

Answer

High astigmatism

Answer

High hypermetropia

Question 10

Intrastromal corneal ring segments (Intacs) are used in all conditions EXCEPT?

Accepted Answer

Irregular astigmatism

Answer

Post-LASIK keratectasia

Answer

Keratoconus

Answer

Low myopia

Refractive Surgery — MCQs

Refractive Surgery — MCQs

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