Small Incision Lenticule Extraction — MCQs
Identify the surgical step shown in the image given below
Method followed to decrease post-op infection in cataract surgery:
Which keratometry reading is most accurate in post-LASIK eyes for IOL power calculation?
Gold standard procedure to reduce recurrence of pterygium after surgical excision is
Which of the following is used for the treatment of Myopia?
Which of the following are treatment modalities for myopia?
What is the wavelength of laser (in nanometers) used for shaping the cornea in refractive surgery?
Which of the following lasers is used for the treatment of myopia?
Excimer laser is used in which of the following conditions?
What is the main corneal mechanism holding the LASIK flap in place after surgery?
Small Incision Lenticule Extraction Indian Medical PG Practice Questions and MCQs
Question 1: Identify the surgical step shown in the image given below
- A. Capsulorrhexis
- B. Hydrodissection
- C. Intraocular lens implantation
- D. Lens aspiration (Correct Answer)
Explanation: ***Lens aspiration*** - The image shows a **phacoemulsification handpiece** (the instrument with the shining tip and central bore tube) actively fragmenting and aspirating the lens material, indicated by the cloudy material being removed. - This step is part of cataract surgery where the cataractous lens material is removed from the eye. *Capsulorrhexis* - This involves creating a **continuous curvilinear tear** in the anterior lens capsule, typically done at the beginning of cataract surgery. - The image does not show a tearing or incising action on the capsule; instead, it depicts material removal. *Hydrodissection* - This step involves injecting a **fluid wave** between the lens capsule and the lens cortex to separate them, facilitating nuclear rotation and removal. - The image depicts the removal of lens material, not the injection of fluid to separate layers. *Intraocular lens implantation* - This step involves inserting the **artificial lens** into the capsular bag after the cataractous lens has been removed. - The visual cues in the image indicate material removal and emulsification, not the insertion of a new lens.
Question 2: Method followed to decrease post-op infection in cataract surgery:
- A. Topical antibiotics and sterile draping
- B. Topical antibiotics alone
- C. Topical antibiotics and sterile instruments
- D. Intracameral antibiotics and betadine wash (Correct Answer)
Explanation: ***Intracameral antibiotics and betadine wash*** - **Intracameral antibiotics** (e.g., cefuroxime, moxifloxacin) directly target the anterior chamber during surgery, effectively reducing the risk of **endophthalmitis**. - A **betadine (povidone-iodine) wash** of the ocular surface preoperatively significantly reduces bacterial load, preventing introduction of microbes into the surgical field. *Topical antibiotics and sterile draping* - While **topical antibiotics** are important, they may not achieve sufficient intraocular concentrations to prevent deep infection effectively. - **Sterile draping** is essential for maintaining a sterile field but does not address potential intrinsic bacterial flora on the conjunctiva or adnexa as thoroughly as a betadine wash. *Topical antibiotics alone* - **Topical antibiotics** alone are often insufficient to prevent **intraocular infections** because they may not penetrate the eye adequately to eradicate all pathogens. - This approach lacks the comprehensive germicidal action of a **betadine wash** on the ocular surface and the direct intraocular effect of intracameral antibiotics. *Topical antibiotics and sterile instruments* - **Sterile instruments** are a fundamental and non-negotiable part of any surgical procedure to prevent infection from external sources. - However, relying solely on **topical antibiotics** and sterile instruments overlooks the importance of reducing the patient's own **periocular bacterial flora** (addressed by betadine wash) and directly treating potential intraocular contamination (addressed by intracameral antibiotics).
Question 3: Which keratometry reading is most accurate in post-LASIK eyes for IOL power calculation?
- A. Topography-derived K
- B. Total corneal power (Correct Answer)
- C. Manual keratometry
- D. Automated keratometry
Explanation: ***Total corneal power*** * After LASIK, the **anterior and posterior corneal curvatures** are altered, leading to discrepancies in standard keratometry readings. * **Total corneal power** methods, such as those derived from **corneal tomography** or **anterior segment OCT**, account for both surfaces, providing a more accurate estimation of the true refractive power. * *Topography-derived K* * While corneal topography is valuable for assessing the anterior corneal surface and identifying **irregular astigmatism**, it traditionally focuses on the anterior curvature and may not fully account for the altered **posterior corneal surface** after LASIK. * Standard topography-derived K values often rely on assumptions about the posterior-to-anterior corneal curvature ratio, which are invalid after refractive surgery. * *Manual keratometry* * Manual keratometry measures the **anterior corneal curvature** at a few discrete points and is highly susceptible to inaccuracies due to the post-LASIK changes in corneal shape. * It tends to **overestimate the corneal power** in eyes that have undergone myopic LASIK and **underestimate it** in hyperopic LASIK, leading to significant IOL power calculation errors. * *Automated keratometry* * Similar to manual keratometry, automated keratometry primarily measures the **anterior corneal surface** and relies on a fixed refractive index ratio that is no longer valid after corneal reshaping. * These devices generally provide **inaccurate keratometry readings** in post-refractive surgery eyes, contributing to refractive surprises after cataract surgery.
Question 4: Gold standard procedure to reduce recurrence of pterygium after surgical excision is
- A. Thiotepa
- B. Amniotic membrane grafting
- C. Conjunctival autograft (Correct Answer)
- D. Beta-radiation
Explanation: ***Conjunctival autograft*** - **Conjunctival autografting** involves transplanting a piece of healthy conjunctiva from the superior bulbar conjunctiva to the bare scleral bed after pterygium excision, acting as a barrier to fibrovascular proliferation. - This technique has consistently shown the **lowest recurrence rates** in comparative studies, making it the **gold standard** for preventing pterygium recurrence due to its high success rate and safety profile. *Thiotepa* - **Thiotepa** is an **antimetabolite** that inhibits DNA synthesis and cell proliferation, used topically post-excision to reduce recurrence by suppressing fibroblast activity. - While it can lower recurrence rates compared to simple excision, its efficacy is generally **less than conjunctival autografting**, and it carries risks of corneal toxicity and limbal stem cell deficiency. *Amniotic membrane grafting* - **Amniotic membrane grafting** involves placing processed amniotic membrane over the scleral bed, which has anti-inflammatory, anti-scarring, and pro-epithelialization properties. - It is an effective option, especially for **large pterygia** or for patients at high risk of recurrence, but its recurrence rates are generally **not as low as those achieved with conjunctival autografting**, and the graft can sometimes detach. *B- radiation* - **Beta-radiation** (strontium-90) is a form of adjuvant therapy applied to the scleral bed immediately after pterygium excision to inhibit fibroblast proliferation and reduce recurrence. - It is effective but associated with potential complications such as **scleral melt**, corneal scarring, and cataract formation, making it a less preferred option than conjunctival autografting, especially in primary cases.
Question 5: Which of the following is used for the treatment of Myopia?
- A. Nd–YAG LASER
- B. Excimer Laser (Correct Answer)
- C. Carbamazepine
- D. SSRI
Explanation: **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.
Question 6: Which of the following are treatment modalities for myopia?
- A. Radial keratotomy
- B. LASER Keratomileusis
- C. Epikeratophaki
- D. LASER Keratoplasty (Correct Answer)
Explanation: **Explanation:** The treatment of myopia focuses on decreasing the refractive power of the eye, typically by flattening the central cornea. **LASER Keratoplasty** (specifically Excimer laser-based procedures like PRK and LASIK) is the gold standard for surgical correction. It works by photoablative decomposition, where the laser breaks molecular bonds to reshape the corneal stroma with extreme precision, effectively reducing the corneal curvature to focus light directly on the retina. **Analysis of Options:** * **Radial Keratotomy (RK):** While historically used for myopia, it involves making deep radial incisions in the peripheral cornea to flatten the center. It is largely obsolete due to complications like diurnal vision fluctuation and globe instability. * **LASER Keratomileusis:** This is a component of LASIK (Laser-Assisted In Situ Keratomileusis). While technically used, "Keratoplasty" is the broader, more encompassing term used in clinical nomenclature for corneal reshaping surgeries in this context. * **Epikeratophakia:** This involves suturing a pre-lathed donor corneal lenticule onto the surface of the patient's cornea. It was primarily used for aphakia or high myopia in children but is rarely performed today due to poor predictability. **High-Yield Clinical Pearls for NEET-PG:** * **Excimer Laser:** Uses Argon-Fluoride (ArF) gas, emitting UV light at **193 nm**. * **LASIK Criteria:** Stable refraction for 1 year, age >18 years, and a residual stromal bed thickness of at least **250 µm** to prevent corneal ectasia. * **Femtosecond Laser:** Used in "Bladeless LASIK" to create the corneal flap and in **SMILE** (Small Incision Lenticule Extraction) for flapless myopia correction.
Question 7: What is the wavelength of laser (in nanometers) used for shaping the cornea in refractive surgery?
- A. 193 nm (Correct Answer)
- B. 451 nm
- C. 532 nm
- D. 1064 nm
Explanation: **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.
Question 8: Which of the following lasers is used for the treatment of myopia?
- A. Nd-YAG LASER
- B. Excimer Laser (Correct Answer)
- C. Harmonium Laser
- D. Argon Laser
Explanation: **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).
Question 9: Excimer laser is used in which of the following conditions?
- A. Glaucoma
- B. Cataract
- C. Uveitis
- D. None of the above (Correct Answer)
Explanation: ### 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).
Question 10: What is the main corneal mechanism holding the LASIK flap in place after surgery?
- A. Endothelial pump (Correct Answer)
- B. Stromal collagen adhesions
- C. Bowman's layer-stromal adhesions
- D. Endothelial-Descemet's membrane forces
Explanation: 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.
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