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
A lady wants LASIK surgery for her daughter. All the following are indications for performing LASIK surgery, except:
Which of the following is used for the treatment of Myopia?
Which of the following are treatment modalities for myopia?
Radial keratotomy is used as a treatment modality for what condition?
What is the wavelength of the excimer laser used for corneal refractive surgery?
What is the wavelength of laser (in nanometers) used for shaping the cornea in refractive 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: A lady wants LASIK surgery for her daughter. All the following are indications for performing LASIK surgery, except:
- A. Stable refraction for 1 year
- B. Corneal thickness of 600 microns
- C. Age of 15 years (Correct Answer)
- D. Myopia of 4 Diopters
Explanation: ***Age of 15 years*** - LASIK surgery is generally not recommended for individuals under the age of 18, as their eyes and **refractive error** are still developing and stabilizing. - Performing LASIK on a 15-year-old could lead to **regression** of the refractive correction as the eye continues to grow. *Myopia of 4 Diopters* - A **myopia** of 4 Diopters (D) falls within the treatable range for LASIK, which can effectively correct moderate degrees of nearsightedness. - This is a common indication for individuals seeking freedom from glasses or contact lenses. *Stable refraction for 1 year* - **Stable refraction** for at least one year is a crucial criterion for LASIK, ensuring that the patient's prescription is unlikely to change significantly post-surgery. - Unstable refraction could result in suboptimal visual outcomes and the need for further correction. *Corneal thickness of 600 microns* - A **corneal thickness** of 600 microns is considered well within the safe range for LASIK surgery, allowing sufficient residual stromal bed after flap creation and ablation. - Adequate corneal thickness is essential to prevent complications such as **corneal ectasia**.
Question 6: 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 7: 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 8: Radial keratotomy is used as a treatment modality for what condition?
- A. Small degree myopia (Correct Answer)
- B. Progressive non-healing ulcer
- C. High astigmatism
- D. High hypermetropia
Explanation: **Radial Keratotomy (RK)** is a historical refractive surgical procedure used primarily for the correction of **low to moderate degrees of myopia** (typically -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 using a diamond knife. These incisions cause the peripheral cornea to bulge outward under intraocular pressure, which results in a compensatory **flattening of the central cornea**. Since myopia is characterized by an over-refractive or "too steep" cornea, this central flattening reduces the refractive power, allowing light to focus correctly on the retina. ### Why Other Options are Incorrect * **B. Progressive non-healing ulcer:** RK is a refractive procedure, not a therapeutic one. In fact, corneal thinning or infection (keratitis) are contraindications for RK. * **C. High astigmatism:** While "Astigmatic Keratotomy" (limbal relaxing incisions) exists, RK is specifically designed for spherical myopia. High astigmatism requires toric implants or laser-based reshaping. * **D. High hypermetropia:** RK flattens the cornea, which would worsen hypermetropia (which requires steepening). Hypermetropia is treated with thermal keratoplasty or convex lenses. ### High-Yield Clinical Pearls for NEET-PG * **Historical Significance:** RK has largely been replaced by LASIK and PRK due to predictability issues. * **Complications:** A classic side effect is **diurnal fluctuation of vision** (vision changes throughout the day) and **progressive hyperopic shift** (patients become more farsighted years later). * **Structural Integrity:** RK weakens the cornea significantly; patients are at high risk of **globe rupture** following even minor blunt trauma. * **Incision Depth:** Incisions are typically made to 90% of the corneal thickness, sparing the visual axis.
Question 9: What is the wavelength of the excimer laser used for corneal refractive surgery?
- A. 190 nm
- B. 191 nm
- C. 193 nm (Correct Answer)
- D. 195 nm
Explanation: **Explanation:** The **Excimer laser** (Excited Dimer) is the cornerstone of corneal refractive surgeries such as LASIK, PRK, and LASEK. It utilizes a gas combination of **Argon and Fluorine (ArF)**. When these gases are electrically stimulated, they form a pseudo-molecule that emits coherent ultraviolet light at a specific wavelength of **193 nm**. **Why 193 nm is the Correct Answer:** At 193 nm, the laser possesses high photon energy capable of breaking intermolecular carbon-carbon bonds in the corneal stroma without generating heat. This process is known as **Photoablation**. Because there is no thermal damage to the surrounding tissues (cold ablation), the cornea can be reshaped with sub-micron precision, ensuring optical clarity and predictable refractive outcomes. **Analysis of Incorrect Options:** * **190 nm, 191 nm, and 195 nm:** These are simply incorrect values. While they fall within the far-ultraviolet spectrum, they do not correspond to the specific energy emission peak of the Argon-Fluoride gas mixture used in medical-grade excimer units. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Photoablation (Photochemical decomposition). * **Gas Mixture:** Argon + Fluorine (ArF). * **Tissue Interaction:** Each pulse of the excimer laser removes approximately **0.25 microns** of corneal tissue. * **Safety:** The 193 nm wavelength is absorbed completely by the cornea and does not penetrate the lens or retina, preventing intraocular damage. * **Contrast with Femtosecond Laser:** While the Excimer laser (193 nm) is used for tissue ablation, the **Femtosecond laser (1053 nm)** is an infrared laser used for creating the LASIK flap via photodisruption.
Question 10: 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.
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