PRK and LASEK — MCQs
In a case of myopia, LASIK can correct up to how many diopters?
All are true about phakic IOLs EXCEPT:
The laser procedure, most often used for treating iris neovascularization is
A lady wants LASIK surgery for her daughter and asks for your opinion. All the following are suitable 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?
Which of the following lasers is used for the treatment of myopia?
PRK and LASEK Indian Medical PG Practice Questions and MCQs
Question 1: In a case of myopia, LASIK can correct up to how many diopters?
- A. -4D
- B. -12D (Correct Answer)
- C. -20D
- D. -6D
Explanation: ***-12D*** - LASIK can effectively correct myopia up to approximately **-12 diopters** in suitable candidates, though this can vary slightly based on individual corneal thickness and health. - The excimer laser reshapes the **cornea** to reduce its curvature, thereby decreasing the focusing power of the eye and correcting the myopic error. *-20D* - While some highly myopic individuals might desire such a correction, LASIK is generally not recommended or effective for myopia higher than **-12 to -14 diopters** due to limitations in corneal tissue removal and potential for complications. - Correcting very high myopia with LASIK would require removing too much corneal tissue, potentially leading to **corneal instability** or vision-threatening complications like **ectasia**. *-6D* - This is a common and highly successful range for LASIK correction, but it represents only a **moderate level of myopia** and not the maximum correctable range. - Patients with myopia of -6D typically achieve excellent visual outcomes with very low complication rates after LASIK. *-4D* - This is a relatively low level of myopia, and LASIK is very effective for this amount of correction, but it is far from the **upper limit** of what LASIK can achieve. - This level of correction requires minimal corneal reshaping and typically results in a very high success rate and predictable outcomes.
Question 2: All are true about phakic IOLs EXCEPT:
- A. Better quality vision (Correct Answer)
- B. Suitable for thin cornea
- C. Higher endothelial loss
- D. Reversible procedure
Explanation: ***Better quality vision*** - This is the EXCEPT answer because "better quality vision" is a **comparative claim** rather than an absolute characteristic of phakic IOLs - While phakic IOLs can provide excellent optical quality, claiming they provide "better" vision is **not universally established** compared to modern LASIK or SMILE techniques - The other options describe **objective, established characteristics** specific to phakic IOLs (suitability for thin corneas, endothelial loss risk, reversibility) - Vision quality depends on multiple factors including proper sizing, centration, and absence of complications like cataract formation or glaucoma *Suitable for thin cornea* - **TRUE** - Phakic IOLs are implantable lenses placed without removing the natural lens, making them ideal for patients with **thin corneas** who are not candidates for LASIK or PRK - They do not alter corneal tissue, avoiding issues related to corneal ectasia or instability - This is a **key indication** for phakic IOL surgery *Higher endothelial loss* - **TRUE** - Phakic IOLs, especially anterior chamber types, are associated with **chronic endothelial cell loss** due to proximity to the corneal endothelium - Posterior chamber ICLs (Implantable Collamer Lens) also cause endothelial loss, though typically less than anterior chamber IOLs - Regular **endothelial cell count monitoring** is mandatory post-implantation - This is a well-documented **complication and concern** with phakic IOLs *Reversible procedure* - **TRUE** - Phakic IOL implantation is **reversible** as the lens can be explanted if complications arise or refractive needs change - This is a **major advantage** over irreversible corneal ablative procedures like LASIK or PRK - The natural crystalline lens remains intact, preserving accommodation in young patients
Question 3: The laser procedure, most often used for treating iris neovascularization is
- A. Panretinal photocoagulation (PRP) (Correct Answer)
- B. Laser iridoplasty
- C. Laser trabeculoplasty
- D. Goniophotocoagulation
Explanation: ***Panretinal photocoagulation (PRP)*** - **PRP** is the most effective laser procedure for **iris neovascularization** and **neovascular glaucoma**, as it ablates the ischemic retina, reducing the production of **vascular endothelial growth factor (VEGF)**. - By destroying the ischemic peripheral retina, PRP reduces the **angiogenic drive** that leads to new vessel formation on the iris and in the angle. *Laser iridoplasty* - This procedure involves applying laser energy to the peripheral iris to cause contraction and widen the **anterior chamber angle**, primarily used for **angle-closure glaucoma**. - While it can open a closed angle, it does not address the underlying **ischemic drive** causing neovascularization. *Laser trabeculoplasty* - This procedure targets the **trabecular meshwork** to improve aqueous humor outflow, commonly used for **open-angle glaucoma**. - It does not directly affect **iris neovascularization** or the ischemic factors driving its development. *Goniophotocoagulation* - This involves directly lasering new vessels in the **anterior chamber angle**, often as an adjunct to PRP, but it's not the primary treatment to prevent **iris neovascularization**. - It treats existing vessels but does not address the underlying cause of **retinal ischemia** that promotes new vessel growth.
Question 4: A lady wants LASIK surgery for her daughter and asks for your opinion. All the following are suitable for performing LASIK surgery except:
- A. Stable refraction for 1 year
- B. Corneal thickness of 600 microns
- C. Myopia of 4 Diopters
- D. Age of 15 years (Correct Answer)
Explanation: ***Age of 15 years*** - LASIK surgery is generally not recommended for individuals under the age of 18-21 years because their **refractive error** may still be changing. - **Refractive stability** is a critical prerequisite to ensure a lasting surgical outcome. *Myopia of 4 Diopters* - This level of **myopia** (nearsightedness) typically falls within the treatable range for LASIK, which can correct moderate to high degrees of refractive error. - LASIK is highly effective for reducing or eliminating dependence on **glasses or contact lenses** for this range. *Stable refraction for 1 year* - **Refractive stability** is an essential criterion for LASIK candidacy, indicating that the patient's prescription has not significantly changed over a specific period. - This ensures that the surgical correction will be durable and accurate, preventing the need for future enhancements due to progression of refractive error. *Corneal thickness of 600 microns* - A **corneal thickness** of 600 microns is considered adequate for LASIK, as it allows for sufficient residual stromal bed thickness after ablation. - The minimum required **residual stromal bed thickness** is typically around 250-300 microns to maintain corneal integrity and prevent ectasia.
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: 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 8: 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 9: 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 10: 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).
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