Refractive Surgery Practice Questions

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.

Q: LASIK is used in which of the following refractive errors?

Myopia. **Explanation:** **LASIK (Laser-Assisted In Situ Keratomileusis)** is a refractive surgical procedure that utilizes an **Excimer laser** (193 nm) to reshape the corneal stroma. 1. **Why Myopia is the Correct Answer:** In myopia, the anteroposterior diameter of the eyeball is too long or the corneal curvature is too steep, causing light to focus in front of the retina. LASIK corrects this by **central corneal flattening**. By removing tissue from the central stromal bed, the refractive power of the cornea is reduced, allowing light to focus precisely on the retina. It is the most common indication for LASIK, typically correcting up to -10.0 Diopters. 2. **Analysis of Other Options:** * **Hypermetropia:** While LASIK *can* be used for hypermetropia (by steepening the central cornea), it is less predictable and has a higher rate of regression compared to myopia. In the context of standard MCQ patterns, myopia is the primary and most successful indication. * **Astigmatism:** LASIK can correct astigmatism by smoothing an asymmetrical cornea into a more spherical shape, but it is usually performed in conjunction with myopia or hypermetropia correction rather than as a standalone indication. * **Presbyopia:** This is an age-related loss of accommodation, not a corneal curvature issue. While "Presby-LASIK" exists, it is not the standard application of the technology. **High-Yield Clinical Pearls for NEET-PG:** * **Prerequisites:** Patient must be >18 years old with a stable refraction for at least 1 year. * **Contraindications:** Keratoconus (absolute), thin cornea (<450 μm), and severe dry eye. * **The "Rule of 250":** After the flap is created and the laser ablation is done, the **Residual Stromal Bed (RSB)** must be at least **250 μm** to prevent corneal ectasia. * **Complications:** The most common complication is **Dry Eye**; the most serious is **Iatrogenic Keratectasia**.

Q: What is the typical wavelength of a femtosecond laser used in ophthalmic procedures?

1053 nm. ### Explanation The **Femtosecond laser** is an infrared laser that operates at a wavelength of **1053 nm**. It works on the principle of **photodisruption** (laser-induced optical breakdown). By delivering ultra-short pulses (one quadrillionth of a second) to a specific depth within the corneal stroma, it creates micro-cavitation bubbles consisting of gas and water. These bubbles expand and coalesce to create a precise surgical plane, allowing for the creation of LASIK flaps or performing SMILE (Small Incision Lenticule Extraction) with minimal collateral thermal damage. **Analysis of Options:** * **A. 514 nm:** This is the wavelength of the **Argon Green laser**, commonly used for retinal photocoagulation (e.g., in Diabetic Retinopathy). * **B. 1064 nm:** This is the wavelength of the **Nd:YAG laser**. While also an infrared laser used for photodisruption, it operates in the *nanosecond* range. It is used for posterior capsulotomy and peripheral iridotomy. * **C. 1053 nm (Correct):** The specific wavelength for the Neodymium-glass laser used in femtosecond technology. * **D. 714 nm:** This does not correspond to a standard laser used in common ophthalmic refractive procedures. **High-Yield Clinical Pearls for NEET-PG:** * **Excimer Laser:** Uses **193 nm** (Argon-Fluoride gas) and works by **photoablation** (breaking molecular bonds). It is used to reshape the stroma in LASIK/PRK. * **Femtosecond Laser Uses:** LASIK flap creation (Bladeless LASIK), SMILE, Femtosecond Laser-Assisted Cataract Surgery (FLACS), and penetrating keratoplasty. * **Key Advantage:** Unlike the Excimer laser, the Femtosecond laser can pass through transparent tissue without affecting it until it reaches its specific focal point.

Q: What type of laser is used in LASIK?

Excimer laser. **Explanation:** **1. Why Excimer Laser is Correct:** LASIK (Laser-Assisted In Situ Keratomileusis) utilizes the **Excimer laser** (specifically the Argon-Fluoride gas laser with a wavelength of **193 nm**). The underlying mechanism is **photoablation**, where the high-energy ultraviolet light breaks intermolecular bonds in the corneal stroma without generating heat (cold ablation). This allows for precise reshaping of the cornea to correct refractive errors (myopia, hyperopia, and astigmatism) with sub-micron accuracy and minimal damage to surrounding tissues. **2. Why Other Options are Incorrect:** * **Argon Diode Laser:** Primarily used for retinal photocoagulation (e.g., in Diabetic Retinopathy) or laser trabeculoplasty in glaucoma. It works via photothermal effects. * **Nd:YAG Laser (1064 nm):** A "cold" laser that works via **photodisruption**. It is the gold standard for Posterior Capsulotomy (after PCO) and Peripheral Iridotomy. * **Double frequency Nd:YAG Laser (532 nm):** Also known as the "Green Laser." It is used for retinal procedures similar to the Argon laser but is more stable and commonly used for pan-retinal photocoagulation (PRP). **3. High-Yield Clinical Pearls for NEET-PG:** * **Wavelength of Excimer:** 193 nm (UV range). * **Femtosecond Laser:** Often used in "Bladeless LASIK" to create the initial corneal flap (wavelength 1053 nm), while the Excimer laser performs the actual ablation. * **Contraindications for LASIK:** Thin cornea (<450-480 μm), Keratoconus (most important), and active ocular infections. * **SMILE (Small Incision Lenticule Extraction):** The latest advancement which uses *only* the Femtosecond laser, eliminating the need for a flap or Excimer laser.

Q: Which of the following is a contraindication for LASIK?

Keratoconus. **Explanation:** **LASIK (Laser-Assisted In Situ Keratomileusis)** is a refractive procedure that involves creating a corneal flap and reshaping the underlying stroma using an excimer laser. **Why Keratoconus is the Correct Answer:** Keratoconus is an absolute contraindication for LASIK. It is a progressive non-inflammatory thinning of the cornea. Since LASIK involves removing corneal tissue (ablating the stroma), performing it on an already thin and unstable cornea would severely weaken the structural integrity, leading to **iatrogenic corneal ectasia** and permanent vision loss. **Analysis of Incorrect Options:** * **Age of 21 years or older (Option A):** This is actually a **requirement**, not a contraindication. Refractive stability is essential; hence, patients must be at least 18–21 years old with a stable refraction for at least one year. * **Normal Cornea (Option B):** A normal cornea with adequate thickness (usually >500 µm) and healthy topography is the ideal candidate for LASIK. * **Myopia of -8D (Option D):** LASIK can typically correct myopia up to **-10D to -12D**, provided the residual stromal bed remains thick enough (at least 250 µm). While -8D is a high correction, it is not a contraindication. **High-Yield Clinical Pearls for NEET-PG:** * **Absolute Contraindications:** Keratoconus, active ocular infection (e.g., Herpes Simplex Keratitis), thin corneas (<450-480 µm), and unrealistic patient expectations. * **Residual Stromal Bed (RSB):** To prevent ectasia, the RSB after ablation must be **at least 250 µm**. * **Calculations:** RSB = [Central Corneal Thickness] – [Flap Thickness] – [Ablation Depth]. * **Topography:** Look for "Bow-tie" patterns; asymmetric or skewed patterns suggest subclinical keratoconus (Forme Fruste), which also contraindicates LASIK.

Q: LASIK (Laser assisted in situ keratomileusis) is useful in the treatment of which of the following refractive errors?

All of the above. **Explanation:** LASIK (Laser-assisted in situ keratomileusis) is a versatile refractive procedure that utilizes an **Excimer laser (193 nm)** to reshape the corneal stroma after creating a thin flap. It is the most commonly performed refractive surgery because it can address a wide range of refractive errors by altering the corneal curvature. * **Myopia (A):** The laser flattens the central cornea to reduce its refractive power, allowing light to focus correctly on the retina. * **Hypermetropia (C):** The laser steepens the central cornea by removing tissue from the periphery, increasing the eye's refractive power. * **Astigmatism (B):** The laser reshapes the cornea into a more spherical contour by removing tissue along a specific meridian. Since LASIK is effective for all three conditions, **Option D** is the correct answer. **Why individual options are insufficient:** While LASIK is famously used for myopia, selecting only A, B, or C would be incomplete. Modern Excimer laser platforms are equipped with sophisticated software (like wavefront-guided technology) that allows for the simultaneous correction of spherical and cylindrical errors. **High-Yield Clinical Pearls for NEET-PG:** * **Ideal Candidate:** Age >18 years with a stable refraction for at least 1 year. * **Contraindications:** Keratoconus (absolute), thin corneas (<450-480 μm), severe dry eye, and active ocular inflammation. * **The "Rule of Thumbs":** Post-LASIK, the residual stromal bed (RSB) must be at least **250 μm** to prevent corneal ectasia. * **Complications:** The most common side effect is **Dry Eye**; the most serious vision-threatening complication is **Microbial Keratitis** or **Iatrogenic Ectasia**. **DLK (Diffuse Lamellar Keratitis)**, also known as "Sands of Sahara," is a specific sterile inflammatory complication.

Q: What does the given image show?

Radial keratotomy. ***Radial keratotomy*** - The image clearly displays multiple **radial incisions** in the cornea, characteristic of a radial keratotomy procedure. - These incisions are made to flatten the central cornea and correct **myopia**. *Keratomileusis* - This procedure involves reshaping the cornea by removing a **thin layer of corneal tissue**, typically done using a microkeratome or laser. - It does not involve making the distinct radial incisions seen in the image. *Blue dot cataract* - A blue dot cataract (or **punctate cerulean cataract**) refers to small, bluish opacities within the lens, which are not visible here. - This image shows features of the **cornea,** not the lens. *Stellate cataract* - A stellate cataract describes a cataract with a **star-shaped pattern**, often found in the posterior subcapsular area of the lens. - The image does not present any lens opacities, let alone a stellate pattern.

Q: Scleral Expansion Bands are used in the management of:

Presbyopia. ***Presbyopia*** - **Scleral expansion bands** are a surgical treatment strategy designed to restore the eye's ability to accommodate by altering the biomechanics of the sclera and ciliary body. - They aim to improve the range of motion of the ciliary body, thereby allowing the **lens to change shape** more effectively for near vision in **presbyopic** patients. *Astigmatism* - **Astigmatism** is primarily caused by an **irregularly shaped cornea** or lens, leading to blurred vision at all distances. - It is typically managed with corrective lenses (glasses or contact lenses) or refractive surgeries like **LASIK** or **PRK**, which reshape the cornea. *Keratoconus* - **Keratoconus** is a progressive eye disease where the **cornea thins** and bulges into a cone-like shape, causing distorted vision. - Treatments include rigid gas permeable contact lenses, **corneal collagen cross-linking** to halt progression, and in severe cases, corneal transplant. *Myopia* - **Myopia**, or nearsightedness, occurs when the eye focuses images in front of the retina, often due to an **elongated eyeball** or excessive corneal curvature. - It is commonly corrected with concave lenses, contact lenses, or refractive surgeries such as **LASIK** or **PRK** to flatten the cornea.

Question 1

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

Accepted Answer

Irregular astigmatism

Answer

Post-LASIK keratectasia

Answer

Keratoconus

Answer

Low myopia

Question 2

LASIK is used in which of the following refractive errors?

Accepted Answer

Myopia

Answer

Hypermetropia

Answer

Astigmatism

Answer

Presbyopia

Question 3

What is the typical wavelength of a femtosecond laser used in ophthalmic procedures?

Accepted Answer

1053 nm

Answer

514 nm

Answer

1064 nm

Answer

714 nm

Question 4

What type of laser is used in LASIK?

Accepted Answer

Excimer laser

Answer

Argon diode laser

Answer

Nd:YAG Laser

Answer

Double frequency Nd: YAG Laser

Question 5

Which of the following is a contraindication for LASIK?

Accepted Answer

Keratoconus

Answer

Age of 2 years or older

Answer

Normal cornea

Answer

Myopia of -8D

Question 6

LASIK (Laser assisted in situ keratomileusis) is useful in the treatment of which of the following refractive errors?

Accepted Answer

All of the above

Answer

Myopia

Answer

Astigmatism

Answer

Hypermetropia

Question 7

A 35-year-old patient underwent LASIK surgery for myopia correction 2 weeks ago. The patient now complains of glare and halos around lights at night. Visual acuity is 20/25 bilaterally. What is the most appropriate next step in management?

Accepted Answer

Reassure patient that symptoms typically resolve over 3-6 months

Answer

Prescribe topical corticosteroids

Answer

Perform enhancement LASIK procedure immediately

Answer

Perform corneal topography and wavefront analysis

Question 8

Which of the following lasers is used in refractive surgery?

Accepted Answer

Excimer laser

Answer

Argon

Answer

Diode

Answer

Nd:YAG

Question 9

What does the given image show?

Accepted Answer

Radial keratotomy

Answer

Keratomileusis

Answer

Blue dot cataract

Answer

Stellate cataract

Question 10

Scleral Expansion Bands are used in the management of:

Accepted Answer

Presbyopia

Answer

Astigmatism

Answer

Keratoconus

Answer

Myopia

Refractive Surgery — MCQs

Refractive Surgery — MCQs

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