Contact Lenses for Astigmatism — MCQs
How do you differentiate between mechanical obstruction and paralytic ileus?
Which is an example of Simple Myopic Astigmatism?
Which of the following is an example of an incorrect correction for astigmatism?
A 15-year-old girl with myopic astigmatism does not want to wear glasses. What is the best alternative for her?
What type of refractive error is astigmatism, which is characterized by non-spherical curvature of the cornea or lens?
A patient with contact lens use for the past 2 years presents with the ocular findings shown in the image below. What is the most probable diagnosis?
What is the power of lens attached to this instrument to visualize the entire retina?
A patient presents with eye pain, redness, and blurred vision after sleeping in contact lenses. Fluorescein staining reveals a corneal ulcer. What is the most appropriate management?
All of the following are true about Keratoconus, except:
What is the most common type of cataract found in a newborn?
Contact Lenses for Astigmatism Indian Medical PG Practice Questions and MCQs
Question 1: How do you differentiate between mechanical obstruction and paralytic ileus?
- A. Presence of multiple air-fluid levels in the bowel (Correct Answer)
- B. Presence of abdominal distension
- C. Absence of rectal gas shadow in imaging studies
- D. Elevation of hemidiaphragm on imaging
Explanation: ***Presence of multiple air-fluid levels in the bowel*** - The presence of multiple **air-fluid levels** on upright abdominal X-rays or CT scans is a hallmark of **mechanical bowel obstruction**, indicating a blockage preventing the normal progression of gas and fluid. - In a paralytic ileus, bowel loops are generally **gas-filled but without distinct air-fluid levels**, as there is no physical blockage impeding fluid movement. *Absence of rectal gas shadow in imaging studies* - An **absent rectal gas shadow** can be seen in both severe **mechanical obstruction** and **paralytic ileus**, particularly if the obstruction or ileus is significant and prolonged, making it a less specific differentiating feature. - While it suggests an empty distal bowel, it does not reliably distinguish between the two conditions without additional findings. *Presence of abdominal distension* - **Abdominal distension** is a common finding in both **mechanical obstruction** (due to trapped gas and fluid proximal to the blockage) and **paralytic ileus** (due to generalized bowel dilation). - Therefore, its presence alone does not help differentiate between these two conditions. *Elevation of hemidiaphragm on imaging* - An **elevated hemidiaphragm** can occur in various abdominal conditions, including large collections of fluid or gas pushing up the diaphragm, or conditions affecting diaphragmatic motion itself (e.g., phrenic nerve palsy). - It is not a specific finding to differentiate between **mechanical obstruction** and **paralytic ileus**.
Question 2: Which is an example of Simple Myopic Astigmatism?
- A. +2.00 sphere
- B. +1.00 -3.00 × 90°
- C. -2.00 sphere
- D. plano -2.00 × 90° (Correct Answer)
Explanation: ***plano -2.00 × 90°*** - This prescription indicates a **spherical equivalent of zero (plano)** in one meridian and **-2.00 diopters of myopia** in the meridian 90 degrees away. - This perfectly fits the definition of **simple myopic astigmatism**, where one principal meridian is emmetropic and the other is myopic. *+2.00 sphere* - This prescription represents **simple hyperopia**, meaning the eye is **farsighted** but without any astigmatism. - All light rays focus behind the retina, and there is no difference in refractive power between the principal meridians. *-2.00 sphere* - This represents **simple myopia**, where the eye is **nearsighted** but without any astigmatism. - All light rays focus in front of the retina, and there is no difference in refractive power between the principal meridians. *+1.00 -3.00 × 90°* - This prescription is an example of **mixed astigmatism**, where one principal meridian is hyperopic (+1.00 D) and the other is myopic (-2.00 D, calculated as +1.00 + [-3.00]). - This differs from simple myopic astigmatism where one meridian is emmetropic.
Question 3: Which of the following is an example of an incorrect correction for astigmatism?
- A. -3 cyl 180
- B. +2 cyl 180
- C. -1.25 cyl 90
- D. -2 spherical 180 (Correct Answer)
Explanation: ***-2 spherical 180*** - This option describes a **spherical lens** correction, which is used for **myopia** (nearsightedness) or **hyperopia** (farsightedness), not astigmatism. - Astigmatism specifically requires a **cylindrical lens** to correct the uneven curvature of the cornea or lens. - A spherical lens has the same power in all meridians and **cannot correct the different refractive powers** in different meridians that characterize astigmatism. *-1.25 cyl 90* - This is a valid correction for astigmatism, indicating a **cylindrical power** of -1.25 diopters at an **axis of 90 degrees**. - The "cyl" notation signifies a cylindrical lens, which is necessary to correct for astigmatism. *-3 cyl 180* - This represents a valid cylindrical correction for astigmatism, with a **cylindrical power** of -3 diopters at an **axis of 180 degrees**. - The presence of "cyl" and an axis indicates a correction specifically designed for astigmatism. *+2 cyl 180* - This is also a valid cylindrical correction for astigmatism, with a **cylindrical power** of +2 diopters at an **axis of 180 degrees**. - Positive cylindrical powers are used for **hyperopic astigmatism**, while negative ones are for **myopic astigmatism**.
Question 4: A 15-year-old girl with myopic astigmatism does not want to wear glasses. What is the best alternative for her?
- A. LASIK
- B. Spherical Specs
- C. Contact lenses (Toric) (Correct Answer)
- D. FEMTO Lasik
Explanation: ***Contact lenses (Toric)*** - **Toric contact lenses** are specifically designed to correct **astigmatism**, along with myopia or hyperopia, by having different refractive powers in different meridians. - They offer a non-surgical alternative to glasses, addressing the patient's desire not to wear spectacles, and are generally safe and effective for teenagers. *LASIK* - **LASIK (Laser-Assisted In Situ Keratomileusis)** is a surgical procedure to correct refractive errors, but it is not typically recommended for individuals under **18-21 years of age** due to continued eye growth and refractive changes. - The patient's age of 15 makes her an unsuitable candidate for LASIK at this time. *Spherical Specs* - **Spherical spectacles** are designed to correct myopia or hyperopia but cannot adequately correct **astigmatism**, which is a significant component of this patient's refractive error. - The patient also explicitly states she does not want to wear glasses, making this option undesirable. *FEMTO Lasik* - **FEMTO LASIK** is an advanced form of LASIK that uses a femtosecond laser to create the corneal flap, offering higher precision and safety. - However, similar to traditional LASIK, it is a **refractive surgical procedure** and typically not performed on patients younger than **18 years old** due to ongoing eye development.
Question 5: What type of refractive error is astigmatism, which is characterized by non-spherical curvature of the cornea or lens?
- A. Spherical aberration
- B. Curvatural ametropia (Correct Answer)
- C. Index ametropia
- D. Axial ametropia
Explanation: ***Curvatural ametropia*** - Astigmatism, due to its **irregular corneal or lenticular curvature**, falls under the category of curvatural ametropia. - This type of ametropia occurs when the **optical power of the eye varies in different meridians**, leading to light focusing at multiple points rather than a single focal point. *Spherical aberration* - **Spherical aberration** is an optical error where light rays passing through the periphery of a lens focus at a different point than those passing through the center. - It results in a **loss of image clarity** but is distinct from astigmatism's power variation across meridians. *Axial ametropia* - **Axial ametropia** refers to refractive errors caused by an abnormal **length of the eyeball** (either too long or too short). - **Myopia** and **hyperopia** are primary examples of axial ametropia, where the eyeball length dictates whether light focuses in front of or behind the retina, respectively. *Index ametropia* - **Index ametropia** arises from variations in the **refractive index of the ocular media**, such as the cornea, lens, or vitreous humor. - Changes in the refractive index can alter how light bends, but astigmatism is primarily due to surface curvature, not changes in media refractive index.
Question 6: A patient with contact lens use for the past 2 years presents with the ocular findings shown in the image below. What is the most probable diagnosis?
- A. Trachoma
- B. Giant Papillary conjunctivitis (Correct Answer)
- C. Ocular Surface Squamous Neoplasia (OSSN)
- D. Vernal Keratoconjunctivitis
Explanation: ***Giant Papillary conjunctivitis*** - The image shows **large, elevated papillae** on the **tarsal conjunctiva**, which are characteristic findings of giant papillary conjunctivitis. - This condition is common among **contact lens wearers**, caused by chronic mechanical irritation and an allergic response to lens material or deposits. *Trachoma* - Trachoma is a **chronic infectious disease** caused by *Chlamydia trachomatis*, leading to scarring of the conjunctiva. - It typically presents with **follicles** in the early stages, followed by **scarring** and **pannus formation**, not the large papillae seen here. *Ocular Surface Squamous Neoplasia (OSSN)* - OSSN refers to a spectrum of conditions from **dysplasia to squamous cell carcinoma** affecting the conjunctiva or cornea. - It usually presents as a **gelatinous, fleshy, or leukoplakic lesion**, often at the limbus, which is distinct from the diffuse papillae shown. *Vernal Keratoconjunctivitis* - Vernal keratoconjunctivitis (VKC) is a **severe form of allergic conjunctivitis** but primarily affects children and young adults with a history of atopy. - While it can cause large papillae (cobblestone papillae), it is not specifically associated with contact lens wear and usually has other systemic allergic manifestations.
Question 7: What is the power of lens attached to this instrument to visualize the entire retina?
- A. 20 D (Correct Answer)
- B. 58 D
- C. 78 D
- D. 90 D
Explanation: ***20 D*** - The image depicts a **binocular indirect ophthalmoscope (BIO)**, which is used for wide-field examination of the retina. - The **20 D lens** is the **most commonly used condensing lens** with a BIO for visualizing the entire retina. - It provides the **widest field of view** (approximately 45-50 degrees) with adequate magnification, making it ideal for comprehensive peripheral retinal examination. - Other standard BIO lenses include 14 D, 28 D, and 30 D, but **20 D offers the optimal balance** of field of view and magnification for complete retinal visualization. *58 D* - A **58 D lens** is not a standard condensing lens used with binocular indirect ophthalmoscopy. - While high-power lenses can be used with various ophthalmoscopic techniques, they are not conventional for BIO examination of the entire retina. *78 D* - A **78 D lens** is typically used with a **slit lamp biomicroscope** for a magnified view of the posterior pole and macular details. - It does not provide the wide-field view necessary for visualizing the **entire retina** when used with a BIO. - This lens is excellent for detailed examination of the optic disc and macula but has a limited field of view. *90 D* - A **90 D lens** is also primarily used with a **slit lamp biomicroscope** for excellent magnification of the macula and optic nerve head. - It provides a high-resolution, magnified view of a *limited area*, making it unsuitable for a comprehensive survey of the entire retina. - Like the 78 D, it's designed for detailed central retinal examination, not peripheral screening.
Question 8: A patient presents with eye pain, redness, and blurred vision after sleeping in contact lenses. Fluorescein staining reveals a corneal ulcer. What is the most appropriate management?
- A. Topical antibiotics (Correct Answer)
- B. Oral antibiotics
- C. Topical corticosteroids
- D. Saline irrigation
Explanation: ***Topical antibiotics*** - A **corneal ulcer**, especially in a contact lens wearer, is highly suspicious for **bacterial infection**, necessitating immediate and aggressive topical antibiotic therapy. - **Broad-spectrum antibiotics** (e.g., fluoroquinolones) are often started empirically and adjusted based on culture results. *Oral antibiotics* - **Systemic antibiotics** are generally not indicated for uncomplicated bacterial corneal ulcers, as they don't achieve sufficient concentrations in the cornea to be effective. - They may be considered for severe cases with limbal involvement or scleral extension, or if there is a concern for concurrent systemic infection. *Topical corticosteroids* - **Corticosteroids** are contraindicated in the initial management of suspected infectious corneal ulcers because they can suppress the immune response and worsen the infection. - They may be cautiously used later in treatment to reduce inflammation after the infection is well-controlled. *Saline irrigation* - While helpful for removing foreign bodies or debris, **saline irrigation alone** is insufficient to treat a bacterial corneal ulcer. - It does not eradicate the infection and delaying definitive antibiotic treatment can lead to severe complications.
Question 9: All of the following are true about Keratoconus, except:
- A. Astigmatism
- B. Increased curvature of cornea and Astigmatism
- C. Thick cornea (Correct Answer)
- D. Fleischer's ring
Explanation: ***Thick cornea*** - Keratoconus is characterized by **progressive corneal thinning** and weakening, not thickening. - This corneal thinning leads to a conical protrusion, causing significant visual distortion and irregular astigmatism. *Increased curvature of cornea and Astigmatism* - Keratoconus features **increased corneal curvature** with progressive steepening into a cone-shaped configuration. - This results in **irregular astigmatism**, a hallmark feature causing distorted vision at all distances. *Astigmatism* - **Irregular astigmatism** is a cardinal feature of keratoconus due to the asymmetric corneal shape. - Causes blurred and distorted vision that is difficult to correct with spectacles alone. *Fleischer's ring* - **Fleischer's ring** is an iron deposit ring at the base of the cone in keratoconus, visible on slit-lamp examination. - It represents hemosiderin deposition in the basal epithelial cells and is a characteristic clinical sign of keratoconus.
Question 10: What is the most common type of cataract found in a newborn?
- A. Zonular (Correct Answer)
- B. Nuclear
- C. Snowflake
- D. Cortical
Explanation: **Explanation:** **Zonular (Lamellar) Cataract** is the most common type of congenital cataract. It is characterized by opacification of a specific layer (zone) of the lens fibers, typically surrounding a clear embryonic nucleus. This occurs due to a transient environmental or nutritional insult (such as Vitamin D deficiency or hypocalcemia) during a specific stage of lens development. Because it often allows some light to pass through the clear areas, it is frequently associated with relatively good visual prognosis if managed early. **Analysis of Incorrect Options:** * **Nuclear Cataract:** While common in age-related (senile) cataracts, it is less frequent in newborns. It involves the central core of the lens and is often associated with intrauterine infections like Rubella. * **Snowflake Cataract:** This is a classic finding in **Diabetes Mellitus** (specifically juvenile diabetes). It consists of subcapsular white opacities and is not a standard congenital presentation. * **Cortical Cataract:** This is typically an age-related change characterized by "cuneiform" or wedge-shaped opacities in the lens cortex. It is rarely seen as a primary congenital finding in newborns. **Clinical Pearls for NEET-PG:** * **Most common cause of Congenital Cataract:** Idiopathic (followed by genetic/hereditary factors). * **Most common infection:** Rubella (presents as "Pearls in the center" or dense nuclear cataract). * **Oil droplet cataract:** Classic for Galactosemia. * **Sunflower cataract:** Seen in Wilson’s disease (Chalcosis). * **Management:** If the cataract is visually significant (central opacity >3mm), surgery (Lens aspiration + Primary Posterior Capsulotomy + Anterior Vitrectomy) is ideally performed within the first 4–6 weeks of life to prevent amblyopia.
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