Diseases of the Cornea — MCQs

A 30-year-old male from a rural background presents with a 10-day history of difficulty in vision. He reports vegetative material falling into his left eye 15 days prior. Examination reveals an ulcerative lesion in the cornea with feathery margins and creamy exudates, along with a few satellite lesions. What is the most likely etiologic agent?

Diseases of the Cornea Indian Medical PG Practice Questions and MCQs

Question 11: Which of the following organisms can penetrate the normal cornea?

A. Gonococcus
B. Pseudomonas
C. Diphtheria
D. Staphylococcus epidermidis (Correct Answer)

Explanation: The intact corneal epithelium acts as a formidable mechanical and biological barrier against most pathogens. Only a select few organisms possess the specific virulence factors (enzymes and toxins) required to penetrate a **normal, healthy cornea** without a pre-existing abrasion or trauma. ### **Explanation of the Correct Answer** The correct answer is **Staphylococcus epidermidis** (based on the provided key). However, in standard ophthalmology textbooks (like Khurana), the classic list of organisms that can penetrate an intact cornea includes: 1. *Neisseria gonorrhoeae* 2. *Neisseria meningitidis* 3. *Corynebacterium diphtheriae* 4. *Listeria monocytogenes* 5. *Haemophilus aegyptius* **Note on Option D:** In many clinical scenarios and standard MCQ banks, *Staphylococcus epidermidis* is considered a commensal that requires a breach in the epithelium to cause infection. If this is the designated correct answer for your specific curriculum, it implies a focus on its role in opportunistic infections or biofilm formation, though it is traditionally **not** part of the "intact epithelium" list. ### **Analysis of Incorrect Options** * **A. Gonococcus (*N. gonorrhoeae*):** This is a classic organism that **can** penetrate the intact cornea. If the question asks which *cannot* penetrate, this would be an incorrect choice. * **B. Pseudomonas:** While highly virulent and capable of causing rapid corneal melting (via proteases), it generally **requires a breach** in the epithelium (e.g., contact lens wear or trauma) to initiate infection. * **C. Diphtheria (*C. diphtheriae*):** This is another classic organism that **can** penetrate the intact cornea. ### **High-Yield Clinical Pearls for NEET-PG** * **The "Big Four":** Memorize the mnemonic **"N-L-C-H"** (Neisseria, Listeria, Corynebacterium, Haemophilus) for organisms that penetrate intact epithelium. * **Pseudomonas:** Most common cause of bacterial keratitis in **contact lens users**. It produces "soupy" discharge and rapid perforation. * **Acanthamoeba:** Suspect in contact lens users with pain out of proportion to clinical findings and **ring-shaped infiltrates**. * **Fungal Keratitis:** Characterized by **feathery margins** and **satellite lesions**; often follows trauma with vegetative matter.

Question 12: All of the following are true about corneal endothelium except?

A. Cell density is about 3000 cells/mm² at birth.
B. Corneal decompensation occurs when cell count is decreased by 50 percent. (Correct Answer)
C. Endothelial cells contain an active pump mechanism.
D. Endothelium is best examined by specular microscopy.

Explanation: ### Explanation The corneal endothelium is a single layer of hexagonal cells responsible for maintaining corneal transparency by regulating stromal hydration. **1. Why Option B is the Correct Answer (The False Statement):** Corneal decompensation does not occur at a fixed percentage decrease (like 50%). Instead, it occurs when the cell density falls below a **critical threshold**, typically **500 to 700 cells/mm²**. Since the average adult density is ~2500 cells/mm², a 50% loss would leave ~1250 cells/mm², which is usually sufficient to maintain clarity. Decompensation leads to stromal edema and bullous keratopathy. **2. Analysis of Other Options:** * **Option A:** At birth, the cell density is high, approximately **3000–4000 cells/mm²**. This number gradually declines with age (about 0.6% per year) and trauma. * **Option C:** The endothelium maintains "deturgescence" (relative dehydration) via an **active Na⁺/K⁺ ATPase pump** and a passive bicarbonate pump, counteracting the osmotic gradient that draws water into the stroma. * **Option D:** **Specular Microscopy** is the gold standard for non-invasive evaluation of the endothelium, allowing for the assessment of cell density, **pleomorphism** (variation in shape), and **polymegethism** (variation in size). **Clinical Pearls for NEET-PG:** * **No Regeneration:** Human endothelial cells do not undergo mitosis; they heal by enlargement and migration (sliding). * **Pachymetry:** Used to measure corneal thickness; an increase in thickness is often the first sign of endothelial pump failure. * **Fuchs’ Endothelial Dystrophy:** A common cause of progressive endothelial cell loss characterized by "guttae." * **Hassall-Henle bodies:** Physiological hyaline outgrowths of Descemet’s membrane seen in the periphery (normal aging change).

Question 13: Which of the following are types of corneal dystrophies?

A. Granular, Lattice, Mooren, Fuchs
B. Macular, Granular, Lattice, Mooren
C. Macular, Lattice, Mooren, Fuchs
D. Macular, Granular, Lattice, Fuchs (Correct Answer)

Explanation: **Explanation:** Corneal dystrophies are a group of genetic, bilateral, symmetric, and slowly progressive corneal opacifications that are not associated with inflammation or systemic disease. They are classified based on the layer of the cornea they affect. **Why Option D is Correct:** The correct answer includes four classic types of corneal dystrophies: * **Macular, Granular, and Lattice Dystrophies:** These are the primary **stromal dystrophies**. * **Fuchs’ Endothelial Corneal Dystrophy (FECD):** This is the most common **posterior (endothelial) dystrophy**, characterized by "guttae" and stromal edema. **Why Other Options are Incorrect:** Options A, B, and C are incorrect because they include **Mooren’s Ulcer**. Mooren’s ulcer is an idiopathic, peripheral ulcerative keratitis (PUK) that is inflammatory and often painful. It is **not** a dystrophy; it is an autoimmune-mediated destruction of the corneal stroma. **NEET-PG High-Yield Clinical Pearls:** To differentiate stromal dystrophies, remember the mnemonic **"Marilyn Monroe Got Herself Some Lettuce In City"**: 1. **M**acular – **M**ucopolysaccharide – **A**lcian Blue (Most severe, Autosomal Recessive). 2. **G**ranular – **H**yaline – **S**affron/Masson Trichrome (Breadcrumb appearance). 3. **L**attice – **A**myloid – **C**ongo Red (Refractile lines, Apple-green birefringence). * **Inheritance:** Most dystrophies are Autosomal Dominant, **except Macular**, which is Autosomal Recessive. * **Fuchs’ Dystrophy:** Look for "beaten metal appearance" on specular microscopy and the hallmark symptom of early morning blurring of vision.

Question 14: Keratomalacia is due to which deficiency?

A. Vitamin A deficiency (Correct Answer)
B. Keratoconus
C. Vitamin E deficiency
D. Retinitis pigmentosa

Explanation: **Explanation:** **Keratomalacia** is the most severe ocular manifestation of **Vitamin A deficiency**. Vitamin A (Retinol) is essential for maintaining the integrity of epithelial surfaces. In its absence, the conjunctival and corneal epithelium undergo **squamous metaplasia**, losing their goblet cells and ability to secrete mucus. This leads to extreme dryness (xerosis). If untreated, the cornea undergoes **liquefactive necrosis**, leading to softening, stromal melting, and potential perforation. This rapid destruction is what defines keratomalacia. **Analysis of Options:** * **Vitamin A deficiency (Correct):** It is the primary cause of Xerophthalmia, a spectrum of eye signs ranging from night blindness (Nyctalopia) to Bitot’s spots, corneal xerosis, and finally, keratomalacia. * **Keratoconus:** This is a non-inflammatory, progressive thinning and cone-like ectasia of the cornea, typically associated with collagen disorders or eye rubbing, not nutritional deficiencies. * **Vitamin E deficiency:** While Vitamin E is an antioxidant, its deficiency primarily manifests as neuromuscular issues (ataxia) and hemolytic anemia, not corneal melting. * **Retinitis pigmentosa:** This is a genetic dystrophy of the retinal photoreceptors (rods and cones) leading to tunnel vision and night blindness, but it does not affect the structural integrity of the cornea. **High-Yield Clinical Pearls for NEET-PG:** * **WHO Classification of Xerophthalmia:** X1A (Conjunctival xerosis), X1B (**Bitot’s spots**—foamy patches on bulbar conjunctiva), X2 (Corneal xerosis), X3A (Keratomalacia <1/3rd cornea), X3B (Keratomalacia >1/3rd cornea). * **Treatment:** Immediate administration of Vitamin A (200,000 IU orally on days 0, 1, and 14). * **Earliest Symptom:** Night blindness (Nyctalopia). * **Earliest Sign:** Conjunctival xerosis.

Question 15: Fleischer ring is due to which type of deposition?

A. Iron deposition (Correct Answer)
B. Copper deposition
C. Aluminum deposition
D. Molybdenum deposition

Explanation: **Explanation:** **1. Why Iron Deposition is Correct:** The **Fleischer ring** is a classic clinical sign of **Keratoconus**. It consists of a partial or complete yellowish-to-brown ring located at the base of the cone in the corneal epithelium. It is caused by the deposition of **hemosiderin (iron)** within the basal epithelial cells. The iron accumulates due to the pooling of tears in the gutter created by the thinning and protrusion of the cornea. **2. Why Other Options are Incorrect:** * **Copper deposition:** This is associated with the **Kayser-Fleischer (KF) ring**, seen in **Wilson’s disease**. Unlike the Fleischer ring, the KF ring occurs in the **Descemet’s membrane** at the limbus. * **Aluminum and Molybdenum:** These metals are not typically associated with specific, named corneal ring depositions in clinical ophthalmology. **3. High-Yield Clinical Pearls for NEET-PG:** * **Fleischer Ring vs. Kayser-Fleischer Ring:** Do not confuse them. Fleischer = Keratoconus (Iron); Kayser-Fleischer = Wilson’s Disease (Copper). * **Other Iron Lines in the Cornea:** * **Hudson-Stahli line:** Found at the junction of the upper 2/3 and lower 1/3 of the cornea (age-related). * **Stocker’s line:** Found at the head of a Pterygium. * **Ferry’s line:** Found at the edge of a filtering bleb (Glaucoma surgery). * **Keratoconus Signs:** Look for Munson’s sign (V-shaped indentation of lower lid on downgaze), Vogt’s striae (vertical stress lines), and Rizutti’s sign.

Question 16: The cornea receives all its nutrition from?

A. Corneal vessels
B. Atmosphere
C. Iris
D. Aqueous humor (Correct Answer)

Explanation: ### Explanation The cornea is a unique, **avascular** structure. Its transparency is vital for vision, necessitating the absence of blood vessels within the central optical zone. To maintain its metabolic functions, the cornea relies on three primary sources for nutrition and oxygen: **1. Why Aqueous Humor is the Correct Answer:** The **aqueous humor** is the primary source of nutrition for the cornea, particularly for the **endothelium** and the **posterior stroma**. It provides essential nutrients such as **glucose** and amino acids via simple diffusion. Since the cornea is constantly bathed in aqueous humor posteriorly, this remains the most significant metabolic supply line. **2. Analysis of Incorrect Options:** * **Corneal Vessels (A):** In a healthy state, the cornea is avascular. Small loops of **limbal capillaries** provide some nutrition to the extreme periphery only. Pathological neovascularization occurs only in disease states. * **Atmosphere (B):** While the atmosphere is the major source of **oxygen** (dissolved in the precorneal tear film) for the corneal epithelium, it does not provide glucose or other solid nutrients. * **Iris (C):** The iris does not directly supply nutrition to the cornea; it is separated from the cornea by the anterior chamber. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Oxygen Supply:** In open-eye conditions, oxygen comes from the **atmosphere**. In closed-eye conditions (sleep), oxygen is derived from the **palpebral conjunctival capillaries**. * **Glucose Source:** Almost 100% of the cornea's glucose is derived from the **aqueous humor**. * **Metabolism:** The cornea primarily utilizes **anaerobic glycolysis** (Emdon-Meyerhof pathway) for energy. * **Transparency:** Maintained by the "Pump-Leak" mechanism of the endothelium, which regulates stromal hydration (optimal at 78%).

Question 17: Cornea melts without inflammation in which condition?

A. Gout
B. Sarcoidosis
C. Keratomalacia (Correct Answer)
D. Rheumatoid arthritis

Explanation: **Explanation:** The hallmark of **Keratomalacia** is the rapid, liquefactive necrosis of the corneal stroma in a **"quiet eye"** (absence of significant inflammation). This condition is the end-stage ocular manifestation of severe **Vitamin A deficiency**. Vitamin A is essential for maintaining the health of epithelial surfaces; its deficiency leads to squamous metaplasia and loss of goblet cells. Without adequate mucus and epithelial integrity, the cornea undergoes "melting" due to the activation of collagenases and proteases, often leading to perforation if not treated urgently. **Analysis of Incorrect Options:** * **Gout:** While it can cause scleritis or episcleritis, it does not typically cause non-inflammatory corneal melting. * **Sarcoidosis:** This is a granulomatous multi-system disorder. Ocular involvement usually presents as granulomatous uveitis or lacrimal gland enlargement, rather than stromal melting. * **Rheumatoid Arthritis (RA):** RA is a common cause of **Peripheral Ulcerative Keratitis (PUK)** or "melting." However, in RA, the process is typically **inflammatory** (vasculitis-mediated) and associated with significant pain and perilimbic injection, unlike the "quiet" melt of keratomalacia. **High-Yield Clinical Pearls for NEET-PG:** * **WHO Classification of Xerophthalmia:** X1A (Conjunctival xerosis), X1B (Bitot’s spots), X2 (Corneal xerosis), **X3A/X3B (Keratomalacia)**. * **Bitot’s Spots:** Triangular, foamy patches on the bulbar conjunctiva (usually temporal) caused by *Corynebacterium xerosis*. * **Nyctalopia (Night blindness):** The earliest clinical symptom of Vitamin A deficiency. * **Treatment:** Immediate high-dose Vitamin A supplementation (200,000 IU orally on days 0, 1, and 14).

Question 18: A satellite lesion in a corneal ulcer with a feathery margin and fixed hypopyon is a feature of which of the following?

A. Trachoma
B. Fungal keratitis (Correct Answer)
C. Angular conjunctivitis
D. Herpes simplex keratitis

Explanation: ### Explanation **Correct Answer: B. Fungal Keratitis** The clinical presentation described is classic for **Fungal Keratitis** (Mycotic Keratitis), typically caused by filamentous fungi like *Aspergillus* or *Fusarium*. 1. **Feathery Margins:** Unlike bacterial ulcers which have well-defined borders, fungal hyphae penetrate the corneal stroma laterally, creating indistinct, "feathery" or finger-like extensions. 2. **Satellite Lesions:** These are small, isolated infiltrates surrounding the main ulcer, caused by the centrifugal spread of fungal hyphae. 3. **Fixed Hypopyon:** Fungal ulcers often present with a "fixed" hypopyon (immobile pus in the anterior chamber) due to the presence of fungal elements or thick inflammatory exudate, unlike the fluid hypopyon seen in bacterial infections. --- ### Why Other Options are Incorrect: * **A. Trachoma:** Caused by *Chlamydia trachomatis* (Serotypes A, B, Ba, C). It primarily affects the conjunctiva (follicles, Herbert’s pits) and leads to cicatricial changes like entropion and trichiasis, rather than acute suppurative corneal ulcers. * **C. Angular Conjunctivitis:** Caused by *Moraxella axenfeld* or *Staphylococcus*. It presents with excoriation of the skin at the inner and outer canthi, not corneal ulceration with satellite lesions. * **D. Herpes Simplex Keratitis:** Characteristically presents with **dendritic ulcers** (linear, branching with terminal bulbs) and diminished corneal sensations. It does not typically feature feathery margins or satellite lesions. --- ### High-Yield Clinical Pearls for NEET-PG: * **Risk Factor:** The most common predisposing factor for fungal keratitis is **trauma with vegetative matter** (e.g., a branch, leaf, or agricultural injury). * **Dry Appearance:** Fungal ulcers often appear "dry" and grayish-white with elevated edges. * **Immune Ring (Wessely Ring):** Sometimes seen in fungal keratitis due to the host's antigen-antibody reaction. * **Diagnosis:** Gold standard is **SDA (Sabouraud Dextrose Agar)**; KOH mount (10-20%) is the rapid bedside test of choice. * **Treatment:** Topical **Natamycin (5%)** is the drug of choice for filamentous fungi.

Question 19: Kayser-Fleischer rings are characteristic of which condition?

A. Hemosiderosis
B. Wilson disease (Correct Answer)
C. Tyrosinemia
D. Hereditary cataract

Explanation: **Explanation:** **Wilson Disease (Hepatolenticular Degeneration)** is the correct answer. The Kayser-Fleischer (KF) ring is a hallmark clinical sign of this autosomal recessive disorder characterized by abnormal copper metabolism. Due to a deficiency in the copper-transporting protein **ceruloplasmin**, copper deposits in various tissues. In the eye, copper accumulates specifically in the **Descemet’s membrane** of the peripheral cornea. * **Clinical Appearance:** It appears as a golden-brown or greenish-brown ring at the limbus. It is best visualized using a **Slit-lamp examination**, though it may be visible to the naked eye in advanced cases. * **Significance:** It is present in 95% of patients with neurological symptoms and about 50-60% of those with hepatic presentations. Notably, the ring disappears with effective chelation therapy (e.g., Penicillamine). **Analysis of Incorrect Options:** * **A. Hemosiderosis:** Iron deposition in the cornea typically forms a **Hudson-Stahli line** (iron line in the epithelium) or occurs following a metallic foreign body, but not a KF ring. * **C. Tyrosinemia:** Type II Tyrosinemia (Richner-Hanhart syndrome) presents with **pseudodendritic keratitis** and painful palmoplantar hyperkeratosis, not copper deposition. * **D. Hereditary cataract:** This refers to lens opacification from birth/childhood and does not involve corneal pigment rings. **High-Yield Pearls for NEET-PG:** 1. **Sunflower Cataract:** Another ocular feature of Wilson disease (copper deposition in the anterior lens capsule). 2. **Fleischer Ring:** Do not confuse with KF ring; Fleischer rings are iron deposits seen at the base of the cone in **Keratoconus**. 3. **Chalcosis:** The term for intraocular copper deposition (usually from a foreign body).

Question 20: A 30-year-old male from a rural background presents with a 10-day history of difficulty in vision. He reports vegetative material falling into his left eye 15 days prior. Examination reveals an ulcerative lesion in the cornea with feathery margins and creamy exudates, along with a few satellite lesions. What is the most likely etiologic agent?

A. Corynebacterium diphtheria
B. Fusarium sp. (Correct Answer)
C. Acanthomoeba sp.
D. Streptococcus pneumoniae

Explanation: ### Explanation **Correct Option: B. Fusarium sp.** The clinical presentation is classic for **Fungal Keratitis (Keratomycosis)**. The key diagnostic clues in the history and examination are: 1. **History of trauma with vegetative material:** This is the most significant risk factor for fungal corneal ulcers, especially in rural settings. 2. **Feathery margins:** Fungal hyphae infiltrate the corneal stroma, creating a characteristic "branching" or feathery appearance. 3. **Satellite lesions:** These are small, isolated infiltrates surrounding the main ulcer, representing the spread of fungal elements. 4. **Creamy exudates/Hypopyon:** Fungal ulcers often present with a thick, "fixed" hypopyon. Among fungi, **Fusarium** and **Aspergillus** are the most common filamentous fungi causing keratitis in India. **Analysis of Incorrect Options:** * **A. Corynebacterium diphtheria:** This is a rare cause of membranous conjunctivitis. While it can penetrate an intact corneal epithelium, it does not present with feathery margins or a history of vegetative trauma. * **C. Acanthamoeba sp.:** Typically associated with **contact lens wear** or exposure to contaminated water. It is characterized by intense pain (out of proportion to clinical signs) and a **ring-shaped infiltrate**. * **D. Streptococcus pneumoniae:** A common cause of bacterial keratitis (Ulcus Serpens). It typically presents with a **serpiginous (creeping) ulcer** with a sharp overhanging border and an associated hypopyon, but lacks feathery margins and satellite lesions. **NEET-PG High-Yield Pearls:** * **Gold Standard Diagnosis:** Corneal scraping followed by **KOH mount** (shows hyphae) and culture on **Sabouraud’s Dextrose Agar (SDA)**. * **Drug of Choice:** Topical **Natamycin (5%)** is the first-line treatment for filamentous fungi like *Fusarium*. * **Clinical Sign:** Fungal ulcers are often "dry" in appearance and may have an immune ring (Wessely ring).

Practice by Chapter

Corneal Anatomy and Physiology

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Bacterial Keratitis

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Viral Keratitis

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Fungal Keratitis

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Protozoan Keratitis

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Corneal Degenerations

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Corneal Dystrophies

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Keratoconus and Ectatic Disorders

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Corneal Transplantation

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Corneal Topography and Imaging

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Dry Eye Disease

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Corneal Trauma

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