Diseases of the Cornea — MCQs

Diseases of the Cornea Indian Medical PG Practice Questions and MCQs

Question 91: Irido-Corneal Endothelial syndrome is characterized by?

A. Opacity of the cornea with edema of the stroma
B. Deposition of abnormal collagen in Descemet's membrane (Correct Answer)
C. Deposition of glycosaminoglycans in Descemet's membrane
D. Diffuse bilateral senile iris degeneration

Explanation: **Explanation:** **Irido-Corneal Endothelial (ICE) Syndrome** is a rare, typically unilateral condition characterized by an abnormal corneal endothelial proliferation. The hallmark of this condition is the migration of these abnormal endothelial cells across the anterior chamber angle and onto the iris surface. 1. **Why Option B is Correct:** In ICE syndrome, the abnormal endothelial cells behave like epithelial cells. They secrete a **basement membrane-like material (abnormal collagen)** that is deposited posterior to the existing Descemet’s membrane. This leads to the formation of a "multilayered" or thickened Descemet’s membrane, which eventually contracts, causing iris features like corectopia, ectropion uveae, and secondary angle-closure glaucoma. 2. **Why Other Options are Incorrect:** * **Option A:** While corneal edema occurs due to endothelial pump failure, "opacity with stromal edema" is a non-specific finding seen in many conditions (like Fuchs’ dystrophy) and does not define the underlying pathology of ICE syndrome. * **Option C:** Glycosaminoglycans (GAGs) are primary components of the corneal stroma, not the pathological deposition seen in ICE syndrome. * **Option D:** ICE syndrome is characteristically **unilateral** and occurs in young to middle-aged adults, not as a "bilateral senile" degeneration. **High-Yield Clinical Pearls for NEET-PG:** * **The ICE Triad:** It includes three clinical variants: 1. **Progressive Iris Atrophy:** Severe iris thinning and hole formation (polycoria). 2. **Chandler Syndrome:** Most common variant; presents primarily with corneal edema and mild iris changes. 3. **Cogan-Reese Syndrome:** Characterized by "pedunculated" nodules on the iris surface. * **Specular Microscopy:** Shows a characteristic **"beaten silver"** or "hammered silver" appearance of the endothelium. * **Gender Predilection:** More common in females.

Question 92: Which of the following statements is NOT true regarding the corneal stroma?

A. Measures 500 micrometers
B. Type 1 collagen is most abundant; types 4 & 6 are also found
C. Transmits 90% of incoming light
D. Derives its oxygen from aqueous humor (Correct Answer)

Explanation: ### Explanation The corneal stroma constitutes approximately 90% of the total corneal thickness. Understanding its physiology and anatomy is crucial for NEET-PG. **Why Option D is the Correct Answer (The False Statement):** The primary source of oxygen for the corneal stroma (and the cornea in general) is the **atmospheric oxygen** dissolved in the **pre-corneal tear film**. While the posterior layers receive some oxygen from the aqueous humor, the stroma relies heavily on atmospheric diffusion. When the eyes are closed, oxygen is supplied by the palpebral conjunctival capillaries. The aqueous humor primarily provides **glucose** and nutrients, not the bulk of the oxygen. **Analysis of Other Options:** * **Option A:** The central corneal thickness is approximately 520–540 μm. Since the stroma makes up about 90% of this, it measures roughly **500 μm**. * **Option B:** The stroma consists of lamellae made of collagen fibers. **Type I collagen** is the most abundant. Type VI helps in spacing, and Type IV is found in the basement membranes (though predominantly in Bowman’s and Descemet’s). * **Option C:** Due to the precise lattice arrangement of collagen fibrils (Maurice’s Theory) and their small diameter relative to the wavelength of light, the stroma is highly transparent, transmitting over **90% of visible light**. **High-Yield Clinical Pearls for NEET-PG:** * **Transparency:** Maintained by the "Lattice Theory" and the dehydrating action of the endothelial pump. * **Keratocytes:** These are the specialized fibroblasts found between stromal lamellae, essential for repair. * **Dua’s Layer:** A thin, tough layer (approx. 15 μm) located between the stroma and Descemet’s membrane, discovered recently. * **Corneal Edema:** If the endothelium fails, the stroma thickens, leading to loss of transparency (Ground-glass appearance).

Question 93: Tear film break-up-time is defined as the time:

A. Between the last blink and the appearance of the first dry spot on the cornea (Correct Answer)
B. For the appearance of a dry spot between two blinks
C. Taken by successive blinks to break the tear film
D. For the disappearance of dry spots on the cornea

Explanation: **Explanation:** **Tear Film Break-Up Time (BUT)** is a clinical test used to assess the **stability of the precorneal tear film**. 1. **Why Option A is Correct:** The test is performed by instilling fluorescein dye into the lower fornix and asking the patient to blink. The patient is then instructed to keep their eyes open without blinking while being examined under a slit lamp with a cobalt blue filter. The BUT is defined as the interval **between the last blink and the appearance of the first dry spot** (black hole/streak) in the greenish-yellow fluorescein-stained tear film. A value of **less than 10 seconds** is considered abnormal and indicates tear film instability. 2. **Why Other Options are Incorrect:** * **Option B:** While it occurs between blinks, the definition specifically requires the starting point to be the *last* blink to ensure a standardized measurement of time. * **Option C:** Successive blinks actually reform and stabilize the tear film; they do not break it. * **Option D:** The test measures the *formation* of dry spots (evaporation/rupture), not their disappearance. **High-Yield Clinical Pearls for NEET-PG:** * **Significance:** A low BUT is a hallmark of **Evaporative Dry Eye** (often due to Meibomian Gland Dysfunction) and **Mucin deficiency** (e.g., Vitamin A deficiency, Stevens-Johnson Syndrome). * **Normal BUT:** 15 to 35 seconds. * **Schirmer’s Test:** Unlike BUT (which measures stability), Schirmer’s test measures the **quantity** of aqueous tear production. * **Rose Bengal Stain:** Specifically stains dead and devitalized epithelial cells and is highly sensitive for diagnosing Keratoconjunctivitis Sicca.

Question 94: All of the following conditions result in loss of corneal sensations except?

A. Acute congestive glaucoma
B. Dendritic ulcer
C. Absolute glaucoma
D. Exposure keratitis (Correct Answer)

Explanation: **Explanation:** Corneal sensation is primarily mediated by the **long ciliary nerves** (branches of the Ophthalmic division of the Trigeminal nerve). Loss of sensation (corneal anesthesia) occurs when these nerve endings are damaged by infection, high intraocular pressure, or surgical trauma. **Why Exposure Keratitis is the correct answer:** In **Exposure Keratitis**, the primary pathology is the drying of the cornea due to incomplete lid closure (lagophthalmos). Crucially, the corneal sensations remain **intact or may even be hypersensitive** in the early stages. The damage is mechanical and evaporative, not neurological. **Analysis of Incorrect Options:** * **Acute Congestive Glaucoma:** The sudden, massive rise in intraocular pressure (IOP) causes mechanical compression and edema of the corneal nerve endings, leading to a temporary loss of sensation. * **Dendritic Ulcer (Herpes Simplex Keratitis):** This is a classic cause of corneal anesthesia. The HSV virus resides in the trigeminal ganglion and causes neurotrophic damage to the corneal nerves during reactivation. * **Absolute Glaucoma:** This is the final stage of glaucoma where the eye is blind and the IOP is chronically very high. The prolonged high pressure leads to permanent degeneration of the corneal nerve plexus. **High-Yield Clinical Pearls for NEET-PG:** * **Common causes of reduced corneal sensation:** HSV Keratitis (most common), Diabetes Mellitus, Leprosy, Acoustic Neuroma (compressing the 5th nerve), and Topical anesthetic abuse. * **Cogan’s Syndrome:** Associated with interstitial keratitis but usually preserves sensation. * **Neurotrophic Ulcer:** A non-healing ulcer that occurs specifically *because* the cornea is anesthetic (loss of trophic factors). * **Testing:** Corneal reflex is tested using a wisp of cotton; the afferent limb is the **Trigeminal nerve (V1)** and the efferent limb is the **Facial nerve (VII)**.

Question 95: Which one of the following drugs is contraindicated in the treatment of a dendritic corneal ulcer?

A. Atropine
B. Cefazolin
C. Acyclovir
D. Dexamethasone (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. Dexamethasone**. **Why Dexamethasone is Contraindicated:** A dendritic ulcer is the hallmark clinical presentation of **Herpes Simplex Keratitis (HSK)**, specifically the epithelial stage caused by active viral replication. **Corticosteroids** like Dexamethasone are strictly contraindicated in active epithelial viral infections. Steroids suppress the local immune response and enhance viral replication, which can lead to the transformation of a controlled dendritic ulcer into a larger, more invasive **geographic ulcer**. This can result in deep stromal involvement, corneal perforation, and permanent vision loss. **Analysis of Incorrect Options:** * **A. Atropine:** This is a cycloplegic used as supportive therapy. It relieves ciliary spasm (reducing pain) and prevents the formation of posterior synechiae if there is associated secondary iridocyclitis. * **B. Cefazolin:** While not the primary treatment for a viral ulcer, topical antibiotics like Cefazolin are often prescribed as prophylaxis to prevent **secondary bacterial superinfection** of the denuded corneal epithelium. * **C. Acyclovir:** This is the **drug of choice**. Topical Acyclovir (3% ointment, 5 times daily) directly inhibits viral DNA polymerase, treating the root cause of the dendritic ulcer. **Clinical Pearls for NEET-PG:** * **Morphology:** Dendritic ulcers have characteristic **terminal bulbs** (knobs) which contain live virus, distinguishing them from "pseudodendrites" seen in Acanthamoeba or HZV. * **Staining:** The floor of the ulcer stains with **Fluorescein** (green), while the virus-swollen cells at the margin (terminal bulbs) stain with **Rose Bengal** (pink). * **Sensation:** Corneal sensations are typically **diminished or absent** in HSK. * **Steroid Rule:** Steroids are only used in HSK for **Disciform Keratitis** (stromal involvement), which is an immune-mediated reaction, and only under the strict cover of antiviral drugs.

Question 96: A "golden-brown" ring in the cornea is typically a sign of which condition?

A. Siderosis
B. Chalcosis
C. Mustard gas exposure (Correct Answer)
D. Lindane exposure

Explanation: ### Explanation The correct answer is **Mustard gas exposure**. **1. Why Mustard Gas Exposure is Correct:** Mustard gas (sulfur mustard) is a potent alkylating agent used in chemical warfare. Ocular involvement is common, and a characteristic late-stage finding is the **"Golden-brown ring"** (also known as the **Mustard gas ring**). This ring is formed by the deposition of pigment and lipid-like material in the corneal stroma, typically located in the peripheral cornea within the palpebral aperture. It is often associated with delayed-onset keratitis, corneal vascularization, and thinning, which can occur years after the initial exposure. **2. Why the Other Options are Incorrect:** * **Siderosis (A):** Caused by an intraocular iron foreign body. It typically presents with a **"Rusty"** discoloration of the lens (siderosis lentis) and iris, but not a specific golden-brown corneal ring. * **Chalcosis (B):** Caused by an intraocular copper foreign body. The classic corneal finding is the **Kayser-Fleischer (KF) ring**, which is a golden-brown or greenish-brown deposit of copper in the **Descemet’s membrane**. While the color is similar, the term "golden-brown ring" in standardized exams specifically refers to mustard gas unless KF ring is specified. * **Lindane exposure (D):** Lindane is an organochlorine insecticide. While it can cause ocular irritation and conjunctivitis, it is not associated with a specific pigmented corneal ring. **3. NEET-PG High-Yield Pearls:** * **Kayser-Fleischer Ring:** Associated with Wilson’s Disease (Copper). Found in Descemet’s membrane. * **Hudson-Stahli Line:** Iron deposition at the junction of the upper 2/3 and lower 1/3 of the cornea (age-related). * **Flecked Cornea:** Seen in Mustard gas keratitis (delayed manifestation). * **Vossius Ring:** A ring of pigment on the **anterior lens capsule** following blunt trauma (not corneal).

Question 97: What is the nerve supply of the cornea?

A. Maxillary division of the trigeminal nerve
B. Facial Nerve
C. Auriculotemporal nerve
D. Ophthalmic division of Cranial nerve V (Correct Answer)

Explanation: ### Explanation **1. Why the Correct Answer is Right:** The cornea is one of the most sensitive tissues in the human body, primarily supplied by the **Ophthalmic division (V1)** of the **Trigeminal nerve (CN V)**. Specifically, the sensory pathway follows this route: * **Trigeminal Nerve (CN V) → Ophthalmic Division (V1) → Nasociliary Nerve → Long Ciliary Nerves.** These nerves enter the peripheral corneal stroma, lose their myelin sheaths (to maintain corneal transparency), and form the subepithelial and intraepithelial plexuses. This rich innervation is responsible for the **corneal reflex** (afferent limb). **2. Why the Other Options are Wrong:** * **A. Maxillary division (V2):** This supplies the lower eyelid, cheek, and upper lip, but does not provide sensory innervation to the globe or cornea. * **B. Facial Nerve (CN VII):** This is the **motor** nerve for the orbicularis oculi muscle. It forms the **efferent limb** of the corneal reflex (eye closure), not the sensory supply. * **C. Auriculotemporal nerve:** This is a branch of the Mandibular division (V3) of the Trigeminal nerve. It supplies the skin of the temple and the TMJ, not the eye. **3. Clinical Pearls for NEET-PG:** * **Corneal Reflex:** Afferent is V1 (Nasociliary); Efferent is VII (Temporal/Zygomatic branches). * **Transparency:** Nerves become **demyelinated** after traveling 1-2 mm into the cornea to ensure optical clarity. * **Neurotrophic Keratitis:** Occurs when there is damage to the Trigeminal nerve (e.g., post-Herpetic or surgery), leading to loss of sensation, poor wound healing, and corneal ulcers. * **Herpes Zoster Ophthalmicus:** If the tip of the nose is involved (**Hutchinson’s sign**), it indicates Nasociliary nerve involvement, signaling a high risk of corneal complications.

Question 98: Cloudy cornea is a feature of which of the following conditions?

A. Hurler's disease
B. Morquio's disease
C. Maroteaux-Lamy disease
D. All of the above (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. All of the above**. The underlying medical concept involves **Mucopolysaccharidoses (MPS)**, a group of metabolic disorders caused by the deficiency of lysosomal enzymes required to break down glycosaminoglycans (GAGs). When GAGs are not degraded, they accumulate in various tissues, including the corneal stroma. In the cornea, this accumulation disrupts the regular arrangement of collagen fibrils, leading to opasification or **corneal clouding**. * **Hurler’s Disease (MPS I-H):** This is the prototype for corneal clouding. It is characterized by a deficiency of alpha-L-iduronidase, leading to severe, progressive corneal opacification early in life. * **Morquio’s Disease (MPS IV):** Caused by a deficiency of galactosamine-6-sulfatase (Type A) or beta-galactosidase (Type B). It presents with fine, diffuse stromal haze. * **Maroteaux-Lamy Disease (MPS VI):** Caused by a deficiency of arylsulfatase B. It is associated with significant corneal clouding along with skeletal deformities. **Why other options are not "wrong" but part of the whole:** Since Hurler’s, Morquio’s, and Maroteaux-Lamy all feature corneal clouding as a primary clinical sign, "All of the above" is the most accurate choice. **High-Yield Clinical Pearls for NEET-PG:** 1. **Hunter’s Syndrome (MPS II):** This is the high-yield exception. It is X-linked recessive and is the only MPS where **corneal clouding is absent** (though clear corneas may still develop pigmentary retinopathy). 2. **Sanfilippo Syndrome (MPS III):** Corneal clouding is typically absent or very mild. 3. **Scheie’s Syndrome (MPS I-S):** A milder form of MPS I that also presents with significant corneal clouding, often later in life than Hurler’s. 4. **Mnemonic:** "The **Hunter** needs **clear** vision to see the **X** (X-linked)."

Question 99: Which organism does not invade an intact cornea?

A. Gonococci
B. C. diphtheriae
C. Meningococci
D. Pseudomonas (Correct Answer)

Explanation: **Explanation:** The corneal epithelium acts as a formidable natural barrier against most microorganisms. For a corneal ulcer to develop, there usually must be a prior breach in this epithelium (e.g., trauma, contact lens wear, or dry eye). However, a select group of highly virulent organisms possesses the enzymatic capability to penetrate a completely **intact** corneal epithelium. **Why Pseudomonas is the Correct Answer:** * **Pseudomonas aeruginosa** is a common cause of aggressive bacterial keratitis, but it **cannot** invade an intact cornea. It requires a pre-existing epithelial defect to initiate infection. Once inside, it produces proteases and exotoxins that cause rapid liquefactive necrosis (keratomalacia). **Why the other options are incorrect:** The mnemonic **"CHALM"** or **"N-H-G-C-L"** is often used to remember organisms that **can** invade an intact cornea: * **A & C (Gonococci & Meningococci):** *Neisseria gonorrhoeae* and *Neisseria meningitidis* can penetrate intact surfaces. Gonococcal keratitis is a medical emergency due to its risk of rapid perforation. * **B (C. diphtheriae):** *Corynebacterium diphtheriae* is a classic example of an organism that can invade intact epithelium, often associated with membranous conjunctivitis. * **Other notable organisms:** *Listeria monocytogenes* and *Haemophilus aegyptius* (Koch-Weeks bacillus) also have this capability. **High-Yield Clinical Pearls for NEET-PG:** 1. **Pseudomonas Keratitis:** Characterized by a rapid onset, **greenish-yellow purulent discharge**, and a "soupy" appearance of the stroma. It is the most common cause of corneal ulcers in **contact lens users**. 2. **Emergency:** Any *Neisseria* species infection of the eye is considered a surgical emergency because it can lead to corneal perforation within 24–48 hours. 3. **Acanthamoeba:** While not on this list, remember it typically requires a minor abrasion (often from contaminated contact lens solution) to cause its characteristic **ring-shaped infiltrate**.

Question 100: Corneal deposits are seen in all except?

A. Reis-Bucklers corneal dystrophy (Correct Answer)
B. Fuchs' endothelial dystrophy
C. Hunter syndrome
D. Hurler syndrome

Explanation: **Explanation:** The question asks for the condition where corneal **deposits** are typically absent. While many corneal dystrophies involve the accumulation of abnormal material, the distinction lies in the pathophysiology of the specific layer involved. **1. Why Reis-Bücklers Dystrophy (Option A) is the Correct Answer:** Reis-Bücklers is a superficial variant of **Granular Corneal Dystrophy Type III**. It primarily involves the replacement of the **Bowman’s layer** with sheet-like connective tissue (collagen). While it causes opacification and scarring, it is clinically characterized by **reticular (honeycomb) opacities** and recurrent erosions rather than the discrete metabolic "deposits" seen in systemic storage diseases or specific endothelial changes. *Note: In some contexts, all dystrophies are considered "deposits," but compared to the other options, this is the least characteristic.* **2. Analysis of Incorrect Options:** * **Hunter (C) and Hurler (D) Syndromes:** These are **Mucopolysaccharidoses (MPS)**. In these lysosomal storage disorders, glycosaminoglycans (GAGs) accumulate within the corneal stroma, leading to diffuse, ground-glass **corneal clouding (deposits)**. (Exception: Hunter syndrome is often classically described as having clearer corneas than Hurler, but histological deposits still occur). * **Fuchs’ Endothelial Dystrophy (B):** This condition is characterized by the formation of **Guttae**, which are excrescences (droplet-like deposits) of abnormal collagen on Descemet’s membrane. **NEET-PG High-Yield Pearls:** * **Mnemonic for MPS & Cornea:** "Shes (Scheie) Hurrying (Hurler) to see the Cloudy weather; Hunter (Hunter) is looking for the X (X-linked) with Clear eyes." * **Reis-Bücklers:** Associated with **TGFBI gene** mutation on Chromosome 5q31. * **Vogt-Koyanagi-Harada (VKH):** Often confused in exams; remember it involves the uvea, not primary corneal deposits. * **Whorl-like deposits (Verticillata):** Seen in Fabry’s disease and Amiodarone use.

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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