Diseases of the Cornea Practice Questions

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

Derives its oxygen from aqueous humor. ### 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).

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

Exposure keratitis. **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)**.

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

Mustard gas exposure. ### 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).

Q: What is the nerve supply of the cornea?

Ophthalmic division of Cranial nerve V. ### 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.

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

All of the above. **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 1

Irido-Corneal Endothelial syndrome is characterized by?

Accepted Answer

Deposition of abnormal collagen in Descemet's membrane

Answer

Opacity of the cornea with edema of the stroma

Answer

Deposition of glycosaminoglycans in Descemet's membrane

Answer

Diffuse bilateral senile iris degeneration

Question 2

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

Accepted Answer

Derives its oxygen from aqueous humor

Answer

Measures 500 micrometers

Answer

Type 1 collagen is most abundant; types 4 & 6 are also found

Answer

Transmits 90% of incoming light

Question 3

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

Accepted Answer

Between the last blink and the appearance of the first dry spot on the cornea

Answer

For the appearance of a dry spot between two blinks

Answer

Taken by successive blinks to break the tear film

Answer

For the disappearance of dry spots on the cornea

Question 4

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

Accepted Answer

Exposure keratitis

Answer

Acute congestive glaucoma

Answer

Dendritic ulcer

Answer

Absolute glaucoma

Question 5

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

Accepted Answer

Dexamethasone

Answer

Atropine

Answer

Cefazolin

Answer

Acyclovir

Question 6

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

Accepted Answer

Mustard gas exposure

Answer

Siderosis

Answer

Chalcosis

Answer

Lindane exposure

Question 7

What is the nerve supply of the cornea?

Accepted Answer

Ophthalmic division of Cranial nerve V

Answer

Maxillary division of the trigeminal nerve

Answer

Facial Nerve

Answer

Auriculotemporal nerve

Question 8

Cloudy cornea is a feature of which of the following conditions?

Accepted Answer

All of the above

Answer

Hurler's disease

Answer

Morquio's disease

Answer

Maroteaux-Lamy disease

Question 9

Which organism does not invade an intact cornea?

Accepted Answer

Pseudomonas

Answer

Gonococci

Answer

C. diphtheriae

Answer

Meningococci

Question 10

Corneal deposits are seen in all except?

Accepted Answer

Reis-Bucklers corneal dystrophy

Answer

Fuchs' endothelial dystrophy

Answer

Hunter syndrome

Answer

Hurler syndrome

Diseases of the Cornea — MCQs

Diseases of the Cornea — MCQs

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