Diseases of the Cornea — MCQs

Diseases of the Cornea Indian Medical PG Practice Questions and MCQs

Question 241: KISA% is associated with which of the following conditions?

A. Keratoconus (Correct Answer)
B. Keratoglobus
C. Hypermetropia with astigmatism
D. Terrien's marginal degeneration

Explanation: **Explanation:** **KISA%** is a quantitative screening index used for the diagnosis and classification of **Keratoconus**. It was developed by Rabinowitz and Rasheed to distinguish normal corneas from those with subclinical or clinical keratoconus using corneal topography data. The index is calculated using four specific parameters: 1. **K:** Central keratometry (K-value). 2. **I-S:** Inferior-Superior dioptric asymmetry. 3. **AST:** Degree of regular astigmatism. 4. **SRAX:** Skewed Radial Axis index. A **KISA% value >100** is considered diagnostic for Keratoconus, while values between 60–100 are suggestive of "suspect" or early disease. **Analysis of Incorrect Options:** * **B. Keratoglobus:** While it is an ectatic dystrophy, it involves generalized thinning and protrusion of the entire cornea (limbus to limbus), unlike the localized paracentral thinning seen in keratoconus where KISA% is specifically applied. * **C. Hypermetropia with astigmatism:** KISA% is a tool for corneal ectasia, not simple refractive errors. * **D. Terrien's marginal degeneration:** This is a peripheral corneal thinning condition characterized by "painless vascularized guttering," usually starting superiorly. It does not utilize the KISA% index for diagnosis. **High-Yield Clinical Pearls for NEET-PG:** * **Munson’s Sign:** V-shaped indentation of the lower lid on down-gaze (late sign). * **Vogt’s Striae:** Vertical stress lines in the deep stroma/Descemet’s membrane. * **Fleischer’s Ring:** Iron deposition at the base of the cone (best seen with cobalt blue filter). * **Rizutti’s Sign:** Conical reflection on the nasal cornea when light is shone from the temporal side. * **Treatment of choice for progression:** Collagen Cross-Linking (CXL/C3R).

Question 242: A patient presents to the eye outpatient department with disc-shaped edema over the cornea. The patient has a history of vesicles over the lips a few weeks prior. There is no ulceration upon staining. What is the most likely diagnosis?

A. Disciform viral keratitis (Correct Answer)
B. Marginal ulcer
C. Metherpetiform keratitis
D. None of the above

Explanation: ### Explanation The clinical presentation of **disc-shaped corneal edema** (disciform keratitis) following a history of **vesicles over the lips** (suggestive of Herpes Simplex Virus - Labialis) is a classic description of **Disciform Viral Keratitis**. **1. Why Option A is Correct:** Disciform keratitis is a form of **endotheliitis** caused by a delayed-type hypersensitivity reaction (Type IV) to the Herpes Simplex Virus (HSV) antigen. Unlike epithelial keratitis, there is **no active viral replication** in the epithelium, which explains why there is **no ulceration** upon staining. The hallmark clinical sign is a central or paracentral zone of stromal edema with an intact epithelium, often accompanied by "keratic precipitates" (KPs) underlying the edema. **2. Why Other Options are Incorrect:** * **Option B (Marginal Ulcer):** These are typically hypersensitivity reactions to Staphylococcal exotoxins. They present as peripheral infiltrates with a clear space between the limbus and the ulcer, not as central disciform edema. * **Option C (Metaherpetic/Trophic Keratitis):** This is a mechanical failure of epithelial healing due to basement membrane damage and loss of corneal sensations (neurotrophic). It presents as a **non-healing ulcer** with smooth, rounded borders, which contradicts the "no ulceration" finding in this case. **Clinical Pearls for NEET-PG:** * **Gold Standard Treatment:** Topical steroids (to control the immune response) combined with prophylactic topical antivirals (to prevent viral reactivation). * **Wessely Ring:** An immune ring of stromal precipitation sometimes seen in disciform keratitis. * **Sensation:** Corneal sensations are typically **reduced** in HSV infections. * **Dendritic Ulcer:** The most common presentation of primary/recurrent epithelial HSV; it stains with Fluorescein (bed) and Rose Bengal (edges).

Question 243: A condition characterized by collagenous degeneration of the conjunctiva with invasion of the corneal epithelium, leading to destruction of the stromal layer and Bowman's membrane?

A. Conjunctivitis
B. Trachoma
C. Pinguecula
D. Pterygium (Correct Answer)

Explanation: ### Explanation **Pterygium** is a triangular, wing-shaped fold of conjunctiva that encroaches upon the cornea. The hallmark of its pathology is **elastotic degeneration** of the subepithelial conjunctival collagen. As it progresses, it invades the cornea, where it actively destroys the **Bowman’s membrane** and the superficial stroma. This invasive nature distinguishes it from other surface growths. #### Why the other options are incorrect: * **Conjunctivitis:** This is a simple inflammation of the conjunctiva. While it may cause discharge and hyperemia, it does not involve collagenous degeneration or the destruction of corneal layers. * **Trachoma:** Caused by *Chlamydia trachomatis*, it leads to follicular hypertrophy and scarring (Arlt’s line). While it can cause corneal pannus, it is an infectious/inflammatory process rather than a primary collagenous degenerative invasion. * **Pinguecula:** This is also a collagenous degeneration (yellowish patch), but it is **stationary** and does not invade the cornea. It remains confined to the bulbar conjunctiva. #### High-Yield Clinical Pearls for NEET-PG: * **Stocking’s Line:** An iron deposition line seen on the corneal epithelium at the leading edge (head) of a pterygium. * **Fuchs’ Islets:** Small, white, precursor opacities seen at the advancing edge. * **Treatment of Choice:** Surgical excision with **Limbal Conjunctival Autograft (CAG)** is the gold standard to prevent recurrence. * **Etiology:** Strongly associated with chronic **UV-B light exposure** (common in outdoor workers). * **Complication:** Significant **with-the-rule astigmatism** due to flattening of the horizontal meridian.

Question 244: What is the treatment for Mooren's ulcer?

A. Topical steroids
B. Corneal graft
C. Immunosuppressives
D. All of the above (Correct Answer)

Explanation: **Explanation:** Mooren’s ulcer is a rare, idiopathic, peripheral ulcerative keratitis (PUK) characterized by a chronic, painful, "creeping" ulceration that begins at the limbus and spreads circumferentially and centrally. Because it is an **autoimmune-mediated destruction** of the corneal stroma, the management is typically a **stepped approach** involving multiple modalities. 1. **Topical Steroids (Option A):** These are the first line of treatment to control local inflammation and inhibit the collagenolytic activity. 2. **Immunosuppressives (Option C):** In bilateral cases or cases refractory to steroids (especially the "malignant" type seen in young patients), systemic immunosuppressants like Methotrexate, Azathioprine, or Cyclosporine are essential to halt the underlying autoimmune process. 3. **Surgical Intervention/Corneal Graft (Option B):** Surgery is indicated for complications. **Conjunctival resection (peritomy)** is often done to remove the source of inflammatory mediators. If the ulcer leads to extreme thinning or perforation, a **lamellar or penetrating keratoplasty (corneal graft)** is required for structural integrity. **Why "All of the above" is correct:** Since Mooren’s ulcer is a progressive disease, treatment often requires a combination of local anti-inflammatories, systemic immune modulation, and surgical repair. **High-Yield Clinical Pearls for NEET-PG:** * **Key Feature:** It is a diagnosis of exclusion; there is **no associated systemic disease** (unlike PUK associated with Rheumatoid Arthritis). * **Morphology:** Characterized by an **overhanging (undermined) edge** at the advancing border. * **Two Types:** * *Type 1 (Benign):* Unilateral, older patients, responds well to treatment. * *Type 2 (Malignant):* Bilateral, younger patients (often males), rapidly progressive, poor prognosis.

Question 245: The outer epithelium of the cornea is derived from which germ layer?

A. Endoderm
B. Mesoderm
C. Surface ectoderm (Correct Answer)
D. Neural ectoderm

Explanation: ### Explanation The development of the cornea involves a coordinated contribution from two primary embryonic sources: **Surface Ectoderm** and **Neural Crest Cells** (mesectoderm). **1. Why Surface Ectoderm is Correct:** The cornea consists of five main layers. The outermost layer, the **corneal epithelium**, is derived directly from the **surface ectoderm** that covers the optic vesicle after it invaginates to form the optic cup. This is consistent with the general rule that surface ectoderm gives rise to the epithelial coverings of the body and its specialized appendages. **2. Why the Other Options are Incorrect:** * **Neural Ectoderm (D):** This gives rise to the retina, the posterior layers of the iris, the ciliary body epithelium, and the optic nerve. It does not contribute to the cornea. * **Mesoderm (B):** While traditionally thought to form the stroma, current embryology confirms that the corneal stroma and endothelium are derived from **Neural Crest Cells** (migrating cells of ectodermal origin), not true mesoderm. Mesoderm primarily forms the extraocular muscles and vascular endothelium. * **Endoderm (A):** The endoderm does not contribute to any ocular structures. **3. High-Yield Clinical Pearls for NEET-PG:** * **Corneal Layers & Origin:** * **Surface Ectoderm:** Epithelium. * **Neural Crest Cells:** Stroma (Substantia propria), Descemet’s membrane, and Endothelium. (Note: Bowman’s membrane is a condensation of the stroma). * **The "Rule of Surface Ectoderm":** In the eye, it forms the **Lens**, **Corneal epithelium**, **Conjunctival epithelium**, and the **Lacrimal apparatus**. * **Clinical Correlation:** Defects in neural crest cell migration can lead to anterior segment dysgenesis, such as **Axenfeld-Rieger syndrome** or **Peters anomaly**.

Question 246: Which of the following is NOT a corneal sign of Trachoma?

A. Arlt's line
B. Pannus
C. Opacity
D. Herbert's pits (Correct Answer)

Explanation: **Explanation:** The question asks for the option that is **NOT** a corneal sign. While all listed options are clinical features of Trachoma (caused by *Chlamydia trachomatis* serotypes A, B, Ba, and C), they are anatomically divided into conjunctival and corneal signs. **Why "Herbert’s Pits" is the correct answer:** Herbert’s pits are indeed a pathognomonic sign of Trachoma, but they are located at the **limbus**, not the cornea proper. They represent scarred, depressed areas left behind after the resolution of limbal follicles. In the context of strict anatomical classification used in NEET-PG, they are categorized as limbal signs. **Analysis of Incorrect Options (Corneal Signs):** * **Pannus (Option B):** This is a hallmark corneal sign. It involves subepithelial infiltration and superficial vascularization, typically starting at the upper limbus (progressive vs. regressive pannus). * **Opacity (Option C):** Corneal scarring and opacification occur in the cicatricial stage (Stage IV) due to chronic irritation from trichiasis and entropion, leading to visual impairment. * **Arlt’s Line (Option A):** This is the **correct answer's "distractor"** because Arlt's line is actually a **conjunctival sign**. It is a horizontal band of scarring found in the palpebral conjunctiva (at the junction of the anterior 1/3rd and posterior 2/3rd). *Note: There appears to be a technical discrepancy in the provided key. Anatomically, both Arlt's line (conjunctival) and Herbert's pits (limbal) are not "corneal" signs. However, in many clinical classifications, Herbert's pits are grouped with limbal/corneal changes, whereas Arlt's line is strictly palpebral.* **High-Yield Clinical Pearls for Trachoma:** * **WHO Classification (FISTO):** **F**ollicles, **I**ntense Inflammation, **S**carring, **T**richiasis, **O**pacity. * **SAFE Strategy:** **S**urgery, **A**ntibiotics (Azithromycin), **F**acial cleanliness, **E**nvironmental improvement. * **Halberstaedter-Prowazek (HP) Bodies:** Intracytoplasmic inclusion bodies seen on Giemsa stain. * **Most common cause of preventable blindness worldwide.**

Question 247: Hypopyon ulcer may be produced by which of the following organisms?

A. Pneumococcus
B. Pseudomonas
C. Gonococcus
D. All of the above (Correct Answer)

Explanation: ### Explanation A **Hypopyon Ulcer** (Ulcus Serpens) is a purulent corneal ulcer associated with a collection of inflammatory cells (pus) in the anterior chamber. The presence of a hypopyon indicates a severe inflammatory response, usually triggered by bacterial toxins or fungal elements. **Why "All of the above" is correct:** While **Pneumococcus** (*Streptococcus pneumoniae*) is classically the most common cause of a typical "creeping" ulcus serpens, several other virulent bacteria can produce a hypopyon: * **Pneumococcus (Option A):** Historically the most common cause. It typically produces a grayish-white disc-shaped ulcer that tends to spread over the cornea in a serpiginous (creeping) manner. * **Pseudomonas (Option B):** A highly virulent gram-negative organism often associated with contact lens wear. It produces a rapidly progressing ulcer with a characteristic greenish-yellow discharge and a large hypopyon due to the release of proteolytic enzymes. * **Gonococcus (Option C):** *Neisseria gonorrhoeae* is one of the few organisms capable of penetrating an intact corneal epithelium. It causes hyperacute purulent conjunctivitis and severe corneal melting with hypopyon. **Clinical Pearls for NEET-PG:** * **Sterile Hypopyon:** In bacterial ulcers, the hypopyon is usually **sterile** because it is a reaction to toxins, not a direct invasion of bacteria into the anterior chamber (unless there is a perforation). * **Fungal Hypopyon:** Fungal keratitis (e.g., *Aspergillus*, *Fusarium*) often presents with a **non-sterile, thick, and immobile** hypopyon. Look for "feathery borders" and "satellite lesions" in the clinical vignette. * **Organisms penetrating intact epithelium:** Remember the mnemonic **CHLNS** (Corynebacterium, Haemophilus, Listeria, Neisseria, Shigella). * **Treatment:** Intensive topical fortified antibiotics (e.g., Cefazolin and Tobramycin) or fluoroquinolones are the mainstay of management. Atropine is added to relieve ciliary spasms and prevent synechiae.

Question 248: Which of the following is the most highly innervated structure of the eye?

A. Iris
B. Cornea (Correct Answer)
C. Retina
D. Sclera

Explanation: ### Explanation **Correct Answer: B. Cornea** The **cornea** is the most highly innervated tissue in the entire human body. It is supplied by the **long ciliary nerves** (branches of the Ophthalmic division of the Trigeminal nerve, CN V1). These nerves form a dense subepithelial plexus, with nerve endings concentrated primarily in the anterior stroma and epithelium. The density of pain receptors (nociceptors) in the cornea is approximately **300 to 600 times greater than that of the skin**, which explains why even a microscopic foreign body or a minor epithelial abrasion causes intense pain, photophobia, and reflex lacrimation. **Analysis of Incorrect Options:** * **A. Iris:** While the iris is richly supplied by the long and short ciliary nerves (providing sensory, sympathetic, and parasympathetic fibers), its nerve density does not match the extreme concentration found in the corneal epithelium. * **C. Retina:** The retina is composed of neural tissue but lacks sensory pain receptors (nociceptors). This is why retinal detachments or hemorrhages are typically painless. * **D. Sclera:** The sclera is relatively poorly vascularized and innervated compared to the cornea. Pain in scleritis is usually due to the involvement of the overlying episclera and underlying uvea. --- ### NEET-PG High-Yield Pearls * **Nerve Supply:** The cornea is supplied by the **Long Ciliary Nerves** (CN V1). * **Corneal Reflex:** The afferent limb is the **Trigeminal nerve (V1)**; the efferent limb is the **Facial nerve (VII)**, leading to the blink response. * **Nerve Distribution:** Corneal nerves lose their myelin sheath after entering the limbus (to maintain transparency) and are absent in the posterior stroma, Descemet’s membrane, and endothelium. * **Clinical Correlation:** In **Herpes Simplex Keratitis**, there is a characteristic **loss of corneal sensation** (hypesthesia) due to nerve damage.

Question 249: Corneal ulcer is defined as?

A. Erosion of epithelium only
B. Erosion of endothelium only
C. Erosion of epithelium with underlying inflammation (Correct Answer)
D. Loss of endothelium with loss of corneal sensation

Explanation: **Explanation:** A **corneal ulcer** is defined as a breach in the continuity of the corneal epithelium associated with necrosis of the underlying corneal stroma (inflammation). 1. **Why Option C is correct:** For a lesion to be classified as an "ulcer," there must be two components: a loss of the protective epithelial layer and an active inflammatory response in the stroma. Without stromal involvement/inflammation, the condition is merely a superficial injury. 2. **Why other options are incorrect:** * **Option A (Erosion of epithelium only):** This is the definition of a **Corneal Erosion**. In an erosion, the epithelium is lost, but the underlying stroma remains healthy and clear without infiltration or necrosis. * **Option B & D (Endothelium involvement):** The endothelium is the innermost layer. Loss of endothelium leads to corneal edema (bullous keratopathy) but does not define an ulcer. While loss of sensation (Option D) is a feature of neurotrophic ulcers, it is not the definition of a corneal ulcer itself. **High-Yield Clinical Pearls for NEET-PG:** * **Hypopyon:** A collection of pus/WBCs in the anterior chamber, often seen in bacterial (sterile) or fungal (infected) ulcers. * **Acanthamoeba Ulcer:** Characterized by a "Ring Infiltrate" and severe pain out of proportion to clinical signs; common in contact lens users. * **Herpes Simplex Keratitis:** Presents as a "Dendritic ulcer" with terminal bulbs. It is stained by Fluorescein (bed) and Rose Bengal (margins). * **Fungal Ulcer:** Look for "Feathery margins," "Satellite lesions," and a dry, greyish-white appearance. Often follows trauma with vegetative matter.

Question 250: What substance is deposited in band keratopathy?

A. Calcium sulfate
B. Calcium phosphate (Correct Answer)
C. Magnesium sulfate
D. Magnesium phosphate

Explanation: **Explanation:** **Band Keratopathy** is a degenerative condition characterized by the deposition of **calcium salts** in the sub-epithelial layers of the cornea, specifically within the **Bowman’s membrane**, the anterior stroma, and the epithelial basement membrane. **Why Calcium Phosphate is correct:** The primary substance deposited is **calcium phosphate** (hydroxyapatite). The physiological basis lies in the evaporation of tears at the exposed interpalpebral fissure, which leads to an increase in local pH (alkalinity). Since calcium phosphate is less soluble at a higher pH, it precipitates out of the tear film and aqueous humor into the corneal tissue. **Why other options are incorrect:** * **Calcium sulfate (A):** While a calcium salt, it is not the biological mineral involved in corneal calcification. * **Magnesium sulfate/phosphate (C & D):** Magnesium is not the primary cation involved in this degenerative process. Band keratopathy is strictly a disorder of calcium metabolism or local ocular calcium homeostasis. **NEET-PG High-Yield Pearls:** 1. **Clinical Appearance:** Presents as a "horizontal grey-white band" in the interpalpebral area with a characteristic **"Swiss-cheese appearance"** (due to clear holes where nerves pierce the Bowman’s membrane). 2. **Etiology:** * **Ocular:** Chronic uveitis (most common in children with JIA), phthisis bulbi, or silicone oil in the anterior chamber. * **Systemic:** Hypercalcemia (Hyperparathyroidism, Vitamin D toxicity, Sarcoidosis, Milk-alkali syndrome). 3. **Treatment of Choice:** Chelation therapy using **1.5% Disodium EDTA** after removing the corneal epithelium.

Practice by Chapter

Corneal Anatomy and Physiology

Practice Questions

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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