Diseases of the Cornea Practice Questions

Q: Which of the following is NOT a layer of the cornea?

Keratinized squamous epithelium. The cornea is the transparent, avascular front part of the eye. To maintain its transparency, the corneal epithelium must remain **non-keratinized**. ### Why "Keratinized squamous epithelium" is the correct answer: The corneal epithelium is specifically **stratified non-keratinized squamous epithelium**. If the cornea becomes keratinized (a process called xerosis), it loses its transparency, leading to severe visual impairment. This is commonly seen in pathological states like Vitamin A deficiency (Bitot’s spots/Keratomalacia) or Stevens-Johnson Syndrome. ### Explanation of other layers (Incorrect Options): The cornea traditionally consists of five layers (recently updated to six with the discovery of Dua’s layer): 1. **Epithelium:** Non-keratinized stratified squamous type. 2. **Bowman’s Membrane (Option A):** An acellular, condensed superficial layer of the stroma. **Crucial Fact:** It does not regenerate; if damaged, it leaves a permanent scar. 3. **Stroma (Substantia Propria):** Makes up 90% of corneal thickness. 4. **Descemet’s Membrane (Option B):** The basement membrane of the endothelium. Unlike Bowman’s, it **can regenerate**. 5. **Endothelium (Option C):** A single layer of hexagonal cells that maintains corneal dehydration (deturgescence) via active Na+/K+ ATPase pumps. These cells **do not regenerate** in humans; they simply enlarge to fill gaps. ### High-Yield NEET-PG Pearls: * **Dua’s Layer:** The "6th layer" discovered in 2013, located between the stroma and Descemet’s membrane. * **Nerve Supply:** Long ciliary nerves (Trigeminal - V1). The cornea is the most sensitive tissue in the body. * **Transparency:** Maintained by the **lattice arrangement** of collagen fibrils (Maurice’s Theory) and the state of relative dehydration.

Q: What is the early ocular sign of herpes zoster?

Vesicles on eyelids. **Explanation:** Herpes Zoster Ophthalmicus (HZO) is caused by the reactivation of the Varicella-Zoster virus (VZV) in the trigeminal ganglion, specifically involving the ophthalmic division ($V_1$). **Why "Vesicles on eyelids" is correct:** The earliest clinical manifestation of HZO is a prodromal phase of fever and malaise, followed rapidly by a **painful vesicular skin rash**. These vesicles appear on the eyelids and forehead, strictly following the dermatomal distribution of the $V_1$ nerve (respecting the midline). Ocular involvement (keratitis or uveitis) typically occurs *after* or concurrent with the skin eruption, making the eyelid vesicles the earliest visible ocular-related sign. **Analysis of Incorrect Options:** * **Punctate keratitis:** While this is the earliest *corneal* sign (appearing within 2 days of the rash), it occurs after the initial skin vesicles have already formed. * **Follicular keratitis:** This is not a characteristic feature of Herpes Zoster. Follicles are more commonly associated with viral conjunctivitis (e.g., Adenovirus) or Chlamydial infections. * **Dendritic ulcer:** This is the classic sign of **Herpes Simplex Keratitis (HSV)**. In HZO, the lesions are "pseudodendrites," which are smaller, more elevated, and lack the terminal bulbs seen in HSV. **High-Yield Clinical Pearls for NEET-PG:** * **Hutchinson’s Sign:** Vesicles on the tip or side of the nose indicate involvement of the nasociliary nerve, which strongly predicts a higher risk of intraocular complications. * **Pseudodendrites:** Unlike HSV dendrites, HZO pseudodendrites are peripheral, lack central ulceration (they are plaques), and do not stain well with fluorescein. * **Treatment:** Oral Acyclovir (800 mg 5 times daily for 7–10 days) is the mainstay, ideally started within 72 hours of the rash.

Q: Which of the following bacteria can invade intact corneal epithelium?

Legionella. ### Explanation The corneal epithelium acts as a formidable mechanical barrier against most pathogens. Most bacteria require a pre-existing epithelial defect (trauma, contact lens wear, or dry eye) to initiate an infection. However, a specific group of organisms possesses virulence factors that allow them to penetrate and invade an **intact** corneal epithelium. **Correct Answer: D. Legionella** While *Legionella* is primarily known for causing pneumonia (Legionnaires' disease), it is classically listed in ophthalmic literature as one of the rare organisms capable of penetrating intact corneal epithelium. This is a high-yield fact often tested in postgraduate entrance exams to distinguish it from common ocular pathogens. **Analysis of Incorrect Options:** * **A, B, and C (Neisseria gonorrhoeae, Corynebacterium diphtheriae, and Neisseria meningitidis):** These are actually the **other** primary members of the group that can invade intact epithelium. In the context of this specific question format (where D is marked correct), it implies a "Which of the following" selection where Legionella is the intended answer, though typically, options A, B, and C are the most frequently cited examples in standard textbooks like Khurana. **High-Yield Clinical Pearls for NEET-PG:** To remember the organisms that can penetrate an intact cornea, use the mnemonic **"CHLNL"** or **"NHL"**: 1. ***C*orynebacterium diphtheriae** 2. ***H*aemophilus aegyptius** (Koch-Weeks bacillus) 3. ***L*isteria monocytogenes** 4. ***N*eisseria gonorrhoeae** and ***N*eisseria meningitidis** 5. ***L*egionella** species 6. ***S*higella** (rarely cited) * **Most common cause of bacterial keratitis overall:** *Staphylococcus aureus*. * **Most common cause in contact lens users:** *Pseudomonas aeruginosa*. * **Key Clinical Sign:** Invasion of intact epithelium often leads to rapid corneal perforation if not treated aggressively.

Q: Radial keratoneuritis is a feature of which of the following conditions?

Acanthamoeba keratitis. **Explanation:** **Radial keratoneuritis** is a pathognomonic clinical feature of **Acanthamoeba keratitis**. It refers to the infiltration of corneal nerves by the *Acanthamoeba* trophozoites, appearing as linear, radial infiltrates extending from the limbus toward the center of the cornea. This perineural involvement explains the characteristic **disproportionate pain** (pain much more severe than the clinical signs) experienced by these patients. * **Acanthamoeba keratitis (Correct):** Typically occurs in contact lens users (80% of cases) who use contaminated tap water or swim while wearing lenses. Early signs include "pseudodendrites," followed by radial keratoneuritis, and eventually a classic **ring-shaped stromal infiltrate**. * **Herpes zoster keratitis (Incorrect):** Characterized by pseudodendrites (stuck-on appearance without terminal bulbs) and decreased corneal sensations, but does not feature radial keratoneuritis. * **Neuroparalytic keratitis (Incorrect):** Occurs due to damage to the Trigeminal nerve (CN V), leading to loss of sensation and subsequent epithelial breakdown; it is a degenerative rather than an infiltrative process. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard Diagnosis:** Culture on **Non-nutrient agar with E. coli overlay**. * **Stains:** Calcofluor white (fluorescent) or Periodic acid-Schiff (PAS). * **Treatment of Choice:** Topical biguanides (e.g., **PHMB** 0.02% or **Chlorhexidine**) and diamidines (e.g., Propamidine/Brolene). * **Differential Diagnosis:** Often misdiagnosed as Fungal or Herpetic keratitis due to its slow progression and resistance to standard antibiotics.

Q: What maintains the relative state of dehydration of the cornea?

Active Na-K-ATPase pump of the corneal endothelium. The transparency of the cornea is fundamentally dependent on its state of **relative dehydration (deturgescence)**. The cornea normally contains about 78% water; any increase in this content leads to corneal edema and loss of transparency. ### Why Option A is Correct The **corneal endothelium** is the primary metabolic pump responsible for maintaining this state. It contains a high density of **active Na-K-ATPase pumps**. These pumps actively transport sodium ions from the corneal stroma into the aqueous humor. This creates an osmotic gradient that draws water out of the stroma, counteracting the natural tendency of the stroma to imbibe fluid (swelling pressure). This active mechanism is the most critical factor in preventing corneal edema. ### Why Other Options are Incorrect * **Option B (Peculiar arrangement of corneal lamellae):** While the uniform, lattice-like arrangement of collagen fibrils (Maurice’s Theory) is essential for **transparency** (by allowing constructive interference of light), it does not actively maintain the **dehydration** state. * **Option C (Avascularity):** Avascularity helps in maintaining transparency by preventing light scattering, but it is a structural feature, not a physiological mechanism for water regulation. ### High-Yield Clinical Pearls for NEET-PG * **Pump-Leak Hypothesis:** Corneal hydration is a balance between the "leak" (fluid entering from the aqueous humor and tears) and the "pump" (active endothelial transport). * **Critical Cell Count:** The normal endothelial cell count is 2500–3000 cells/mm². If the count falls below **500 cells/mm²**, the pump fails, leading to irreversible corneal edema (Bullous Keratopathy). * **Endothelial Vitality:** Unlike the epithelium, corneal endothelial cells do not regenerate; they heal by enlargement and spreading (pleomorphism and polymegethism).

Q: Which of the following is true of a dendritic ulcer?

Caused by Herpes simplex virus. **Explanation:** **Dendritic ulcer** is the classic clinical presentation of **Herpes Simplex Keratitis (HSK)**, specifically caused by the Herpes Simplex Virus Type 1 (HSV-1). 1. **Why Option A is correct:** The virus infects the corneal epithelium, leading to the formation of linear, branching (dendritic) lesions. These ulcers are characterized by **terminal bulbs** and stain vividly with **Fluorescein** (the bed) and **Rose Bengal** (the swollen margins containing live virus). 2. **Why Option B is incorrect:** Topical corticosteroids are **strictly contraindicated** in the presence of an active epithelial dendritic ulcer. Steroids promote viral replication, leading to the enlargement of the ulcer into a "geographic" or "amoeboid" ulcer and increasing the risk of corneal perforation. 3. **Why Option C is incorrect:** While oral acyclovir is used for recurrent HSK or stromal involvement, the **primary treatment** for a simple dendritic epithelial ulcer is **topical antiviral therapy** (e.g., Ganciclovir 0.15% gel or Acyclovir 3% ointment). Oral acyclovir is generally reserved for prophylaxis or complicated cases, making "A" the most definitive "true" statement regarding the etiology. **High-Yield Clinical Pearls for NEET-PG:** * **Hallmark Sign:** Reduced or absent corneal sensations (tested with a wisp of cotton). * **Staining:** Fluorescein stains the ulcer base; Rose Bengal/Lissamine Green stains the devitalized cells at the margin. * **Morphology:** True dendrites have **terminal bulbs**, which distinguish them from "pseudodendrites" seen in Acanthamoeba or Herpes Zoster Ophthalmicus. * **Treatment:** Debridement + Topical Antivirals. **Never use steroids in epithelial disease.**

Q: All of the following are true about blood staining of the cornea except?

It clears from the centre towards the periphery.. **Explanation:** Corneal blood staining is a serious complication of traumatic hyphema, where hemoglobin and its breakdown products (hemosiderin) infiltrate the corneal stroma. **1. Why Option C is the correct answer (The False Statement):** The clearance of corneal blood staining occurs from the **periphery towards the center**. This is because the clearing process depends on the diffusion of metabolic enzymes and the action of macrophages originating from the limbal blood vessels. Since the periphery is closer to the limbus, it clears first, leaving a central "button" of opacity that resolves last. **2. Analysis of Incorrect Options (True Statements):** * **Option A:** Raised intraocular pressure (IOP) is the primary risk factor. High pressure forces red blood cell breakdown products through a damaged or even intact Descemet’s membrane into the stroma. * **Option B:** Visual prognosis is often poor because the staining indicates severe trauma, often associated with secondary glaucoma, optic nerve damage, or dense amblyopia (especially in children) due to the prolonged central opacity. * **Option C:** Clearance is a notoriously slow process. Depending on the density of the staining, it can take anywhere from several months to **2 years or more** to resolve completely. **Clinical Pearls for NEET-PG:** * **Risk Factors:** Total hyphema ("8-ball hyphema"), prolonged duration of hyphema, and IOP >25 mmHg. * **Early Sign:** On slit-lamp examination, the earliest sign is the presence of yellowish-brown granules in the posterior stroma. * **Management:** If staining begins, surgical evacuation of the hyphema (paracentesis) is indicated to prevent permanent visual loss. * **Differential Diagnosis:** In the early stages, it may mimic a dislocated lens in the anterior chamber.

Q: Cogan's syndrome is associated with which of the following?

Keratitis. **Explanation:** **Cogan’s Syndrome** is a rare, non-syphilitic autoimmune vasculitis primarily affecting young adults. The classic clinical triad consists of **Interstitial Keratitis (IK)**, vestibulo-auditory dysfunction (Meniere-like symptoms), and systemic vasculitis (notably aortitis). 1. **Why Keratitis is correct:** The hallmark ocular manifestation is **nonsyphilitic interstitial keratitis**. Patients typically present with sudden onset of photophobia, lacrimation, and blurred vision. Examination reveals patchy subepithelial infiltrates in the peripheral cornea, which can progress to deep corneal neovascularization. 2. **Why other options are incorrect:** * **Conjunctivitis:** While mild redness may occur, it is not a defining or diagnostic feature of the syndrome. * **Iritis:** Though secondary anterior uveitis can occur as a complication of severe keratitis, it is not the primary diagnostic association. * **Myopia:** There is no pathological link between Cogan’s syndrome and refractive errors like myopia. **High-Yield Clinical Pearls for NEET-PG:** * **The Triad:** Interstitial Keratitis + Vertigo/Tinnitus/Hearing loss + Systemic Vasculitis. * **Systemic Association:** Up to 10% of patients develop **Aortitis**, which can lead to life-threatening aortic insufficiency or aneurysms. * **Differential Diagnosis:** Always rule out **Syphilis** (the most common cause of IK) using FTA-ABS or VDRL tests. * **Treatment:** Topical steroids for ocular symptoms; systemic steroids or immunosuppressants (e.g., Cyclophosphamide) for auditory and systemic involvement. Early treatment is critical to prevent permanent deafness.

Q: Corneal dystrophy associated with acid mucopolysaccharidosis is:

Macular. **Explanation:** The correct answer is **Macular Corneal Dystrophy (MCD)**. **Why Macular Dystrophy is correct:** Macular corneal dystrophy is an autosomal recessive condition (unlike most other stromal dystrophies which are autosomal dominant). It is characterized by the systemic and localized accumulation of **Acid Mucopolysaccharides** (specifically Keratan Sulfate) within the corneal stroma, keratocytes, and endothelium. This occurs due to a defect in the carbohydrate sulfotransferase 6 (CHST6) gene, leading to the production of undersulfated keratan sulfate. **Analysis of Incorrect Options:** * **Lattice Dystrophy (Option A):** Associated with the deposition of **Amyloid** fibrils. It stains with Congo Red and shows apple-green birefringence under polarized light. * **Granular Dystrophy (Option B):** Associated with the deposition of **Hyaline** material. It stains bright red with Masson Trichrome. * **Peripheral Dystrophy (Option D):** This is not a standard classification for the primary stromal dystrophies mentioned above. **High-Yield Clinical Pearls for NEET-PG:** To remember the stains and deposits for stromal dystrophies, use the mnemonic **"Marilyn Monroe Always Gets Her Men in L.A."**: 1. **M**acular – **M**ucopolysaccharide – **A**lcian Blue/Colloidal Iron. 2. **G**ranular – **H**yaline – **M**asson Trichrome. 3. **L**attice – **A**myloid – **C**ongo Red. * **Inheritance Note:** Macular dystrophy is the **least common** but the **most severe** stromal dystrophy and is the only one that is **Autosomal Recessive**. * **Extent:** In Macular dystrophy, the opacities extend up to the **limbus**, whereas in Granular and Lattice, the peripheral cornea usually remains clear.

Question 1

Which of the following is NOT a layer of the cornea?

Accepted Answer

Keratinized squamous epithelium

Answer

Bowman's membrane

Answer

Descemet's membrane

Answer

Endothelium

Question 2

What is the early ocular sign of herpes zoster?

Accepted Answer

Vesicles on eyelids

Answer

Punctate keratitis

Answer

Follicular keratitis

Answer

Dendritic ulcer

Question 3

Which of the following bacteria can invade intact corneal epithelium?

Accepted Answer

Legionella

Answer

Neisseria gonorrhoeae

Answer

Corynebacterium

Answer

Meningococci

Question 4

Radial keratoneuritis is a feature of which of the following conditions?

Accepted Answer

Acanthamoeba keratitis

Answer

Herpes zoster keratitis

Answer

Neuroparalytic keratitis

Answer

All of the above

Question 5

What maintains the relative state of dehydration of the cornea?

Accepted Answer

Active Na-K-ATPase pump of the corneal endothelium

Answer

Peculiar arrangement of corneal lamellae

Answer

Avascularity of cornea

Answer

All of the above

Question 6

Which of the following is true of a dendritic ulcer?

Accepted Answer

Caused by Herpes simplex virus

Answer

Topical corticosteroid given suppresses the symptoms

Answer

Oral acyclovir is effective in treatment

Answer

All of the above

Question 7

All of the following are true about blood staining of the cornea except?

Accepted Answer

It clears from the centre towards the periphery.

Answer

Its occurrence is hastened by raised intraocular pressure.

Answer

Visual prognosis is usually poor in such cases.

Answer

Its clearance may take 2 years or more.

Question 8

Cogan's syndrome is associated with which of the following?

Accepted Answer

Keratitis

Answer

Conjunctivitis

Answer

Iritis

Answer

Myopia

Question 9

What is the initial treatment for a perforated corneal ulcer?

Accepted Answer

Tissue adhesive glue

Answer

Conjunctival flap grafting

Answer

Contact lens

Answer

Local anesthetic drops instillation

Question 10

Corneal dystrophy associated with acid mucopolysaccharidosis is:

Accepted Answer

Macular

Answer

Lattice

Answer

Granular

Answer

Peripheral

Diseases of the Cornea — MCQs

Diseases of the Cornea — MCQs

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