Diseases of the Cornea — MCQs

Diseases of the Cornea Indian Medical PG Practice Questions and MCQs

Question 51: Corneal sensation is decreased in which condition?

A. Viral infection (Correct Answer)
B. Fungal infection
C. Tuberculosis
D. None of the above

Explanation: **Explanation:** The assessment of corneal sensation is a critical clinical step in differentiating types of keratitis. Corneal sensation is mediated by the **long ciliary nerves**, which are branches of the **Ophthalmic division (V1) of the Trigeminal nerve**. **Why Viral Infection is Correct:** Decreased corneal sensation (hypoesthesia or anesthesia) is a hallmark of **Herpetic Keratitis**, caused by the **Herpes Simplex Virus (HSV)** or **Varicella-Zoster Virus (VZV)**. The virus resides in the trigeminal ganglion; during reactivation, it travels down the nerve fibers, causing inflammation and subsequent damage to the corneal nerve plexus. This leads to a loss of the protective blink reflex and delayed epithelial healing (neurotrophic keratopathy). **Why Other Options are Incorrect:** * **Fungal Infection:** Fungal keratitis typically presents with **intact or even heightened sensation** due to intense inflammatory response and lack of direct neurotropism. * **Tuberculosis:** While TB can cause interstitial keratitis or phlyctenular keratoconjunctivitis, it is an immune-mediated or granulomatous response and does not characteristically involve the destruction of corneal nerves. **High-Yield Clinical Pearls for NEET-PG:** 1. **Other causes of decreased corneal sensation:** Diabetes Mellitus (neurotrophic), Leprosy (damage to CN V), Acoustic Neuroma (compression of CN V), and chronic contact lens wear. 2. **Testing:** Sensation is clinically tested using a **wisp of cotton** (Cochet-Bonnet esthesiometer is the gold standard for quantification). 3. **Dendritic Ulcer:** In HSV, the ulcer has **terminal bulbs** and stains with Fluorescein (bed) and Rose Bengal (margins). 4. **Acanthamoeba Keratitis:** Characterized by **radial keratoneuritis** (infiltration around nerves), which causes pain out of proportion to clinical signs, though sensation may eventually decrease.

Question 52: Keratic precipitates are found on which layer of the cornea?

A. Epithelium
B. Endothelium (Correct Answer)
C. Stroma
D. Bowman's membrane

Explanation: **Explanation:** **Keratic Precipitates (KPs)** are inflammatory cell deposits (leukocytes) that settle on the posterior surface of the cornea. These cells originate from the uveal tract (iris and ciliary body) and are shed into the aqueous humor during episodes of **anterior uveitis**. 1. **Why Endothelium is correct:** The corneal endothelium is the innermost layer of the cornea, directly in contact with the aqueous humor. Due to gravity and convection currents within the anterior chamber, inflammatory cells (lymphocytes, monocytes, or macrophages) adhere to the sticky, damaged endothelial cells. 2. **Why other options are incorrect:** * **Epithelium:** This is the outermost layer. Deposits here are usually foreign bodies or punctate erosions, not KPs. * **Stroma:** This is the thickest middle layer. While it can show edema or infiltration (keratitis), KPs are surface deposits, not parenchymal ones. * **Bowman’s Membrane:** This is a thin acellular layer between the epithelium and stroma; it does not come into contact with the aqueous humor. **Clinical Pearls for NEET-PG:** * **Arlt’s Triangle:** KPs typically settle in a triangular pattern on the inferior endothelium due to convection currents. * **Mutton-fat KPs:** Large, greasy-looking clusters of epithelioid cells and macrophages, pathognomonic for **Granulomatous Uveitis** (e.g., Sarcoidosis, TB). * **Small/Fine KPs:** Composed of neutrophils and lymphocytes, seen in **Non-granulomatous Uveitis**. * **Stellate KPs:** Star-shaped precipitates distributed over the entire endothelium, characteristic of **Fuchs’ Heterochromic Iridocyclitis** and Viral Uveitis.

Question 53: Which condition is always bilateral?

A. Infantile glaucoma
B. Megalocornea (Correct Answer)
C. Acute congestive glaucoma
D. All of the above

Explanation: ### Explanation **Correct Answer: B. Megalocornea** **1. Why Megalocornea is the correct answer:** Megalocornea is a non-progressive, non-glaucomatous condition characterized by an increased corneal diameter (typically >13 mm) at birth. It is almost **always bilateral and symmetrical**. It is most commonly inherited as an **X-linked recessive** trait (affecting males). Because it is a developmental anomaly of the anterior segment (specifically the ciliary ring), the enlargement is structural and inherent to both eyes from birth, without the involvement of elevated intraocular pressure (IOP). **2. Why the other options are incorrect:** * **A. Infantile Glaucoma:** While frequently bilateral (70-80% of cases), it can be **unilateral** in approximately 25-30% of patients. It is caused by developmental anomalies of the angle (trabeculodysgenesis) leading to high IOP and secondary corneal enlargement (buphthalmos). * **C. Acute Congestive Glaucoma:** This is a clinical manifestation of Primary Angle Closure Glaucoma. While the anatomical predisposition (shallow anterior chamber) is usually bilateral, the **acute attack** itself is almost always **unilateral** at the time of presentation. * **D. All of the above:** Incorrect because options A and C can present unilaterally. **3. NEET-PG High-Yield Pearls:** * **Megalocornea vs. Buphthalmos:** In Megalocornea, the IOP is normal, the optic disc is normal, and there are no Haab’s striae. In Buphthalmos (Infantile Glaucoma), IOP is high, the disc is cupped, and Haab’s striae are present. * **Associated Conditions:** Megalocornea is associated with lens subluxation (due to zonular stretching) and Marfan syndrome. * **Corneal Diameter:** Normal newborn diameter is ~10 mm; adult diameter is reached by age 2 (~11.7 mm). Megalocornea is diagnosed when the diameter exceeds 13 mm.

Question 54: Which of the following is true regarding corneal dystrophy?

A. Inflammatory
B. Neovascularization
C. Bilateral (Correct Answer)
D. All of the above

Explanation: ### Explanation Corneal dystrophies are a group of genetic, non-inflammatory disorders characterized by the accumulation of abnormal material within the corneal layers. **Why "Bilateral" is the Correct Answer:** Corneal dystrophies are **hereditary** (mostly autosomal dominant) conditions. Because they are rooted in a genetic mutation present in all cells of the corneal tissue, they characteristically manifest as **bilateral, symmetrical, and slowly progressive** opacities. They typically appear in the first or second decade of life and are not associated with systemic diseases. **Why Other Options are Incorrect:** * **A. Inflammatory:** By definition, dystrophies are **non-inflammatory**. If inflammation (redness, pain, or cellular infiltration) is present, the diagnosis is more likely a corneal *degeneration* or *keratitis*. * **B. Neovascularization:** Corneal dystrophies are **avascular**. The cornea remains clear of blood vessels unless a secondary complication (like a persistent epithelial erosions or infection) occurs. Neovascularization is a hallmark of degenerations or chronic inflammatory states, not primary dystrophies. **High-Yield Clinical Pearls for NEET-PG:** * **Dystrophy vs. Degeneration:** Dystrophies are bilateral, central, and hereditary; Degenerations are often unilateral, peripheral, and associated with aging or inflammation. * **Most Common Dystrophy:** Fuchs’ Endothelial Corneal Dystrophy (FECD). * **Staining Mnemonics (Very High Yield):** * **M**any **A**mericans **G**et **R**ocky **M**ountains: **M**acular = **A**lcian Blue; **G**ranular = **R**odent (Masson) Trichrome; **L**attice = **M**any (Congo) Red. * **Layer Involvement:** * *Epithelial:* Meesmann’s. * *Stromal:* Granular, Macular, Lattice (Lattice is the most common stromal dystrophy). * *Endothelial:* Fuchs’, CHED (Congenital Hereditary Endothelial Dystrophy).

Question 55: All of the following may lead to corneal opacity in a newborn except?

A. Endothelial dystrophy
B. Sclerocornea
C. Mucopolysaccharidosis
D. Droplet keratopathy (Correct Answer)

Explanation: To approach this question, remember the high-yield mnemonic **STUMPED**, which lists the common causes of congenital corneal opacities (cloudy cornea at birth). ### **Explanation of the Correct Answer** **D. Droplet Keratopathy (Spheroidal Degeneration):** This is an **acquired** degenerative condition, not a congenital one. It is caused by chronic exposure to ultraviolet (UV) light, wind, and sand. It typically presents in adult males working outdoors (e.g., farmers or fishermen) as golden-yellow, translucent proteinaceous droplets in the superficial corneal stroma. It is never seen in newborns. ### **Analysis of Incorrect Options** * **A. Endothelial Dystrophy:** Specifically, **Congenital Hereditary Endothelial Dystrophy (CHED)** is a major cause of bilateral corneal edema and clouding at birth due to a primary dysfunction of the corneal endothelium. * **B. Sclerocornea:** A congenital anomaly where the limbus is ill-defined, and the vascularized scleral tissue extends into the cornea, making it opaque. It is often associated with cornea plana. * **C. Mucopolysaccharidosis (MPS):** Certain systemic metabolic disorders (like Hurler syndrome or Scheie syndrome) lead to the accumulation of glycosaminoglycans in the corneal stroma, resulting in progressive clouding, often starting in infancy. ### **Clinical Pearls for NEET-PG** * **STUMPED Mnemonic for Congenital Cloudy Cornea:** * **S** - Sclerocornea * **T** - Tears in Descemet’s membrane (Trauma/Forceps delivery or Congenital Glaucoma) * **U** - Ulcer (Infectious) * **M** - Metabolic (Mucopolysaccharidosis) * **P** - Peters Anomaly (Central opacity with iridocorneal adhesions) * **E** - Endothelial Dystrophy (CHED) * **D** - Dermoid (Limbal dermoid) * **Haab Striae:** Horizontal or curvilinear breaks in Descemet’s membrane seen in **Congenital Glaucoma** (Buphthalmos). * **Forceps Trauma:** Typically causes **vertical** or oblique tears in Descemet’s membrane.

Question 56: Interstitial keratitis may be associated with which of the following conditions?

A. Congenital syphilis
B. Malaria
C. Sarcoidosis
D. All of the above (Correct Answer)

Explanation: **Explanation:** **Interstitial Keratitis (IK)** is a chronic non-ulcerative inflammation of the corneal stroma, characterized by cellular infiltration and vascularization without primary involvement of the epithelium or endothelium. It is typically an **immune-mediated response** to a systemic infection or inflammatory condition rather than a direct infection of the cornea. 1. **Congenital Syphilis (Option A):** This is the **most common cause** of IK (responsible for ~90% of cases historically). It typically presents bilaterally in late childhood or adolescence as part of the late manifestations of congenital syphilis. 2. **Malaria (Option B):** While rare, protozoal infections like Malaria and Leishmaniasis are documented systemic causes of IK. 3. **Sarcoidosis (Option C):** Non-infectious systemic granulomatous diseases, including Sarcoidosis and Cogan’s syndrome, are well-recognized etiologies of interstitial keratitis. Since all three conditions listed can trigger the immune-mediated stromal response characteristic of IK, **Option D (All of the above)** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **Hutchinson’s Triad:** A classic sign of late congenital syphilis consisting of Interstitial Keratitis, Hutchinson’s teeth (notched incisors), and Sensorineural deafness (8th nerve deafness). * **Salmon Patch Appearance:** In the active stage of IK, deep vascularization gives the cornea a pinkish-orange hue. * **Ghost Vessels:** After the inflammation subsides, the cleared vessels remain as empty channels in the stroma, visible on slit-lamp examination. * **Wessely Ring:** An immune ring of precipitate often seen in the stroma during the acute phase. * **Other Causes:** Tuberculosis, Leprosy, Herpes Simplex (most common viral cause), and Lyme disease.

Question 57: Corneal diameter is increased in which of the following conditions?

A. Megalocornea
B. Keratoglobus
C. Keratoconus
D. All of the above (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. All of the above**, as each of these conditions involves an increase in the horizontal or overall corneal diameter, though the underlying mechanisms differ. 1. **Megalocornea:** This is a non-progressive, bilateral, X-linked recessive condition where the horizontal corneal diameter is **>13 mm** at birth or in adulthood. Importantly, the intraocular pressure (IOP) and corneal thickness are usually normal, distinguishing it from congenital glaucoma (buphthalmos). 2. **Keratoglobus:** This is a rare, non-inflammatory corneal ectasia where the entire cornea becomes extremely thin (especially at the periphery) and bulges forward in a **globular shape**. This protrusion leads to a significant increase in the measured corneal diameter and surface area. 3. **Keratoconus:** While primarily characterized by localized paracentral thinning and cone-shaped protrusion, advanced cases of keratoconus involve significant stretching of the corneal tissue. This ectasia results in an increased chord length and overall diameter of the cornea. **Clinical Pearls for NEET-PG:** * **Buphthalmos vs. Megalocornea:** In Buphthalmos (congenital glaucoma), the cornea is large (>12 mm before age 1) but is associated with **Haab’s striae** (tears in Descemet’s membrane) and raised IOP. Megalocornea has a clear cornea and normal IOP. * **Microcornea:** Defined as a diameter **<10 mm** at any age or **<9 mm** in a newborn. It is often associated with Nanophthalmos. * **Keratoglobus Risk:** Patients are at high risk of corneal perforation even with minor trauma due to extreme peripheral thinning. * **Normal Diameter:** The average adult horizontal corneal diameter is **11.7 mm**.

Question 58: In human corneal transplantation, what is the typical source of donor tissue?

A. Synthetic polymer
B. Donated human cadaver eyes (Correct Answer)
C. Donated eyes from live human beings
D. Monkey eyes

Explanation: **Explanation:** The cornea is a transparent, avascular tissue that acts as the eye's primary refractive surface. In corneal transplantation (keratoplasty), the goal is to replace diseased or scarred host tissue with healthy donor tissue to restore vision or structural integrity. **1. Why Option B is Correct:** The standard source for corneal grafts is **donated human cadaver eyes**. Corneas are harvested from deceased individuals (ideally within 6 hours of death). Because the cornea is **avascular**, it enjoys "immune privilege," meaning it does not require systemic HLA matching, making cadaveric tissue highly successful for transplantation. **2. Why Other Options are Incorrect:** * **Option A (Synthetic polymer):** While "Keratoprostheses" (e.g., Boston KPro) exist, they are synthetic implants used only as a last resort in cases where traditional human grafts have repeatedly failed (e.g., severe chemical burns or Stevens-Johnson Syndrome). * **Option C (Live human beings):** Unlike kidneys or liver segments, a cornea cannot be harvested from a living donor without causing permanent blindness and structural damage to the donor's eye. * **Option D (Monkey eyes):** Xenotransplantation (cross-species) is not clinically practiced in ophthalmology due to severe immunological rejection and the risk of zoonotic infections. **High-Yield Clinical Pearls for NEET-PG:** * **Storage Media:** The most common short-term storage medium is **McCarey-Kaufman (MK) medium** (up to 4 days). Long-term storage uses **Optisol-GS** (up to 14 days). * **Contraindications for Donation:** Death of unknown cause, slow virus infections (Rabies, Creutzfeldt-Jakob disease), HIV, Hepatitis B/C, and systemic malignancies like Leukemia/Lymphoma. * **Layer-specific surgery:** Modern trends favor **Lamellar Keratoplasty** (e.g., DALK for stroma, DSAEK/DMEK for endothelium) over traditional Penetrating Keratoplasty (PKP) to reduce rejection rates.

Question 59: Which of the following types of corneal degeneration is most commonly seen in patients with trachoma?

A. Terrien's disease
B. Band keratopathy
C. Labrador keratopathy
D. Salzmann's nodular degeneration (Correct Answer)

Explanation: **Explanation:** **Salzmann’s Nodular Degeneration (SND)** is the correct answer because it is a non-inflammatory condition characterized by the formation of bluish-white or greyish subepithelial nodules. It typically occurs as a late sequela to **chronic keratitis** or long-standing ocular surface inflammation. **Trachoma** is a leading cause of chronic keratoconjunctivitis, and the resulting chronic irritation and scarring predispose the cornea to these nodular deposits (composed of hyaline and collagen). **Analysis of Incorrect Options:** * **A. Terrien’s Disease:** This is a peripheral corneal thinning (marginal degeneration) characterized by vascularization, lipid deposition, and "gutter" formation. It is idiopathic and not typically associated with trachoma. * **B. Band Keratopathy:** This involves the deposition of calcium salts in the Bowman’s membrane. It is most commonly associated with chronic uveitis (especially in Juvenile Idiopathic Arthritis), hypercalcemia, or long-term silicone oil in the eye. * **C. Labrador Keratopathy (Spheroidal Degeneration):** Also known as Climatic Droplet Keratopathy, it is caused by chronic exposure to **UV radiation**, wind, and sand. It presents as amber-colored granules in the superficial stroma. **High-Yield Clinical Pearls for NEET-PG:** * **SND Appearance:** Nodules are often arranged in a circular fashion around the pupillary area or at the edge of old corneal scars. * **SND Management:** Usually asymptomatic; however, if vision is affected or irritation occurs, treatment involves superficial keratectomy or PTK (Phototherapeutic Keratectomy). * **Trachoma Association:** Remember the "SAFE" strategy for Trachoma (Surgery, Antibiotics, Facial cleanliness, Environmental improvement). SND is a late degenerative change, unlike the acute inflammatory signs like Herbert’s pits or Arlt’s line.

Question 60: Which corneal layer is responsible for deturgescence?

A. Bowman's membrane
B. Endothelium (Correct Answer)
C. Epithelium
D. Stroma

Explanation: **Explanation:** The **corneal endothelium** is a single layer of hexagonal cells that plays a critical role in maintaining **corneal deturgescence**—the state of relative dehydration (approx. 78% water content) required for corneal transparency. It achieves this through two mechanisms: 1. **Active Endothelial Pump:** Na⁺/K⁺-ATPase pumps actively transport ions from the stroma into the aqueous humor, creating an osmotic gradient that draws water out. 2. **Leaky Barrier:** While it acts as a physical barrier, it allows controlled leakage of nutrients from the aqueous into the stroma. **Analysis of Incorrect Options:** * **Bowman’s Membrane (A):** An acellular, condensed layer of collagen. It provides structural integrity but has no metabolic or pumping function. It does not regenerate if damaged. * **Epithelium (C):** While the epithelium acts as a highly effective physical barrier to water (preventing tears from entering the stroma), it lacks the active metabolic "pump" capacity of the endothelium. * **Stroma (D):** The thickest layer (90%), composed of regularly arranged collagen fibrils. It is naturally hydrophilic (due to GAGs) and tends to swell; it is the *beneficiary* of deturgescence, not the cause. **High-Yield Clinical Pearls for NEET-PG:** * **Critical Cell Count:** Normal endothelial cell count is 2500–3000 cells/mm². If the count falls below **500 cells/mm²**, the pump fails, leading to corneal edema (Bullous Keratopathy). * **Regeneration:** Endothelial cells **do not regenerate** in vivo; they heal by enlargement and migration (pleomorphism and polymegethism). * **Specular Microscopy:** The gold standard investigation to assess endothelial cell density and morphology.

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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