Diseases of the Cornea Practice Questions

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.

Q: Recurrent corneal erosion is commonly seen in which of the following conditions?

Corneal dystrophy. **Explanation:** **Recurrent Corneal Erosion (RCE)** is a clinical syndrome characterized by repeated episodes of spontaneous breakdown of the corneal epithelium. The underlying pathophysiology involves **defective basement membrane adhesion**, where the hemidesmosomes fail to anchor the epithelium to the underlying Bowman’s layer. 1. **Why Corneal Dystrophy is Correct:** RCE is most strongly associated with **Anterior Basement Membrane Dystrophy (ABMD)**, also known as Map-Dot-Fingerprint dystrophy. In this condition, the basement membrane is redundant and multi-layered, leading to weak epithelial attachment. Other dystrophies, such as **Reis-Bücklers** and **Lattice dystrophy**, are also high-yield causes of RCE. 2. **Why Other Options are Incorrect:** * **Keratoglobus & Keratoconus:** These are non-inflammatory ectatic disorders characterized by thinning and protrusion of the corneal stroma. While they can lead to corneal scarring or hydrops (rupture of Descemet’s membrane), they do not typically cause recurrent epithelial erosions. * **Peutz-Jeghers Syndrome:** This is an autosomal dominant gastrointestinal polyposis syndrome associated with mucocutaneous hyperpigmentation. It has no clinical association with corneal pathology. **Clinical Pearls for NEET-PG:** * **Most common cause of RCE:** Fingernail injury or organic trauma (mechanical) is the most common cause overall, but among the options provided, **Corneal Dystrophy** is the primary systemic/genetic association. * **Classic Presentation:** Sudden onset of sharp pain, photophobia, and lacrimation, typically occurring **early in the morning** upon opening the eyes (as the eyelid pulls off the loosely adherent epithelium). * **Treatment:** Acute management involves lubricants and bandage contact lenses; definitive treatment may include **Phototherapeutic Keratectomy (PTK)** or anterior stromal puncture.

Q: Which of the following is the drug of choice for the treatment of corneal ulcers caused by filamentous fungi?

Natamycin. Natamycin is the drug of choice for fungal keratitis (corneal ulcers) caused by filamentous fungi, such as Aspergillus and Fusarium species. It is a polyene antifungal that works by binding to ergosterol in the fungal cell membrane, leading to cell lysis. It is preferred because it is the only topical antifungal formulation specifically FDA-approved for ophthalmic use and demonstrates superior efficacy in clinical trials (notably the MUTT trial) compared to other agents for filamentous infections. Analysis of Incorrect Options: * Itraconazole (A): While effective against many fungi, it has poor ocular penetration when given topically. It is generally reserved as an oral adjunct for deep-seated or severe infections. * Nystatin (C): Although a polyene like natamycin, it is primarily used for mucocutaneous candidiasis (yeast). It is not the standard of care for filamentous corneal ulcers due to its spectrum and lack of suitable ophthalmic preparations. * Ketoconazole (D): This is an older azole with significant side effects and lower efficacy compared to newer triazoles or natamycin. It is rarely used as a primary treatment for fungal keratitis. High-Yield Clinical Pearls for NEET-PG: * Drug of Choice for Yeast (Candida) Keratitis: Topical Amphotericin B (0.15%) or Fluconazole [2, 5]. * Gold Standard Diagnosis: Corneal scraping followed by KOH mount and culture on Sabouraud’s Dextrose Agar (SDA). * Clinical Sign: Fungal ulcers often present with feathery margins, satellite lesions, and an immune ring (Wessely ring). * Contraindication: Never use topical steroids in suspected fungal keratitis, as they worsen the infection and can lead to corneal perforation.

Q: Which of the following type of corneal degeneration is associated with calcific changes in the Bowman's membrane with a characteristic Swiss cheese pattern?

Band keratopathy. **Explanation:** **Band Keratopathy (BK)** is a chronic degenerative condition characterized by the deposition of **calcium salts** (hydroxyapatite) in the subepithelial layers, specifically the **Bowman’s membrane**, the anterior stroma, and the epithelial basement membrane. The "Swiss cheese" appearance is a classic histopathological and clinical hallmark. This occurs because small clear holes are seen within the calcified band, representing the areas where **nerve canals** penetrate the Bowman’s membrane. The calcification typically starts at the periphery (3 and 9 o'clock positions) and progresses centrally as a horizontal band across the interpalpebral fissure. **Why other options are incorrect:** * **Arcus senilis:** This is the most common peripheral corneal degeneration, caused by **lipid (cholesterol) deposition** in the stroma. It does not involve calcification or the Bowman’s membrane. * **Spheroid degeneration:** Also known as Climatic Droplet Keratopathy, it involves the deposition of **hyaline-like proteinaceous material** (amber-colored granules) in the superficial stroma, typically due to UV exposure. * **Salzmann’s degeneration:** Characterized by bluish-white **hyaline nodules** located anterior to the Bowman’s membrane, usually occurring in eyes with chronic keratitis. **High-Yield Clinical Pearls for NEET-PG:** * **Etiology:** Associated with chronic intraocular inflammation (Uveitis—especially in JIA), ocular trauma, or systemic hypercalcemia (e.g., hyperparathyroidism, Vitamin D toxicity, Sarcoidosis). * **Treatment:** The gold standard is **Chelation therapy** using **EDTA** (Ethylenediamine tetraacetic acid) after removing the overlying epithelium. * **Location:** It is strictly limited to the **interpalpebral area**, with a characteristic clear zone between the limbus and the calcification.

Q: What is the normal endothelial cell count in the cornea?

2500-3000 cells / sq.mm. **Explanation:** The corneal endothelium is a single layer of hexagonal cells responsible for maintaining corneal transparency through its "pump-leak" mechanism. In a healthy young adult, the normal endothelial cell density (ECD) typically ranges between **2500 and 3000 cells/sq.mm**. These cells do not regenerate; instead, they compensate for cell loss by stretching and increasing in size (polymegathism). * **Option D (Correct):** 2500–3000 cells/sq.mm is the physiological standard for healthy adults. * **Option C (2000–2500):** This range is often seen in older adults. There is a physiological decline in cell count of approximately 0.6% per year throughout life. * **Option B (1500–2000):** This represents a moderate decrease, often seen post-intraocular surgery or in early corneal dystrophies. * **Option A (500–1000):** This is a critical zone. When the count falls below the **"Critical Threshold" of 500 cells/sq.mm**, the pump mechanism fails, leading to irreversible corneal edema and bullous keratopathy. **High-Yield Clinical Pearls for NEET-PG:** 1. **Specular Microscopy:** The gold standard investigation to measure endothelial cell count and morphology. 2. **Pleomorphism:** Variation in cell shape (loss of hexagonality); an early sign of endothelial stress. 3. **Polymegathism:** Variation in cell size. 4. **Fuchs’ Endothelial Dystrophy:** A common condition leading to progressive loss of these cells, characterized by "beaten metal" appearance (Guttae). 5. **Surgical Clearance:** Surgeons generally prefer a count >1500 cells/sq.mm before proceeding with elective cataract surgery (Phacoemulsification) to ensure post-operative corneal clarity.

Q: A 23-year-old female presented with blurred vision in her soft contact lenses, which were purchased six months prior. Her visual acuity was 6/18 in one eye with a refraction of -7.0 D sph / +3.5 D cyl X 145. What is the most likely diagnosis?

Keratoconus. **Explanation:** The clinical presentation is highly suggestive of **Keratoconus**, a progressive non-inflammatory thinning of the corneal stroma. **Why Keratoconus is correct:** 1. **Age and Refraction:** Keratoconus typically manifests in the second decade of life. The patient presents with **high myopic astigmatism** (-7.0 D sph / +3.5 D cyl), which is a hallmark of the disease as the cornea becomes cone-shaped. 2. **Contact Lens Intolerance:** A classic "red flag" in NEET-PG vignettes is a patient who previously tolerated soft contact lenses but now experiences blurred vision or discomfort. As the cornea becomes increasingly irregular, standard soft lenses no longer provide adequate vision, often requiring Rigid Gas Permeable (RGP) lenses. **Why other options are incorrect:** * **Nuclear Cataract:** While it causes a myopic shift ("second sight"), it is rare in a 23-year-old and typically presents with a spherical shift rather than high cylindrical power. * **Dry Eyes:** Can cause blurred vision and contact lens discomfort, but it does not explain the high, specific astigmatic refractive error. * **Irregular Astigmatism:** This is a *finding*, not a diagnosis. Keratoconus is the most common primary cause of irregular astigmatism in this age group. **Clinical Pearls for NEET-PG:** * **Early Sign:** "Scissors reflex" on retinoscopy and "Oil droplet sign" on distant direct ophthalmoscopy. * **Late Signs:** Munson’s sign (v-shaped indentation of lower lid on downgaze), Vogt’s striae (vertical stress lines), and Fleischer’s ring (iron deposition at the base of the cone). * **Management:** Collagen Cross-linking (CXL/C3R) to stop progression; RGP lenses for visual rehabilitation; Penetrating Keratoplasty for advanced cases.

Q: Which organism can invade the intact corneal epithelium and produce a purulent corneal ulcer?

Neisseria meningitidis. **Explanation:** The corneal epithelium acts as a formidable mechanical barrier against most microorganisms. Most bacteria require a pre-existing epithelial defect (trauma, contact lens wear, or dry eye) to cause an infection. However, a select group of highly virulent organisms possesses the enzymatic capability to penetrate a completely **intact corneal epithelium**. **Why Neisseria meningitidis is correct:** *Neisseria meningitidis*, along with *Neisseria gonorrhoeae*, *Corynebacterium diphtheriae*, and *Listeria monocytogenes*, are the classic organisms capable of invading healthy, intact epithelium. They produce potent proteases and toxins that bypass the corneal defense mechanisms, leading to rapidly progressive, purulent corneal ulcers. **Why the other options are incorrect:** * **B. Pseudomonas pyocyanea (aeruginosa):** While it is the most common cause of bacterial corneal ulcers (especially in contact lens users) and is highly destructive due to proteases, it typically **requires an epithelial breach** to initiate infection. * **C. Pneumococcus (Streptococcus pneumoniae):** This is a common cause of hypopyon corneal ulcers (Ulcus Serpens), but it generally necessitates a prior injury to the corneal surface. * **D. Streptococcus haemolyticus:** Like most pyogenic bacteria, it lacks the specific invasive mechanisms required to penetrate an intact epithelial layer. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Intact Epithelium Invasion:** **"CHNL"** (**C**orynebacterium diphtheriae, **H**aemophilus aegyptius, **N**eisseria (gonorrhoeae/meningitidis), and **L**isteria). Some texts also include *Shigella*. * **Pseudomonas** is notorious for causing a "soupy" corneal melt and a greenish-blue discharge. * **Pneumococcus** is the most common cause of **Ulcus Serpens** (creeping ulcer). * **Neisseria** infections are ocular emergencies as they can lead to corneal perforation within 24–48 hours.

Q: Decreased corneal sensations can be seen in which of the following conditions?

Leprosy. **Explanation:** Corneal sensation is mediated by the **long ciliary nerves**, which are branches of the ophthalmic division of the **Trigeminal nerve (CN V1)**. Any pathology affecting these nerves or the corneal plexus leads to neurotrophic keratitis and decreased sensitivity. **Why Leprosy is Correct:** Leprosy (*Mycobacterium leprae*) is a classic cause of decreased corneal sensation. The bacilli have a predilection for peripheral nerves. In the eye, they cause **demyelination and destruction of the ciliary nerves**, leading to an anesthetic cornea. This lack of sensation, combined with lagophthalmos (due to CN VII involvement), often leads to exposure keratopathy and secondary ulceration. **Analysis of Incorrect Options:** * **Bacterial & Mycotic Corneal Ulcers:** These are typically characterized by **intense pain**, photophobia, and **increased or preserved sensitivity** due to the acute inflammatory response and stimulation of nerve endings. (Exception: *Acanthamoeba* is known for pain out of proportion to clinical signs). * **Interstitial Keratitis:** This is an inflammation of the corneal stroma (often due to Syphilis). While it causes significant corneal scarring and vascularization, it does not typically result in the loss of sensation unless it is a late-stage complication of specific viral etiologies. **High-Yield Clinical Pearls for NEET-PG:** * **Common causes of decreased corneal sensation (The "H-L-A-D" Mnemonic):** **H**erpes (Simplex/Zoster), **L**eprosy, **A**coustic Neuroma (compresses CN V), and **D**iabetes Mellitus. * **Topical medications:** Chronic use of topical anesthetics or beta-blockers (Timolol) can decrease sensation. * **Surgical cause:** Post-LASIK surgery is a common modern cause of transiently decreased sensation. * **Clinical Test:** Corneal reflex is tested using a wisp of cotton to touch the limbus (Afferent: CN V1; Efferent: CN VII).

Question 1

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 2

Corneal dystrophy associated with acid mucopolysaccharidosis is:

Accepted Answer

Macular

Answer

Lattice

Answer

Granular

Answer

Peripheral

Question 3

Recurrent corneal erosion is commonly seen in which of the following conditions?

Accepted Answer

Corneal dystrophy

Answer

Keratoglobus

Answer

Keratoconus

Answer

Peutz-Jeghers syndrome

Question 4

Which of the following is the drug of choice for the treatment of corneal ulcers caused by filamentous fungi?

Accepted Answer

Natamycin

Answer

Itraconazole

Answer

Nystatin

Answer

Ketoconazole

Question 5

Which of the following statements is NOT true about corneal opacity?

Accepted Answer

A dense leucoma that is strictly localized interferes more than a thin, diffuse nebula covering the pupillary area.

Answer

Anterior staphyloma involves iris tissue incorporated within the scar tissue.

Answer

Adherent leucoma can form as a result of healing of a perforated corneal ulcer.

Answer

Some opacities may persist despite the destruction of Bowman's membrane.

Question 6

Which of the following type of corneal degeneration is associated with calcific changes in the Bowman's membrane with a characteristic Swiss cheese pattern?

Accepted Answer

Band keratopathy

Answer

Arcus senilis

Answer

Spheroid degeneration

Answer

Salzmann's degeneration

Question 7

What is the normal endothelial cell count in the cornea?

Accepted Answer

2500-3000 cells / sq.mm

Answer

500-1000 cells / sq.mm

Answer

1500-2000 cells / sq.mm

Answer

2000-2500 cells / sq.mm

Question 8

A 23-year-old female presented with blurred vision in her soft contact lenses, which were purchased six months prior. Her visual acuity was 6/18 in one eye with a refraction of -7.0 D sph / +3.5 D cyl X 145. What is the most likely diagnosis?

Accepted Answer

Keratoconus

Answer

Nuclear cataract

Answer

Dry eyes

Answer

Irregular astigmatism

Question 9

Which organism can invade the intact corneal epithelium and produce a purulent corneal ulcer?

Accepted Answer

Neisseria meningitidis

Answer

Pseudomonas pyocyanea

Answer

Pneumococcus

Answer

Streptococcus haemolyticus

Question 10

Decreased corneal sensations can be seen in which of the following conditions?

Accepted Answer

Leprosy

Answer

Bacterial corneal ulcer

Answer

Mycotic corneal ulcer

Answer

Interstitial keratitis

Diseases of the Cornea — MCQs

Diseases of the Cornea — MCQs

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