Diseases of the Cornea — MCQs

Diseases of the Cornea Indian Medical PG Practice Questions and MCQs

Question 21: In which one of the following infections is a dendritic ulcer seen?

A. Herpes simplex (Correct Answer)
B. Measles
C. Pseudomonas
D. Gonococcal infection

Explanation: **Explanation:** The hallmark of **Herpes Simplex Keratitis (HSK)** is the **dendritic ulcer**. This occurs due to the active replication of the Herpes Simplex Virus (HSV-1) in the corneal epithelium, leading to cell lysis. **Why Herpes Simplex is correct:** The ulcer is characterized by a linear, branching (arborescent) pattern with **terminal bulbs** (knobs) at the ends of the branches. These bulbs contain live virus. A key clinical feature is **decreased corneal sensations** due to viral damage to the trigeminal nerve endings. Staining with Rose Bengal or Lissamine Green highlights the devitalized cells at the ulcer margins, while Fluorescein stains the basement membrane in the center. **Why other options are incorrect:** * **Measles:** Typically causes a **superficial punctate keratitis** (SPK) rather than a dendritic pattern. * **Pseudomonas:** Causes a rapidly progressing **suppurative bacterial ulcer** characterized by a "soupy" appearance and greenish-blue discharge. * **Gonococcal infection:** Causes a hyperacute purulent conjunctivitis that can lead to corneal perforation; it is unique because *N. gonorrhoeae* can **penetrate an intact corneal epithelium**. **High-Yield Clinical Pearls for NEET-PG:** * **Geographic Ulcer:** Formed when a dendritic ulcer enlarges (often due to inappropriate use of topical steroids). * **Treatment:** Topical **Acyclovir (3%)** or Ganciclovir. *Note: Steroids are contraindicated in epithelial (dendritic) keratitis but used in stromal (disciform) keratitis.* * **Differential Diagnosis:** "Pseudo-dendrites" (no terminal bulbs) are seen in **Acanthamoeba keratitis**, Herpes Zoster Ophthalmicus, and Tyrosinemia Type II.

Question 22: Which of the following is NOT a feature of fungal corneal ulcer?

A. Mucopurulent discharge may be present
B. Satellite lesions may be present around the ulcer
C. Flat and mobile hypopyon (Correct Answer)
D. Fungi can penetrate into the anterior chamber without perforation

Explanation: **Explanation:** In fungal corneal ulcers (keratomycosis), the hypopyon is typically **thick, immobile, and non-sterile**. This is because fungal elements and inflammatory cells create a dense exudate that often adheres to the corneal endothelium (endothelial plaque). In contrast, a **flat and mobile hypopyon** is a classic feature of **bacterial corneal ulcers** (e.g., Pneumococcus), where the pus is less viscous and shifts with head movement. **Analysis of Options:** * **Option A (Mucopurulent discharge):** While fungal ulcers are often "dry" with a leathery surface, a secondary bacterial infection or severe inflammation can lead to mucopurulent discharge. * **Option B (Satellite lesions):** These are a hallmark diagnostic feature of fungal keratitis. They represent small, isolated infiltrates in the stroma surrounding the main ulcer, caused by the centrifugal spread of hyphae. * **Option D (Penetration without perforation):** Fungi have a unique ability to penetrate an intact Descemet’s membrane via fungal hyphae. This allows them to enter the anterior chamber and cause endophthalmitis even if the cornea has not perforated. **Clinical Pearls for NEET-PG:** * **Etiology:** Most common cause in India is *Fusarium* (filamentous fungi), often following trauma with **vegetative matter**. * **Morphology:** Look for "feathery finger-like margins," "immune rings" (Wessely ring), and a "dry, leathery" appearance. * **Diagnosis:** Gold standard is culture on **Sabouraud’s Dextrose Agar (SDA)**. Initial screening is done via KOH mount or Calcofluor white. * **Treatment:** Topical **Natamycin (5%)** is the drug of choice for filamentous fungi; Amphotericin B is preferred for *Candida*.

Question 23: Which of the following drugs is NOT used in the treatment of herpes simplex keratitis?

A. Idoxuridine 0.1%
B. 5-Fluorouracil
C. Adenosine arabinoside
D. Pimarcin (Correct Answer)

Explanation: **Explanation:** The correct answer is **Pimarcin (Natamycin)**. Herpes Simplex Keratitis (HSK) is a viral infection caused by the DNA virus Herpes Simplex (HSV-1). Treatment requires **antiviral agents** that inhibit viral DNA synthesis. **Pimarcin**, also known as Natamycin, is a polyene **antifungal** medication. It is the drug of choice for filamentous fungal keratitis (e.g., *Aspergillus* or *Fusarium*) but has no efficacy against viruses. **Analysis of Options:** * **Idoxuridine (0.1%):** This was the first antiviral agent developed for HSK. It is a thymidine analogue that incorporates into viral DNA, though it is rarely used today due to high ocular toxicity and the availability of better alternatives like Ganciclovir. * **5-Fluorouracil (5-FU):** While primarily known as a chemotherapy agent, 5-FU is a pyrimidine analogue with antiviral properties. In the context of this classic question, it is categorized among agents that interfere with DNA synthesis, unlike Pimarcin. * **Adenosine Arabinoside (Vidarabine):** A purine analogue effective against HSV. It is particularly useful in patients who are allergic to or resistant to Idoxuridine. **NEET-PG High-Yield Pearls:** * **Drug of Choice (DOC):** Topical **Ganciclovir (0.15% gel)** is currently the preferred treatment for dendritic ulcers due to lower toxicity. * **Contraindication:** Topical **Corticosteroids** are strictly contraindicated in the presence of an active epithelial (dendritic) ulcer as they can lead to a "Geographic Ulcer." * **Classic Sign:** The hallmark of HSK is the **Dendritic Ulcer**, characterized by true terminal bulbs and stained with Rose Bengal (at the margins) and Fluorescein (at the base).

Question 24: What is the drug of choice for a fungal corneal ulcer?

A. Nystatin
B. Caspofungin
C. Natamycin (Correct Answer)
D. Amphotericin

Explanation: **Explanation:** **Natamycin** is the established **drug of choice** for filamentous fungal keratitis (the most common cause of fungal corneal ulcers, e.g., *Aspergillus* and *Fusarium*). Its efficacy was definitively proven in the **Mycotic Ulcer Treatment Trial (MUTT)**, which showed that topical Natamycin (5%) resulted in significantly better visual outcomes and lower rates of corneal perforation compared to other antifungals. **Mechanism:** It is a polyene antifungal that binds to ergosterol in the fungal cell membrane, increasing permeability and leading to cell death. It is particularly effective because it adheres well to the corneal surface. **Analysis of Incorrect Options:** * **Nystatin (A):** While a polyene, it is primarily used for mucosal candidiasis. It has poor ocular penetration and is not used as a first-line agent for keratitis. * **Caspofungin (B):** An echinocandin that inhibits cell wall synthesis. While used for systemic candidiasis, its role in fungal keratitis is limited and considered second or third-line. * **Amphotericin B (D):** This is the **drug of choice for yeast infections** (e.g., *Candida*). However, since most fungal ulcers are caused by filamentous fungi, Natamycin remains the overall primary choice. Amphotericin is also more epitheliotoxic than Natamycin. **High-Yield Clinical Pearls for NEET-PG:** * **Risk Factor:** Vegetative trauma (e.g., injury with a branch or leaf) is the most common predisposing factor. * **Clinical Signs:** Look for "Feathery margins," "Satellite lesions," and a "Dry, leathery appearance." * **Diagnosis:** The gold standard is corneal scraping for **KOH mount** (shows fungal hyphae) and culture on **Sabouraud’s Dextrose Agar (SDA)**. * **Contraindication:** Topical steroids are strictly contraindicated as they worsen the infection and can lead to rapid perforation.

Question 25: Which of the following conditions is a type of neurocristopathy?

A. Macular dystrophy
B. Arcus senilis
C. ICE syndrome (Correct Answer)
D. Band shaped keratopathy

Explanation: ### Explanation **Correct Option: C. ICE syndrome** **Concept:** Neurocristopathies are a group of disorders arising from the abnormal migration, differentiation, or proliferation of **Neural Crest Cells (NCCs)**. In the eye, the corneal endothelium, stroma, and iris stroma are derived from neural crest cells. **ICE (Iridocorneal Endothelial) syndrome** is considered a neurocristopathy because it involves an acquired proliferative abnormality of the corneal endothelial cells (which are neural crest-derived). These cells migrate across the iridocorneal angle and onto the iris, leading to the classic triad of iris atrophy, basement membrane contraction (causing corectopia/ectropion uveae), and secondary angle-closure glaucoma. **Analysis of Incorrect Options:** * **A. Macular dystrophy:** This is a stromal corneal dystrophy caused by a mutation in the *CHST6* gene leading to abnormal keratan sulfate metabolism. While the stroma is NCC-derived, the pathology is metabolic/genetic, not a primary neurocristopathy. * **B. Arcus senilis:** This is a common degenerative change characterized by the deposition of lipid (cholesterol/phospholipids) in the peripheral corneal stroma. It is age-related and not a developmental or proliferative NCC disorder. * **C. Band-shaped keratopathy:** This involves the deposition of calcium hydroxyapatite crystals in the **Bowman’s layer**. It is usually secondary to chronic intraocular inflammation (uveitis) or hypercalcemia. **High-Yield Clinical Pearls for NEET-PG:** * **ICE Syndrome Variants:** Includes Progressive Iris Atrophy, Chandler Syndrome (most common, significant corneal edema), and Cogan-Reese Syndrome (iris nodules/nevus). * **Key Feature:** Typically **unilateral**, occurs in young to middle-aged females. * **Specular Microscopy:** Shows a characteristic "beaten silver" or "hammered silver" appearance of the endothelium. * **Other Ocular Neurocristopathies:** Axenfeld-Rieger syndrome and Peters anomaly.

Question 26: Which organismal infection is highly virulent and may cause corneal ulcer perforation within 48 hours?

A. Herpes simplex
B. Pseudomonas (Correct Answer)
C. Staphylococci
D. Aspergillus

Explanation: **Explanation:** The correct answer is **Pseudomonas aeruginosa**. This organism is notorious in ophthalmology for its extreme virulence and rapid progression. **Why Pseudomonas is correct:** *Pseudomonas* produces potent extracellular enzymes, specifically **proteases, elastases, and collagenases**. These enzymes cause rapid liquefactive necrosis of the corneal stroma (often described as a "soupy" or "melting" appearance). Due to this aggressive enzymatic destruction, a *Pseudomonas* ulcer can lead to corneal perforation in as little as **24 to 48 hours**. It is classically associated with **contact lens wear** and produces a characteristic **greenish-yellow discharge**. **Why the other options are incorrect:** * **Herpes simplex (A):** Typically causes dendritic or geographic ulcers. While it can lead to stromal keratitis and scarring, it is a chronic, viral process and does not cause hyperacute perforation via liquefactive necrosis. * **Staphylococci (C):** These are common causes of bacterial keratitis but usually result in well-circumscribed, slower-progressing ulcers compared to *Pseudomonas*. * **Aspergillus (D):** Fungal ulcers have an insidious onset and a protracted course. They are characterized by "feathery margins" and "satellite lesions" rather than rapid 48-hour perforation. **High-Yield Clinical Pearls for NEET-PG:** * **Most common cause of bacterial corneal ulcer:** *Staphylococcus aureus*. * **Most common cause in contact lens users:** *Pseudomonas*. * **Organisms that can penetrate an intact epithelium:** *Neisseria gonorrhoeae, Corynebacterium diphtheriae, Listeria,* and *Haemophilus*. * **Treatment:** Fortified antibiotics (e.g., Tobramycin and Cephazolin) are the mainstay of management for suspected bacterial keratitis.

Question 27: Intact cornea can be penetrated by which of the following microorganisms?

A. Gonococcus (Correct Answer)
B. Pseudomonas
C. Streptococcus
D. Pneumococcus

Explanation: **Explanation:** The corneal epithelium acts as a formidable mechanical barrier against most pathogens. Under normal circumstances, microorganisms require a pre-existing epithelial defect (trauma or ulceration) to invade the corneal stroma. However, a select group of organisms possesses specific invasive mechanisms to penetrate an **intact corneal epithelium**. **Why Gonococcus is Correct:** *Neisseria gonorrhoeae* (Gonococcus) is the classic example of a pathogen that can penetrate an intact cornea. It produces proteases and utilizes pili for attachment, allowing it to breach the epithelial surface. This is clinically significant in **Hyperacute Bacterial Conjunctivitis** and **Ophthalmia Neonatorum**, where the infection can rapidly progress to corneal perforation if not treated aggressively. **Why Other Options are Incorrect:** * **B, C, and D (Pseudomonas, Streptococcus, Pneumococcus):** These are common causes of bacterial keratitis, but they are **opportunistic**. They generally require a breach in the corneal epithelium (caused by contact lens wear, trauma, or foreign bodies) to initiate an infection. While *Pseudomonas* is highly virulent and produces collagenases that cause rapid liquefactive necrosis, it typically cannot invade a healthy, intact epithelium. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for organisms penetrating intact cornea:** "**CHL**N**G**" 1. ***C***orynebacterium diphtheriae 2. ***H***aemophilus aegyptius (Koch-Weeks bacillus) 3. ***L***isteria monocytogenes 4. ***N***eisseria gonorrhoeae 5. ***N***eisseria meningitidis 6. ***G***igantic (Shigella) - *rarely mentioned* * **Most common cause of hypopyon corneal ulcer:** *Streptococcus pneumoniae* (Pneumococcus). * **Most common cause of corneal ulcer in contact lens users:** *Pseudomonas aeruginosa*.

Question 28: Which one of the following corneal stromal dystrophies is a recessive condition?

A. Lattice dystrophy
B. Granular dystrophy
C. Macular dystrophy (Correct Answer)
D. Fleck dystrophy

Explanation: **Explanation:** In Ophthalmology, corneal stromal dystrophies are frequently tested based on their inheritance patterns and histological staining. **Why Macular Dystrophy is correct:** Macular corneal dystrophy is the **only** major stromal dystrophy that follows an **Autosomal Recessive (AR)** inheritance pattern. It is caused by a mutation in the *CHST6* gene, leading to abnormal keratan sulfate metabolism. Clinically, it is the most severe of the three classic dystrophies, characterized by ill-defined opacities that extend to the limbus and involve the full thickness of the stroma. **Why the other options are incorrect:** * **Lattice Dystrophy (Option A):** Inherited as Autosomal Dominant (AD). It is characterized by amyloid deposits (stained by Congo Red). * **Granular Dystrophy (Option B):** Inherited as Autosomal Dominant (AD). It is characterized by hyaline deposits (stained by Masson Trichrome). * **Fleck Dystrophy (Option C):** A rare, usually asymptomatic stromal dystrophy inherited as Autosomal Dominant (AD). **High-Yield NEET-PG Pearls:** To remember the stains and inheritance for stromal dystrophies, use the mnemonic **"Marilyn Monroe Got Hers in Los Angeles"**: 1. **M**acular – **M**icrosulfated keratan sulfate (**M**uicarmine/Alcian Blue) – **AR** (The "Odd One Out") 2. **G**ranular – **H**yaline (Masson Trichrome) – **AD** 3. **L**attice – **A**myloid (Congo Red) – **AD** *Note:* Macular dystrophy is the **least common** but **most severe**, often requiring keratoplasty earlier than Lattice or Granular types.

Question 29: Placido disc is used for which condition?

A. Uveitis
B. Keratoconus (Correct Answer)
C. Retinoblastoma
D. Retinal detachment

Explanation: **Explanation:** **Placido Disc** (also known as a keratoscope) is a diagnostic tool used to assess the **curvature and regularity of the anterior surface of the cornea**. It consists of a series of concentric black and white rings. When light from the disc reflects off the tear film (acting as a convex mirror), the clinician observes the reflected images (Purkinje-Sanson image I). * **Why Keratoconus is correct:** In a normal cornea, the reflected rings are perfectly circular and concentric. In **Keratoconus**, the cornea assumes a conical shape, causing the reflected rings to appear **distorted, irregular, and crowded** (typically inferiorly). This makes it a classic bedside screening tool for irregular astigmatism and corneal ectasia. **Analysis of Incorrect Options:** * **Uveitis:** This is an intraocular inflammatory condition. Diagnosis relies on slit-lamp examination to look for aqueous cells, flare, and keratic precipitates, not corneal topography. * **Retinoblastoma:** This is a primary intraocular malignancy of childhood. Diagnosis is made via indirect ophthalmoscopy, B-scan ultrasonography, and MRI to identify a calcified mass. * **Retinal Detachment:** This involves the separation of the neurosensory retina from the retinal pigment epithelium. It is diagnosed using indirect ophthalmoscopy and B-scan USG. **High-Yield Clinical Pearls for NEET-PG:** * **Modern Equivalent:** Computerized Video-keratography (Corneal Topography) is the modern evolution of the Placido disc. * **Photokeratoscopy:** The process of photographing the Placido disc reflections. * **Limitation:** Placido-based systems only analyze the **anterior** corneal surface; they cannot provide data on posterior corneal curvature (unlike Scheimpflug imaging/Pentacam). * **Other Keratoconus Signs:** Munson’s sign, Vogt’s striae, Fleischer’s ring, and Rizutti’s sign.

Question 30: Pachymeter is used to measure:

A. Corneal thickness (Correct Answer)
B. Corneal diameter
C. Corneal density
D. Conjunctival thickness

Explanation: **Explanation:** **Pachymetry** is the clinical procedure used to measure **corneal thickness**. The term is derived from the Greek word *pachus* (thick). It is a fundamental tool in ophthalmology because central corneal thickness (CCT) significantly influences the accuracy of Intraocular Pressure (IOP) readings. 1. **Why Option A is Correct:** A pachymeter measures the distance between the corneal epithelium and the endothelium. This is critical for: * **Glaucoma Management:** A thin cornea leads to an underestimation of IOP, while a thick cornea leads to an overestimation. * **Refractive Surgery (LASIK):** To ensure there is enough residual stromal bed to prevent post-operative ectasia. * **Keratoconus:** Monitoring corneal thinning. 2. **Why Other Options are Incorrect:** * **Corneal Diameter (B):** Measured using a **Keratometer** or calipers (White-to-White distance). Normal horizontal diameter is ~11.7 mm. * **Corneal Density (C):** Assessed via **Densitometry** (often integrated into Scheimpflug imaging like Pentacam) to quantify corneal haze or scarring. * **Conjunctival Thickness (D):** Not a standard clinical measurement; however, Anterior Segment OCT (AS-OCT) can visualize it, but it is not the function of a pachymeter. **High-Yield Clinical Pearls for NEET-PG:** * **Average CCT:** Approximately **540–560 μm**. * **Types of Pachymeters:** 1. **Optical:** Uses a slit-lamp attachment (Haag-Streit). 2. **Ultrasound (Gold Standard):** Uses a high-frequency (20 MHz) probe. 3. **Optical Coherence Tomography (OCT):** Non-contact method. * **Surgical Note:** In LASIK, a minimum residual stromal bed of **250 μm** must be maintained to prevent corneal ectasia.

Practice by Chapter

Corneal Anatomy and Physiology

Practice Questions

Bacterial Keratitis

Practice Questions

Viral Keratitis

Practice Questions

Fungal Keratitis

Practice Questions

Protozoan Keratitis

Practice Questions

Corneal Degenerations

Practice Questions

Corneal Dystrophies

Practice Questions

Keratoconus and Ectatic Disorders

Practice Questions

Corneal Transplantation

Practice Questions

Corneal Topography and Imaging

Practice Questions

Dry Eye Disease

Practice Questions

Corneal Trauma

Practice Questions

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