Diseases of the Cornea — MCQs

Diseases of the Cornea Indian Medical PG Practice Questions and MCQs

Question 31: A dendritic ulcer is produced by which of the following agents?

A. Pneumococcus
B. Herpes zoster virus
C. Gonococcus
D. Herpes simplex virus (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Herpes simplex virus** **Medical Concept:** Dendritic ulcers are the hallmark clinical presentation of **Herpes Simplex Keratitis (HSV-1)**. The virus infects the corneal epithelium, leading to live viral replication and cell lysis. This creates a characteristic linear, branching (dendritic) pattern. Key features include **knob-like terminal bulbs** at the ends of the branches and **diminished corneal sensations** due to trigeminal nerve involvement. These ulcers stain brilliantly with **Fluorescein** (the floor) and **Rose Bengal** (the devitalized margins). **Analysis of Incorrect Options:** * **A. Pneumococcus (*S. pneumoniae*):** Typically causes a **Hypopyon corneal ulcer** (Ulcus Serpens). It is characterized by a violent, creeping ulcer with a significant inflammatory response in the anterior chamber. * **B. Herpes zoster virus (HZV):** Causes **"Pseudodendrites."** Unlike true HSV dendrites, these are elevated, lack terminal bulbs, and do not stain well with fluorescein. They are part of Herpes Zoster Ophthalmicus. * **C. Gonococcus (*N. gonorrhoeae*):** Known for causing hyperacute purulent conjunctivitis. It is one of the few bacteria capable of **penetrating an intact corneal epithelium**, leading to rapid perforation. **High-Yield Clinical Pearls for NEET-PG:** * **Treatment Contraindication:** Never use **topical steroids** in an active dendritic ulcer; it can lead to a "Geographic ulcer" (amoeboid shape). * **Drug of Choice:** Topical **Acyclovir (3%)** ointment or Ganciclovir gel. * **Recurrence:** HSV remains latent in the **Trigeminal Ganglion**. * **Differential Diagnosis:** Acanthamoeba keratitis can mimic early HSV but is associated with contact lens use and disproportionate pain (radial keratoneuritis).

Question 32: Topical steroids are contraindicated in which ocular condition?

A. Anterior uveitis
B. Posterior uveitis
C. Fungal corneal ulcer (Correct Answer)
D. Mooren's ulcer

Explanation: **Explanation:** **Why Fungal Corneal Ulcer is the Correct Answer:** Topical steroids are strictly contraindicated in fungal corneal ulcers because they exacerbate the infection through two primary mechanisms: 1. **Immunosuppression:** Steroids inhibit the local inflammatory response and leukocyte migration, allowing fungi to proliferate unchecked. 2. **Enhancement of Fungal Virulence:** Steroids promote the growth of fungi (especially *Fusarium*) and stimulate the release of fungal proteases and collagenases, which accelerate corneal melting and increase the risk of perforation. **Analysis of Incorrect Options:** * **Anterior & Posterior Uveitis:** Steroids are the **mainstay of treatment** here. They reduce intraocular inflammation, prevent the formation of synechiae, and minimize damage to the ciliary body and retina. * **Mooren’s Ulcer:** This is an idiopathic, peripheral ulcerative keratitis of **autoimmune origin**. Since the pathology is immune-mediated rather than infectious, topical and systemic steroids are used to suppress the destructive immune response. **High-Yield Clinical Pearls for NEET-PG:** * **The "Double-Edged Sword":** Steroids are also contraindicated in the **epithelial stage of Herpes Simplex Keratitis (Dendritic Ulcer)** as they promote viral replication, leading to a "Geographic Ulcer." * **Diagnostic Clue:** If a corneal ulcer worsens rapidly after the accidental use of steroids, always suspect a fungal etiology or Acanthamoeba. * **Steroid Side Effects:** Long-term topical steroid use can lead to **Steroid-induced Glaucoma** (due to decreased aqueous outflow) and **Posterior Subcapsular Cataract (PSC)**.

Question 33: Prominent corneal nerves are seen in all of the following conditions, EXCEPT:

A. Keratoconus
B. Band shaped keratopathy (Correct Answer)
C. Acanthamoebic keratitis
D. Refsum syndrome

Explanation: **Explanation:** The visibility of corneal nerves is a specific clinical sign. Normally, corneal nerves are invisible or very faint. They become "prominent" or thickened due to infiltration, degeneration, or structural changes in the corneal stroma. **Why Band-shaped Keratopathy (BSK) is the correct answer:** BSK is characterized by the deposition of **calcium salts** (hydroxyapatite) in the subepithelial space, Bowman’s layer, and anterior stroma. It typically presents as a horizontal "band" in the interpalpebral fissure. It does **not** involve the thickening or prominence of corneal nerves; rather, it is a degenerative calcific process. **Analysis of Incorrect Options (Conditions with Prominent Corneal Nerves):** * **Keratoconus:** Structural thinning and stretching of the cornea make the normal nerves appear more crowded and prominent (often seen at the apex). * **Acanthamoebic Keratitis:** Characterized by **radial keratoneuritis** (infiltrates along the corneal nerves), which is a pathognomonic sign and causes exquisite pain. * **Refsum Syndrome:** A metabolic disorder (phytanic acid storage) where thickened corneal nerves are a classic ocular finding. **High-Yield Clinical Pearls for NEET-PG:** To remember the causes of prominent corneal nerves, use the mnemonic **"KANSAR"** or **"MEN"**: 1. **K**eratoconus 2. **A**canthamoeba keratitis 3. **N**eurofibromatosis (Type 1) 4. **S**prings (Vernal Keratoconjunctivitis) 5. **A**myloidosis 6. **R**efsum syndrome 7. **MEN Type 2B** (Multiple Endocrine Neoplasia) – *Very high yield!* 8. **Leprosy** (often presents with beaded corneal nerves) 9. **Fuchs' Endothelial Dystrophy**

Question 34: What is the radius of curvature of the anterior surface of the cornea?

A. 8.4 mm
B. 7.8 mm (Correct Answer)
C. 5.8 mm
D. 4.8 mm

Explanation: ### Explanation The cornea is the primary refractive element of the eye, contributing approximately **+43 to +45 Diopters** to the total refractive power. Its optical properties are determined by its radius of curvature and the refractive index. **1. Why 7.8 mm is Correct:** The anterior surface of the cornea is an elliptical structure. The average **radius of curvature of the anterior surface is 7.8 mm**. This surface is in contact with the air-tear film interface, where the greatest change in refractive index occurs, making it the most significant refractive boundary of the eye. **2. Analysis of Incorrect Options:** * **Option A (8.4 mm):** This value is too high for a normal cornea. A flatter cornea (larger radius) is seen in conditions like *cornea plana*. * **Option C (5.8 mm):** This is the average **radius of curvature of the posterior surface** of the cornea. Because the posterior surface is steeper than the anterior surface, the cornea acts as a "minus lens" centrally, though its overall power remains positive. * **Option D (4.8 mm):** This value is significantly lower than normal. A very steep cornea (small radius) is characteristic of advanced **keratoconus** or *keratoglobus*. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Refractive Index:** The refractive index of the cornea is **1.376**. * **Corneal Thickness:** Central thickness is ~0.52 mm (520 microns), while peripheral thickness is ~0.67 mm. * **Power Calculation:** The anterior surface has a power of **+48.8 D**, while the posterior surface has a power of **-5.8 D**, resulting in a net corneal power of approximately **+43 D**. * **Keratometry:** This clinical procedure measures the radius of curvature of the central 3 mm of the anterior corneal surface to calculate its refractive power.

Question 35: Which of the following statements regarding Acanthamoeba Keratitis is NOT true?

A. Common in contact lens users
B. Ring abscess may be seen
C. Pain is typically very severe
D. Can be cultured on nutrient agar enriched with E. coli (Correct Answer)

Explanation: **Explanation:** Acanthamoeba Keratitis is a rare but vision-threatening parasitic infection of the cornea, often associated with poor contact lens hygiene. **Why Option D is the Correct Answer (The False Statement):** Acanthamoeba is a free-living amoeba that cannot be cultured on standard nutrient agar. It requires **Non-Nutrient Agar (NNA)** seeded with a lawn of Gram-negative bacteria, most commonly **E. coli**. The amoebae feed on the bacteria to grow. The distinction between "Nutrient Agar" and "Non-Nutrient Agar" is a frequent trap in NEET-PG questions. **Analysis of Other Options:** * **Option A (True):** Approximately 80-90% of cases occur in **contact lens users**, particularly those who use tap water to rinse lenses or swim while wearing them. * **Option B (True):** A **Ring Infiltrate (or Ring Abscess)** is the classic late-stage clinical sign of Acanthamoeba keratitis, resulting from an immune response to the parasites. * **Option C (True):** **Pain out of proportion to clinical findings** is a hallmark of this condition. This occurs because the organism has a predilection for nerves (radial keratoneuritis). **High-Yield Clinical Pearls for NEET-PG:** * **Stains:** Best visualized using **Calcofluor White** (fluorescent stain) or Periodic Acid-Schiff (PAS). * **Early Sign:** Radial Keratoneuritis (infiltrates along corneal nerves). * **Late Sign:** Ring Infiltrate. * **Treatment:** Topical biguanides like **PHMB (Polyhexamethylene biguanide)** or **Chlorhexidine**. Propamidine isethionate (Brolene) is also used. * **Differential Diagnosis:** Often misdiagnosed as Herpes Simplex Keratitis in early stages.

Question 36: What is the most common causative organism of corneal ulcer?

A. Pneumococci
B. Streptococci
C. Staphylococci (Correct Answer)
D. Fungal

Explanation: ### Explanation **Correct Answer: C. Staphylococci** **Why Staphylococci is correct:** In modern clinical practice, **Staphylococci** (specifically *Staphylococcus aureus* and *Staphylococcus epidermidis*) are recognized as the most common bacterial cause of corneal ulcers worldwide. This shift is attributed to the high prevalence of these organisms on the normal skin and eyelid flora, which can easily inoculate the cornea following minor trauma or contact lens wear. *Staphylococcus aureus* typically produces a well-defined, yellowish-white, creamy suppuration. **Why the other options are incorrect:** * **A & B. Pneumococci / Streptococci:** Historically, *Streptococcus pneumoniae* (Pneumococcus) was considered the leading cause of bacterial keratitis (hypopyon ulcer). While still a significant pathogen—especially in cases involving the lacrimal sac (Dacryocystitis)—it has been overtaken by Staphylococci in overall frequency. * **D. Fungal:** Fungal keratitis is a major cause of corneal ulcers, particularly in tropical climates and among agricultural workers following trauma with vegetative matter. However, globally and statistically, bacterial infections remain more frequent than fungal ones. **High-Yield Clinical Pearls for NEET-PG:** * **Most common overall:** *Staphylococcus aureus*. * **Most common in Contact Lens users:** *Pseudomonas aeruginosa* (characterized by rapid progression and greenish-blue discharge). * **Most common following vegetative trauma:** Filamentous fungi (e.g., *Aspergillus*, *Fusarium*). * **Most common cause of Hypopyon Ulcer (Ulcus Serpens):** *Streptococcus pneumoniae*. * **Acanthamoeba:** Suspect in contact lens users with pain out of proportion to clinical findings and "radial keratoneuritis."

Question 37: A 28-year-old male complains of glare in both eyes. The cornea shows whorl-like opacities of the epithelium. He also has a history of long-term amiodarone treatment. What is the most likely diagnosis?

A. Terrien's marginal degeneration
B. Cornea verticillata (Correct Answer)
C. Band-shaped keratopathy
D. Arcus juvenilis

Explanation: **Explanation:** The clinical presentation of bilateral, whorl-like epithelial opacities (vortex keratopathy) in a patient taking **Amiodarone** is a classic description of **Cornea Verticillata**. **1. Why Cornea Verticillata is correct:** Cornea verticillata is characterized by fine, golden-brown or grayish-white deposits in the basal layer of the corneal epithelium, radiating from a point below the pupil in a whorl-like pattern. It is a form of **drug-induced lipidosis**. Amiodarone is the most common systemic medication associated with this condition (occurring in nearly 100% of patients on long-term therapy). While usually asymptomatic, it can cause symptoms of glare or colored halos. **2. Why the other options are incorrect:** * **Terrien’s marginal degeneration:** A non-inflammatory, bilateral thinning of the peripheral cornea, typically starting superiorly and associated with vascularization and lipid deposition (pseudopterygium). * **Band-shaped keratopathy:** Characterized by horizontal calcium deposits in the Bowman’s layer, often seen in chronic uveitis or hypercalcemia. It presents as a "Swiss-cheese" appearance, not a whorl. * **Arcus juvenilis:** A peripheral lipid deposit (similar to arcus senilis) occurring in younger patients, usually associated with hyperlipidemia, not drug toxicity. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Cornea Verticillata (CHAI-T):** **C**hloroquine/Hydroxychloroquine, **H**ealthy (Fabry’s disease - the only non-drug cause), **A**miodarone, **I**ndomethacin, **T**amoxifen. * **Fabry’s Disease:** If a question mentions whorl-like opacities in a patient with renal failure or skin rashes (angiokeratomas) instead of drug history, think Fabry’s disease (alpha-galactosidase A deficiency). * **Management:** Amiodarone-induced deposits are usually reversible upon discontinuation of the drug, though stopping the medication is rarely necessary as vision is seldom significantly affected.

Question 38: All of the following clinical signs are seen in Keratoconus except?

A. Fleischer ring
B. Rizzuti sign
C. Haab's striae (Correct Answer)
D. Oil droplet reflex

Explanation: **Explanation:** The correct answer is **C. Haab's striae**. **Why Haab's striae is the correct answer:** Haab's striae are horizontal or curvilinear breaks in the **Descemet’s membrane** caused by increased intraocular pressure and globe enlargement. They are a hallmark clinical sign of **Primary Congenital Glaucoma**, not Keratoconus. In contrast, Keratoconus involves vertical stress lines in the deep stroma and Descemet’s membrane known as **Vogt’s striae**. **Analysis of incorrect options (Signs of Keratoconus):** * **Fleischer ring:** A partial or complete ring of **iron deposition** (hemosiderin) in the basal epithelium at the base of the cone. It is best visualized using a cobalt blue filter. * **Rizzuti sign:** A sharply focused triangle of light on the nasal iris when a penlight is shone from the temporal side. This occurs due to the conical shape of the cornea acting as a lens. * **Oil droplet reflex:** Seen during distant direct ophthalmoscopy; the protrusion of the cornea creates a dark shadow resembling a drop of oil against the red reflex. **High-Yield Clinical Pearls for NEET-PG:** * **Munson’s Sign:** V-shaped indentation of the lower eyelid on down-gaze. * **Vogt’s Striae:** Vertical stress lines that disappear upon applying digital pressure over the globe. * **Hydrops:** Acute corneal edema caused by a rupture in the Descemet’s membrane (managed conservatively, not with surgery initially). * **Treatment of Choice:** Collagen Cross-Linking (CXL/C3R) to arrest progression; Penetrating or Deep Anterior Lamellar Keratoplasty (DALK) for advanced cases.

Question 39: What is the afferent pathway of the corneal reflex?

A. Trigeminal nerve (Correct Answer)
B. Facial nerve
C. Oculomotor nerve
D. Abducens nerve

Explanation: The corneal reflex (blink reflex) is an involuntary blinking of the eyelids elicited by stimulation of the cornea. It is a polysynaptic reflex arc essential for protecting the ocular surface. ### **Mechanism of the Reflex Arc** 1. **Afferent Limb (Sensory):** When the cornea is touched, the impulse is carried by the **long ciliary nerves**, which are branches of the **Ophthalmic division (V1) of the Trigeminal nerve**. These fibers travel to the sensory nucleus of the trigeminal nerve in the pons. 2. **Interneurons:** From the trigeminal nucleus, impulses are sent bilaterally to the facial nerve nuclei. 3. **Efferent Limb (Motor):** The **Facial nerve (VII)** carries the motor impulse to the **orbicularis oculi** muscle, resulting in a bilateral blink (direct and consensual response). ### **Analysis of Options** * **A. Trigeminal nerve (Correct):** It provides the sensory innervation to the cornea via the ophthalmic division (V1), forming the afferent limb. * **B. Facial nerve:** This is the **efferent** (motor) limb of the reflex. Damage to the facial nerve results in an absent motor response despite intact sensation. * **C. Oculomotor nerve:** Involved in eyelid elevation (Levator palpebrae superioris) and most extraocular movements, but not the corneal reflex. * **D. Abducens nerve:** Responsible for lateral rectus movement; it has no role in the corneal reflex arc. ### **High-Yield Clinical Pearls for NEET-PG** * **Consensual Response:** Stimulating one eye causes both eyes to blink. If the afferent (V) is damaged, neither eye blinks. If the efferent (VII) is damaged on one side, only the contralateral eye blinks. * **Contact Lens Wearers:** Long-term use can lead to decreased corneal sensitivity and a diminished corneal reflex. * **Acoustic Neuroma:** An absent corneal reflex is often the **earliest clinical sign** of a cerebellopontine (CP) angle tumor due to pressure on the trigeminal nerve.

Question 40: Which of the following is associated with Acanthamoeba keratitis?

A. Trauma with vegetable matter
B. Wearing of soft contact lenses (Correct Answer)
C. Dry eyes
D. Entropion

Explanation: **Acanthamoeba keratitis** is a rare but vision-threatening parasitic infection of the cornea caused by a free-living amoeba. It is most commonly associated with **contact lens wearers** (accounting for approximately 85% of cases). ### **Explanation of Options** * **Option B (Correct):** The use of soft contact lenses, especially when combined with poor hygiene practices—such as using tap water for cleaning, swimming while wearing lenses, or using contaminated solutions—is the primary risk factor. The amoeba adheres to the lens surface and subsequently invades the corneal epithelium. * **Option A:** Trauma with vegetable matter is the classic risk factor for **Fungal Keratitis** (e.g., *Aspergillus* or *Fusarium*), not Acanthamoeba. * **Option C & D:** Dry eyes and Entropion (inward turning of the eyelid) can lead to corneal erosions and secondary bacterial infections, but they are not specific predisposing factors for Acanthamoeba. ### **High-Yield Clinical Pearls for NEET-PG** * **Classic Presentation:** The hallmark is **"Pain out of proportion to clinical findings"** (due to radial keratoneuritis). * **Early Sign:** **Radial Keratoneuritis** (infiltrates along the corneal nerves). * **Late Sign:** **Ring-shaped stromal infiltrate** (pathognomonic). * **Diagnosis:** * Gold standard culture: **Non-nutrient agar with E. coli overlay**. * Stain: **Calcofluor white** (shows double-walled cysts under fluorescence). * **Treatment:** Topical biguanides like **PHMB (Polyhexamethylene biguanide)** or **Chlorhexidine**. Propamidine isethionate (Brolene) is also used.

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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