Diseases of the Cornea Practice Questions

Q: Neurotrophic keratopathy is caused by damage to which nerve?

Trigeminal nerve (Cranial nerve V). **Explanation:** **Neurotrophic Keratopathy (NK)** is a degenerative corneal disease caused by an impairment of corneal innervation. The correct answer is the **Trigeminal nerve (CN V)**, specifically its **Ophthalmic division (V1)** via the long ciliary nerves. The underlying medical concept is that sensory nerves do more than just transmit pain; they provide **trophic support** to the corneal epithelium. They release neuropeptides (like Substance P and Nerve Growth Factor) that are essential for epithelial cell turnover, wound healing, and maintaining the tear film reflex. When CN V is damaged, the cornea becomes anesthetic, leading to epithelial breakdown, poor healing, and eventually painless corneal ulcers. **Analysis of Incorrect Options:** * **Facial nerve (CN VII):** Damage to this nerve causes **Exposure Keratopathy** due to lagophthalmos (inability to close the eyelid). While it affects corneal health, it is a mechanical/exposure issue, not a neurotrophic one. * **Trochlear nerve (CN IV):** This is a motor nerve supplying the Superior Oblique muscle. Damage results in diplopia (double vision), not corneal pathology. **High-Yield Clinical Pearls for NEET-PG:** * **Most Common Cause:** Herpes Simplex (HSV) or Herpes Zoster Ophthalmicus (HZO) infections. Other causes include acoustic neuroma (damaging the CN V ganglion) and diabetes. * **Hallmark Sign:** A **painless** corneal ulcer with "rolled-up" epithelial edges. * **Staging:** Uses the **Mackie Classification** (Stage 1: Epithelial irregularity; Stage 2: Persistent epithelial defect; Stage 3: Corneal ulcer/perforation). * **Treatment Tip:** Avoid preservatives; use lubricants. Severe cases may require **Tarsorrhaphy** or the newer recombinant human nerve growth factor (**Cenegermin**).

Q: Giant dendritic ulceration on the cornea is typically seen in which of the following conditions?

Herpes Simplex Virus (HSV) infection. **Explanation:** The correct answer is **Herpes Simplex Virus (HSV) infection**. **1. Why HSV is correct:** The hallmark of **Herpes Simplex Keratitis (HSK)** is the formation of a **dendritic ulcer**. This occurs due to the active replication of the virus in the corneal epithelium, leading to cell death in a linear, branching pattern. These ulcers have characteristic **terminal bulbs** (knob-like ends) and stain brilliantly with **Fluorescein** (the floor of the ulcer) and **Rose Bengal** (the devitalized margins). If left untreated or if topical steroids are inappropriately used, these dendrites can enlarge to form a **Geographic (Giant) ulcer**. **2. Why other options are incorrect:** * **Fungal infection:** Typically presents with a "dry" looking infiltrate, **feathery margins**, and **satellite lesions**. It does not form branching dendritic patterns. * **Chlamydial infection:** Usually presents as chronic follicular conjunctivitis or **Trachoma**, characterized by Arlt’s line, Herbert’s pits, and pannus, rather than epithelial ulceration. * **Pneumococcal infection:** *S. pneumoniae* is a common cause of **Hypopyon corneal ulcers** (Ulcus Serpens). It typically causes a deep, purulent, rapidly progressing oval ulcer with a shaggy base, not a dendritic pattern. **Clinical Pearls for NEET-PG:** * **Dendritic ulcer with terminal bulbs:** Pathognomonic for HSV. * **Pseudodendrite:** Seen in **Acanthamoeba keratitis** and **Herpes Zoster Ophthalmicus (HZO)**. Unlike HSV, these lack terminal bulbs and are slightly elevated. * **Corneal Sensations:** Characteristically **decreased or absent** in HSV keratitis (tested using a wisp of cotton). * **Treatment:** Topical **Acyclovir (3%)** or Ganciclovir gel. **Topical steroids are strictly contraindicated** in epithelial (dendritic) disease as they can trigger a geographic ulcer.

Q: Munson sign is seen in:

Keratoconus. **Explanation:** **Munson sign** is a classic clinical finding in advanced **Keratoconus**. It refers to the V-shaped bulging or indentation of the lower eyelid when the patient looks downward. This occurs because the progressive thinning and ectasia of the central cornea cause it to assume a conical shape; this cone physically displaces the lower lid margin during downgaze. **Analysis of Options:** * **A. Corneal dystrophy:** These are typically bilateral, genetic, non-inflammatory opacifications (e.g., Fuchs’ or Lattice dystrophy). While they affect corneal clarity, they do not cause the structural "coning" required to produce Munson sign. * **B. Perforated corneal ulcer:** This is an ocular emergency characterized by a full-thickness defect and often a flat anterior chamber. While the cornea is deformed, it is due to tissue loss and hypotony, not the progressive ectasia seen in Munson sign. * **C. Keratoconus (Correct):** The hallmark of this condition is progressive non-inflammatory thinning of the corneal stroma, leading to a cone-like protrusion and irregular astigmatism. * **D. Marfan syndrome:** While Marfan syndrome is associated with ocular issues like *Ectopia lentis* (superior-temporal subluxation) and flat corneas (*Cornea plana*), it is not a primary cause of Munson sign. **High-Yield Clinical Pearls for Keratoconus:** * **Fleischer’s ring:** Iron deposition at the base of the cone (best seen with cobalt blue filter). * **Vogt’s striae:** Vertical stress lines in the deep stroma/Descemet’s membrane. * **Rizutti’s sign:** A conical reflection on the nasal cornea when light is shone from the temporal side. * **Hydrops:** Acute corneal edema due to a rupture in Descemet’s membrane. * **Management:** Rigid Gas Permeable (RGP) lenses for vision; Collagen Cross-linking (CXL) to stop progression; Keratoplasty for advanced cases.

Q: Corneal sensation is tested by which instrument?

Aesthesiometer. ### Explanation **Correct Answer: C. Aesthesiometer** Corneal sensation is a vital indicator of the integrity of the **Trigeminal nerve (Ophthalmic division - V1)** via the long ciliary nerves. The instrument used to quantify this sensation is the **Aesthesiometer**. The most commonly used clinical device is the **Cochet-Bonnet aesthesiometer**, which utilizes a retractable nylon monofilament. By varying the length of the filament, the pressure applied to the cornea is adjusted; a longer filament applies less pressure, while a shorter one applies more. A decrease in sensation (hypesthesia) is a hallmark of conditions like Herpes Simplex Keratitis, Neurotrophic Keratopathy, and chronic contact lens wear. **Why other options are incorrect:** * **A. Keratometry:** Measures the **curvature** of the anterior corneal surface. It is primarily used for IOL power calculation and diagnosing astigmatism or keratoconus. * **B. Pachymeter:** Measures **corneal thickness**. It is essential in glaucoma (to adjust IOP readings) and preoperative evaluation for refractive surgeries like LASIK. * **D. Specular microscopy:** Used to study the **corneal endothelium**. It provides data on endothelial cell density and morphology (pleomorphism and polymegethism). **High-Yield Clinical Pearls for NEET-PG:** * **Corneal Reflex:** The afferent limb is the **Trigeminal nerve (V1)**, and the efferent limb is the **Facial nerve (VII)**. * **Neurotrophic Keratitis:** Characterized by a "silent" (painless) ulcer due to loss of corneal sensation. Common causes include Diabetes Mellitus, Herpes Zoster Ophthalmicus, and Acoustic Neuroma. * **Normal Central Corneal Thickness (CCT):** Approximately **540 microns**.

Q: What is used to prevent keratoconus?

None. **Explanation:** Keratoconus is a non-inflammatory, progressive ectatic dystrophy characterized by thinning and cone-like protrusion of the cornea. The correct answer is **None** because there is currently no pharmacological or optical intervention that can *prevent* the onset of the disease. Management focuses on visual rehabilitation and halting progression, rather than prevention. **Analysis of Options:** * **Antibiotics (A):** Keratoconus is a structural and degenerative condition, not an infectious one. Antibiotics have no role in its etiology or prevention. * **Cycloplegics (B):** These are used to paralyze the ciliary muscle (e.g., in uveitis or refraction). They do not influence corneal biomechanics or prevent ectasia. * **Glasses (C):** While glasses (and later, rigid gas permeable lenses) are used to *correct* the irregular astigmatism caused by keratoconus to improve vision, they do not stop the cornea from thinning or prevent the disease from occurring. **Clinical Pearls for NEET-PG:** 1. **Cessation of Eye Rubbing:** This is the most critical behavioral advice. Chronic eye rubbing is strongly associated with the progression of keratoconus (often linked to Vernal Keratoconjunctivitis). 2. **Corneal Collagen Cross-linking (CXL/C3R):** This is the **only** procedure proven to **halt the progression** of keratoconus by increasing corneal rigidity using Riboflavin (Vitamin B2) and UVA light. It does not "prevent" the initial onset but stabilizes existing disease. 3. **Early Signs:** Look for "Munson’s sign" (V-shaped indentation of the lower lid on downgaze), "Fleischer’s ring" (iron deposition at the base of the cone), and "Vogt’s striae" (vertical stress lines in the stroma). 4. **Gold Standard Diagnosis:** Corneal Topography (Pentacam) is the most sensitive method for early detection.

Q: Iridocorneal endothelial syndrome is associated with which of the following?

Progressive atrophy of iris stroma. **Explanation:** **Iridocorneal Endothelial (ICE) Syndrome** is a rare group of conditions characterized by an abnormal corneal endothelial cell layer that migrates across the anterior chamber angle and onto the iris surface. **Why Option A is correct:** The hallmark of ICE syndrome is the proliferation of a "pathological endothelial membrane." As this membrane contracts over the iris, it leads to high-yield clinical features: **progressive atrophy of the iris stroma**, corectopia (displaced pupil), and ectropion uveae. This contraction also causes peripheral anterior synechiae (PAS), leading to secondary angle-closure glaucoma. **Analysis of Incorrect Options:** * **Option B:** ICE syndrome is characteristically **unilateral** and typically affects young to middle-aged women. While corneal edema occurs due to endothelial pump failure, the iris involvement is atrophic, not edematous. * **Options C & D:** The pathology involves the migration of abnormal endothelial cells that secrete a **new basement membrane** (posterior collagenous layer) over the angle and iris. It is not characterized by the primary deposition of collagen or GAGs specifically within the Descemet’s membrane itself. **High-Yield Clinical Pearls for NEET-PG:** * **The Triad:** ICE syndrome consists of three clinical variants: 1. **Progressive Iris Atrophy:** Severe iris thinning and hole formation (pseudopolycoria). 2. **Chandler Syndrome:** Most common variant; presents primarily with corneal edema and mild iris changes. 3. **Cogan-Reese Syndrome:** Characterized by "iris nodules" (pedunculated nodules on the iris surface). * **Specular Microscopy:** Shows a characteristic "beaten silver" appearance or "ICE cells" (dark areas with central highlights). * **Key Association:** It is often linked to a latent **Herpes Simplex Virus (HSV)** infection in the corneal endothelium.

Q: Corneal thickness is measured using which diagnostic tool?

Pachymetry. **Explanation:** **Corneal Pachymetry** is the gold standard diagnostic tool used to measure the thickness of the cornea. This measurement is clinically vital because corneal thickness influences the accuracy of Intraocular Pressure (IOP) readings (thinner corneas lead to underestimated IOP) and is a critical screening parameter for refractive surgeries like LASIK and the management of Keratoconus. **Analysis of Options:** * **Pachymetry (Correct):** It can be performed using **ultrasound** (contact method) or **optical** methods (non-contact, e.g., Pentacam or OCT). The average central corneal thickness (CCT) is approximately **540–560 μm**. * **Keratometer:** This instrument measures the **curvature** of the anterior corneal surface. It is used to calculate the power of Intraocular Lenses (IOL) and to diagnose astigmatism. * **CT Scan:** While useful for orbital trauma or tumors, it lacks the resolution required to measure microscopic corneal dimensions. * **Aesthesiometry:** This measures **corneal sensitivity** (nerve function). The Cochet-Bonnet aesthesiometer is the classic tool used for this purpose, often to evaluate viral keratitis (e.g., Herpes Simplex) or neurotrophic ulcers. **High-Yield Clinical Pearls for NEET-PG:** * **Goldmann Applanation Tonometry (GAT):** It is calibrated for a CCT of 520 μm. If the cornea is thicker, the IOP reading will be falsely high. * **Keratoconus:** Characterized by progressive **corneal thinning** and steepening. * **Fuch’s Dystrophy:** Leads to corneal edema, resulting in an **increased** pachymetry reading. * **Refractive Surgery:** A minimum residual stromal bed of **250–300 μm** must remain after LASIK to prevent corneal ectasia.

Q: Prominent corneal nerves are seen in all conditions except?

Macular dystrophy. **Explanation:** The presence of **prominent corneal nerves** is a classic clinical sign in ophthalmology, often associated with specific systemic and ocular conditions. **Why Macular Dystrophy is the correct answer:** Macular corneal dystrophy is a stromal dystrophy characterized by the accumulation of acid mucopolysaccharides. It typically presents with diffuse stromal haze and focal gray-white opacities. It **does not** cause enlargement or increased visibility of corneal nerves. In fact, most corneal dystrophies (except occasionally Lattice dystrophy) are not associated with prominent nerves. **Analysis of Incorrect Options (Conditions with Prominent Nerves):** * **Ectodermal Dysplasia:** A group of genetic disorders affecting skin, hair, and nails; prominent corneal nerves are a recognized ocular feature. * **Ichthyosis:** Specifically X-linked ichthyosis is frequently associated with thickened corneal nerves and deep stromal opacities. * **Refsum’s Syndrome:** A metabolic disorder (phytanic acid storage disease) that presents with retinitis pigmentosa and prominent corneal nerves. **High-Yield Clinical Pearls for NEET-PG:** To remember the causes of prominent corneal nerves, use the mnemonic **"MEN'S HIRE"**: * **M:** **M**ultiple Endocrine Neoplasia (MEN) Type 2B (Most common association) * **E:** **E**ctodermal dysplasia / **E**dema (Corneal) * **N:** **N**eurofibromatosis Type 1 (NF-1) * **S:** **S**iogren’s syndrome * **H:** **H**ansen’s disease (Leprosy) * **I:** **I**chthyosis * **R:** **R**efsum’s syndrome * **E:** **E**hlers-Danlos syndrome / **E**xophthalmos (Grave’s disease) **Key Fact:** The most common systemic association tested in exams for thickened corneal nerves is **MEN Type 2B** (associated with Medullary Thyroid Carcinoma and Pheochromocytoma).

Q: Which organism does not invade an intact cornea?

Pseudomonas. **Explanation:** The corneal epithelium acts as a formidable mechanical barrier against most microorganisms. For a pathogen to cause a corneal ulcer, there usually must be a prior breach in this epithelium (e.g., trauma, contact lens wear, or dry eye). **Why Pseudomonas is the correct answer:** *Pseudomonas aeruginosa* is a highly virulent gram-negative rod, but it **cannot** penetrate a healthy, intact corneal epithelium. It requires a pre-existing epithelial defect to initiate infection. Once inside the stroma, however, it produces proteases and collagenases that cause rapid liquefactive necrosis (the "soupy" cornea). **Why the other options are incorrect:** There are five specific organisms known for their unique ability to penetrate a completely **intact** corneal epithelium. These are often remembered by the mnemonic **"CHNL-G"**: 1. **C**orynebacterium diphtheriae (Option B) 2. **H**aemophilus aegyptius (Koch-Weeks bacillus) 3. **N**eisseria gonorrhoeae (Option A) 4. **L**isteria monocytogenes 5. **G**onococci/Meningococci (Option C) These organisms possess specific surface proteins or enzymes that allow them to bypass the epithelial defense without prior trauma. **High-Yield Clinical Pearls for NEET-PG:** * **Pseudomonas:** The most common cause of bacterial corneal ulcers in **contact lens users**. It is characterized by a greenish-yellow discharge. * **Neisseria gonorrhoeae:** Can cause hyperacute conjunctivitis leading to rapid corneal perforation due to its ability to invade intact tissue. * **Acanthamoeba:** Another organism that typically requires a breach (often associated with contaminated contact lens solution) but is notorious for causing a "ring-shaped infiltrate."

Question 1

Neurotrophic keratopathy is caused by damage to which nerve?

Accepted Answer

Trigeminal nerve (Cranial nerve V)

Answer

Facial nerve (Cranial nerve VII)

Answer

Both trigeminal and facial nerves

Answer

Trochlear nerve (Cranial nerve IV)

Question 2

Giant dendritic ulceration on the cornea is typically seen in which of the following conditions?

Accepted Answer

Herpes Simplex Virus (HSV) infection

Answer

Fungal infection

Answer

Chlamydial infection

Answer

Pneumococcal infection

Question 3

Munson sign is seen in:

Accepted Answer

Keratoconus

Answer

Corneal dystrophy

Answer

Perforated corneal ulcer

Answer

Marfan syndrome

Question 4

Corneal sensation is tested by which instrument?

Accepted Answer

Aesthesiometer

Answer

Keratometry

Answer

Pachymeter

Answer

Specular microscopy

Question 5

Which is the metabolically active layer of the cornea?

Accepted Answer

Descemet membrane

Answer

Endothelium

Answer

Stroma

Answer

Epithelium

Question 6

What is used to prevent keratoconus?

Accepted Answer

None

Answer

Antibiotics

Answer

Cycloplegics

Answer

Glasses

Question 7

Iridocorneal endothelial syndrome is associated with which of the following?

Accepted Answer

Progressive atrophy of iris stroma

Answer

Bilateral stromal edema of iris and cornea

Answer

Deposition of collagen in Descemet's membrane

Answer

Deposition of glycosaminoglycan in Descemet's membrane

Question 8

Corneal thickness is measured using which diagnostic tool?

Accepted Answer

Pachymetry

Answer

Keratometer

Answer

CT scan

Answer

Aesthesiometry

Question 9

Prominent corneal nerves are seen in all conditions except?

Accepted Answer

Macular dystrophy

Answer

Ectodermal dysplasia

Answer

Ichthyosis

Answer

Refsum's syndrome

Question 10

Which organism does not invade an intact cornea?

Accepted Answer

Pseudomonas

Answer

Gonococci

Answer

C. diphtheriae

Answer

Meningococci

Diseases of the Cornea — MCQs

Diseases of the Cornea — MCQs

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