Diseases of the Cornea — MCQs

Diseases of the Cornea Indian Medical PG Practice Questions and MCQs

Question 181: Corneal sensations are diminished in which of the following conditions?

A. Herpes simplex (Correct Answer)
B. Conjunctivitis
C. Fungal infections
D. Marginal keratitis

Explanation: **Explanation:** The corneal sensation is mediated by the **long ciliary nerves**, which are branches of the **Ophthalmic division (V1) of the Trigeminal nerve**. Diminished or absent corneal sensation (hypoesthesia/anesthesia) is a hallmark clinical sign of neurotrophic keratitis. **1. Why Herpes Simplex is Correct:** Herpes Simplex Virus (HSV) resides in the trigeminal ganglion. During reactivation, the virus travels down the sensory nerves to the cornea, causing inflammation and subsequent damage to the corneal nerve plexus. This leads to a significant reduction in corneal sensitivity, which is a classic diagnostic feature used to differentiate HSV keratitis from other forms of keratitis. **2. Why the other options are incorrect:** * **Conjunctivitis:** This involves inflammation of the conjunctiva, not the corneal nerves; sensations remain intact. * **Fungal infections:** While fungal keratitis causes severe tissue destruction, it does not typically target the nerve plexus specifically to cause early loss of sensation; in fact, these ulcers are often very painful. * **Marginal keratitis:** This is a hypersensitivity reaction to Staphylococcal exotoxins. It affects the peripheral cornea but does not cause a generalized loss of corneal sensation. **High-Yield Clinical Pearls for NEET-PG:** * **Causes of Diminished Corneal Sensation:** Remember the mnemonic **"7H + L"**: **H**erpes simplex, **H**erpes zoster, **H**ansen’s disease (Leprosy), **H**ypovitaminosis A, **H**ydrops (Acute), **H**yperthyroidism (due to exposure), **H**ereditary (Riley-Day syndrome), and **L**asik surgery. * **Acoustic Neuroma:** Compression of the CN V root can also lead to a lost corneal reflex. * **Diabetes Mellitus:** A common systemic cause of decreased corneal sensitivity due to peripheral neuropathy. * **Testing:** Corneal sensation is clinically assessed using a **Cochet-Bonnet esthesiometer** or a simple wisp of cotton.

Question 182: Corneal ulcer can lead to which of the following complications?

A. Anterior staphyloma (Correct Answer)
B. Posterior staphyloma
C. Lenticonus
D. Keratoconus

Explanation: **Explanation:** A corneal ulcer, particularly if it progresses to perforation, can lead to the formation of an **Anterior Staphyloma**. When a corneal ulcer causes a large perforation, the iris prolapses through the defect. Over time, this prolapsed iris becomes covered by a thin layer of fibro-cicatricial tissue (pseudocornea). Due to the weakness of this new tissue and the associated rise in intraocular pressure (secondary glaucoma), the area bulges forward, resulting in a slate-colored protrusion known as an anterior staphyloma. **Analysis of Incorrect Options:** * **Posterior Staphyloma:** This is a protrusion of the weakened sclera lined by uveal tissue at the posterior pole of the eye. It is a hallmark of **Pathological Myopia**, not corneal ulceration. * **Lenticonus:** This is a congenital localized cone-shaped protrusion of the anterior or posterior lens surface. Anterior lenticonus is classically associated with **Alport Syndrome**. * **Keratoconus:** This is a non-inflammatory, progressive thinning and ectasia of the central or paracentral cornea. While it involves corneal bulging, it is a degenerative condition and not a direct complication of an acute infectious corneal ulcer. **High-Yield Clinical Pearls for NEET-PG:** * **Descemetocele:** This occurs when a corneal ulcer erodes everything except Descemet’s membrane; it appears as a transparent, bulging vesicle and is a precursor to perforation. * **Secondary Glaucoma:** This is the most common cause of the "bulge" in an anterior staphyloma. * **Management:** A small perforation is managed with Cyanoacrylate glue, while a large perforation requires a tectonic keratoplasty.

Question 183: A patient presents with acute eye pain and watering for 3 days. Examination reveals a 3x2 mm corneal ulcer with rolled out margins, feathery, finger-like projections, and minimal hypopyon. What is the most likely diagnosis?

A. Bacterial keratitis
B. Fungal keratitis (Correct Answer)
C. Acanthamoeba keratitis
D. Herpes Simplex Virus keratitis (HSV-I)

Explanation: The correct answer is **Fungal keratitis**. ### **Explanation of the Correct Answer** The clinical presentation described is classic for fungal keratitis (keratomycosis), most commonly caused by filamentous fungi like *Aspergillus* or *Fusarium*. The key diagnostic features in the question are: * **Feathery, finger-like projections:** These represent fungal hyphae infiltrating the corneal stroma. * **Rolled-out (elevated) margins:** Characteristic of fungal growth patterns. * **Minimal/Fixed Hypopyon:** Unlike bacterial ulcers, fungal hypopyons are often sterile and "immobile" because they contain fungal elements and inflammatory cells. * **Dry, leathery appearance:** Fungal ulcers often appear less "wet" than bacterial ones. ### **Why Other Options are Incorrect** * **Bacterial Keratitis:** Typically presents with a more acute onset, intense inflammation, and a "wet" ulcer with distinct, non-feathery margins. The hypopyon is usually fluid and shifts with head position. * **Acanthamoeba Keratitis:** Characterized by **disproportionate pain** (pain much worse than clinical signs) and a pathognomonic **radial keratoneuritis** (perineural infiltrates). It is strongly associated with contact lens use in tap water. * **HSV-I Keratitis:** Usually presents as a **dendritic ulcer** (linear, branching with terminal bulbs) or a geographic ulcer. It is associated with decreased corneal sensations. ### **High-Yield Clinical Pearls for NEET-PG** * **Predisposing Factor:** Trauma with **vegetative matter** (e.g., a branch or leaf) is the most common risk factor for fungal keratitis. * **Satellite Lesions:** Small, isolated infiltrates around the main ulcer are highly suggestive of fungal etiology. * **Investigation of Choice:** Potassium Hydroxide (**KOH**) mount is the initial screening test; **Sabouraud’s Dextrose Agar (SDA)** is the gold standard culture medium. * **Treatment:** Topical **Natamycin** (5%) is the drug of choice for filamentous fungi.

Question 184: Neuroparalytic keratitis is associated with paralysis of which cranial nerve?

A. 3rd cranial nerve
B. 4th cranial nerve
C. 6th cranial nerve
D. 7th cranial nerve (Correct Answer)

Explanation: **Explanation:** **Neuroparalytic keratitis** (also known as exposure keratitis) occurs due to the paralysis of the **7th cranial nerve (Facial nerve)**. The facial nerve supplies the **orbicularis oculi** muscle, which is responsible for eyelid closure. When this nerve is paralyzed (as seen in Bell’s palsy or acoustic neuroma surgery), the patient develops **lagophthalmos**—the inability to close the eyelids. This leads to constant exposure of the cornea, causing drying of the tear film, epithelial desiccation, and subsequent ulceration. **Analysis of Incorrect Options:** * **3rd Cranial Nerve (Oculomotor):** Paralysis causes **ptosis** (drooping of the eyelid). Because the eye remains covered by the lid, the cornea is actually protected from exposure. * **4th (Trochlear) & 6th (Abducens) Cranial Nerves:** These nerves supply extraocular muscles (Superior Oblique and Lateral Rectus, respectively). Paralysis leads to diplopia and squint but does not affect eyelid closure or corneal integrity. **Clinical Pearls for NEET-PG:** 1. **Neuroparalytic vs. Neurotrophic Keratitis:** Do not confuse the two. * **Neuroparalytic (7th Nerve):** Motor loss leading to exposure. * **Neurotrophic (5th Nerve/Trigeminal):** Sensory loss leading to loss of corneal reflex and poor epithelial healing. 2. **Bell’s Phenomenon:** This is the upward and outward rolling of the eyeball during attempted lid closure. It acts as a protective mechanism in 7th nerve palsy. 3. **Management:** Initial treatment involves frequent lubricants and taping the lids at night. For permanent palsy, **Tarsorrhaphy** (suturing the lids together) is the definitive surgical treatment.

Question 185: All of the following are signs of mycotic corneal ulcer, EXCEPT:

A. Large hypopyon
B. Sterile immune ring
C. Corneal vascularization (Correct Answer)
D. Feathery, finger-like extensions into the stroma

Explanation: **Explanation:** The hallmark of a **mycotic (fungal) corneal ulcer** is its indolent nature and the relative absence of early vascularization. Unlike bacterial ulcers, which often trigger an acute inflammatory response leading to rapid neovascularization, fungal ulcers are characterized by **lack of corneal vascularization**. The fungi produce toxins and enzymes that suppress the host's early angiogenic response, making the ulcer appear "dry" and gray. **Analysis of Options:** * **Corneal vascularization (Correct Answer):** This is typically absent in fungal keratitis. Its presence usually suggests a bacterial etiology, a healing stage, or a chronic viral infection (like HSV). * **Large hypopyon:** Fungal ulcers often present with a massive, thick, and non-sterile hypopyon. It is frequently "immobile" due to its high fibrin content and may even be present when the ulcer is relatively small. * **Sterile immune ring (Wessely ring):** This is a classic sign of fungal keratitis, representing a host antigen-antibody reaction (Type III hypersensitivity) where fungal antigens meet host antibodies in the stroma. * **Feathery, finger-like extensions:** These are characteristic "satellite lesions" or hyphal extensions that project from the main ulcer into the surrounding stroma, reflecting the infiltrative growth pattern of filamentous fungi (e.g., *Aspergillus*, *Fusarium*). **High-Yield Clinical Pearls for NEET-PG:** * **Most common cause:** *Aspergillus* (overall), but *Fusarium* is common in trauma with vegetative matter (e.g., a branch hitting the eye). * **Key Signs:** Dry, leathery appearance, raised margins, satellite lesions, and a "fixed" hypopyon. * **Diagnosis:** KOH mount (shows hyphae) and Sabouraud’s Dextrose Agar (SDA). * **Treatment:** Topical Natamycin (5%) is the drug of choice for filamentous fungi.

Question 186: Which of the following does not cause cornea verticillata?

A. Indomethacin
B. Chloroquine
C. Fabry disease
D. Tay-Sachs disease (Correct Answer)

Explanation: **Explanation:** **Cornea Verticillata** (also known as vortex keratopathy) is characterized by bilateral, symmetrical, golden-brown or greyish-white whorl-like opacities in the basal epithelium of the cornea. **Why Tay-Sachs disease is the correct answer:** Tay-Sachs disease is a lysosomal storage disorder (deficiency of Hexosaminidase A) characterized by a **cherry-red spot** at the macula due to ganglioside accumulation in retinal ganglion cells. It does **not** involve the corneal epithelium and therefore does not cause cornea verticillata. **Analysis of incorrect options:** * **Fabry Disease:** This is the most common systemic disease associated with cornea verticillata. It is an X-linked lysosomal storage disorder (alpha-galactosidase A deficiency) where glycolipids deposit in the corneal epithelium. * **Amiodarone & Chloroquine/Hydroxychloroquine:** These are the most common pharmacological causes. The drugs (or their metabolites) bind to lipids within the lysosomes of the corneal epithelium. * **Indomethacin:** Though less common than Amiodarone, Indomethacin is a well-documented cause of whorl-like corneal deposits. **NEET-PG High-Yield Pearls:** * **Mnemonic for Cornea Verticillata (CHAI-T):** **C**hloroquine, **H**ydroxychloroquine, **A**miodarone (most common), **I**ndomethacin, **T**amoxifen. * **Fabry Disease:** Cornea verticillata is often the first clinical sign and is present in almost all affected males and many female carriers. * **Clinical Significance:** Most drug-induced vortex keratopathies are asymptomatic and do not require drug discontinuation, as they rarely affect visual acuity. * **Differential for Cherry-red spot:** Tay-Sachs, Central Retinal Artery Occlusion (CRAO), Niemann-Pick disease, and Gaucher disease.

Question 187: What is Dellen?

A. Localized thinning of the peripheral cornea (Correct Answer)
B. Raised lesions in the corneoscleral junction
C. Age-related macular degeneration
D. Marginal keratitis

Explanation: **Explanation:** **Dellen** (Fuchs’ Dellen) refers to a localized, saucer-shaped thinning of the peripheral cornea. It occurs due to **tear film instability** and localized dehydration of the corneal stroma. 1. **Why Option A is Correct:** The underlying mechanism is **focal stromal dehydration**. When there is an adjacent elevation (like a pterygium, chemosis, or a large subconjunctival hemorrhage), the eyelid is "tented" up, preventing the tear film from wetting the adjacent corneal surface. This leads to rapid evaporation and secondary thinning of the stroma. On examination, it appears as a dry, depressed area with clear margins. 2. **Why Other Options are Incorrect:** * **Option B:** Raised lesions at the corneoscleral junction are characteristic of conditions like **Phlyctenular keratoconjunctivitis** or Limbal Dermoids, whereas Dellen is a depression/thinning. * **Option C:** **Age-related macular degeneration (ARMD)** is a posterior segment disease affecting the retina, unrelated to corneal thinning. * **Option D:** **Marginal keratitis** is an inflammatory/hypersensitivity reaction to Staphylococcal exotoxins, characterized by infiltrates and ulcers, not simple dehydration-induced thinning. **High-Yield Clinical Pearls for NEET-PG:** * **Pathogenesis:** Discontinuity of the precorneal tear film (not an inflammatory process). * **Clinical Feature:** A "saucer-like" depression near the limbus. Fluorescein pools in the depression but does not necessarily stain it (unless the epithelium is breached). * **Treatment:** Frequent application of artificial tears and lubricants; occasionally patching to rehydrate the stroma. * **Prognosis:** Usually reversible once the adjacent elevation is removed or the area is rehydrated.

Question 188: What is the approximate refractive power of the cornea?

A. 30 Diopters
B. 44 Diopters (Correct Answer)
C. 55 Diopters
D. 60 Diopters

Explanation: **Explanation:** The total refractive power of the human eye is approximately **+60 Diopters (D)**. The cornea is the major refractive element, contributing roughly two-thirds of this power, while the crystalline lens contributes the remaining one-third. 1. **Why 44 Diopters is correct:** The anterior surface of the cornea (interface with air) has a power of about +48 D, and the posterior surface (interface with aqueous) has a power of about -4 D. This results in a net refractive power of approximately **+43 to +44 D**. This high power is due to the significant difference in refractive indices between air (1.00) and the corneal epithelium (1.376). 2. **Why other options are incorrect:** * **30 D:** This value is too low for the cornea; however, the crystalline lens has a power of approximately **+15 to +20 D** in its resting state. * **55 D:** This exceeds the physiological power of the cornea. * **60 D:** This represents the **total refractive power** of the entire eye (Gullstrand’s schematic eye), not just the cornea. **High-Yield Clinical Pearls for NEET-PG:** * **Refractive Indices:** Cornea (1.376), Aqueous/Vitreous (1.336), Lens (1.39–1.40). * **Radius of Curvature:** The anterior surface of the cornea is flatter (7.8 mm) than the posterior surface (6.5 mm). * **Keratometry:** This is the clinical procedure used to measure the corneal curvature and estimate its refractive power, essential for IOL power calculation. * **Astigmatism:** Since the cornea provides the bulk of the eye's refractive power, minor irregularities in its shape lead to significant refractive errors.

Question 189: What is the most common cause of anterior staphyloma?

A. Corneal Ulcer (Correct Answer)
B. Herpes Keratitis
C. Myopia
D. Hypermetropia

Explanation: **Explanation:** **Anterior staphyloma** is a condition characterized by a bulging, ectatic cicatrix (scar tissue) formed by the incorporation of the iris into a thinned, perforated cornea. **Why Corneal Ulcer is the correct answer:** The most common underlying cause is a **perforating corneal ulcer** (often due to bacterial or fungal infections). When a central corneal ulcer perforates, the iris prolapses forward to plug the defect. Over time, the iris becomes covered by a thin layer of fibrous tissue and epithelium (pseudocornea). Because this newly formed tissue is weaker than the original cornea and cannot withstand normal intraocular pressure (IOP), it stretches and bulges forward, resulting in a dark, lobulated protrusion. **Why the other options are incorrect:** * **Herpes Keratitis:** While it can cause corneal scarring or thinning, it rarely leads to the massive perforation and iris incorporation required to form a staphyloma unless there is secondary bacterial superinfection or severe necrotizing keratitis. * **Myopia:** High myopia is associated with **posterior staphyloma** (bulging of the sclera at the posterior pole), not anterior staphyloma. * **Hypermetropia:** This is a refractive error associated with a shorter axial length and is not a cause of ectatic corneal diseases. **High-Yield Clinical Pearls for NEET-PG:** * **Appearance:** The staphyloma appears bluish-black because the pigmented iris tissue is visible through the thin, stretched pseudocornea. * **Vision:** Vision is typically reduced to "Projection of Rays" (PR) or "Hand Movements" (HM) due to total corneal opacity. * **Management:** For a blind, disfigured eye, the treatment of choice is **Evisceration** or **Staphylectomy**. * **Distinction:** Do not confuse this with **Keratectasia**, which is a protrusion of the cornea without iris involvement.

Question 190: Which of the following are true about keratoconus?

A. Increased curvature of the cornea (Correct Answer)
B. Astigmatism
C. Kayser-Fleischer ring seen
D. Thick cornea

Explanation: **Explanation:** **Keratoconus** is a progressive, non-inflammatory ectatic dystrophy characterized by localized **thinning** and protrusion of the central or paracentral cornea. 1. **Why Option A is Correct:** The hallmark of keratoconus is the cornea assuming a conical shape. This leads to a significant **increase in the curvature** of the cornea (steepening), which can be measured via keratometry or topography (K-values >47D). 2. **Why Options B, C, and D are Incorrect:** * **Option B (Astigmatism):** While keratoconus *causes* high irregular astigmatism, "Increased curvature" is the primary structural definition of the disease. (Note: In many exams, if multiple are true, the most definitive structural change is preferred). * **Option C (Kayser-Fleischer ring):** This is seen in Wilson’s Disease (copper deposition in Descemet’s membrane). In keratoconus, we see the **Fleischer ring**, which is an iron deposition ring at the base of the cone. * **Option D (Thick cornea):** Keratoconus is characterized by progressive **stromal thinning** (pachymetry shows a thin cornea), not thickening. **High-Yield Clinical Pearls for NEET-PG:** * **Early Signs:** Scissoring reflex on retinoscopy, Vogt’s striae (vertical stress lines), and Rizzuti’s sign. * **Late Signs:** **Munson’s sign** (V-shaped indentation of the lower lid on downgaze) and Hydrops (acute rupture of Descemet’s membrane). * **Management:** * Early: Glasses or Rose-K contact lenses. * To stop progression: **CXL (Corneal Collagen Cross-linking)** using Riboflavin and UVA light. * Advanced: Penetrating or Deep Anterior Lamellar Keratoplasty (DALK).

Practice by Chapter

Corneal Anatomy and Physiology

Practice Questions

Bacterial Keratitis

Practice Questions

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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