Diseases of the Cornea — MCQs

Diseases of the Cornea Indian Medical PG Practice Questions and MCQs

Question 161: 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?

A. Nuclear cataract
B. Dry eyes
C. Keratoconus (Correct Answer)
D. Irregular astigmatism

Explanation: **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.

Question 162: Which of the following is the least common corneal dystrophy?

A. Macular dystrophy (Correct Answer)
B. Lattice type I
C. Lattice type III
D. Granular corneal dystrophy

Explanation: **Explanation:** Corneal dystrophies are a group of genetic, bilateral, non-inflammatory opacifications of the cornea. Among the stromal dystrophies, **Macular Corneal Dystrophy (MCD)** is the **least common** but clinically the most severe. **Why Macular Dystrophy is the correct answer:** While Lattice and Granular dystrophies are more prevalent worldwide, Macular dystrophy is rare. It is unique because it is the only stromal dystrophy inherited in an **Autosomal Recessive (AR)** pattern (the others are Autosomal Dominant). It involves the deposition of **Acid Mucopolysaccharides** (Glycosaminoglycans) due to a mutation in the *CHST6* gene. It affects the entire thickness of the stroma and extends to the periphery, leading to early vision loss. **Analysis of Incorrect Options:** * **Lattice Type I:** This is the most common type of stromal dystrophy. It is characterized by amyloid deposits (stained by Congo Red) forming lattice-like branching lines. * **Granular Dystrophy:** This is relatively common and characterized by "crumb-like" hyaline deposits (stained by Masson Trichrome). It typically spares the peripheral cornea. * **Lattice Type III:** While rarer than Type I, it is still considered a variant of the most common dystrophy group and is more frequent in specific populations (e.g., Japan) compared to the global rarity of Macular dystrophy. **NEET-PG High-Yield Pearls:** * **Mnemonic for Stains (Marilyn Monroe Always Gets Her Men in L.A.):** * **M**acular: **A**lcian Blue (**M**ucopolysaccharide) * **G**ranular: **H**yaline (**M**asson Trichrome) * **L**attice: **A**myloid (Congo Red/Apple-green birefringence) * **Inheritance:** All are AD except Macular (AR). * **Recurrence:** Macular dystrophy has the highest rate of recurrence after corneal transplantation (Keratoplasty).

Question 163: Which organism can invade the intact corneal epithelium and produce a purulent corneal ulcer?

A. Neisseria meningitidis (Correct Answer)
B. Pseudomonas pyocyanea
C. Pneumococcus
D. Streptococcus haemolyticus

Explanation: **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.

Question 164: What anatomical structure is defined by Schwalbe's line?

A. The posterior limit of Descemet's membrane of the cornea (Correct Answer)
B. The posterior limit of Bowman's membrane of the cornea
C. The anterior limit of Descemet's membrane of the cornea
D. The anterior limit of Bowman's membrane of the cornea

Explanation: **Explanation:** **Schwalbe’s line** represents the anatomical junction where the corneal endothelium and **Descemet’s membrane** terminate and the trabecular meshwork begins. Specifically, it is the **posterior limit (termination) of Descemet’s membrane**. On gonioscopy, it appears as a thin, pearly-white line and serves as the most anterior landmark of the iridocorneal angle. * **Why Option A is correct:** Descemet’s membrane ends abruptly at the peripheral cornea; this termination point is histologically and clinically identified as Schwalbe’s line. * **Why Options B and D are incorrect:** Bowman’s membrane is a more superficial layer of the cornea. It ends peripherally before reaching the limbus and does not contribute to the structures of the iridocorneal angle. * **Why Option C is incorrect:** The anterior limit of Descemet’s membrane is located centrally (near the corneal apex), whereas Schwalbe’s line is a peripheral structure. **High-Yield Clinical Pearls for NEET-PG:** 1. **Gonioscopy Landmark:** Schwalbe’s line is the first structure identified during gonioscopy. It is crucial for orienting the examiner to the angle structures (from anterior to posterior: Schwalbe’s line → Non-pigmented TM → Pigmented TM → Scleral spur → Ciliary body band → Iris root). 2. **Sampaolesi Line:** In conditions like Pigmentary Glaucoma or Pseudoexfoliation Syndrome, pigment may deposit on or anterior to Schwalbe’s line, forming a "Sampaolesi line." 3. **Posterior Embryotoxon:** An abnormally thickened and anteriorly displaced Schwalbe’s line is known as Posterior Embryotoxon, which can be an isolated finding or associated with Alagille syndrome or Axenfeld-Rieger syndrome.

Question 165: Decreased corneal sensations can be seen in which of the following conditions?

A. Bacterial corneal ulcer
B. Mycotic corneal ulcer
C. Leprosy (Correct Answer)
D. Interstitial keratitis

Explanation: **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 166: What causes satellite lesions in the eye?

A. Herpes zoster
B. Herpes simplex
C. Aspergillosis (Correct Answer)
D. Trachoma

Explanation: **Explanation:** The presence of **satellite lesions** is a hallmark clinical feature of **Fungal Keratitis**, most commonly caused by filamentous fungi like *Aspergillus* and *Fusarium*. **1. Why Aspergillosis is correct:** Fungal hyphae have the ability to penetrate deep into the corneal stroma and spread sideways, bypassing the host's inflammatory response. Satellite lesions are small, isolated infiltrates located away from the main ulcer margin, connected by invisible fungal filaments. Other characteristic features of fungal ulcers include a "dry, leathery" appearance, feathery margins, and an immune ring (Wessely ring). **2. Why the other options are incorrect:** * **Herpes Simplex (HSV):** Typically presents with a **dendritic ulcer** (linear, branching with terminal bulbs) or a geographic ulcer. It is characterized by decreased corneal sensations. * **Herpes Zoster (VZV):** Presents with **pseudodendrites** (elevated, no terminal bulbs, stain poorly with fluorescein) and follows a dermatomal distribution (Hutchinson’s sign). * **Trachoma:** Caused by *Chlamydia trachomatis* (Serotypes A-C). It is characterized by **Herbert’s pits**, Arlt’s line, and follicles on the superior tarsal conjunctiva, not satellite stromal lesions. **High-Yield Clinical Pearls for NEET-PG:** * **Risk Factor:** History of trauma with **vegetative matter** (e.g., a branch or leaf) is the most common predisposing factor for fungal keratitis. * **Hypopyon:** Fungal ulcers often present with a **fixed hypopyon** (does not move with head tilt) due to the sticky nature of the exudate. * **Diagnosis:** The gold standard is corneal scraping followed by **KOH mount** (shows hyphae) or culture on **Sabouraud’s Dextrose Agar (SDA)**. * **Treatment:** Topical **Natamycin (5%)** is the drug of choice for filamentous fungi like *Aspergillus*.

Question 167: Hypopyon corneal ulcer is caused by which microorganism?

A. Pneumococcus (Correct Answer)
B. Pseudomonas
C. Herpes simplex
D. Neisseria gonorrhoeae

Explanation: **Explanation:** The correct answer is **Pneumococcus (*Streptococcus pneumoniae*)**. A **Hypopyon corneal ulcer** (also known as *Ulcus Serpens*) is characterized by a creeping, grayish-white disc-shaped ulcer with a collection of sterile pus in the anterior chamber (hypopyon). Pneumococcus is the most common causative organism for this specific clinical presentation. The hypopyon is formed due to the diffusion of bacterial toxins into the anterior chamber, which triggers an inflammatory response from the iris and ciliary body vessels, leading to the accumulation of leucocytes. **Analysis of Options:** * **Pneumococcus (Correct):** Classically associated with *Ulcus Serpens*. It typically occurs following minor trauma, often with organic matter, and is frequently associated with chronic dacryocystitis. * **Pseudomonas:** While it causes a very aggressive and rapidly spreading corneal ulcer, it is characterized by a **greenish-yellow discharge** and extensive liquefactive necrosis (melting) of the cornea. * **Herpes simplex:** Causes **Dendritic ulcers** (true ulcers) or Geographic ulcers. These are viral and do not typically present with a classic bacterial hypopyon unless there is a secondary bacterial infection. * **Neisseria gonorrhoeae:** Notable for its ability to **penetrate an intact corneal epithelium**, causing hyperacute purulent conjunctivitis and rapid ulceration, but it is not the primary cause of the classic "hypopyon ulcer." **Clinical Pearls for NEET-PG:** * **Ulcus Serpens:** The name refers to the "creeping" nature of the ulcer margin. * **Source of Infection:** Always check the lacrimal sac in cases of Pneumococcal ulcers; **Chronic Dacryocystitis** is a common silent reservoir. * **Sterile Hypopyon:** In fungal and bacterial ulcers, the hypopyon is usually sterile (no actual bacteria in the AC) because the toxins, not the organisms, penetrate the Descemet’s membrane. * **Fungal Hypopyon:** Unlike bacterial hypopyon, fungal hypopyon is often thick, non-mobile, and may contain actual fungal hyphae.

Question 168: Which of the following is the least common corneal dystrophy?

A. Macular dystrophy (Correct Answer)
B. Lattice type I
C. Lattice type III
D. Granular corneal dystrophy

Explanation: **Explanation:** Corneal dystrophies are a group of genetic, bilateral, non-inflammatory opacifications. Among the stromal dystrophies, **Macular Corneal Dystrophy (MCD)** is the **least common** but clinically the **most severe**. **1. Why Macular Dystrophy is the correct answer:** While Granular and Lattice dystrophies are more prevalent worldwide, Macular dystrophy is rare. It is unique because it is the only stromal dystrophy inherited in an **Autosomal Recessive (AR)** fashion (others are Autosomal Dominant). It involves the accumulation of **Acid Mucopolysaccharides** (stained by **Alcian Blue** or Colloidal Iron) and affects the entire thickness of the stroma, extending to the periphery, leading to early vision loss. **2. Why other options are incorrect:** * **Lattice Dystrophy (Type I):** This is the **most common** type of stromal dystrophy. It is characterized by amyloid deposits (stained by **Congo Red**) forming branching filaments. * **Granular Dystrophy:** This is a common dystrophy characterized by "crumb-like" opacities. It involves **Hyaline** deposits (stained by **Masson Trichrome**). * **Lattice Type III:** While rarer than Type I, it is still a recognized variant of the most common dystrophy group. In the context of "least common" among the primary types, Macular Dystrophy is the standard textbook answer. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Stains (M-A-G-H-L-A):** * **M**acular: **A**lcian Blue * **G**ranular: **H**yaline (Masson Trichrome) * **L**attice: **A**myloid (Congo Red) * **Inheritance:** All stromal dystrophies are **AD** except **Macular**, which is **AR**. * **Recurrence:** Lattice dystrophy has the highest rate of recurrence after keratoplasty.

Question 169: Ascorbic acid transport in the cornea is mediated by which mechanism?

A. Carbonic anhydrase pump
B. Na+/K+ pump (Correct Answer)
C. Myoinositol pump
D. Passive diffusion

Explanation: ### Explanation **Correct Answer: B. Na+/K+ pump** The corneal endothelium is responsible for maintaining **corneal deturgescence** (a state of relative dehydration), which is essential for corneal transparency. This is achieved through a "Pump-Leak" mechanism. The **Na+/K+ ATPase pump**, located on the basolateral membrane of the corneal endothelial cells, is the primary driver of this process. It actively transports sodium ions out of the stroma into the aqueous humor. This creates an osmotic gradient that draws water out of the stroma. **Ascorbic acid (Vitamin C)**, which is present in high concentrations in the aqueous humor to protect against oxidative stress, is co-transported into the cornea via mechanisms coupled with these active ion gradients established by the Na+/K+ pump. #### Analysis of Incorrect Options: * **A. Carbonic anhydrase pump:** While carbonic anhydrase is present in the endothelium and aids in bicarbonate transport (which contributes to the osmotic gradient), it is not the primary mediator for ascorbic acid transport. * **C. Myoinositol pump:** This is primarily associated with the lens metabolism and the pathophysiology of diabetic cataracts, rather than corneal electrolyte/ascorbate balance. * **D. Passive diffusion:** While small molecules and water "leak" into the cornea via passive diffusion, the transport of ascorbic acid against a concentration gradient requires active, mediated transport. #### NEET-PG High-Yield Pearls: * **Transparency:** Maintained by the Na+/K+ ATPase pump and the anatomical arrangement of collagen fibrils (Lattice theory of Maurice). * **Endothelial Cell Count:** Normal is **2500–3000 cells/mm²**. If the count falls below **500 cells/mm²**, corneal decompensation and edema occur. * **Energy Source:** The cornea derives its glucose primarily from the **aqueous humor** and its oxygen from the **atmosphere** (via the precorneal tear film). * **Storage:** Ascorbic acid acts as a potent antioxidant in the anterior segment, protecting the cornea and lens from UV-induced free radical damage.

Question 170: Radial keratotomy is performed for which of the following refractive errors or conditions?

A. Myopia (Correct Answer)
B. Hypermetropia
C. Corneal scar
D. All the above

Explanation: **Explanation:** **Radial Keratotomy (RK)** is a refractive surgical procedure designed specifically to correct **Myopia** (nearsightedness). 1. **Why Myopia is Correct:** In myopia, the eye is either too long or the cornea is too steep, causing light to focus in front of the retina. RK involves making a series of deep, non-perforating radial incisions (usually 4 to 8) in the peripheral cornea using a diamond knife. These incisions weaken the peripheral corneal structure, causing the intraocular pressure to push the periphery outward. This results in a compensatory **flattening of the central cornea**, thereby reducing its refractive power and shifting the focal point back onto the retina. 2. **Why other options are incorrect:** * **Hypermetropia:** This requires *steepening* of the central cornea, not flattening. Procedures like Hexagonal Keratotomy or Conductive Keratoplasty were historically used, but RK would worsen hypermetropia. * **Corneal Scar:** RK is a refractive procedure performed on clear corneas. A corneal scar would interfere with the precision of the incisions and likely worsen visual acuity. Scars are typically managed with Keratoplasty (PK or DALK) or PTK (Phototherapeutic Keratectomy). **High-Yield Clinical Pearls for NEET-PG:** * **Lans’ Laws:** The physiological basis of RK is based on Lans’ Law, which states that an incision in the cornea causes flattening in the meridian of the incision. * **Complications:** A classic side effect of RK is **diurnal fluctuation of vision** and **progressive hyperopic shift** (the eye becomes more farsighted over years). * **Historical Context:** RK has largely been replaced by laser-based procedures like LASIK, PRK, and SMILE due to better predictability and safety. * **Contraindication:** RK is strictly contraindicated in patients with Keratoconus.

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

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Keratoconus and Ectatic Disorders

Practice Questions

Corneal Transplantation

Practice Questions

Corneal Topography and Imaging

Practice Questions

Dry Eye Disease

Practice Questions

Corneal Trauma

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