Diseases of the Cornea Practice Questions

Q: A 30-year-old male presents with a 10-day history of decreased vision in his left eye. He reports trauma to the left eye with vegetative matter 10-15 days prior. Examination reveals an ulcerative corneal lesion with a raised, creamy infiltrate at the base. The ulcer margin is feathery and shows hyphae, with a few satellite lesions present. What is the most probable etiological agent?

Fusarium. **Explanation:** The clinical presentation is a classic case of **Fungal Keratitis**. The diagnosis is established through the history of trauma with **vegetative matter** (e.g., a stick or leaf) and specific morphological features of the ulcer. **Why Fusarium is correct:** * **Vegetative Trauma:** This is the most common predisposing factor for fungal keratitis. * **Clinical Signs:** The presence of a **creamy-white/grayish infiltrate**, **feathery margins** (representing fungal hyphae spreading into the stroma), and **satellite lesions** (smaller infiltrates away from the main ulcer) are pathognomonic for filamentous fungi like *Fusarium* and *Aspergillus*. *Fusarium* is the most common cause of fungal keratitis in tropical regions like India. **Why other options are incorrect:** * **Acanthamoeba:** Typically associated with contact lens wear or exposure to contaminated water. It presents with disproportionate pain and a characteristic **ring-shaped infiltrate**. * **Corynebacterium diphtheriae:** A rare cause of bacterial keratitis that is unique because it can penetrate an **intact corneal epithelium**. It usually presents with membranous conjunctivitis. * **Streptococcus pneumoniae:** A common cause of bacterial keratitis (Ulcus Serpens). It typically presents as a rapidly progressing, painful ulcer with a **shaggy base** and a prominent **hypopyon**, but lacks feathery margins or satellite lesions. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard Investigation:** Corneal scraping for **KOH mount** (shows hyphae) and culture on **Sabouraud’s Dextrose Agar (SDA)**. * **Drug of Choice:** Topical **Natamycin (5%)** is the first-line treatment for filamentous fungi like *Fusarium*. * **Key Distinction:** Bacterial ulcers usually have "wet" suppuration and well-defined margins, whereas fungal ulcers have a "dry" look with "feathery" margins.

Q: What is the characteristic feature of Herpes Simplex Keratitis?

Dendritic ulcer. **Explanation:** **1. Why Dendritic Ulcer is Correct:** The hallmark of **Herpes Simplex Keratitis (HSK)**, specifically the epithelial form, is the **dendritic ulcer**. This occurs due to active viral replication in the corneal epithelium. The ulcer is characterized by a linear, branching (arborescent) pattern with **terminal bulbs** (knob-like ends). These ulcers stain brilliantly with **Fluorescein** (staining the floor/bed) and **Rose Bengal** (staining the devitalized cells at the margins). A key clinical finding is **decreased corneal sensations** due to trigeminal nerve involvement. **2. Analysis of Incorrect Options:** * **A. Disciform keratitis:** While this is a manifestation of HSK, it is an **endotheliitis** (immune-mediated) rather than the primary characteristic epithelial lesion. It presents as central stromal edema without an active ulcer. * **C. Haab’s striae:** These are horizontal or curvilinear breaks in Descemet’s membrane seen in **Congenital Glaucoma** (Buphthalmos) due to increased intraocular pressure. * **D. Band keratopathy:** This refers to the horizontal deposition of calcium in the Bowman’s layer, typically seen in chronic uveitis, hypercalcemia, or silicone oil in the eye. **3. High-Yield Clinical Pearls for NEET-PG:** * **Treatment:** Topical **Acyclovir (3%)** or Ganciclovir gel. **Steroids are strictly contraindicated** in dendritic ulcers as they can lead to a "Geographic ulcer." * **Geographic Ulcer:** A large, amoeboid ulcer formed when a dendritic ulcer expands, often due to inappropriate steroid use. * **Recurrence:** HSV remains latent in the **Trigeminal Ganglion**. * **Differential Diagnosis:** *Herpes Zoster Keratitis* also causes dendrites, but they are "pseudodendrites" (elevated, no terminal bulbs, and stain poorly with fluorescein).

Q: What are the causes of corneal neovascularisation?

All of the above. **Explanation:** The cornea is a unique, **avascular** structure. Its transparency is maintained by a delicate balance between angiogenic factors (like VEGF) and anti-angiogenic factors (like PEDF). **Corneal neovascularization (CNV)** occurs when this balance is disrupted by chronic hypoxia, inflammation, or limbal stem cell deficiency, leading to the ingrowth of vessels from the limbal vascular plexus. * **Transplantation Rejection (Option A):** Immune-mediated inflammation following a keratoplasty triggers the release of inflammatory cytokines and pro-angiogenic factors. Neovascularization is both a sign of rejection and a risk factor for future graft failure. * **Infection (Option B):** Keratitis (bacterial, viral like HSV, or fungal) causes significant tissue hypoxia and inflammatory cell infiltration, which stimulates the growth of new vessels as part of the wound-healing response. * **Contact Lens Use (Option C):** This is a common cause of **chronic hypoxia**. Tight-fitting or extended-wear lenses reduce the oxygen supply to the corneal epithelium, triggering the release of VEGF and subsequent superficial neovascularization (pannus). Since all three conditions are established triggers for the loss of corneal angiogenic privilege, **Option D** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **Pannus:** Superficial vascularization accompanied by infiltration of granulation tissue (commonly seen in Trachoma and Phlyctenular Keratoconjunctivitis). * **Ghost Vessels:** Regressed, non-perfused vessels that remain in the stroma after the primary stimulus is removed; they can be seen on slit-lamp examination. * **Management:** Topical steroids or NSAIDs are used to reduce inflammation; anti-VEGF agents (e.g., Bevacizumab) are increasingly used to regress active vessels.

Q: What is true about the cornea?

All of the above.. The cornea is the primary refractive element of the eye, contributing approximately two-thirds of its total optical power. ### **Detailed Explanation** * **Option A (Refractive Power):** The total refractive power of the eye is roughly +60 D. The cornea accounts for approximately **+43 to +45 D**, while the crystalline lens contributes the remaining +15 to +19 D. * **Option B (Air-Tear Interface):** Refraction occurs when light passes between media of different refractive indices. The greatest change in refractive index occurs at the **air (1.000) to tear film/corneal epithelium (1.376) interface**, making this the site where the majority of light bending occurs. * **Option C (With-the-Rule Astigmatism):** In "With-the-rule" (WTR) astigmatism, the **vertical meridian is steeper** than the horizontal meridian (resembling a football lying on its side). This is common in children and young adults due to the pressure exerted by the eyelids on the globe. As people age, they often shift toward "Against-the-rule" astigmatism (horizontal meridian steeper). Since all statements are physiologically accurate, **Option D** is the correct answer. ### **High-Yield Clinical Pearls for NEET-PG** * **Refractive Indices:** Cornea (1.376), Aqueous/Vitreous (1.336), Lens (1.39–1.41). * **Corneal Layers:** There are 6 layers (Dua’s layer is the 6th, located between the stroma and Descemet’s membrane). * **Metabolism:** The cornea derives its oxygen primarily from the **atmosphere** (via tears) and its glucose from the **aqueous humor**. * **Transparency:** Maintained by the **pump-leak mechanism** (Endothelial Na+/K+ ATPase pump) and the lattice-like arrangement of collagen fibrils (Maurice’s theory).

Q: What is the definition of Keratoconus?

Cornea thins near the center and bulges forwards. **Explanation:** **Keratoconus** is a non-inflammatory, progressive ectatic dystrophy of the cornea. The correct answer is **C** because the hallmark of the disease is the progressive **thinning and weakening of the corneal stroma**, which causes the cornea to lose its spherical shape and bulge forward into a **cone-like configuration**. This typically occurs paracentrally (usually inferonasally), leading to high irregular myopic astigmatism. **Analysis of Incorrect Options:** * **Option A:** Degeneration of the conjunctiva refers to conditions like **Pinguecula** or **Pterygium**, which do not involve the corneal curvature or thickness. * **Option B:** Cornea undergoing necrosis due to Vitamin A deficiency is the definition of **Keratomalacia**, a severe stage of Xerophthalmia. * **Option C:** Recurrent corneal ulcerations are characteristic of conditions like **Herpes Simplex Keratitis** or recurrent corneal erosion syndrome, not structural ectasia. **High-Yield Clinical Pearls for NEET-PG:** * **Early Signs:** Fleischer’s ring (iron deposition at the base of the cone) and Vogt’s striae (vertical stress lines in the stroma). * **Late Signs:** Munson’s sign (indentation of the lower lid on down-gaze) and Rizutti’s sign (conical reflection on the nasal iris). * **Acute Hydrops:** Caused by a rupture in **Descemet’s membrane**, leading to sudden corneal edema. * **Management:** Rigid Gas Permeable (RGP) lenses for vision; **Collagen Cross-linking (CXL/C3R)** to stop progression; Keratoplasty for advanced cases. * **Association:** Often associated with Down syndrome, Atopy (eye rubbing), and Marfan syndrome.

Question 1

A Fleischer ring is a distinct feature of which of the following conditions?

Accepted Answer

Pterygium

Answer

Keratoconus

Answer

Congenital ocular melanosis

Answer

Congenital epithelial melanosis

Question 2

A patient on amiodarone presents with cornea verticillata. What is the management?

Accepted Answer

Penetrating keratoplasty

Answer

Stop the drug

Answer

Lamellar keratoplasty

Answer

No intervention needed

Question 3

Which of the following statements regarding corneal transplantation is true?

Accepted Answer

Specular microscopy analysis is used to assess endothelial cell count

Answer

Whole eye needs to be preserved in tissue culture

Answer

Donor age greater than 60 years is not accepted

Answer

HLA matching is mandatory

Question 4

A 30-year-old male presents with a 10-day history of decreased vision in his left eye. He reports trauma to the left eye with vegetative matter 10-15 days prior. Examination reveals an ulcerative corneal lesion with a raised, creamy infiltrate at the base. The ulcer margin is feathery and shows hyphae, with a few satellite lesions present. What is the most probable etiological agent?

Accepted Answer

Fusarium

Answer

Acanthamoeba

Answer

Corynebacterium diphtheriae

Answer

Streptococcus pneumoniae

Question 5

A person with prolonged usage of contact lenses presented with irritation of the left eye. After examination, a diagnosis of keratitis was made, and corneal scrapings revealed the growth of Pseudomonas aeruginosa. The bacteria were observed to be multidrug resistant. Which of the following best explains the mechanism of antimicrobial resistance in these isolated Pseudomonas aeruginosa strains?

Accepted Answer

Ability of Pseudomonas to produce biofilms

Answer

Ability to transfer resistance genes from adjacent commensal flora

Answer

Improper contact lens hygiene

Answer

Frequent and injudicious use of topical antibiotics

Question 6

What is the characteristic feature of Herpes Simplex Keratitis?

Accepted Answer

Dendritic ulcer

Answer

Disciform keratitis

Answer

Haab's striae

Answer

Band keratopathy

Question 7

What are the causes of corneal neovascularisation?

Accepted Answer

All of the above

Answer

Transplantation rejection

Answer

Infection

Answer

Contact lens use

Question 8

What is true about the cornea?

Accepted Answer

All of the above.

Answer

Its refractive power is 43 D.

Answer

The majority of refraction occurs at the air-tear interface.

Answer

With-the-rule astigmatism is present because the vertical meridian is steeper than the horizontal meridian.

Question 9

What is the percentage of endothelial cell loss in Descemet's Stripping Automated Endothelial Keratoplasty?

Accepted Answer

30 - 40%

Answer

5%

Answer

10 - 20%

Answer

50 - 60%

Question 10

What is the definition of Keratoconus?

Accepted Answer

Cornea thins near the center and bulges forwards

Answer

Degeneration of conjunctiva

Answer

Cornea undergoes necrosis due to vitamin A deficiency

Answer

Recurrent corneal ulcerations of the cornea

Diseases of the Cornea — MCQs

Diseases of the Cornea — MCQs

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