Diseases of the Cornea Practice Questions

Q: Which nerve is involved in exposure keratopathy?

Seventh cranial nerve. **Explanation:** **Exposure Keratopathy** occurs when the cornea dries out due to incomplete eyelid closure (lagophthalmos). **Why Option C is Correct:** The **Seventh Cranial Nerve (Facial Nerve)** provides motor innervation to the **Orbicularis Oculi** muscle. This muscle is responsible for closing the eyelids. In Facial Nerve Palsy (e.g., Bell’s Palsy), the inability to close the eye leads to constant exposure of the corneal surface, evaporation of the tear film, and subsequent corneal desiccation, ulceration, and scarring. **Why Other Options are Incorrect:** * **Option A (Third Nerve):** The Oculomotor nerve supplies the *Levator Palpebrae Superioris*, which **opens** the eyelid. Damage results in Ptosis (drooping), which actually protects the cornea from exposure. * **Option B (Fifth Nerve):** The Trigeminal nerve (Ophthalmic division) provides **sensory** innervation to the cornea. Damage leads to **Neurotrophic Keratopathy** (loss of trophic factors and blink reflex), not exposure keratopathy. * **Option D (Ninth Nerve):** The Glossopharyngeal nerve is involved in taste and pharyngeal sensations; it has no role in eyelid mechanics or corneal health. **High-Yield Clinical Pearls for NEET-PG:** * **Bell’s Phenomenon:** A protective mechanism where the eyeball rolls upwards and outwards during attempted closure. If this is absent, the risk of exposure keratopathy in 7th nerve palsy increases significantly. * **Management:** Frequent lubricants, taping the lids at night, or **Tarsorrhaphy** (suturing the lids together) in severe cases. * **Differential:** Remember: **7th Nerve** = Exposure Keratopathy; **5th Nerve** = Neurotrophic Keratopathy.

Q: Placido disc is used for which condition?

Keratoconus. **Explanation:** **Placido Disc** (also known as a keratoscope) is a diagnostic tool used to assess the **curvature and regularity of the anterior surface of the cornea**. It consists of a series of concentric black and white rings. When light from the disc reflects off the tear film (acting as a convex mirror), the clinician observes the reflected images (Purkinje-Sanson image I). * **Why Keratoconus is correct:** In a normal cornea, the reflected rings are perfectly circular and concentric. In **Keratoconus**, the cornea assumes a conical shape, causing the reflected rings to appear **distorted, irregular, and crowded** (typically inferiorly). This makes it a classic bedside screening tool for irregular astigmatism and corneal ectasia. **Analysis of Incorrect Options:** * **Uveitis:** This is an intraocular inflammatory condition. Diagnosis relies on slit-lamp examination to look for aqueous cells, flare, and keratic precipitates, not corneal topography. * **Retinoblastoma:** This is a primary intraocular malignancy of childhood. Diagnosis is made via indirect ophthalmoscopy, B-scan ultrasonography, and MRI to identify a calcified mass. * **Retinal Detachment:** This involves the separation of the neurosensory retina from the retinal pigment epithelium. It is diagnosed using indirect ophthalmoscopy and B-scan USG. **High-Yield Clinical Pearls for NEET-PG:** * **Modern Equivalent:** Computerized Video-keratography (Corneal Topography) is the modern evolution of the Placido disc. * **Photokeratoscopy:** The process of photographing the Placido disc reflections. * **Limitation:** Placido-based systems only analyze the **anterior** corneal surface; they cannot provide data on posterior corneal curvature (unlike Scheimpflug imaging/Pentacam). * **Other Keratoconus Signs:** Munson’s sign, Vogt’s striae, Fleischer’s ring, and Rizutti’s sign.

Q: Topical steroids are contraindicated in which ocular condition?

Fungal corneal ulcer. **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)**.

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

Band shaped keratopathy. **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**

Q: Pigment deposition on the cornea is seen in which of the following conditions?

Chloroquine toxicity. **Explanation:** **Chloroquine toxicity** is the correct answer because this drug has a high affinity for melanin-containing tissues. In the cornea, chloroquine (and hydroxychloroquine) deposits in the basal layer of the epithelium, leading to a condition known as **Vortex Keratopathy** (also called **Cornea Verticillata**). This appears as fine, golden-brown or greyish-pigmented deposits arranged in a whorl-like pattern. While these corneal deposits are usually asymptomatic and reversible upon discontinuation, they serve as a clinical marker for potential systemic toxicity. **Analysis of Incorrect Options:** * **Digoxin toxicity:** Primarily causes visual disturbances known as **Dyschromatopsia** (specifically **Xanthopsia**, where objects appear yellow). It does not cause physical pigment deposition on the cornea. * **Ranitidine side effect:** This H2-receptor antagonist is not associated with any specific corneal pigmentary changes or significant ocular toxicity. **High-Yield Clinical Pearls for NEET-PG:** * **Cornea Verticillata (Whorl Keratopathy) Mnemonic:** "CHAI-T" * **C**hloroquine/Hydroxychloroquine * **H**eiodarone (Amiodarone) - Most common cause * **A**tovaquone * **I**ndomethacin * **T**amoxifen (also **Fabry’s Disease**, an X-linked metabolic disorder) * **Chloroquine Retinopathy:** Characterized by a **"Bull’s Eye Maculopathy"** due to RPE atrophy sparing the fovea. * **Amiodarone:** Causes both Cornea Verticillata and anterior subcapsular lens opacities.

Q: What is the radius of curvature of the anterior surface of the cornea?

7.8 mm. ### 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.

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

Can be cultured on nutrient agar enriched with E. coli. **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.

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

Staphylococci. ### 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 1

Which nerve is involved in exposure keratopathy?

Accepted Answer

Seventh cranial nerve

Answer

Third cranial nerve

Answer

Fifth cranial nerve

Answer

Ninth cranial nerve

Question 2

Which of the following conditions is a type of neurocristopathy?

Accepted Answer

ICE syndrome

Answer

Macular dystrophy

Answer

Arcus senilis

Answer

Band shaped keratopathy

Question 3

Placido disc is used for which condition?

Accepted Answer

Keratoconus

Answer

Uveitis

Answer

Retinoblastoma

Answer

Retinal detachment

Question 4

Topical steroids are contraindicated in which ocular condition?

Accepted Answer

Fungal corneal ulcer

Answer

Anterior uveitis

Answer

Posterior uveitis

Answer

Mooren's ulcer

Question 5

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

Accepted Answer

Band shaped keratopathy

Answer

Keratoconus

Answer

Acanthamoebic keratitis

Answer

Refsum syndrome

Question 6

Pigment deposition on the cornea is seen in which of the following conditions?

Accepted Answer

Chloroquine toxicity

Answer

Digoxin toxicity

Answer

Ranitidine side effect

Answer

All of the above

Question 7

What is the radius of curvature of the anterior surface of the cornea?

Accepted Answer

7.8 mm

Answer

8.4 mm

Answer

5.8 mm

Answer

4.8 mm

Question 8

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

Accepted Answer

Can be cultured on nutrient agar enriched with E. coli

Answer

Common in contact lens users

Answer

Ring abscess may be seen

Answer

Pain is typically very severe

Question 9

What is the most common causative organism of corneal ulcer?

Accepted Answer

Staphylococci

Answer

Pneumococci

Answer

Streptococci

Answer

Fungal

Question 10

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?

Accepted Answer

Cornea verticillata

Answer

Terrien's marginal degeneration

Answer

Band-shaped keratopathy

Answer

Arcus juvenilis

Diseases of the Cornea — MCQs

Diseases of the Cornea — MCQs

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