Diseases of the Cornea — MCQs

Diseases of the Cornea Indian Medical PG Practice Questions and MCQs

Question 431: What is the most common cause of corneal neovascularization in developed countries?

A. Hypoxia from contact lens use (Correct Answer)
B. Transplant rejection
C. Viral infection
D. All of the options

Explanation: ***Hypoxia from contact lens use*** - **Chronic or severe corneal hypoxia** due to prolonged or improper contact lens wear is the **most frequent cause** of corneal neovascularization in developed countries. - The cornea, being avascular, depends on atmospheric oxygen. When deprived, it attempts to compensate by growing new blood vessels from the limbal arcade. - This is particularly common with **extended-wear contact lenses**, poorly fitting lenses, or **overwear syndrome** that restricts oxygen transmission to the cornea. - Modern **high-Dk (oxygen permeability) lenses** have reduced this complication, but it remains the leading cause. *Transplant rejection* - While corneal transplant rejection can cause inflammation and neovascularization, it affects only the **post-keratoplasty population**, making it far less common as an overall cause. - Rejection typically presents with **epithelial or stromal edema**, keratic precipitates, and graft clouding, with neovascularization being a secondary feature. *Viral infection* - Viral infections, particularly **herpes simplex keratitis**, can cause **significant corneal neovascularization** through chronic inflammation and stromal damage. - While HSV keratitis is an important cause, especially in recurrent cases, contact lens-related hypoxia affects a much larger population in developed countries. *All of the options* - While transplant rejection and viral infection can lead to corneal neovascularization, **hypoxia from contact lens use is the most prevalent cause** in modern clinical practice in developed countries. - The other options represent important but less frequent causes or affect smaller patient populations.

Question 432: Which of the following statements is true regarding fungal corneal ulcers?

A. Immunosuppressant therapy increases vulnerability to fungal infections.
B. Aspergillus and Fusarium are common organisms causing fungal corneal ulcers. (Correct Answer)
C. Microbiological confirmation is ideal before starting antifungal treatment but may not always be mandatory.
D. Symptoms are more prominent than signs in patients with fungal corneal ulcers

Explanation: ***Aspergillus and Fusarium are common organisms causing fungal corneal ulcers.*** - *Aspergillus* and *Fusarium* species are the two most frequently isolated fungi in cases of **fungal keratitis**, especially in tropical and subtropical regions. - These fungi are commonly found in the environment and can cause infection after **corneal trauma** involving organic matter (vegetative matter, soil). - Aspergillus is more common in temperate climates, while Fusarium predominates in tropical regions. *Immunosuppressant therapy increases vulnerability to fungal infections.* - While this statement is medically correct, systemic immunosuppression has less direct impact on **fungal keratitis** risk compared to local factors. - More important risk factors include: **corneal trauma** (especially with vegetative matter), **chronic topical corticosteroid use**, **contact lens wear**, and **pre-existing corneal disease**. - Systemic immunosuppression is more relevant for deep/systemic fungal infections rather than superficial corneal infections. *Microbiological confirmation is ideal before starting antifungal treatment but may not always be mandatory.* - While this statement has practical merit, **microbiological confirmation is strongly recommended** in all suspected cases of fungal keratitis. - **Corneal scraping** for KOH mount, Gram stain, and culture should be performed before starting treatment whenever possible. - However, in clinically suspicious cases, **empiric antifungal therapy may be initiated** while awaiting culture results to prevent disease progression. - This option is incorrect because standard practice emphasizes the importance of obtaining microbiological diagnosis, even if empiric treatment is started simultaneously. *Symptoms are more prominent than signs in patients with fungal corneal ulcers.* - This is **incorrect** - fungal keratitis typically presents with **prominent clinical signs** including: - Feathery or irregular infiltrate borders - Satellite lesions - Endothelial plaque - Ring infiltrate (in severe cases) - These characteristic signs are often **more impressive than the symptoms**, especially in the early stages. - Fungal keratitis has a more indolent course compared to bacterial keratitis, with signs often preceding severe symptoms.

Question 433: Xerophthalmia Grade X-3A is

A. Corneal xerosis
B. Bitot spot
C. Corneal ulcer affecting more than 1/3 of corneal surface
D. Corneal ulcer affecting less than 1/3 of the corneal surface (Correct Answer)

Explanation: ***Corneal ulcer affecting less than 1/3 of the corneal surface*** - **Xerophthalmia Grade X-3A** specifically denotes corneal ulceration with **xerosis**, affecting **less than one-third of the corneal surface**. - This classification is crucial for assessing the severity of **vitamin A deficiency-induced ocular damage**. *Corneal xerosis* - This condition is classified as **Xerophthalmia Grade X-2** and refers to dryness of the cornea without ulceration. - While present in X-3A, it alone does not define the grade; ulceration is the defining feature of X-3A. *Bitot spot* - **Bitot spots** are classified as **Xerophthalmia Grade X-1B** and are characterized by foamy, white patches on the conjunctiva due to keratinization. - This is a less severe manifestation of vitamin A deficiency, affecting the conjunctiva rather than the cornea with ulceration. *Corneal ulcer involving more than 1/3 of corneal surface* - A **corneal ulcer involving more than one-third of the corneal surface** is classified as **Xerophthalmia Grade X-3B**. - This grade indicates more severe involvement and a higher risk of permanent visual impairment compared to X-3A.

Question 434: Density of cells in adult corneal endothelium is

A. 2000 cells/mm2
B. 3000 cells/mm2 (Correct Answer)
C. 4000 cells/mm2
D. 5000 cells/mm2

Explanation: ***3000 cells/mm2*** - The **normal density** of corneal endothelial cells in a young adult is approximately **3000-3500 cells/mm²**. - This density is crucial for maintaining corneal clarity through its **pump function**. *2000 cells/mm2* - A density of **2000 cells/mm²** or lower in the corneal endothelium indicates a significantly reduced cell count. - This level is often considered the **minimum threshold** below which the cornea may lose its ability to remain clear, leading to **corneal edema**. *4000 cells/mm2* - While some individuals, especially younger ones, might have slightly higher densities, **4000 cells/mm²** is generally above the typical average for an adult. - This higher density is more common in **infants and young children**, where cell count is higher and gradually declines with age. *5000 cells/mm2* - A cell density of **5000 cells/mm²** is significantly higher than the normal adult range and is usually observed only in **neonates** or very young infants. - Such high densities are indicative of a developing or very young endothelium, not a typical adult state.

Question 435: What is the primary cause of snow blindness?

A. UV rays (Correct Answer)
B. Infrared radiation
C. Microwave radiation
D. Defect in optical devices

Explanation: **UV rays** - **Snow blindness**, clinically known as **photokeratitis**, is primarily caused by exposure of the eyes to high levels of **ultraviolet (UV) radiation**. - This radiation is particularly intense in snow-covered environments due to the **high reflectivity of snow**, which can reflect up to 80% of UV rays, effectively exposing the eyes to double the amount of UV. *Infrared radiation* - While infrared radiation can cause **heat-related injury** to the eyes (e.g., glassblower's cataract), it does not directly lead to the corneal damage characteristic of snow blindness. - Infrared radiation is sensed as heat and is not responsible for the **phototoxic effect** on the cornea. *Microwave radiation* - Microwave radiation can cause internal heating of tissues, but it is not a direct cause of photokeratitis or snow blindness. - Exposure to high levels of microwave radiation can lead to other ocular issues like **cataracts**, but through different mechanisms. *Defect in optical devices* - While defective optical devices (e.g., sunglasses without proper UV protection) can *contribute* to snow blindness by failing to block UV radiation, they are not the primary cause themselves. - The underlying harmful agent is the **UV radiation**, and the defect merely allows the exposure to occur.

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

Practice Questions

Keratoconus and Ectatic Disorders

Practice Questions

Corneal Transplantation

Practice Questions

Corneal Topography and Imaging

Practice Questions

Dry Eye Disease

Practice Questions

Corneal Trauma

Practice Questions

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