Diseases of the Cornea Practice Questions

Q: Corneal sensation is lost in which of the following conditions?

Herpes simplex. ***Herpes simplex*** - **Herpes simplex keratitis** frequently causes **corneal hypoesthesia** or **anesthesia** due to viral damage to corneal nerves. - This loss of sensation can predispose to **neurotrophic keratopathy** and impaired healing. *Conjunctivitis* - While conjunctivitis can cause **ocular irritation** and pain, it generally **does not directly affect corneal sensation** as it primarily involves the conjunctiva. - Corneal sensation typically remains intact unless there's an associated corneal involvement like a severe keratitis. *Fungal infection* - **Fungal keratitis** can be severe and affect the integrity of the cornea, but **loss of corneal sensation** is not a primary or characteristic feature. - Patients often present with pain, blurred vision, and a dense infiltrate, but **nerve damage leading to hypoesthesia** is less common than in herpes simplex. *Trachoma* - Trachoma is a chronic **chlamydial infection** primarily affecting the conjunctiva, leading to scarring, most notably of the tarsal conjunctiva, and potentially **trichiasis** and corneal opacification. - It does not typically cause **loss of corneal sensation**; instead, irritation results from entropion and trichiasis.

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

Hypoxia from contact lens use. ***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.

Q: What is the primary cause of snow blindness?

UV rays. **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.

Q: Density of cells in adult corneal endothelium is

3000 cells/mm2. ***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 1

Corneal sensation is lost in which of the following conditions?

Accepted Answer

Herpes simplex

Answer

Conjunctivitis

Answer

Fungal infection

Answer

Trachoma

Question 2

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

Accepted Answer

Hypoxia from contact lens use

Answer

Transplant rejection

Answer

Viral infection

Answer

All of the options

Question 3

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

Accepted Answer

Aspergillus and Fusarium are common organisms causing fungal corneal ulcers.

Answer

Immunosuppressant therapy increases vulnerability to fungal infections.

Answer

Microbiological confirmation is ideal before starting antifungal treatment but may not always be mandatory.

Answer

Symptoms are more prominent than signs in patients with fungal corneal ulcers

Question 4

Xerophthalmia Grade X-3A is

Accepted Answer

Corneal ulcer affecting less than 1/3 of the corneal surface

Answer

Corneal xerosis

Answer

Bitot spot

Answer

Corneal ulcer affecting more than 1/3 of corneal surface

Question 5

What is the primary cause of snow blindness?

Accepted Answer

UV rays

Answer

Infrared radiation

Answer

Microwave radiation

Answer

Defect in optical devices

Question 6

Density of cells in adult corneal endothelium is

Accepted Answer

3000 cells/mm2

Answer

2000 cells/mm2

Answer

4000 cells/mm2

Answer

5000 cells/mm2

Diseases of the Cornea — MCQs

Diseases of the Cornea — MCQs

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