Diseases of the Cornea Practice Questions

Q: Which of the following organisms can penetrate a normal intact cornea?

Gonococcus. ***Gonococcus*** - *Neisseria gonorrhoeae* is unique among bacteria in its ability to directly penetrate the **intact corneal epithelium**. - This characteristic makes it a highly virulent cause of **rapidly progressive corneal ulceration** and endophthalmitis, especially in neonates born to infected mothers. *Staphylococcus aureus* - *Staphylococcus aureus* typically requires some form of **corneal epithelial defect** (e.g., abrasion, foreign body) to invade and cause keratitis. - While it is a common cause of bacterial keratitis, it does not penetrate an **undamaged cornea**. *Streptococcus pneumoniae* - Similar to *S. aureus*, *Streptococcus pneumoniae* usually needs a **breach in the corneal epithelium** to establish an infection. - It is a frequent cause of **bacterial conjunctivitis** and keratitis but is not known for invading an intact cornea. *Listeria monocytogenes* - *Listeria monocytogenes* is an important human pathogen but is primarily known for causing **meningitis, sepsis, and perinatal infections**. - It is not a common cause of bacterial keratitis, and there is no evidence to suggest it can penetrate an **intact corneal surface**.

Q: What is the most effective treatment for central nebular corneal opacity?

Phototherapeutic keratectomy. ***Phototherapeutic keratectomy*** - **Phototherapeutic keratectomy (PTK)** is the most effective treatment for superficial **central nebular corneal opacities** as it uses an excimer laser to remove anterior corneal tissue with precision. - This **surgical procedure** aims to improve visual acuity by reducing the opacity's density while preserving the main corneal structure. - PTK is preferred over more invasive procedures for superficial opacities. *Penetrating keratoplasty* - **Penetrating keratoplasty (PK)**, or full-thickness corneal transplant, is reserved for **deep stromal opacities** or those that significantly impair vision beyond the scope of PTK. - This **surgical procedure** involves replacing the entire central cornea, which carries higher risks such as graft rejection and requires longer recovery compared to PTK. *Gas permeable contact lens* - **Gas permeable (GP) contact lenses** are used for correcting irregular astigmatism and improving visual acuity in cases of mild corneal surface irregularities. - They provide a smooth refracting surface but do not address the underlying pathology of the opacity and are not effective for treating dense central opacities. *Soft contact lens* - **Soft contact lenses** are primarily used for correcting refractive errors like myopia, hyperopia, and astigmatism, or for therapeutic purposes such as protecting the ocular surface. - They are generally not effective in improving vision significantly in the presence of a central corneal opacity, as they conform to the corneal shape and do not mask the opacity.

Q: Which of the following statements about Fuchs' corneal dystrophy is true?

It is a type of endothelial dystrophy. ***It is a type of endothelial dystrophy*** - **Fuchs' endothelial corneal dystrophy (FECD)** is the **classic posterior/endothelial corneal dystrophy**, classified in the **IC3D classification system** as a primary endothelial dystrophy. - It involves **progressive loss of corneal endothelial cells** and formation of **guttata** (excrescences in Descemet's membrane), leading to endothelial dysfunction. - The dysfunctional endothelium cannot maintain corneal deturgescence, resulting in **corneal edema** and eventually **bullous keratopathy** in advanced cases. *It is characterized by bilateral involvement* - While Fuchs' dystrophy is **typically bilateral**, it can be **asymmetric** in presentation and progression. - Bilaterality is a common feature but not the most defining characteristic of the disease. *It primarily occurs in older adults* - Fuchs' dystrophy typically manifests in **middle age (40s-50s)** and progresses with age. - However, the condition has a **genetic basis** and cellular changes begin earlier than symptom onset. - Symptomatic disease is more common in older adults, but this doesn't define the disease entity itself. *Glaucoma is not a common association* - Studies have shown **increased prevalence of glaucoma** in patients with Fuchs' dystrophy compared to the general population. - The association may relate to **endothelial dysfunction** affecting aqueous outflow or shared risk factors. - This statement is **false** - glaucoma association has been documented.

Q: Which of the following conditions is associated with Stocker's line?

Pterygium. ***Pterygium*** - **Stocker's line** is a characteristic brownish iron deposition line seen at the **leading edge (head) of a pterygium**. - This line is caused by the accumulation of iron within the corneal epithelium due to chronic tear pooling and iron pigment deposition at the advancing edge of the pterygium. - It appears as a **horizontal brownish line** anterior to the pterygium head. *Pinguecula* - A **pinguecula** is a yellow-white patch or bump on the conjunctiva, typically on the nasal side. - It does **not invade the cornea** and therefore does not have an associated Stocker's line. - It represents a **degenerative collagenous change** of the conjunctival stroma with elastotic degeneration. *Fleischer's ring* - **Fleischer's ring** is another type of corneal iron deposition line, but it is associated with **keratoconus**, not pterygium. - It appears as a **brownish ring** at the base of the cone in keratoconus. - This is a distinct clinical entity from Stocker's line and helps differentiate various causes of corneal iron deposition. *Congenital ocular melanosis* - This is a condition of **increased pigmentation of the ocular tissues**, such as the uveal tract or sclera, present from birth. - It is a diffuse pigmentation disorder and does **not involve iron deposition** or the formation of Stocker's line. - Also known as **ocular melanocytosis**, it carries a slight increased risk of uveal melanoma.

Q: What does the hypopyon in a fungal corneal ulcer contain?

Purulent material. ***Purulent material*** - A **hypopyon** is an accumulation of **inflammatory cells** (primarily neutrophils) and fibrin in the anterior chamber of the eye. - In a fungal corneal ulcer, this material is **purulent** (pus) due to the severe inflammatory response triggered by the fungal infection. *Fungal filaments* - While fungal filaments (hyphae) are the causative agents of the infection and are present within the corneal tissue, they do not typically form the bulk of the **hypopyon** in the anterior chamber. - The hypopyon represents the host's inflammatory response rather than the direct fungal elements. *Fungal spores* - Similar to fungal filaments, **spores** are fungal reproductive structures and are found within the infected cornea, not as the primary component of the anterior chamber hypopyon. - The inflammatory exudate is composed of immune cells responding to the infection. *Sterile material* - A **hypopyon** associated with an active infection, such as a fungal corneal ulcer, is by definition **not sterile**. - It contains immune cells and inflammatory mediators, and often live microorganisms or their products, forming pus.

Q: What is the innermost stratum of the tear film?

Mucus layer. ***Mucus layer*** - The **mucus layer** is the innermost layer of the tear film, directly adjacent to the **corneal epithelium**. - It consists primarily of **mucin** secreted by goblet cells, which helps anchor the tear film to the ocular surface and promotes even spreading of tears. - This layer converts the hydrophobic corneal epithelial surface into a hydrophilic surface. *Aqueous layer* - The **aqueous layer** is the thickest middle layer of the tear film, located between the mucus layer and the lipid layer. - Produced by the main and accessory lacrimal glands, it contains water, electrolytes, antibacterial proteins (lysozyme, lactoferrin), and nutrients. *Oily layer* - The **oily layer** (lipid layer) is the outermost layer of the tear film, produced by the **Meibomian glands**. - Its primary function is to prevent evaporation of the aqueous layer and provide a smooth optical surface. *Lipid layer* - This is another name for the oily/lipid layer, which is the **outermost** layer, not the innermost. - The lipid layer reduces surface tension and retards evaporation of the tear film.

Q: All are corneal signs of trachoma except which of the following?

Conjunctival follicles. ***Conjunctival follicles*** - While **conjunctival follicles** are a hallmark sign of trachoma, they are located on the **conjunctiva**, not directly on the cornea. - These follicles represent collections of lymphocytes in the subconjunctival tissue, particularly in the **tarsal conjunctiva**. *Corneal opacity* - **Corneal opacity** is a late-stage complication of trachoma, resulting from chronic inflammation and scarring. - It significantly impairs vision and can lead to blindness, being a direct corneal involvement. *Pannus* - **Pannus** is the invasion of the cornea by blood vessels and fibrous tissue, often starting at the superior limbus. - It is a characteristic corneal sign of chronic trachoma, indicating corneal inflammation and neovascularization. *Corneal scarring* - **Corneal scarring** is a severe and irreversible consequence of chronic trachoma, often following repeated episodes of infection and inflammation. - It primarily results from the healing of corneal ulcers and the breakdown of Bowman's layer in the cornea.

Q: Which of the following is not a typical sign of Herpes simplex involvement of the eye?

Purulent discharge. ***Purulent discharge*** - **Herpes simplex virus (HSV)** infections of the eye, whether **keratitis** or **conjunctivitis**, typically do **not** cause a **purulent (pus-like) discharge**. - **Purulent discharge** is more characteristic of acute **bacterial conjunctivitis**. *Corneal anaesthesia* - **Corneal nerve damage** is a common and characteristic feature of chronic or recurrent **herpetic keratitis**. - This can lead to **reduced corneal sensation**, making the eye more vulnerable to further injury. *Iridocyclitis* - **Iridocyclitis** (inflammation of the **iris** and **ciliary body**) can occur as a complication of intraocular anterior **uveitis** in **Herpes simplex eye infections**. - It often leads to symptoms like **pain**, **photophobia**, and **blurred vision**. *Vesicular lesions* - **Vesicular lesions** on the **eyelids** or around the eye (HSV **blepharitis** or **dermatitis**) are typical during the primary or recurrent outbreaks of **Herpes simplex infections**. - These lesions contain **infectious virus** and can shed, potentially leading to **corneal involvement**.

Q: Corneal endothelial cell count is done by:

Specular microscopy. ***Specular microscopy*** - **Specular microscopy** is the gold standard for **non-invasive quantitative and qualitative analysis** of the corneal endothelium. - It uses reflected light to visualize and count individual endothelial cells, providing critical information about cell density, morphology, and polymegethism. *Keratometry* - **Keratometry** measures the **curvature of the anterior corneal surface**, primarily used to assess corneal astigmatism and fit contact lenses. - It does not provide information about the **endothelial cell layer**. *Gonioscopy* - **Gonioscopy** is a clinical technique used to **visualize the anterior chamber angle** of the eye. - It is crucial for diagnosing and classifying glaucoma but does not evaluate the **corneal endothelium**. *Slit lamp* - A **slit lamp** provides a magnified view of the anterior and posterior segments of the eye for general examination. - While it can help identify gross corneal abnormalities, it is **not precise enough** to quantify or qualitatively assess individual endothelial cells in detail.

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.

Question 1

Which of the following organisms can penetrate a normal intact cornea?

Accepted Answer

Gonococcus

Answer

Staphylococcus aureus

Answer

Streptococcus pneumoniae

Answer

Listeria monocytogenes

Question 2

What is the most effective treatment for central nebular corneal opacity?

Accepted Answer

Phototherapeutic keratectomy

Answer

Penetrating keratoplasty

Answer

Gas permeable contact lens

Answer

Soft contact lens

Question 3

Which of the following statements about Fuchs' corneal dystrophy is true?

Accepted Answer

It is a type of endothelial dystrophy

Answer

Glaucoma is not a common association.

Answer

It is characterized by bilateral involvement

Answer

It primarily occurs in older adults

Question 4

Which of the following conditions is associated with Stocker's line?

Accepted Answer

Pterygium

Answer

Pinguecula

Answer

Fleischer's ring

Answer

Congenital ocular melanosis

Question 5

What does the hypopyon in a fungal corneal ulcer contain?

Accepted Answer

Purulent material

Answer

Fungal spores

Answer

Sterile material

Answer

Fungal filaments

Question 6

What is the innermost stratum of the tear film?

Accepted Answer

Mucus layer

Answer

Aqueous layer

Answer

Oily layer

Answer

Lipid layer

Question 7

All are corneal signs of trachoma except which of the following?

Accepted Answer

Conjunctival follicles

Answer

Corneal opacity

Answer

Pannus

Answer

Corneal scarring

Question 8

Which of the following is not a typical sign of Herpes simplex involvement of the eye?

Accepted Answer

Purulent discharge

Answer

Corneal anaesthesia

Answer

Iridocyclitis

Answer

Vesicular lesions

Question 9

Corneal endothelial cell count is done by:

Accepted Answer

Specular microscopy

Answer

Keratometry

Answer

Gonioscopy

Answer

Slit lamp

Question 10

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

Diseases of the Cornea — MCQs

Diseases of the Cornea — MCQs

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