Diseases of the Cornea — MCQs

Diseases of the Cornea Indian Medical PG Practice Questions and MCQs

Question 421: Which of the following organisms can penetrate a normal intact cornea?

A. Gonococcus (Correct Answer)
B. Staphylococcus aureus
C. Streptococcus pneumoniae
D. Listeria monocytogenes

Explanation: ***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**.

Question 422: What is the most effective treatment for central nebular corneal opacity?

A. Phototherapeutic keratectomy (Correct Answer)
B. Penetrating keratoplasty
C. Gas permeable contact lens
D. Soft contact lens

Explanation: ***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.

Question 423: Which of the following statements about Fuchs' corneal dystrophy is true?

A. Glaucoma is not a common association.
B. It is a type of endothelial dystrophy (Correct Answer)
C. It is characterized by bilateral involvement
D. It primarily occurs in older adults

Explanation: ***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.

Question 424: Which of the following conditions is associated with Stocker's line?

A. Pterygium (Correct Answer)
B. Pinguecula
C. Fleischer's ring
D. Congenital ocular melanosis

Explanation: ***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.

Question 425: What does the hypopyon in a fungal corneal ulcer contain?

A. Fungal spores
B. Sterile material
C. Fungal filaments
D. Purulent material (Correct Answer)

Explanation: ***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.

Question 426: What is the innermost stratum of the tear film?

A. Mucus layer (Correct Answer)
B. Aqueous layer
C. Oily layer
D. Lipid layer

Explanation: ***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.

Question 427: All are corneal signs of trachoma except which of the following?

A. Corneal opacity
B. Pannus
C. Conjunctival follicles (Correct Answer)
D. Corneal scarring

Explanation: ***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.

Question 428: Which of the following is not a typical sign of Herpes simplex involvement of the eye?

A. Corneal anaesthesia
B. Iridocyclitis
C. Purulent discharge (Correct Answer)
D. Vesicular lesions

Explanation: ***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**.

Question 429: Corneal endothelial cell count is done by:

A. Specular microscopy (Correct Answer)
B. Keratometry
C. Gonioscopy
D. Slit lamp

Explanation: ***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.

Question 430: Corneal sensation is lost in which of the following conditions?

A. Herpes simplex (Correct Answer)
B. Conjunctivitis
C. Fungal infection
D. Trachoma

Explanation: ***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.

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

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