Diseases of the Cornea Practice Questions

Q: Why is fluorescein staining used in the diagnosis of corneal ulcers?

Reveals epithelial damage under blue light. ***Reveals epithelial damage under blue light*** - **Fluorescein** is a dye that stains areas of **epithelial disruption** on the cornea. - When viewed under a **cobalt blue light**, the stained areas fluoresce bright green, clearly indicating the presence and extent of a **corneal ulcer** or abrasion. *It assesses intraocular pressure.* - **Intraocular pressure** is measured using tonometry, not fluorescein staining. - Fluorescein can be minimally used with applanation tonometry but its primary role is not pressure assessment. *It detects viral particles in the cornea.* - Viral particles are too small to be directly detected by fluorescein staining. - Diagnosis of viral keratitis typically involves clinical appearance, sometimes confirmed by PCR or viral culture. *Highlights bacterial colonies on the corneal surface.* - While fluorescein outlines the area of infection, it does **not directly stain bacterial colonies**. - Bacterial colonies themselves are often visible with a slit lamp but fluorescein primarily stains the underlying epithelial defect.

Q: Which test is commonly used to diagnose keratoconus in patients with progressive myopia and irregular astigmatism?

Corneal topography. ***Corneal topography*** - **Corneal topography** is the gold standard for diagnosing and monitoring keratoconus as it provides detailed maps of the anterior and posterior corneal surfaces, allowing for the detection of subtle and overt corneal thinning and steepening. - It visualizes the characteristic **cone-shaped protrusion** and irregular astigmatism, which are hallmarks of the disease. *Fluorescein staining* - **Fluorescein staining** is primarily used to detect epithelial defects, ulcers, or abrasions on the cornea, not for assessing its shape or curvature. - While a severe case of keratoconus might show a **Fleischer's ring** (iron deposition) visible with cobalt blue light and fluorescein, it's not the primary diagnostic tool for the corneal shape itself. *Tonometry* - **Tonometry** measures intraocular pressure (IOP) and is used to screen for or monitor glaucoma. - It does not provide information about the **corneal shape, thickness**, or the presence of keratoconus. *Optical coherence tomography* - **Optical coherence tomography (OCT)** is an imaging technique used for high-resolution cross-sectional imaging of the retina and optic nerve, and increasingly for anterior segment structures including corneal thickness. - While anterior segment OCT can provide valuable information about **corneal thickness and posterior corneal surface**, it is not as comprehensively diagnostic for the overall corneal curvature and irregularity of keratoconus as corneal topography.

Q: Which layer of the cornea is affected in keratoconus?

Stroma. ***Stroma*** - **Keratoconus** is primarily a **stromal disease** characterized by progressive thinning and weakening of the corneal stroma, the thickest layer comprising 90% of corneal thickness. - The fundamental pathology involves **stromal collagen disorganization**, reduced keratocyte density, and biomechanical instability leading to the characteristic conical protrusion. - Stromal thinning with loss of collagen lamellae is the **primary and earliest significant change** that drives the ectatic process. - Clinical signs like Vogt's striae (stress lines in stroma) and Fleischer ring (iron deposition at cone base) reflect stromal pathology. *Bowman's layer* - Bowman's layer shows **breaks and ruptures** in keratoconus, but these are **secondary changes** resulting from the progressive stromal ectasia and biomechanical stress. - These breaks occur in **moderate to advanced disease**, not as the initiating pathological event. - Acute hydrops (rupture of Descemet's membrane with stromal edema) can occur when ectasia is severe. *Epithelium* - The **epithelium** remains largely intact but shows **compensatory thinning** over the apex of the cone and thickening in the periphery. - Epithelial iron deposition (Fleischer ring) and recurrent erosions may occur but are not the primary pathology. *Endothelium* - The **endothelium** is typically **well-preserved** in keratoconus until very advanced stages. - Endothelial dysfunction is characteristic of other corneal diseases like Fuchs' endothelial dystrophy, not keratoconus.

Q: Which of the following is used in the diagnosis of corneal dystrophies?

Specular microscopy. ***Specular microscopy*** - This technique is the **gold standard for diagnosing corneal endothelial dystrophies** as it allows for **direct visualization and quantitative analysis of endothelial cells** and their morphology. - Many corneal dystrophies, particularly **Fuchs endothelial dystrophy**, are characterized by specific changes in endothelial cell density, pleomorphism, and polymegathism that are best evaluated with specular microscopy. - Provides **cellular-level detail** that is critical for early detection and monitoring of endothelial dystrophies. *Fluorescein angiography* - This diagnostic tool is primarily used for evaluating **retinal and choroidal vasculature**, especially in conditions like **diabetic retinopathy** or **age-related macular degeneration**. - It involves injecting fluorescein dye and observing its flow through posterior segment vessels, which is **not relevant for corneal diagnosis**. *Optical coherence tomography* - While **anterior segment OCT (AS-OCT) is indeed used for imaging corneal dystrophies** and provides excellent cross-sectional visualization of corneal layers, stromal opacities, and epithelial changes, it does **not provide the cellular-level endothelial detail** offered by specular microscopy. - AS-OCT is useful for stromal dystrophies (granular, lattice, macular) and measuring corneal thickness, but **specular microscopy remains superior for endothelial assessment**, which is crucial for the most commonly tested corneal dystrophies. *Fundus photography* - This technique captures **images of the posterior pole of the eye**, including the retina, optic disc, and macula. - It is utilized for documenting and monitoring conditions affecting the **retina and optic nerve**, not the anterior corneal structures.

Q: A 22-year-old male presents with intense pain, photophobia, and a ring-like corneal infiltrate in his left eye. He frequently swims in lakes. What is the most likely diagnosis?

Acanthamoeba keratitis. ***Acanthamoeba keratitis*** - Intense pain, photophobia, and a **ring-like corneal infiltrate** are classic signs of Acanthamoeba keratitis. - Exposure to **contaminated water**, such as swimming in lakes, is a common risk factor, especially for contact lens wearers. *Herpes simplex keratitis* - Typically presents with a **dendritic ulcer pattern** on the cornea, which is not described here. - While it can cause pain and photophobia, the characteristic ring infiltrate points away from HSV. *Bacterial keratitis* - Often presents with a **purulent discharge** and a **rapidly progressing stromal infiltrate**, which may or may not be ring-shaped. - While it can cause intense pain, the specific exposure to lake water and the clear description of a ring infiltrate make Acanthamoeba more likely. *Fungal keratitis* - Usually follows **ocular trauma with vegetative matter** or in immunocompromised individuals, often presenting with a feathery-edged infiltrate. - While contact lens wear is a risk factor, the description of a **ring infiltrate** and association with fresh water directly points to Acanthamoeba.

Q: A 35-year-old male presents with severe eye pain, photophobia, and blurred vision. Examination reveals a dendritic ulcer on the cornea. What is the initial treatment?

Topical antiviral medication. ***Topical antiviral medication*** - A **dendritic ulcer** is the classic pathognomonic sign of **herpes simplex keratitis**, which requires prompt antiviral treatment. - Topical antivirals like **ganciclovir gel** or **trifluridine ophthalmic solution** are first-line to inhibit viral replication and promote healing. *Topical antibiotic drops* - While topical antibiotics are used for **bacterial keratitis**, they are ineffective against viral infections like herpes simplex. - Inappropriate use of antibiotics can lead to **antibiotic resistance** and may delay effective treatment. *Oral corticosteroids* - **Corticosteroids** are generally contraindicated in active epithelial herpes simplex keratitis because they can worsen the infection and promote viral replication. - They might be used cautiously in later stages for **immune-mediated stromal keratitis** under specialist supervision. *Cycloplegic drops* - **Cycloplegics**, such as atropine or cyclopentolate, relieve ciliary spasm and pain associated with corneal inflammation. - While they serve as useful **adjunctive therapy** for symptom relief, they do not treat the underlying **viral infection** and are not the **initial/primary treatment** for herpes simplex keratitis.

Q: A 28-year-old female with a history of contact lens wear presents with a painful red eye and decreased vision. A slit-lamp examination reveals a central corneal ulcer with hypopyon. What is the most likely causative organism?

Pseudomonas aeruginosa. ***Pseudomonas aeruginosa*** - This organism is a common cause of **severe bacterial keratitis** in contact lens wearers due to its ability to adhere to lenses and produce potent toxins. - Its rapid progression can lead to a **central corneal ulcer** with significant inflammation and often a **hypopyon**. *Staphylococcus aureus* - While *S. aureus* can cause bacterial keratitis and corneal ulcers, it is less commonly associated with the rapid, aggressive course often seen with contact lens-related infections, which characteristically involve a prominent **hypopyon**. - Its infections tend to be more indolent or localized in comparison to *Pseudomonas*. *Herpes simplex virus* - HSV keratitis presents with characteristic **dendritic ulcers** or geographic ulcers, which differ in morphology from typical bacterial ulcers. - While it can cause pain, redness, and decreased vision, it is not primarily associated with contact lens wear and usually does not cause a pronounced **hypopyon** without secondary bacterial infection. *Candida albicans* - Fungal keratitis, including that caused by *Candida*, usually occurs after **trauma** involving plant matter or in immunocompromised individuals, not typically in routine contact lens wear. - Fungal ulcers tend to have a **feathery border** and **satellite lesions**, distinct from the described central corneal ulcer.

Q: A 40-year-old woman presents with recurrent corneal erosions and has a history of trauma to the eye. Which layer of the cornea is most likely involved?

Epithelium. ***Epithelium*** - **Recurrent corneal erosions** often result from a defect in the adhesion of the **corneal epithelium** to the underlying Bowman's layer and basement membrane. - A history of **trauma** can disrupt these adhesion complexes, making the epithelium prone to repeated detachments. *Stroma* - The **corneal stroma** is the thickest layer and provides structural integrity; conditions affecting it typically lead to scarring, opacification, or thinning, rather than recurrent erosions. - While stromal injury can occur with trauma, recurrent erosions specifically point to issues with the superficial adhesive layers, not the bulk of the stroma itself. *Endothelium* - The **corneal endothelium** is the innermost layer responsible for maintaining corneal deturgescence (fluid balance) through its pump function. - Endothelial dysfunction typically causes **corneal edema** and cloudiness, not recurrent erosions. *Descemet's membrane* - **Descemet's membrane** is the basement membrane of the endothelium and is highly resistant to trauma. - Damage to Descemet's membrane is usually associated with significant *blunt trauma* or specific genetic disorders, and its rupture can lead to acute hydrops or swelling, not recurrent erosions.

Q: Placido disc is used for diagnosing which of the following conditions?

Keratoconus. ***Keratoconus*** - A **Placido disc**, or **keratoscope**, uses concentric rings projected onto the cornea to assess its shape and detect irregularities. - In **keratoconus**, the cornea thins and protrudes into a cone-like shape, distorting the reflected rings of the Placido disc. *Uveitis* - **Uveitis** is an inflammation of the uvea, the middle layer of the eye, which is diagnosed through examination of intraocular structures and symptoms like pain, redness, and light sensitivity. - The **Placido disc** is not used for diagnosing intraocular inflammation but rather for assessing corneal surface abnormalities. *Retinoblastoma* - **Retinoblastoma** is a malignant tumor of the retina, typically diagnosed with ophthalmoscopy (to visualize the retina), imaging studies (like ultrasound or MRI), and genetic testing. - The **Placido disc** examines the corneal surface and has no role in detecting retinal tumors. *Retinal detachment* - **Retinal detachment** involves the separation of the retina from its underlying support structures, diagnosed through ophthalmoscopy to visualize the detached retina. - The **Placido disc** evaluates the cornea, not the retina, and therefore cannot diagnose retinal detachment.

Q: Which of the following is not a feature of fungal corneal ulcer?

Symptoms are more pronounced than signs. ***Symptoms are more pronounced than signs*** - This statement is characteristic of ***viral keratitis***, where the patient's discomfort and symptoms can be disproportionately severe compared to the objective clinical findings. - In ***fungal corneal ulcers***, the signs (like the ulcer's appearance, feathery margins) are typically more prominent and extensive relative to the patient's milder symptomatic complaints. *Fixed hypopyon* - A ***fixed hypopyon***, which is a collection of pus in the anterior chamber that does not shift with head movements, is a classic feature of ***fungal corneal ulcers***. - This is due to the robust inflammatory response and the tendency of fungi to produce a more viscous exudate that settles and adheres. *Ulcer with sloughing margins* - ***Sloughing margins*** are indicative of tissue necrosis and liquefaction, which can be seen in aggressive fungal infections of the cornea. - This appearance suggests extensive tissue destruction and can contribute to the deeper penetration of the infection. *Fungal hyphae are seen on KOH mount* - The presence of ***fungal hyphae*** on a ***potassium hydroxide (KOH) mount*** of corneal scrapings is a definitive diagnostic feature of a fungal corneal ulcer. - KOH dissolves cellular debris, making the fungal elements (hyphae or spores) more visible under a microscope.

Question 1

Why is fluorescein staining used in the diagnosis of corneal ulcers?

Accepted Answer

Reveals epithelial damage under blue light

Answer

It assesses intraocular pressure.

Answer

It detects viral particles in the cornea.

Answer

Highlights bacterial colonies on the corneal surface.

Question 2

Which test is commonly used to diagnose keratoconus in patients with progressive myopia and irregular astigmatism?

Accepted Answer

Corneal topography

Answer

Fluorescein staining

Answer

Tonometry

Answer

Optical coherence tomography

Question 3

Which layer of the cornea is affected in keratoconus?

Accepted Answer

Stroma

Answer

Epithelium

Answer

Endothelium

Answer

Bowman's layer

Question 4

Which of the following is used in the diagnosis of corneal dystrophies?

Accepted Answer

Specular microscopy

Answer

Fluorescein angiography

Answer

Optical coherence tomography

Answer

Fundus photography

Question 5

A 22-year-old male presents with intense pain, photophobia, and a ring-like corneal infiltrate in his left eye. He frequently swims in lakes. What is the most likely diagnosis?

Accepted Answer

Acanthamoeba keratitis

Answer

Herpes simplex keratitis

Answer

Bacterial keratitis

Answer

Fungal keratitis

Question 6

A 35-year-old male presents with severe eye pain, photophobia, and blurred vision. Examination reveals a dendritic ulcer on the cornea. What is the initial treatment?

Accepted Answer

Topical antiviral medication

Answer

Topical antibiotic drops

Answer

Oral corticosteroids

Answer

Cycloplegic drops

Question 7

A 28-year-old female with a history of contact lens wear presents with a painful red eye and decreased vision. A slit-lamp examination reveals a central corneal ulcer with hypopyon. What is the most likely causative organism?

Accepted Answer

Pseudomonas aeruginosa

Answer

Staphylococcus aureus

Answer

Herpes simplex virus

Answer

Candida albicans

Question 8

A 40-year-old woman presents with recurrent corneal erosions and has a history of trauma to the eye. Which layer of the cornea is most likely involved?

Accepted Answer

Epithelium

Answer

Stroma

Answer

Endothelium

Answer

Descemet's membrane

Question 9

Placido disc is used for diagnosing which of the following conditions?

Accepted Answer

Keratoconus

Answer

Uveitis

Answer

Retinoblastoma

Answer

Retinal detachment

Question 10

Which of the following is not a feature of fungal corneal ulcer?

Accepted Answer

Symptoms are more pronounced than signs

Answer

Ulcer with sloughing margins

Answer

Fixed hypopyon

Answer

Fungal hyphae are seen on KOH mount

Diseases of the Cornea — MCQs

Diseases of the Cornea — MCQs

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