Corneal Anatomy and Physiology — MCQs
All are true regarding cornea except:
Sensory innervation of the cornea is by which nerve?
Density of cells in adult corneal endothelium is
Conjunctival epithelium is a type of what?
Which among the following is the BEST irrigating fluid during ECCE?
A 20-year-old male complains of repeated changes in glasses prescription. This is most likely caused by:
In uveitis, site of keratic precipitate is:
Which of the following statements about Fuchs' corneal dystrophy is true?
What does a visual acuity test primarily assess?
A patient, three years post-surgery, presents with the condition shown in the image and complains of decreased vision. What is the most likely diagnosis?
Corneal Anatomy and Physiology Indian Medical PG Practice Questions and MCQs
Question 1: All are true regarding cornea except:
- A. The cornea is richly vascular. (Correct Answer)
- B. Endothelium help in maintaining dehydrated state
- C. Oxygen is mostly derived by epithelium directly from the air through tear film
- D. Corneal thickness is greater at periphery than center
Explanation: ***The cornea is richly vascular.*** - The cornea is an **avascular** tissue, meaning it lacks blood vessels, which is crucial for its transparency. - This avascularity helps prevent light scatter and maintains clear vision. - The cornea receives nutrition from the **aqueous humor**, **tear film**, and **limbal blood vessels** through diffusion. *Endothelium help in maintaining dehydrated state* - The **corneal endothelium** actively pumps fluid out of the corneal stroma via **Na-K-ATPase pumps**, preventing swelling and maintaining its relative state of dehydration. - This **deturgescence** is essential for the cornea's transparency and optimal refractive power. *Oxygen is mostly derived by epithelium directly from the air through tear film* - The corneal **epithelium** primarily obtains oxygen directly from the atmosphere via the **tear film** when the eyes are open. - During sleep, oxygen is primarily supplied by the **palpebral conjunctival vessels**. *Corneal thickness is greater at periphery than center* - The cornea is **thinner at the center** (around 520-540 µm) and gradually **thicker towards the periphery** (around 600-640 µm). - This structural difference contributes to its optical properties and mechanical stability.
Question 2: Sensory innervation of the cornea is by which nerve?
- A. 5th (ophthalmic division of the trigeminal nerve) (Correct Answer)
- B. 6th (Abducens nerve)
- C. 3rd (Oculomotor nerve)
- D. 4th (Trochlear nerve)
Explanation: ***5th (ophthalmic division of the trigeminal nerve)*** - The **trigeminal nerve (CN V)** is responsible for sensory innervation of the face, and its **ophthalmic division (V1)** specifically supplies the cornea. - This extensive sensory innervation explains the **extreme sensitivity of the cornea** to touch, temperature, and chemicals, and is crucial for the **corneal reflex**. *6th (Abducens nerve)* - The **abducens nerve (CN VI)** is a **motor nerve** responsible for innervating the **lateral rectus muscle**, which abducts the eye. - It has no role in the sensory innervation of the cornea. *3rd (Oculomotor nerve)* - The **oculomotor nerve (CN III)** is primarily a **motor nerve** responsible for innervating most of the **extraocular muscles** (superior, inferior, medial recti, inferior oblique) and the **levator palpebrae superioris**. - It also carries **parasympathetic fibers** for pupillary constriction and accommodation, but it does not provide sensory innervation to the cornea. *4th (Trochlear nerve)* - The **trochlear nerve (CN IV)** is a **motor nerve** that innervates the **superior oblique muscle**, which depresses and internally rotates the eye. - It has no function in corneal sensation.
Question 3: 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 4: Conjunctival epithelium is a type of what?
- A. Pseudostratified
- B. Stratified columnar
- C. Stratified non keratinised squamous (Correct Answer)
- D. Transitional
Explanation: ***Stratified non keratinised squamous*** - The **conjunctival epithelium** is primarily **stratified squamous epithelium**, meaning it has multiple layers of flattened cells. - It is **non-keratinized**, indicating that it does not produce keratin, which helps keep the surface moist and flexible. *Pseudostratified* - **Pseudostratified epithelium** appears to have multiple layers due to the varying heights of cells and nuclei at different levels, but all cells are in contact with the basement membrane. - A common example is in the **trachea**, where it is usually ciliated with goblet cells, not typically found in the conjunctiva. *Stratified columnar* - **Stratified columnar epithelium** has multiple layers of cells, with the outermost layer consisting of columnar cells. - This type of epithelium is relatively rare, found in certain ducts and parts of the urethra, and is not characteristic of the conjunctiva. *Transitional* - **Transitional epithelium**, also known as urothelium, is a specialized stratified epithelium found in the **urinary tract** (e.g., bladder, ureters). - It is unique for its ability to **stretch** and change shape, which is not a primary function of the conjunctival surface.
Question 5: Which among the following is the BEST irrigating fluid during ECCE?
- A. Ringer lactate
- B. Normal saline
- C. Balanced salt solution
- D. Balanced salt solution + glutathione (Correct Answer)
Explanation: ***Balanced salt solution + glutathione*** - **Balanced salt solution with glutathione** is considered the best irrigating fluid for ECCE because it closely mimics the **natural aqueous humor**, maintaining corneal endothelial cell health and viability during surgery. - The addition of **glutathione** provides an antioxidant effect, protecting the corneal endothelium from oxidative stress and maintaining its metabolic function during prolonged irrigation. *Ringer lactate* - While **Ringer's lactate** is a balanced electrolyte solution, it lacks the specific components and buffering capacity present in specialized ophthalmic irrigating solutions. - It does not contain **glutathione** or other agents crucial for maintaining corneal endothelial viability and function during intraocular surgery. *Normal saline* - **Normal saline (0.9% NaCl)** lacks essential ions (calcium, magnesium, potassium) and appropriate pH buffering required for intraocular use. - Its use can lead to **corneal edema** and endothelial cell damage due to ionic imbalance and the absence of protective components found in balanced salt solutions. *Balanced salt solution* - A **plain balanced salt solution (BSS)** is a significant improvement over normal saline or Ringer's lactate as it is physiologically balanced for intraocular use, containing essential electrolytes. - However, it lacks the **antioxidant properties of glutathione**, which provides superior protection to corneal endothelial cells during extended surgical procedures.
Question 6: A 20-year-old male complains of repeated changes in glasses prescription. This is most likely caused by:
- A. Keratoconus (Correct Answer)
- B. Cataract
- C. Glaucoma
- D. Pathological myopia
Explanation: ***Keratoconus*** - **Keratoconus** is a progressive disorder where the cornea thins and protrudes into a cone shape, leading to irregular astigmatism and frequent changes in glasses prescription. - This condition commonly presents in young adults and is characterized by **rapid, repeated changes** in both spherical and cylindrical components due to progressive corneal distortion. - The irregular corneal shape makes it difficult to achieve stable, satisfactory vision correction with glasses alone. *Cataract* - A **cataract** is a clouding of the eye's natural lens, which causes blurred vision, glare, and difficulty seeing at night. - While it can cause a "myopic shift" leading to prescription changes, it is more common in older individuals (>50 years) and the changes are typically slower and less frequent than in keratoconus. *Glaucoma* - **Glaucoma** is a group of eye conditions that damage the optic nerve, often due to high intraocular pressure, leading to peripheral vision loss and eventually blindness. - It does not cause changes in refractive error or require frequent updates to glasses prescriptions. - Visual changes are related to field defects, not refractive changes. *Pathological myopia* - **Pathological myopia** is a severe form of nearsightedness where the eye elongates excessively, leading to progressive increases in myopic refractive error. - While it can cause prescription changes in young adults, the progression is typically more **gradual and predictable** (mainly increasing spherical myopia) compared to the **rapid, irregular changes** seen in keratoconus. - Keratoconus is distinguished by frequent changes in astigmatism due to irregular corneal shape, whereas pathological myopia mainly affects spherical power.
Question 7: In uveitis, site of keratic precipitate is:
- A. Lens anterior capsule
- B. Corneal endothelium (Correct Answer)
- C. Lens posterior capsule
- D. Corneal stroma
Explanation: ***Corneal endothelium*** - **Keratic precipitates (KPs)** are inflammatory cellular deposits that adhere to the **posterior surface of the cornea**, specifically the endothelial layer, in uveitis. - They represent aggregates of inflammatory cells, such as macrophages and lymphocytes, that have migrated from the inflamed anterior chamber. *Lens anterior capsule* - The **anterior capsule of the lens** is a smooth, acellular membrane and does not typically accumulate inflammatory deposits like **keratic precipitates**. - While inflammatory cells can be observed in the **anterior chamber**, they do not specifically adhere to the lens capsule in this manner. *Lens posterior capsule* - Similar to the anterior capsule, the **posterior capsule of the lens** is not the site for deposition of **keratic precipitates**. - Inflammation affecting the lens would typically present as cataract formation or direct lens inflammation, not KPs. *Corneal stroma* - The **corneal stroma** is the thickest layer of the cornea and is primarily composed of collagen fibrils and keratocytes. - While inflammation can affect the stroma (e.g., in stromal keratitis), **keratic precipitates** specifically form on the **innermost layer**, the endothelium, facing the anterior chamber.
Question 8: 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 9: What does a visual acuity test primarily assess?
- A. Ability to perceive light
- B. Ability to differentiate colors
- C. Ability to recognize shapes and details (Correct Answer)
- D. Ability to detect contrast
Explanation: ***Ability to recognize shapes and details*** - A visual acuity test, typically using a **Snellen chart**, measures the sharpness of vision, specifically the ability to discern letters or symbols at a given distance. - It assesses the eye's capacity to resolve fine **spatial detail**, which is crucial for tasks like reading and recognizing faces. - This is the fundamental definition of visual acuity and what these tests are specifically designed to measure. *Ability to perceive light* - This refers to **light perception (LP)**, the most basic form of vision, indicating whether a person can detect the presence or absence of light. - While essential for vision, it is a much simpler function than what visual acuity tests measure and is assessed separately. *Ability to differentiate colors* - This is assessed by **color vision tests**, such as the Ishihara plates, which evaluate the function of cone photoreceptors. - It specifically checks for **color blindness** (e.g., red-green or blue-yellow deficiencies) and is distinct from the sharpness of vision. *Ability to detect contrast* - This is measured by **contrast sensitivity tests**, which evaluate the ability to distinguish objects from their background at various contrast levels. - While related to overall visual quality, it is a different aspect of vision than the ability to recognize fine details at high contrast.
Question 10: A patient, three years post-surgery, presents with the condition shown in the image and complains of decreased vision. What is the most likely diagnosis?
- A. Corneal Dystrophy
- B. Posterior Subcapsular Cataract (PSC)
- C. Pseudophakic Bullous Keratopathy
- D. Posterior Capsular Opacification (Correct Answer)
Explanation: ***Posterior Capsular Opacification*** - The image (especially part B, the **red reflex view**) shows a cloudy membrane with **Elschnig pearls** and fibrous tissue behind the intraocular lens, which is characteristic of **PCO**. - PCO commonly occurs months to years after cataract surgery and causes **decreased vision** due to scattering of light. *Corneal Dystrophy* - Corneal dystrophies primarily affect the **cornea**, leading to various forms of corneal opacification, and would typically appear as cloudiness or irregularities within the corneal layers. - While it can cause decreased vision, the opacification seen in the image is clearly behind the iris plane and involves the posterior capsule, not the cornea. *Pseudophakic Bullous Keratopathy* - This condition involves **corneal edema** and **bullae formation** due to endothelial cell dysfunction, leading to a hazy cornea. - The image does not show corneal edema or bullae; instead, the primary pathology is located at the **posterior capsule** of the intraocular lens. *Posterior Subcapsular Cataract (PSC)* - A PSC is a type of cataract that forms **before cataract surgery** and affects the natural crystalline lens. - The patient is three years post-surgery, indicating that the natural lens has been replaced, making a PSC (of the natural lens) an impossible diagnosis in this context.
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