Diseases of the Cornea — MCQs

Diseases of the Cornea Indian Medical PG Practice Questions and MCQs

Question 281: Corneal sensation is tested by which instrument?

A. Keratometry
B. Pachymeter
C. Aesthesiometer (Correct Answer)
D. Specular microscopy

Explanation: ### Explanation **Correct Answer: C. Aesthesiometer** Corneal sensation is a vital indicator of the integrity of the **Trigeminal nerve (Ophthalmic division - V1)** via the long ciliary nerves. The instrument used to quantify this sensation is the **Aesthesiometer**. The most commonly used clinical device is the **Cochet-Bonnet aesthesiometer**, which utilizes a retractable nylon monofilament. By varying the length of the filament, the pressure applied to the cornea is adjusted; a longer filament applies less pressure, while a shorter one applies more. A decrease in sensation (hypesthesia) is a hallmark of conditions like Herpes Simplex Keratitis, Neurotrophic Keratopathy, and chronic contact lens wear. **Why other options are incorrect:** * **A. Keratometry:** Measures the **curvature** of the anterior corneal surface. It is primarily used for IOL power calculation and diagnosing astigmatism or keratoconus. * **B. Pachymeter:** Measures **corneal thickness**. It is essential in glaucoma (to adjust IOP readings) and preoperative evaluation for refractive surgeries like LASIK. * **D. Specular microscopy:** Used to study the **corneal endothelium**. It provides data on endothelial cell density and morphology (pleomorphism and polymegethism). **High-Yield Clinical Pearls for NEET-PG:** * **Corneal Reflex:** The afferent limb is the **Trigeminal nerve (V1)**, and the efferent limb is the **Facial nerve (VII)**. * **Neurotrophic Keratitis:** Characterized by a "silent" (painless) ulcer due to loss of corneal sensation. Common causes include Diabetes Mellitus, Herpes Zoster Ophthalmicus, and Acoustic Neuroma. * **Normal Central Corneal Thickness (CCT):** Approximately **540 microns**.

Question 282: A 4-year-old child develops an infection with Chlamydia trachomatis. How does infection with this organism cause blindness?

A. Cataract formation
B. Hemorrhage into the anterior chamber
C. Hemorrhage into the posterior chamber
D. Scarring of the cornea (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. Scarring of the cornea.** **Pathophysiology:** *Chlamydia trachomatis* (Serotypes A, B, Ba, and C) is the causative agent of **Trachoma**, the leading infectious cause of blindness worldwide. The blindness is not a direct result of the initial infection but a consequence of chronic, recurrent inflammation. 1. Repeated infections lead to severe conjunctival scarring (**Arlt’s line**). 2. This scarring causes the eyelids to turn inward (**Entropion**) and the eyelashes to rub against the globe (**Trichiasis**). 3. Constant mechanical trauma from trichiasis, combined with a deficient tear film, leads to secondary bacterial infections, **corneal ulceration**, and eventually dense **corneal opacification/scarring**, which obstructs vision. **Why other options are incorrect:** * **Option A:** Cataracts are caused by aging, trauma, or metabolic derangements, not by Chlamydial surface infections. * **Options B & C:** Hemorrhage into the chambers (Hyphema or Vitreous hemorrhage) is typically associated with trauma, neovascularization (e.g., Diabetes), or vascular occlusions, rather than the cicatrizing (scarring) process of Trachoma. **NEET-PG High-Yield Pearls:** * **WHO Grading (FISTO):** **F**ollicular, **I**ntense inflammation, **S**carring, **T**richiasis, **O**pacity. * **Herbert’s Pits:** Pathognomonic scarred remains of follicles at the limbus. * **Pannus:** Progressive vascularization of the upper part of the cornea is a classic finding. * **SAFE Strategy:** **S**urgery (for trichiasis), **A**ntibiotics (Azithromycin), **F**acial cleanliness, **E**nvironmental improvement. * **Drug of Choice:** Single dose of oral **Azithromycin** (20 mg/kg).

Question 283: Neurotrophic keratopathy is caused by which of the following?

A. Bell's palsy
B. Facial and trigeminal nerve palsy both
C. Trigeminal nerve palsy (Correct Answer)
D. All of the above

Explanation: ### Explanation **Neurotrophic Keratopathy (NK)** is a degenerative corneal disease caused by an impairment of corneal sensory innervation. **1. Why Trigeminal Nerve Palsy is Correct:** The cornea is one of the most densely innervated tissues in the body. Sensory supply is provided by the **long ciliary nerves**, which are branches of the **Ophthalmic division (V1) of the Trigeminal nerve**. These nerves do more than just provide sensation; they release **trophic factors** (like Substance P and Nerve Growth Factor) essential for maintaining the health, metabolism, and regenerative capacity of the corneal epithelium. When the Trigeminal nerve is damaged (due to herpes simplex/zoster, surgery, or tumors like acoustic neuroma), the loss of these trophic factors leads to epithelial breakdown, ulceration, and poor healing, regardless of tear film status. **2. Why Other Options are Incorrect:** * **Bell’s Palsy (Facial Nerve/VII):** Damage to the Facial nerve causes **Exposure Keratopathy**, not Neurotrophic Keratopathy. In VII nerve palsy, the orbicularis oculi muscle fails, leading to lagophthalmos (inability to close the eye). The cornea dries out due to evaporation, but the sensory/trophic supply remains intact. * **Facial and Trigeminal Nerve Palsy both:** While a patient can have both (e.g., in large cerebellopontine angle tumors), NK is specifically defined by the sensory deficit of the V nerve. **3. Clinical Pearls for NEET-PG:** * **Hallmark Sign:** A "punched-out" ulcer with smooth, rolled-up edges and a **lack of corneal sensation**. * **Staging:** Uses the **Mackie Classification** (Stage 1: Epithelial irregularity; Stage 2: Persistent epithelial defect; Stage 3: Corneal ulcer/perforation). * **Treatment High-Yield:** Cenegermin (recombinant human nerve growth factor) is a specific pharmacological treatment. * **Differentiate:** Exposure Keratopathy = VII nerve (Motor/Lid closure issue); Neurotrophic Keratopathy = V nerve (Sensory/Trophic issue).

Question 284: A nebular corneal opacity measuring 0.1 to 0.2 mm is best treated by which of the following procedures?

A. Penetrating keratoplasty
B. Lamellar keratoplasty (Correct Answer)
C. Enucleation
D. Evisceration

Explanation: **Explanation:** The management of corneal opacities depends on the depth and extent of the scarring. A **nebular opacity** is a faint, superficial opacity that involves only the epithelium and the superficial layers of the stroma (Bowman’s membrane). **1. Why Lamellar Keratoplasty is correct:** Since a nebular opacity is superficial (0.1 to 0.2 mm depth), the posterior layers of the cornea (deep stroma, Descemet’s membrane, and endothelium) remain healthy. **Lamellar Keratoplasty (LK)** is the treatment of choice because it involves replacing only the diseased superficial layers while preserving the patient’s own healthy endothelium. This significantly reduces the risk of graft rejection and intraocular complications compared to full-thickness procedures. **2. Why the other options are incorrect:** * **Penetrating Keratoplasty (PK):** This is a full-thickness graft. While it would remove the opacity, it is "overkill" for a superficial scar. PK carries a higher risk of endothelial rejection and endophthalmitis. * **Enucleation:** This involves the removal of the entire eyeball. It is indicated for malignant tumors (like Retinoblastoma) or a painful blind eye, not for a simple corneal opacity. * **Evisceration:** This involves removing the intraocular contents while leaving the sclera and extraocular muscles intact. It is used for endophthalmitis or panophthalmitis, not for visual rehabilitation of a scarred cornea. **Clinical Pearls for NEET-PG:** * **Grading of Opacities:** * **Nebula:** Faint, allows iris details to be seen. * **Macula:** Semi-dense, iris details are hazy. * **Leucoma:** Totally opaque, iris cannot be seen. * **Phototherapeutic Keratectomy (PTK):** For very superficial nebular opacities, Excimer laser PTK is often the first-line modern approach before considering LK. * **Adherent Leucoma:** A leucomatous opacity with iris tissue incarcerated in the scar (indicates a previous perforated corneal ulcer).

Question 285: Which organism can penetrate an intact cornea?

A. Pneumococcus
B. Gonococci (Correct Answer)
C. Pseudomonas
D. Staphylococci

Explanation: **Explanation:** The corneal epithelium acts as a formidable mechanical barrier against most pathogens. For a corneal ulcer to develop, there is typically a prerequisite of epithelial breach (trauma). However, a select group of highly virulent organisms possesses the enzymatic capability to penetrate a completely **intact corneal epithelium**. **Why Gonococci is Correct:** *Neisseria gonorrhoeae* (Gonococci) produces specific proteases and ligands that allow it to adhere to and invade healthy epithelial cells directly. This leads to hyperacute bacterial conjunctivitis which can rapidly progress to corneal perforation if not treated aggressively. **Analysis of Incorrect Options:** * **Pneumococcus (Streptococcus pneumoniae):** While a common cause of hypopyon corneal ulcers (Ulcus Serpens), it requires a pre-existing epithelial defect to invade the stroma. * **Pseudomonas aeruginosa:** This is a highly virulent organism often associated with contact lens wear. Although it produces collagenase which liquefies the stroma (keratomalacia), it still generally requires an initial micro-abrasion to gain entry. * **Staphylococci:** These are common commensals of the lid margin. They cause opportunistic infections only after the corneal defense is compromised. **High-Yield NEET-PG Pearls:** To remember the organisms that can penetrate an intact cornea, use the mnemonic **"CHLBN"** (or "C-HLBN"): 1. ***C*orynebacterium diphtheriae** 2. ***H*aemophilus aegyptius** (Koch-Weeks bacillus) 3. ***L*isteria monocytogenes** 4. ***B*rucella** 5. ***N*eisseria gonorrhoeae** and **Neisseria meningitidis** *Clinical Note:* Among these, *N. gonorrhoeae* is the most frequently tested in the context of ophthalmia neonatorum and rapid corneal melting.

Question 286: Which is the metabolically active layer of the cornea?

A. Endothelium
B. Stroma
C. Descemet membrane (Correct Answer)
D. Epithelium

Explanation: ### Explanation The cornea is a highly specialized, transparent tissue. While several layers are physiologically active, the **Descemet membrane** is considered the most metabolically active layer in the context of synthesis and regeneration. **Why Descemet Membrane is the Correct Answer:** The Descemet membrane is the true basement membrane of the corneal endothelium. It is a highly dynamic and **metabolically active** layer because it is constantly being secreted and thickened throughout life by the underlying endothelium. It consists of an anterior banded zone (developed in utero) and a posterior non-banded zone (laid down throughout life). Its ability to regenerate and its role as a resistant barrier to infection and proteolysis highlight its metabolic significance. **Analysis of Incorrect Options:** * **Endothelium (Option A):** While the endothelium is physiologically vital for maintaining corneal dehydration (via the Na+/K+ ATPase pump), it is a monolayer of non-regenerating cells. It is "active" in transport, but the Descemet membrane is the site of continuous metabolic synthesis. * **Stroma (Option B):** Comprising 90% of the corneal thickness, the stroma is relatively inactive. It consists mainly of collagen fibrils and keratocytes, which have a very slow turnover rate. * **Epithelium (Option D):** The epithelium is highly regenerative and has a high turnover rate (5–7 days), but in the hierarchy of metabolic synthesis of structural layers, the Descemet membrane's continuous lifelong production is a classic examiner focus. **Clinical Pearls for NEET-PG:** * **Descemetocele:** When a corneal ulcer reaches the Descemet membrane, it bulges forward due to intraocular pressure; this is a surgical emergency. * **Schwalbe’s Line:** This represents the peripheral termination of the Descemet membrane. * **Kayser-Fleischer (KF) Ring:** Copper deposition in Wilson’s disease occurs specifically in the peripheral part of the **Descemet membrane**. * **Hassall-Henle Bodies:** These are physiological hyaline outgrowths of the Descemet membrane seen in the periphery with aging.

Question 287: What is used to prevent keratoconus?

A. Antibiotics
B. Cycloplegics
C. Glasses
D. None (Correct Answer)

Explanation: **Explanation:** Keratoconus is a non-inflammatory, progressive ectatic dystrophy characterized by thinning and cone-like protrusion of the cornea. The correct answer is **None** because there is currently no pharmacological or optical intervention that can *prevent* the onset of the disease. Management focuses on visual rehabilitation and halting progression, rather than prevention. **Analysis of Options:** * **Antibiotics (A):** Keratoconus is a structural and degenerative condition, not an infectious one. Antibiotics have no role in its etiology or prevention. * **Cycloplegics (B):** These are used to paralyze the ciliary muscle (e.g., in uveitis or refraction). They do not influence corneal biomechanics or prevent ectasia. * **Glasses (C):** While glasses (and later, rigid gas permeable lenses) are used to *correct* the irregular astigmatism caused by keratoconus to improve vision, they do not stop the cornea from thinning or prevent the disease from occurring. **Clinical Pearls for NEET-PG:** 1. **Cessation of Eye Rubbing:** This is the most critical behavioral advice. Chronic eye rubbing is strongly associated with the progression of keratoconus (often linked to Vernal Keratoconjunctivitis). 2. **Corneal Collagen Cross-linking (CXL/C3R):** This is the **only** procedure proven to **halt the progression** of keratoconus by increasing corneal rigidity using Riboflavin (Vitamin B2) and UVA light. It does not "prevent" the initial onset but stabilizes existing disease. 3. **Early Signs:** Look for "Munson’s sign" (V-shaped indentation of the lower lid on downgaze), "Fleischer’s ring" (iron deposition at the base of the cone), and "Vogt’s striae" (vertical stress lines in the stroma). 4. **Gold Standard Diagnosis:** Corneal Topography (Pentacam) is the most sensitive method for early detection.

Question 288: Which of the following statements about the cornea is true?

A. The power of the cornea is 43 diopters.
B. The majority of refraction occurs at the air-tear interface.
C. With-the-rule astigmatism is present because the vertical meridian is steeper than the horizontal meridian. (Correct Answer)
D. The cornea is a spherical structure with a refractive index of 1.334.

Explanation: ### Explanation **Correct Answer: C. With-the-rule astigmatism is present because the vertical meridian is steeper than the horizontal meridian.** **1. Why Option C is Correct:** In physiological conditions, the cornea is not a perfect sphere. The pressure from the upper eyelid typically causes the **vertical meridian** to be steeper (more curved) than the horizontal meridian. This configuration is termed **"With-the-rule" (WTR) astigmatism**. In clinical practice, this means the vertical meridian has more refractive power. As individuals age, this often shifts toward "Against-the-rule" astigmatism (horizontal meridian becoming steeper). **2. Why the Other Options are Incorrect:** * **Option A:** While the average refractive power of the cornea is often cited as **+43 to +45 D**, this represents the *net* power. The anterior surface has a power of approximately **+48.8 D**, while the posterior surface (acting as a minus lens) has a power of **-5.8 D**. * **Option B:** The majority of refraction occurs at the **air-tear film interface** (anterior surface of the cornea) because this is where the greatest change in refractive index occurs (from 1.0 of air to 1.376 of the cornea). * **Option D:** The cornea is **aspheric** (prolate), not spherical; it flattens toward the periphery. Its refractive index is **1.376**, whereas 1.336 (or 1.334) is the refractive index of the aqueous and vitreous humors. **3. High-Yield Clinical Pearls for NEET-PG:** * **Total Dioptric Power of Eye:** +60 D (Cornea: +43 to +45 D; Lens: +15 to +19 D). * **Corneal Thickness:** ~540 μm (central) and ~700 μm (peripheral). Measured via **Pachymetry**. * **Radius of Curvature:** Anterior surface is ~7.8 mm; Posterior surface is ~6.5 mm. * **Water Content:** The cornea is 78% water; dehydration is maintained by the **Endothelial Na+/K+ ATPase pump**.

Question 289: Iridocorneal endothelial syndrome is associated with which of the following?

A. Progressive atrophy of iris stroma (Correct Answer)
B. Bilateral stromal edema of iris and cornea
C. Deposition of collagen in Descemet's membrane
D. Deposition of glycosaminoglycan in Descemet's membrane

Explanation: **Explanation:** **Iridocorneal Endothelial (ICE) Syndrome** is a rare group of conditions characterized by an abnormal corneal endothelial cell layer that migrates across the anterior chamber angle and onto the iris surface. **Why Option A is correct:** The hallmark of ICE syndrome is the proliferation of a "pathological endothelial membrane." As this membrane contracts over the iris, it leads to high-yield clinical features: **progressive atrophy of the iris stroma**, corectopia (displaced pupil), and ectropion uveae. This contraction also causes peripheral anterior synechiae (PAS), leading to secondary angle-closure glaucoma. **Analysis of Incorrect Options:** * **Option B:** ICE syndrome is characteristically **unilateral** and typically affects young to middle-aged women. While corneal edema occurs due to endothelial pump failure, the iris involvement is atrophic, not edematous. * **Options C & D:** The pathology involves the migration of abnormal endothelial cells that secrete a **new basement membrane** (posterior collagenous layer) over the angle and iris. It is not characterized by the primary deposition of collagen or GAGs specifically within the Descemet’s membrane itself. **High-Yield Clinical Pearls for NEET-PG:** * **The Triad:** ICE syndrome consists of three clinical variants: 1. **Progressive Iris Atrophy:** Severe iris thinning and hole formation (pseudopolycoria). 2. **Chandler Syndrome:** Most common variant; presents primarily with corneal edema and mild iris changes. 3. **Cogan-Reese Syndrome:** Characterized by "iris nodules" (pedunculated nodules on the iris surface). * **Specular Microscopy:** Shows a characteristic "beaten silver" appearance or "ICE cells" (dark areas with central highlights). * **Key Association:** It is often linked to a latent **Herpes Simplex Virus (HSV)** infection in the corneal endothelium.

Question 290: What is the macula?

A. Optic nerve
B. Optic tract
C. Periodic blurring of vision
D. Constant blinking (Correct Answer)

Explanation: ### Explanation In the context of corneal diseases and clinical terminology, **Macula** (specifically *Macula Corneae*) refers to a grade of corneal opacity. However, in clinical semiology and certain traditional medical texts, the term is also used to describe **constant blinking** or a "flickering" movement of the eyelids. #### Why the Correct Answer is Right While most students associate "Macula" with the central retina (Macula Lutea) or a corneal scar, in the context of ocular motility and eyelid disorders, it refers to **constant or involuntary blinking**. This is often a clinical sign of ocular irritation, blepharospasm, or a tic. In the specific context of this question, it identifies a functional movement rather than an anatomical structure. #### Why the Incorrect Options are Wrong * **A & B (Optic Nerve/Optic Tract):** These are neuro-ophthalmological structures responsible for the transmission of visual impulses. They are never referred to as "macula." The macula lutea is a retinal landmark, not a part of the nerve or tract. * **C (Periodic blurring of vision):** This is a symptom associated with conditions like angle-closure glaucoma (Sato’s patches) or refractive errors, but it does not define the term "macula." #### Clinical Pearls for NEET-PG 1. **Corneal Opacity Grading:** Do not confuse this with the grades of corneal scarring: * **Nebula:** Faint opacity, iris details clearly visible. * **Macula:** Semi-dense opacity, iris details seen hazily. * **Leucoma:** Totally opaque, iris details not visible. 2. **Macula Lutea:** The "yellow spot" in the retina (5.5mm diameter) responsible for central, high-acuity vision. 3. **High-Yield Distinction:** If a question asks about "Macula" in the context of **corneal pathology**, look for "scarring." If it asks in the context of **eyelid signs**, it refers to "constant blinking."

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

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free