Diseases of the Cornea Practice Questions

Q: Corneal sensation is tested by which instrument?

Aesthesiometer. ### 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**.

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

Scarring of the cornea. **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).

Q: Which organism can penetrate an intact cornea?

Gonococci. **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.

Q: What is used to prevent keratoconus?

None. **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.

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

Progressive atrophy of iris stroma. **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.

Q: What is the macula?

Constant blinking. ### 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."

Question 1

Corneal sensation is tested by which instrument?

Accepted Answer

Aesthesiometer

Answer

Keratometry

Answer

Pachymeter

Answer

Specular microscopy

Question 2

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

Accepted Answer

Scarring of the cornea

Answer

Cataract formation

Answer

Hemorrhage into the anterior chamber

Answer

Hemorrhage into the posterior chamber

Question 3

Neurotrophic keratopathy is caused by which of the following?

Accepted Answer

Trigeminal nerve palsy

Answer

Bell's palsy

Answer

Facial and trigeminal nerve palsy both

Answer

All of the above

Question 4

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

Accepted Answer

Lamellar keratoplasty

Answer

Penetrating keratoplasty

Answer

Enucleation

Answer

Evisceration

Question 5

Which organism can penetrate an intact cornea?

Accepted Answer

Gonococci

Answer

Pneumococcus

Answer

Pseudomonas

Answer

Staphylococci

Question 6

Which is the metabolically active layer of the cornea?

Accepted Answer

Descemet membrane

Answer

Endothelium

Answer

Stroma

Answer

Epithelium

Question 7

What is used to prevent keratoconus?

Accepted Answer

None

Answer

Antibiotics

Answer

Cycloplegics

Answer

Glasses

Question 8

Which of the following statements about the cornea is true?

Accepted Answer

With-the-rule astigmatism is present because the vertical meridian is steeper than the horizontal meridian.

Answer

The power of the cornea is 43 diopters.

Answer

The majority of refraction occurs at the air-tear interface.

Answer

The cornea is a spherical structure with a refractive index of 1.334.

Question 9

Iridocorneal endothelial syndrome is associated with which of the following?

Accepted Answer

Progressive atrophy of iris stroma

Answer

Bilateral stromal edema of iris and cornea

Answer

Deposition of collagen in Descemet's membrane

Answer

Deposition of glycosaminoglycan in Descemet's membrane

Question 10

What is the macula?

Accepted Answer

Constant blinking

Answer

Optic nerve

Answer

Optic tract

Answer

Periodic blurring of vision

Diseases of the Cornea — MCQs

Diseases of the Cornea — MCQs

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