Protozoan Keratitis — MCQs
A patient presents with urethral discharge. Gram stain shows intracellular gram-negative diplococci. What is the causative organism?
Unilateral frontal blisters with upper lid edema and conjunctivitis is seen in?
A young boy who used to wash his contact lenses in tap water or with unhygienic lens fluid developed keratitis. Microscopy revealed an organism with spiked or star-shaped structures. Identify the correct organism responsible.
Herpetic keratitis is treated by which of the following?
In a patient suspected to have Rabies, a corneal smear sample was taken. Which of the following is the MOST SENSITIVE investigation for this specimen?
Interstitial keratitis is associated with all of the following except:
A 56 year old patient presents after 3 days of cataract surgery with a history of increasing pain and diminution of vision after an initial improvement. The most likely cause would be:
Corneal vascularization is caused by which of the following?
Which of the following will be the most important adjuvant therapy in a case of fungal corneal ulcer?
In microcornea, the diameter of the cornea is less than:
Protozoan Keratitis Indian Medical PG Practice Questions and MCQs
Question 1: A patient presents with urethral discharge. Gram stain shows intracellular gram-negative diplococci. What is the causative organism?
- A. Mycoplasma genitalium
- B. Treponema pallidum
- C. Chlamydia trachomatis
- D. Neisseria gonorrhoeae (Correct Answer)
Explanation: ***Neisseria gonorrhoeae*** - The presence of **intracellular gram-negative diplococci** in urethral discharge is a classic microscopic finding for *Neisseria gonorrhoeae*. - This organism directly invades host cells, and its unique gram staining characteristic makes it readily identifiable in clinical samples. *Mycoplasma genitalium* - This organism does not have a **cell wall** and therefore will not gram stain. It cannot be identified by Gram stain. - Diagnosis typically requires molecular methods like **PCR**. *Treponema pallidum* - This spirochete is too thin to be visualized with standard Gram stain and is typically identified using **dark-field microscopy** or serological tests. - It does not present as gram-negative diplococci. *Chlamydia trachomatis* - *Chlamydia trachomatis* is an **obligate intracellular bacterium** but does not stain well with Gram stain due to its unique cell wall structure (lacks peptidoglycan). - It is often diagnosed using **nucleic acid amplification tests (NAATs)**.
Question 2: Unilateral frontal blisters with upper lid edema and conjunctivitis is seen in?
- A. Herpes Simplex
- B. Herpes Zoster Ophthalmicus (Correct Answer)
- C. Neuroparalytic Keratitis
- D. Acanthamoeba Keratitis
Explanation: ***Herpes Zoster Ophthalmicus*** - This condition is characterized by a **unilateral vesicular rash** (blisters) in the **trigeminal dermatome (V1)**, which includes the forehead and upper eyelid, along with significant **lid edema** and **conjunctivitis**. - **Hutchinson's sign** (lesions on the tip, side, or root of the nose) indicates a high risk of ocular involvement due to the nasociliary nerve innervation. *Acanthamoeba Keratitis* - This is an **amoebic infection** of the cornea typically associated with **contact lens wear** and often presents with severe pain and a **ring infiltrate** in the cornea. - It does not typically present with unilateral frontal blisters or significant lid edema. *Herpes Simplex* - Herpes simplex typically causes **recurrent corneal ulcers** (dendritic or geographic) and sometimes blepharitis, but not the widespread **unilateral frontal blisters** seen in the trigeminal distribution. - While it can cause conjunctivitis and lid edema, the pattern of skin lesions is the key differentiator. *Neuroparalytic Keratitis* - This condition results from **trigeminal nerve damage**, leading to corneal anesthesia and subsequent **trophic corneal ulceration**. - It presents primarily with **corneal findings** (epithelial defects, ulcers) due to impaired sensation and tear film stability, not initial vesicular skin lesions or prominent lid edema.
Question 3: A young boy who used to wash his contact lenses in tap water or with unhygienic lens fluid developed keratitis. Microscopy revealed an organism with spiked or star-shaped structures. Identify the correct organism responsible.
- A. Balantidium
- B. Pseudomonas
- C. Acanthamoeba (Correct Answer)
- D. Staphylococcus aureus
Explanation: ***Acanthamoeba*** - *Acanthamoeba* is a **free-living amoeba** found in water, soil, and inadequately disinfected contact lens solutions, specifically linked to **keratitis** in contact lens wearers. - Its characteristic morphology, often described as having **spiked or star-shaped structures**, refers to the **acanthopodia** (spine-like pseudopods) that are distinctive features visible microscopically. *Balantidium* - *Balantidium coli* is a **ciliated protozoan** and primarily causes **intestinal infections** (balantidiasis), not keratitis. - It would be distinguished microscopically by its **large size**, **kidney-shaped macronucleus**, and **cilia**, not spiked structures. *Pseudomonas* - *Pseudomonas aeruginosa* is a **bacterium** and a common cause of **bacterial keratitis**, especially in contact lens wearers, but it is not a protozoan. - Microscopically, it would appear as **rod-shaped bacteria**, not organisms with spiked or star-shaped structures. *Staphylococcus aureus* - *Staphylococcus aureus* is a **bacterium** and a frequent cause of various infections, including **bacterial keratitis**. - Under a microscope, it presents as **Gram-positive cocci in clusters**, not as an amoeba with spiked or star-shaped protrusions.
Question 4: Herpetic keratitis is treated by which of the following?
- A. Analgesics
- B. Atropine
- C. Steroids
- D. Acyclovir (Correct Answer)
Explanation: ***Acyclovir*** - **Acyclovir** is an **antiviral agent** that specifically targets the **herpes simplex virus**, which is the causative agent of herpetic keratitis. - It works by inhibiting viral DNA replication, thereby reducing viral load and preventing further damage to the cornea. *Analgesics* - **Analgesics** are used to manage pain but do not address the **viral etiology** of herpetic keratitis. - While they can improve patient comfort, they are not a definitive treatment for the underlying infection. *Atropine* - **Atropine** is a **cycloplegic agent** used to paralyze the ciliary muscle and dilate the pupil, often to reduce pain from ciliary spasms in uveitis. - It does not have **antiviral properties** and is not effective against the herpes virus. *Steroids* - **Corticosteroids** can suppress inflammation but are generally **contraindicated** in active herpetic keratitis, especially in the epithelial form. - They can worsen the viral infection by compromising the immune response, potentially leading to **corneal ulceration** and perforation.
Question 5: In a patient suspected to have Rabies, a corneal smear sample was taken. Which of the following is the MOST SENSITIVE investigation for this specimen?
- A. Virus isolation
- B. Immunofluorescence test
- C. Negri body visualization
- D. RT PCR (Correct Answer)
Explanation: ***RT PCR*** - **Reverse transcriptase polymerase chain reaction (RT-PCR)** is the **most sensitive molecular method** for detecting **rabies virus RNA** in corneal smear samples. - It provides **rapid, highly sensitive, and specific** detection of rabies viral nucleic acid, making it the preferred method for antemortem diagnosis from this specimen. - RT-PCR has **higher sensitivity than immunofluorescence** for corneal samples. *Immunofluorescence test* - **Direct fluorescent antibody (DFA) test** can be performed on corneal impression smears and is an established antemortem diagnostic method. - However, its **sensitivity is lower than RT-PCR** for this specific sample type, with higher false-negative rates. - DFA remains the gold standard primarily for **post-mortem brain tissue examination**. *Virus isolation* - Virus isolation is **time-consuming, less sensitive**, and requires specialized biosafety level 3 facilities. - **Corneal smears** have lower viral loads, making isolation less reliable compared to molecular methods. - Not routinely used for rapid diagnosis. *Negri body visualization* - **Negri bodies** are pathognomonic cytoplasmic inclusion bodies found in neurons, particularly in the **hippocampus and cerebellum**. - These can **only be visualized in brain tissue** through histopathological examination (post-mortem). - **Cannot be detected in corneal smears** as they are neuronal inclusions.
Question 6: Interstitial keratitis is associated with all of the following except:
- A. Syphilis
- B. Acanthamoeba (Correct Answer)
- C. Chlamydia Trachomatis
- D. Herpes Zoster Virus (HZV)
Explanation: ***Acanthamoeba*** - **Acanthamoeba keratitis** is a **suppurative keratitis** characterized by a painful, ring-shaped infiltrate with epithelial ulceration, typically associated with contact lens use and contaminated water exposure. - It causes **ulcerative stromal inflammation**, not the **non-ulcerative deep stromal inflammation** that characterizes classic interstitial keratitis. - **This is NOT a cause of interstitial keratitis.** *Syphilis* - **Congenital syphilis** is the **CLASSIC cause** of bilateral **interstitial keratitis**, often presenting in late childhood with "salmon patch" appearance, photophobia, lacrimation, and eventual ghost vessels. - The inflammation is **non-ulcerative and chronic**, affecting the **deep corneal stroma** with preservation of epithelium. - This is the most important association with interstitial keratitis to remember. *Chlamydia Trachomatis* - **Chlamydia trachomatis** causes **trachoma**, a chronic keratoconjunctivitis leading to **superficial keratitis with pannus formation** (superficial vascularization from the limbus). - The corneal involvement in trachoma is **superficial**, not the deep stromal inflammation seen in classic interstitial keratitis. - While listed in some references, **Chlamydia is NOT a standard cause of interstitial keratitis** in major ophthalmology textbooks. - **Note:** This option is potentially debatable, but Acanthamoeba is the more definitively incorrect answer. *Herpes Zoster Virus (HZV)* - **Herpes zoster ophthalmicus** can lead to **interstitial keratitis** and **disciform keratitis** (immune-mediated stromal inflammation with disc-shaped corneal edema). - Similarly, **HSV (Herpes Simplex Virus)** causes stromal keratitis, a form of interstitial keratitis. - The corneal involvement includes **deep stromal inflammation, scarring**, and potential neurotrophic changes leading to vision impairment.
Question 7: A 56 year old patient presents after 3 days of cataract surgery with a history of increasing pain and diminution of vision after an initial improvement. The most likely cause would be:
- A. Endophthalmitis (Correct Answer)
- B. Central retinal vein occlusion
- C. Posterior capsular opacification (PCO)
- D. Retinal detachment
Explanation: ***Endophthalmitis*** - **Endophthalmitis** is a severe inflammation of the intraocular fluids (vitreous and aqueous humor), most commonly caused by infection following cataract surgery. - The presentation of **increasing pain** and **diminution of vision** a few days after initial improvement is a classic sign of acute post-operative endophthalmitis. *Central retinal vein occlusion* - **Central retinal vein occlusion (CRVO)** typically causes sudden, painless vision loss. - It is not commonly associated with **increasing pain** or a temporal relationship to recent cataract surgery in this manner. *Posterior capsular opacification (PCO)* - **Posterior capsular opacification (PCO)** develops weeks or months after cataract surgery, not within a few days. - It presents as gradual, painless blurring of vision without significant pain. *Retinal detachment* - **Retinal detachment** typically presents with sudden vision loss, flashes of light (photopsia), and floaters. - While it can occur after cataract surgery, it is less likely to present with **increasing pain** as the primary symptom described.
Question 8: Corneal vascularization is caused by which of the following?
- A. Graft rejection
- B. Chemical burn
- C. Contact lens use
- D. All of the above (Correct Answer)
Explanation: **Explanation:** Corneal vascularization (neovascularization) is a pathological condition where new blood vessels grow into the normally avascular cornea. This occurs when the balance between angiogenic factors (like VEGF) and anti-angiogenic factors is disrupted, usually due to inflammation, hypoxia, or limbal stem cell deficiency. **Analysis of Options:** * **Graft Rejection (Option A):** This is an inflammatory immune response. Neovascularization is both a risk factor for and a sign of corneal graft rejection. Vessels provide a pathway for immune cells to reach the donor tissue, leading to an "immune attack." * **Chemical Burn (Option B):** Alkali burns are particularly notorious. They cause extensive limbal stem cell damage and severe inflammation. The loss of the limbal barrier allows conjunctival vessels to encroach upon the cornea (conjunctivalization). * **Contact Lens Use (Option C):** Chronic use, especially with low-permeability lenses or overwear, leads to **corneal hypoxia**. The lack of oxygen triggers the release of vasoproliferative factors, causing superficial or deep stromal vessels to grow from the limbus. Since all three conditions are well-established causes of corneal neovascularization, **Option D** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **Pannus:** This refers to superficial vascularization accompanied by infiltration of granulation tissue (commonly seen in Trachoma and Phlyctenular keratoconjunctivitis). * **Micropannus:** Defined as vessel growth <2mm beyond the limbus (common in Trachoma). * **Ghost Vessels:** These are non-perfused, empty vascular channels that remain after the inciting inflammatory stimulus has subsided (classic in interstitial keratitis/Syphilis). * **Management:** Topical steroids or NSAIDs are used to reduce inflammation; anti-VEGF agents (e.g., Bevacizumab) are emerging treatments.
Question 9: Which of the following will be the most important adjuvant therapy in a case of fungal corneal ulcer?
- A. Atropine sulphate eye ointment (Correct Answer)
- B. Dexamethasone eye drops
- C. Pilocarpine eye drops
- D. Lignocaine eye drops
Explanation: ### Explanation In the management of a fungal corneal ulcer, **Atropine sulphate (1%) eye ointment** is the most critical adjuvant therapy alongside antifungal agents. **Why Atropine is the Correct Choice:** Fungal keratitis is almost always associated with **secondary anterior uveitis** and **iridocyclitis** due to the penetration of fungal toxins into the anterior chamber. Atropine acts as a potent **cycloplegic and mydriatic**, serving three vital functions: 1. **Relieves Ciliary Spasm:** It reduces the intense pain associated with the spasm of the ciliary body. 2. **Prevents Posterior Synechiae:** By keeping the pupil dilated, it prevents the iris from adhering to the lens. 3. **Increases Blood Supply:** By reducing congestion in the ciliary body, it improves ocular blood flow, which aids in the healing process. **Analysis of Incorrect Options:** * **B. Dexamethasone eye drops:** Steroids are strictly **contraindicated** in active fungal ulcers. They promote fungal growth, inhibit collagen synthesis (leading to perforation), and suppress the local immune response. * **C. Pilocarpine eye drops:** This is a miotic. It would worsen the pain by causing ciliary muscle contraction and increase the risk of forming small, fixed pupils (annular synechiae). * **D. Lignocaine eye drops:** While a local anesthetic, it is toxic to the corneal epithelium and inhibits wound healing. It should never be used for long-term pain management in ulcers. **Clinical Pearls for NEET-PG:** * **Drug of Choice (Medical):** Topical **Natamycin (5%)** is the first-line treatment for filamentous fungi (e.g., *Aspergillus*, *Fusarium*). * **The "Immune Ring":** Wessely’s ring (an immune ring of Ag-Ab complex) is often seen in fungal ulcers. * **Surgical Intervention:** If medical therapy fails or perforation is imminent, a **therapeutic penetrating keratoplasty (TPK)** is indicated.
Question 10: In microcornea, the diameter of the cornea is less than:
- A. 9 mm
- B. 10 mm (Correct Answer)
- C. 11 mm
- D. 8 mm
Explanation: **Explanation:** **Microcornea** is a congenital anomaly where the cornea is abnormally small but otherwise anatomically normal in structure and thickness. 1. **Why Option B is correct:** The standard clinical definition of microcornea is a horizontal corneal diameter of **less than 10 mm** in an adult, or **less than 9 mm** in a newborn. Since the question refers to the general diagnostic threshold, 10 mm is the established benchmark. The condition occurs due to an arrest in the growth of the cornea after the 5th month of gestation, while the rest of the eye may grow normally. 2. **Why other options are incorrect:** * **Option A (9 mm):** This is the threshold for a **newborn**. In an adult, a 9 mm cornea is already well within the range of microcornea. * **Option C (11 mm):** The average adult corneal diameter is approximately 11.5 to 12 mm. A diameter of 11 mm is considered a "small-normal" cornea but does not meet the pathological criteria for microcornea. * **Option D (8 mm):** While an 8 mm cornea is indeed microcorneal, it is not the *threshold* definition. 10 mm is the upper limit for the diagnosis. **High-Yield Clinical Pearls for NEET-PG:** * **Refractive Status:** Microcornea usually results in **hypermetropia** (flat cornea) and predisposes the patient to **closed-angle glaucoma** due to a crowded anterior segment. * **Associations:** It can occur in an otherwise normal eye (isolated) or as part of **Microphthalmos** (small globe). * **Systemic Associations:** Often linked with **Fetal Alcohol Syndrome**, Turner syndrome, and Ehlers-Danlos syndrome. * **Contrast with Megalocornea:** Megalocornea is defined as a horizontal diameter **>13 mm**.
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