Contact Lens — MCQs

Contact Lens Indian Medical PG Practice Questions and MCQs

Question 141: Keratitis in contact lens wearers is caused by all except?

A. Chlamydia
B. Aspergillus
C. Pseudomonas
D. Pneumococcus (Correct Answer)

Explanation: ***Pneumococcus*** - While *Streptococcus pneumoniae* (Pneumococcus) can cause bacterial keratitis, it is **classically associated with corneal ulcers following trauma** rather than contact lens wear. - In contact lens-related keratitis, Pneumococcus is **significantly less common** compared to *Pseudomonas*, which dominates as the primary bacterial pathogen in this setting. - Pneumococcal keratitis typically presents with a **well-demarcated, dense purulent ulcer with hypopyon**, often following corneal injury. *Pseudomonas* - **_Pseudomonas aeruginosa_** is **the most common cause of bacterial keratitis in contact lens wearers**, accounting for the majority of severe cases. - It thrives in moist environments such as contaminated contact lens cases and solutions, producing **exotoxins and proteases that cause rapid corneal destruction and tissue melt**. - Presents with a **rapidly progressive, dense stromal infiltrate** with a characteristic **ground-glass appearance** and potential for perforation. *Aspergillus* - **_Aspergillus_ species** are an important cause of **fungal keratitis**, particularly associated with contact lens wear, poor lens hygiene, and contaminated lens solutions. - Fungal keratitis presents with **feathery-edged infiltrates, satellite lesions**, and ring-shaped infiltrates, often requiring antifungal therapy. - More common in tropical climates and agricultural settings. *Chlamydia* - **_Chlamydia trachomatis_** is primarily a cause of **trachoma** (chronic follicular conjunctivitis leading to scarring) and **adult inclusion conjunctivitis**. - While it can cause **superficial punctate keratitis and pannus formation** in trachoma, it is **NOT a typical cause of acute suppurative keratitis in contact lens wearers**. - The acute bacterial and fungal keratitis seen in contact lens wearers is a different clinical entity from chlamydial conjunctivitis/keratopathy.

Question 142: Which organism is most commonly associated with the wearing of soft contact lenses?

A. Acanthamoeba
B. Pseudomonas aeruginosa (Correct Answer)
C. Aspergillus
D. Staphylococcus aureus

Explanation: ***Pseudomonas aeruginosa*** - This is the **most common bacterial pathogen** causing contact lens-related microbial keratitis, accounting for 30-50% of cases. - Particularly associated with **soft contact lens wear**, it is known for rapid progression and severe corneal ulceration. - Risk factors include **overnight wear**, poor lens hygiene, and contaminated lens storage cases. - Can lead to **sight-threatening keratitis** within 24-48 hours if untreated. *Acanthamoeba* - While strongly associated with contact lens wear (especially poor hygiene and water exposure), it is **much less common** than bacterial causes. - Acanthamoeba keratitis is a severe protozoal infection but has a relatively low incidence (~1-2 per million contact lens wearers). - Characterized by severe pain disproportionate to clinical signs and ring-shaped stromal infiltrate. *Staphylococcus aureus* - A common cause of bacterial keratitis but **less specifically associated** with soft contact lens wear compared to Pseudomonas. - More commonly causes blepharitis and external eye infections. *Aspergillus* - Fungal keratitis is **rarely associated** with contact lens wear in developed countries. - More commonly linked to ocular trauma with vegetative matter in agricultural settings.

Question 143: What is the most common cause of superficial corneal vascularization?

A. Graft rejection
B. Chemical burn
C. Interstitial keratitis
D. Contact lens (Correct Answer)

Explanation: ***Contact lens*** - **Inappropriate contact lens wear**, particularly extended wear or poor hygiene, is the most frequent cause of **corneal neovascularization**. - This occurs due to **chronic hypoxia** or **inflammation** from the lens leading to vessel growth into the normally avascular cornea. *Graft rejection* - While graft rejection in corneal transplantation can lead to vascularization, it is a less common cause compared to contact lens wear. - **Neovascularization** in this context often signifies a severe immune response impacting graft survival. *Chemical burn* - Chemical burns to the eye can cause significant **corneal damage** and subsequent vascularization as a **healing response** to severe injury. - However, the overall incidence of chemical burns leading to neovascularization is lower than that associated with long-term contact lens use. *Interstitial keratitis* - **Interstitial keratitis** involves inflammation of the corneal stroma, which can lead to ghost vessels or active vascularization but is a less prevalent cause of superficial corneal vascularization than contact lens-related issues. - It is often associated with systemic infections like **syphilis** or **Lyme disease**.

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