Question

A 17 year old girl with keratitis and severe pain in the eye came to the hospital, and Acanthamoeba keratitis was suspected. The patient gave a history of the following four points. Which one of these is NOT a risk factor for Acanthamoeba keratitis?

• A. Extended wear contact lenses
• B. Exposure to dirty water
• C. Corneal trauma
• D. Squamous blepharitis

Hint:

Acanthamoeba keratitis needs an outside exposure route: contact lenses, dirty water, or trauma. Lid margin disease does not fit that pattern.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The girl has painful keratitis and Acanthamoeba is the suspected cause. We have to pick out the one listed point that does not raise her risk of this infection.

Step 2: Key Concept:
Acanthamoeba is a free living ameba found in soil, dust, tap water, swimming pools, and poorly cleaned contact lens cases. It reaches the cornea when the eye is exposed to a contaminated source or when the surface barrier is broken.

Step 3: Detailed Explanation:
Extended wear contact lenses trap the ameba against the cornea for long hours, especially when lenses are rinsed in tap water or home made saline instead of sterile solution. This is the single biggest risk factor for Acanthamoeba keratitis worldwide, so option (1) is a true risk factor.
Exposure to dirty water, such as pond water, well water, or hot tubs, carries the ameba straight to the eye and is a well known risk factor, particularly in people who do not wear contact lenses at all. So option (2) is also a true risk factor.
Corneal trauma, especially with soil or vegetable matter, breaks the epithelial surface and lets the ameba invade the stroma. This makes option (3) a genuine risk factor as well.
Squamous blepharitis is chronic inflammation of the lid margin, usually from Staphylococcus, and it predisposes to marginal bacterial keratitis, recurrent styes, and dry eye. It has no established link to Acanthamoeba keratitis, which needs an outside exposure route like lenses, dirty water, or trauma, not lid margin disease.

Step 4: Final Answer:
The one point that is not a risk factor for Acanthamoeba keratitis is squamous blepharitis.
Hence, the correct answer is option (4).