Conjunctiva and cornea: preservative toxicity: practice question

A Ophthalmology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

Try it

Ophthalmology · Conjunctiva and cornea: preservative toxicity

Sample item

A glaucoma patient on four topical drops daily for three years develops diffuse punctate epithelial erosions, redness and burning, with normal tear production. Which constituent of the bottles is most responsible?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

B. Benzalkonium chloride

Benzalkonium chloride is the common preservative in multidose bottles and is toxic to the corneal and conjunctival surface with chronic use. Switching to preservative-free preparations helps. Buffers and tonicity agents are not typical causes of this epithelial toxicity.

Option by option

  • A. Phosphate buffer

    Phosphate buffer is a minor excipient and does not cause this toxic keratopathy.

  • B. Benzalkonium chloride (correct)

    Correct. Chronic benzalkonium chloride exposure damages the ocular surface epithelium.

  • C. Acidic vehicle pH

    Most formulations are near physiological pH, and tear buffering neutralises small differences.

  • D. Sodium chloride tonicity agent

    The sodium chloride tonicity agent is isotonic and not toxic at these concentrations.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

More Ophthalmology questions

Questions about this Ophthalmology question

What is the answer to this Ophthalmology question?

The best answer is B, Benzalkonium chloride. Benzalkonium chloride is the common preservative in multidose bottles and is toxic to the corneal and conjunctival surface with chronic use.

Why is "Phosphate buffer" not the answer?

Phosphate buffer is a minor excipient and does not cause this toxic keratopathy.

Why is "Acidic vehicle pH" not the answer?

Most formulations are near physiological pH, and tear buffering neutralises small differences.

Why is "Sodium chloride tonicity agent" not the answer?

The sodium chloride tonicity agent is isotonic and not toxic at these concentrations.

What concept does this question test?

It tests Conjunctiva and cornea: preservative toxicity in Ophthalmology. Switching to preservative-free preparations helps. Buffers and tonicity agents are not typical causes of this epithelial toxicity.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Conjunctiva and cornea: preservative toxicity?

Group the red eye by what to examine and what the pupil does. Then use the flashcards and the other Ophthalmology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.