Anatomy and physiology of the eye: endothelial pump: 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.

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Ophthalmology · Anatomy and physiology of the eye: endothelial pump

Sample item

After intraocular surgery damages the corneal endothelium, the stroma swells and the cornea turns hazy even though the epithelium is intact. Which function of the endothelium normally keeps the stroma deturgesced?

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

The answer and the reasoning

B. Na+/K+ ATPase pump activity on its lateral membranes

The endothelium pumps ions, and water follows, so the stroma stays at about 78 percent water despite its tendency to imbibe. It also acts as a leaky barrier. When too many cells are lost, the pump fails and bullous keratopathy follows.

Option by option

  • A. Evaporation of water from the tear film surface

    Evaporation contributes only a little to dehydration and cannot rescue a failed endothelium.

  • B. Na+/K+ ATPase pump activity on its lateral membranes (correct)

    Correct. Active ion transport and the barrier function maintain deturgescence.

  • C. Mechanical tension from Bowman layer

    Bowman layer is an acellular condensation of stroma and exerts no pumping action.

  • D. Higher pressure in the stroma than the anterior chamber

    Intraocular pressure is higher than stromal pressure, so it pushes water into the stroma, not out.

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.

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Questions about this Ophthalmology question

What is the answer to this Ophthalmology question?

The best answer is B, Na+/K+ ATPase pump activity on its lateral membranes. The endothelium pumps ions, and water follows, so the stroma stays at about 78 percent water despite its tendency to imbibe.

Why is "Evaporation of water from the tear film surface" not the answer?

Evaporation contributes only a little to dehydration and cannot rescue a failed endothelium.

Why is "Mechanical tension from Bowman layer" not the answer?

Bowman layer is an acellular condensation of stroma and exerts no pumping action.

Why is "Higher pressure in the stroma than the anterior chamber" not the answer?

Intraocular pressure is higher than stromal pressure, so it pushes water into the stroma, not out.

What concept does this question test?

It tests Anatomy and physiology of the eye: endothelial pump in Ophthalmology. It also acts as a leaky barrier. When too many cells are lost, the pump fails and bullous keratopathy follows.

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 Anatomy and physiology of the eye: endothelial pump?

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.