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Anterior Segment Eye OSCE Examination Quiz

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A 47-year-old woman has a pen torch shone from the temporal side across the front of one eye. The temporal half of the iris is lit up, but a crescent of shadow falls on the nasal iris. There is no fluid level in the anterior chamber. A slit-lamp exam with a thin beam is then used at the edge of the cornea. Which result and interpretation best match the pen torch finding?

A peripheral chamber gap equal to the corneal thickness, indicating a deep chamber and an open angle A peripheral chamber gap wider than the corneal thickness, indicating a deep chamber but a raised risk of angle closure from plateau iris A peripheral chamber gap of one quarter corneal thickness, indicating sectoral narrowing but a low overall risk of angle closure A narrow peripheral chamber gap compared with the corneal thickness, indicating a shallow chamber and a drainage angle that may close White cells drifting in the aqueous with flare visible in a narrow bright beam, indicating active anterior uveitis as the direct cause of the nasal shadow

A A peripheral chamber gap equal to the corneal thickness, indicating a deep chamber and an open angle
B A peripheral chamber gap wider than the corneal thickness, indicating a deep chamber but a raised risk of angle closure from plateau iris
C A peripheral chamber gap of one quarter corneal thickness, indicating sectoral narrowing but a low overall risk of angle closure
D A narrow peripheral chamber gap compared with the corneal thickness, indicating a shallow chamber and a drainage angle that may close ✓
E White cells drifting in the aqueous with flare visible in a narrow bright beam, indicating active anterior uveitis as the direct cause of the nasal shadow

The answer is D: A narrow peripheral chamber gap compared with the corneal thickness, indicating a shallow chamber and a drainage angle that may close

Explanation

Why D is correct

See Anterior Chamber. Option D is correct. When you shine a pen torch from the temporal side across the front of the eye, the iris is normally lit evenly. If the anterior chamber (the fluid-filled space between the cornea and the iris) is shallow, the iris is bowed forwards and blocks part of the light, so a crescent of shadow falls on the nasal side. The slit lamp then confirms this with the van Herick technique: a thin bright beam is directed at the edge of the cornea, and you compare the gap between the cornea and iris at the periphery with the thickness of the cornea beside it. A narrow gap means a shallow peripheral chamber and an angle that may close. The angle is the junction of the iris and cornea where fluid (aqueous humour) drains, and if the peripheral iris blocks it, pressure in the eye can rise suddenly, which is acute angle-closure glaucoma. A memory aid: a shadow on the far side means a shallow chamber, and a shallow chamber means a risk of a blocked drain.

Torch test: light from the temporal side normally lights the iris evenly.
Shallow chamber: the bowed iris casts a crescent of shadow on the nasal side.
Slit lamp: the van Herick technique shows a narrow gap between the cornea and iris at the periphery.
Risk: the angle may close, causing acute angle-closure glaucoma.

Why the other options are incorrect

A. A peripheral chamber gap equal to the corneal thickness, indicating a deep chamber and an open angle: A gap equal to the corneal thickness is the van Herick pattern of a deep chamber and an open angle, so it does not match the shallow chamber suggested by the pen torch nasal shadow.
B. A peripheral chamber gap wider than the corneal thickness, indicating a deep chamber but a raised risk of angle closure from plateau iris: A wide peripheral gap suggests a deep chamber, so it does not fit the nasal shadow; plateau iris causes angle closure through an anteriorly rotated ciliary body rather than a wide peripheral gap.
C. A peripheral chamber gap of one quarter corneal thickness, indicating sectoral narrowing but a low overall risk of angle closure: A gap of one quarter corneal thickness is a narrow peripheral chamber, and a nasal pen torch shadow points to generalised shallowing with angle-closure risk, not a low-risk sectoral variant.
E. White cells drifting in the aqueous with flare visible in a narrow bright beam, indicating active anterior uveitis as the direct cause of the nasal shadow: White cells and flare seen in a narrow bright beam are signs of active anterior uveitis, inflammation in the front of the eye. They do not cast a shadow across the iris, so they do not explain the pen torch finding.

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More questions from this set. Start the quiz to answer them and see each explanation.

1
You have finished examining the anterior segment of a patient with a painful, light-sensitive red eye and a focal corneal opacity. What is the best way to complete the examination?
2
A 28-year-old woman has a painful red eye and photophobia. On inspection, the redness is most intense as a ring right around the cornea rather than being greatest at the outer conjunctiva. Which interpretation best matches this pattern?

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