In simple myopic astigmatism, where does the circle of least confusion lie relative to the retina?
- A Anterior to the retina ✓
- B On the retina
- C Posterior to the retina
- D Its position varies with pupil size
Correct answer: A. Anterior to the retina
Explanation
In Sturm's conoid of simple myopic astigmatism, one focal line falls exactly on the retina while the other falls in front of it. The circle of least confusion always lies between the two focal lines, so in this variety it sits in front of the retina. It would fall posterior to the retina in simple hypermetropic astigmatism. Pupil size affects the brightness of the conoid images, not their axial position.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
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