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The measurement used in A-scan biometry to determine the axial length of the globe is from the anterior corneal surface to the retina. This is crucial for calculations related to intraocular lens (IOL) power, especially before cataract surgery.

In this context, the anterior corneal surface is the front part of the eye where light enters, and the retina is the light-sensitive layer at the back of the eye. The distance between these two points reflects the total length of the eyeball, which is important for achieving optimal visual outcomes after lens replacement surgery. Accurately measuring this distance allows ophthalmologists to select the proper IOL for the patient, ensuring that the focal point is appropriately set for clear vision.

The other options do not measure the total axial length of the globe, which is why they are less relevant in this context. Measurements taken from the anterior corneal surface to the iris or the anatomical center to the retina do not provide the full axial length required for effective lens calculations. Similarly, measuring from the posterior pole to the lens does not capture the essential distance to the retina, making the selected measurement the most appropriate choice.