In A-scan biometry, which measurement provides the axial length of the globe?

In A-scan biometry, the axial length of the globe is measured from the corneal surface to the retinal surface. This measurement is essential for calculating the appropriate intraocular lens (IOL) power for cataract surgery, as it directly influences how light is focused within the eye.

The measurement encompasses the full depth of the eye from the front (cornea) to the back (retina), providing a comprehensive representation of the size of the eye. This axial length is critical since variations can lead to refractive errors if not properly accounted for when selecting an IOL.

The other options do not provide a complete measure of axial length. The distance between the corneal surface and the lens only accounts for part of the eye structure, not reaching the retinal surface. The distance between the iris and the retina also excludes the crucial section of the cornea, while the distance from the sclera to the cornea considers only the outer structures of the eye, failing to reach the retinal back end. Thus, the correct measure for the axial length in A-scan biometry is indeed the distance from the corneal surface to the retinal surface.