Which measurement provides the axial length of the globe in A-scan biometry?

In A-scan biometry, the measurement that provides the axial length of the globe is taken from the anterior corneal surface to the macula. This measurement is crucial for determining the length of the eye, which is essential for calculating the correct intraocular lens (IOL) power for cataract surgery.

The axial length is measured in millimeters, and this distance represents the straight-line length from the front of the eye (the anterior cornea) to the back of the eye where the macula is located, which is part of the retina. This information is critical for ophthalmologists to ensure that the lens implanted during surgery will provide the optimal focus for the patient.

In contrast, other options do not measure the axial length. Corneal thickness is related to the health of the cornea and may influence various factors in eye surgery but does not provide axial length. Macular thickness assesses retinal health and potential diseases but is not a direct measure of the globe's length. The distance from the ciliary body to the retina also does not represent the full axial length of the eye, as it does not encompass the full distance to the anterior segment. Thus, the correct answer is based on the direct relationship of the measurement to the overall axial length