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

The axial length of the globe in A-scan biometry is measured from the anterior corneal surface to the macula. This measurement is crucial for various applications, particularly in calculating the power of intraocular lenses for cataract surgery and in assessing conditions related to refractive errors.

Measuring from the anterior corneal surface provides a reference point that allows for accurate determination of how far light travels within the eye, ultimately reaching the macula, which is essential for visual function. A-scan biometry uses ultrasound technology to provide this measurement, allowing practitioners to obtain precise data that inform treatment decisions.

The other options involve measurements that do not accurately represent the total axial length of the globe. For instance, measuring from the posterior corneal surface to the retina would not start from the anterior segment of the eye, potentially leading to an inaccurate assessment of axial length. Similarly, measuring corneal thickness to the lens or anterior chamber depth to the retina would focus on different aspects of ocular anatomy that do not correlate to the overall axial length.