A scan biometer is primarily used in ophthalmology for measuring the axial length of the eye, which is crucial for selecting the correct power of intraocular lenses (IOLs) in cataract surgery. It aids in the preoperative evaluation of patients, assists in IOL power calculations, and helps diagnose and monitor eye conditions such as glaucoma. A scan biometry plays a vital role in ensuring accurate vision correction and improving patient outcomes in ophthalmic procedures.