What is the primary function of a lensometer?

The primary function of a lensometer is to measure the patient's current spectacle prescription. This instrument is designed to determine the prescription of lenses by analyzing the refractive power of the spectacles being tested. When a pair of glasses is placed in the lensometer, it allows the technician to precisely identify the power of each lens and evaluate the prescription written for the lenses, which is crucial for ensuring that the patient has the correct vision correction.

In contrast, measuring corneal curvature typically involves tools like a keratometer, which specifically assesses the shape of the cornea—important for fitting contact lenses, but not the primary function of a lensometer. Checking intraocular pressure is done with an instrument called a tonometer, which plays a critical role in glaucoma assessments and monitoring eye health, rather than lens prescriptions. Assessing retinal health involves techniques such as fundus photography or optical coherence tomography, neither of which are within the scope of what a lensometer provides. Thus, the ability of the lensometer to accurately measure spectacle prescriptions makes it a vital tool in ophthalmic practices for ensuring proper vision correction.