What is the first step to take when measuring with a keratometer?

The first step when measuring with a keratometer is to focus the eyepiece. This is essential for ensuring that the user can clearly see the reflected mires, which are the concentric ring patterns created on the cornea. Proper focusing is crucial for obtaining accurate measurements, as it allows the examiner to assess the corneal curvature effectively.

Achieving a sharp focus helps the practitioner to discern the details needed for precise readings and ensures that subsequent steps can be carried out accurately. When the eyepiece is not properly focused, it can lead to mistakes in measurement interpretation and can affect the overall fitting of contact lenses.

While calibrating the instrument and aligning the patient's head are important steps in the overall process of keratometry, they are not the very first steps needed to obtain a clear view of the measurement field. Adjusting the light source is also important but comes after ensuring that the viewer has a proper focus on the eyepiece.