Conventionally, the first number in a written keratometry reading corresponds to?

In a keratometry reading, the first number represents the flattest corneal meridian, which is a crucial component in assessing the curvature of the cornea. This measurement is important for various aspects of ocular health, particularly when evaluating astigmatism and planning for contact lens fittings or surgical procedures such as cataract surgery or refractive surgery.

This first value gives practitioners an understanding of the corneal shape and how it may affect visual acuity. By knowing the flattest corneal meridian, eye care professionals can better interpret the overall corneal topography, as it corresponds to the area of the cornea that has the least curvature. This information is particularly useful in diagnosing conditions like keratoconus or other corneal irregularities.

The other options do not accurately represent the first number in a keratometry reading. For instance, while the steepest corneal meridian provides additional information about the cornea's curvature, it is not what the first number indicates. Similarly, the total refracting power and the axis of the flatter meridian serve different purposes in a comprehensive examination but are not the focus of that initial measurement. Thus, understanding that the first number reflects the flattest corneal meridian is key for