Eyeglass Prescription - Spherical Lenses and Spherical Correction

Spherical Lenses and Spherical Correction

Usually:

• the spherical component is the main correction
• the cylindrical component is "fine tuning".

Depending on the optical setup, lenses can act as magnifiers, lenses can introduce blur, and lenses can correct blur.

Whatever the setup, spherical lenses act equally in all meridians: they magnify, introduce blur, or correct blur the same amount in every direction.

An ordinary magnifying glass is a kind of spherical lens. In a simple spherical lens, each surface is a portion of a sphere. When a spherical lens acts as a magnifier, it magnifies equally in all meridians. Here, note that the magnified letters are magnified both in height and in width.

Similarly, when a spherical lens puts an optical system out of focus and introduces blur, it blurs equally in all meridians:

Here is how this kind of blur looks when viewing an eye chart. This kind of blur involves no astigmatism at all; it is equally blurred in all meridians.

Spherical equivalent refraction is normally used to determine soft lens power and spherical glasses power. Individuals who are applying for different positions in police or military may be given a certain maximum spherical equivalent they can have.