ABO NOCE Practice Test

When adjusting for spherical equivalent, what adjustment is made to the cylinder?

1. It is ignored

2. It is halved

3. It is doubled

4. It is tripled

The correct answer is: It is halved

When adjusting for spherical equivalent in a prescription, the correct approach is to halve the cylinder value. This is done because the spherical equivalent is calculated by combining the sphere power with half of the cylinder power. This ensures that the overall vision correction accounts for the astigmatic component without overcompensating, which can happen if the full cylinder value were used. The spherical equivalent formula is often expressed as: Spherical Equivalent = Sphere + (Cylinder / 2) Therefore, by halving the cylinder, the adjustment accurately reflects the astigmatic correction in relation to the spherical component of the prescription. This method leads to a more balanced correction that optimally addresses both spherical and cylindrical errors in a patient's vision.