A spherical RGP lens bearing on the eye shows a horizontal dumbbell shape of bearing. This indicates which astigmatism orientation?

A spherical RGP lens bearing on the eye shows a horizontal dumbbell shape of bearing. This indicates which astigmatism orientation?

• A. WTR
• B. ATR
• C. Oblique
• D. No astigmatism

Answer: (A)

Bearing patterns on a spherical RGP lens reveal the orientation of corneal astigmatism. A horizontal dumbbell shape indicates the lens is bearing more on the left–right sides, which corresponds to the vertical meridian of the cornea being steeper. When the vertical meridian is steeper, that’s called with-the-rule astigmatism, and the cylinder axis for WTR is horizontal (0 or 180 degrees). So the horizontal bearing pattern points to a horizontal axis of astigmatism, i.e., with-the-rule. If the bearing pattern were vertical, it would suggest ATR (vertical axis), and a circular or evenly distributed bearing would suggest no significant astigmatism.

Bearing patterns on a spherical RGP lens reveal the orientation of corneal astigmatism. A horizontal dumbbell shape indicates the lens is bearing more on the left–right sides, which corresponds to the vertical meridian of the cornea being steeper. When the vertical meridian is steeper, that’s called with-the-rule astigmatism, and the cylinder axis for WTR is horizontal (0 or 180 degrees). So the horizontal bearing pattern points to a horizontal axis of astigmatism, i.e., with-the-rule. If the bearing pattern were vertical, it would suggest ATR (vertical axis), and a circular or evenly distributed bearing would suggest no significant astigmatism.