Question

Astigmatic cornea: What are two types of astigmatism that are important to consider for ortho-K fitting?

A. With-the-rule (WTR) and against-the-rule (ATR)
B. Regular and irregular
C. Central and peripheral
D. Corneal and lenticular

Answer 1

With-the-rule (WTR) and Against-the-rule (ATR) are the two types of astigmatism that are important to consider for ortho-K fitting.

Step-by-step explanation:

For orthokeratology (ortho-K) fitting, two types of astigmatism that are important to consider are With-the-rule (WTR) and Against-the-rule (ATR).

With-the-rule (WTR) astigmatism: This type of astigmatism occurs when the steepest meridian is vertical (at a 90-degree angle) and the flattest meridian is horizontal. In this case, the cornea is more curved in the vertical direction, causing light to focus closer in the horizontal direction and resulting in blurred vision in that meridian.

Against-the-rule (ATR) astigmatism: This type of astigmatism occurs when the steepest meridian is horizontal and the flattest meridian is vertical. In this case, the cornea is more curved in the horizontal direction, causing light to focus closer in the vertical direction and resulting in blurred vision in that meridian.