What is the dioptric difference between the flat and steep keratometry readings in Ks 43/43.50 at 090?

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Multiple Choice

What is the dioptric difference between the flat and steep keratometry readings in Ks 43/43.50 at 090?

Explanation:
Keratometry measures the cornea in two principal meridians: a flatter one and a steeper one. The amount of corneal astigmatism is the difference between those two powers. Here, the flat meridian is 43.00 D and the steep meridian is 43.50 D. Subtracting gives 0.50 D. The axis at 090 simply indicates the orientation of the meridians, but does not change the difference in diopters. So the dioptric difference is 0.50 diopters.

Keratometry measures the cornea in two principal meridians: a flatter one and a steeper one. The amount of corneal astigmatism is the difference between those two powers. Here, the flat meridian is 43.00 D and the steep meridian is 43.50 D. Subtracting gives 0.50 D. The axis at 090 simply indicates the orientation of the meridians, but does not change the difference in diopters. So the dioptric difference is 0.50 diopters.

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