With a spectacle prescription of -3.00 -1.50 x 180 and K readings of 43.50 @180 and 46.50 @ 90, what would be the residual astigmatism?

With a spectacle prescription of -3.00 -1.50 x 180 and K readings of 43.50 @180 and 46.50 @ 90, what would be the residual astigmatism?

• A. +1.50 x 90
• B. +1.50 x 180
• C. -1.50 x 90
• D. -1.50 x 180

Answer: (B)

To determine the residual astigmatism, one needs to analyze the spectacle prescription and the corneal curvature measurements (K readings). The spectacle prescription is given as -3.00 -1.50 x 180. This indicates that there is a spherical component of -3.00D and a cylindrical component of -1.50D with a 180-degree axis. The K readings indicate the flat and steep meridians of the cornea: 43.50 diopters at 180 degrees, and 46.50 diopters at 90 degrees. The difference between these two readings gives an amount of corneal astigmatism, which can be calculated as follows: 1. **Calculate the K astigmatism**: \[ K \text{ astigmatism} = K_{\text{steep}} - K_{\text{flat}} = 46.50 - 43.50 = 3.00D \] This astigmatism is aligned at 90 degrees (the steep meridian). 2. **Combine the sphere and cylinder from the spectacle prescription**: The total refractive power in the horizontal (180 degrees) meridian would be:

To determine the residual astigmatism, one needs to analyze the spectacle prescription and the corneal curvature measurements (K readings). The spectacle prescription is given as -3.00 -1.50 x 180. This indicates that there is a spherical component of -3.00D and a cylindrical component of -1.50D with a 180-degree axis.

The K readings indicate the flat and steep meridians of the cornea: 43.50 diopters at 180 degrees, and 46.50 diopters at 90 degrees. The difference between these two readings gives an amount of corneal astigmatism, which can be calculated as follows:

1. Calculate the K astigmatism:

[

K \text{ astigmatism} = K_{\text{steep}} - K_{\text{flat}} = 46.50 - 43.50 = 3.00D

]

This astigmatism is aligned at 90 degrees (the steep meridian).

2. Combine the sphere and cylinder from the spectacle prescription:

The total refractive power in the horizontal (180 degrees) meridian would be: