If given K's of 42.50 @180 and 44.50 @90 with a prescription of -3.50-2.50X 90, what lens power should be ordered if the lenses are to be one half diopter steeper than K?

To determine the appropriate lens power that should be ordered, it's essential to understand the relationship between the K readings (keratometry readings) and the desired lens power for this prescription. The K readings indicate the curvature of the cornea and are given as 42.50 diopters at 180 degrees and 44.50 diopters at 90 degrees.

When the question states that the lenses are to be one half diopter steeper than K, this means that we need to find the average value of the K readings first. The average K value is calculated as follows:

• First, take the two K values: 42.50 and 44.50.
• Add these together: 42.50 + 44.50 = 87.00.
• Divide by 2 to find the average K: 87.00 / 2 = 43.50D.

Now that we have the average K value of 43.50, we then need to determine what "one half diopter steeper" means. This means we will add 0.50D to our average K value:

• 43.50D + 0.50D = 44.00D.

Next, to arrive