In the last post we described with graphics how the patients were before surgery and how they were after it, the simulated data can be found here. In this one we will relate those results to each other. The first graphic can be seen quite a lot in publications, here is the attempted vs achieved spherical equivalent (SE):


pre post1


The black thick diagonal is the attempted = achieved SE and ideally all points should be on it. The blue diagonals are the attempted = achieved +/- 1 D, the points falling in the light blue region achieve a SE within +/- 1 D of the attempted SE. The interesting thing about this graphic is that is independent of the target refraction, it doesn´t matter if we want to end up emmetrope or with -1 D for monovision for example, the target refraction has already been taking into account in the attempted SE.

The second graphic shows the SE preop vs the SE postop:


pre post2


I actually prefer this graphic to the first one, probably because it´s easier to see deviations from a horizontal line than from a diagonal. On the other hand, here ideally the points would be on the thicker horizontal bar crossing the 0 but only if the target refraction is emmetropia, the vertical thick line is for a SE preop of 0 D. To solve the target refraction problem we could separate the points by target. Since the data I am using doesn´t have a target refraction I will assume all men have a target refraction of -0.75 D and all women a target refraction of 0, here is the result:


 pre post3


Now we have a panel per target refraction. From here on we can focus on different aspects and make more subdivisions depending on what we are interested to see and add more elements to the graphic, here is an example:


pre post4



In this graphic we have two panels one for patients under 40 years old and other for patients above 40, within each panel the points are coloured by sex. The black line surrounded by a gray shaded area is the linear regression for all the points in that panel, the shaded area is the 95 % confidence interval for that regression line.

Up to know we haven´t taken the astigmatism into account and we still don´t know what is happening with it, obviously it´s not the same a +0.50 sph. -1.00 cyl. at 180º and a +1.00 sph. -2.00 cyl. at 90º although both SE are 0. In the next post I will make graphics that will show more about the cilinder and the axis.