# "doublePlot" Function. Astigmatism representation in a plot of double angle

This function draws, in a double angle plot, the data from an astigmatism sample. The mean and standard deviation is computed and represented over the plot by means of a square and an ellipse, respectively.

Astigmatism analysis is based on vector arithmetic. The current standard method in Ophthalmology practice is the Alpins method^{1} whereas in Optometry practice is more common to use the Thibos method.^{2} In the practice, both methods result in similar outputs.

Matlab Toolbox “refractiveAnalysis” developed by Manuel Rodríguez-Vallejo for research purposes included in the version 1.0.0 the "doublePlot" function. This function plots a double angle figure and overlaps the values from an astigmatism sample together with the mean and standard deviation.

Below you have the help of the function. For more information about "refractiveAnalysis" Toolbox please Contact the author

```
% Creates a plot which includes a set of astigmatism data.
% DESCRIPTION
% You can create any plot for describing mean and standard deviation.
% PARAMETERS
% V Matrix of two columns. First column with the magnitude of the astigmatism and second column the orientation.
% stepSector Dioptric power corresponding to each ring of the double angle plot.
% RELATED FUNCTIONS
% meanA
% EXAMPLE
% doublePlot(V, stepSector)
% VERSION 1.0.0
```

References

- Alpins NA. A new method of analyzing vectors for changes in astigmatism. J. Cataract Refract. Surg. 1993; 19: 524–33. 2.
- Thibos LN, Wheeler W, Horner D. Power vectors: an application of Fourier analysis to the description and statistical analysis of refractive error. Optom Vis Sci. 1997; 74: 367–75.