BESST II IOL POWER CALCULATOR                                    

 
 
BESSt 2.0 Formula:
This new improved algorithm allows more accurate IOL power prediction in eyes which previously underwent Myopic or Hyperopic Laser refractive surgery (e.g. PRK, LASEK, Epi-LASIK, LASIK, Femtosecond LASIK etc..) compared to BESSt 1.0 and other methods.

BESSt 1.0 Formula:
The old formula (still useful to estimate True Corneal Power following laser ablation) is still available, but now it has to be used only in those rare cases in which it’s unknown whether the eye has had a laser refractive treatment for Myopia or for Hypermetropia.

3rd Generation formulas including Hoffer Q and SRK/T:
The software includes the correct versions of the most widely used 3rd Generation formulas. This includes the most updated version of the SRK/T and Hoffer Q formula (the latter takes into account both the erratum published in 1994 and the one published in the January 2007 issue of the JCRS). The use of both the Hoffer Q and SRK/T formula in our software is officially recognised by their respective authors.

Off-line biometry directly from your laptop:
If installed on your laptop or theatre-PC, the program can also become an excellent tool to repeat or simply double check your IOL power calculations in theatre at the last minute even in standard non post-laser refractive surgery cases when a different lens or a different target refraction becomes necessary. 

Double-K adjustment after laser refractive surgery:
If for any reason you choose to use standard 3rd Generation Formulas rather than BESSt 2.0 (why?!) to estimate IOL power after laser refractive surgery, we recommend that at least you use the Aramberri’s Double-K adjustment to limit the possible refractive surprises. Double-K adjustments are available with the refraction calculated either at the Corneal (cp) or Spectacle (sp) plane. Some authors recommend the use of the Spectacle plane value to prevent a hyperopic outcome. 

Real time IOL Power prediction plotting for any desired biometry formula:
This unique feature allows real time plotting of IOL Power prediction curves for any desired combination of AL and K values using any desired formula. The graphs so created allow to immediately identify those not-so-rare cases in which the SRK/T formula may be inaccurate (this can happen in very steep corneas such as after keratoplasty or in keratoconus) or when striking differences are present between one formula and another.


BESSt II IOL Power Calculator - IOL Power plotting (click to enlarge).

Warning messages with automatic detection of the SRK/T formula’s "Zero Argument" and "Cusp" phenomena:
This advanced function present in the software automatically detects those cases in which this formula yields incorrect results due to the occurrence of either the "Zero Argument" or the "Cusp" phenomenon.

SRK/T formula’s zero argument (or Negative Square Root) phenomenon: 
For certain combinations of AL and K readings (or anterior corneal radii), and most frequently for very steep corneas (such as post-corneal transplant), the formula as it was published yields an error and would not allow the calculation to be performed (Figure 2). This happens when the argument of the square root in the Estimated ACD equation [ACDest = ACDconst - 3.336 + r – SQRT (r2 - Cw2/4)] becomes negative. With reference to Figure 2, all the area of the curve indicated by the asterisk can not be calculated when this occurs.

Figure 2. Zero argument (or negative square root) phenomenon of the SRK/T formula.

In the IOL Master TM this problem was addressed so that the formula would not hang up and return a result for the calculation. However, this is achieved by assigning the value zero to the argument of the square root of the Estimated ACD equation in all cases when such value happens to be negative. This allows a result to be displayed but generates  inaccurate IOL power values in some cases. Our software would automatically warn when this phenomenon occurs and will advise to use alternative formulae such as for example the Hoffer Q in those cases.

SRK/T formula’s cusp phenomenon: 
The SRK/T’s cusp phenomenon is a direct consequence of the zero argument problem of the above formula and it occurs only for certain combinations of AL and K values. This gives rise to a sharp increase (hence the term “cusp”) of the estimated IOL power, which is very likely to result in a serious refractive surprise. The following are the combinations of AL and K values which are at greater risk of incurring into this problem: AL< 22 mm and K>52.5; AL 22-24 mm and K>49.5; AL>24 mm and K>48.3. Again, the software would automatically warn the user when this happens.

Figure 3. Cusp phenomenon of the SRK/T formula.
Calculation Print-out:
The printout page shows IOL power calculations using the different formulae. The results are displayed in 0.50 D increments and range +/- 3.00 D from the desired Target Refraction. The program shows the actual value of the IOL power required to achieve the Target Refraction (e.g. 22.68 D), rather than a value rounded to the 0.50 decimal (e.g. 23.00 D).  
Now the printout also displays information on Pentacam values and pre- and post-refractive surgery K values and Refraction, all in a single page.
BESSt2 IOL Power Calculator - IOL Power calculation printout (click to enlarge).
IOL Power Plot Print-out:
The IOL Power graphs generated with the Plot function can be printed either on traditional paper or as PDF files. To avoid confusion with too many curves simultaneously on the graph, only the ones selected in the plot window will be shown.


BESSt2 IOL Power Calculator - IOL power plot printout (click to enlarge).

Import/Export function to calculate large data sets at once:
This extremely powerful function allows to import large sets of data from any program which is able to handle .CSV (Comma Separated Values) files such as Microsoft Excel™. You can import all the values from the .CSV file into our software for batch calculation and then to export all the results to any program like Excel for further statistical analysis or to create graphs. This is performed with a simple click of the mouse, making it the ideal tool for scientific research. 


BESSt2 IOL Power Calculator - Import.csv file (click to enlarge).

BESSt_vc Formula for Virgin Corneas (no previous surgery):
This formula is experimental and we recommend you use it only in the very unlikely case that you do not have any other instrument but the OCULUS Pentacam to measure corneal power in eyes that need cataract surgery and have never undergone any kind of surgery. It uses a regression analysis that predicts IOL Master equivalent K readings from Anterior and Posterior corneal radius measurements taken with the Pentacam.

A-Constant values:
An A-Constant value has to be entered in this field in order to calculate IOL power. We recommend always using customized values rather than the labeled ones for greater accuracy. Instructions are available on internet on how to customise your values once you have enough patients. A minimum of 10 eyes is required and the customisation is very simple using the IOL Master.  

OTHER FEATURES:
Recalculate a single entry:
When you recalculate an entry, you can choose whether you want to overwrite the current one with new input values or if you want to create an entirely new record. In this last case the original calculation results will not be affected.
Calculate All Entries:
Calculates all the records present in the database at once. You will need to do so after importing a dataset from a .CSV file before you can export the calculated results in a separate file. 
Show Results:
Shows the results of the calculation as they appear in the calculation window. Select this option when you want to review the results of a calculation that you have already performed and don’t wish to change any parameter. If you are using the Trial version, no calculation will be deducted using this option.
Print on pdf:
You can easily save the Calculation Results Printout or the IOL Power Plot Printout in PDF format. This is ideal if you want to send the results by email or if you want to file them in an electronic record. This option requires that you have a PDF file creator software installed on your computer. Several freeware programs are available on the internet for this purpose. 
Keyboard Short Cuts:
Ctrl + N = Perform a (N)ew calculation
Ctrl + R = (R)ecalculate an entry changing some input variables
Ctrl + G = Plot a (G)raph of the IOL power curve
Ctrl + P = (P)rint results
Ctrl + S = (S)how results 
Ctrl + I =  (I)mport data from .csv file
Ctrl + E = (E)xport the calculated results onto a .csv file

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