Information
DISCLAIMER : Physicians are solely responsible for the IOL power choice before cataract surgery. By using the PEARL-DGS Calculator, the user agrees to waive all claims against and hold the authors (Dr Debellemanière, Dr Saad and Dr Gatinel) harmless from any claims arising out of his/her use of this tool. The PEARL-DGS calculator outputs are not intended to serve as surgical instructions.
Always double-check your calculations using different formulas.
"REGULAR" MODE :
Regular mode is for non-operated eyes with native, healty corneas.
Select the IOL Model you intend using, or the closest model. If your IOL model is not in the list, select "Other". Use your optimized SRK/T A constant.
K1 and K2 should be the biometer's keratometric measurements. Usually, biometric devices are calibrated in such a way that their K mean value, for a given population, is equal to the K mean value delivered by the IOLMaster. Select the keratometric index which is used by your biometer to display K from the anterior corneal radius measurement.
The K1 / K2 fields must exclusively be filled with measurements reflecting an anterior corneal radius measurement : SimK from a biometer or topographer, or (in specific cases, see below) keratometric measurements obtained from the Anterior Keratometry map from a topographer.
Do not use Total Keratometry, TCRP, Holladay EKR... in the K1/K2 fields in the PEARL-DGS calculator: the formula will not work as intended and your calculation will be unreliable.
ACD is from epithelium to endothelium. It is sometimes referred to as "AQD+CCT".
"COMPLEX" MODE :
"Laser Vision Correction History" should be activated if the eye underwent a LASIK or PRK: you will have to determine the kind of treatment (Myopic or Hyperopic). Usually, the kind of treatment can be determined by asking the patient details about his/her vision before laser vision surgey, and confirmed by studying the corneal topography. When astigmatism was treated, determine the spherical equivalent of the treatment, if you have this information. For the specific case of pure astigmatism with a treated spherical equivalent of zero, just select "Non-physiological cornea".
"Pre-LVC anterior corneal radius" and "Corrected ametropia" are historical data allowing to refine the calculation. "Pre-LVC anterior corneal radius" is the anterior corneal radius in mm, measured before LASIK surgery (native ARC). If filled, this value will be used as a reference to predict the posterior corneal radius. "Corrected ametropia" is the amount of laser treatment delivered. Only positive values are allowed (the correct sign is added in the formula thanks to the kind of laser treatment you selected).
It is always good to compare the predictions given by post-LASIK formulas with treatment informations (corrected ametropia and/or pre-LVC ARC) and without treatment informations. It is also useful to compare the predictions with and without TK/PRC measurements for those eyes.
Select "Radial Keratotomy" the eye underwent this procedure. This option should be selected for every post-RK eye.
If the eye underwent RK + subsequent PRK or LASIK, activate "Laser Vision Correction History" AND activate RK. If the eye underwent RK only, don't activate "Laser Vision Correction History".
"Non-physiological cornea" allows to remove K from the lens position predictors. It is useful for scarred corneas, after PTK, after penetrating keratoplasty/DALK/DMEK, keratoconic eyes... Please note that there is no specific post-keratoconus version of the PEARL formula for the moment : K measured by biometric devices are most of the time over-evaluated in keratoconus and you should decrease those measurements.
It is useless to check the "non-physiological cornea" option if the post-LVC or post-RK options are activated. It is mandatory to check it otherwise if the cornea has been modified by any pathology or surgery.
"ICL" should be selected if an implantable collamer lens is in place during the biometric measurement. AL measurement is slightly impacted.
"Total keratometry" allows to use the TK measurement delivered by the IOLMaster 700.
"Measured Posterior Corneal Radius" allows to enter a measured posterior corneal radius value, measured by a corneal topographer. Please enter the mean posterior corneal radius (positive value), not the posterior corneal power (negative value) ! If your biometer or topographer only displays the posterior corneal power, you can calculate the posterior corneal radius as follows : posterior radius = (1.336-1.376) / posterior corneal power x 1000 --> -40 / posterior corneal power.
Example : Posterior corneal power = -6.5 D --> -40/-6.5 = 6.15. Posterior corneal radius is 6.15mm.
For very complex eyes, you can use paracentral anterior topographic Ks for K1/K2 and the central PRC measurement, and compare with TCRP predictions.
TCRP in PEARL-DGS is the 3mm Zone Total Corneal Refractive Power : it is the corneal power measured by ray-tracing, using a corneal refractive index of 1.376 and an aqueous refractive index of 1.336, in the central 3mm zone. Don't use other measurement diameters, or other way to determine the corneal power (like TCP, Holladay's equivalent K readings...), in this field.
We don't recommend using "TCRP" in simple post-refractive cases. This field is especially useful for complex eyes with history of multiple procedures, irregular corneas...
For very complex eyes (RK + LASIK, "extreme" RKs, very scarred corneas, post-keratomileusis, epikeratophakias...), we suggest comparing the output given by the formula with the TCRP + "Non-physiological cornea" option activated, and with the biometer's SimK (or manually determined paracentral Ks if the cornea is very irregular) + topographic central posterior corneal radius value in mm + "Non-physiological cornea" option activated.
"SECOND EYE" MODE :
Calculation is done the standard way, but preoperative biometry of the first operated eye, and its post-operative outcome, must be entered.
IOL model has to be the same between both eyes. History and kind of laser vision correction have to be the same between both eyes.
TORIC CALCULATION :
First, complete a calculation. Then select the IOL power you want to implant.
Complete K1 axis (flat anterior corneal axis), SIA (your surgical induced astigmatism, usually between 0.1 and 0.3 D) , your incision axis, the toric IOL style of the IOL model you are using (usually posterior or bitoric), and how you want the residual refractive cylinder to be displayed.
You also can use measured posterior corneal astigmatism values : enter PK1/PK2 OR PR1/PR2 OR posterior cylinder (negative value) PLUS the corresponding posterior corneal measurement axis.
If you want to evaluate the formula, do not enter the calculations by hand... we will be happy to perform them for you. Please write at contact@pearldgscalculator.com. We will ask you : the 5 biometric parameters (AL, K, ACD, LT, CCT), the IOL model that was used, and the mean postoperative refraction of the dataset (to adjust the constant). For post-operative surgery eyes, the type of surgery must also be provided.
The PEARL-DGS calculator was developed using the methodology described in the paper "The PEARL-DGS formula: the development of an open-source machine learning-based thick IOL calculation formula", by Debellemanière G, Dubois M, Gauvin M, Wallerstein A, Brenner Luis F, Rampat R, Saad A, Gatinel D. Am J Ophthalmol. 2021 May 13:S0002-9394(21)00276-2. doi: 10.1016/j.ajo.2021.05.004.
The source code of the methodology used is available at https://github.com/gdebel/pearldgs_toolbox
We do not store calculation data.