Updated: Jul 22
In an earlier article in this site, named "Refractive Surprise Post IOL implantation - How to check what went wrong ? ", I had described three basic things that one must check in order to understand the cause of a refractive surprise or sub optimal outcome. A physician trying to understand what went wrong, may have to get the answer to three basic questions - 1. The postoperative ELP ( measuring the pseudophakic ACD ), 2. Co relating the pseudophakic AL with the phakic AL, and 3. Determining the right IOL power in the eye by measuring the IOL central optic thickness. The last option is however difficult and may not be always possible due to complexity of the task. But the last option may be the least important of the three, as chances of implanting a wrong IOL power, or a wrongly labelled IOL power is extremely rare.
It is herein, the Biometry Validation Tool_V2.0 may be extremely useful. Not only does the Biometry Validation Tool_2.0 help biometricians to quick-check and validate their data, its Post operative Validation Tool helps with the first two steps in case of refractive surprises. To be precise, the Biometry Validation Tool_V2.0 ( with inbuilt Post operative Validation Tool) helps us to not only validate biometry data (thus saving us from bad outcomes) but also helps in troubleshooting, postopratively.
Biometry Validation Tool_V2.0 - Let me here describe the Biometry Validation Tool first. The first step to validate the biometry is to do a two eye biometry, except in those cases where patient is one eyed. Other than this, there should be no other reason for a practice to not do a two eye biometry. Once the data from the two eye biometry is input into, the tool will co relate the two eye data and look for any discrepancy in values based on biometry rules.
The colour codes assigned to each cell ( green is good, yellow is caution, and red denotes out of bound values) helps biometrician to take a print out and attach to the patient file for the physician to cross check before deciding on premium IOLs. Thus the physician/doctor, biometrician and counsellors are now all in one page and can take informed decision with regard to the candidacy of the patient for premium IOLs.
Note, worldwide, on an average the conversion to premium IOLs like multifocals and torics is no more than 5-6%, barring a few countries like Australia. What this means is that an account has to scout through 100 patients to select at best 5 to 6 patients for premium IOLs. Herein the Biometry Validation tool would help physicians and practices to streamline the process in determining candidacy for premium IOLs.
Here is the list of capabilities of the Biometry Validation Tool_V2.0
a. Gives you a colour code (green, yellow, or red) once you enter Axial Length of two eyes and Keratometry readings
b. Checks two eye axial length and Keratometry readings difference and provides you colour code based on biometry rules
c. As you enter Standard Deviation of Axial Length, K readings and axis, colour codes guides you.
d. If you have entered patient manifest refraction, it helps you to validate Keratometry readings and axis with patient manifest refraction.
e. In case of long axial lengths, it automatically calculates optimized Wang&Koch values for SRK T.
f. Optical axis and pupillary axis deviations from corneal vertex is key to determine candidacy for multifocal IOLs. The Biometry Validation Tool_V2.0 has inbuilt algorithm to guide you on patient selection.
Post oprative Validation Tool
Let me now discuss how this tool can help you to trouble shoot in case of refractive surprise you may have had already.
1. The Post operative Validation Tool helps you to corelate Pseudophakic Axial Length with Phakic Axial Length and helps you understand if the axial length measured before the cataract surgery, was trustworthy. To do this, you will have to enter -
a. IOL central optic thickness vis-a-vis, the dioptre implanted
b. Speed of sound in IOL material implanted.
c. The pseudophakic AL measured at sound velocity of 1532m/sec
With these values entered, the calculator will give you the phakic AL and help you match with the AL values earlier entered.
2. As in the earlier article on 'Refractive Surprise Post IOL implantation - How to check what went wrong ?' I had mentioned, measuring pseudophaic ACD is the key to understand refractive surprises, this tool helps you to understand the refractive shift of the patient from the measured pseudophakic ACD.
For this you have to enter :-
The phakic ACD - The calculator will then calculate the targeted pseudophakic ACD depth and any deviation of this value from the real measured pseudophakic ACD post surgery, would determine the refractive shift. The algorithm to determine refractive shift however is complex and depends on other factors like phakic Axial Length.
Silicone Oil Filled Eyes
The last but not the least is the value this tool brings in to help you determine the True AL of the patient in case of Silicone Oil Filled Eyes. The calculator needs the measured AL, ideally with phakic velocity of 1532m/sec, and would then give you the True AL.
I hope with this tool, V_2.0, you find a way to validate biometry that biometricians input data. This tool will be continuously upgraded, but more importantly it is a free tool I designed in the interest of patients without financial interest, and available at quickguide.org
Click on the Biometry Validation tool at quickguide.org,
or follow the link here :