Best devices for biometry and IOL intraocular lens calculations, 2019 edition

Editor’s note: this guest post is by Matt Swanic, world renowned lasik surgeon at the Las Vegas Eye Institute. Dr. Swanic is a cornea and refractive fellowship trained ophthalmologist who has been in solo practice for the last 6 years. His practice focus is refractive cataract surgery, LASIK, and SMILE.

Our friend Matt is up to date with the newest equipment and also wrote this article about choosing an OCT.

 We are fortunate to be at a time in ophthalmology where nearly all ophthalmologists have easy access to devices that can yield incredible results with IOL power selection.  However, not all devices are the same and they can vary widely in cost.  This article is set out to go over the big players in biometry in 2019.  

 

Haag-Streit Lenstar LS900 and the IOLMaster (v3.0, v5.4, and 500)

The Lenstar came out in 2009, 10 years after the IOLmaster that came out in 1999. It was the first major competitor to the IOLMaster. For this section we are generally referring to the original IOLMasters that came before the IOLMaster 700 as they all functioned quite similarly (the v3, v5.4 and 500) but had differences in software and some mild hardware differences.  

It is important to recognize the differences between the two devices and what made the Lenstar an immediately viable alternative to the IOLMaster. Both devices use OCT technology to measure length of the eye but only the Lenstar uses the OCT to also measure the corneal thickness, anterior chamber depth, and lens thickness with the OCT.  

The older IOLmaster models cannot measure lens thickness and they use a slit beam to measure anterior chamber depth rather than OCT which is mildly less accurate and doesn’t give corneal thickness data.  This also takes longer as the Lenstar is capturing all of these measurements at once, while the IOLmaster takes it’s OCT for axial length separately from its slit beam to capture ACD.  

The only real practical advantage this gives the Lenstar is that some modern formulas, most notably Olsen, Barrett, and Holladay II,can utilize this information to help try to estimate the effective lens position.  

This seemed like a huge leap forward to know lens thickness and to use it to help determine IOL power, however in the last decade we have not found it to be overwhelmingly better in this regard. In fact the recent Hill-RBF pattern recognition software did not find lens thickness to be a useful piece of data for IOL power selection.

If you talk to most Lenstar users they will tell you the main advantage of the Lenstar is its incredible ability as a keratometer.   I am a cornea and refractive specialist and have been able to compare its ability to the Iolmaster 5.4, iOpticsCassini, Nidek OPD, and most recently the J&J iDesign.  My experience is that the Lenstar axis and power values are excellent and comparable to the anterior K values from Cassini which is the best device I have found for determining corneal power.

Why does the Lenstar perform so much better than the IOLmaster at determining astigmatism axis? 

It comes down to that the original IOLmaster came out at a time when toric IOLs did not exist and so it was developed with only 6 lights to reflect off the cornea to determine K values. This was generally fine to determine the average corneal power of the eye but with so few spots there was significant extrapolation of data to determine the axis.  

The IOLmaster would capture these 6 points 3 times, so your entire corneal data was based off of 18 points.  The Lenstar in comparison captures 32 points per capture and they are at 2 different optical zones (1.65 and 2.3 mm.)  This alone was huge but then it captures them 4 times per scan and 5 scans are performed so you have 640 data points versus 18 for the IOLmaster. Because the points are so much closer together it also can really narrow in on what the exact axis of astigmatism is.  

Having owned both an IOLmaster 5.4 and a Lenstar LS900 I can definitely confirm that the axis determination is better. However, for non toric cases the 6 points were accurate enough for me to essentially get the same lens selection assuming the formulas were the same. However, in actuality the formulas between the devices are not the same…

What is the difference in formulas available on the Lenstar and IOLmaster?

The Lenstar and IOLmaster have all of the standard theoretical formulas, including SRK/T, Haigis, Holladay 1, and Hoffer Q.  The IOLmaster 5.4 and the 500 have the Haigis-L formula built in (not found on the older v3) so that you can choose lenses for patients that have had prior myopic or hyperopic LASIK without having to input data into the ASCRS online calculator (and risk a potentially devastating transcription error.)  

The Lenstar has the Olsen, Barrett Universal II, and the Hill-RBF formulas built in to help improve accuracy on standard cases.  The Olsen and Barrett II formulas both consider lens thickness that is captured by the Lenstar but not captured by the IOLmaster (it is now captured on the IOLmaster 700.)  

In my experience the Hill-RBF 2.0 and Barrett are excellent formulas that have improved my accuracy as a cataract and refractive surgeon and are welcome additions to the Lenstar.  

I currently have my software on the Lenstar setup to display lenses for Holladay 1 (still an excellent formula), Olsen (can be useful in abnormal eye anatomy), Barrett, and Hill-RBF.  

This setup is very useful because if these 4 superb formulas do not agree on IOL power this allows me to caution patients that we may miss our targets. A high level of disagreement may even have me steer away from a multifocal or extended depth of focus IOL where accuracy of lens selection is paramount.  

Lastly, the Lenstar comes well equipped for post refractive cases with Barrett True K, Masket, and Shammas formulas built right in.  Of these three I find the Barrett True K to be the most accurate in my practice.

What has changed on the new IOLmaster 700?

The Iolmaster 700 is a big leap forward from the original IOLmaster designs (v3.0, 5.4, 500.)  The IOLmaster 700 has integrate swept source OCT to measure axial length.

This is huge because it allows for penetration of dense cataracts, determination of lens thickness (not available on the prior IOLmasters), and visualization of the foveal pit to both ensure alignment of the image and possibly detect pathology like ERMs or CSME (however the recommendation is still to perform a dedicated OCT for this determination.)  

Also, the IOLmaster700 has gone from its original 6 spots for keratometry to 18 spots.  This has improved its ability to determine the appropriate axis of astigmatism. Lastly, Zeiss recently introduced the TK or Total Keratometry upgrade which allows it to integrate posterior corneal data, derived from its swept source OCT, with its anterior keratometry to estimate total corneal power and astigmatism.  

At the time this article was written we don’t have great peer reviewed date to show how effective this is, however given my experience with total corneal power from the OptovueOCT I suspect this will be effective and an improvement on the Optovue.  

The Optovue is not likely to be as effective as this method because keratometry (integrated into the IOLmaster700) is an instantaneous and highly accurate way of measuring the anterior cornea.  

In contrast, the Optovue needs to rely on essentially thickness/elevation data alone from the OCT, which is not as accurate for determining corneal power (this was seen with the Pentacam as well.)

The IOLmaster 700 also has several new formulas that are very good for post refractive and placement of Toric IOLs.   The integration of the Barret Suite allows it to integrate Barrett True K for post refractive patients, Barrett Toric for Toric IOLs, and Barrett Universal II for everyone else.  

Granted these formulas are also included in the Lenstar.  Graham Barrett has also made 2 new formulas for the IOLmaster 700 that is based on the Zeiss TK software.  Barrett TK universal II and Barrett TK toric have been created to hopefully improve on the already stellar Barrett formulas by integrating posterior corneal curvature.

 

What about the Argos Movu, isn’t that also swept source OCT?

The Argus Muvo is indeed swept source OCT and is really a phenomenal value in this segment.  I have a friend that owns this product and is very happy with it.  I had a chance to see and use it as well and I found that it was fast and easy to use.  

The Movu’s claim to fame is really that (much like the IOLmaster700) it can power through nearly all cataracts that enter your clinic due to its swept source OCT technology.  The Movu also uses an infrared ring of LEDs to determine its keratometry values.  

Unfortunately, at the present time they are not integrating its swept source OCT data to attempt to determine total corneal power. It does include a competitive array of formulas including the Barrett True K and Shammas for prior refractive surgery patients and the Barrett Universal II formula for standard patients.  

It also includes a toric IOL calculator.  If getting through nearly all densities of lenses at a lower cost to the IOLmaster 700 is a priority for your practice I would strongly consider contacting them for a price quote.

 

I want a full topographer built in, what about the Topcon Aladdin?

The Topcon Aladdin is an interesting device in that it does integrate a full topographer into the device. This is great for small practices that don’t already own a topographer or practices that want to maximize efficiency by obtaining the topography at the same time as the biometry.  

The Aladdin does not utilize swept source OCT and it does not have the capability to measure posterior corneal astigmatism like the IOLmaster 700.  A nice feature of the Aladdin is that because it is a full topographer it can give you wavefront data about the anterior corneal surface.  This is helpful for the post-refractive patient where you are trying to determine if they have had myopic or hyperopic refractive surgery. Generally, if the spherical aberration is highly positive (>0.30) then the person likely had myopic LASIK and if the value is near zero, or negative, then the patient likely had hyperopic LASIK.  Lastly, the Aladdin Topographer comes with an impressive suite of formulas including Barrett True K for post refractive, Barrett Toric calculator tor toric lenses, and the Barrett Universal II and Olsen (with lens thickness integration) for standard cases.

 

So, what should I buy?

Hopefully this article has shown you that in 2019 we have lots of great options (I left out the Pentacam AXL and Galilei G6 due to cost.)  I think it comes down to the practice you currently are running, or are planning to run, along with cost.  The IOLMaster 700 is the most expensive of the devices this article has focused on, however, it may be the most future proof (as seen with their recent introduction of TK) and Zeiss is not likely to be going away any time soon.  

The Haag Streit Lenstar is a phenomenal device, that I use in my own clinic and get incredible outcomes from.  It is generally available on the used market, and even brand new is substantially less expensive than the IOLmaster 700.  I don’t think anyone could go wrong with this device but it does have no capabilities for measuring posterior corneal astigmatism and it is getting a little long in the tooth (Haag Streit has been working on its replacement for years.)  

I think the Movu has much of the functionality of the Lenstar with the added benefit of being able to penetrate denser lenses, unfortunately support could be more problematic for a device without widespread market penetration.

If you are a small practice on a budget, and don’t have the space or money for a topographer, then the Topcon Aladdin is an excellent choice.  

My practice has moved away from Placido Disc topography in favor of the Cassini for cataract surgery as I find this device more accurate and it gives me posterior corneal power and astigmatism.  Yet, the Cassini is costly and not a great purchase for a practice that is just starting and may have financial limitations.

I would generally avoid purchasing an IOLmaster 500 brand new in 2019 due to its technical limitations described in the article. However, a used Iolmaster 5.4 can be an excellent purchase at a great price.  I started my practice with this device (prior to changing to the Lenstar), and for standard cataract surgery it yielded excellent results.

Overall, I think any device discussed in this article would get the job done and we are fortunate to live at a time when our results can be so incredibly accurate and even small solo eye docs can deliver exceptional results.