Advancing Cataract Surgery

Changing demographics and improved access to health care around the world is resulting in an increase in cataract surgeries performed each year. By 2020, the World Health Organisation estimates that more than 32 million cataract surgeries will take place per annum.¹

Standards for cataract surgery are also increasing and with that, demand for the latest innovations and equipment,² because regardless of a surgeon’s expertise or intent, there is always room for human error.

A study I presented to the Foresight meeting in Hong Kong during July, and submitted for publication has demonstrated that the Verion Image Guided System, developed by Alcon Laboratories, and comprised of the Verion Reference Unit and the Verion Digital Marker, reduces the risk of human error, and should result in improved refractive outcomes following cataract surgery.

I have a measurement system that takes me from pre-op to surgery and post-op seamlessly with a certainty around measurements that was not previously available

The platform integrates digital planning and surgical positioning tools, which were traditionally accessed via a number of different technologies during the entire patient pathway, into one system.

Commenting in Ophthalmology Times, Dr. Stephen S. Lane, medical director at Associated Eye Care in Minnesota, adjunct clinical professor of ophthalmology, University of Minnesota, Minneapolis, and a consultant for Alcon, said, “Verion is a multifaceted technology that has been designed to accurately measure the eye, image anterior segment landmarks, perform IOL calculations, including astigmatic corrections, and then guide the surgeon in the placement of corneal incisions and IOLs, including both toric and multifocal IOLs, by seamlessly exporting the information to other synergistic technologies”.³

He said the system “is essentially the‘glue’ that integrates the preoperative planning phase of a cataract procedure

to the intraoperative guidance of the surgeon during key steps in the cataract procedure. This allows for improvements in efficiency, accuracy, and precision,all key factors in improving the surgeon’s ability to hit the refractive target”.

Patient data entered into the Verion Reference Unit is automatically carried forward to the Verion Planner and the Verion Digital Marker, which is compatible with the LenSx Laser (Alcon Laboratories) and most surgical microscopes. This process ensures the same patient data collected at the planning stage is used during surgery, eliminating the risk of human error that can occur when data is re-entered multiple times and inaccuracies that can occur when data is collected at different times throughout the patient pathway.

The Verion Reference Unit measures keratometry, white to white corneal diameter and the undilated pupil size and position. Additionally, it captures a high-resolution reference image of the eye, with the patient in an upright position. The image presents scleral vessels, limbus, pupil and iris features that can be used during surgery and in postoperative follow-up.

This information is electronically transferred to the Verion Digital Marker which generates a tracking overlay that provides a real-time visualisation guide for the surgeon when creating incisions, capsulotomy, and IOL alignment. The system tracks for eye movement and automatically adjusts for cyclotorsional rotation, taking into account the fact that the image was taken with the patient in an upright position. This is available both at the femtosecond laser and through the operating microscope.

The Verion Reference Unit also assists surgeons by combining multiple, proven algorithms to help surgeons determine the most appropriate IOL and lens power for patients with and without astigmatism.

The study I led at Vision Eye Institute, looked at the information collected from 262 eyes in total using a Verion and compared them with information collected using Autokeratometry (242 eyes), Zeiss IOL Master (212 eyes) and Pentacam Topography (249 eyes). Specifically, it compared data on mean keratometry, cylinder magnitude and axis location. The study found that, the Verion provided data that was at least comparable, and in some cases more reliable than the established methods. However, further research is required to compare these values with postoperative outcomes. In conclusion, Verion was both reliable and beneficial for planning and positioning, making the process of cataract surgery more streamlined and reducing the potential for human error.

Comment

What we attempted to do with this study was use the Verion reference unit preoperatively to measure corneal astigmatism, both axis and magnitude, and compare this to our established methods which were IOL Master keratometry, autokeratometry and corneal topography, specifically using the Pentacam device. We measured routine eyes, but also a number of post laser refractive eyes and also post corneal transplant eyes, so they were both the routine and the complex. Bland Altman plots were used as they are an accepted method of evaluating agreement among different instruments or measurement techniques. They allow us to investigate the existence of any systematic difference between instruments. In particular, the mean difference between devices is the estimated bias, and the standard deviation of the differences measures the random fluctuations around this mean.

We found that the Verion measurements correlate most closely to IOL Master. Specifically the average keratometry on Verion was 43.76D where on IOL Master it was 43.54 with a Spearman correlation coefficient of 0.976, a difference of the mean of 0.23 and the standard deviation of the difference of the mean at 0.31. Similarly the Verion averaged slightly steeper keratometry compared to Auto Keratometry, whereas compared to Pentacam, topography was slightly flatter but with a greater standard deviation of the difference of the mean.

When we examined the magnitude of the astigmatism, again the measurements were closest to IOL Master with the mean astigmatism in the Verion group of 0.89 dioptres and the IOL Master 0.98 with a Spearman correlation coefficient of 0.85 and a difference of the mean of 0.10 and a standard deviation of the difference of the mean at 0.25. The magnitude of astigmatism was slightly less on Verion compared to Auto Keratometry, mirroring the measurements we saw when comparing Verion to IOL Master. The results, however, were tighter when compared to IOL Master than anything else.

When we looked at the axis there was a reasonable correlation. Axis alignment is a little more difficult to both measure and interpret, because when corneal astigmatism measures 0.5 dioptres or less, there is quite a lot of noise in most systems whether it be IOL Master, topography or Auto Keratometry. This was also seen with Verion, but axis alignment when measuring astigmatism of greater than 0.5 dioptres was quite close to IOL Master axis. This was also reflected in vector analysis using the methods described by Thibos and Horner. In vector analysis there is a much greater spread with topography and Auto Keratometry. It is tighter with IOL Master and tighter still with Verion.

Having used this device for nine months routinely in the clinic and operating room, it is now my preferred method to determine average keratometry, steep and flat axes and magnitude of astigmatism and I rely on the Verion rather than IOL Master, Auto Keratometry or topography to guide me in IOL selection. The Verion does not currently perform biometry so this information has to be tested separately. How this translates into more accurate results, time and data will tell. The fact that the Verion is used pre-operatively, during femtosecond laser cataract surgery, during the lens insertion and post-operatively to help refine results, means I have a measurement system that takes me from pre-op to surgery and post-op seamlessly with a certainty around measurements that was not previously available. I also very much enjoy the comfort that comes with knowing that the measurements are taken in the sitting up position in an undilated pupil and that these true measurements can flow through into the operating room when I place, in particular, a toric intraocular lens but also when I wish to place a lens in the centre of the undilated pupil.

This does open up a whole body of work as to where the ideal placement of the capsulotomy should be – whether it should be at the geometric centre of the cornea, the best estimate of the visual axis via the first Pukinjie image, or whether it should be the centre of the undilated pre-operative pupil. It also brings up the question; if the capsulotomy can be placed in an ideal position, will the intraocular lens remain there? There is much to learn and understand, and this technology allows us to explore these possibilities in a way that was not previously possible.

References

1. MarketScope, 2013 Comprehensive Report on the Global Cataract Surgical Equipment Market.

2. Helen Keller International. Cataract treatment. www.hki.org/preventing-blindness/cataract-treatment/.

3. www.ophthalmologytimes.modernmedicine.com/ophthalmologytimes/news/new-system-helps-cataract-surgeons-improve-refractive-precision?page=full

IOL Power Calculators for Best Practice

Current Post Refractive IOL power calculators offer surgeons the ability to achieve refractive outcomes that are comparable with virgin corneas, according to a retrospective study completed by Vision Eye Institute, and recently submitted for publication.

The study, conducted between April 2012 and January 2013, analysed 60 eyes proceeding to laser assisted cataract surgery, which had previously undergone corneal refractive laser surgery.

It compared results achieved against the benchmark for refractive outcomes following cataract surgery in normal eyes established by the National Health Service – targets of ±0.50 D for 55 per cent of eyes and within ±1.00 D for 85 per cent. Furthermore overall results were compared to previously published cohorts for post-refractive IOL cases.

The clinic found that 98.3 per cent and 83.3 per cent fell within 1.00D and 0.50D, respectively, of the intended refractive outcome for patients who had previously undergone laser cataract surgery (Figure 1). It reported an absolute mean difference from intended result of 0.33 ± 0.27D. Fifty-five per cent of patients were within ± 0.50D of both intended sphere and cylinder values.

To select the appropriate IOL power for each patient, surgeons used multiple methodologies, including The ASCRS Post Refractive IOL calculator (www.iolcalc.org), APACRS True-K IOL formula (www.apacrs.org), respective personalised A constants, and previous internal audits.

Standard femtosecond capsulotomy, cataract fragmentation and corneal incision procedures were followed, and lens segmentation was completed according to the surgeon’s preference either with an Akahoshi blunt prechopper or a direct chop technique. The procedure was completed with routine phacoemulsification and intraocular lens implantation.

The researchers proposed that laser technology may have contributed to the improved outcomes achieved.

They wrote, “Femtosecond lasers offer precision cutting unparalleled by manual alternatives. Consistent, central capsulotomies enable enhanced IOL centration with uniform overlap of the capsulotomy bag. This in turn allows for reduced aberrations culminating in improved functional visual outcomes.

Nagy et al have also demonstrated improved predictability of refractive outcomes. Patients undertaking laser vision correction will have some form of ammetropia therefore it is not unreasonable to assume that the biometry of these patients may be significantly different from the average population. The proposed benefits of LCS may be augmented in this population as evidenced by the equivalent outcomes across eyes in our cohort with short, medium and long axial lengths. Further research is required to establish this theory.”

The overall results exceeded an established benchmark for standard cataract surgical outcomes and were shown to be as good as, if not greater than, previously published methods. The post refractive IOL calculators, in conjunction with frequent auditing, offer the surgeon ease of use and refractive outcomes that are at least equivalent to standard outcomes. Further implementation of femtosecond laser technology in conjunction with the automation of the Verion Guidance System may offer the potential for further improvement in these unusual cases.

After more than 20 years of experience in Australia, the number of patients who have previously undergone refractive laser procedures and have matured to cataract surgery is reaching significant levels. The study showed that today, readily available solutions exist for surgeons to overcome the inherent issues of dealing with this group of patients.

Comment

Patients who have previously had corneal laser surgery are coming to cataract surgery in increasing numbers. These are complex eyes, sometimes longer or shorter than the routine given their previous refractive error, but they don’t have the inherent problems of radial keratotomy or, from the very early days of laser corneal surgery, small optical zones and/or considerable irregular corneal astigmatism.

Laser corneal surgery undertaken since the late 1990s is consistent with good quality corneal contours and the issues now relate to achieving an outcome with cataract and lens surgery, which meets the patient’s needs. These patients are demanding and often want some degree of spectacle independence. Discussions revolve around the possibilities of achieving this, the best lens for an individual whose cornea has been either flattened or steepened with prior corneal surgery, how the corneal aberration profile impacts IOL choice, and what possibilities there are for enhancement if the target is not met.

At least as far as accuracy goes we are getting close to what can be achieved in normal eyes. We shouldn’t be complacent however because even in normal eyes there is room for improvement. Achieving a target of +/- 0.50 dioptres on both sphere and cylinder is necessary for patients to be content with their post-op outcome and this is still not achieved in all patients.

Many studies look simply at the spherical outcome within half a dioptre of intended, but it is important to look at the astigmatic outcome as well. In our data it is still only 55 per cent of patients who are within half a dioptre of intended on both sphere and cylinder.

The femtosecond laser brings precision and reproducibility that should enable us to do better and the Verion image guided system from pre-op, to surgery, and post-op should also allow us to further improve our refractive outcomes. It is a time when we shouldn’t be worried about these patients, but we should embrace the opportunities that technology is now giving us to help them achieve visual outcomes they would expect from modern surgery.

Dr. Michael Lawless has been involved in laser eye surgery for many decades, performing the first LASIK procedure in Sydney. He is also the first eye surgeon in the Southern Hemisphere to perform cataract surgery using laser technology. Dr. Lawless has performed over 20,000 surgical procedures, which include LASIK, ASLA, refractive lens exchange, cataract and lens surgery and corneal transplant. Dr. Lawless is a surgeon with Vision Eye Institute in Chatswood, Sydney and a Clinical Associate Professor at Sydney Medical School, University of Sydney.