Thursday November 18 2010
Cataract removal is one of the most common types of surgery
“Laser treatment could make eye operations safer for the hundreds of thousands of elderly Britons who have cataract surgery each year,” the Daily Mail reported.
The article is based on a study of whether a specially designed precision laser system could improve cataract surgery. The laser beam is designed to cut through to the lens of the eye and cut it into fragments for removal. The researchers claim that the cuts were twice as strong and five times as precise as the current surgical method of treating cataracts. In a trial of 59 eyes with cataract, there were no differences in important outcomes, such as safety, side effects or improvements in vision, between those treated by laser and those by conventional surgery. However, the procedure did take longer than conventional surgery and would be more expensive.
This study illustrates the potential of the new device and procedure. Laser treatment could be a preferable alternative to current surgery techniques, but this needs confirmation in larger randomised trials. Cataract removal is one of the most performed surgical procedures, and the current technique has been used successfully and safely for many years.
Where did the story come from?
This study was carried out by researchers from Stanford University and the Dominican Republic. It was funded in part by OptiMedica Corp., the makers of the precision laser system used in the study. The research was published in the journal Science Translational Medicine.
The Daily Mail covered relevant aspects to the study and the background of cataract surgery. The newspaper also mentions that one of the researchers promoting the technique has shares in the company and that there are other companies developing similar systems.
What kind of research was this?
The researchers say that cataract removal is one of the most common types of surgery in the developed world, and about one-third of people will have the surgery at some point in their lifetime. They explain that while there have been advances in surgical technique over the last several decades, some critical steps can still only be performed with limited precision.
The aim of this study was to see if a specially designed precision laser system could improve the procedure by replacing one of these inconsistent, manual steps. Currently, the initial opening that is made in the outer shell of the eye to enable the cataract to be removed is made by hand.
The researchers discuss the process in which they developed their technique and equipment. First, they carried out pre-clinical research in pigs to test the technical aspects of the new laser system. A safety study in six rabbits followed to test that the laser did not damage the retinal light perceiving cells. Finally, after designing and refining the system for human use, they tested it in a series of 50 patients. They then performed a comparative non-randomised study of 29 patients treated with the laser with 30 treated with manual surgery.
What did the research involve?
Using the preclinical studies as guidance, the researchers decided on a specific wavelength pulse duration and energy for their laser. They combined the laser with Optical Coherence Tomography (OCT), which is an imaging system taking light from the same path as the laser. The OCT allowed them to precisely direct the line of the laser and adjust it to the right depth.
The laser system is designed to replace the cuts made with a scalpel in manual surgery. Four cuts are usually made: capsulotomy (a circular incision in the lens capsule), lens fragmentation (segmenting and softening of the lens to prepare for removal), relaxing incisions (cuts to correct any astigmatism or unevenness in the surface), and cataract incisions (cuts to allow insertion of the surgical tools).
The technique was used in 50 consecutive patients who were having cataract removal in one eye. Improvement in vision was compared between 29 of these patients with 30 control patients who had the manual technique. A standard reading chart was used to measure changes in best-corrected visual acuity (BCVA); this is how many extra smaller letter lines on the chart could be read while wearing spectacles.
Participants with cataracts between the ages of 50 and 80 were enrolled to this part, and they agreed to comply with the treatment and follow-up schedule. Other requirements included having a visual acuity in the range of 20/30 to 20/80, and pupil dilation diameter of no fewer than seven millimetres. In the final study, 60% of participants were female and 40% were male.
The researchers report all the technical improvements they attributed to the new technique, such as sizing of the lens (thought to be important for visual outcomes) and the precision and repeatability of the procedure. Important outcomes assessed included the strength of the sack around the lens (capsule), as this contributes to the complication of capsule rupture, a possible consequence of any cataract surgery.
What were the basic results?
In the comparative non-randomised study, the average gain in visual acuity was 4.3 (± 3.8) lines in the laser group, compared to 3.5 (± 2.1) lines in the control group. This difference was within the standard error for the analysis and therefore it was not statistically significant.
The researchers say that the similarity in the visual outcomes of the laser and manual surgery confirms the safety of the laser treatment and that there were no side effects on visual function.
They also found a twelve-fold improvement in precision of sizing the capsulotomy compared with the manual technique, and a five-fold improvement in the precision of the capsulotomy shape. There was a two-fold improvement in capsulotomy strength.
How did the researchers interpret the results?
The researchers conclude that the superiority of the visual outcomes with the laser treatment will need to be evaluated in a large comparative clinical trial. They say that their integrated system, comprised of the imaging, laser and the software designed for the special pattern cutting, can provide multiple benefits for cataract surgery.
The laser allows for exact placement of the cutting patterns determined by the surgeon before and during surgery. They say this allows the technique to be more precise and reproducible.
The multiple parts to this research have been well-reported and produce a logical story of why these researchers believe this innovation to be an improvement on the current techniques that are used. They mention a few limitations, some of which revolve around the early nature of the research:
- The scanning beam that helps the surgeons see into the eye has the effect of heating up the retina at the back of the eye, and strict safety protocols would be needed to limit this. The researchers do say the vapour bubbles produced by the laser heating up the fluid at the front of the eye can provide some protection to the back of the eye, preventing it from getting too hot. This aspect of safety will need further evaluation in larger studies.
- The laser itself can also heat the retina especially at high repetition rates. However, the researchers say that the energy delivered by this laser was well below the damage threshold.
- Although the eyes in the clinical study were reported as being randomly allocated to either laser treatment or control manual surgery, the researchers do not say how this was done. The researchers also say this was a case-control and do not report the characteristics of the two groups. This means that the randomisation is unlikely to have been done effectively. Importantly, they do not mention any differences in the visual acuity of the people in the two groups measured at the start and therefore the non-significant differences between these two groups could have been due to different visual acuity before the study began.
- The uptake of this technique by the NHS will be determined by its cost-effectiveness. This is a measure of how much extra benefit a procedure provides for a unit of increased cost. It is not correct to say, as the Daily Mail has, that “because it is more expensive that the traditional method, it is unlikely to be available on the NHS”.
This is a well-reported study with favourable pre-clinical and clinical results. These suggest that a properly designed randomised trial is now required to test the safety, acceptability and outcomes of the innovative technique.