Dr Daphne Han, SMG Vision Centre
The popularity of refractive surgery, whose aim is to change the power of the eye in the past 15 years had made these procedures commonplace and relatively affordable. These surgeries, the commonest being LASIK, reduce the individual’s dependence on glasses and contact lenses. LASIK, and its alternatives such as Relex Smile and advanced surface ablations alter the power of the cornea (the front “window” of the eye) permanently. Generally, these cornea-reshaping procedures are suitable for individuals in their 20s to 50s. Special considerations are necessary for management of presbyopia in the 40s and above.
Despite LASIK being so commonly performed nowadays, the most commonly performed “refractive operation” is actually cataract surgery. In cataract surgery, an artificial lens is implanted after the cataract to replace the focusing power of the “original” lens. That there is a large variety of artificial lenses to choose from is what makes my job as a cataract and refractive surgeon so interesting. My role is to help my patients choose a suitable lens implant to best suit their lifestyle, aiming for the maximum accuracy current technology can provide.
Individuals who had LASIK surgery before need more care from their eye surgeons when planning cataract operations. Calculations for their cataract surgeries after LASIK are more complex as their corneas had been reshaped. Preferably, the surgeon should have a full history of the LASIK surgery. Even when this is available, an accurate measurement of the eye dimensions is still vital to ensure an accurate outcome.
Current equipment and formulae to measure the dimensions of the eye for cataract surgery provide fairly accurate outcome, but outcome in eyes that had LASIK done cannot match virgin eyes. In a scientific article that my team and I published in March 2015, 71% of eyes that had cataract surgery done after previous LASIK for short-sightedness in Singapore had a result that is within 100 degree of target power, compared to 85% in virgin eyes. That is to say, almost 30% of eyes that had LASIK before will be off by more than 100 degrees (1 diopter) after their cataract operations. Compare this to LASIK predictability which is at least 93% within 100 degrees. Such inaccuracies can lead to further operations, such as exchanging the lens that had been implanted, or a LASIK enhancement.
To improve the accuracy of lens calculation, the Galilei G6 machine, a next-generation biometer (a machine to measure lens power for cataract operations) was recently introduced by the Singapore Medical Group at its newly established SMG Vision Center, Gleneagles Hospital. The only one in its class currently, this device incorporates a 360° measurement on both the front and back surfaces of the cornea (using a technology called the double Scheimpflug) and the overall eye length in one complete calculation, hence eliminating the need for multiple, possibly incompatible devices. The first in a private eye center, the Galilei G6 measures approximately 100,000 points on the cornea compared to other more commonly used devices, which measure either 6 or 32 points. This is particularly helpful in cases such as post-LASIK eyes, those with cornea scars or just cases aiming for higher accuracy in premium lens implants.
A patient comes to mind who could have benefited from more accurate lens measurements — a middle aged lady whose cataract I treated many years ago in a peripheral hospital. A subtle scar in a far corner of the cornea had resulted in increased astigmatism that was difficult to measure with the routine devices. In the end we had to reject her initial wish for an astigmatic-correcting lens implant due to the ambiguity. She ended up with a satisfactory outcome but still required glasses for correcting high astigmatism.
Another case fresh in mind that would undoubtedly have benefited from the Galilei G6 device was that of a post-LASIK patient, who already had a cataract operation done with a multifocal lens implant in her other eye. In order to ensure a balanced and accurate outcome for her second eye cataract surgery, at least 4 tests were performed to measure her post-LASIK eye, each a different device. Not only did multiple tests cost more, they also took time. The final task on the surgeon, i.e. me, was to put the results all together to select the “correct” lens for her eye. Fortunately the mathematics worked in our favour, and she ended up with excellent result, happy that the worst case scenario of having to exchange the lens implant was far from reality. (Incidentally, implanting an incorrect lens in cataract surgery is considered a reportable event by the Ministry of Health in Singapore).
So far, at SMG, our audited cataract surgery results with the G6 had been 100% within 50 degrees of accuracy, using a range of lenses. We look forward to making our cataract surgery, with the use of a combination of advanced measuring device, micro-incision and image-guidance techniques, the LASIK of the golden years.
This article is written by Dr Daphne Han, Ophthalmologist of Singapore Vision Centre, a Singapore Medical Group (SMG) Clinic.