By Dr Robert Bourke MBBS, FRANZCO
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By Dr André Horak MBChB, MMed, FRCSEd, FRANZCO
By Dr Devinder Chauhan MBBS, FRCOphth, MD, FRANZCO
In surgery it is hard to try before you buy. It is therefore important to assess the patient’s true visual needs prior to embarking on cataract surgery or lens exchange, for an incorrect decision can be difficult to rectify. Not all patients seek emmetropia and many are happy with spectacle correction for reading following cataract surgery or even being left myopic. It is after all what most in that age group have been used to. Monovision in the non-dominant eye, particularly a low minus of 1D or less, has a pseudo-accommodative effect giving more bang than expected for the buck. Many patients then find they need readers only for fine print, much to our surprise.
Having been an early adopter of both the multifocal lens technology and the accommodative lens where do I feel we are at present? My initial experience with the Restor Multifocal was a series of highs and lows. Some wonderful results, grateful patients then a few grumblers, including some in whom lens removal and exchange was required and many more requiring refractive laser correction than I would have suspected. That was back some 7 years ago and after a first 100 back then I implanted very few Restor lenses until the last year.
What has changed? The new Restor is aspheric, has a decreased reading add giving a more comfortable reading distance and most importantly has incorporated a toric correction allowing for astigmatism correction down to 0.6D. The result has been significantly fewer comments from patients about haloes at night and I have had no issues with those who drive at night. The improved lens formulae and the toric lenses have meant 40% of my patients have a toric lens implant. No lenses have been explanted so far.
There are other manufacturers of lens implants that also offer multifocality but not all have a toric option. The particular acrylic material and lens design makes the Restor toric very stable from the moment of implantation with little likelihood of lens rotation off axis, a key to a predictable outcome.
Whom do I exclude from consideration of a multifocal lens today? The myope whose expectations re near vision are so much greater, any difficulty in lens power estimation (Keratoconus, high astigmatism, previous refractive surgery) and any suggestion of macula disease, including any diabetic retinopathy and amblyopia. Care must be taken to reduce the likelihood of CMO post operatively and for these patients especially there is a role for the NSAID drugs (Voltaren or Acular) postoperatively.
Personally, I will not use a multifocal on an emmetrope looking for presbyopic correction. I don’t believe the risk justifies the end result and would still prefer a monovision refractive laser in this situation.
Who does best? The initial hypermetropes appear to enjoy the benefits, especially those greater than +2D. So far I have not required a refractive laser top up in these more recently implanted eyes but expect with the refractive surprises that occur from lens positioning that they will be needed for some. I also feel patients do best with bilateral implantation and plan for this a week apart or as soon as the patient can schedule the second surgery.
My current practice involves less than 20% Restor multifocal lens implantation in my cataract patients and over 80% (in the refractive lens exchange grou)p are Acrysof Spherical or toric with a few Raynor Toric for very high astigmatism.
Reading glasses offer a wonderful solution for presbyopia for many patients but for those who would prefer to be less dependent on glasses there are a number of surgical options that will improve unaided near vision. None of these is perfect and each involves some compromise.
Perhaps the most difficult group has been the emmetropic presbyope; the 50 year old who has never needed glasses but now finds reading glasses unavoidable. Kamra is the only surgical intervention specifically tailored for this patient and offers significant reduction in dependence upon reading glasses.
Corneal Inlay uses pinhole effect
Kamra offers a unique solution for the emmetropic presbyope being appealing both for preservation of distance vision and its reversibility; as an implanted device it can be readily removed in the future, restoring the eye to its pre operated state.
An Intracorneal Inlay KAMRA (Acufocus) as a treatment for presbyopia acts as a small aperture to increase depth of focus by selectively allowing passage of the central light rays and blocking the less well focused peripheral rays. It has no refractive effect so does not change the overall focusing of the eye.
The intracorneal inlay is fully registered in Australia with the TGA and available to patients in Sydney and Melbourne. Two clinics in Australia participated in the early FDA clinical studies demonstrating the safety and efficacy of the implant.
The implant is made of a synthetic material with a thickness of just 5 um – similar to the size of a red blood cell. The central aperture measures 1.6mm and the overall size of the device is 3.8mm. Whilst the device acts optically as a simple small aperture its design is sophisticated. Nutrition of the overlying cornea is maintained by more than 8,000 nutrient holes passing through the device to allow flow of nutrients through the implant. Evolution of the devices design has optimised the size and direction of these nutrient channels to enhance the health of the overlying cornea whilst minimising the passage of stray light. The device material is well tolerated by the cornea with good biocompatibility. Confocal analysis shows minimal keratocyte activation or elaboration of inflammatory markers.
Although implanted unilaterally the inlay does not create monovision. The eye with the implant remains emmetropic so retains normal unaided distance vision and both eyes continue to work together (binocularity is preserved). As there is no refractive change to the implanted eye image magnification does not occur and there is no aniseikonia. Examination and imaging of the eye with the inlay is unaffected and there is no change to visual field testing.
Surgery – Implanting the inlay
Only one eye ( the non dominant eye) is implanted. The inlay is implanted into a femtosecond ( laser) created corneal pocket at a depth of 200um. Some centres create a corneal flap of 200um but there are clear advantages to avoiding a thick flap. The pocket technique minimises post surgery dry eye effects and there is minimal impact on corneal biomechanical stability. Flap problems such as striae can not occur. A new system of surgical alignment (Acutarget) has been developed to facilitate predictable positioning of the inlay on the patients line of sight.
Surgery is performed using anaesthetic drops and takes around 10 minutes to complete. Eye movement and rubbing is not a problem as there is no flap to disturb. The patient is advised to go home and sleep for a few hours. Improved near vision occurs by day 1 and continues to improve for up to 12 months after surgery.
Pooled data from various arms of the clinical trials demonstrates that patients are capable of achieving N5 unaided near vision and distance vision within one line of pre operative measurements. Near vision is light dependant and patients need to know that they will continue to need reading glasses under some conditions – poor lighting, reduced contrast or very small print.
While acknowledging that all my colleagues have their own approaches to treating presbyopia, Kamra is my preferred option for the emmetropic presbyope. Surgery is straightforward and patients achieve functional vision for both near and far with high rates of spectacle independence. There is minimal if any compromise to distance vision so for many patients this is a better option than monovision.