By Dr Patrick Versace, MBBS, FRANZCO, Dip Anaes
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.