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Utilizing corneal inlays for the correction of presbyopia
Surgeon provides a step-by-step look at his approach to correcting presbyopia.
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Once a person passes 40 years of age, he or she usually has to deal with presbyopia, which has a negative effect on quality of life, and the individual has to correct this presbyopia with reading glasses or other available therapeutic modalities.
Surgical correction of presbyopia may be considered the final frontier in the world of refractive surgery. The surgical approach can be focused on different target tissues, namely the cornea, the lens or the sclera, with differing techniques, all directed at resolving presbyopia.
Corneal techniques to manage presbyopia include monovision LASIK or PRK, presbyLASIK, conductive keratoplasty and intrastromal corneal implants, which are not yet approved by the U.S. Food and Drug Administration. For the sclera, anterior sclerotomy or scleral expansion techniques have been studied, although they have yet to be widely accepted by refractive surgeons. Combining lens-based surgical procedures, such as cataract surgery or clear lens exchange, with various multifocal IOLs continues to gain acceptance among ophthalmic surgeons all over the world. The relative downside to these procedures is their association with photopic phenomenon and contrast sensitivity degradation.
In this column, OSN Refractive Surgery Section Editor Daniel S. Durrie, MD, describes a step-by-step surgical approach to placing the Kamra corneal inlay (AcuFocus) within the cornea to correct presbyopia.
Thomas “TJ” John, MD
OSN Surgical Maneuvers Editor
Daniel S. Durrie
The surgical technique for the Kamra corneal inlay has evolved over 6.5 years of clinical investigation and commercial use. With the trial nearly complete, the procedure commercially available in 48 countries and nearly 20,000 inlays implanted to date, the medical community is starting to assign names to each possible procedure to improve communication. The mainstay of the clinical trial was the implantation of the inlay into a corneal pocket in emmetropic patients. Pocket emmetropic Kamra is a highly evolved surgical technique that is dependent on femtosecond laser technology.
A successful procedure depends on proper patient selection. Patients who do not have a high degree of astigmatism or hyperopia will have better results, and individuals with uncontrolled dry eye, blepharitis or keratoconus should not have the procedure. However, if dry eye and blepharitis are treated and controlled, these patients can still be good candidates.
The technique
The first step of an inlay procedure is to determine where to place the inlay. This can be achieved through the use of the AcuTarget diagnostic unit (AcuFocus). The AcuTarget provides a map of unique ocular landmarks, including the patient’s first Purkinje image and pupil center, and correlates them in terms of distance and direction. With this information, the most appropriate location for inlay placement can be determined.
Figure 1. Using a 4-mm ring marker, a circular mark is placed on the cornea over the first Purkinje (P1) reflex, or midway between pupil centroid and P1 in cases of large angle kappa, to provide an intraoperative guide for optimal placement for the corneal inlay.
Figure 2. A corneal pocket is created at a depth of 200 µm using a femtosecond laser. Laser settings should be set such that the resulting resection is as smooth as possible.
Images: Durrie DS
Figure 3. The lamellar pocket is carefully and fully dissected without introduction of epithelial cells.
Figure 4. Following pocket creation and dissection, the inlay is inserted into the pocket using special forceps.
Figure 5. After ensuring the inlay is correctly positioned, the inlay is carefully released and the forceps are slowly removed from the pocket.
The next step is to prep the patient for surgery and mark the cornea where the inlay needs to be placed, based on the AcuTarget information. I mark a 4-mm circle in the desired location on the cornea using rose bengal, which can easily be seen but does not block the laser. I then use a femtosecond laser to cut a pocket 200 µm deep in the cornea, with the laser set to a 6 × 6 spot/line separation or tighter. Several of the femtosecond lasers on the market have developed pocket software for this purpose, and the others are planning to make it available in the near future.
After the femtosecond laser procedure, a special spatula is used to dissect the lamellar pocket. It is important at this point to make sure the pocket is completely open, paying careful attention to avoid any epithelium transferring from outside to inside the pocket. The inlay is then loaded into special forceps and inserted into the pocket. I have found it useful to insert the inlay beyond the intended location and then to draw back a small amount while releasing it. I then grab it and pull it into the mark I made preoperatively. The reason for this is that it is much easier to pull the inlay into the desired position as opposed to pushing it into position.
When the inlay is in the desired location, gently open the forceps and slowly remove them from the pocket. When working with a 5-µm-thin inlay in a pocket, it is very easy to bend or fold the inlay. Therefore, I recommend having an extra inlay on hand for the first few procedures in case a bent or folded inlay needs to be replaced. It is also important to remember that all inlay procedures are dry procedures, so there should be no irrigation of the pocket interface.
After I have placed the inlay, I inspect the eye with the slit lamp to ensure that there is no debris in the pocket and that the inlay does not have any folds.
Postoperative course
The postoperative medication regimen includes antibiotics four times a day for 1 week; a stronger steroid four times a day for 1 week; and then a milder steroid four times a day for the next 3 weeks, tapering the dosing to three times a day and two times a day over the next 2 months. This regimen helps manage the corneal response to the inlay. I have not had any patients with corneal thinning, but some have a mild wound healing response. This clears over time and can be effectively managed through steroid therapy. Patients are seen postoperatively at 1, 3 and 6 months and then yearly.
To set proper expectations, I advise patients that their vision will vary during the first 3 months, and at their 3-month visit, I check to make sure they have reached their refractive target. However, I have found that the majority of patients have functional vision within a few days.
Overall, the pocket emmetropic Kamra procedure is enjoyable to perform and provides excellent outcomes for patients. There is an amazing amount of data behind the optimal depth of the implant and how to center it, so if physicians follow the guidelines set out by AcuFocus, they will have a great success with the Kamra inlay.