More than 1.8 billion people worldwide had presbyopia in 2015. That number is expected to be 2.1 billion by 2030.1 Nonsurgical treatment options include contact lenses and glasses set up for monovision or as bifocals. Options for surgical correction include laser vision correction for monovision and refractive clear lens exchange with either a monofocal IOL targeted for monovision or a multifocal IOL.
The corneal inlay is a more novel surgical solution that allows a subset of patients to continue the use of their remaining accommodation while preserving improved distance vision compared to traditional monovision. Implantation is not difficult for surgeons to learn, but they need to be very careful in patient selection. Let us explain.
What it is
The Kamra inlay (CorneaGen) is currently the only FDA-approved corneal inlay, receiving approval in April 2015. Kamra is an opaque annulus with an overall diameter of 3.8 mm. The inlay is 6 μm thick and creates a pinhole effect through a 1.6-mm central aperture. The Kamra inlay is made of polyvinylidene fluoride and has 8,400 micro-perforations arranged in a random pattern, allowing for improved corneal metabolic nutrition.2
The Kamra corneal inlay maintains efficacy despite the continued loss of accommodation due to the small aperture (or pinhole effect). The Kamra is placed in the nondominant eye. Regardless of ocular age and related pathologies, theoretically, the patient will not lose their distance and near vision as the eye ages. The majority of patients lose zero to one line of distance vision for about a five- to six-line improvement in near vision.3,4
Keep MOD in mind
An excellent pneumonic to help create the ideal Kamra candidate is MOD (Myopia, Ocular surface, Depth). The optimal refractive error is -0.75 D with less than -0.50 D of astigmatism. In most Kamra cases, the patient needs to have LASIK or PRK to optimize the “sweet spot” target of -0.75 D.
The ocular surface needs to be pristine, because any deficit creates visual symptoms. The surface should be optimized with either punctal plugs or medications such as Restasis (cyclosporine, Allergan) or Xiidra (lifitegrast, Shire) in any patient with signs of dry eye or consistent symptoms of dry eye.
Preferably, the patient has a minimum of 500 μm of central corneal thickness. The inlay can also be placed in postoperative PRK or LASIK patients depending on corneal thickness and flap depth. For safety, the inlay must be placed at least 100 μm below the original LASIK flap. The preferred depth for the inlay is at 250 to 300 μm and at least 200 μm in front of the endothelium. The deeper the inlay is placed, the less inflammation is created and the earlier visual rehabilitation occurs.
The Kamra-ready candidate
We discuss Kamra with patients 45 to 55 years old; the ideal candidate is a healthy 48- to 52-year-old hyperopic male (less dry eye than females) with no history of autoimmune disorders or dry eye and an occupation not requiring perfect near or distance vision. This patient’s goal should be to obtain functional vision throughout most activities, and the patient should be content with the possibility of occasionally relying on spectacles for the best possible vision.
On initial screening, we always review present refraction, age, gender, occupation, medical history, dry eye history, Pentacam (Oculus) results, corneal thickness, ocular scatter index with the AcuTarget HD instrument (Visiometrics) and goals of surgery.
Preoperatively, the surgical results can be demonstrated to patients with a pinhole occluder by placing it over the patient’s nondominant eye. With the dominant eye covered, the patient can appreciate the vision through the pinhole at both distance and near. Then, monovision laser vision correction can be demonstrated by placing a +1.50 D trial lens over the nondominant eye and covering the dominant eye, having the patient look at both distance and near. This gives the patient a clear understanding of the possible results and the positive and negative aspects of monovision laser correction vs. the Kamra inlay.
Beyond the ideal
For patients over 55, we begin to consider lens extraction with a multifocal IOL as a better option. Mini-monovision (-0.50 to -0.75 D) with later option for Kamra implantation is discussed with patients younger than 45. We spend time understanding the patient’s occupation and hobbies. It is crucial to relay to the patient that the Kamra will not completely eliminate the occasional use of spectacles for challenging scenarios such as night driving or reading a menu in a dimly lit restaurant.
The Kamra probably won’t be the only inlay in town for long.
The Presbia Flexivue Microlens has completed enrollment in its Phase 3 FDA trial. This corneal inlay utilizes bifocal optics to provide distance vision through a plano central zone surrounded by multiple rings of varying power to provide near vision.2,5 It is a transparent hydrogel-based implant made from a hydrophilic copolymer of hydroxyethyl methacrylate and methyl methacrylate; it is 3-mm in diameter and a little less than 20 μm thick.
The Microlens is placed in a femtosecond-created corneal pocket 280 to 300 μm deep. The central zone is optically neutral with a refractive peripheral zone that provides add powers between +1.25 to +3.5 D. The central portion of the inlay has a 0.15-mm opening that facilitates metabolism across the cornea.6
Another alternative treatment for presbyopia is the Transform allogenic inlay by Allotex. The company plans to provide surgeons with corneal tissue that they can then reshape with their femtosecond or excimer lasers. The proposed benefits include improved biocompatibility, range of optical zone sizes and removal without residual complications.
The Transform is currently in a multicenter clinical trial in Europe.
Providers should be especially cautious with emmetropes and myopes. It is very challenging for those patients to truly understand that they will be compromising any vision in exchange for the near vision provided by Kamra. Likewise, patients with goals of perfect vision at all distances, comments indicating lack of proper expectations and those with occupations requiring outstanding vision should be counseled extensively.
Exams and meds
We conduct postoperative exams at day one, week one, month three, month six and every six months thereafter. At each visit, we check uncorrected near visual acuity (UNVA), uncorrected distance visual acuity (UDVA), manifest refraction spherical equivalent, ocular surface index with the AcuTarget HD, tear film index, centration and topography.
We direct patients to use an antibiotic drop for one week four times a day. We also instruct them to use prednisolone acetate for one month in a 4-3-2-1 taper strategy followed by one month of fluorometholone b.i.d. and a third month of fluorometholone daily to prevent haze.
Keep on top of these
Postop dry eye management initially includes committing to any of the normal preop management strategies that have not yet been attempted. If all common strategies have been attempted, we begin discussing additional therapies like oral doxycycline, supplemental omega-3 and procedures such as LipiFlow. The earlier the detection of decentration, the better for inlay repositioning.
It is also important to monitor the IOP, watching for steroid response.
WHAT WE’VE LEARNED
In our practice, the visual outcomes of the Kamra inlay have been promising. We have followed 262 eyes over a two-year period. Monocularly, in the inlay eye, 20/40 or better UNVA was observed in 97% at 12 months and 94% at 24 months. UDVA was 20/40 or better in 83% at 12 months and 88% at 24 months. UNVA of 20/25 or better was seen in 71% at 12 months and 73% at 24 months. UDVA of 20/25 or better was seen in 64% at 12 months and 70% at 24 months.
Six inlays were explanted with return of preoperative vision in all but one patient, who had an irregular central flattening.
Patient education is essential
Setting preoperative expectations is crucial because vision tends to recover slowly. Optimal uncorrected distance and near visual acuity typically comes between four to eight weeks postoperatively. In general, hyperopic patients adapt quickly while myopic patients require more time to achieve satisfaction.
Also, it is critical to remind patients that they may still need to rely on glasses in dim lighting or for night driving.
We perform simultaneous LASIK and Kamra inlay implantation on the majority of our patients without affecting healing time. The combined surgery has proven convenient for both patient and surgeon.
The Kamra inlay provides some distinct advantages over monovision and is one of our best alternatives to address presbyopia at this time. Still, preoperative patient selection is the single most important aspect of success.
As our experienced has deepened, we continue to elevate the threshold required to optimistically recommend the inlay to our patients. OM
- Fricke TR, Tahhan N, Resnikoff S, et al. Global Prevalence of Presbyopia and Vision Impairment from uncorrected Presbyopia: Systematic Review, Meta-Analysis, and Modeling. Ophthalmology. 2018;125:1492-1499.
- Arlt E, Krall E, Moussa S, Grabner G, Dexl A. Implantable inlay devices for presbyopia: the evidence to date. Clin Ophthalmol Auckl NZ. 2015;9:129-137.
- Alarcon A, Anera RG, Villa C, Jimenez del Barco L, Gutierrez R. Visual quality after monovision correction by laser in situ keratomileusis in presbyopic patients. J Cataract Refract Surg. 2011;37:1629-1635.
- Linn S, Hoopes PC. Stereopsis in patients implanted with a small aperture corneal inlay. Invest Ophthalmol Vis Sci. 2012;53:1392.
- Greenwood M, Bafna S, Thompson V. Surgical correction of presbyopia: lenticular, corneal, and scleral approaches. Internat Ophthal Clinics. 2016;56:149-166.
- Limnopoulou AN, Bouzoukis DI, Kymionis GD, et al. Visual outcomes and safety of a refractive corneal inlay for presbyopia using femtosecond laser. J Refract Surg. 2013;29:12-18.