Corneal Inlays for Presbyopia Correction
Corneal Inlays for Presbyopia Correction
The Kamra Inlay (AcuFocus, Inc., Irvine, California, USA) is a microperforated, opaque inlay made of polyvinylidene fluoride (Fig. 2). It relies on the principle of pinhole optics to increase the eye's depth of focus by blocking unfocused light. The current-generation Kamra inlay has an overall diameter of 3.8 mm and a central aperture of 1.6 mm. It is just 5 μm thick and is intended for implantation in a lamellar pocket or under a 200-μm femtosecond laser flap. It has 8400 laser-drilled porosity holes to facilitate the flow of nutrition through the cornea.
(Enlarge Image)
Figure 2.
The Kamra inlay. The Kamra inlay is a smallaperture, microperforated, opaque inlay made of polyvinylidene fluoride. It relies on the principle of pinhole optics to increase the eye's depth of focus by blocking unfocused light. Source: AcuFocus.
The Kamra inlay has been studied in natural emmetropes, post-LASIK emmetropes, in conjunction with a LASIK correction as a simultaneous or 2-step procedure and in pseudophakes after implantation of a monofocal IOL.
It is commercially available in many countries outside the USA, with more than 18 000 inlays implanted worldwide to date. All of us have participated in the now completed US Phase III clinical trials of this inlay. There is extensive information about the Kamra inlay in the published literature.
Rabbit studies show that although there is an early increase in stromal cell death and inflammation 48 h after surgery in eyes that underwent a femtosecond laser pocket creation and Kamra inlay insertion compared to eyes with the pocket only, the differences disappear by 6 weeks after surgery.
In the human studies with the longest follow-up, there have been no inflammatory reactions or cases of ulceration or stromal fibrosis and there does not appear to be any negative effect on endothelial cell density.
Implantation of the inlay does not appear to cause any localized changes or scotomas in the visual field. Changes in pattern standard deviation have been less than would be theoretically assumed. Brooker et al. reported no significant difference in pattern standard deviation from baseline (using Zeiss Humphrey 24–2 SITA perimetry), nor any decrease in the reliability of the testing compared with the nonimplanted eye 3 years after implantation.
Together, the published body of work demonstrates that monocular implantation of a small-aperture inlay results in sustained improvement in near and intermediate vision while maintaining good distance vision.
The largest reported series with any presbyopia-correcting inlay to date – 180 eyes implanted with the current version of the Kamra inlay that also underwent simultaneous LASIK – was recently published by Tomita et al.. At 6 months, with data available for about one-third of the eyes, mean UCNVA in the treated eyes improved by seven lines in hyperopic eyes, six lines in emmetropic eyes, and two lines in myopic eyes; mean UCDVA improved by three lines, one line, and 10 lines, respectively. All patients had binocular UCDVA of 0.00 LogMAR (20/20) or better.
Over the long term, we believe the most rewarding results with this procedure will be achieved with a combination of LASIK and the inlay to ideally target the refraction in both eyes.
Yilmaz et al. now have 4-year follow-up on 39 natural and post-LASIK emmetropes in Turkey, whereas Seyeddain et al. have 3-year follow-up on 32 emmetropic patients in Austria. All of the patients in these long-term studies were implanted with an older version of the Kamra inlay, and so did not have the benefits of recent improvements to the device and surgical technique. Nevertheless, mean UCNVA in both studies was J1 with 96 to 97% of treated eyes seeing J3 or better, and no significant loss of binocular UCDVA.
Intermediate visual acuity with this small-aperture inlay is quite good, with 91% seeing at least 20/32 at intermediate and significant improvements in the ability to perform intermediate tasks without correction. This is a major advantage over multifocal options for the presbyopes, which typically provide relatively poor intermediate acuity.
Both clinical experience and optical modeling indicate that visual acuity with small-aperture inlays is optimized with some residual myopia in the implanted eye. Leaving -0.75 D myopia results in an average depth of focus of 2.5 D with a near visual acuity of J1 or better, whereas in perfect emmetropic eyes, the depth of focus decreases to around 1.75 D. Although small-aperture inlays are quite forgiving of both astigmatism and higher-order aberration (HOA), correcting astigmatism greater than 0.5 D will also improve performance.
There is a small loss of contrast sensitivity in eyes with the inlay, but contrast sensitivity remains within normal limits and the loss is minor compared with the gain in near and intermediate vision. A prospective study has shown no significant change in stereopsis 6 months after implantation.
The ability to perform common tasks without spectacles may be a better measure of functional success than visual acuity. In two prospective, interventional case series, Austrian researchers have shown that emmetropic presbyopes implanted with the Kamra inlay improved on all measures of reading performance ( Table 2 ). Those improvements are sustained and even slightly improved through longer follow-up of 1 or 2 years.
Subjectively, small-aperture inlay patients report a statistically significant reduction in their dependence on glasses for near and intermediate tasks. They rate their ability to perform these tasks better in bright light than in dim and better for larger print material than for very fine work (e.g., books > package inserts).
In published reports, patient satisfaction with uncorrected vision with a small-aperture inlay has been high, especially among emmetropes and hyperopes.
We and others have had little difficulty visualizing the retina in eyes with a small-aperture inlay. One author performed extensive retinal imaging in two eyes postimplantation and reported that normal visualization of the central and peripheral fundus is possible, as well as good quality central and peripheral imaging and optical coherence tomography scans.
We are just beginning to see the first cases of patients with corneal inlays go on to need cataract surgery. Yilmaz reported uneventful small-incision phacoemulsification in two such patients. Two of us (R.L.L. and P.C.H.) have personal experience with patients who required cataract surgery following corneal inlays for presbyopia. The procedures were uneventful and the patients continued to enjoy good vision with the inlays after monofocal IOL implantation. Although not yet published, early experience implanting small-aperture inlays in pseudophakic patients has also been positive.
There have been no serious, sight-threatening complications with the current surgical techniques for implanting the small-aperture inlay. A few cases of epithelial ingrowth have been reported, but were resolved and/or did not affect the visual axis.
The most commonly reported complaints are glare and halo, dry eye, and night vision problems. These are mostly mild to moderate and are similar to the increase in visual symptoms following LASIK. In our experience, the ocular surface should be treated aggressively before and after inlay implantation, as pre-existing dry eye is common in the presbyopic population and will likely be exacerbated by the creation of a flap or pocket.
Some small-aperture inlays have been removed for a variety of reasons, including dissatisfaction with vision or visual symptoms, refractive shift, and flap problems. Fortunately, removal of the inlay has been easily accomplished, even years after implantation, and vision recovers with little residual effect.
Centration of any corneal inlay is very important to achieve its best refractive result. Although we find the small-aperture design more forgiving to center than other inlay designs, optical modeling suggests that even with a small aperture, decentration of as little as 0.5 mm can reduce image quality. The inlay should be centered on the visual axis, which is typically slightly inferonasal to the center of the pupil, but is difficult to precisely locate in practice. It is best identified by marking the first Purkinje reflection or the coaxially sighted corneal reflex. In the future, devices to aid in centration may be more widely available. Small aperture inlays can be successfully recentered with improvement in vision.
Small-Aperture Inlays
The Kamra Inlay (AcuFocus, Inc., Irvine, California, USA) is a microperforated, opaque inlay made of polyvinylidene fluoride (Fig. 2). It relies on the principle of pinhole optics to increase the eye's depth of focus by blocking unfocused light. The current-generation Kamra inlay has an overall diameter of 3.8 mm and a central aperture of 1.6 mm. It is just 5 μm thick and is intended for implantation in a lamellar pocket or under a 200-μm femtosecond laser flap. It has 8400 laser-drilled porosity holes to facilitate the flow of nutrition through the cornea.
(Enlarge Image)
Figure 2.
The Kamra inlay. The Kamra inlay is a smallaperture, microperforated, opaque inlay made of polyvinylidene fluoride. It relies on the principle of pinhole optics to increase the eye's depth of focus by blocking unfocused light. Source: AcuFocus.
The Kamra inlay has been studied in natural emmetropes, post-LASIK emmetropes, in conjunction with a LASIK correction as a simultaneous or 2-step procedure and in pseudophakes after implantation of a monofocal IOL.
It is commercially available in many countries outside the USA, with more than 18 000 inlays implanted worldwide to date. All of us have participated in the now completed US Phase III clinical trials of this inlay. There is extensive information about the Kamra inlay in the published literature.
Safety
Rabbit studies show that although there is an early increase in stromal cell death and inflammation 48 h after surgery in eyes that underwent a femtosecond laser pocket creation and Kamra inlay insertion compared to eyes with the pocket only, the differences disappear by 6 weeks after surgery.
In the human studies with the longest follow-up, there have been no inflammatory reactions or cases of ulceration or stromal fibrosis and there does not appear to be any negative effect on endothelial cell density.
Implantation of the inlay does not appear to cause any localized changes or scotomas in the visual field. Changes in pattern standard deviation have been less than would be theoretically assumed. Brooker et al. reported no significant difference in pattern standard deviation from baseline (using Zeiss Humphrey 24–2 SITA perimetry), nor any decrease in the reliability of the testing compared with the nonimplanted eye 3 years after implantation.
Visual Acuity and Quality
Together, the published body of work demonstrates that monocular implantation of a small-aperture inlay results in sustained improvement in near and intermediate vision while maintaining good distance vision.
The largest reported series with any presbyopia-correcting inlay to date – 180 eyes implanted with the current version of the Kamra inlay that also underwent simultaneous LASIK – was recently published by Tomita et al.. At 6 months, with data available for about one-third of the eyes, mean UCNVA in the treated eyes improved by seven lines in hyperopic eyes, six lines in emmetropic eyes, and two lines in myopic eyes; mean UCDVA improved by three lines, one line, and 10 lines, respectively. All patients had binocular UCDVA of 0.00 LogMAR (20/20) or better.
Over the long term, we believe the most rewarding results with this procedure will be achieved with a combination of LASIK and the inlay to ideally target the refraction in both eyes.
Yilmaz et al. now have 4-year follow-up on 39 natural and post-LASIK emmetropes in Turkey, whereas Seyeddain et al. have 3-year follow-up on 32 emmetropic patients in Austria. All of the patients in these long-term studies were implanted with an older version of the Kamra inlay, and so did not have the benefits of recent improvements to the device and surgical technique. Nevertheless, mean UCNVA in both studies was J1 with 96 to 97% of treated eyes seeing J3 or better, and no significant loss of binocular UCDVA.
Intermediate visual acuity with this small-aperture inlay is quite good, with 91% seeing at least 20/32 at intermediate and significant improvements in the ability to perform intermediate tasks without correction. This is a major advantage over multifocal options for the presbyopes, which typically provide relatively poor intermediate acuity.
Both clinical experience and optical modeling indicate that visual acuity with small-aperture inlays is optimized with some residual myopia in the implanted eye. Leaving -0.75 D myopia results in an average depth of focus of 2.5 D with a near visual acuity of J1 or better, whereas in perfect emmetropic eyes, the depth of focus decreases to around 1.75 D. Although small-aperture inlays are quite forgiving of both astigmatism and higher-order aberration (HOA), correcting astigmatism greater than 0.5 D will also improve performance.
There is a small loss of contrast sensitivity in eyes with the inlay, but contrast sensitivity remains within normal limits and the loss is minor compared with the gain in near and intermediate vision. A prospective study has shown no significant change in stereopsis 6 months after implantation.
Task Performance and Satisfaction
The ability to perform common tasks without spectacles may be a better measure of functional success than visual acuity. In two prospective, interventional case series, Austrian researchers have shown that emmetropic presbyopes implanted with the Kamra inlay improved on all measures of reading performance ( Table 2 ). Those improvements are sustained and even slightly improved through longer follow-up of 1 or 2 years.
Subjectively, small-aperture inlay patients report a statistically significant reduction in their dependence on glasses for near and intermediate tasks. They rate their ability to perform these tasks better in bright light than in dim and better for larger print material than for very fine work (e.g., books > package inserts).
In published reports, patient satisfaction with uncorrected vision with a small-aperture inlay has been high, especially among emmetropes and hyperopes.
Post-inlay Exams and Surgery
We and others have had little difficulty visualizing the retina in eyes with a small-aperture inlay. One author performed extensive retinal imaging in two eyes postimplantation and reported that normal visualization of the central and peripheral fundus is possible, as well as good quality central and peripheral imaging and optical coherence tomography scans.
We are just beginning to see the first cases of patients with corneal inlays go on to need cataract surgery. Yilmaz reported uneventful small-incision phacoemulsification in two such patients. Two of us (R.L.L. and P.C.H.) have personal experience with patients who required cataract surgery following corneal inlays for presbyopia. The procedures were uneventful and the patients continued to enjoy good vision with the inlays after monofocal IOL implantation. Although not yet published, early experience implanting small-aperture inlays in pseudophakic patients has also been positive.
Complications
There have been no serious, sight-threatening complications with the current surgical techniques for implanting the small-aperture inlay. A few cases of epithelial ingrowth have been reported, but were resolved and/or did not affect the visual axis.
The most commonly reported complaints are glare and halo, dry eye, and night vision problems. These are mostly mild to moderate and are similar to the increase in visual symptoms following LASIK. In our experience, the ocular surface should be treated aggressively before and after inlay implantation, as pre-existing dry eye is common in the presbyopic population and will likely be exacerbated by the creation of a flap or pocket.
Some small-aperture inlays have been removed for a variety of reasons, including dissatisfaction with vision or visual symptoms, refractive shift, and flap problems. Fortunately, removal of the inlay has been easily accomplished, even years after implantation, and vision recovers with little residual effect.
Centration of any corneal inlay is very important to achieve its best refractive result. Although we find the small-aperture design more forgiving to center than other inlay designs, optical modeling suggests that even with a small aperture, decentration of as little as 0.5 mm can reduce image quality. The inlay should be centered on the visual axis, which is typically slightly inferonasal to the center of the pupil, but is difficult to precisely locate in practice. It is best identified by marking the first Purkinje reflection or the coaxially sighted corneal reflex. In the future, devices to aid in centration may be more widely available. Small aperture inlays can be successfully recentered with improvement in vision.
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