From ReVision Advanced Laser Eye Center, Columbus, Ohio; and the Division of Ophthalmology, St Joseph’s Translational Research Institute, Atlanta, Georgia.
The author has financial interest and serves as World Surgical Monitor for AcuFocus Inc (Irvine, California).
Presented at the Wavefront & Presbyopic Refractive Corrections meeting; February 25–27, 2011; Vancouver, Canada.
The author acknowledges all global investigators for the US AcuFocus IDE trial.
Correspondence: George O. Waring IV, MD, ReVision Advanced Laser Eye Center, 1080 Polaris Pkwy, Columbus, OH 43240. Tel: 404.593.8763; E-mail: firstname.lastname@example.org
Presbyopia is characterized by the progressive age-related loss of accommodation with resultant inability to focus on near objects with a typical onset between the ages of 40 and 50 years.1 Current nonsurgical treatments include multifocal spectacles, multifocal contact lenses, or monovision with contact lenses, which can be lost or dislodged and require regular removal, cleaning, and care.2 Corneal-based procedures include conductive keratoplasty and LASIK monovision. Conductive keratoplasty can be used to reshape the cornea but may need to be repeated as the effect may regress over time.3,4 Laser in situ keratomileusis monovision can reduce the need for bifocal lenses, but not everyone adapts well to monovision.5 New excimer laser treatments to create a presbyopic cornea or to increase depth of focus by inducing spherical aberration are evolving.6 Recently, corneal inlays have emerged as a corneal-based option in the surgical treatment of presbyopia.7
Corneal inlays have a long history; they were first described by José Barraquer in 1949.8 The original corneal inlays, designed to correct ametropia, had poor refractive predictability and loss of visual acuity over time, as well as progressive haze, perilenticular opacity, and decentration.9–11 Improvements in material and design have led to the development of a number of new intracorneal inlays. In this study, the KAMRA (AcuFocus Inc, Irvine, California) corneal inlay was evaluated for the treatment of emmetropic presbyopia. The KAMRA inlay is a small-aperture corneal inlay made of polyvinylidine fluoride. The inlay is 5-μm thick and 3.8 mm in total diameter with a 1.6-mm central aperture that increases depth of focus and improves near visual acuity by restricting bent light rays from entering the eye similar in concept to reducing the aperture (f-stop) in a camera. Corneal metabolic, catabolic, and hydrational flows are maintained by 8400 microperforations in the inlay. The inlay is placed beneath a LASIK flap or in a pocket created within the corneal stroma. It has the advantage of being minimally invasive, predictable, and removable.12 In addition, the small aperture allows for stable improvement in depth of focus despite the progressive nature of presbyopia.
The interim efficacy results of the United States Investigational Device Exemption (US IDE) study of the KAMRA corneal inlay for the treatment of emmetropic presbyopia are presented herein.
Patients and Methods
This study is a prospective, nonrandomized, clinical trial conducted at 24 sites in the United States, Europe, and Asia Pacific (CTGI #NCT00850031). The study received institutional review board approval and adhered to the tenets of the Declaration of Helsinki. All patients signed informed consent before any study procedures were initiated. Patients were naturally occurring presbyopic emmetropes between 45 and 60 years of age. Study inclusion criteria were: spherical equivalent (SE) between +0.50 and −0.75 diopters (D) with cylinder ≤0.75 D, uncorrected near visual acuity (UNVA) between 20/40 and 20/100, and corrected distance visual acuity (CDVA) of at least 20/20 in both eyes.
Eye dominance was tested with both sensory and motor dominance assessment techniques. If they differed, the patient completed a contact lens test. The KAMRA inlay was implanted in the nondominant eye unless psychophysical testing determined that the inlay should be implanted in the dominant eye. For example, if a patient displayed a preference for use of the dominant eye for near activity as evidenced by previous monovision contact lens wear, a contact lens trial, or loose lens testing (near dominance), the inlay was implanted in the dominant eye. A lamellar dissection or pocket placed a minimum of 180-μm deep was created with a femtosecond laser or microkeratome. The inlay was placed on the stromal bed beneath the dissection or within the pocket and centered on the first Purkinje image with the patient coaxially fixated.
All visual testing was performed on the implanted eye. Visual acuities were measured with 100% contrast ETDRS acuity charts. Mesopic (3 cd/m2) and photopic (85 cd/m2) corrected distance contrast sensitivities were evaluated using Functional Acuity Contrast Test (FACT) sine-wave grating charts with the self-illuminated and self-calibrated Optec 6500 Vision Tester (Stereo Optical Co Inc, Chicago, Illinois). Photopic contrast sensitivity was tested at 3, 6, 12, and 18 cycles per degree (cpd), mesopic contrast sensitivity was tested at 1.5, 3, 6, and 12 cpd. Data were expressed as mean±standard deviation. Dunnett test was used to compare means, with significance set to P≤.05.
A total of 507 eyes from 508 patients were implanted under the study protocol. In 1 enrolled patient, the flap was thinner than planned and the inlay was not implanted. Figures 1–3 show the change in mean UNVA, uncorrected intermediate visual acuity (UIVA), and uncorrected distance visual acuity (UDVA) from preoperative to 18 months postoperative. Near and intermediate visual acuities improved at 1 month postoperative and continued to improve to 18-month follow-up. Mean UNVA was statistically significantly improved (P<.0001) from preoperative at all postoperative follow-ups, ranging from J8 (0.482±0.925 logMAR) preoperatively to between J2 and J3 (0.139±0.851 log-MAR) at 18 months postoperative.
Figure 1. Mean monocular uncorrected near visual acuity (UNVA) in the implanted eye. A notable improvement is seen in UNVA that is statistically significant at all follow-up examinations (P<.0001). Error bars indicate ±1 standard deviation.
Figure 3. Mean monocular uncorrected distance visual acuity in the implanted eye. Uncorrected distance visual acuity is statistically significantly different from preoperative at all follow-up examinations (P<.001). The maximum change in distance acuity is three letters, which is within the normal range of observer variability for distance acuity testing.13 Error bars indicate ±1 standard deviation.
The increase in mean UIVA from preoperative was statistically significant at all postoperative follow-ups (P<.0001). Mean postoperative UIVA was within two lines of preoperative levels. Mean UIVA changed from 20/35 (0.239±0.837 logMAR) preoperatively to 20/26 (0.139±0853 logMAR) at 18 months (P<.0001). A slight decline was noted in mean UDVA to 20/20 (0.178±0.887 logMAR) at 1-month follow-up that remained stable to 20/20 (0.011±0.890 logMAR) at 18 months. The maximum decrease in mean UDVA was three letters, which is within the normal variability of distance visual acuity tests.13 The difference from preoperative UDVA was statistically significant at every postoperative follow-up (P<.0001).
The decrease in photopic contrast sensitivity was statistically significant at all spatial frequencies (P<.001) (Fig 4). Mean mesopic contrast sensitivity of the implanted eye (Fig 5) also decreased slightly from preoperative to 12 months postoperative (P<.0001). However, both photopic and mesopic contrast sensitivity results for the implanted eye were within the range of the normal population for preoperative and 12-month follow-ups at all frequencies.14
Figure 4. Mean monocular photopic contrast sensitivity in the implanted eye preoperatively and at 12-month follow-up. The difference between preoperative and 12 months is statistically significant (P<.001); however, the postoperative contrast sensitivity scores are within the range of the normal population.
Figure 5. Mean monocular mesopic contrast sensitivity in the implanted eye preoperatively and at 12-month follow-up. The difference between preoperative and 12 months is statistically significant (P<.0001); however, postoperative contrast sensitivity scores are within the range of the normal population.
Interim visual acuity results from the US IDE study of the KAMRA corneal inlay for the treatment of emmetropic presbyopes demonstrate substantial improvements in near and intermediate visual acuities with minimal disruption of UDVA or mesopic contrast sensitivity.
These results are in agreement with reports from a European study of 32 presbyopic natural emmetropes implanted with a previous iteration of the KAMRA corneal inlay that was 10-μm thick with 1600 microperforations. In this study, the mean UNVA of the implanted eye improved from J6 preoperatively to J2 at 2 years postoperative and mean UIVA improved from 20/40 to 20/25, with no major loss of monocular UDVA.15 Patients from that same study also demonstrated significant improvement in reading performance. Mean reading distance decreased from 48.1±5.4 cm preoperative to 40.6±4.3 cm at 2 years postoperative, mean reading acuity increased from 0.38±0.14 logRAD to 0.24±0.11 logRAD, and reading speed improved from 142±13 words per minute (wpm) to 149±17 wpm. All of these changes were statistically significant.16
Corneal inlays are a promising modality for the treatment of presbyopia. Further advances in centration, wound-healing modulation, and stromal bed smoothness will improve outcomes. To date, the KAMRA small aperture corneal inlay has shown good efficacy in improving UNVA and UIVA without significant diminution of UDVA or contrast sensitivity. In conjunction with LASIK, this inlay may also be suitable for ametropic presbyopes.
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- Mulet ME, Alio JL, Knorz MC. Hydrogel intracorneal inlays for the correction of hyperopia: outcomes and complications after 5 years of follow-up. Ophthalmology. 2009;116(8):1455–1460. doi:10.1016/j.ophtha.2009.05.019 [CrossRef]
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- Yilman OF, Bayraktar S, Agca A, Yilmaz B, McDonald MB, van de Pol C. Intracorneal inlay for the surgical correction of presbyopia. J Cataract Refract Surg. 2008;34(11):1921–1927. doi:10.1016/j.jcrs.2008.07.015 [CrossRef]
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- Dexl AK, Seyeddain O, Riha W, Hohensinn M, Hitzl W, Grabner G. Reading performance after implantation of a small-aperture corneal inlay for the surgical correction of presbyopia: two-year follow-up. J Cataract Refract Surg. 2011;37(3):525–531. doi:10.1016/j.jcrs.2010.10.044 [CrossRef]
Figure 2. Mean monocular uncorrected intermediate visual acuity (UIVA) in the implanted eye. The improvement in UIVA is statistically significant at all follow-up examinations (P<.0001). The improvement is ≥1 line at 1 and 18 months. Error bars indicate ±1 standard deviation.