Surgical Correction of Presbyopia

Lenticular, Corneal, and Scleral Approaches

Michael Greenwood, MD; Shamik Bafna, MD; Vance Thompson, MD

Disclosures

Int Ophthalmol Clin. 2016;56(3):149-166. 

In This Article

Small-aperture Inlays

The KAMRA inlay (AcuFocus, Irvine, CA) is the only FDA-approved inlay available in the United States at the time of publication (Fig. 1). It is an opaque inlay composed of polyvinylidene fluoride. It uses the small aperture to increase depth of field by blocking bent light rays, thereby minimizing refraction. The KAMRA inlay is 5 μm thick and has 8400 laser-etched porosity holes in a pseudorandom pattern to maintain metabolic flow and hydrational homeostasis, and also to help reduce any diffraction issues at night. The 1.6 mm central annulus acts as a pinhole, and the outer diameter is 3.8 mm. The inlay is implanted in a lamellar pocket at a depth of 250 μm. If previous LASIK has been performed, the inlay is then placed into a pocket at least 100 μm below the LASIK flap. Placement of the inlay can also be performed simultaneously with photorefractive keratectomy, a procedure known as PRKAMRA.

Figure 1.

KAMRA inlay in a presbyopic patient.

The KAMRA inlay continuously compensates for the progressive loss of accommodative amplitude in phakic patients by means of improvement in depth of focus with the small aperture. Stereoacuity is preserved with a small-aperture inlay, which is not done with blended vision.[14] The KAMRA inlay can be used in natural emmetropes, post-LASIK emmetropes, combined with a LASIK correction as a simultaneous or 2-step procedure, and pseudophakic patients after implantation of a monofocal IOL or a phakic IOL.[17] Patients tend to do best with a refraction between plano and -0.75 D with <0.75 D of astigmatism in the nondominant eye.

Complications related to the KAMRA inlay include standard risks with refractive surgery. The major risk is related to the healing response. The primary response is increased stromal thickening over the inlay, which leads to flattening of the overlying epithelium and a hyperopic shift. There have also been reports of infectious keratitis,[18] corneal epithelial iron deposits, and corneal haze.[19] In the case of an undesired outcome, the inlay may be removed with no loss of corrected visual acuity, although the refraction may shift.[20]

Results of the KAMRA inlay have been encouraging, with studies showing improved near vision, stable or improved intermediate vision, and stable or mildly worse distance vision in the surgical eye. Seyeddain et al[21] reported data in 32 eyes and found that 96.9% of patients read J3 or better in the implanted eye with mean binocular uncorrected near visual acuity improvement from J6 preoperatively to J1 after 24 months. Mean binocular uncorrected intermediate visual acuity (UIVA) was 20/20 at 1 month and remained 20/20 throughout 24-month follow-up and mean uncorrected distance visual acuity of 20/20 in the implanted eye and a binocular uncorrected distance visual acuity of 20/16. Yilmaz and colleagues reported on 39 presbyopic patients; 12 were naturally emmetropic and 27 had emmetropia resulting from previous hyperopic laser in situ keratomileus. Of the 39 inlays implanted, 3 were explanted during the study. The mean UNVA improved from J6 to J1+ at 1 year. All implanted eyes had a UNVA of J3 or better and 85.3% of J1 or better. Binocularly, the mean UNVA remained J1 or better throughout the study. The mean UDVA in eyes with an inlay did not change significantly from preoperatively and remained 20/20 throughout the study period. All 3 eyes with inlay explantation returned to within ±1.00 D of the preoperative refractive state for near and distance vision, with no loss of corrected distance visual acuity (CDVA).[20] Tomita and colleagues reported 6-month data on 128 eyes evaluating the safety and efficacy of bilateral LASIK with simultaneous implantation of a KAMRA inlay in the nondominant eye. The mean logMAR UNVA in the eye with the inlay improved 7 lines in hyperopic eyes, 6 lines in emmetropic eyes, and 2 lines in myopic eyes. The mean logMAR UDVA improved by 3 lines, 1 line, and 10 lines, respectively.[22] Dexl et al[19] provide the longest follow-up of 5 years, with no statistically significant change in refractive error following placement of the inlay. The mean UNVA in the surgical eyes improved from J7/J8±0.8 lines preoperatively to J1±1.4 lines (P<0.001) at 12 months, remained stable until 36 months (J1±1.2 lines), and decreased slightly at 60 months (J3±2.0 lines) (P<0.001). The mean UIVA in the surgical eyes improved from 0.2 logMAR±1.6 lines (~20/32) preoperatively to 0.1 logMAR±1.2 lines (~20/25) (P<0.001) at 12 months, remained stable until 36 months [0.0 logMAR±1.0 lines (~20/20)], and decreased slightly at 60 months [0.2 logMAR±1.5 lines (~20/32)]. The mean UDVA in the surgical eyes decreased slightly from -0.1 logMAR±0.6 lines (~20/16) to 0.0 logMAR±1.1 lines (~20/20) at 12 months (P<0.001), then was stable until 36 months [0.0 logMAR±1.1 lines (~20/20)] and decreased again at 60 months [0.1 logMAR±1.8 lines (~20/25)].

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