Long-term changes in keratometry and refraction after small aperture corneal inlay implantation

Abstract

PurposeTo assess longitudinal refractive, keratometric, and topographic changes following KAMRA small-aperture inlay implantation.Design and settingProspective study at a single site refractive surgery center.MethodsFifty patients underwent KAMRA small-aperture corneal inlay implantation for the correction of presbyopia. Uncorrected near visual acuity (UNVA), uncorrected distance visual acuity, manifest refractive spherical equivalent (MRSE), mean keratometry (Km), corneal topography, and surgically induced astigmatism vector analysis assessments were performed preoperatively and at 1, 3, 6, 12, 24, and 36 months postoperatively.ResultsThe study comprises 50 eyes. An average shift of 0.15±0.63 D (range −1.63 to 2.00 D) occurred between preoperative baseline and 36 months. At 36 months, 54% of patients had hyperopic MRSE and 40% had myopic MRSE compared with baseline. Km was significantly elevated at all postoperative measurements compared with baseline, with the largest Km measured at 12 months. Eighty-six percent of patients had UNVA of 20/32 or better and 88% uncorrected distance visual acuity of 20/25 or better at 36 months. Longitudinal corneal topography revealed a pattern of corneal steepening over the body of the inlay and flattening over the aperture, correlating with a hyperopic shift. There was no significant surgically induced astigmatism.ConclusionKAMRA inlay may cause an increase in Km compared with baseline. Corneal steepening may occur in a specific pattern with steepening over the inlay and flattening over the aperture. This topographic pattern causes a hyperopic shift, which may be relevant for subsequent procedures, such as cataract extraction.

Impact of corrected refractive power on the corneal denervation and ocular surface in small-incision lenticule extraction and LASIK

“…This further confirms that SMILE has less damage to the corneal sensory neural loop. 29 In this study, there were only 7 eyes that underwent high myopic LASIK because SMILE is a preferable surgical option for high myopic patients in our clinic. The data of earlier timepoints, such as 1 week postoperatively, can be considered in future studies to minimize the effect of the possible nerve regeneration activity within postoperative 1 month.…”

Applications of the pinhole effect in clinical vision science

“…39 In a follow-up of 36 months, the inlay causes the anterior cornea to steepen over the inlay, but flatten over the aperture; this hyperopic shift in refraction should be taken into account when planning the refractive outcome or in subsequent procedures such as cataract extraction. 35,85 In a case series by Amigó et al, 4 of 5 cases manifested a hyperopic shift while 1 case manifested a myopic shift more than 6 to 19 months postoperatively. 86 Decentration of the inlay may increase transverse chromatic aberration and lead to monocular diplopia, blur, and lateral spread of light rays.…”

Complications of Small Aperture Intracorneal Inlays: A Literature Review

“…Refractive instability is also a predictable consequence after KAMRA surgery and has been reported by several authors [ 41 , 47 , 52 ]. Moshirfar et al [ 53 ], in a case series of 50 patients, reported keratometric and topographic changes that led to a change in refraction. At 3 years, 54% of the eyes implanted with a KAMRA had a hyperopic manifest refractive spherical equivalent (MRSE), 40% were myopic with respect to the initial value, and the mean keratometry (K m ) was significantly increased at all postoperative measurements compared with baseline.…”

“…KAMRA inlay implantation has been described as successful in the majority of patients; in the actual scientific literature the decentration and repositioning rate ranges from 1.2% to 8.8% [ 33 ]. The small-aperture corneal inlay implantation technique creates an intrastromal pocket with a femtosecond laser and the pinhole device is later placed into this pocket via a small incision [ 53 ]. The criteria for KAMRA inlay placement are targeted in the center of the Purkinje reflex.…”