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

Abstract

Purpose: To assess longitudinal refractive, keratometric, and topographic changes following KAMRA small-aperture inlay implantation.

Design and setting: Prospective study at a single site refractive surgery center.

Methods: Fifty 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.

Results: The 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.

Conclusion: KAMRA 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.

Keywords: IOL calculation; KAMRA; presbyopia; wound healing.

Figure 1

Change in MRSE between postoperative time points for the entire patient cohort. Note: *Statistically significant change. Abbreviations: MRSE, manifest refractive spherical equivalent; preop, preoperative.

Figure 2

Change in MRSE with respect to baseline MRSE for all postoperative follow-up time points. Note: *Statistically significant change. Abbreviation: MRSE, manifest refractive spherical equivalent.

Figure 3

Change in Km between postoperative time points for the entire patient cohort. Note: *Statistically significant change. Abbreviations: Km, mean keratometry; preop, preoperative.

Figure 4

Change in Km with respect to baseline Km for all postoperative follow-up time points. Note: *Statistically significant change. Abbreviation: Km, mean keratometry.

Figure 5

Demonstration of topographic pattern of annular steepening with central flattening occurring over the 36-month follow-up period with a corresponding hyperopic shift in four patients (#1–4).

Figure 6

Longitudinal corneal topographic changes associated with MRSE changes in a single patient. Pronounced correlation of topographic “ring” disappearance and myopic regression in late postoperative interval. Note: The inset images represent the corneal topographical changes at the corresponding 3, 6, 12, and 36 postop months. Abbreviations: MRSE, manifest refractive spherical equivalent; postop, postoperative; preop, preoperative.

Figure 7

(A) Central steepening and annular flattening topography at 36 months in a patient with significant myopic shift. (B) Central flattening and annular steepening topography at 36 months in a patient with significant hyperopic shift.

Figure 8

Depictions of corneal astigmatisms and axis for left and right eyes in vector format. Notes: (A) Red line shows mean corneal astigmatism in corresponding axis preoperatively for left eyes; (B) red line shows mean corneal astigmatism in corresponding axis at 36 months postoperatively for left eyes; (C) red line shows mean corneal astigmatism in corresponding axis preoperatively for right eyes; (D) red line shows mean corneal astigmatism in corresponding axis at 36 months postoperatively for right eyes. Abbreviation: preop, preoperative.