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Maria Gomez-Valcarcel, Jaime Tejedor, Antonio Guirao; Surgically Induced Aberrations in the Cornea after Conductive Keratoplasty. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5775.
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To investigate the optical aberrations induced in the cornea by conductive keratoplasty (CK).
Twelve eyes of 8 presbyopic patients (41 to 57 yrs old; mean: 50 yrs) treated with CK were studied. Preoperative spherical equivalent was +0.8 D (0.25 to 1.75 D), and astigmatism lower than 0.75 D. Emmetropes were treated in the non-dominant eye for monovision presbyopic correction. In hyperopes, the contralateral eye was also corrected for mild hyperopia. Attempted correction ranged from 0.75 to 2.75 D (mean: 1.8 D). Spots (8 or 16) of radio frequency (View Point CK, Refractec LLC) were applied through an annuli at diameters of 6, 7 and/or 8 mm depending on the patient’s nomogram. Videoqueratography was measured (Orbscan, Orbtek Inc.) before, and 1 week and 3 moths after surgery. Corneal aberrations were calculated for a 6-mm pupil up to 4th order. Pre and postoperative corneal aberrations were compared and the surgically induced changes were statistically evaluated.
There was an initial overcorrection on average (-0.4 D at 1week) followed by regression of effect (0.1 D at 3 months). After 3 months, 50% of eyes were ±0.25 D of attempted correction, and 80% were within ±1.25 D. The achieved correction measured by subjective refraction and from topography correlated (r=0.9). There was a surgically induced astigmatism of 0.5 ±0.3 D on average (0 to 1.25D). High-order aberrations changed individually with surgery and did not increase on average (RMS: 0.78 microns, pre; 0.73 microns, 3 months post). Some patients with preoperative corneas of low optical quality experienced a reduction of aberrations. Coma aberration increased only slightly (0.44 microns, pre; 0.52 and 0.47 microns, 1 week and 3 months post), with no preferential induced axis. Spherical aberration greatly changed, moving from negative to positive values (-0.29 microns, pre; -0.07 and -0.12 microns, 1 week and 3 months post). This change was correlated with the attempted correction (r=0.5).
CK does not systematically increase aberrations: the better corneas slightly deteriorate, and the ones with worse optical quality tend to improve. The corneal steepening created by surgery produces a significant change in spherical aberration. This change could explain in part the slight multifocal effect in these patients. The impact of surgery manifests in the short term, with larger changes at one week and regression and stability after the third month, probably due to the healing process.
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