Search

Purpose: To evaluate the visual refractive and aberrometric outcomes of laser-assisted in situ keratomileusis (LASIK) surgery for the correction of high mixed astigmatism using a new-generation excimer laser and optimized aspherical profiles., Design: Retrospective interventional case series., Methods: Fifty-two eyes of 36 patients (21-53 years) with primary mixed astigmatism over 3.0 diopters (D) were included. All cases underwent LASIK surgery using the sixth-generation excimer laser Amaris with cyclotorsion control and a femtosecond platform for flap creation. Visual, refractive, corneal topographic, and aberrometric outcomes were evaluated during a 3-month follow-up. Refractive astigmatic changes were analyzed by Alpins method., Results: A significant reduction of refractive sphere and cylinder was observed 3 months postoperatively (P = .001), with an associated improvement of uncorrected distance visual acuity (P = .001). Best-corrected distance visual acuity (CDVA) remained unchanged in 31 eyes (59.6%), while 3 eyes (5.76%) lost 2 lines of CDVA. Fourteen eyes (26.9%) had spherical equivalent (SE) within ±0.5 D of emmetropia and 34 (65.3%) had SE within ±1.0 D of emmetropia. No significant difference was observed when comparing surgically induced and target astigmatism. A significant induction of higher-order aberration attributable to increase of spherical aberration was found (P = .003). Seven eyes (13.4%) required retreatment., Conclusions: LASIK for primary high mixed astigmatism using optimized aspherical profiles and a fast-repetition-rate excimer laser with cyclotorsion control is a safe, effective, and predictable procedure. Induction of higher-order aberrations is still present in the correction of the refraction error of the magnitude included in this study., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Purpose: We compared surgically induced astigmatism after penetrating keratoplasty performed by supervised cornea fellows and experienced cornea surgeons., Methods: Data were collected by retrospective chart review of 166 cases (166 eyes) of penetrating keratoplasty: 63 performed by two cornea surgeons and 103 by four cornea fellows. Astigmatism was calculated using scalar and vector methods. Vector analysis was performed on 109 of 166 eyes. Two techniques were compared: intraoperative keratometry and suture adjustment and the torque-antitorque running suture technique with no intraoperative keratometry or suture adjustment., Results: Mean surgically induced scalar astigmatism changed from preoperative astigmatism by 3.27 diopters (fellows) and 2.94 diopters (attending surgeons). In 109 cases, surgically induced vector cylinder changed from peroperative astigmatism by 4.21 diopters at 98 degrees (fellows) and 4.25 diopters at 114 degrees (surgeons). Surgically induced vector astigmatism changed from preoperative astigmatism by 4.67 diopters at 93 degrees in the first 6 months (fellows) and by 3.79 diopters at 103 degrees in the second 6 months. Analysis of x-axis and y-axis components of the surgically induced vector cylinder showed that the majority of the astigmatism was induced in the y-axis and that this difference was significant (P < .001) in all comparisons, independent of technique or surgeon group., Conclusions: Penetrating keratoplasty performed by supervised cornea fellows resulted in similar rates of surgically induced vector astigmatism, surface asymmetry, and surface regularity as that by experienced surgeons. Fellows induced significantly more with-the-rule astigmatism, but this tendency decreased with further training. Penetrating keratoplasty astigmatic outcomes were not significantly different whether or not intraopertive keratometry and suture adjustment were utilized. This study supports the concept that increased experience with corneal transplantation improves the outcome of penetrating keratoplasty by using the criterion of postoperative astigmatism as a measures.

Purpose: To assess the accuracy with which the Keratron keratoscope (Optikon 2000, Rome, Italy) measured astigmatic test surfaces by a profile reconstruction algorithm within a plane geometry model and to discriminate between error caused by the model and error caused by other factors., Methods: Height was reported by the Keratron for eight surfaces with central astigmatism ranging from 4 to 16 diopters. A three-dimensional ray tracing simulation produced theoretic reflected ring patterns on which the Keratron's reconstruction algorithm was performed. The Keratron's measurements were compared with the surfaces' formulas and the ray-traced simulations., Results: With a new mathematical filter for smoothing ring data, now part of the Keratron's software, maximum error was 0.47% of the total height and was usually less than 1% of local power for surfaces with 4 diopters of astigmatism. For surfaces with 16 diopters of astigmatism, maximum error was as high as 2.9% of total height and was usually less than 2.5% of local power. The reconstruction algorithm accounted for 40% and 70% of height error, respectively., Conclusions: The efficacy of keratoscopes cannot be assumed from their design theories but must be tested. Although plane geometry surface reconstruction contributed greatly to total height error, total error was so small that it is unlikely to affect clinical use.

Keratometry provides useful information about the cornea's image-forming properties, such as corneal astigmatism, but is inaccurate on irregular corneas. Quantitative corneal topographic information is now obtainable on irregular corneas, but is difficult for the clinician to interpret. We developed a method to determine the spherical power, astigmatism, and topographic irregularity of a cornea by finding the best-fit spherocylinder that was closest to its measured topography. Keratometric measurements and two videokeratographs were gathered prospectively on 262 normal and abnormal corneas. The best-fit measurements of spherical power, astigmatism, and topographic irregularity were reproducible with one standard deviation of 0.75 diopter or better; agreement with keratometric measurements in normal eyes was good (0.60 diopter or better). Topographic irregularity averaged 0.1 diopter on precision spheres, 0.4 diopter on 146 normal eyes, 0.8 diopter on 29 eyes after radial keratotomy, 2.0 diopters on 58 eyes after penetrating keratoplasty, and 3.0 diopters on 29 eyes with advanced keratoconus. We conclude the following: basic corneal image-forming properties can be measured from videokeratographs; the properties can be determined, by our methods, on irregular corneas in which keratometry is unreliable; and topographic irregularity provides a measure of irregular astigmatism.

We performed resections and recessions of scleral flaps on human cadaver eyes in order to measure the induced change in keratometric astigmatism. We prepared 3-mm scleral flaps that were 3, 5, 7, or 10 mm long and resected or recessed these flaps up to 1 mm in 0.25-mm increments. Scleral flap resection resulted in up to 10.1 D of net corneal steepening along the meridian of the incision. Scleral flap recessions resulted in up to 7.7 D of net corneal flattening along the meridian of the incision; the effect increased with increasing flap length in the recessed eyes. There was a tendency toward mean corneal flattening with resections and mean corneal steepening with recessions.

To clarify the mechanisms by which incisions and sutures produce corneal astigmatism, we made incisions and wedge resections closed by sutures in the corneoscleral limbus of human eye bank eyes, studying the changes in corneal curvature by shadowgraph photography of the corneal contour, by central keratometry, and by measurement of corneal diameter. The compression of tissue within the sutures or the closure of an excision of a wedge of tissue by sutures induced astigmatism in the meridian of surgery regardless of changes in the sagittal depth of the anterior chamber. Sutures and wedge resections closed by sutures in the anterior part of the cornea compressed or removed more tissue from the anterior part than the posterior part, producing a depression of the limbal cornea toward the anterior chamber and steepening the central cornea in the meridian of surgery. The corneal diameter decreased in that meridian. In the opposite meridian, the cornea flattened, the corneal diameter increased, and the sagittal depth decreased.

We used a corneal topography analysis system to evaluate nine eyes of seven patients in whom the diagnosis of keratoconus was suspected. There was no slit-lamp evidence of the condition. In seven of nine eyes a cone was identified. Large amounts of corneal distortion were seen in selected patients even though they had excellent spectacle-corrected visual acuity and little or no distortion of the keratometer mires. These findings suggest that corneal topography analysis systems are useful in the detection and description of corneal irregularity in the early stages of keratoconus. The radial keratotomy surgeon should be aware that normal results on slit-lamp examination and normal keratometry and refractive data do not rule out the presence of early keratoconus.