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PubMed1982

Control of astigmatism after surgery and trauma.

Since the introduction of microsurgical accuracy in the closure of corneal wounds, there have been fewer complications due to imperfect wound closure. As a result the eye is much safer after intraocular surgery or trauma. There may, however, be an undesirable and irregular refractive error. Much thought has been given to the prevention of this by attention to other details during closure of wounds. Interest has been revived in surgery for the correction of inherent refractive errors. The methods used for such conditions may also be applied to residual distortion after surgery or trauma. The possibility of adjustment during the early postoperative period has escaped detailed consideration. This neglected approach to the control of astigmatism is discussed in this paper.

Astigmatism↗
PubMed1985

Control of astigmatism after surgery and trauma: a new technique.

Five patients were subjected to a new technique designed to correct high astigmatism not responding to suture removal or adjustment. The method is described and its use illustrated in five case histories. Four of the five cases were successfully treated. The reasons for the one failure are discussed. All procedures were uncomplicated. The technique is simple, safe, and reversible.

Adult↗
PubMed1987

Corneal thickness, astigmatism, and atopy.

Keratometry and regional pachometry were performed on atopic patients with no history or signs of atopic keratoconjunctivitis. In a series of 80 eyes there was a skewed distribution towards thinner corneas (p less than 0.01) and a preponderance of against-the-rule astigmatism. The maternal age at birth of this group of patients was higher than that in the general population. These findings are discussed in the context of the known association of atopy with keratoconus.

Adult↗
PubMed1988

Corneal shape and astigmatism: with a note on myopia.

The elliptical shape and the physiological astigmatism of the normal neonatal human cornea are attributed to the ellipsoidal shape of the eyeball. This in turn is a feature of ocular development. The analysis is used to examine earlier observations on myopia.

Anthropometry↗
PubMed2006

Analysis of an approach to astigmatism correction during cataract surgery.

PURPOSE: To determine if a system of astigmatic keratomy at the time of cataract surgery is safe and effective. SETTING: Academic Ophthalmology Center. METHODS: One hundred and ten consecutive patients with greater than 0.50 diopters (d) of cylinder with the rule (WTR) and 0.75 d against the rule (ATR) were enrolled. Those with an axis between 16 and 74 degrees and 106 and 164 degrees were defined as oblique axis. Peripheral clear corneal relaxing incisions 600 mum deep were used with a nomogram of 60 degrees length per 1.0 d of attempted correction. Keratometry was taken from IOL Master biometry and refractive results at 4-12 weeks were compared. RESULTS: 60.5% of ATR, 62% of WTR and 23% of oblique attempted correction was achieved. Splitting the patients to under and over 70 years of age had no impact on the results. Of the 14 overcorrected, 7 had oblique cylinder (p = 0.009) and 10 had less than 1 d of preoperative cylinder (p = 0.00015). CONCLUSIONS: Using the IOL Master topography with this nomogram was quite effective in reducing preoperative cylinder. Oblique axis results were unpredictable, however, and much more likely to lead to an overcorrection.

Aged↗
PubMed1985

Intraocular lenses, tilt and astigmatism.

Concern has been expressed in the literature regarding the frequency and amount of astigmatism found in patients with intraocular lens implants. Postoperative tilting of the implants is one suggested cause. We have measured the effect of tilt on focal length in lenses supplied by two companies. The method used involved photographing the refractive effect of lenses on fine parallel laser beams as the lenses were tilted to varying degrees. The results show that: (a) drastic tilting (e.g. 20 degrees) is required to produce significant amounts of variation in focal length, (b) the effect on back vertex power is more important, (c) spherical aberration of the lenses is minimized.

Astigmatism↗
PubMed1989

Topographical analysis of the effects of corneal relaxing incisions on high postkeratoplasty astigmatism.

We used simple visual inspection of keratoscope mires to determine proper placement of corneal relaxing incisions in 4 patients with high postkeratoplasty astigmatism. Retrospectively, the LSU topography analysis system was used to evaluate the pattern of power distribution seen pre- and postoperatively in this group. Analysis of preoperative photographs showed that none of the patients had a classic spherocylindrical pattern of corneal power distribution. Areas of maximum steepening of corneal slope were often present in the peripheral portions of the graft away from the steep hemimeridians suggested by visual inspection of the keratoscope photographs. Since these areas were not recognized preoperatively, steepening remained in the areas postoperatively. These results suggest that preoperative computer analysis of keratoscope photographs may be superior to visual inspection of the photographs in determining proper placement of relaxing incisions.

Astigmatism↗
PubMed2004

Polarization-based compensation of astigmatism.

One approach to aberration compensation of an imaging system is to introduce a suitable phase mask at the aperture plane of an imaging system. We utilize this principle for the compensation of astigmatism. A suitable polarization mask used on the aperture plane together with a polarizer-retarder combination at the input of the imaging system provides the compensating polarization-induced phase steps at different quadrants of the apertures masked by different polarizers. The aberrant phase can be considerably compensated by the proper choice of a polarization mask and suitable selection of the polarization parameters involved. The results presented here bear out our theoretical expectation.

Astigmatism↗
PubMed1992

Visual instrument image quality metrics and the effects of coma and astigmatism.

We examine subjective contrast and edge sharpness discrimination in the presence of different amounts of coma, astigmatism, and combinations of these two aberrations. We also examine the correlation between subjective results and objective image quality measures. These include the integral of the modulation transfer function (MTF) across the frequency range of interest (MTFa), the Strehl ratio, the variance of the wave-front aberration, and the radius of 84% encircled energy of the point-spread function (R84). For the target orientation that is most affected by the aberrations, we find that the MTFa and R84 give good correlation, while the Strehl ratio and the variance do not. In addition, we find that the MTFa correlates with subjective results for all target orientations. We discuss the implications of the results on the automated assessment of the image quality of visual instruments.

Astigmatism↗
PubMed1996

Centration of excimer laser photorefractive keratectomy and changes in astigmatism.

One of the most important factors that influence the success of PRK might be corneal centration during treatment. We evaluated our centration rate in 49 eyes by using computer-assisted corneal topography. Only single zone treated eyes were chosen for the analysis and 91.5% of the eyes were centered within a 1 mm treatment zone while 51% were within 0.5 mm. At the end of the follow-up time of 10.4 months, these centration zones were found to have no influence on the attempted spherical refractive outcome, whereas increasing decentration induced an increase in postoperative astigmatism.

Adult↗
PubMedDate not supplied

Tracker-assisted versus manual ablation zone centration in laser in situ keratomileusis for myopia and astigmatism.

PURPOSE: Eye tracker systems have been developed concomitantly with small scanning beams to theoretically reduce ablation zone decentration and for accurate registration of all the laser pulses on the cornea. The purpose of the study was to compare the tracker-assisted with the manual centration method. METHODS: Twenty-five patients (48 eyes) with myopia and/or astigmatism had laser in situ keratomileusis (LASIK) between August 1998 and February 1999 with the Technolas 117C laser. Twenty patients (38 eyes, 80%) were available for follow-up at 3 months after surgery. Eyes were assigned randomly to one of two ablation zone centration methods: Group 1: Tracker-assisted (20 eyes), Group 2: Manual (18 eyes). RESULTS: Mean distance between the ablation zone center and the pupillary center in the tracker-assisted centration group was 0.55 +/- 0.30 mm (range, 0.10 to 1.4 mm), and in the manual centration group, 0.43 +/- 0.23 mm (range, 0.10 to 1.0 mm) (P = .177). There was no statistically significant difference in postoperative contrast sensitivity, glare, and Topographical Corneal Surface Regularity Index (SRI) between the two groups. CONCLUSIONS: We obtained good results with both centration methods. We did not find superiority of the tracker-assisted over manual regarding ablation zone centration, vision quality, or regularity of the ablation.

Adult↗
PubMedDate not supplied

Laser in situ keratomileusis for correction of hyperopia and hyperopic astigmatism with the Technolas 117C.

PURPOSE: To evaluate the effectiveness, predictability, and safety of laser in situ keratomileusis (LASIK) for correction of hyperopia and hyperopic astigmatism. METHODS: Fifty-four hyperopic eyes of 35 patients with a spherical equivalent refraction between +1.00 and +6.00 D were followed for at least 12 months following LASIK. All surgery was performed with the scanning Chiron Technolas Keracor 117C excimer laser. Data on uncorrected and spectacle-corrected visual acuity, predictability, stability of refraction, and complications were analyzed. RESULTS: At 12 months, the average residual refraction was +0.29 +/- 0.78 D; 83.3% of eyes (45 eyes) were in the range of +/- 1.00 D and 61.1% of eyes (33 eyes) were within +/- 0.50 D of emmetropia. Fifty eyes (92.6%) had uncorrected visual acuity of 20/40 or better and 34 (63.0%) eyes had 20/20 or better. One eye (1.9%) lost two lines of best spectacle-corrected visual acuity and two eyes (3.7%) gained two or more lines. Two patients (two eyes, 3.7%) had complaints of halos and one patient (one eye, 1.9%) had glare at 12 months after LASIK for hyperopia. CONCLUSIONS: LASIK was used to treat hyperopia from +1.00 to +6.00 D with good predictability and safety. Primary and second hyperopia require different nomograms, according to our experience.

Adolescent↗
PubMedDate not supplied

Wavefront-guided photorefractive keratectomy for myopia and myopic astigmatism.

PURPOSE: To evaluate the results of wavefront-supported customized ablation (WASCA) in eyes treated with photorefractive keratectomy (PRK) to correct spherical myopia and myopic astigmatism. METHODS: One-hundred fifty eyes of 104 patients (mean age 33.4 +/- 4.4 years) were included in the study. An Asclepion Shack-Hartmann wavefront aberrometer was used to assess lower and higher order refractive aberrations of eyes, and customized PRK treatments were carried out using the Asclepion-Meditec MEL 70 G-Scan excimer laser. Follow-up time was 6 months. RESULTS: The mean preoperative spherical equivalent refraction was -4.02 +/- -1.04 D, and mean uncorrected visual acuity (UCVA) was 0.06 +/- 0.02. Postoperatively, mean UCVA was 1.04 (better than 20/20), mean best spectacle-corrected visual acuity was 1.22 (20/16), and average spherical equivalent refraction was -0.12 D; 98.6% (148 of 150 eyes) were within +/-0.50 D of intended refraction, and 100% were within +/-1.00 D. Concerning safety, in 71.1% of eyes (107 of 150) BSCVA was the same as preoperatively, and in 8.2% (11 of 150) it increased by two or more Snellen lines. None of the eyes lost two or more lines of BSCVA. The root mean square value for higher order aberrations increased 1.4 times following PRK. CONCLUSIONS: WASCA-guided PRK was efficacious, safe and predictable; BSCVA may be improved by the WASCA method compared to results achievable with a traditional PRK technique, in spite of an increase in the root mean square value for higher-order aberrations.

Adult↗
PubMedDate not supplied

Laser subepithelial keratomileusis for myopia of -6 to -10 diopters with astigmatism with the MEL60 laser.

PURPOSE: To evaluate the efficacy, predictability, and safety of laser subepithelial keratomileusis (LASEK) for treatment of high myopia with astigmatism. METHODS: LASEK was performed in 61 eyes of 36 consecutive patients with myopic spherical equivalent refraction of -6.00 to -10.00 D using the Aesculap-Meditec MEL60 excimer laser. Data were collected prospectively with a follow-up of 6 to 17 months. Main outcome measures recorded were UCVA, BSCVA, residual refractive error, corneal haze, and complications. RESULTS: Ninety-six percent of eyes achieved 20/40 or better UCVA at 1 month. At 12 months, 64% of eyes achieved 20/20 and 92% achieved 20/40 or better UCVA. Two eyes lost 2 lines of BSCVA at 6 or 12 months. Accuracy of correction was +/- 0.50 D from emmetropia in 82% of eyes, and +/- 1.00 D in 90% at 12 months. No eye showed more than grade 1 haze. Grade 1 haze was observed in three eyes at 12 months. One patient had mild postoperative keratitis, which was successfully treated. CONCLUSIONS: LASEK with the Aesculap-Meditec MEL60 excimer laser appeared to be safe, effective, and highly predictable in treating high myopia.

Adult↗
PubMedDate not supplied

Laser in situ keratomileusis for residual hyperopic astigmatism after conductive keratoplasty.

PURPOSE: To report a case of laser in situ keratomileusis (LASIK) in a patient with previous conductive keratoplasty. METHODS: A 48-year-old man underwent conductive keratoplasty for low hyperopic astigmatism (manifest refraction OD: +2.25 -0.50 x 77 degrees; OS: +2.50 -0.50 x 105 degrees). Three months postoperatively, UCVA was 20/25 and BSCVA was 20/20 in both eyes; manifest refraction OD: -0.25 -0.75 x 110 degrees; OS: +0.75 -0.75 x 50 degrees. Sixteen months after the operation, regression of refractive outcome was (manifest) OD: +1.75 -1.25 x 90 degrees; OS: +2.50 -0.50 x 85 degrees; UCVA was 20/40 in the right eye and 20/63 in the left eye and BSCVA was 20/20 in both eyes. LASIK was performed for hyperopic regression in the left eye using an automated microkeratome (Alcon SKBM, 130-microm plate; Aesculap-Meditec MEL 70 excimer laser). RESULTS: LASIK was uneventful and no intraoperative or postoperative complications related to the previous conductive keratoplasty procedure or LASIK were observed. Three months after LASIK and 19 months after the initial conductive keratoplasty, the patient's left eye was emmetropic; UCVA was 20/20(-2), BSCVA was 20/20 and manifest refraction was +0.25 -0.25 x 35 degrees. There was a uniform increase in topographical steepening. Visual acuity, refraction and topographic findings remained unchanged at 6 months. CONCLUSIONS: Even though our experience is limited, treatment of hyperopia with LASIK in an eye with refractive regression following previous conductive keratoplasty resulted in a predicted refractive outcome, with no complications, and improvement in visual acuity at 6 months follow-up.

Astigmatism↗
PubMed2006

Topography-guided treatment of irregular astigmatism with the wavelight excimer laser.

PURPOSE: To evaluate the feasibility, safety, and predictability of correcting high irregular astigmatism in symptomatic eyes with the use of topography-guided photoablation. METHODS: In a prospective, non-comparative case series, 16 consecutive symptomatic eyes of 11 patients with small hyperopic and myopic excimer laser optical zones, decentered and irregular ablation after corneal graft, and corneal scars were operated. Uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), manifest and cycloplegic refraction, and corneal topography, with asphericity and regularity, were analyzed. LASIK (n = 10) and photorefractive keratectomy (n = 6) were performed using the ALLEGRETTO WAVE excimer laser and T-CAT software (Topography-guided Customized Ablation Treatment; WaveLight Laser Technologie AG, Erlangen, Germany). RESULTS: In the LASIK group, UCVA improved from 0.81 +/- 0.68 IogMAR (20/130) (range: 0.2 to 2.0) to 0.29 +/- 0.21 logMAR (20/39) (range: 0.1 to 0.7) at 6 months. In the PRK group, mean UCVA improved from 0.89 +/- 0.87 IogMAR (20/157) (range: 0.1 to 2.0) to 0.42 +/- 0.35 logMAR (20/53) (range: 0.1 to 1.0) at 6 months. Best spectacle-corrected visual acuity did not change significantly in either group. One PRK patient lost one line of BSCVA. Refractive cylinder for the LASIK group improved from -2.53 +/- 1.71 diopters (D) (range: -0.75 to -5.75 D) to -1.28 +/- 0.99 D (range: 0 to -2.50 D) at 6 months. Refractive cylinder in the PRK group improved from -2.21 +/- 2.11 D (range: -0.25 to -5.50 D) to -1.10 +/- 0.42 D (range: -0.50 to -1.50 D). Index of surface irregularity showed a decrease from 60 +/- 12 (range: 46 to 89) to 50 +/- 9 (range: 32 to 63) at 6 months in the LASIK group whereas no significant change was noted in the PRK group. Subjective symptoms, such as glare, halos, ghost images, starbursts, and monocular diplopia, were not present postoperatively. CONCLUSIONS: Topography-guided LASIK and PRK resulted in a significant reduction of refractive cylinder and increase of UCVA, without a significant loss of BSCVA.

Adolescent↗
PubMed2006

The effect of scleral buckling surgery on corneal astigmatism, corneal thickness, and anterior chamber depth.

PURPOSE: To evaluate the effect of scleral buckling surgery on corneal topography, corneal thickness, and anterior chamber depth. METHODS: Thirty-two eyes of 32 patients who underwent encircling buckling surgery for rhegmatogenous retinal detachment were included in the study. Fellow eyes comprised the control group. Orbscan II topography system was used to determine the changes in corneal topography, corneal thickness, and anterior chamber depth before surgery and 1 week, 1 month, and 3 months after surgery. Statistical analyses used in the study were independent t test, paired t test, one way analysis of variance, and correlation analyses. RESULTS: Postoperatively, mean central corneal astigmatism at 1 week, 1 month, and 3 months was 4.3 +/- 2.0 diopters (D), 3.3 +/- 1.6 D, and 3.1 +/- 1.0 D, respectively. The change between 1 week and 3 months was statistically significant. Central cornea was thickened at the first postoperative week. The thickness gradually decreased to the preoperative levels at 3 months. Anterior chamber depth decreased, and the anterior chamber remained shallow after the surgery. The comparison between preoperative (2.94 +/- 0.6 mm) and postoperative anterior chamber depth was statistically significant at 1 week (2.57 +/- 0.7 mm), 1 month (2.83 +/- 0.7 mm), and 3 months (2.73 +/- 0.6 mm). CONCLUSIONS: Corneal changes after scleral buckling surgery were mild to moderate and the cornea almost resumed its preoperative parameters in 3 months' time. However, the anterior chamber remained shallow during 3 months of follow-up.

Adolescent↗