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PubMed2001

Astigmatism after corneal thermal injury.

A 42-year-old woman developed significant astigmatism after localized thermal injury to the cornea during a cosmetic eyelid procedure. The induced astigmatism regressed substantially over the ensuing months. One year after the injury, astigmatic keratotomy (AK) was performed, further reducing the astigmatism and improving the patient's subjective vision. Patients with induced astigmatism from thermal corneal injury should be monitored for regression. When refractive stability is achieved, AK can reduce the remaining astigmatism. This case reviews concepts that apply to refractive thermal keratoplasty.

Adult↗
PubMed2002

Corneal astigmatic change after photorefractive keratectomy and photoastigmatic refractive keratectomy.

PURPOSE: To evaluate and compare the efficacy, safety, predictability, and surgically induced astigmatism (SIA) of photorefractive keratectomy (PRK) and photoastigmatic refractive keratectomy (PARK). SETTING: Department of Ophthalmology, National Taiwan University Hospital, Taipei, Taiwan. METHODS: In this retrospective study, 70 eyes were treated for myopia and 70 eyes were treated for myopic astigmatism. Refraction, corneal topography, slitlamp findings, and visual acuity in the 2 groups at 1, 3, and 6 months were evaluated and compared. Vector analysis was performed to determine the SIA in both groups. RESULTS: The mean preoperative spherical equivalent at the glasses plane in the PRK and PARK groups was -6.06 diopters (D) and -7.18 D, respectively. At 6 months, the mean reduction in astigmatism in the PARK group was 61.0%. Predictability was within +/-1.0 D in 85.2% of eyes in the PRK group and 62.5% in the PARK group. An uncorrected visual acuity of 20/40 or better was achieved in 91.8% and 83.9% of eyes, respectively. The mean SIA was 0.64 D in the PRK group, with a general with-the-rule axis shift. The results of vector analysis were more favorable when calculated from refractive values than from Sim-K corneal topography values. The mean astigmatism correction index and index of success calculated from refractive data were 0.75 and 0.38 in the PARK group. The mean magnitude and angle of error were 0.22 +/- 0.52 D and -2.13 +/- 24.41 degrees, respectively. CONCLUSIONS: Photorefractive keratectomy and PARK were effective and safe procedures for the correction of myopia and myopic astigmatism. However, SIA occurred with spherical myopic treatments. This small SIA may be a confounding factor in low astigmatic treatments.

Adult↗
PubMed2002

Effect of temporal and nasal unsutured limbal tunnel incisions on induced astigmatism after phacoemulsification.

PURPOSE: To compare the surgically induced corneal astigmatism after unsutured temporal and nasal unsutured limbal tunnel incisions. SETTING: Departments of Ophthalmology, Marienhospital, Aachen, and Johann Wolfgang Goethe-University, Frankfurt am Main, Germany. METHODS: In a prospective clinical study, 42 eyes of 21 patients with a mean age of 75.1 years had phacoemulsification and implantation of a foldable hydrophobic acrylic intraocular lens using a 3.6 to 3.8 mm unsutured limbal tunnel incision. The right eye always received a temporal incision and the left eye, a nasal incision. Computerized videokeratography was performed preoperatively and 2 weeks and 6 months postoperatively. Surgically induced astigmatism was calculated by vector analysis using the Holladay-Cravy-Koch formula. The 2 groups were compared using a paired Wilcoxon test. RESULTS: The mean surgically induced corneal astigmatism in the temporal incision group was 0.62 diopters (D) +/- 0.48 (SD) 2 weeks postoperatively and 0.47 +/- 0.32 D at 6 months and in the nasal incision group, 1.55 +/- 0.84 D and 1.05 +/- 0.57 D, respectively. The difference between the groups was statistically significant (P <.05). CONCLUSIONS: There was a highly statistically significant difference in surgically induced corneal astigmatism after temporal and nasal unsutured limbal tunnel incisions. The degree of induced astigmatism and the difference between the temporal and the nasal incisions decreased over time. A nasal tunnel incision is not appropriate for astigmatism-neutral surgery.

Adult↗
PubMed2002

Combined toric intraocular lens implantation and relaxing incisions to reduce high preexisting astigmatism.

PURPOSE: To evaluate whether combining toric intraocular lens (IOL) implantation with astigmatic keratotomy (AK) can correct higher levels of astigmatism while minimizing undue effects on the optical qualities of the cornea. SETTING: St. Luke's Cataract and Laser Institute, Tarpon Springs, Florida, USA. METHODS: Thirteen eyes with corneal astigmatism greater than 2.50 diopters (D) (mean 5.54 D) had implantation of a Staar toric IOL combined with AK. RESULTS: All eyes had less than 1.00 D of refractive astigmatism postoperatively. Sixty-nine percent achieved an uncorrected visual acuity of 20/40 or better, and no patient lost best corrected visual acuity. CONCLUSIONS: Implanting a toric IOL in patients with high astigmatism reduced the amount of incisional surgery required. Combining techniques can correct all or most of even very high astigmatism (>5.00 D) while avoiding induced corneal irregularities.

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PubMed2003

Fourier analysis of induced irregular astigmatism. Photorefractive keratectomy versus laser in situ keratomileusis in a bilateral cohort of hyperopic patients.

PURPOSE: To analyze corneal topographic data by Fourier analysis to determine differences in irregular astigmatism following spherical hyperopic correction by photorefractive keratectomy (PRK) or laser in situ keratomileusis (LASIK). SETTING: Department of Ophthalmology, St. Thomas' Hospital, London, United Kingdom. METHODS: Thirty-six eyes of 18 patients with moderate hyperopia had LASIK in 1 eye and PRK in the other eye. The flap was cut on a nasal hinge with a Moria LSK One microkeratome. The laser was a Summit SVS Apex Plus with an optical zone of 6.5 mm and a blending zone of 1.5 mm. Corneal topographic data were acquired with a TMS-1 topographer (Computed Anatomy Inc.) preoperatively and 1, 3, 6, and 12 months postoperatively. The ASCII files containing the dioptric power values were extracted and analyzed with custom-written software to extract the Fourier harmonics. RESULTS: The irregular astigmatism increased in both groups postoperatively, peaking at 3 months and then decreasing over the next 9 months. There was no statistically significant difference between the 2 groups at any time point (P<.05). The change in the topographically derived equivalent sphere showed undercorrection in both groups at all time points. Regular astigmatism showed a marginal statistically significant increase in the LASIK group at 12 months (P =.049). CONCLUSION: Irregular astigmatism, equivalent sphere, and regular astigmatism were not significantly different in the PRK and LASIK groups during the follow-up. Based on the corneal topography, the 2 procedures induced an equal amount of irregular astigmatism.

Adult↗
PubMed1993

Astigmatism after a large scleral pocket incision in extracapsular cataract extraction.

In this four-month prospective study, we measured astigmatism in 116 patients who had extracapsular cataract extraction through a 13 mm scleral pocket incision. In one group, the wound was closed with five radial 10-0 polypropylene sutures. Early and late postoperative astigmatism in this group was approximately 2 diopters (D), but a significant shift to against-the-rule astigmatism occurred. In a second group, an additional 10-0 polypropylene horizontal suture was placed anteriorly to the radial suture at the 12 o'clock meridian. This reduced the against-the-rule astigmatic decay. Moreover, this group had less postoperative astigmatism. Mean corneal astigmatism was 2.27 D at one week, 1.76 D at one month, 1.37 D at two months, and 1.70 D at four months. In neither group was cutting the sutures necessary.

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PubMed1994

Quantitative assessment of corneal astigmatic surgery: expanding the polar values concept.

The purpose of astigmatic corneal surgery is to flatten the steeper meridian of the preoperative cylinder, to steepen the flatter meridian, or both. Therefore, it may be useful to quantitate the surgical effect by calculating the equivalent dioptric value of the postoperative cylinder in these principal meridians. In this study, the dioptric value projected on the preoperatively steeper meridian is termed the with-the-power (WTP) component, the portion projected on the flatter meridian, the against-the-power (ATP) component. Consider a preoperative net astigmatism of the power N in the meridian a. After astigmatic corneal surgery, the postoperative corneal cylinder is M in the meridian b. For the postoperative cylinder, the WTP component = M x sin2([b + 90]-a). The ATP component = M x cos2([b + 90]-a). The astigmatic polar value is defined as the difference between these magnitudes: AKP = M x (sin2[(b + 90)-a] - cos2[(b + 90)-a]). By calculating the astigmatic polar value, the surgeon immediately knows the outcome of the surgical procedure (i.e., whether the preoperative astigmatism has been undercorrected, overcorrected, or perfectly corrected). We describe the theory behind this new formula and discuss its applications and limitations.

Astigmatism↗
PubMed1994

Postoperative astigmatism after no-stitch, small incision cataract surgery with 3.5 mm and 4.5 mm incisions.

We studied postoperative astigmatism in 107 patients who were followed for 12 months after phacoemulsification and posterior chamber lens implantation. A scleral incision of 3.5 mm was used in Group A patients and one of 4.5 mm in Group B patients. In both groups a no-stitch wound closure technique was used. A high correlation between preoperative and 12-month postoperative height and time shift of keratometric values was found. In both groups the mean difference was less than 0.60 diopters (D). The mean postoperative cylinder increase was less than 0.50 D; it was less than 0.25 D after six months. The induced astigmatism was confirmed by three different methods. Immediately after surgery, a negative induced astigmatism was found in both groups. After 12 months, induced astigmatism in Group A was -0.37 D and in Group B, -0.67 D. Immediately after surgery there was an axis change; a decrease of with-the-rule astigmatism occurred concurrently with an increase toward oblique and against-the-rule astigmatism. This axis change was somewhat evident after 12 months.

Astigmatism↗
PubMed1993

Induced astigmatism and its decay with a frown incision.

Forty consecutive patients selected for cataract extraction by phacoemulsification were studied to evaluate prospectively the amount of and changes in surgically induced astigmatism from a 5 mm to 6 mm pocket incision with the external opening made convex against the limbus (frown incision). All incisions had an internal corneal valve and were closed by a single X-stitch to counteract the relaxing effect of the pocket in the 90-degree meridian. Surgically induced astigmatism calculated by simple subtraction was 0.64 +/- 0.90 diopters (D) (P < .0001) on the first postoperative day, 0.03 +/- 0.58 D (P = .75) six weeks after surgery, and -0.18 +/- 0.44 D (P = .01) six months after surgery. Calculated from polar equivalents, the induced astigmatism on the first postoperative day was 0.98 D +/- 1.03 D (P = .0001), after six weeks -0.11 D +/- 0.64 D (P = .30), and after six months -0.28 D +/- 0.49 D (P = .0009). On the first postoperative day 42% of eyes had less than 0.5 D of induced astigmatism, 68% had less than 1.0 D, and 79% had less than 1.5 D. After six weeks the respective percentages increased to 61%, 97%, and 97% and after six months to 84%, 100%, and 100%. The distribution of patients with against-the-rule, oblique, and with-the-rule astigmatism preoperatively was nine, 20, and 11, respectively, and 11, 19, and nine after six months. The amount of astigmatism induced from the 5 mm to 6 mm frown incision did not differ from that found in previously published studies of smaller incisions (to about 4 mm).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Modified corneoscleral incision to reduce postoperative astigmatism after 6 mm diameter intraocular lens implantation.

I modified the corneoscleral incision for cataract surgery so the incision is located between the 9 o'clock and 12 o'clock positions and termed it the BENT incision (abbreviated from "between nine and twelve o'clock"). I made the incision on 110 patients for phacoemulsification and 6.0 mm diameter poly(methyl methacrylate) intraocular lens implantation and analyzed postoperative corneal astigmatism. The results revealed that the surgically induced astigmatism was 0.3 diopters of with-the-rule shift in the early postoperative weeks and remained virtually unchanged for the subsequent 24 weeks. This amount of astigmatism was significantly smaller and more stable than that of the conventional superior incision performed on 59 patients. A more rapid stabilization of astigmatism after the BENT approach resulted in better uncorrected visual acuity in the early postoperative period. These findings suggest that corneal astigmatism after cataract surgery is affected by the mechanical force of eyelids and extraocular muscles. The BENT incision would effectively minimize the wound-stretching forces and result in earlier stabilization of a lesser degree of postoperative corneal astigmatism.

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PubMed1995

Intraoperative semiquantitative keratometry using the keratoscopic astigmatic ruler.

Intraoperative keratometry enables the surgeon to set an appropriate amount of corneal astigmatism with the suture tension. Errors in estimating or measuring the astigmatism can occur with hand-held keratometers because the distance an object is held from an astigmatic cornea influences the shape of the elliptical image. Thus hand-held instruments should be held at a calibrated distance. We have designed a new hand-held keratometer, the keratoscopic astigmatic ruler, to assess the magnitude of corneal astigmatism. It consists of a rack of elliptical keratoscopic lenses corresponding to increasing magnitudes of astigmatism and is made from inexpensive autoclavable injection-molded plastic. The ruler's keratoscopic lenses refract light, creating a real aerial image above the cornea that produces a bright and easily determined corneal reflection. The ruler incorporates a sight to allow the user to hold the ruler at the correct distance.

Astigmatism↗
PubMed1996

Clinical results of arcuate incisions to correct astigmatism.

PURPOSE: To evaluate the effectiveness of arcuate incisions for correcting congenital, post-cataract, post-radial keratotomy, and post-trapezoidal keratotomy astigmatism. SETTING: Buzard Eye Institute, Las Vegas, Nevada. METHODS: In this retrospective study, 46 eyes of 29 patients had arcuate incisions to correct astigmatism. The average age of patients was 52 years. RESULTS: Mean preoperative astigmatism was 3.51 +/- 1.57 D (keratometric) and 3.41 +/- 1.44 D (manifest). Mean preoperative uncorrected visual acuity was 20/80, ranging from 20/30 to 20/400. Thirty eyes had a pair of 45-degree arcuate incisions, 10 eyes had a pair of 60-degree arcuate incisions, and 6 eyes had a pair of 90-degree arcuate incisions. Mean follow-up was 6 months. Mean postoperative astigmatism was 1.46 +/- 1.07 D (keratometric) and 1.05 +/- 0.94 D (manifest), with a reduction of astigmatism in all operated eyes. Mean postoperative uncorrected visual acuity was 20/32, ranging from 20/20 to 20/60. The analysis of the vector astigmatic change showed that only two patients were overcorrected after the procedure. CONCLUSION: The predictability and safety of arcuate incisions are reflected in these results.

Adult↗
PubMed1996

Astigmatism reduction: no-stitch 4.0 mm versus sutured 12.0 mm clear corneal incisions.

PURPOSE: To compare the effect on astigmatism of phacoemulsification using a 4.0 mm, no-stitch, clear corneal incision with that of extracapsular cataract extraction (ECCE) using a 12.0 mm, sutured, clear corneal incision. SETTING: Augenklinik, Städtisches Klinikum Karlsruhe, Germany. METHODS: The study comprised 211 patients who had cataract extraction and intraocular lens implantation through a superior clear corneal incision; 108 patients had phacoemulsification with a 4.0 mm no-stitch incision, and 103 had ECCE using a 12.0 mm sutured corneal incision. The main outcome measure was amount of astigmatism preoperatively and at 1 week and 3 and 6 months postoperatively. Corresponding medians (lower and upper quartiles) were evaluated. RESULTS: Median surgically induced cylinder was 1.00 diopter (D) (range 0.56 to 1.50 D) in the 4.0 mm no-stitch incision group and 1.75 D (range 1.00 to 2.62 D) in the 12.0 mm sutured incision group. In eyes with preoperative with-the-rule astigmatism, astigmatism decreased from a median of 0.75 D (range 0.50 to 1.00 D) to 0.50 D (range 0 to 1.50 D) in the 4.0 mm incision group. The difference between preoperative and postoperative astigmatism in the 12.0 mm incision group was not statistically significant. CONCLUSION: Clear corneal cataract surgery leads to a predictable reduction in astigmatism when performed on the steeper axis with a small, no-stitch incision. Larger sutured incisions are not suitable for planned refractive changes but are still recommended in certain cases such as hard cataract and glaucoma.

Astigmatism↗
PubMed1996

Transverse incisions for mixed and myopic idiopathic astigmatism.

PURPOSE: To determine the efficacy and safety of the Casebeer transverse nomogram for correcting idiopathic astigmatism using transverse incisions (T-incisions) with variable optical zones. SETTING: Rancho Bernardo Eye Center, San Diego, California. METHODS: This retrospective study comprised 173 eyes of 100 consecutive patients who had T-incisions according to the Casebeer transverse nomogram to correct mixed or myopic astigmatism. Preoperative cylinder ranged from 0.75 to 6.00 diopters (D). The nomogram was modified for eyes with preoperative cylinder from 1.75 to 6.00 D. Principal outcome measures were net residual astigmatism for all eyes and uncorrected visual acuity in eyes with the highest preoperative cylinder (3.25 to 6.00 D). RESULTS: A comparison of preoperative astigmatism (mean 3.07 D +/- 1.53 [SD]) and net residual astigmatism showed significant reduction in all diopter categories. Enhancements were done in 16.2% of eyes, mostly those with high preoperative cylinder. Patient age did not seem to affect results. No patient, including those with smaller optical zones, lost two or more Snellen lines of best corrected visual acuity. CONCLUSION: Use of the Casebeer transverse nomogram with T-incisions and variable optical zones effectively and safely reduced most idiopathic astigmatism between 0.75 and 5.50 D. Modifications to the nomogram yielded similar results in eyes with a higher preoperative cylinder.

Adult↗
PubMed1996

Evaluating surgically induced astigmatism by Fourier analysis of corneal topography data.

PURPOSE: To evaluate surgically induced astigmatism using Fourier harmonic series analysis of corneal topography data. SETTING: Aarhus Kommunehospital, Aarhus University, Denmark. METHODS: We evaluated the results of 46 phacoemulsifications with a 4 or 6 mm scleral tunnel sutureless incision based on the axis of the steepest meridian. We performed conventional keratometry and corneal topography before and up to 1 month after surgery. Using Fourier analysis, the corneal topographic images were broken into spherical power, regular astigmatism, and nonregular astigmatism for individual or aggregate analysis of surgically induced astigmatism. The induced refractive change (average of the difference between preoperative and postoperative corneal topographies) was analyzed and normalized according to the surgical meridian and to right/left eye. RESULTS: Regular astigmatism calculated by Fourier analysis of mires from the keratometer zone correlated well with conventional keratometry readings. Surgery induced a localized flattening in the superior region and a with-the-rule regular astigmatism component in the central area. CONCLUSION: Surgically induced corneal topography changes can be analyzed by Fourier series harmonic analysis, allowing aggregate data to be broken into optically meaningful quantities.

Adult↗
PubMedDate not supplied

Long-term course of induced astigmatism after clear corneal incision cataract surgery.

PURPOSE: To determine whether a small clear corneal temporal incision produces less surgically induced astigmatism than a larger incision. METHODS: One hundred three consecutive cases of postoperative astigmatism after clear corneal incision cataract surgery were studied for a minimum of 1 year. Only self-sealing incisions from the temporal side were made as follows: 3.2 mm (Group A); 4.0 mm (Group B); 5.2 mm (Group C). We considered the amount and axes of the keratometric readings at different times as well as their course over time. Induced astigmatism was calculated using three methods. Axial changes were also analyzed. RESULTS: Immediately after the surgery, there was a small, surgically induced, with-the-rule astigmatic shift in all groups, which in most cases decreased to near preoperative levels with time. One year postoperatively. mean induced astigmatism was 0.09 diopter (D) in Group A, 0.26 D in Group B, and 0.54 D in Group C. Most cases had minimal axial changes. In Group A, 86% had an axial change of fewer than 30 degrees; in Group B, 76%; and Group C, 73%. CONCLUSIONS: The smallest incision group had the least surgically induced astigmatism and axial change. All incision groups remained stable and had satisfactory clinical results.

Astigmatism↗
PubMed1997

Long-term astigmatic changes after clear corneal cataract surgery.

PURPOSE: To assess long-term astigmatic changes after clear corneal cataract surgery. SETTING: Städtisches Klinikum, Augenklinik, Karlsruhe, Germany. METHODS: We evaluated the first 100 of 2,800 patients having cataract surgery with a superior or lateral corneal self-assessing incision and implantation of a 5.0 mm poly(methyl methacrylate) intraocular lens. Surgically induced astigmatism (IA) and absolute astigmatism (AA) were evaluated after 1 week and 1 and 2 years using keratometry and corneal topography. Statistical analysis was done using the Wilcoxon signed-rank test. RESULTS: In eyes with a 12 o'clock incision (n = 50), the mean IA was 1.18 diopters (D) +/- 0.79 (SD) after 1 year and 1.53 +/- 0.95 D after 2 years. In eyes that had with-the-rule astigmatism preoperatively (n = 15), the mean AA was 0.62 +/- 0.57 D after 1 year and 0.93 +/- 0.56 after 2 years. In eyes with lateral incisions (n = 50), the mean IA was 0.96 +/- 0.74 after 1 year and 0.64 +/- 0.50 after 2 years. In eyes with against-the-rule astigmatism preoperatively (n = 15), the mean AA was 0.66 +/- 0.70 after 1 year and 0.52 +/- 0.65 after 2 years. The between-group difference in astigmatism after 2 years was statistically significant. CONCLUSION: The 12 o'clock incision was associated with a statistically insignificant increase in AA 2 years postoperatively and the lateral incision, with a statistically significant decrease. We currently recommend routine use of clear corneal incisions in cataract surgery.

Astigmatism↗
PubMed1997

Surgically induced astigmatism following a 4.0 mm sclerocorneal valve incision.

PURPOSE: To determine whether sutureless small incision cataract surgery reduces induced astigmatism over the long term. SETTING: University Eye Hospital, Vienna, Austria. METHODS: In a prospective study, we investigated surgically induced astigmatism in 63 cases of no-stitch, small incision cataract surgery with a 4.0 mm square sclerocorneal tunnel and implantation of a flexible intraocular lens. Follow-up was 4 to 5 years. Keratometry was measured with a Zeiss keratometer preoperatively and after 1 day, 1 week, 1, 3, and 9 months, and a median of 4.4 years. In 21 nonoperated eyes, we investigated the natural course of astigmatism over 5 years. RESULTS: The mean keratometric cylinder stabilized at 0.8 diopter (D) after 1 week and slightly decreased to 1.0 D after 4 to 5 years. Cravy's vector analysis showed an immediate against-the-rule (ATR) shift of -0.2 D that remained relatively stable until 9 months. Between 9 months and 4.4 years postoperatively, there was a statistically significant increase in ATR induced astigmatism from -0.2 to -0.5 D. The natural course of astigmatism in the nonoperated eyes showed an ATR shift of -0.1 D for the same period. CONCLUSION: The result show a small, though statistically significant amount of postoperatively induced astigmatism 4 to 5 years after no-stitch, small incision cataract surgery.

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