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PubMed1992

Outcome of preoperative against-the-rule astigmatism after phacoemulsification: characteristic changes over time. Part II.

To determine the outcome of preoperative against-the rule (AR) astigmatism among 1,648 phacoemulsification and aspiration (PEA) procedures, we analyzed the post-cataract time course of astigmatism over 6 months in 618 eyes divided into three groups. In preoperative AR astigmatism less than 0.75 dptr (n = 208), the astigmatism increase 1 week postoperatively was rapid. In preoperative AR astigmatism greater than or equal to 1.5 dptr (n = 185), no difference in the power of astigmatism was apparent between 1 and 3 months postoperatively. The third group (0.75 less than or equal to preoperative AR astigmatism less than 1.5 dptr, n = 143) showed intermediate characteristics. The eyes with preoperative low AR astigmatism showed exacerbation of astigmatism after the PEA procedure, whereas the degree of astigmatism, corneal curvatures and the rate of AR astigmatism became lower in the eyes with higher preoperative AR astigmatism.

Aged↗
PubMed1999

Bivariate analysis of surgically induced regular astigmatism. Mathematical analysis and graphical display.

OBJECTIVE: The purpose of the study was to develop methods for simultaneous description of astigmatic direction and magnitude on aggregate data, with special reference to refractive surgery. DESIGN: Mathematical analysis of astigmatisms employing bivariate statistical methods. RESULTS: The mean of several astigmatisms is a new astigmatism of specific direction and magnitude, while the confidence region is an area, which may be determined exactly. CONCLUSIONS: Astigmatisms may conveniently be symbolized as an astigmatic direction and magnitude, but are actually composed of refractive powers in the form of polar values. We are operating with two different entities, a net astigmatism and a power vector in the form of polar values. There is an unequivocal point-to-point correlation between these entities. Mathematical conversions can only be performed with polar values, but never by using net astigmatisms. All net astigmatisms must be converted to their appropriate refractive powers and the relevant calculations performed with these entities. The final result, such as an average of several astigmatisms, variances or confidence areas, may be point-to-point reconverted to and symbolized by a net astigmatism. These principles allow for exact description and comparison of surgical methods, but may be employed to describe and analyze any other population of astigmatisms, such as subjective cylinders and spectacle corrections.

Astigmatism↗
PubMed1991

[Astigmatism in corneal graft. Prevention and treatment].

The tremendous development of the photokeratoscope and corneal topography analysis explains the development of corneal astigmatism study in corneal graft. Our study consists in a review of the bibliography. The prevention of the astigmatism needs the following: before the trephination, the astigmatism has to be treated (correction of against the rule astigmatism which is usual in the aphake people); during the trephination, to minimize the deformation of the eye ball, to choose a good diameter for the keratoconus case, to use a pneumatic trephine in order to have a perpendicular cut (the use of the laser Excimer seams promising); The suture of the corneal graft can be done with a double running suture 10/0 and 11/0. The 10/0 is removed at the third month, the visual recovery is faster but the average astigmatism is not as good as with the interrupted 10/0 sutures and running suture 11/0. This technique is good for an old patient or a one eyed people specially interested in a faster recovery of visual acuity. The second possibility is to use 16 interrupted sutures with and 11/0 running suture. With this technique, the sutures are removed selectively depending on the keratometry and the photokeratoscopy. The visual recovery is longer but the astigmatism at the end is very low. When all the sutures have been removed, the residual astigmatism can be treated when there is not any misalignement between the cornea and the graft. The keratometry, photokeratoscopy allows to find the meridian which is abnormal and to find out if the astigmatism is symmetrical or asymmetrical. The astigmatism is symmetrical if the deformation is the same at either side of the meridian. When the abnormal meridian is the steepest, the only thing to do is a relaxing incision (one or two if is asymmetric, two if the astigmatism is symmetric). The size of the relaxing incision is determined by the photokeratoscopy and the deepness by the effect obtained during surgery looking at a qualitative keratometer. On the table, the effect must be about 50% of over correction. When, the abnormal meridian is the flattest, the only thing to do is a wedge resection (if the astigmatism is asymmetric) or two wedge resections (if the astigmatism is symmetric). The size of the cuneiform resection is choosen with photokeratoscopy. The study of the literature about the Ruiz incision adapted to corneal graft cannot nowadays conclude to the accuracy and safety of this technique.(ABSTRACT TRUNCATED AT 400 WORDS)

Astigmatism↗
PubMed1996

[Vector analysis of surgically-induced astigmatism in cataract operation with 4 tunnel incision techniques].

UNLABELLED: Evaluation of astigmatism induced by cataract surgery requires the calculation of surgically induced astigmatism using vector analysis. This method was performed for four tunnel-incision techniques and compared with the results of computer-assisted videokeratoscopy. METHODS: Phacoemulsification with IOL implantation was performed in 59 eyes using four different incisions (4- or 5- to 6-mm scleral tunnel and 4- or 5.5-mm clear cornea). Surgically induced astigmatism was calculated by vector subtraction using the formulas of Retzlaff. In addition, corneal topography was performed and astigmatism was calculated within three concentric corneal zones (3 mm, 3-5 mm, 5-7 mm). RESULTS: Surgically induced astigmatism after a 4-mm scleral tunnel incision was 0.55 D (pre-op 0.58 D, post-op 0.72 D), the 5-6-mm incision induced 0.89 D (pre-op 0.97 D and post-op 1.02 D). The 4-mm clear cornea incision induced 2.00 D (from 0.89 D to 1.56 D), the 5.5-mm corneal incision, performed in the steepest meridian to reduce preexisting astigmatism, induced 3.57 D; pre-op 3.38 D, post-op 2.09 D. Corneal topography revealed a slight increase in astigmatism within all corneal zones (4-mm scleral tunnel: 0.26 D, 5-6-mm scleral tunnel: 0.36 D and 4-mm clear cornea incision: 0.22 D). After a 5.5-mm clear cornea incision, however, astigmatism of the central 3-mm zone was reduced by 1 D, while astigmatism of the 5-7 mm zone increased by 0.22 D. CONCLUSION: The 4- and 5- to 6-mm scleral tunnel as well as the 4-mm clear cornea incision were shown to be nearly astigmatism-neutral. The 5.5-mm clear cornea incision reduced astigmatism of the central cornea by about 35%, but induced irregular astigmatism in the periphery.

Astigmatism↗
PubMed2000

Correlation among refractive, keratometric and topographic astigmatism after myopic photorefractive keratectomy.

BACKGROUND: Photorefrative keratectomy can be used to flatten the curvature of the anterior cornea and reduce the myopic refraction of the eye. This leads to unphysiological topographical changes of the cornea and may alter the conditions for examinations of corneal surface topography. The purpose of this study was to check for mutual agreement of three different methods of assessment of astigmatism before and after myopic photorefractive keratectomy (PRK). PATIENTS AND METHODS: Forty-seven eyes of 28 patients (age 32.7+/-6.6 years) following PRK using an 193-nm excimer laser were included in this study. 37 eyes were treated for pure myopia (-4.9+/-2.4 D) and 10 eyes for myopic astigmatism (sphere -2.0 to -7.0 D, cylinder -1.0 to -3.0 D). Preoperatively and at 18 months postoperatively, subjective refractometry, keratometry and topography analysis were performed. The axes of topographic and keratometric cylinder were standardized periodically (180 degrees) with respect to the refractive cylinder axis. RESULTS: Pre- and postoperatively, the absolute astigmatism values correlated highly significantly between all three methods (P< or =0.001). The mean refractive cylinder was 0.65+/-0.61 D preoperatively and 0.46+/-0.41 D postoperatively (P=0.2). The mean keratometric astigmatism was 1.14+/-0.64 D before and 0.94+/-0.50 D after PRK treatment (P=0.2). Among the three methods, the mean topographic astigmatism was the highest (P<0.001) preoperatively (1.31+/-0.56 D) and postoperatively (1.21+/-0.52 D) (P=0.3). In eyes treated for pure myopia, no difference between pre- and postoperative refractive, keratometric and topographic astigmatism was detected (P>0.5). The axes of both topographic and keratometric astigmatism correlated highly significantly with the refractive cylinder axis (R> or =30.9, P<0.0001). CONCLUSION: Up to 2 years after myopic PRK, the difference between refractive and keratometric astigmatism does not differ from the preoperative value, indicating an even corneal surface. The absolute astigmatism values and the cylinder axis correlated well between subjective and objective methods of astigmatism assessment. Thus, objective measurements may be helpful in determining the cylinder component of best spectacle correction after PRK. However, topographic analysis overestimates astigmatism values systematically before and after PRK.

Adult↗
PubMed2005

Prescribing eyeglass correction for astigmatism in infancy and early childhood: a survey of AAPOS members.

PURPOSE: To determine prescribing practices of pediatric ophthalmologists for astigmatism and astigmatic anisometropia in infants and young children. METHODS: A survey was sent to the 700 North American AAPOS members listed in the 2004 web site directory. RESULTS: A total of 412/700 surveys (59%) were returned. The level of astigmatism at which pediatric ophthalmologists prescribe eyeglasses for astigmatism varies considerably across the age range from birth to 3 years. The level at which 50% would prescribe glasses was > or =4.00 D from 0 to <6 months and decreased to > or =2.00 D by 2 to <3 years. Furthermore, one-fifth indicated that they would not prescribe eyeglasses for astigmatism in infants <6 months of age. Prescribing practices for astigmatic anisometropia were slightly less variable across age, with 50% of respondents indicating that they would prescribe eyeglasses for astigmatic anisometropia > or =3.00 D from 0 to <6 months, decreasing to > or =1.50 D by 2 to <3 years. CONCLUSIONS: The American Academy of Ophthalmology Preferred Practice Patterns guidelines accurately reflect prescribing practices of pediatric ophthalmologists for 1- and 2-year-old children for bilateral astigmatism and astigmatic anisometropia. However, the AAO guidelines do not accurately reflect the prescribing practices for children in the 0 to <1-year age range. For children 0 to <6 months of age, pediatric ophthalmologists indicate that they typically require a higher amount of astigmatism or astigmatic anisometropia than that recommended by the AAO guidelines, or they do not prescribe glasses at all.

Academies and Institutes↗
PubMed2003

Myopic astigmatism and presbyopia trial.

PURPOSE: No prospective double-masked study has evaluated whether low astigmatism benefits or harms patients with presbyopia, whose intermediate and near vision might theoretically benefit from enhanced depth of focus provided by astigmatism. The purpose of the first Myopic Astigmatism and Presbyopia (MAP I) study was to determine whether low myopic astigmatism enhances or harms the visual acuity, stereopsis, or quality of life in patients with presbyopia. DESIGN: Prospective, randomized, double-masked, crossover design clinical trial. METHODS: Fifteen patients with presbyopia aged 45 to 68 years were recruited from an academic center population. These patients were given a baseline eye examination, including manifest refraction, Early Treatment of Diabetic Retinopathy Study (ETDRS) logarithm of minimal angle of resolution (logMAR) visual acuity at distance, intermediate, and near, accommodative amplitudes, and stereo vision. Each patient was then cycled in random order through three masked pairs of soft contact lenses. The power of each contact lens pair was calculated by the subtraction method to maintain a spherical equivalent of -0.5 diopters, while providing either no astigmatism (spherical arm, SPH), 1 diopter of with-the-rule (WTR) astigmatism, or 1 diopter of against-the-rule (ATR) astigmatism. Actual refractive errors produced were measured by masked examiner. Outcomes measured at the end of 1 week of usage of each contact lens arm were binocular (ETDRS) logMAR visual acuity at three distances (far [4 m], intermediate [1 m], and near [33cm]); near stereoacuity, using the quantitative Titmus Stereotest; and quality of life, measured using the Refractive Status and Vision Profile (RSVP), a standardized questionnaire. RESULTS: Visual acuity results across the three arms were similar. However, 1-m logMAR visual acuity was better for the spherical arm than either astigmatic arm (-0.06 SPH, +0.01 WTR, +0.02 ATR). Near (33 cm) and distance (4 m) acuities were similar across arms. Stereoacuity was better in ATR than WTR (50 vs 102 seconds, P =.01). Subjects preferred SPH slightly over the WTR astigmatic arm by the RSVP quality-of-life survey instrument (101 vs 104, P =.05). Other intergroup comparisons showed no difference in RSVP scores. CONCLUSIONS: This study has demonstrated that intermediate distance acuity and refractive quality of life are slightly better with spherical low myopic refractive error vs either astigmatic arm. Near and far distance acuity were unaffected by low myopic astigmatism compared with spherical low myopia. Near stereopsis was best in the ATR arms, but this did not produce better near visual acuity or RSVP quality of life.

Aged↗
PubMed1998

Arcuate keratotomy to treat corneal astigmatism after cataract surgery: a prospective evaluation of predictability and effectiveness.

OBJECTIVE: Although several nomograms are available for the incisional keratotomy to correct naturally occurring astigmatism, astigmatic keratotomy in eyes after cataract surgery has not been well analyzed. The predictability and effectiveness of arcuate keratotomy in pseudophakic eyes were studied. DESIGN: A prospective, multicenter study. PARTICIPANTS: One hundred four eyes of 86 patients with residual corneal astigmatism of 1.5 diopters (D) or more after cataract surgery were examined. INTERVENTION: Arcuate keratotomy was performed in nine centers by nine surgeons. MAIN OUTCOME MEASURES: The amount of astigmatic correction was calculated using the vector analysis of preoperative and 6-month postoperative refractive cylinder results. RESULTS: Multiple regression analysis showed that optical zone size, number of incisions, and incision length had significant correlations with the amount of astigmatic correction. The regression equation was expressed as effects = (-0.643 x optical zone size) + (0.998 x incision number) + (0.057 x incision length) + 2.356. The parameter of predictability (r2: 35%) was lower than that reported for congenital astigmatism (48 to approximately 56%). A new nomogram was derived based on the multiple regression equation. CONCLUSIONS: Astigmatic keratotomy in pseudophakic eyes is less predictable than that in eyes with idiopathic astigmatism, but the procedure is sufficiently effective in reducing the residual astigmatism after cataract surgery. Individual nomograms are necessary for astigmatic keratotomy in eyes with naturally occurring and postsurgical astigmatism.

Aged↗
PubMed2001

Analysis of astigmatism in anterior segment surgery.

PURPOSE: To demonstrate techniques for analyzing astigmatism in the context of anterior segment surgery. The techniques are applied to refractive and corneal astigmatism and to astigmatism associated with the surgery. METHOD: The analysis is based on the 3-dimensional first-order ray optics known as linear optics, in which astigmatism is axial. Anterior segment surgery, whose only direct effect is to change corneal curvature, is optically equivalent to placing a thin lens immediately in front of the (preoperative) eye; the surgery can be described as anterior thin-lens equivalent. In principle, however, surgery may also change the relative axial positions of refracting elements. In such cases, anterior segment surgery is anterior thick-system equivalent and the analysis of astigmatism is considerably more complicated, with astigmatism manifesting in power and in other ways. Fundamentally, the method is based on the ray transference, a 4 x 4 matrix that contains the 4 fundamental optical properties of a system. Each property may contain an antistigmatic component, and it is this component that is analyzed. RESULTS: The data are not consistent with the anterior thin-lens model of anterior segment surgery but rather with the anterior thick-lens model. Many components of refraction and corneal power, their means, and their surgically induced changes were calculated and are presented in tabular and graphical form. Graphical representations include polar profiles and stereo-pair scatterplots in dioptric power space. Results are also presented for all the fundamental properties of the surgery. CONCLUSION: Ocular astigmatism can manifest in more ways than just refraction and corneal power. Traditional approaches, which treat astigmatism as cylinder in some sense and only as manifested in power, are unsatisfactory. In particular, current approaches weight astigmatism too heavily relative to stigmatism and to other optical phenomena and are inadequate for thick systems such as the eye. The ray transference and the 4 fundamental properties it contains provide the basis for the only methods that can adequately cope with analysis of astigmatism in general and in surgically induced astigmatism in particular.

Adult↗
PubMedDate not supplied

New method of targeting vectors to treat astigmatism.

PURPOSE: To describe a method for optimizing the treatment of astigmatism using vector analysis of both refractive and corneal topographic values. SETTING: Cheltenham Eye Centre, Melbourne, Australia. METHODS: This study evaluated a method of vector analysis for planning surgery that uses both preoperative topographic and refractive values and determined how to select the relative treatment emphasis to be given to each. In addition, the significance of the phenomenon of ocular residual astigmatism (ORA) was explored. Its presence provides an inherent limitation on eliminating astigmatism from the eye's optical system. RESULTS: Various comparisons of preoperative and ORA values are plotted in a series of 100 excimer laser photoastigmatic refractive keratectomy patients. These ORA values are equivalent to the expected corneal astigmatism resulting from surgery where treatment is performed by refractive astigmatism values alone. A theoretical example is given in which the corneal astigmatism remaining from surgery is reduced by giving less emphasis to completely eliminating refractive astigmatism and consequently greater emphasis to completely eliminating topographic astigmatism. CONCLUSION: Using vectors in astigmatism surgery enables the incorporation of topography and refractive values into the surgical plan. This would achieve a greater reduction in corneal astigmatism and potentially a better visual outcome than using refractive astigmatism values alone.

Astigmatism↗
PubMed1999

Surgically induced astigmatism after photorefractive keratectomy and laser in situ keratomileusis. Summit PRK-LASIK Study Group.

PURPOSE: To compare the axis and magnitude of surgically induced astigmatism in photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK). SETTING: Multicenter clinical trial. METHODS: In this prospective randomized trial, 220 eyes of 220 patients entered the study cohort: 105 randomized to PRK and 115 to LASIK. All patients received a single-pass, multizone excimer laser ablation as part of a PRK or LASIK procedure. Attempted corrections ranged from -6.00 to -15.00 diopters (D). The LASIK procedures were performed with nasal hinges. Absolute changes in astigmatism and axis and magnitude of surgically induced astigmatism were analyzed. Patients were followed for up to 6 month. RESULTS: In the PRK group, the mean change in absolute astigmatism was +0.14, +0.16 and +0.32 D at 1, 3, and 6 months, respectively; in the LASIK group, the mean change was -0.15, -0.08, and -0.03 D, respectively. At all time points, a greater proportion of PRK than LASIK eyes had an increase in absolute magnitude of astigmatism. In the PRK group, the axis of vectoral-induced astigmatism was significantly different from random at 3 and 6 months (P = .01, P < .001), respectively) with a tendency for induced with-the-rule shifts postoperatively. In the LASIK group, the axis of vectoral-induced astigmatism was significantly different from random at only 1 month (P = .04), and there was no preponderant direction of axis shift. Despite these findings, other analyses showed no statistically significant between-group differences in vectoral axis or magnitude of surgically induced astigmatism. CONCLUSIONS: Induced astigmatism was generally less and more random in axis in LASIK than in PRK; a general trend for induced with-the-rule astigmatism in PRK was not seen in LASIK. Hypothetically, the lamellar corneal flap in LASIK may counteract the tendency toward steepening at 90 degrees seen in PRK by retracting toward the hinge, by masking underlying induced astigmatism in the ablation zone, or by its mitigating influence on postoperative corneal healing.

Astigmatism↗
PubMed1999

Possible factors modifying the surgically induced astigmatism in cataract surgery.

PURPOSE: To investigate possible modifiers of the surgically induced astigmatism with special reference to age, gender, preoperative astigmatism, and the intraocular pressure. METHODS & PATIENTS: Data for one hundred and one cataract patients operated on with extracapsular cataract extraction and intraocular lens implantation were prospectively recorded and followed for six years. Different explanatory variables like age, gender, preoperative astigmatism and postoperative intraocular pressure (IOP) were considered. Astigmatic changes were calculated as Naeser's polar values. RESULTS: The surgically induced astigmatism was not significant at one year, but was significantly increased 3- and 6-years postoperatively. At the same time the keratometric axis made a shift toward against-the-rule astigmatism. The postoperative mean-IOP was lower at all controls. Multiple regression analysis showed that a large preoperative astigmatism, a low postoperative IOP, and high age resulted in more surgically induced astigmatism against-the-rule. CONCLUSION: The length and the architecture of the incision are known to have an influence on the surgically induced astigmatism in cataract surgery. In the present study we used a multiple regression analysis model to show a significant correlation between the surgically induced astigmatism and age, preoperative astigmatism, and postoperative IOP.

Adult↗
PubMed1996

[Corneal astigmatism after pterygium excision and subsequent phototherapeutic keratectomy with the excimer laser (193 rm)].

BACKGROUND: Phototherapeutic keratectomy with the excimer laser is a suitable procedure for corneal smoothing after pterygium excision. In this study the effect of postoperative excimer laser smoothing on induced and absolute astigmatism after pterygium surgery was investigated. MATERIALS AND METHODS: 60 of 53 eyes underwent pterygium surgery using a bare sclera technique. In addition 30 of the treated eyes underwent postoperative phototherapeutic keratectomy of the wound region with the excimer laser. Astigmatism was measured preoperatively and postoperatively after 6 months up to four years. RESULTS: Absolute astigmatism of patients treated with excimer laser decreased significantly from 1.38 +/- 0.83 D preoperative to 0.35 +/- 0.32 D postoperative (p < 0.0001). In this group mean induced astigmatism was 1.37 +/- 0.93 D. There was no correlation between the induced astigmatism and the number of excimer pulses applied (r = 0.0287; p = 0.905). Absolute astigmatism of the control group decreased from 1.10 +/- 0.85 D to 0.72 +/- 0.56 D (p < 0.05). There were no significant differences between the excimer- and the control group concerning preoperative astigmatism. Postoperative absolute astigmatism of the excimer group was significantly lower than absolute astigmatism of the control group (p < 0.0001). Mean induced astigmatism of the control group was 1.15 +/- 0.95 D and not significantly different from the excimer treated group (p = 0.2654). CONCLUSION: Phototherapeutic keratectomy with an excimer laser for corneal smoothing after pterygium excision reduces astigmatism significantly.

Adult↗
PubMed1997

The axis of astigmatism in right and left eye pairs.

This study was designed to investigate the relationship between the astigmatic axes of right and left eye pairs, with particular attention given to determining the degree to which either direct or mirror symmetry (enantiomorphism) of the astigmatic axes exists. A sample of 192 "nonvisually" selected adults participated, with refractive error and corneal curvature data being measured using autokerato-refractive equipment. Total, corneal, and residual astigmatism were investigated, with residual astigmatism being taken as the vector difference between total and corneal astigmatism. There was no evidence for a predominance of either mirror or direct symmetry of the astigmatic axes within this sample. The patterns of astigmatic axis distribution of right and left eyes were remarkably similar but, within this context, there was no definite evidence for a definable association between the axis of the left and right pairs of individuals. These findings remained unchanged when the effect of the modulus of astigmatism was incorporated, either through weighting the frequency distributions or through analyzing a subgroup of the overall population (those individuals with greater than 0.50 D of astigmatism). We believe these findings contradict commonly held clinical impressions regarding the symmetry of astigmatic axes, and should be considered when performing statistical analysis of astigmatic data.

Adolescent↗
PubMed2004

Incidence and progression of astigmatism in Singaporean children.

PURPOSE: This study investigated the incidence and progression, as well as factors associated with changes in astigmatism in school children. METHODS: This was a prospective cohort study. Children 7 to 9 years of age, of Chinese, Malay, and Asian Indian ethnicity, were examined annually over a 4-year period. Cycloplegic autorefraction was performed. A questionnaire was used to evaluate risk factors for incidence and progression of astigmatism. RESULTS: The cumulative 3-year incidence rate of astigmatism was 33.6% (cylinder power of 0.5 D or worse) or 11.5% (cylinder power of 1.0 D or worse). Myopic children had a higher incidence rate of astigmatism than nonmyopes (P <0.001). The mean J0 change per year was 0.012 D (95% CI: 0.007-0.018), whereas J45 did not show a significant change each year (mean, 0.001 D per year). Chinese children had greater worsening of J0 per year (P <0.001). Girls also had significantly greater progression of J0 than did boys (P <0.001). Similarly, myopia at baseline (P <0.001) and the hours of computer use (P=0.049) were associated with a greater progression rate of J0. J0 tended to improve in children with compound hyperopic astigmatism, worsen in children with compound myopic astigmatism, and remain stable in mixed astigmatics. CONCLUSIONS: Although there was minimal progression of astigmatism in school age children (0.44-0.53 D) over this period of follow-up, incident cases of astigmatism (>1.0 D) were not uncommon. The progression rate of astigmatism was affected by the ethnicity, presence of myopia, axis, and subtype of astigmatism.

Astigmatism↗
PubMedDate not supplied

Astigmatism outcomes following spherical photorefractive keratectomy for myopia.

BACKGROUND: Our aim was to examine the change in astigmatism after spherical photorefractive keratectomy (PRK). These effects are essential to optimizing photoastigmatic refractive keratectomy (PARK) to correct astigmatism to within fractions of a diopter. METHODS: We retrospectively reviewed 98 eyes of 178 patients with mild to moderate myopia and cylinder < or = 1.00 diopter (D) treated with spherical PRK (VISX 20/20 STAR excimer laser system); 31 eyes had epithelium removed mechanically with a blade and 67 eyes by a laser-scrape technique. RESULTS: Refractive astigmatism was reduced by greater than 0.25 D in 27 eyes (28%); refractive astigmatism was induced by greater than 0.25 D in 31 eyes (32%); the average vector-corrected difference between an eye's astigmatism before and after surgery was 0.01 +/- 0.52 D (P = .85). Eyes with high topographic astigmatism but low refractive cylinder before PRK showed an average of 0.07 +/- -0.60 D change in refractive cylinder after PRK. Refractive astigmatism of more than 0.25 D was induced in 16 eyes (44%) that received manual removal of epithelium versus 15 eyes (24%) that received laser removal of epithelium (odds ratio 2.51, P < .01). CONCLUSIONS: When using PRK for astigmatism correction, refractive cylinder before surgery rather than topographic astigmatism may be the most appropriate method for targeting the astigmatism correction, especially when the two values are discordant. An unpredictable mild increase or decrease in astigmatism may be expected.

Adult↗
PubMedDate not supplied

Laser in situ keratomileusis for myopic astigmatism.

PURPOSE: To evaluate the refractive results of laser in situ keratomileusis (LASIK) for myopic astigmatic eyes, and to assess the efficacy, accuracy, stability, and safety of the procedure. METHODS: LASIK was performed on 113 eyes of 73 patients for correction of myopic astigmatism ranging from 1.00 to 5.00 D, as measured by manifest refraction, with a mean baseline refractive astigmatism of 2.09 +/- 1.12 D. The Chiron Automated Corneal Shaper was used to create a corneal flap, and laser ablation was performed using the Chiron-Technolas Keracor 116 excimer laser. Follow-up time was 12 months for all eyes. RESULTS: Refractive astigmatism was stable by 3 months after surgery. At 1 year after LASIK, refractive astigmatism was reduced to a mean of 0.25 +/- 0.31 D (range 0 to 1.00 D). Sixty-one eyes (54%) had no residual astigmatism and 98 eyes (86.7%) had 0 to 0.50 D of refractive astigmatism. The mean percent reduction of preoperative astigmatism was 87.9 +/- 14.9%. The mean axis deviation of the surgically induced astigmatism was 2.1 +/- 3.1 degrees, with 96 eyes (84.9%) within 5 degrees of the desired axis. The percent correction of preoperative astigmatism in the proper axis was 97.1 +/- 15.5%. Spectacle-corrected visual acuity improved by 2 lines in 11 eyes (9.7%), and was reduced by 1 line only in 1 eye. There were no other significant complications. CONCLUSION: LASIK with the Chiron-Technolas Keracor 116 excimer laser was effective for correction of myopic astigmatism, with good stability after 3 months. The results were predictable with an acceptable degree of accuracy. LASIK is a safe procedure with very few complications.

Astigmatism↗
PubMedDate not supplied

Laser in situ keratomileusis for myopic astigmatism with the Nidek EC-5000 laser.

PURPOSE: We studied the efficacy, predictability, and safety of laser in situ keratomileusis (LASIK) for moderate to high simple and compound myopic astigmatism. METHODS: Ninety-two eyes of 46 consecutive patients who had LASIK for myopic astigmatism (64 eyes, astigmatism 3.00 to 9.00 D; myopia 0 to -20.00 D), or simple myopia (28 eyes, myopia -4.00 to -20.00 D; astigmatism 0 to 0.50 D) were retrospectively studied. Mean baseline spherical equivalent refraction (SE) in the myopia group was -8.11 +/- 3.94 D and in the astigmatism group, -8.55 +/- 4.49 D. All eyes underwent LASIK using the Nidek EC-5000 laser by the same surgeon. RESULTS: At 6 months after LASIK in the myopia group versus the astigmatism group, 24 eyes (85%) vs. 54 eyes (84%) were available for follow-up, 12 eyes (50%) vs. 13 eyes (24%) had uncorrected visual acuity (UCVA) of 20/20, 19 eyes (79%) vs. 44 eyes (81%) had UCVA of 20/40, 8 eyes (33%) vs. 18 eyes (33%) had SE within +/- 0.50 D, 15 eyes (62%) vs. 39 eyes (72%) had SE within +/- 1.00 D, and mean SE was -1.22 +/- 1.17 D vs. -0.74 +/- 1.46 D. Mean astigmatism (vertexed to the corneal plane) in the astigmatism group was 2.77 D at 0 degrees before surgery and 0.32 D at 7 degrees at 6 months. None of the myopic eyes and three of the astigmatic eyes (5%) lost > or = 2 lines of best spectacle-corrected visual acuity. CONCLUSION: LASIK with the Nidek EC-5000 laser for myopic astigmatism was reasonably effective, predictable, and safe. Astigmatism was under-corrected with the nomogram implemented in this study.

Adult↗