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PubMed2001

Laser in situ keratomileusis for the correction of myopia and myopic astigmatism.

PURPOSE: To evaluate the efficacy, safety, predictability, and surgically induced astigmatism (SIA) of laser in situ keratomileusis (LASIK) for the correction of myopia and myopic astigmatism. SETTING: Department of Ophthalmology, National Taiwan University Hospital, Taipei, Taiwan. METHODS: This retrospective study comprised 69 eyes that had LASIK to correct myopia and 74 eyes that had LASIK to correct myopic astigmatism. The excimer laser keratectomy was performed using a Summit Apex Plus machine. Refraction, visual acuity, and computerized corneal videokeratography data from the preoperative and postoperative examinations were collected. The astigmatic change was calculated by the Alpins vector analysis method. RESULTS: The preoperative spherical equivalent at the glasses plane in the myopia and myopic astigmatism groups was -8.08 diopters (D) and -9.73 D, respectively. At 6 months, the spherical equivalent and residual corneal astigmatism were -0.25 D and 0.85 D, respectively, in the myopia group and -0.71 D and 0.82 D, respectively, in the myopic astigmatism group. In the myopia group, 88% of eyes were within +/-1.0 D of the intended myopia correction and in the myopic astigmatism group, 85% were within +/-1.0 D of the targeted spherical equivalent and 90% were within +/-1.0 D of the intended astigmatism correction. The uncorrected visual acuity was 20/40 or better in 94.1% of eyes in the myopia group and 92.5% of eyes in the myopic astigmatism group. The SIA magnitude was 0.66 D with the axis randomly distributed in the myopia group. The mean astigmatism correction index was 0.97, the mean magnitude of error was 0.13 D +/- 0.62 (SD), and the mean angle of error was -3.70 +/- 13.73 degrees in the myopic astigmatism group. CONCLUSION: Laser in situ keratomileusis had similar predictability, safety, and efficacy in the treatment of myopia and myopic astigmatism. The astigmatism correction was effective, but the results suggest that subjective astigmatism of less than 1.0 D need not be treated with the Summit Apex Plus laser.

Adult↗
PubMed2005

Astigmatism in monkeys with experimentally induced myopia or hyperopia.

PURPOSE: Astigmatism is the most common ametropia found in humans and is often associated with large spherical ametropias. However, little is known about the etiology of astigmatism or the reason(s) for the association between spherical and astigmatic refractive errors. This study examines the frequency and characteristics of astigmatism in infant monkeys that developed axial ametropias as a result of altered early visual experience. METHODS: Data were obtained from 112 rhesus monkeys that experienced a variety of lens-rearing regimens that were intended to alter the normal course of emmetropization. These visual manipulations included form deprivation (n = 13); optically imposed defocus (n = 48); and continuous ambient lighting with (n = 6) or without optically imposed defocus (n = 6). In addition, data from 19 control monkeys and 39 infants reared with an optically imposed astigmatism were used for comparison purposes. The lens-rearing period started at approximately 3 weeks of age and ended by 4 to 5 months of age. Refractive development for all monkeys was assessed periodically throughout the treatment and subsequent recovery periods by retinoscopy, keratometry, and A-scan ultrasonography. RESULTS: In contrast to control monkeys, the monkeys that had experimentally induced axial ametropias frequently developed significant amounts of astigmatism (mean refractive astigmatism = 0.37 +/- 0.33 D [control] vs. 1.24 +/- 0.81 D [treated]; two-sample t-test, p < 0.0001), especially when their eyes exhibited relative hyperopic shifts in refractive error. The astigmatism was corneal in origin (Pearson's r; p < 0.001 for total astigmatism and the JO and J45 components), and the axes of the astigmatism were typically oblique and bilaterally mirror symmetric. Interestingly, the astigmatism was not permanent; the majority of the monkeys exhibited substantial reductions in the amount of astigmatism at or near the end of the lens-rearing procedures. CONCLUSIONS: In infant monkeys, visual conditions that alter axial growth can also alter corneal shape. Similarities between the astigmatic errors in our monkeys and some astigmatic errors in humans suggest that vision-dependent changes in eye growth may contribute to astigmatism in humans.

Animals↗
PubMed1998

Astigmatic change following congenital ptosis surgery.

BACKGROUND: High astigmatism is frequently associated with congenital ptosis. Ptosis surgery itself may also induce astigmatic refractive change that will cause amblyopia in young children. The purpose of this study was to assess postoperative astigmatic change and the effect of different ptosis surgical procedures on astigmatism. METHODS: An analysis of 63 consecutive surgical cases of congenital ptosis was conducted. The preoperative incidences of anisometropia, amblyopia, strabismus and high astigmatism were evaluated. All patients underwent levator resection or received frontalis sling. The postoperative astigmatic change after the follow-up period of 12 months was assessed in 28 patients. It included a total of 40 ptotic eyelids from 12 bilateral and 16 unilateral cases of ptosis. The eyes on the contralateral side in unilateral cases served as the control group. RESULTS: In 63 cases of congenital ptosis, 30.2% (19/63) were associated with anisometropia and 39.7% (25/63) with amblyopia, and 11.1% (7/63) were combined with strabismus. Most cases of amblyopia were associated with high astigmatism (64%). The incidence of high astigmatism (> 2.5 diopters, D) in congenital ptosis was 25.3%. Of 40 ptotic eyelids included for the study of postoperative astigmatism change, 15% showed an increase of more than 0.5 D, whereas 27.5% showed a decrease of more than 0.5 D, and no significant change was observed in 57.5%. An average decrease of 0.18 D in astigmatism was observed, while no statistical difference was found between the study group and the control group for astigmatic change. Moreover, both the levator resection and frontalis sling groups showed a decrease in average cylinder, and again, demonstrated no statistically significant difference in astigmatic change. CONCLUSIONS: A high incidence of amblyopia was associated with astigmatism in congenital ptosis. Postoperative astigmatic study also revealed some change in astigmatic power, but no new cases of amblyopia developed after ptosis surgery. Patients with congenital ptosis should have cycloplegic refraction as soon as possible, and long-term postoperative refraction check-up is also recommended.

Adolescent↗
PubMed1992

Postcataract against-the-rule astigmatism after phacoemulsification procedure. Characteristic changes over time.

To further determine whether postoperative astigmatism is related to the amount of preoperative astigmatism, we analyzed two types of against-the-rule (AR) astigmatism induced by phacoemulsification and aspiration (PEA) procedures. The operations all utilized 10-0 polyester (Mersilene) in double running fashion for the closure of the corneoscleral incisions. The induction and spontaneous regression of several types of astigmatism were analyzed over 6 months. Surgery was all done by one surgeon, with the same surgical procedure and the same number of sutures. In postoperative AR astigmatism less than 0.7 D at 6 months, although the amount of the astigmatism 1 week postoperatively was remarkably increased (2.66 +/- 0.17 D), postoperative astigmatism was decreased 6 months following surgery. On the other hand, in postoperative AR astigmatism greater than 1.5 D at 6 months, the power of the astigmatism 1 week postoperatively (2.12 +/- 0.13 D) was not much higher than the preoperative level (1.38 +/- 0.08 D), but tended to continue increasing even 6 months after surgery. There was no difference in the power of astigmatism between 1 and 3 months postoperatively. The eyes with preoperative astigmatism (e.g. 1.38 +/- 0.08 D) and especially preoperative AR astigmatism (e.g. 1.60 +/- 0.11 D), showed an increase of their astigmatism after the PEA procedure. We discussed some risk factors which may induce greater postoperative AR astigmatism.

Astigmatism↗
PubMed1997

[Factors modifying postoperative astigmatism after no-stitch cataract surgery].

BACKGROUND: One of the main advantages of the no-stitch technique in cataract surgery is that induced astigmatism occurs less frequently than with any other procedure and stabilizes within a very short time postoperatively. The resultant high wound strength enabled us to alter the incision parameters in an attempt to identify those which influenced postoperative astigmatism, the ultimate goal being to improve the prognosis of the expected astigmatism. Since the influence of tunnel width and incision length and shape were well known, we investigated the influence of incision depth and site and that of various parameters in a prospective randomized and controlled clinical trial. METHODS: The study included 256 eyes with a 7-mm tunnel incision as examined in 256 patients. The following subgroups of 27 eyes each were investigated: primary incision depth of 300 microns versus 500 microns, limbal incision versus scleral incision, scleral incision in the 12 o'clock position versus temporal scleral incision, and limbal incision in the 12 o'clock position versus temporal limbal incision. In another group the influence of age, IOP, axial length of the globe, preoperative astigmatism, corneal diameter, and postoperative astigmatism as measured by the keratometer were all assessed using Spearman's correlation coefficient. RESULTS: Temporal incisions made 2 mm posterior to the limbus resulted in induced astigmatism of 0.64 +/- 0.22 D 6 months postoperatively, which was less than after incisions in the 12 o'clock position (0.98 +/- 0.40 D). Induced astigmatism was highest after limbal incisions in the 12 o'clock position (1.31 +/- 0.60 D), yet was less if a temporal limbal incision was made (0.84 +/- 0.52 D). Incision depth did not have significant influence on induced astigmatism. Of the parameters, age (Spearman's correlation coefficient after 4 weeks 0.34; P = 0.002; after 6 months 0.28; P = 0.01), and preoperative astigmatism (Spearman's correlation coefficient after 4 weeks 0.28; P = 0.01; after 6 months 0.27; P = 0.01) had a significant influence on postoperative astigmatism. CONCLUSIONS: These findings indicate that induced astigmatism was highest after limbal incisions in the 12 o'clock position and lowest after scleral incisions in the temporal position. Age and preoperative astigmatism were also found to influence induced astigmatism significantly. All of these factors have to taken into account to minimize postoperative astigmatism.

Adult↗
PubMed2005

Changes in astigmatism in children with congenital nystagmus.

BACKGROUND: Astigmatism is commonly reported in children with and without nystagmus. In children less than 4 years of age the astigmatism changes from against the rule (ATR) to with the rule (WTR) astigmatism in children without nystagmus. However, little is known about children with congenital nystagmus. We compared astigmatism in children with congenital nystagmus below 4 years and above 4 years of age. MATERIAL AND METHODS: Three hundred and fifty-six eyes in 178 children who satisfied the study criteria were included. The children were divided into those below 4 years of age (n of eyes = 192) and those above (n of eyes = 164). Cycloplegic refraction (with manual retinoscopy) carried out at presentation and at the last follow-up were recorded and compared. Cycloplegia was achieved using cyclopentolate eye drops. Outcome of eyes with no astigmatism at initial presentation was compared with the final refraction in both the age groups. The visual acuity at the first presentation was compared with the visual acuity at the last presentation. RESULTS: Average follow-up duration was 3.36+/-1.59 years. On presentation, 176 (49.44%) eyes did not have any astigmatism. We found that 26 (25.2%) out of the 103 children below 4 years of age who did not have any astigmatism on presentation developed WTR astigmatism after a mean follow-up of 3.5+/-1.5 years. (p= 0.042). In children >or=4 years of age only 7 (9.6%) children out of 73 developed WTR after a mean follow-up of 3.4+/-1.4 years. The visual acuity change was not found to be significant in the two groups. The majority (90.3%) improved or had same visual acuity in group A and 88.9% improved or had the same visual acuity in group B at the last follow-up (p= 0.77). DISCUSSION: Our incidence of WTR astigmatism in children with congenital nystagmus is similar to those previously reported series. Our data suggest that there is a significant chance that children under 4 years with congenital nystagmus may develop WTR astigmatism compared with children above 4 years of age. CONCLUSION: With the rule (WTR) astigmatism is common in children with nystagmus. Children under 4 years of age presenting with no astigmatism may acquire WTR astigmatism as they grow. The amount of astigmatism increases with age in children with nystagmus. Visual acuity, however, remains stable as the age advances.

Astigmatism↗
PubMed2002

Prevalence of astigmatism in infant monkeys.

PURPOSE: Human infants exhibit a high prevalence of astigmatism. Although macaque monkeys are commonly used as animal models in experiments on early ocular growth and emmetropization, the prevalence of astigmatism in infant monkeys is unexplored. In this study we examine the prevalence and nature of astigmatism in infant monkeys. METHODS: Refractive and corneal astigmatism were measured in 132, 2-5-week-old rhesus monkeys (Macaca mulatta) using cycloplegic retinoscopy and keratometry, respectively. Longitudinal measures of refractive development were obtained from 16 normal infants over the first 6 months of life. RESULTS: Infant monkeys exhibited a low prevalence of astigmatism. Approximately 90% of the 2-5-week-old infants had <1.00 D of either refractive or corneal astigmatism. When refractive astigmatism was observed, it was well correlated with the direction and magnitude of corneal astigmatism. When corneal astigmatism was >1.00 D (n=20), it was predominantly against-the-rule in nature (70.0%). The infant monkeys that were followed longitudinally rarely showed significant astigmatic errors at any time during the observation period. When these infant monkeys exhibited significant astigmatism, it was usually transient and not present on subsequent measurements. CONCLUSIONS: Unlike human infants, infant monkeys exhibit relatively little astigmatism. The low prevalence of astigmatism during early development suggests that astigmatism does not provide an essential cue for vision-dependent eye growth in infant primates.

Aging↗
PubMed2001

Analysis of aggregate surgically induced refractive change, prediction error, and intraocular astigmatism.

PURPOSE: To demonstrate analytical methods for evaluating the results of keratorefractive surgical procedures and emphasize the importance of intraocular astigmatism. SETTING: University of Texas Medical School, Houston, Texas, USA. METHODS: A standard data set, provided by an editor of this journal, comprising the preoperative and postoperative keratometric and refractive measurements of 100 eyes that had keratorefractive surgery was evaluated by 2 methods, vector and spheroequivalent (SEQ) analysis. The individual and aggregate surgically induced refractive changes (SIRCs) and prediction errors were determined from the refractive and keratometric measurements using both methods and then compared. The refraction vertex distance, keratometric index of refraction, and corneal asphericity were used to make the results calculated from refractive data directly comparable to those derived from keratometric data. Doubled-angle and equivalency plots as well as frequency and cumulative histograms were used to display the data. Standard descriptive statistics were used to determine the mean and standard deviation of the aggregate induced astigmatism after converting the polar values (cylinder and axis) to Cartesian (x and y) values. RESULTS: The preoperative SEQ refractive errors were undercorrected by at least 0.25 diopter (D) in most cases (78%). Six percent were corrected within +/- 0.24 D, and 16% were overcorrected by at least 0.25 D SEQ. The mean SEQ was -6.68 D +/- 2.49 (SD) before and -0.61 +/- 0.82 D after surgery, reflecting a SIRC SEQ of -6.07 +/- 2.40 D. The defocus equivalent (DEQ) was 7.41 +/- 2.53 D before and 0.96 +/- 0.74 D after surgery; for a nominal 3.0 mm pupil, this corresponded to an estimated improvement in uncorrected visual acuity (UCVA) from worse than 20/200 to better than 20/25, respectively. The predictability of the treatment decreased as the attempted refractive correction increased. The average magnitude of the refractive astigmatism was 1.46 +/- 0.61 D before and 0.40 +/- 0.38 D after surgery. The centroid of the refractive astigmatism was +0.96 x 87.9 +/- 0.85 D, rho = 0.43 before and +0.11 x 83.1 +/- 0.37, rho = 0.49 after surgery. The decrease in the square root of the centroid standard deviation shape factor (rho1/2) indicated an 8% increase in the amount of oblique astigmatism in the population. The prevalence of preoperative keratometric irregular astigmatism in excess of 0.5 D in this group of patients was 13%. The correlation between keratometric and refractive astigmatism was extremely poor before (r2 = 0.26) and especially after surgery (r2 = 0.02), demonstrating the presence of intraocular astigmatism and the limitations of manual keratometry. The centroid of intraocular astigmatism at the corneal plane was +0.48 x 178 +/- 0.49 D, rho = 0.59, and was compensatory. CONCLUSIONS: The 2 analytical methods are complimentary and permit thorough and quantitative evaluation of SIRCs and allow valid statistical comparisons within and between data sets. The DEQ allows comparison of refractive and visual results. The decrease in refractive predictability with higher corrections is well demonstrated by the SEQ and doubled-angle plots of the SIRC. Doubled-angle plots were particularly useful in interpreting errors of cylinder treatment amount and errors in alignment. The correlation between refractive and keratometric astigmatism was poor for preoperative, postoperative, and SIRC data, indicating the presence of astigmatic elements beyond the corneal surface (ie, intraocular astigmatism). Sources of error in refractive outcome statistics include the use of multiple lens systems in the phoropter, errors in vertex calculations, difficulty in accurately defining the axis of astigmatism, and failure to consider measurement errors when working with keratometric data. The analysis of this particular data set demonstrates the significant clinical benefits of refractive surgery: an 8-fold increase in UCVA, an 11-fold decrease in SEQ refractive error, as well as a 9-fold and nearly a 2 1/2-fold decrease in the magnitude and distribution of astigmatism, respectively.

Adult↗
PubMed2001

Optimal incision sites to obtain an astigmatism-free cornea after cataract surgery with a 3.2 mm sutureless incision.

PURPOSE: To determine the optimal incision to eliminate astigmatism after cataract extraction. SETTING: Hara Eye Hospital, Utsunomiya, Japan. METHODS: Patients having cataract extraction through a 3.2 mm corneal limbal incision without limbal sutures were divided into 2 groups. Group 1 comprised 98 eyes of 80 patients without preoperative astigmatism and Group 2, 72 eyes of 62 patients with no astigmatism postoperatively. In Group 1, the incisions that caused postoperative corneal changes were retrospectively evaluated. In Group 2, the types of incisions that induced an astigmatism-free cornea postoperatively were retrospectively studied. Patients were examined preoperatively and 6 months postoperatively. RESULTS: In Group 1, 23 of 40 eyes (57.5%) with an incision between 9 and 12 o'clock (BENT incision) and 10 of 58 eyes (17.2%) with an incision at 12 o'clock remained astigmatism free postoperatively (P <.0001). One eye (2.5%) with a BENT incision and 17 (29.3%) with a 12 o'clock incision had astigmatism greater than 1.0 diopter (D) postoperatively (P <.001). In Group 2, 72 eyes had less than 1.2 D of preoperative astigmatism. No eye with more than 1.2 D of astigmatism was astigmatism free postoperatively, even when the incision was made at the steepest meridian. CONCLUSIONS: The results indicate that to reduce astigmatism in eyes with preoperative astigmatism of 0.5 D or more, a limbal 3.2 mm BENT incision should be placed at 10:30 o'clock. To prevent astigmatism postoperatively, the incision should be placed at the steepest meridian in eyes with preoperative astigmatism greater than 0.5 D; for preoperative astigmatism greater than 1.2 D, a 3.2 mm incision at the corneal limbus is insufficient and a wider incision or an additional incision is required.

Aged↗
PubMed2002

Astigmatic changes after excimer laser refractive surgery.

PURPOSE: To compare the astigmatic changes induced by spherical and elliptical excimer laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK). SETTING: University-based refractive surgery practice. METHODS: Three-month refractive data from 317 eyes of consecutive patients having spherical PRK, astigmatic PRK (A-PRK), spherical LASIK, and astigmatic LASIK (A-LASIK) by a single surgeon (J.S.P.) using VISX 2020B and Star lasers over 2 years were studied for astigmatic changes resulting from the surgical procedure. RESULTS: At 3 months, the mean change in absolute astigmatism was +0.15 diopter (D) and -0.07 D in the spherical PRK and LASIK groups, respectively. Photorefractive keratectomy tended to induce with-the-rule (WTR) astigmatism, while LASIK was astigmatically neutral. As expected, the eyes treated with A-PRK and A-LASIK achieved a greater reduction in absolute astigmatism (-1.02 D and -1.28 D, respectively) than those treated with spherical PRK and LASIK. The qualitative nature of the astigmatic change was different between flap-based and PRK-based procedures. CONCLUSIONS: Spherical PRK is more likely than spherical LASIK to induce astigmatism, with a tendency toward WTR astigmatism. The eyes treated with spherical LASIK had no preponderant change in the direction of astigmatic magnitude or axis. Astigmatic PRK and LASIK effectively reduced astigmatism along the preoperative axis; A-LASIK tended to induce a random resultant axis in most patients.

Adult↗
PubMed2004

Astigmatism outcomes of horizontal temporal versus nasal clear corneal incision cataract surgery.

PURPOSE: To compare the short- and long-term astigmatism outcomes after cataract surgery using temporal clear horizontal corneal incisions and nasal horizontal clear corneal incisions. SETTING: Wilmer Eye Institute, Johns Hopkins Hospital, Baltimore, Maryland, USA. METHODS: This retrospective study included a consecutive series of eyes having phacoemulsification with implantation of a 6.0 mm foldable acrylic intraocular lens through a 3.5 mm horizontal clear corneal incision at 180 degrees (temporal incision in right eyes, nasal incision in left eyes). Astigmatism was measured by keratometry readings before surgery and 6 weeks and 12 months postoperatively. RESULTS: The mean preoperative astigmatism in the 178 eyes (94 right, 84 left) of 161 patients was 0.78 diopter (D); 54.5% of eyes had against-the-rule (ATR) astigmatism, 22.5% had with-the-rule (WTR) astigmatism, and 14.0% were astigmatically neutral. A significant shift toward WTR astigmatism occurred postoperatively. At 6 weeks, 48.3% of eyes had WTR astigmatism and 23.0% had ATR astigmatism. At 12 months, 43.8% had WTR astigmatism and 25.8% had ATR astigmatism. Vector analysis revealed a mean surgically induced astigmatism (SIA) of 1.17 D at 6 weeks and 1.04 D at 12 months. The side of the incision significantly affected SIA. At 6 weeks, temporal incisions yielded a mean SIA of 0.74 D and the nasal incisions, of 1.65 D. This trend in SIA persisted at 12 months: 0.71 D for temporal incisions and 1.41 D for nasal incisions. CONCLUSIONS: Cataract surgery using a horizontal clear corneal incision induced WTR astigmatism 6 weeks and 12 months postoperatively. Temporal incisions induced significantly less astigmatism than nasal incisions.

Aged↗
PubMedDate not supplied

[Minimizing astigmatism by controlled localization of cataract approach with the no stitch technique. A prospective study].

BACKGROUND: The no-stitch-technique with deliberate localisation of the cataract incision is a method to reduce the postoperative astigmatism. This prompted us to investigate the postoperative astigmatism with varying incision localisation; our aim is to achieve a postoperative astigmatism < or = 1.0 D. PATIENTS AND METHOD: In this study we controlled 319 eyes of 316 cataract patients. We took into consideration the preoperative astigmatism and operated in the 12 o'clock or lateral position. The astigmatism was measured by an ophthalmometer preoperatively, on the first day, after 3-5 months and 8-12 months after surgery. RESULTS: A preoperative astigmatism of up to < or = 1.0 D was present in 82.4% of eyes. On the first day after surgery an astigmatism of < or = 1.0 D was present in 89.3% of eyes. After 3-5 months postoperatively astigmatism was < or = 1.0 D in 97.2% and in 98.8% after 8-12 months postoperatively. 15.7% of patients showed a preoperative astigmatism between 1 and 2 D, but only 1.2% after 8-12 months. There was no astigmatism > 2.0 D after 3-5 months and 8-12 months (preoperative 2%). CONCLUSIONS: The no-stitch-technique permits to control the postoperative astigmatism with deliberate localisation of the cataract incision. Postoperative astigmatism appeared to be stable. We therefore recommend for preoperative "ATR (Against the rule)-Astigmatism" (> or = 1.0 D) operation in lateral position and for preoperative "WTR (With the rule)-Astigmatism" operation in the 12 o'clock position.

Adult↗
PubMed2005

Astigmatism and its determinants in the Tehran population: the Tehran eye study.

PURPOSE: To determine the prevalence of astigmatism and its epidemiological risk factors in Tehran via a population-based study. METHODS: By means of a stratified random cluster sampling, 6497 citizens representing a cross-section of the population of Tehran were selected from 160 clusters. Eligible people were recruited through a door-to-door household survey in the selected clusters and transferred to a clinic for an extensive eye examination and interview. The refractive status was determined with manifest refraction. Astigmatism was defined as cylinder worse than or equal to 0.5 D. High astigmatism was defined as a manifest cylinder > or =1.5 D. RESULTS: Between August and December 2002, 4565 of the 6497 eligible individuals in the sample attended the interview and ophthalmic examination (a participation rate of 70.3%). The age- and gender-standardized prevalence of astigmatism was 50.2% (95% CI, 48.4% to 51.9%) on manifest refraction. High astigmatism was found in 490 right eyes (11.1%; 95% CI, 10.1% to 12.0%). Of 2532 participants with ametropia, 59.6 (95% CI, 57.6-61.5) had astigmatism. The percentages of with-the-rule, against-the-rule and oblique astigmatism were 33.6%, 36.9% and 29.3%, respectively. The proportion of type of astigmatism was significantly related to age (p < 0.001). The univariable analysis of astigmatism between family members yielded odds ratios of 1.47 (95% CI, 1.14 to 1.89, p = 0.003) for the association of astigmatism among siblings. After controlling for age, refractive errors and education, the pairwise sibling association remained statistically significant (OR 1.43, 95% CI, 1.08 to 1.88). CONCLUSION: These findings revealed a high prevalence of astigmatism in the population. Age, education and ametropia were the main predictors of astigmatism in Tehran. Our findings should be considered for case finding and astigmatism correction programs. Our data confirmed a modest familial aggregation for astigmatism.

Adolescent↗
PubMed2004

Astigmatic axis is related to the level of spherical ametropia.

PURPOSE: Against-the-rule (ATR) astigmatism has been shown to be a risk factor for subsequent myopia development. In this study, we evaluated the relationship between astigmatic axis and the level of spherical ametropia in both myopes and hypermetropes. METHODS: Astigmatic axes were analyzed in two distinct cohorts. First, 53 high myopes from families that were recruited for linkage analysis were compared with an age-matched control group derived from family members. Second, cross-sectional data were analyzed for 90,884 subjects attending 19 optometric practices in the north of England. Initially, the relationship between astigmatic axis and cylinder power and between axis and sphere power were analyzed in 21- to 40-year olds and 21- to 30-year olds, respectively, to control for the effects of age. Multivariate logistic regression analysis was then performed using data for all compound astigmats in the cohort to examine the effect of sphere power, cylinder power, age, and sex on the odds of subjects having either ATR or with-the-rule (WTR) astigmatism. RESULTS: In the genetic study cohort, there was an excess of WTR astigmats in the high myopes compared with controls, but this only reached significance for the right eye. In the much larger optometric practice sample, the association of WTR astigmatism with high myopia was highly significant. A parallel increase in WTR astigmatism was also found for high hypermetropes. In addition, the odds of having WTR astigmatism were increased if subjects were young or had a high cylinder power. ATR astigmatism occurred more often with increasing age and in subjects with lower spherical ametropia. Indeed, for 21- to 30-year-old subjects with low myopia (> or =-2.00 DS in the least minus meridian), ATR occurred more often than WTR astigmatism. CONCLUSION: Astigmatic axis was found to be related to the level of ametropia, with both a higher spherical component or higher cylinder power increasing the odds of astigmatism being WTR. Low ametropes, particularly myopes, were more likely to have axes ATR.

Adolescent↗
PubMed2005

The effect of monocularly and binocularly induced astigmatic blur on depth discrimination is orientation dependent.

PURPOSE: Naturally occurring astigmatism varies according to the age of the person. Although uncorrected astigmatism may be associated with meridional amblyopia, there is little information of its effect on stereopsis. The purpose of this study was to determine the effect of astigmatism on depth discrimination and whether this was dependent on the axis of the astigmatism. METHODS: Astigmatic blur was induced in four healthy subjects (mean age, 31.5 years; range, 22 to 42 years) using plain cylinders (-8.75 D to +11.5 D) for orientation control and Jackson cross-cylinders (0 to 12 D) for spherical neutrality. Horizontal, vertical, and oblique astigmatism was induced with five monocular and three binocular axis steps. Depth discrimination was recorded at near using Frisby, TNO, and Titmus stereoacuity tests and at distance (4 m) using the variable distance stereoacuity test. Visual acuity was recorded at 0.4 m and 4 m. RESULTS: Visual acuity and depth discrimination degraded with increasing astigmatic blur. The effect of monocular astigmatic blur on depth discrimination and visual acuity was not dependent on the axis of orientation. For binocular astigmatic blur, the reduction in depth discrimination was dependent on the axis of the induced astigmatism (p < 0.01). The maximum effect occurred with orthogonal-oblique orientations (x45 left; x135 right), followed by against-the-rule (ATR) astigmatism; with-the-rule (WTR) astigmatism had the least effect (p < 0.001). CONCLUSIONS: The lesser effect of WTR compared with ATR astigmatic blur on depth discrimination may reflect the contribution of horizontal compared with nonhorizontal disparity processing in stereopsis. The pronounced effect of oblique astigmatic blur may be because of the effects on horizontal and nonhorizontal disparity and interocular differential image blur.

Adult↗
PubMedDate not supplied

Comparison of cross cylinder ablation using the optimized ablation transition zone and the torsion error detector for correction of astigmatism.

PURPOSE: To compare the safety and efficacy of laser in situ keratomileusis (LASIK) in correcting high myopic astigmatism using two different ablation profiles using the Nidek EC-5000 CX II laser). METHODS: Fifteen patients (25 eyes) had LASIK for compound myopic astigmatism, using the Optimized Ablation Transition Zone (OATz) ablation profile and activated torsion error detection (TED). Results were compared with those obtained with a cross cylinder ablation profile for myopic astigmatism. RESULTS: For eyes treated with TED, on postoperative day 7, 76% had visual acuity equal to or better than baseline best spectacle-corrected visual acuity (BSCVA) and 56% of eyes had overcorrected astigmatism. On postoperative day 20, none of the eyes had residual astigmatism more than 1.00 D and 72% eyes were within +/-0.50 D cylinder; 92% of eyes had residual astigmatism within 30 degrees of the preoperative axis and 12% remained astigmatically overcorrected at 20 days. Eighty-eight percent of eyes were either fully corrected or had mild myopic astigmatism. Comparison of results with cross cylinder ablation showed that 24% had overcorrection and 60% of patients with high astigmatism were overcorrected up to 1.75 D and developed hyperopic astigmatism in the opposite axis. Results with the cross cylinder ablation profile were good up to 2.00 D of myopic astigmatism. CONCLUSIONS: Correction of astigmatism using the OATz profile and TED with the Nidek EC-5000 CX II laser produced good results in high as well as pure astigmatism treatments, compared to the cross cylinder ablation profile. Ablation depth was greater in OATz with TED-based corrections. Overcorrections were less with OATz with TED, and residual astigmatism was at the same baseline axis, thereby increasing patient satisfaction.

Adolescent↗
PubMed2003

[Postoperative astigmatism secondary to cataract surgery].

THE AIM OF THE PAPER: The purpose was to study the cases operated by the extracapsular extraction with the posterior chamber implant from the viewpoint of postoperative astigmatism. MATERIAL AND METHODS: We studied the cases with no postoperative complications along three years (1999-2001). In all cases we noted the placement, length and type of the incision, the suture (by 3 or 5 radiar suture) and the tension of the eye-ball in the time of suture. We determined the refraction at 2-3 and 6 weeks postoperatory and note the astigmatism (by the rule or against the rule) and its value in D. RESULTS: The postoperative astigmatism was found in 246 cases. Depending on the placement, length and type of the incision the postoperative astigmatism was found in 86.18% cases with the rule and in 13.82% cases against the rule, 54.72% postoperative astigmatism with the rule by 1.5-3 D. If we sutured with three radiar suture the astigmatism was with the rule in 86.88% cases, 52.82% astigmatism by 1.5-3D. If we sutured with 5 radiar suture the astigmatism was with the rule in 85.95% cases, 55.35% astigmatism by 1.5-3D. Normotension determined astigmatism by the rule in 90.16% cases and 60.10% by 1.5-3D. The suture with Vicryl 8.00 determined astigmatism by the rule in 86.18% cases and 54.72% was between 1.5-3D. CONCLUSIONS: Postoperative astigmatism depends by many factors more or less predictable. Astigmatism by the rule was found in majority of the cases and it was between 1.5-3D and it was controlled by glasses. Postoperative astigmatism tends to become history in new period of modern cataract surgery methods.

Astigmatism↗
PubMed1997

Natural and imposed astigmatism and their relation to emmetropization in the chick.

This study investigated the ocular response of young chicks to astigmatic errors imposed by spectacle lenses and as a related issue, we examined the nature and prevalence of astigmatism in young chicks, and its relation to corneal development and natural emmetropization. Normal hatchling chicks exhibited significant against-the-rule refractive astigmatism (approx. 8 D) of which 60-90% was corneal. Both types of astigmatism decreased in magnitude with normal corneal development as part of emmetropization. The apparent association with corneal growth is consistent with two further observations: (1) that smaller corneas, induced by constant light rearing, had higher than normal astigmatism (1.5 D greater at 15 days), (ii) that enlarged corneas, due to form deprivation, had reduced astigmatism (2.4 D less). When astigmatism was artificially imposed with (+/-10 DC spectacle lenses), altered ocular growth patterns were observed, although the changes were not consistent with the chicks having emmetropized to the imposed astigmatism. Irrespective of the axis setting used in positioning the lenses (45 degrees, 90 degrees, 180 degrees), eyes became hyperopic with +10 DC lenses (+8.8 +/- 1.3 D), and became slightly myopic with 10 DC lenses (-1.8 +/- 1.9 D). These refractive changes are consistent with the chicks having emmetropized to the more myopic meridian rather than the equivalent mean spherical error imposed (responses of control groups to +5 D and -5 D spherical lenses were +5.2 +/- 1.0 D and -5.1 +/- 0.8 D resp.). The same was true for chicks first prevented from accommodating by prior ciliary nerve section, except for one group wearing the 10 DC lens at 45 degrees axis where astigmatic changes consistent with partial compensation were seen, although this may represent an artefact of the surgery. These results argue against 'astigmatic emmetropization' as a normal phenomenon. Also consistent with this finding was the lack of significant astigmatic changes with accommodation-stimulating and inhibiting drugs (nicotine and vercuronium resp.), for normal chicks. These results imply that accommodation, while the most likely mechanism for astigmatic emmetropization, has little capacity to compensate for imposed astigmatic focussing errors.

Accommodation, Ocular↗