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PubMed1994

Accommodation in astigmatic eyes.

PURPOSE: To investigate the effect of target chart contours and the severity of astigmatism on accommodation in astigmatic eyes. METHODS: The accommodative responses of 30 subjects were measured with an automated refractometer (Canon RK-1) using star pattern and bar pattern targets. RESULTS: The mean accommodative response was greatest when the bar pattern was parallel to the stronger principal meridian of the eye, followed by the star pattern and the bar pattern parallel to the weaker meridian on both meridians. Similar results were obtained in subjects with astigmatism greater or less than 1.25 D. The mean slopes of AR/AS plots decreased in the same order as the accommodative response and the change was significant in subjects with astigmatism exceeding 1.25 D. In addition, about one-third of the subjects showed a consistent decrease in astigmatism with accommodation. CONCLUSIONS: These results indicate that the type of target chart and the severity of astigmatism influence the accommodative response.

Accommodation, Ocular↗
PubMed2000

Astigmatism and toric intraocular lenses.

The article reviews some of the basic optics of astigmatism and the correction of astigmatism with cylindric lenses. A simple model of the conoid of Sturm is demonstrated, and an ideal position for the conoid is postulated. The orientation of the conoid shows that leaving patients with some simple myopic "against-the-rule" astigmatism is beneficial to near work, whereas "with-the-rule" astigmatism is beneficial for distant viewing. Surgeons should be less aggressive with patients with with-the-rule and against-the-rule astigmatism and more aggressive with oblique astigmatism. The toric intraocular lens (IOL) should be positioned on axis or, if slightly off axis, err on the side away from the vertical or horizontal meridian so that the resultant cylinder is more vertical or horizontal. Clinically significant rotation of the toric IOL occurs in a few cases, but these can be easily rerotated. Rerotation should be done between the first and second weeks after primary implantation.

Astigmatism↗
PubMed2006

Astigmatism after mersilene and nylon suture use for penetrating keratoplasty.

PURPOSE: To evaluate postoperative astigmatism after the use of Mersilene and nylon sutures for penetrating keratoplasty. METHODS: Two groups of 12 patients each (age, 20-50 years) suffering from keratoconus underwent penetrating keratoplasty. Continuous suturing combined with 12 interrupted sutures was used in each case: Mersilene 11-0 sutures were used in group 1, whereas nylon 10-0 sutures were used in group 2. Sutures were removed to control astigmatism when required. All patients were monitored for 36 months. RESULTS: During the follow-up period, sutures were removed in each eye as indicated by astigmatism or breakage. In group 1 (Mersilene 11-0 sutures), no breakage of sutures was recorded. In group 2 (nylon 10-0 sutures), breakage of sutures was recorded in 11 of 12 cases. However, continuous sutures were removed in 2 patients in group 2. After the first year, the astigmatism remained within +/-1.00 diopter in all except 1 patient in group 1 and in 5 patients in group 2. No suture-related complications were recorded except for scarring with photophobia in 1 patient in group 1 and suture breakage in 11 eyes in group 2. CONCLUSION: Mersilene sutures can provide a stable postoperative astigmatism, whereas nylon sutures have a tendency to break and cause changes in corneal astigmatism.

Adult↗
PubMed2006

Arcuate relaxing incisions guided by corneal topography for postkeratoplasty astigmatism: vector and topographic analysis.

PURPOSE: To determine if using corneal topography for planning arcuate relaxing incision placement for postkeratoplasty astigmatism improves clinical results. METHODS: Twenty-six eyes with high levels (> 5 diopters [D]) of postkeratoplasty astigmatism were studied in a nonrandomized, retrospective, observational case series. Relaxing incisions were placed in the peripheral graft in each steep topographic hemimeridian. The following data were measured: keratometric, topographic, and refractive vector analysis; nonvector astigmatism reduction; surface regularity and asymmetry (surface regularity index and surface asymmetry index); topography patterns; surgical design; and visual acuity. RESULTS: Topographic analysis changed some aspect of the surgery in 51/52 incisions with a 15.7 degrees mean change in incision location. The mean vector correction index (CI) was 0.89 to 0.92 for keratometric, topographic, and refractive indices. Sixty-five percent of eyes had surgically induced astigmatism (SIA) values within 2 D of the surgical goal. Eighty-one percent of eyes had at least a 50% reduction in net astigmatism and 85% had < or = 3-D residual refractive cylinder. The mean logMAR visual acuity increased 2 lines. The preoperative and postoperative spherical equivalent showed a high correlation (rho = 0.914, P = 0.000). The correlation between SIA and targeted induced astigmatism (TIA) was 0.56 (P = 0.003). There was a significant improvement in surface regularity index (P = 0.000) and surface asymmetry index (P = 0.05) values. No statistically significant correlations were found between total incision length and SIA or TIA, or between TIA and correction index. All patients had symmetric (58%) or asymmetric (42%) bowtie topographic patterns preoperatively with 35% achieving round/oval patterns postoperatively. CONCLUSIONS: Topography-guided relaxing incision offers an easy method to plan surgery and has some limited advantages over conventional techniques.

Adult↗
PubMed2006

Comparison of the effect of three suturing techniques on postkeratoplasty astigmatism in keratoconus.

PURPOSE: To compare the effect of 3 common suturing techniques on postkeratoplasty astigmatism and final best corrected visual acuity (BCVA) in patients with keratoconus. METHODS: In this randomized clinical trial, 103 eyes of 103 patients with advanced keratoconus, who were contact lens intolerant, or with contact lens-corrected visual acuity less than 20/80, underwent penetrating keratoplasty with 3 suturing techniques: interrupted (IR), single running (SR), and combined interrupted and running (CIR). Postkeratoplasty astigmatism and BCVA were evaluated during regular examinations 1.5, 3, 6, and 12 months postoperatively and 2 months after complete suture removal. Suture adjustment and selective suture removal were performed 2 to 6 weeks and after 3 months in eyes with more than 4 D of corneal astigmatism in the SR and IR/CIR groups, respectively. RESULTS: Of 87 patients who completed follow-up, 26 eyes underwent PK with interrupted suturing technique (IR), 26 eyes had single running sutures (SR), and in 35 eyes, the suturing technique was combined (interrupted + running sutures; CIR). Mean age was 27.2 +/- 8.4, 28.9 +/- 8.7, and 30.3 +/- 8.7 years, and postoperative astigmatism 1.5 months after surgery was 3.77 +/- 1.68, 5.48 +/- 2.09, and 4.10 +/- 1.79 D in the 3 groups, respectively (P = 0.015). However, 2 months after complete suture removal, final postoperative astigmatism was 3.83 +/- 1.65, 3.37 +/- 1.9, and 3.88 +/- 2.79 D (P = 0.851) and BCVA (log MAR) was 0.08 +/- 0.14, 0.13 +/- 0.23, and 0.09 +/- 0.16, respectively (P = 0.53). Immunologic endothelial rejection reactions were seen in 5 eyes (19.2%) in the IR group, 3 eyes (11.72%) in the SR group, and 6 eyes (17.64%) in the CIR group (P = 0.44). There was no case of graft failure during the follow-up period. CONCLUSION: Postkeratoplasty astigmatism and BCVA are comparable with the 3 common suturing techniques (IR, SR, and CIR) in patients with keratoconus, provided that regular postoperative examinations and topography-guided suture adjustment and/or removal are performed.

Adult↗
PubMed1998

Postoperative suture manipulation for control of corneal graft astigmatism.

PURPOSE: To assess the effect on post-keratoplasty astigmatism of postoperative manipulation of a single running suture. METHODS: All corneal transplant patients in whom a single 10/0 nylon running suture was placed between November 1990 and April 1996 were included in a prospective study of the effect of manipulation of the suture at the earliest possible time after surgery when the keratometry became possible by virtue of the epithelial surface integrity and where this revealed astigmatism of greater than 2 D. RESULTS: One hundred and ninety eyes underwent suture manipulation and were followed up. Follow up on 30 eyes was discontinued. Repeat manipulation of the running suture was the most common reason for discontinuation of follow up. The remaining patients were followed for a mean (+/- SD) 415.5+/-326.4 days. Mean astigmatism of 7.8+/-3.1 D was reduced to 1.7+/-2.0 D immediately after manipulation, but regressed to 3.0+/-1.9 D (n = 76) by 1 year. The suture was removed in 32 patients. Twenty-five eyes had post-removal astigmatism measurements. In these 25 eyes, astigmatic error appeared not to revert to premanipulation levels. The only significant complication was one broken suture at manipulation. CONCLUSIONS: Early suture manipulation is effective in reducing suture in post-keratoplasty astigmatism, but some regression is seen.

Astigmatism↗
PubMed2004

Effect of hinged lamellar keratotomy on post-keratoplasty astigmatism and vision.

PURPOSE: To show that hinged lamellar keratotomy alone affects refraction and vision in post-keratoplasty eyes. METHODS: A retrospective, non-comparative, interventional case series was conducted on 28 eyes of 26 patients who had two-stage laser in situ keratomileusis (LASIK) after penetrating keratoplasty. Records were reviewed with respect to the hinged lamellar keratotomy component of the procedure. The interval between keratoplasty and keratotomy was at least 1 year, and the follow-up period averaged 29 +/- 10 days. The Automated Corneal Shaper with nasal hinge was used. In addition to basic empirical astigmatism calculations, the Alpins method of astigmatism analysis was also employed to ensure that the influence of changes in cylinder axis were correctly taken into account when calculating the refractive change. RESULTS: Surgically induced astigmatism from hinged lamellar keratotomy was not statistically significant in this series; however, the range in values (-9.06 to +7.57 D) has potential clinical ramifications. Nearly 70% of cases studied experienced surgically induced astigmatism of at least 2 D. Mean preoperative uncorrected vision was logMAR 1.06 +/- 0.41, which improved marginally postoperatively to logMAR 1.03 +/- 0.44 (P = 0.36). Best spectacle-corrected visual acuity averaged logMAR 0.21 +/- 0.16 preoperatively, improving to logMAR 0.09 +/- 0.15 (range -0.18 to 0.42) postoperatively, which was a statistically significant improvement (P < 0.01). No difference in refractive or visual outcomes was identified when those with keratoconus were compared to those with other underlying corneal disease processes. CONCLUSION: Although mean surgically induced astigmatism was not statistically significant, hinged lamellar keratotomy caused considerable changes in astigmatism in nearly 70% of post-keratoplasty eyes studied. This suggests that clinically significant inaccuracies may result if a one-stage LASIK procedure is performed on such patients. The authors suggest that reassessment of refraction after keratotomy may improve refractive outcomes.

Adolescent↗
PubMed1995

Corneal astigmatism. The effect of transverse corneal incisions.

The results of transverse or combined transverse and radial keratotomy in eyes with idiopathic corneal astigmatism (N = 11), astigmatism+myopia (N = 9) or early stages of keratoconus (N = 6) are presented. The corneal astigmatism was reduced in all our patients, the absolute reduction being significantly correlated to the degree of preoperative astigmatism (p = 0.007). In the whole study group the mean relative reduction of the corneal astigmatism was 52.7%. In eyes without keratoconus the astigmatism recorded at the last follow-up visit was very similar to that measured a few days after surgery, while greater changes occurred in the keratoconus group.

Adult↗
PubMed1979

Corneal astigmatism after cataract extraction. A comparison of corneal and corneoscleral incisions.

Corneal astigmatism after cataract surgery by way of corneal incision (C, n = 62) and corneo-scleral incision (CS, n = 61) was followed for six months. Corneal incisions were closed by continuous nylon 10--0 (7--25 loops, median 14). Corneo-scleral incisions were sutured with single knots (2--10, median value 5). Keratometric results in the C and CS groups are compared. Concerning the degree of astigmatism, pre-operative median values were 0.5 and 0.7 D, respectively. After one week they were 4.5 and 3.0 D; after two weeks 3.3 and 3.0 D; after four months 3.0 and 2.0 D; after six months (final status) 1.5 and 1.7 D, respectively. The differences between C and CS were not significant. For both, astigmatism after cataract surgery did not quite return to pre-operative levels. Concerning the axis (weaker meridian) of corneal astigmatism, the C cases retained their pre-operative distribution, while the CS cases showed the classical shift towards against-rule astigmatism. Final corrected visual acuity was of the same order in the C and CS group. Due to frequent shifts, also of the axis, it is recommended by early (preliminary) glass prescription not to correct the astigmatism, but to give only the best spherical correction.

Adult↗
PubMed2006

Prevalence and associations of anisometropia and aniso-astigmatism in a population based sample of 6 year old children.

AIM: To study the distribution of anisometropia and aniso-astigmatism in young Australian children, together with clinical and ocular biometry relations. METHOD: The Sydney Myopia Study examined 1765 predominantly 6 year old children from 34 randomly selected Sydney schools during 2003-4. Keratometry, cycloplegic autorefraction, and questionnaire data were collected. RESULTS: Spherical equivalent (SE) anisometropia (> or =1 dioptre) prevalence was 1.6% (95% confidence interval (CI) 1.1% to 2.4%). Aniso-astigmatism (>or =1D) prevalence was 1.0% (CI: 0.6% to 1.6%). Both conditions were significantly more prevalent among moderately hyperopic (SE > or =2.0D) than mildly hyperopic (SE 0.5-1.9D) children. Myopic children (SE < or =-0.5D) had higher anisometropia prevalence. Neither condition varied by age, sex, or ethnicity. In multivariate analyses, anisometropia was significantly associated with amblyopia, odds ratio (OR) 29, (CI: 8.7 to 99), exotropia (OR 7.7, CI: 1.2 to 50), and neonatal intensive care unit (NICU) admission (OR 3.6, CI: 1.1 to 12.6). Aniso-astigmatism was significantly associated with amblyopia (OR 8.2, CI: 1.4 to 47), maternal age >35 years (OR 4.0, CI: 1.3 to 11.9), and NICU admission (OR 4.6, CI: 1.2 to 17.2). Anisometropia resulted from relatively large interocular differences in axial length (p<0.0001) and anterior chamber depth (p = 0.0009). Aniso-astigmatism resulted from differences in corneal astigmatism (p<0.0001). CONCLUSION: In this predominantly 6 year old population, anisometropia and aniso-astigmatism were uncommon, had important birth and biometry associations, and were strongly related to amblyopia and strabismus.

Amblyopia↗
PubMed2003

Effects of lamellar keratotomy on postkeratoplasty astigmatism.

AIM: To determine the changes in postkeratoplasty astigmatism induced by lamellar keratotomy. METHODS: A prospective, non-randomised comparative trial of patients undergoing a hinged lamellar corneal flap for treatment of significant astigmatism after penetrating keratoplasty. Uncorrected visual acuity, best corrected visual acuity, refraction, and corneal topography were assessed at 1 and 3 months after the lamellar keratotomy. RESULTS: 17 eyes in 16 patients (13 M, 3F) were included in the study (mean age 48.2 years; range 20-86 years). Six of 17 eyes (35.3%) changed more than 1 dioptre (D) in spherical equivalent by 3 months. Nine of 17 eyes (52.9%) changed more than 1 D in sphere by 3 months. 12 of 17 eyes (70.6%) changed more than 1 D in refractive cylinder. Seven patients of 15 (46.7%) changed more than 1 D in corneal power as measured topographically. Five of 17 eyes (29.4%) changed in refractive cylinder axis more than 15 degrees and this was similar to the change measured topographically of four of 15 eyes (26.7%). Vector analysis showed 60% of eyes had a surgically induced astigmatism (SIA) vector of more than 1 D, including a net corneal astigmatism decrease of more than 1 D in four eyes and increase of more than 1 D in two eyes at 3 months after surgery. Complications of the lamellar keratotomy included two partial buttonholes and one partial wound dehiscence. CONCLUSIONS: The creation of a lamellar flap alone can have significant effects on the astigmatism following penetrating keratoplasty. LASIK for correction of postkeratoplasty astigmatism may be more accurately performed as a two stage procedure rather than a single stage, after the corneal effects of the lamellar keratotomy have stabilised.

Adult↗
PubMed2006

Amniotic membrane corrects surgically induced astigmatism.

Human amniotic membrane (AM) has been widely used for the reconstruction of ocular surface. We conducted this study to investigate whether AM shows efficacy in maintaining the correction of astigmatism or not. We performed photoastigmatic refractive keratectomy (PARK) on rabbits and grafted AM on the cornea. The effect of AM on the degree of astigmatism was evaluated by topography and cycloplegic refraction. As will be shown, AM did not show any efficacy in maintaining the correction of astigmatism. On the contrary, AM not only eliminated PARK-induced astigmatism but prevented surgically induced astigmatism. We suggest that AM could be a useful tool for controlling the astigmatism induced by laser refractive surgery. Further clinical study is still left to be elucidated.

Amnion↗
PubMed2003

Cost-efficient vision screening for astigmatism in native american preschool children.

PURPOSE: To design and test a cost-efficient, community-based vision screening program for a population of Native American preschool children in which there is a high prevalence of astigmatism. METHODS: Based on analysis of vision screening and eye examination data from a preschool population with a 33% prevalence of astigmatism, comparative costs to conduct a 1000-child screening program with a target sensitivity of 90% were estimated for photoscreening, noncycloplegic autorefraction, autokeratometry, and Lea symbols distance visual acuity testing. Results of the cost analysis and examination of sensitivity and specificity data from the preschool population led to development of a hybrid screening program of autokeratometry and visual acuity screening with referral thresholds of 2.25 D of corneal astigmatism or inability to read a 20/63 Lea symbols line on two separate attempts. The screening program was prospectively implemented in a community-based screening of a similar cohort of 167 children, and its efficiency was evaluated by comparison to results of cycloplegic refraction. RESULTS: The community-based screening showed 96.8% sensitivity and 79.2% specificity for detecting the presence of refractive astigmatism of 1.50 D or more. CONCLUSIONS: Referring children who have at least 2.25 D of corneal astigmatism or acuity worse than 20/63 on two attempts, provides the high sensitivity and specificity associated with automated keratometry while maintaining an acuity component that can detect other causes of reduced acuity in the absence of astigmatism.

Astigmatism↗
PubMedDate not supplied

Prevalence of astigmatism among students in northern Greece.

PURPOSE: To assess the prevalence of astigmatism in a sample of 1738 students (15-18 years old) from Northern Greece. METHODS: Collection of the sample was based on a questionnaire method. Statistical analysis included estimation of the prevalence of astigmatism and the distribution of students according to their cylindrical values. We also checked whether heredity or sex affected the occurrence of astigmatism. RESULTS: The prevalence of astigmatism was 10.2%. It was mostly at low levels, up to 2 D cyl. Females ran a significantly higher risk of astigmatism than males, and heredity seemed to be an important predisposing factor for this refractive error. CONCLUSIONS: There is considerable variability in the prevalence of astigmatism worldwide, as indicated by different studies. However, this refractive error prevails at low levels in the Greek student population, compared with other countries.

Adolescent↗
PubMedDate not supplied

Compound myopic astigmatism correction using a mask in-the-rail excimer laser delivery system. Preliminary results.

PURPOSE: The latest development in the erodible mask technology is an excimer laser containing the mask in the laser optical pathway. This paper reports the results of the first human series of consecutive treatments performed for the correction of compound myopic astigmatism. METHODS: We have treated 83 eyes. Spherical equivalent attempted correction ranged between -1.75 and -11.75 D (mean -7.07+/- 2.45 D), astigmatic attempted correction ranged between -1.00 and -5.00 D (mean -2.42+/- 1.02 D). The sphere correction was made by diaphragm using a multi-zone software with three ablation zones: 100% of the total attempted correction for the central 5.0 mm zone, 70% for the second 6.0 mm zone, 30% for the outer 6.5 mm zone. Cylinder correction was made sequentially after myopic correction using the appropriate mask. RESULTS: One month after treatment, mean refractive error was + 1.07 +/- 1.24 D (range + 4.50/-1.75 D) for spherical equivalent, and -0.49 +/- 0.57 D (range + 0.75/-2.00 D) for astigmatism. Forty-eight eyes (57.8%) had uncorrected visual acuity of 20/40 or better. At six months, mean refractive error was +0.42 +/- 0.97 D (range + 3.75/-1.00 D) for spherical equivalent, and -0.44 +/- 0.51 D (range +0.25/-3.00 D) for astigmatism. Vector analysis showed that 57 eyes (68.7%) had 5 or less degrees rotation. Seventy-two (86.7%) and 54 eyes (65.1%) had uncorrected visual acuity equal or better than 20/40 and 20/25 respectively. One eye (1.2%) showed a best corrected visual acuity loss of more than one line, but 8 eyes (9.6%) had a gain of more than one line. One-year results on a smaller series (33 eyes) overlap with the six-month results. CONCLUSIONS: The mask in-the-rail excimer laser delivery system appears to be effective and predictable in the correction of compound myopic astigmatism. We observed no significant regression of the astigmatic correction over time. Longer follow-up on larger series is necessary to draw final conclusions.

Adolescent↗
PubMedDate not supplied

Comparative study of astigmatism through superior and lateral small incisions.

PURPOSE: To prospectively compare the clinical results of two cataract surgery procedures through a 4.0-mm incision, differing only in the wound location (superior or lateral). METHODS: 168 eyes with cataract were randomly assigned to either procedure. Except for incision location, surgical methods were identical. Uncorrected visual acuity, keratometry and postoperative astigmatism were analyzed up to six months for after surgery. RESULTS: Both groups had similar uncorrected visual acuity. Eyes in the superior incision group had significantly larger "against-the-rule" changes than those in the lateral incision group, and differences were significant at all measurement points from one week through six months after surgery. Patients with preoperative "with-the rule" astigmatism had smaller postoperative astigmatism after a superior incision and those with preoperative "against-the rule" astigmatism had less postoperative cylinder after a lateral incision. Differences between these groups were significant. CONCLUSIONS: Both procedures gave satisfactory clinical results. Postoperative astigmatism could depend on the preoperative astigmatism and the wound location.

Aged↗
PubMed1996

Distribution of astigmatism in the adult population.

We have quantified statistically the astigmatic frequency distribution. Vectorial analysis was used, as it enables formal multivariate statistical techniques to be applied to astigmatic data, allowing the simultaneous inclusion of both modulus and axis in the analytical procedure. These methods were applied to population data for each of total, corneal, and residual astigmatism from a sample of 198 adults. Right and left eyes were analyzed separately. All the distributions were found to depart significantly from a normal distribution. All the distributions were significantly leptokurtic (p < 0.005), and the distributions of total right eye, corneal right eye, and residual left eye astigmatism were also found to be significantly skewed (p < 0.05). Significant mild correlations were found between total and corneal astigmatism (p < 0.05). These findings add to the database of knowledge of astigmatic refractive error and may be of interest to those investigating refractive-error development.

Adolescent↗
PubMedDate not supplied

Changes in astigmatism after congenital cataract surgery and foldable intraocular lens implantation.

PURPOSE: To evaluate the changes in astigmatism after cataract extraction and implantation of a foldable intraocular lens (IOL) in children. Only eyes with astigmatism of 3.0 D or more were included in the study. METHODS: The charts of children who had undergone surgery for nontraumatic cataract using a foldable IOL were retrospectively reviewed. In 13 eyes with astigmatism of 3.0 D or more, the refraction was tested and recorded at 1 week, 3 months, and 5 months postoperatively. A paired t test was used to compare the variables. RESULTS: Mean astigmatism 1 week postoperatively was 4.7 +/- 1.9 D (range, 3.0-10.0 D). Thereafter, the astigmatic component of the refractive error underwent a spontaneous steady decline, reaching a mean value of 0.9 +/- 0.9 D (range, 0-2.25 D) 5 months after surgery. The difference between the mean values at 1 week and 5 months was statistically significant (P < .0001). CONCLUSION: Children who underwent congenital cataract surgery and IOL implantation showed a significant spontaneous reduction in astigmatism postoperatively.

Astigmatism↗