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PubMed1997

Determination of the influence of effectivity upon residual astigmatism.

PURPOSE: A computing scheme is described which allows determination of the astigmatic contribution of ocular surface effectivity towards residual astigmatism. METHODS: This involves paraxial raytracing through astigmatic surfaces at random axes and applies the principle of astigmatic decomposition. Calculations are shown for averaged data from 66 normal right eyes. Frequency distribution graphs demonstrate individual variations. RESULTS: The averaged ratio of corneal thickness:anterior chamber:lens thickness cylinder power contributions due to effectivity (1:5:17) did not match the ratio of their respective intraocular distances (1:7:7); a disproportionate amount of astigmatism arose from lens thickness effectivity. Although previous research has revealed that results for individual eyes are prone to accummulative experimental errors, frequency distribution graphs indicate that effectivity predominantly yelds direct astigmatism (axis 180 degrees +/- 22.5 degrees). CONCLUSIONS: This computing scheme offers a means of examining the functional ocular morphology of astigmatic eyes.

Adolescent↗
PubMed2004

Late onset post-keratoplasty astigmatism in patients with keratoconus.

AIM: 10 eyes of 10 patients are reported where progression of keratoconus in the host cornea occurred more than 10 years after penetrating keratoplasty with resultant increase in astigmatism. The technique and results of graft refractive surgery in seven eyes are presented. METHODS: The clinical features and management of these patients were retrospectively analysed. Graft refractive surgery involved an incision at the graft-host junction adjacent to the host thinning with compressive resuturing. Astigmatic changes were calculated using vector analysis. RESULTS: There were seven men and three women with a mean age of 41.2 years. The average age when undergoing penetrating keratoplasty in the affected eye was 28.4 years and the average time after penetrating keratoplasty until keratoconus appeared in the host cornea defined by host thinning was 13.5 years. The mean cylinder power before host thinning was noted was 5.07 D (SD 2.19) and the mean after host thinning was 11.0 D (2.53). The mean vector calculated disease induced astigmatism magnitude was 7.59 D (3.09). Graft refractive surgery was performed in seven eyes. The mean cylinder power before and after graft refractive surgery was 11.28 D (2.15) and 7.09 D (5.53) respectively. The surgically induced astigmatism vector magnitude was 7.36 D (4.88). CONCLUSION: Progression of keratoconus in the host cornea late after penetrating keratoplasty is characterised by a large astigmatic change where the flat axis of astigmatism passes through an area of host thinning visible on slit lamp examination. Compressive resuturing performed in the area of host thinning resulted in satisfactory reduction of astigmatism.

Adult↗
PubMed2004

Astigmatism in Chinese preschool children: prevalence, change, and effect on refractive development.

AIM: To study the prevalence, type, and progression of astigmatism in Chinese preschool children, and its effect on refractive development. METHODS: A cross sectional study of preschool children was carried out in two randomly selected kindergartens. A cohort study was performed on a subset of children, five years after initial examination. Refractive error (measured by cycloplegic autorefraction) and axial ocular dimensions (measured by ultrasonography) were the main study outcomes. RESULTS: 522 children participated in the study; the mean age was 55.7 months (SD 10.9; range 27 to 77). Mean cylinder reading was -0.65 D (SD 0.58; range 0.00 to -4.75), and with the rule astigmatism was predominant (53%). In the 108 children studied longitudinally, the mean cylinder reading reduced from -0.62 D to -0.50 D (p = 0.019). The presence of astigmatism in initial examination predisposed the eyes towards greater myopisation (p<0.001). In addition, children with increased astigmatism had greater myopic progression (p<0.001) and axial length growth (p = 0.002). CONCLUSIONS: This study reports a high prevalence of astigmatism in Chinese preschool children. The presence of astigmatism, and particularly with increasing astigmatism, appears to predispose the children to progressive myopia. Further studies are warranted.

Analysis of Variance↗
PubMed1988

Changes in astigmatism between the ages of 1 and 4 years: a longitudinal study.

Changes in astigmatism during development were studied in 299 infants with astigmatism as they grew from 1 to 4 years of age. All consecutive cases of 1-year-old infants with an astigmatism of 1.0 D or more in at least one eye found at an ophthalmic screening survey were selected for follow-up. The cycloplegic refraction was longitudinally followed at yearly intervals. During development there was no decrease in the degree of hypermetropia, but there was a significant decrease in the incidence and amount of astigmatism during the test period. The most pronounced decrease in magnitude and incidence of astigmatism occurred between the first and second year of life. The majority of astigmatic eyes of the 1-year-old infants had a horizontal curvature greater than the vertical (plus cylinder axis of 180 degrees), and no changes of the axis of the astigmatism were noted during the following years.

Aging↗
PubMed1988

Control of astigmatism in cataract surgery.

A study is reported on cataract surgery, with intraocular lens implant, with measurement of the preoperative astigmatism and of the postoperative astigmatism over 28 weeks. Nine interrupted 10/0 nylon sutures are used to close a limbal section. Preoperative astigmatism is compensated for in the method of suturing by the placement of additional sutures. Postoperatively sutures are cut in line with the plus cylinder axis in eyes showing excessive astigmatism with the rule. Final postoperative astigmatism is controlled within 2.25 D cyl. 68% of cases lie within 1.0 D cyl with the rule to 1.0 D cyl against the rule. The average case in which sutures are not cut is one having 1.51 D cyl with the rule at one week postoperatively, declining to zero at approximately 12 weeks, and having a final value of 0.17 D cyl against the rule. No significant change in cylinder is seen after 10 weeks. The final postoperative astigmatism is only weakly correlated with the preoperative astigmatism, showing that the surgical method is effective. The spherical equivalent error is shown to shift in the direction of myopia in the postoperative period.

Astigmatism↗
PubMed2000

Arcuate relaxing incisions with a 5.00-mm optical zone for the correction of high postcataract astigmatism.

The purpose of this study was to investigate the efficacy and safety of arcuate cuts with a 5-mm optical zone to correct high postoperative astigmatism after extracapsular cataract extraction. We performed 5-mm optical zone arcuate cuts on 23 eyes of 23 patients with high postoperative astigmatism. Ophthalmic examination included uncorrected visual acuity (UCVA), best spectacle corrected visual acuity (BSCVA) and the amount of the refractive and keratometric cylinder before and 9 months after operation. Surgically induced refractive change was calculated in all cases. A significant reduction in astigmatism was achieved in all cases with minimal axis deviation. No case developed clinically significant irregular astigmatism. The mean magnitude of astigmatism of the surgically induced refractive change calculated from standard keratometry and refractive data was 3.73+/-0.72 and 3.70+/-0.77 dptr, respectively. The mean axis deviation calculated from the keratometric and refractive data was 1.18+/-2.33 and 1.32+/-3.62 degrees, respectively. At the last examination, 78.2% of the eyes had UCVA of 20/40 or better. No eye lost more than two lines of vision, 6 eyes lost one line, 2 eyes gained one and 1 eye gained two lines of BSCVA. The above data show that the 5-mm optical zone arcuate astigmatic keratotomy is an effective and safe method of correcting high postoperative astigmatism.

Adult↗
PubMed1991

[Changes in postoperative corneal astigmatism after laser dissection of corneo-scleral sutures].

In a group of 68 consecutive cases of high surgically induced corneal astigmatism following extracapsular cataract extraction or phacoemulsification, single limbal sutures were released by argon laser. Visual acuity and refractive results 2-6 weeks after treatment were compared to those before laser application. The effect of suture dissection was analyzed according to the number of sutures released, the follow-up time from cataract surgery and previous corneal astigmatism. The effect of suture dissection was not dependent on the interval from surgery up to 20 weeks postoperatively. The reduction in astigmatism amounts 2.25 dptr up to 8 weeks, occasionally 2.5 dptr 8-10 and 11-16 weeks after surgery, and 1.75 dptr up to 20 weeks thereafter (mean values). The longer the interval the more sutures had to be released. If only one suture was dissected, the reduction in astigmatism amounted 1.75 dptr (mean), if two sutures were released the effect was 2.5 dptr, three or more dissected sutures lead to a 3.4-dptr reduction in corneal astigmatism. The axis of astigmatism did not change in 52 of 59 cases, but in some subjects oblique astigmatism appeared after suture dissection.

Astigmatism↗
PubMed1994

Against-the-rule astigmatism judged at one week after phacoemulsification and aspiration procedures.

To determine the characteristics of astigmatism 1 week postoperatively or whether the final astigmatism is predictable from that present 1 week postoperatively, we analyzed 544 postcataract against-the-rule (AR) cases of astigmatism among 1,649 standard phacoemulsification cataract operations, all utilizing 10-0 Mersilene in double-running fashion. Postoperative AR astigmatism < or = 1.0 dpt increased markedly 1 week postoperatively (2.72 +/- 0.09 dpt) but decreased 6 months postoperatively. However, in postoperative AR astigmatism > 2.0 dpt, the increase 1 week postoperatively was not as great (2.16 +/- 0.13 dpt) but tended to continue to increase even 6 months postoperatively, with a flatter corneal curvature being the responsible factor. Eyes with less astigmatism 1 week postoperatively showed exacerbation of final astigmatism 6 months postoperatively. This course was different from that of small incision cataract surgery.

Aged↗
PubMedDate not supplied

Comparison of keratometric and topographic cylinder and axis measurements on normal corneas with low astigmatism.

PURPOSE: To evaluate agreement in measurements of astigmatic axis power and location between keratometry and computer assisted videokeratography (corneal topography) on normal corneas with less than 1.50 D of idiopathic astigmatism. METHODS: Keratometric readings with the 10 SL/O Zeiss ophthalmometer and corneal topographic maps with the TMS-1 were obtained by two independent examiners on 32 normal corneas. Measurement agreement between the two instruments was evaluated in regard to steep and flat meridian power and location, and in astigmatism magnitude (D). RESULTS: The limits of agreement (d-2 SD to d+2 SD) between the two instruments were found to be broad for clinical purposes in measuring the steep meridian power (-0.16 to -1.20 D), flat meridian power (0.43 to -1.25 D), and astigmatism (0.60 to -1.12 D). A constant bias of the TMS-1 towards the 10 SL/O Zeiss ophthalmometer was found, in measuring steeper both principal meridians and higher amount of astigmatism. Mean location difference was 19 degrees (+/-190) for the steep meridian and 17 degrees (+/-20 degrees) for the flat meridian. CONCLUSIONS: Despite the differences seen in measurements between the 10 SL/O ophthalmometer and the TMS-1, these differences may be clinically small enough for the methods to be used interchangeably in measuring only the magnitude of astigmatism on normal corneas. However, the disagreement in astigmatism axes is too great to be ignored.

Adolescent↗
PubMed2003

Dynamic accommodation response in the presence of astigmatism.

It has been suggested that in the presence of astigmatism some individuals make cyclic changes in focus over the astigmatic interval to obtain better visual performance. The aim in the present study was to identify such cyclic accommodative behavior and to characterize the variability of the response in the presence of astigmatism. The dynamic accommodation response in the presence of induced astigmatism was recorded objectively with an infrared optometer in seven young adults. Astigmatism led directly to increased accommodative variability in certain individuals. In two of seven participants there was evidence for aperiodic cyclic accommodative responses between different portions of the astigmatic interval. However, the amplitude of these tracking responses was much smaller than the astigmatic interval.

Accommodation, Ocular↗
PubMedDate not supplied

Posterior polymorphous dystrophy associated with astigmatism and amblyopia in children.

BACKGROUND: Posterior polymorphous dystrophy has been described in the scientific literature as having more than a casual association with keratoconus in adults. We studied four consecutive children with posterior polymorphous dystrophy who had coexisting astigmatism. In our patients, the posterior changes appeared to be associated with the corneal astigmatism, as evidenced by videokeratography. METHODS: Four consecutive cases of posterior polymorphous dystrophy in children were found over a 3-year period by one of the authors (PD). They presented with varying degrees of amblyopia in the eyes with the greater amount of posterior polymorphous dystrophy. Cycloplegic refractions and keratometry readings were performed. The more affected eyes had greater degrees of astigmatism, presumably causing the amblyopia. Whenever possible, the results were supplemented by confirmation by a corneal specialist, specular microscopy, slit-lamp photographs and videokeratography. RESULTS: Greater asymmetry of posterior polymorphous dystrophy was associated with greater astigmatism in the more affected eye. When more astigmatic anisometropia was present there was a greater amblyopia. Videokeratography of one of the patients showed that an area of confluent blebs forming a crescent shape compared exactly with a steep cylinder along the same axis. With-the-rule astigmatism was associated with a more diffuse pattern of blebs. CONCLUSION: Decreases in visual acuity in children with posterior polymorphous dystrophy may sometimes be due to an amblyopia caused by the astigmatism of asymmetric disease.

Amblyopia↗
PubMedDate not supplied

Repeatability and validity of astigmatism measurements.

BACKGROUND: As more patients inquire about refractive surgical procedures, the measurement of astigmatism prior to surgery becomes more important in assessing refractive outcome. Knowledge of the repeatability of the astigmatism measurement allows one to distinguish a true change in cylinder power from measurement error. METHODS: Forty adults with structurally normal eyes and refractive errors were evaluated for the repeatability of astigmatic refractive error measures. Noncycloplegic and cycloplegic measurements of refractive astigmatism were made by retinoscopy, subjective refraction, and autorefraction. All measures were made at 2 visits within 2 weeks by the same examiner. Difference versus mean plots and the 95% limits of agreement of each technique determined the repeatability of a measurement and the agreement between the methods of measurement. RESULTS: The most reliable measure of astigmatic refractive error was cycloplegic autorefraction, with 95% limits of agreement of +/- 0.28 D, followed by noncycloplegic autorefraction (+/- 0.35 D) and cycloplegic subjective refraction (+/- 0.44 D). Noncycloplegic retinoscopy was the least reliable astigmatic refractive error measure, with interoccasion 95% limits of agreement of +/- 1.02 D. The most repeatable measurement of cylinder axis was cycloplegic autorefraction; none of the measurements differed by 10 degrees or more. The least repeatable measurement was noncycloplegic retinoscopy; 40% of the measurements differed by 10 degrees or more. CONCLUSION: For studies seeking to measure changes in astigmatism in normal eyes, cycloplegic autorefraction is the method of choice.

Adult↗
PubMedDate not supplied

Relaxing incision guided by videokeratography for astigmatism after keratoplasty for keratoconus.

PURPOSE: To evaluate the efficacy of topographic measurements for relaxing incisions in astigmatism following penetrating keratoplasty for keratoconus. METHODS: Twenty patients (20 eyes) had relaxing incisions between July 1989 and August 1994 for high astigmatism after penetrating keratoplasty for keratoconus. Ten eyes were evaluated using a HaagStreit keratometer (1989-1991) and 10 eyes were evaluated using EyeSys videokeratography (1991-1994). Relaxing incisions were performed at the steep meridians in the donor/host wound. RESULTS: Mean preoperative astigmatism was 7.75 +/- 2.05 D (range, 4.50 to 12.00 D) for the keratometry group, and 6.49 +/- 3.24 D (range, 1.11 to 10.13 D) for the videokeratography group. Mean astigmatism following relaxing incision was 3.90 +/- 2.02 D (range, 0.93 to 6.50 D) for the keratometry group and 3.06 +/- 1.62 D (range, 0.07 to 5.64 D) for the videokeratography group (no significant difference). Vector analysis revealed a vectorial change of 4.64 +/- 2.54 D for the keratometry group and 4.68 +/- 2.08 D for the videokeratography group (no significant difference). Mean spectacle-corrected visual acuity was significantly improved in the topography-guided group following the procedure (P = .021). Complications included perforations in 3 of 20 eyes. Four patients (4 eyes) in the keratometry group and one patient (1 eye) in the videokeratography group had residual astigmatism greater than 5.00 D. Four patients in the keratometry group needed a second procedure of relaxing incision because of irregular (2 eyes) or high (2 eyes) astigmatism. One patient (1 eye) in the videokeratography group needed a second relaxing incision. CONCLUSIONS: Videokeratography as a guide for relaxing incision has some benefits over standard keratometry. Preoperative evaluation with videokeratography did not significantly improve the postoperative astigmatism. Fewer reoperations were needed when videokeratography was used.

Adolescent↗
PubMed2006

Sequential ablation approach to the correction of mixed astigmatism.

PURPOSE: To evaluate the safety, efficacy, and stability of LASIK, using positive cylinder and negative sphere nomograms in sequence (sequential ablation) to correct mixed astigmatism. METHODS: This prospective study included 40 eyes of 20 patients with mixed astigmatism. Patients underwent bilateral sequential ablation LASIK using the Technolas 217 excimer laser (Bausch & Lomb Surgical, Rochester, NY). The main outcome measures, uncorrected visual acuity (UCVA) and best spectacle-corrected visual acuity (BSCVA), were evaluated 3 and 12 months after surgery. RESULTS: Preoperative astigmatism ranged from +1.75 to +6.00 diopters (D) and negative sphere from -0.50 to -3.00 D. The postoperative refraction at 3 months remained unchanged at 1 year postoperative in all patients. A total of 32 (80%) eyes showed no significant residual astigmatism (<0.50 D); the remaining 8 (20%) eyes had 0.50 to 1.00 D of residual astigmatism. Residual negative sphere was present in 2 eyes of 2 patients with a planned monovision target. In the remaining 38 (95%) eyes, no significant residual negative sphere was present. Sixteen (40%) eyes had one line of improvement in BSCVA. No eye lost lines of visual acuity. The efficacy index shows that uncorrected vision after surgery is equal or better than corrected vision before surgery. Less corneal tissue is removed and fewer laser spots are required compared to other techniques for the correction of mixed astigmatism. CONCLUSIONS: The sequential ablation approach to the correction of mixed astigmatism was efficacious, safe, and stable 1 year after surgery.

Adult↗
PubMed2006

The LADAR6000: results in highly myopic and highly astigmatic eyes.

PURPOSE: To investigate the early clinical outcomes of the Alcon LADAR6000 system in treating two difficult patient populations: those with high myopia and those with high astigmatism. METHODS: Two series of eyes were of interest and subsequently enrolled in the study. Thirty-three eyes with preoperative manifest refraction spherical equivalent (MRSE) > -6.00 diopters (D) (high myopia group) and 25 eyes with preoperative myopic astigmatism > -1.50 D (high myopic astigmatism group) were enrolled. Mean patient age was 35 years in the high myopia group and 33 years in the astigmatism group. For the high myopia group, the mean preoperative MRSE was -8.13 D (range: -6.25 to -12.5 D). For the high myopic astigmatism group, the mean preoperative astigmatism was -1.89 D (range: -1.50 to -4.50 D). All LASIK flaps were made using a femtosecond laser with superior hinge position. Stromal ablation was performed using the LADAR6000 system for conventional treatment. All eyes were targeted for emmetropia. RESULTS: Both groups of eyes experienced excellent clinical outcomes with 100% of eyes within +/-1.00 D of attempted correction at 1 month. For the high myopia group, mean postoperative MRSE was -0.10 D at 1 month. For the high myopic astigmatism group, mean postoperative MRSE was -0.06 D at 1 month. CONCLUSIONS: The LADAR6000 system produced excellent early clinical outcomes in two challenging patient groups using LASIK with femtosecond laser flaps.

Adult↗
PubMed1998

[The evolution of corneal astigmatism after cataract surgery].

The study is a prospective one based on the observations of 186 eyes. The preexisting astigmatism was measured and the patients were divided in two main groups based on this astigmatism: by-the-rule and against-the-rule astigmatism. I evaluated the effects on the corneal astigmatism of different types of cataracts surgical procedures. The measurements sustain the results published in the specialty literature. By-the-rule astigmatism increases post-operatively and decreases in time, passing in an against-the-rule astigmatism. Against-the-rule astigmatism passes into an by-the-rule one and in the final he regains his previous type.

Adolescent↗
PubMed2000

[Postoperative induced astigmatism].

PURPOSE: Is to evaluate the astigmatism induced by cataract surgery, ethiological factors and ways of prophilaxies and treatment. MATERIAL AND METHOD: We followed a number of 211 eyes operated for cataract by planned extracapsular extraction with intraocular lens implantation, in Ophthalmological Clinic from Cluj-Napoca. All the pacients had limbal incision and the suture was performed with 9.0 suture, after the operation the treatment consisted in local drops with steroids. REZULTS: The astigmatism induced by the surgery was direct in 53.08% of cases and indirect in 46.92%. The position of the axes was 0-900 in 72.51% and oblique in 27.48%. The optical correction of astigmatism was with combined spherocylinder glases in 57.34% and only with cilinder in 42.65% of cases. CONCLUSIONS: 1. The induced astigmatism by cataract surgery is in relation with the incision, suture and IOL. 2. Correction of astigmatism is possible with optical correction, repearing the suture or with refractive surgery. 3. The prevention of astigmatism over 1.5 D is by using Troutmann keratometer and to evidence the congenital astigmatism.

Adolescent↗
PubMedDate not supplied

Clinically significant corneal astigmatism and pars plana vitrectomy.

PURPOSE: To report a rare and previously unappreciated potential wound-related complication of repeat pars plana vitrectomy (PPV) combined with anterior segment surgery. METHODS: From a total of 135 patients who had undergone PPV over a period of 15 months, 7 patients were identified on the basis of a visually disabling degree of astigmatism persisting at 3 to 4 months following their surgery. These patients were retrospectively studied from the standpoint of the numbers and combination of procedures they had experienced. Videokeratoscopy was employed as an objective method of documenting the astigmatism. RESULTS: The average astigmatism at the corneal plane in these 7 eyes was 4.5 diopters (D). In the 5 patients who required suture lysis for visual rehabilitation, the average corneal astigmatism was slightly greater than 5.0 D. In all cases, the astigmatism was a symmetric "bow-tie" pattern and was in the meridian corresponding to the superonasal and inferotemporal sclerotomies. All 5 of the patients requiring suture lysis had undergone repeat PPV through the same sclerotomies; all had their astigmatism reduced to an average of 1.5 D. CONCLUSION: Visually disabling astigmatism present months after surgery is almost certainly a rare, wound-related complication of PPV, but remains a previously unappreciated possibility in eyes undergoing repeat procedures through the same sclerotomies. Videokeratoscopy provides a reliable and rapid method of detection, while suture lysis in the steep axis represents a simple remedy.

Aged↗