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PubMed1983

Astigmatism following retinal detachment surgery.

Eighty-three patients on whom successful retinal detachment had been performed were studied to note astigmatic changes following surgery. In the majority of cases the errors following such surgery are of no great clinical importance. However, in some situations a high degree of astigmatism may be produced. This study showed that these sequelae are particularly likely after radial buckling procedures, and surgeons favouring these techniques should be aware that astigmatic errors can be induced. The astigmatic errors may persist for several years after surgery.

Astigmatism↗
PubMed1986

Corneal astigmatism following cataract extraction.

The changes in corneal curvature in the first six months after cataract extraction were studied by performing sequential keratometry on a group of 57 patients. 8/0 Virgin silk interrupted sutures were used for the closure of corneoscleral incisions, and 10/0 monofilament tied in double running (bootlace) or single running (continuous) fashion was used for corneal wound closure. A high degree of with-the-rule astigmatism was evident in all patients two weeks postoperatively, but thereafter the character of the astigmatism produced by 8/0 virgin silk and 10/0 monofilament closure was quite different: in the 8/0 virgin silk group there was an early and pronounced shift in the axis of astigmatism to against-the-rule, whereas in the 10/0 monofilament group there was little further change in the astigmatism unless the sutures were removed. Wound compression and wound gape as factors responsible for these changes are discussed.

Astigmatism↗
PubMed1990

Optic nerve hypoplasia and astigmatism: a new association.

Thirty-one patients with optic nerve hypoplasia (ONH) or septo-optic dysplasia and two patients with segmental ONH underwent retinoscopy. The results were compared with those of 20 normal subjects. There was a higher prevalence of astigmatism in the patients than in the controls. Two patients with segmental ONH had no evidence of astigmatism. The association of astigmatism with ONH has not hitherto been reported. The close association of ONH with astigmatism highlights the importance of performing careful retinoscopy in children with ONH or septooptic dysplasia in order to identify and correct errors of refraction, thereby optimising visual function and diminishing the likelihood of the development of superadded amblyopia.

Adolescent↗
PubMed2005

Effects of corneal thickness, curvature, astigmatism and direction of gaze on Goldmann applanation tonometry readings.

BACKGROUND: The aim of this study was to evaluate the impact of various sources of error in Goldmann applanation tonometry (GAT). OBJECTIVES: We evaluated the effect of corneal thickness, curvature, astigmatism and direction of gaze as sources of error in GAT. METHODS: Orbscan-II (Bausch & Lomb, Inc., Rochester, N.Y., USA) examinations were made on 30 healthy subjects and 9 keratoconus patients, and the intraocular pressure (IOP) was measured with GAT centrally, temporally and inferiorly, with the tonometer prism set horizontally and vertically. Orbscan-II images from 50 younger subjects and 49 older subjects were analysed retrospectively. RESULTS: IOP was lower on nasal gaze (p = 0.009) but higher on upward gaze (p < 0.001) compared with forward gaze. IOP and the corneal thickness were independently correlated (R(2) = 0.04; p = 0.003), as were the difference in astigmatic vector in the horizontal and vertical meridians and the difference in IOP measured with a horizontal and vertical prism (R(2) = 0.17; p < 0.001). No correlation between IOP and corneal curvature was found. In the keratoconus patients, IOPs were generally low, with large astigmatic differences. CONCLUSIONS: Corneal thickness, astigmatism and direction of gaze are clinically important sources of error in GAT. IOP should preferably be measured with the prism both horizontally and vertically. If only one direction is chosen, a vertical prism is less sensitive to different directions of gaze. Direction of gaze should be carefully monitored, especially in an irregular cornea.

Adult↗
PubMed1992

Astigmatism after phacoemulsification and aspiration procedures: BENT versus standard incisions.

We examined the induction and spontaneous regression of corneal astigmatism among 1,023 phacoemulsification and aspiration (PEA) cataract surgeries performed with standard (n = 831) and BENT incisions (n = 192). The BENT (between 9 and 12 o'clock) incision is a method of entering the anterior chamber from the oblique side. In the BENT group, the degree of astigmatism was not significantly different from the standard group, 3 months postoperatively (1.48 +/- 0.07 vs. 1.25 +/- 0.04 dptr.) and 6 months postoperatively (1.30 +/- 0.06 vs. 1.28 +/- 1.28 +/- 0.06 dptr.). However, 1 week and 1 month postoperatively, the astigmatism resulting from the BENT incision was much less than that of the standard PEA incision (1.69 +/- 0.17 vs. 2.96 +/- 0.05 and 1.60 +/- 0.08 vs. 1.80 +/- 0.05 dptr, respectively). Visual acuity also improved faster. The BENT procedure is recommended, because it is a simple way to lessen astigmatism.

Aged↗
PubMedDate not supplied

[Refractional astigmatism prevalence and its relationship with grating acuity in children 2 to 36 months of age].

PURPOSE: To evaluate refractional astigmatism prevalence and its relationship with grating acuity in a cohort of non-verbal children. METHODS: 482 normal children, aged from 2 to 36 months, were submitted to ophthalmological examination. Fourteen subjects were excluded due to ocular disease and the sample remained with 468 subjects (936 eyes); 230 (49%) males e 238 (51%) females. Grating acuity was assessed binocularly and monocularly with Teller acuity cards. All children underwent eye examination including cycloplegic retinoscopy and fundus by indirect ophthalmoscopy. RESULTS: Astigmatism was found in 222 (47.43%) of the children, with the hyperopic and with the rule types most frequently found in all ages. Concerning magnitude, this condition was equal or greater than 1.00 cylindric diopter in 24.35% of the children; equal or greater than 2.00 cylindric diopter in 5.55%; lower than 1.00 in 26.92% and between 1.00 and 2.00 in 18.73%. Grating acuity was normal in 219 of the subjects, despite magnitude, type and orientation of astigmatism. CONCLUSION: Visual acuity assessed by the acuity card procedure was not influenced by astigmatism.

Astigmatism↗
PubMed1993

Excimer laser photorefractive keratectomy for astigmatism.

The effectiveness of excimer laser photorefractive keratectomy (PRK) for astigmatism was evaluated. We treated 136 eyes of naturally occurring myopic astigmatism using the 193-nm excimer laser with an expanding slit and an iris diaphragm, and followed for a minimum of 6 months. At 6 months after operation, the mean refractive cylinder decreased from 1.62 +/- 0.88 D preoperatively to 0.48 +/- 0.48 D. For detailed analysis of the results, the surgically induced refractive change (SIRC) was determined from the preoperative and postoperative refractions by vector analysis of astigmatism. When we compared the cylinder of the SIRC with the preoperative refractive cylinder, the effect of the cylindrical ablation was 93.9 +/- 36.7% at 6 months. The axial error of the cylinder of the SIRC to the preoperative cylindrical axis was 5.9 +/- 10.2 degrees at 6 months. These results suggest that excimer laser PRK with an expanding slit appears to have a significant effect for the correction of astigmatism.

Adult↗
PubMed1997

Epiblepharon of the lower eyelid: classification and association with astigmatism.

To determine a classification system for epiblepharon of the lower eyelid and to evaluate a possible correlation between lower lid epiblepharon and astigmatism. Three morphologic characteristics (skin fold, cilia touching the cornea and corneal erosion) were observed by slit-lamp biomicroscopic examination and Polaroid pictures in 186 eyes of 102 patients with epiblepharon of the lower lid. In 112 eyes, cycloplegic refractions performed. A classification system reflecting the severity of epiblepharon was then sought, and the incidences and type of astigmatism were evaluated. Epiblepharon of the lower lid could be classified according to the height of skin fold, the area of cornea touched by cilia and the area of corneal erosion. There was significant agreement between these three classifications. The incidence of astigmatism of 0.5D or more was 54%; most was 'with-the-rule', regardless of a patient's age. In addition to the representative nature of other characteristics, skin fold height can be easily measured without the need for slit-lamp examination in children and is closely related with the amount of skin which should be excised during surgery to correct epiblepharon. A classification system using skin fold height may therefore be the most appropriate method. In addition, there may be a correlation between lower lid epiblepharon and astigmatism.

Adolescent↗
PubMed2003

Relationship between topographic patterns and corneal astigmatism in Korean adults.

The anterior corneal surface is one of the most important elements determining the optical performance of the eye. Corneal topography provides quantitative data about the anterior corneal surface. We studied the corneal topography of 200 normal corneas in 110 adult subjects. All of the eyes were examined using the Corneal Analysis System (EyeSys 2000, Houston, Texas). The topographic maps were grouped into the following patterns: round, oval, symmetric bow tie, asymmetric bow tie, and irregular. The symmetric and asymmetric bow tie patterns were the most common topographic pattern (33.0%, and 32.5%, respectively) in our study population, followed by oval (14.5%), irregular (12.5%), and round (7.5%) patterns. The mean corneal astigmatism calculated from videokeratographic data was 0.32 D for round, 0.63 D for oval, 1.16 D for symmetric bow tie, 1.21 D for asymmetric bow tie, and 0.43 D for irregular patterns. There were significant differences among the corneal astigmatic values in the topographic patterns (p < 0.01, Gabriel post hoc test). The distributions of symmetric and asymmetric bow tie patterns were skewed toward greater amounts of corneal astigmatism. In conclusion, the results of this study demonstrate the relationship between topographic patterns and corneal astigmatism and should provide one possible normal standard for corneal topography in Korean adults.

Adult↗
PubMedDate not supplied

The relationship between soft tissue anomalies around the orbit and globe and astigmatic refractive errors: a preliminary report.

Corneoscleral limbal masses were created in ten rabbit eyes and upper eyelid colobomas were produced in an additional ten eyes. The resultant changes in corneal curvature were recorded over a one-month period using streak retinoscopy and photokeratometry. By these methods, we have determined that forces at or near the corneoscleral limbus can produce changes in the corneal curvature that lead to refractive errors primarily of the astigmatic variety. There is a shift of the axis of astigmatism towards the meridian 90 degrees away from the external force or an increase of astigmatism along the meridian where the force was exerted. In this study, corneal curvature changed significantly in the coloboma and epibulbar mass groups when compared to the control group. This study supported a causal relationship between soft tissue anomalies and astigmatic refractive errors seen clinically in certain syndromes, such as Goldenhar and mandibulo-facial dysostosis. These findings suggest that patients observed with periorbital soft tissue defects may be at risk for the development of unilateral anisometropic refractive errors and secondary amblyopia. Recognition of this entity is essential in order that adequate therapy can be instituted at an early age.

Animals↗
PubMedDate not supplied

Holmium: YAG laser to treat astigmatism associated with myopia or hyperopia.

The Summit Technology, Inc. (Waltham, Mass.) holmium:YAG laser was used to treat astigmatism in 31 myopic and 8 hyperopic eyes. There was slow but continuing regression of effect even 1 year after treatment. This regression was particularly seen in hyperopic astigmatism, larger amounts of myopic astigmatism, and younger patients. In some cases keratometry readings returned to their pretreatment values. Males and females had similar results. The mean myopic shift in 9 myopic astigmatism eyes at 9-month follow up was 1 D.

Adult↗
PubMedDate not supplied

Holmium:YAG laser thermokeratoplasty for astigmatism in rabbits.

BACKGROUND: Holmium:YAG laser thermokeratoplasty has generated considerable interest as a technique for correcting hyperopia. In this study, the effect of holmium:YAG laser on inducing astigmatism according to application patterns was evaluated. METHODS: An experimental study based on the results of astigmatic holmium:YAG laser thermokeratoplasty using the Summit OmniMed laser system (Summit Technology Inc, Waltham, Mass) in 36 rabbit eyes is presented. We divided the rabbits into four groups: arcuate, reverse arcuate, linear, and control group according to application patterns. All rabbits were followed for 3 months and cycloplegic refractive measurements were carried out. RESULTS: The average surgically induced astigmatism was 1.86 diopters (D) for the arcuate group, 2.93 D for the reverse arcuate group, and 1.31 D for the linear group. No significant complications related to the operation were noted. CONCLUSION: The reverse arcuate pattern of holmium:YAG laser thermokeratoplasty is most effective in inducing astigmatism in rabbits.

Animals↗
PubMed1996

Corneal topography, arcuate keratotomy, and compression sutures for astigmatism after penetrating keratoplasty.

BACKGROUND: Twenty (20) patients with post-penetrating keratoplasty (PKP) (21 eyes) and excessive corneal astigmatism were studied using corneal topography to determine placement of arcuate incisions and compression sutures for astigmatism reduction. METHODS: Keratoplasty wounds and compression sutures were placed asymmetrically based on corneal topography only. Incisions were at the donor-host junction at a depth of 500 microns. RESULTS: A 56% reduction in corneal astigmatism was accomplished with an average cylinder reduction of 5.3 D. Keratometry readings were reduced in 18 of 20 (90%) of eyes and refractive cylinder was reduced in 15 of 20 (75%) of eyes. Corrected visual acuity improved in 15 of 20 (75%) declined in 15%, and did not change in 10%. CONCLUSION: Visual acuity can be improved by manipulating the astigmatism after penetrating keratoplasty using corneal topography maps to determine placement of arcuate incisions and compression sutures.

Aged↗
PubMedDate not supplied

Photorefractive keratectomy for compound myopic astigmatism with an eye cup erodible mask delivery system.

BACKGROUND: The erodible mask is a new energy delivery system for the 193-nm argon fluoride excimer laser. It consists of a polymethyl-methacrylate button, whose profile is transferred by photoablation onto the corneal surface. We present the 6- and 12-month results of this technique in the correction of compound myopic astigmatism. METHODS: We performed the mask procedure on 21 eyes of 16 subjects (mean age, 30.7 years; range, 24 to 46) to correct combined myopia and astigmatism. Attempted myopic correction ranged between -1.50 diopters (D) and -10.00 D (mean, -7.07 D). Attempted astigmatic correction ranged between -1.50 D and -4.00 D (mean, -2.46 D). RESULTS: Mean procedure error was: sphere +0.74 D (range, -3.00/+5.00), cylinder -1.41 D (range, -3.50/0.00) at 1 month after surgery; sphere +0.18 D (range, -2.50/+ 3.50), cylinder -1.56 D (range, -4.00/0.00) at 6 months; and sphere -1.30 D (range, -3.00/0.00), cylinder was -1.25 D (range, -2.00/-0.50) at 12 months (10 eyes). During follow up, haze values were never higher than 1, except for one case of haze 2 that regressed to 0 during follow up. Postoperative uncorrected visual acuity improved in all eyes where emmetropia was envisaged; none of the eyes lost spectacle-corrected visual acuity lines 6 or 12 months after surgery. CONCLUSIONS: The erodible mask proved effective and fairly predictable mainly in the correction of the spherical component of refractive error, while the correction of astigmatism revealed greater unpredictability, with a constant trend to undercorrection.

Adult↗
PubMedDate not supplied

Stability of astigmatism over 3 years after corneal stretch incision.

PURPOSE: To assess long-term corneal stability of self-sealing clear corneal stretch incisions with implantation of 5 mm polymethylmethacrylate (PMMA) intraocular lenses. METHODS: Two hundred consecutive eyes of 3500 cataract patients who had capsulorhexis, phacoemulsification, and preparation of a 1.5 to 2.0 mm corneal tunnel that had an external width of 4.0 to 4.1 mm and an internal width of 6.5 to 7.0 mm (stretch incision), and implantation of a 5 mm PMMA intraocular lens were evaluated clinically and statistically. Slit-lamp microscopy, keratometry, and corneal topography were performed preoperatively and postoperatively after 1 week, 1, 2, and 3 years. RESULTS: The mean surgically induced astigmatism following superior corneal incision amounted to 1.59 +/- 1.06 D after 3 years; following lateral corneal incision, mean surgically induced astigmatism was 0.84 +/- 0.68 D. There were no corneal complications in the long-term follow-up study. CONCLUSION: Our 5-year experience shows that the self-sealing clear corneal stretch incision in connection with implantation of a 5 mm polymethylmethacrylate intraocular lens induces approximately 1.00 D of astigmatism. We prefer the lateral incision and recommend the superior incision only for high preoperative with-the-rule astigmatism.

Astigmatism↗
PubMedDate not supplied

Correction of asymmetric myopic astigmatism with laser in situ keratomileusis.

BACKGROUND: There are many ways to correct different kinds of astigmatism (myopic, hyperopic, mixed) with excimer laser surgery. New methods of correction are under development, including toric ablation in both meridians. Corneal astigmatism may also be present in asymmetric forms. METHODS: Twenty-one eyes of 16 patients (5 male, 11 female) with asymmetric myopic astigmatism were studied. The spherical component ranged from -2.75 to -9.25 D (mean, -6.15 +/- 0.63 D), and the cylinder ranged from 0.75 to 5.00 D (mean, 1.80 +/- 0.13 D). Mean age was 33 years. All patients underwent laser in situ keratomileusis (LASIK) using the Nidek EC-5000 excimer laser and the Hansatome microkeratome (TM 230 HT). RESULTS: Three months after LASIK, average spherical component was -0.50 +/- 0.05 D, and mean cylinder was -0.52 +/- 0.05 D. Uncorrected visual acuity (0.92 +/- 0.096) was close to average preoperative spectacle-corrected visual acuity (0.99 +/- 0.099). No patients reported double vision. CONCLUSION: When treating asymmetric forms of myopic astigmatism, it is possible to obtain good clinical outcomes by decentering the toric ablation and calculating the value and axis of the cylinder using topographic data.

Astigmatism↗
PubMedDate not supplied

Laser in situ keratomileusis for hyeropia and hyperopic astigmatism.

PURPOSE: To evaluate the efficacy, stability, and safety of laser in situ keratomileusis (LASIK) for hyperopia and hyperopic astigmatism using a prospective clinical trial. METHODS: LASIK was performed using the Automatic Corneal Shaper and the Keracor 117C excimer laser on 192 hyperopic eyes with astigmatism of less than 1.00 D (spherical group) and 164 hyperopic eyes with corneal astigmatism of 1.00 to 7.50 D (toric group). RESULTS: At 12 months after LASIK, 110 eyes were available for follow-up examination. In low spherical hyperopia (+1.00 to +3.00 D), 13 eyes (55%) were within +/-0.50 D of emmetropia and none lost 2 or more lines of spectacle-corrected visual acuity. In low toric hyperopia (+1.00 to +3.00 D), 14 eyes (61%) were within +/-0.50 D and none lost 2 or more lines of spectacle-corrected visual acuity. In moderate spherical hyperopia (+3.10 to +5.00 D) 9 eyes (44%) were within +/-0.50 D and none lost 2 or more lines of spectacle-corrected visual acuity and in moderate toric hyperopia (+3.10 to +5.00 D) 5 eyes (36%) were within +/-0.50 D and 2 eyes (14%) lost 2 or more lines of spectacle-corrected visual acuity. In high spherical hyperopia (+5.10 to +9.00 D), 6 eyes (38%) were within +/-0.50 D and 2 eyes (13%) lost 2 or more lines of spectacle-corrected visual acuity, and in high toric hyperopia (+5.10 to +9.50 D) 4 eyes (31%) were within +/-0.50 D and 2 eyes (15%) lost 2 or more lines of spectacle-corrected visual acuity. CONCLUSIONS: LASIK seems to be reasonably effective and safe in spherical hyperopia of +1.00 to +5.00 D but less effective for hyperopic astigmatism. For hyperopia greater than +5.00 D, loss of spectacle-corrected visual acuity occurred in a significant number of eyes and accuracy was sufficiently poor to advise against LASIK in these eyes.

Adult↗
PubMedDate not supplied

Multiple regression and vector analyses of laser in situ keratomileusis for myopia and astigmatism.

PURPOSE: To construct a quantitative model relating refractive results to laser settings and other factors. METHODS: A prospective clinical trial was performed, including 14 surgeons and 523 eyes of 278 patients who desired correction of myopia from -1.00 to -16.00 D (mean, -6.20 D) and astigmatism up to 6.00 D (mean, 1.10 D). Myopia and astigmatism were corrected by laser in situ keratomileusis (LASIK) with sequential spherical and cylindrical ablations using a 5.5-mm ablation zone and a transition zone to 7.0 mm. The Nidek EC-5000 excimer laser and the Chiron Automated Corneal Shaper were used. RESULTS: Surgically induced refractive changes 3 months after surgery were measured. Spherical ablation by LASIK produced a 19% greater refractive change than that predicted by the Nidek PRK algorithm. The laser setting needed to achieve each 1.00 D of cylinder correction induced 1.30 D change in spherical equivalent refraction (0.80 D more than expected). Patient age and nonlinear effects had small but statistically significant influences on refractive outcome. Sex, left/right eye, and surgeon were not significant factors. Residual variations in spherical equivalent refraction included a 0.50-D constant plus 9% of the predicted spherical equivlanet change. Residual variations in the parallel and orthogonal components of cylinder correction were, respectively, 28% and 13% of the predicted cylinder change plus a 0.30-D constant component. The standard deviation of axis alignment error for cylinder ablation was 3.7 degrees. CONCLUSIONS: Cylindrical ablation produced a spherical change that was larger than expected. To compensate for this, spherical ablation should be reduced in eyes with astigmatism. Variability in the correction of astigmatism was proportionally larger than that for spherical correction and was primarily due to magnitude rather than axis error.

Adult↗