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PubMed1977

Asymmetry of central and peripheral corneal astigmatism measured by photokeratoscopy. 1976 Neumeller Award Paper.

The radii of curvature of 10 astigmatic corneas (1.125 to 3.625 D) were measured by photokeratoscopy in 4 semimeridians: 2 axis semimeridians and 2 power semimeridians. Most of the angular separations between adjacent semimeridians differed from 90 deg by more than 2.5 deg; the separations ranged from 55 to 120 deg. Corneal astigmatism, as specified by the difference in curvature between adjacent axis and power semimeridians at corresponding distances from the corneal apex, was also highly asymmetric with decreasing astigmatism in the corneal periphery. An interesting revelation was the interchange of the axis and power semimeridians in the periphery of 3 subjects' corneas.

Astigmatism↗
PubMed1983

Correction of postkeratoplasty astigmatism by razor blade and V-shaped knife wedge resection.

Improvement in microsurgical techniques and tissue storage has resulted in a higher rate of clear grafts after penetrating keratoplasty. The postoperative astigmatism however still remains a major problem. If a high corneal astigmatism cannot be managed successfully with glasses or contact lenses, a surgical approach may be indicated. We developed a V-shaped knife which makes a crescentic wedge resection easier to perform. Before the introduction of the V-shaped knife we obtained an average reduction in corneal astigmatism of 6.6 diopters. With the V-shaped knife the reduction was 8.0 diopters. We think that the V-shaped knife makes a wedge resection easier and safer.

Astigmatism↗
PubMed1978

Corneal astigmatism following cataract surgery.

Seventy-seven cases of intracapsular cataract extraction were analyzed for immediate and long-term induced corneal astigmatic changes. Sutures used were predominantly interrupted, absorbable sutures buried under a limbus-based conjunctival flap. The average induced astigmatism in the first week after surgery was 3.87 diopters with-the-rule. The average induced astigmatism after six weeks was 0.79 diopters against-the-rule. The cause of the induced change is discussed.

Astigmatism↗
PubMed1984

Astigmatic decomposition: an alternative subjective refraction test employing conventional instrumentation.

The Humphrey Vision Analyser introduced the refractive technique of astigmatic decomposition with the aid of Alvarez continuously variable sphere-cylinder lenses. The adaptation of astigmatic decomposition to conventional trial lens systems and a Stokes' lens is described. Refractive errors measured by this technique and by crossed cylinder are compared in 33 optometric patients (one eye each) to assess the relative validity of the method, which compares well with data published on the Humphrey Vision Analyser. Astigmatic decomposition can be considered as an alternative subjective refraction test to more conventional methods.

Astigmatism↗
PubMed1984

Radial keratotomy for astigmatism.

Most ophthalmologists view radial keratotomy as a new and somewhat controversial method to decrease myopia by flattening the corneal curvature. Although the ophthalmologist does not initially perceive radial keratotomy as a means for correcting astigmatism, it follows that if he or she selectively flattens the cornea more in some meridians, the ophthalmologist is effectively correcting astigmatism. Although the predictability is slightly less in correcting astigmatism than that for correction of myopia, it is still rather good as the data herein presented will show. this communication will present the author's techniques as applied over the past three and one-half years in more than 2,500 radial keratotomy eyes, although only 186 patients are reported here so as to have a followup of at least two years on all patients.

Astigmatism↗
PubMed1984

Eye scan therapy for astigmatism.

Two earlier papers introduced a new model of functional astigmatism. The investigation that led to the model indicated a relationship exists between meridional eye scanning habits and the formation of functional astigmatism. The present paper reviews the model and describes a clinical study involving the prescribing of specific eye scan therapy on a meridional basis. The results demonstrate that therapy involving eye scanning procedures has a positive effect on the control and reduction of astigmatism.

Adult↗
PubMed1983

High corneal astigmatism in the adult Navajo population.

Corneal astigmatism was measured in 176 unselected Navajo patients over the age of 45 years old. The result was a 4% incidence of with-the-rule astigmatism of two diopters or more in at least one eye. Conjectures on a reason for the small incidence of high corneal astigmatism in the adult Navajo population as compared to the large incidence that occurs in Navajo children is discussed.

Adult↗
PubMed1981

High corneal astigmatism in Navajo school children and its effect on classroom performance.

809 unselected Navajo school children from kindergarten to sixth grade received visual acuities and keratometry readings. The information obtained was directed at statistical analysis of the degree of corneal curvature of two diopters or more and the distribution of its ranges, grade distribution, sex distribution, unilateral percentage and eye dominancy, uncorrected visual acuities of the high uncorrected astigmat, the mean corneal astigmatism, and the relationship between uncorrected high astigmatism and classroom performance.

Achievement↗
PubMedDate not supplied

Transverse keratotomy combined with spherical photorefractive keratectomy for compound myopic astigmatism.

This is a report of a study of 40 eyes in which transverse keratotomy was performed in conjunction with spherical photorefractive keratectomy. The preoperative range of myopia was -1.50 to -13.50 diopters (D). The mean attempted cylindrical correction was -1.73 D (range -0.75 to -4.00). After 6 months 47.8% achieved unaided visual acuity of 6/6, 60% achieved 6/9 or better and 75% achieved 6/12 or better. The mean postoperative spherical equivalent refraction was -0.01 D at 6 months. The mean astigmatism postoperatively was 0.32 D. A group of 179 eyes with six months follow-up after photorefractive keratectomy who had not had transverse keratotomy was compared. Their mean postoperative spherical equivalent refraction was -0.07 D and mean astigmatism was 0.21 D. Uncorrected visual acuity was 6/12 or better in 93.3%. Until there is an improvement in the mechanism of the ablatable mask this combined procedure offers patients with significant astigmatism the opportunity of achieving good visual results.

Astigmatism↗
PubMed1994

[Induced astigmatism in cataract surgery. Scleral tunneling incisions of 5.5 mm and 6.5 mm after 1-year follow-up].

To evaluate the effect of scleral pocket incisions closed with a single horizontal suture on postoperative astigmatism, 97 patients were enrolled in a prospective study. After 1 year of follow-up the data of 80 patients could be analysed. Routine phacoemulsification was performed in all patients consecutively by one surgeon. 40 patients received a posterior chamber lens with a 5 mm by 6 mm oval polymethylmethacrylate (PMMA) optic (group I), and 40 patients received an intraocular lens with a 6 mm diameter round PMMA optic (group II). The incisions were 5.5 mm and 6.5 mm, respectively. Follow-up visits including keratometry were scheduled 1 day, 5 days, 3 months, 6 months and 1 year postoperatively. The induced astigmatism was calculated using vector analysis. One day after operation the mean induced cylinder was 1.22 D in group I and 1.06 D in group II. After 5 days it amounted to 1.09 D (group I) and 1.03 D (group II), and at 3 months it was 1.07 D and 1.00 D, respectively. Six months after operation the induced cylinder was 1.04 D (group I) and 0.96 D (group II), and at 1 year it was 1.02 D and 0.81 D. There was no statistically significant difference between the groups at any time (Wilcoxon test, P > 0.05). We conclude that scleral pocket incisions closed with a single horizontal suture induce about 1 D of corneal astigmatism, with stability over time. There is no clinical advantage in reducing the incision width by using oval optics.

Aged↗
PubMed1994

[Prevention of postoperative inverse astigmatism during radial keratotomy].

Seventy eight patients (156 eyes) were treated by radial keratotomy. Patients with spherical axial myopia were selected (including 39% of physiological astigmatism cases). After radial conventional technique the against-the-rule astigmatism > 1.0 D is 31.6% and between 1.0 and 2.0 D is 3.4% versus 0.6% (< 1.0 D) and 0.1% (1.0-2.0 D) with the modified technique. To decrease the frequency of the against-the-rule postoperative astigmatism after RK procedure we performed 1 or 2 vertical additional flag-incisions on the horizontal meridian to counteract the effect of the corneal oedema on the superior incisions.

Astigmatism↗
PubMed1993

Surgically induced astigmatism. A comparison of different cataract incisions and closures.

A single center, single surgeon, nonrandomized, prospective clinical trial was performed comparing the keratometric induced astigmatism by different types of incisions and closures, one day, one week, one month and three months after 255 cataract surgeries. After phacoemulsification, or in rare cases after extracapsular cataract extraction, through a scleral pocket or limbal incision, patients received either a 5 x 6 mm, 5.5 mm, or 6 mm diameter polymethylmethacrylate optic posterior chamber intraocular lens. Incision was closed with either none, one horizontal or radial, or running 10-0 nylon suture. Vector analysis calculations of prism diopters of mean postoperative-induced keratometric astigmatism showed a trend to lesser values at each interval in scleral pocket incisions but statistically significant difference only at 1 day and 1 week between 9-mm and 6-mm limbal, and 5-mm and 6-mm scleral pocket incisions. Other subgroup analyses, including incision shape and distance from limbus, and type of suture, did not reach statistical significance. Horizontal, 5-mm, sutureless scleral tunnel incision showed less induced astigmatism with more rapid stable refraction.

Adult↗
PubMed1993

[Vectorial models for analyzing variations of anterior corneal astigmatism].

Several studies have analysed postoperative or spontaneous variations in astigmatism. The methods of quantification of these variations, frequently used in these studies, are based on different ways of calculating: subtraction, vectorial or polar methods: Naylor, Jaffe and Clayman, Cravy, Naeser, Russell et al. and recently, Holladay et al. Although these methods have the advantage of taking into account the axial component of astigmatism and are useful for a single patient, they have many problems and they are more and more numerous (five in the last three years). We have computerized these formulae on a personal computer and studied their performances when the cylinder power decreases without modification of the axes, when the axes are modified without modification of the cylinder power and when the two axes change with the same angular difference. These calculations demonstrate that these formulae are not linear and introduce statistical errors before the statistical decision tests. Moreover, their application is only possible for evaluation of astigmatism axes between 0 degree to 180 degrees and not for semi meridians and corneal topography.

Analysis of Variance↗
PubMed1993

Glaucoma triple procedures leaving the internal corneal valve intact to control induced astigmatism--theoretic considerations.

As glaucoma surgery increasingly tends to be performed in younger patients, stabilizing visual results by reducing the amount of surgically-induced astigmatism will become just as important as controlling intraocular pressure. I describe two glaucoma triple procedures involving small-incision cataract surgery in which, as contrasted with previous techniques, the internal cataract incision is separated from the trabeculectomy, theoretically reducing surgically-induced astigmatism. One method features a standard trabeculectomy with sutures in the scleral flap; the other, an ab externo trabeculectomy in which no sutures are used. The effectiveness of both these methods in actually reducing surgically-induced astigmatism, while controlling intraocular pressure (IOP), remains to be demonstrated, but the possibility that they might, seems well worth exploring.

Astigmatism↗
PubMedDate not supplied

Astigmatism after penetrating keratoplasty using the Krumeich guided trephine system.

BACKGROUND: The use of a suction trephine during penetrating keratoplasty has the potential to reduce trephination errors and astigmatism after suture removal. METHODS: In this study, we evaluated refractive astigmatism after suture removal in 26 eyes that had penetrating keratoplasty for keratoconus using refraction, keratometry, and videokeratography. Group I (11 eyes) had manual trephination with an open disposable blade of both the donor (8.2 mm) and the recipient (8.0 mm). Group II (10 eyes) had manual trephination with an open disposable blade of the donor (8.2 mm) and Krumeich guided trephine system trephination of the recipient (8.0 mm). Group III (5 eyes) had guided trephination of both the donor (8.0 mm) and the recipient (8.0 mm). RESULTS: The guided trephine groups II and III demonstrated statistically significant less refractive cylinder when compared to manual trephination group I (p < .01). The mean keratometric cylinder for group I was 6.50 diopters (D) (range, 1.50 to 9.00 D), for group II was 3.00 D (range, 0.50 to 7.00 D), and for group III was 2.55 D (range, 0 to 4.00 D). CONCLUSION: The Krumeich guided trephine system produced less keratometric astigmatism than manual trephination after penetrating keratoplasty for keratoconus.

Astigmatism↗
PubMed1993

[Suture technic in perforating keratoplasty and postoperative astigmatism].

The authors evaluate postoperative vision, value of astigmatism and keratometry in 25 patients operated in 1992 by perforating keratoplasty, incl. 11 where the disc was fixed by interrupted stitches and 14 by continuous diagonal stitches. After evaluation of the influence of interrupted stitches and continuous diagonal stitches on postoperative astigmatism in perforating keratoplasty the authors recommend the use of diagonal suture. The reason is in the first place the uniform spreading and good adaptation of the transplanted cornea, as well as slighter traumatization and easier removal of stitches. An important role is played also by the larger number of measurable radii of the corneal curvature with regard to possible postoperative correction of astigmatism either by added stitches or differentiated adjustment of the tension of the continuous stitch.

Adult↗
PubMedDate not supplied

Multifocal effect of against-the-rule myopic astigmatism in pseudophakic eyes.

BACKGROUND: In monofocal intraocular lens (IOL) implants we can sometimes obtain a certain degree of pseudoaccommodation. The use of a slight myopic astigmatism is proposed for postoperative refraction to achieve a significant increase in the depth of field and to reestablish a certain degree of pseudoaccommodation in pseudophakic eyes. METHODS: Eighty-one eyes with against-the-rule myopic astigmatism were evaluated in 50 patients who underwent IOL implant surgery. We selected patients with corrected monocular visual acuity greater than or equal to 20/30 and with a refraction ranging from +0.50 to -1.25 diopters sph, from -0.50 to -2.75 D cyl, ax from 55 degrees to 140 degrees. RESULTS: Monocular uncorrected distance visual acuity in 68% of eyes was 20/40 or better, while binocular uncorrected distance visual acuity in 84% of eyes was 20/40 or better and in 66% of eyes was 20/30 or better. Monocular uncorrected near visual acuity in 67% of eyes was J3 or better, while binocular uncorrected near visual acuity in 82% of eyes was J3 or better and in 68% was J2 or better. Sixty-four percent of patients never wear glasses for distance, while 34% use them occasionally and only 2% always wear them. Fifty-four percent of patients never wear glasses for near, 32% use them occasionally, while 14% always wear them. CONCLUSION: These data show that with a low against-the-rule simple myopic astigmatism (about -1.50 D cyl x 90) we can often offer pseudophakic patients a rewarding independence from glasses both for distant and near vision.

Accommodation, Ocular↗
PubMedDate not supplied

[Corneal astigmatism after refraction keratotomy].

Refraction keratotomy, by changing corneal refraction, may cause postoperative astigmatism, including its reverse form. The author suggests to assess astigmatism using astigmatic coefficient (K alpha), which is expressed as the cosine of the angle between the vertical and the direction of the stronger main meridian. Intra-and postoperative use of fibronectin solution is proposed to lower the K alpha and improve the efficacy of surgery.

Astigmatism↗