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PubMed1988

[A study on the effects of different keratectomies for astigmatism in rabbits' eyes].

Three kinds of wedge resections with sutures at limbus were carried out in grown rabbits. Keratometry was performed for 8 weeks. Corneal curvature and corneal astigmatism were not significantly changed by 90 degrees of the circumference. But in the group of 180 degrees resection, the radius perpendicular to the wound increased and 3. 5 D corneal against-the-rule astigmatism was brought about in a week after surgery. Therefore, when operated at the limbus by same extension, one longer wedge resection changed more the radius than 2 symmetric resections did. It was thought this against-the-rule astigmatism was due to the decrease of total surface, another side of the wound being sclera, and other factors. They are properties of suture material, the provoked tissue reaction, and so on. Pulling on domed tissue should be looked at again. Loss of effect was remarkable. So, to get permanent effect, we should study more about the time of suture removal, acting over the sclera and the sutures penetrating cornea. Secondly, two kinds of keratectomies perpendicular to vertical meridian were situated midway between limbus and corneal apex. The changes of total refractive power were followed up by skiascopy for 3 months. As a result, 1.0 D-1.5 D against-the-rule astigmatism was surgically induced in both keratectomies. This was almost due to myopic change of the opposite meridian, which was parallel to the resections. Loss of effect of rectangle-shaped keratectomy was less than that of crescent-shaped. It suggested cutting Ligamentum Circulatum situated near limbus was necessary to prevent the reduction of induced astigmatism with time. In addition, limbus of wedge resection was histologically observed. Markedly wavy appearance of lamellas was seen in the stroma. Like this, reactions to 8-0 virgin silk proved to be intensive. So, suture associated with less inflammatory reaction like 10-0 monofilament is recommended.

Animals↗
PubMed1987

Corneal wedge resection for high astigmatism following penetrating keratoplasty.

Fourteen corneal wedge resections performed between April 1980 and January 1986 at the Wills Eye Hospital were retrospectively reviewed. Mean pre-operative refractive (subjective) astigmatism was 8.13 diopters (D), with a range of 3.75 to 15.0 D. Following wedge resection, the mean residual astigmatism was 3.04 D, with a range of 0 to 5.0 D. Although the mean keratometric astigmatism measurements were generally similar to the astigmatism measured during refraction, there was little correlation between them on a case-by-case basis. Corneal wedge resection appears to remain an effective and moderately predictable technique for managing high astigmatism following penetrating keratoplasty.

Adolescent↗
PubMed1988

The effect of scleral cautery on corneal astigmatism in cadaver eyes.

We studied the effect of scleral cautery on corneal astigmatism in 20 cadaver eyes using the Zeiss wetfield bipolar cautery either at or 2 mm posterior to the corneoscleral limbus. The chord of cauterized area was set at either 5.5 or 11 mm. Cautery induced net corneal steepening along the meridian of the cauterized area, and induced the greatest astigmatism when applied at the limbus. At each location the 11-mm cautery application induced less astigmatism. The majority of the astigmatic change occurred within the first 5 to 10 seconds of application. We found that scleral cautery at or 2 mm posterior to the limbus can induce extensive corneal astigmatism.

Astigmatism↗
PubMed1988

Predicting refractive astigmatism: a suggested simplification of Javal's rule.

In the period of almost 100 years since Javal proposed an empirically determined rule for the prediction of refractive astigmatism on the basis of corneal astigmatism, many authors have made suggestions for the modification of "Javal's Rule." These modifications, rather than being based on clinical data, have been based on concepts of mechanisms that can contribute to refractive astigmatism, but in most cases the modifications do nothing more than complicate the process of predicting refractive astigmatism, with the result that only Javal's original rule is widely used. In this paper, keratometric and refractive data for three groups of subjects are used to demonstrate that a simplified version of Javal's rule is more effective in predicting refractive astigmatism than is Javal's rule itself.

Adolescent↗
PubMed1978

Residual astigmatism in hard and soft contact lens wearers.

Residual astigmatism in a group of hard contact lens wearers and an equal size group of soft contact lens wearers was compared. Generally, the criteria used were to fit patients with refractive astigmatism greater than 0.75 D with hard lenses and those with refractive astigmatism of 0.25 D or less with soft ones. Those with refractive astigmatism between 0.25 D and 0.75 D were fitted with either modality depending upon other factors. The amount of residual astigmatism in the two groups proved to be nearly equal.

Astigmatism↗
PubMed1984

Astigmatism in children: changes in axis and amount from birth to six years.

Noncycloplegic refractions of 1,000 children aged 0-6 years revealed a high incidence of astigmatism, especially in the first 2 years of life. Before age 41/2 years, most of the astigmatism was against-the-rule and after that age most was with-the-rule. Of 19 children who did not show astigmatism in the first year, only one acquired it by 4 years. Of 29 children who had large amounts of astigmatism in the first year, all showed elimination or a large reduction in the amount of the cylindrical error by 4 years. These results are relevant to the etiology of astigmatism.

Age Factors↗
PubMed1982

The natural and modified course of post-cataract astigmatism.

We performed sequential central keratometry on 52 cataract patients for six months. We found no statistically significant difference in the induced postoperative astigmatism between wound closure with interrupted and double shoelace running closure with 10-0 monofilament nylon. In 31 patients, the postoperative astigmatism was always with-the-rule. In 21 patients who underwent wound closure with 8-0 polyglactin suture, we documented a postoperative shift in induced astigmatism from with- to against-the-rule which took place between the fourth and fifth postoperative week. Based on our present study of the natural and modified course of post-cataract astigmatism and based upon previous research, we feel the cataract surgeon now has the appropriate means to reduce and/or control post-cataract astigmatism.

Astigmatism↗
PubMed1995

[Long-term stability of astigmatism after suture correction in penetrating keratoplasty].

Severe astigmatism after penetrating keratoplasty is frequently a major problem. If one uses a technique to adjust a single running 10-0 nylon suture in the early period after keratoplasty, the suture tension can be redistributed and astigmatism reduced. Eighteen eyes with an average of 8.8 D of postkeratoplasty astigmatism underwent suture adjustment. The mean keratometric astigmatism before suture removal was 3.1 D. After suture removal with an follow-up of 25 months, the mean corneal astigmatism was 3.2 D, only one eye did the suture break during adjustment. No infection, vascularization or rejection occurred.

Adolescent↗
PubMed1993

Surface topography of soft contact lenses for neutralizing corneal astigmatism.

We compared the surface topography of 38 soft contact lenses in situ to the corneal topography of 17 patients. The analyzed lenses consisted of patients' spherical and toric lenses as well as additional spherical lenses of various thicknesses. Thirteen brands of contact lenses were worn; corneal astigmatism ranged from 0.12 to 3.81 D. Our hypothesis was that toric soft contact lens neutralization of corneal surface astigmatism occurred through the creation of a more spherical anterior surface. Videokeratoscopy was used to analyze corneal surface changes with contact lens wear. The correction of astigmatism for toric corneas (toricity > 0.75 D) fit with toric lenses (i.e., the difference between the surfaces of the cornea and anterior lens) showed surface astigmatism neutralization of only 34 +/- 38%. The greater the astigmatism, the greater the neutralization. Spherical lenses not only failed to mask corneal toricity, but actually increased it. The topographic map can be a valuable asset for analyzing and possibly improving contact lens fitting of toric contact lenses.

Astigmatism↗
PubMed1976

[Corneal astigmatism after penetrating keratoplasty with direct and indirect sutures (author's transl)].

After a full thickness optic keratoplasty the corneal astigmatism of 116 eyes was checked. 72 cases had been operated on with indirect, 44 with direct sutures. Up to the sixth month after the operation the astigmatism was found to be equally distributed between 0.75 and 12 dpt and until the end of the second year between 0.75 and 8 dpt. Neither the way of suturing nor the diameter of the graft nor the kind of corneal lesion had any influence on the postoperative astigmatism. After six months, the height and the axis of the astigmatism remained approximately constant; however, in four cases of keratokonus followed up for nineteen years the astigmatism gradually increased.

Astigmatism↗
PubMed1994

[1-year follow-up of astigmatism after cataract operation. Wound closure with cross-stitch suture vs. no-stitch suture technique].

Like the type of wound opening, wound closure has an important influence on postoperative astigmatism. In a series of 300 patients, for 1 year we examined postoperative astigmatism after cataract surgery with sutured scleral wound closure and the no-stitch technique. In the early postoperative period, the no-stitch technique. (1.00 dpt +/- 0.83) had less induced astigmatism (vector analysis of Jaffé), compared with sutured scleral wound closure (1.77 dpt +/- 1.36), as well as a smaller standard deviation. Furthermore, with the no-stitch technique a nearly stable situation is reached within the first 4 weeks. In the late postoperative period, the astigmatism induced after sutured scleral wound closure (1.01 dpt +/- 0.57) is only a little greater than with the no-stitch technique (0.85 dpt +/- 0.65). On both techniques more than every second patient shows astigmatism (sutured scleral wound closure: 61%; no-stitch technique: 52%).

Astigmatism↗
PubMed1993

Wedge resection for postkeratoplasty astigmatism.

Twelve patients underwent a modified wedge resection after keratoplasty; 11 of them were followed for 6 to 24 months. The average preoperative astigmatism was 15.40 diopters (range, 12.50 to 22.00 D). The wedge was resected from the donor side and the wound closed with 10-0 or 11-0 Mersilene sutures. Postoperatively, the average astigmatism was 4.36 D (range, 1.50 to 9.00 D), and the visual acuity, corrected with spectacles, was 20/40 or better in five cases (45%). Complications included high residual astigmatism or irregular astigmatism and extensive scarring due to the use of Mersilene sutures. Overall, modified resection of the wedge is an effective technique for managing postkeratoplasty high astigmatism.

Adult↗
PubMed1993

[Astigmatism and its treatments].

Astigmatism is a refractive error related to corneal asphericity. Congenital astigmatism is most frequent, and its correction with spectacles has been known for a long time. Contact lenses may sometimes be useful, but they may not allow a satisfactory visual correction. Anterior segment surgery (cataract, penetrating keratopasty, etc.) may often cause postoperative astigmatism. Improvement in ophthalmic surgery, and the patient's need for a rapid and effective visual recovery (as anatomical result is obtained), have highlighted prevention and treatment of post-surgical astigmatism. Astigmatism treatment is complex and varies according to its intensity and cause. Refractive surgery, modifying corneal shape, may be an elegant solution in cases where vision is low, in spite of a perfect corneal transparency.

Astigmatism↗
PubMed1993

[Keratometric characteristics and astigmatism of globes from eye bank].

We measured by means of keratometry the dioptric power of the main meridians of 142 globes (79 subjects) obtained from an eye bank. The mean dioptric power was 43.56 (standard deviation [SD] 1.97) dioptres. Eyes from female subjects had a significantly higher mean power than those from male subjects (p < 0.05). The keratometric readings were used to quantify corneal astigmatism. The mean degree of astigmatism was 1.03 (SD 0.95) dioptres. There was no significant difference in the amount of astigmatism between age groups, between eyes from female and male subjects, and between left and right eyes. However, subjects with astigmatism in one eye were likely to have it in the fellow eye (p < 0.001). A predominance of "against-the-rule" astigmatism was noted.

Adult↗
PubMed1995

Modified scleral flap incision to reduce corneal astigmatism after intraocular lens implantation.

PURPOSE: To investigate a simple method during extracapsular cataract extraction with posterior chamber intraocular lens implantation in order to reduce surgically induced corneal astigmatism. METHODS: A modified scleral flap incision was used in the extracapsular cataract extraction with intraocular lens implantation and the postoperative changes in corneal astigmatism was observed. RESULTS: The peak value of postoperative corneal astigmatism was 3.60 D, and the corneal astigmatism regression was 2.11 D, surgically induced astigmatism was less significant in modified scleral flap incision group than that in conventional limbal incision group (P < 0.05). CONCLUSIONS: The modified scleral flap incision is an ideal incision for cataract extraction with intraocular lens implantation when phacoemulsifier is not available.

Aged↗
PubMed1995

Optimum form of posterior chamber intraocular lenses to minimize aberrational astigmatism.

To optically determine the optimum form for a posterior chamber intraocular lens (PC IOL), we calculated the aberrational astigmatism induced by tilt and decentration of the PCIOL using an exact raytracing. First, the position and the radii of curvatures of the IOL were determined to make an emmetropic eye model using a paraxial raytracing. Next, the chief rays originating from the fovea centralis were traced backward through the tilted and/or decentrated PC IOL, the center of the pupil and the cornea, using trigonometric raytracing. Finally, the maximum and minimum aberrational astigmatism were calculated based on the Coddington's Equations for the sagittal and the tangential foci of the ray. All the refractive parameters in Gullstrand's No. 1 schematic eye were adopted. The effect of varying anterior corneal asphericity on the results was also examined. Four forms of polymethylmethacrylate PC IOLs (refractive index: 1.491) were analyzed; a plano-convex IOL with the curved surface facing the cornea, and three bi-convex forms with the ratio of anterior-to-posterior radii of curvatures of 1:4, 1:2 and 1:1, respectively. The 1:4 bi-convex form showed the lowest values for the maximum aberrational astigmatism calculated at every combination of tilt and decentration except 0 degrees tilt and/or 0 mm decentration. The aberrational astigmatism with the 1:4 bi-convex form of PC IOL did not exceed 1.0 D at the maximum tilt and decentration. The variation of anterior corneal asphericity did not influence the results. We conclude that the 1:4 bi-convex form of PC IOL minimizes the postoperative astigmatism induced by tilt and/or decentration of the lens.

Astigmatism↗
PubMed1996

A comparison of three subjective tests for astigmatism and their interexaminer reliabilities.

BACKGROUND: Astigmatism is a common cause of blurred vision and asthenopia. Several different tests for the measurement of astigmatism have been described in the literature, but there are few studies that have compared the results of various tests. METHODS: The results of three astigmatism tests performed on 40 subjects by two examiners were compared. Two of the tests, the Jackson cross cylinder (JCC) and the Humphriss immediate contrast (HIC), utilized distance targets; one test, the Pratt test, involved a near target. RESULTS: The mean differences between all tests were less than 0.25D. There was a slight tendency for higher cylinder power to be found on the Pratt test. The three tests agreed within +/- 0.25D on cylinder power 80 to 98 percent of the time and within 10 degrees of cylinder axis 85 to 98 percent of the time. Interexaminer reliability showed mean differences less than 0.12D for each of the three tests, agreement within +/- 0.25D on cylinder power 88 to 90 percent of the time and within 10 degrees on cylinder axis 85 to 93 percent of the time. CONCLUSIONS: The results suggested that any of the three techniques could be substituted for another for astigmatism testing. On theoretical grounds, a binocular refraction method for cylinder axis determination, such as the HIC, is advisable for patients with cyclophorias and significant amounts of astigmatism. The results showed good reliability for each of the three methods.

Adolescent↗
PubMed1997

Astigmatic change after myopic spherical excimer PRK.

85 Patients who underwent a spherical PRK with an average of 6.08 dptr. and who could be followed over a period of 1 year were evaluated. After 1 year an average induced astigmatism of 0.58 dptr. was found. There seems to be a correlation between induced astigmatism and depth of PRK but not between induced astigmatism and pre-existent astigmatism. In cases of decentrated PRK a spontaneous regression of laser-induced astigmatism could be observed.

Adult↗