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PubMed1977

Incidence of astigmatism after cataract surgery. Comparison of continuous and interrupted sutures.

In spite of the increased use of intraocular implants and contact lenses, the majority of cataract cases require spectacles after operation. Too great an amount of astigmatism will cause distortion and spoil an otherwise perfect operation. It is clear that the amount of astigmatism depends upon how the section is made and how it is sutured. In a series of cases employing different kinds of section and different methods of suturing, the postoperative astigmatism for each combination was recorded. A comparison was made between direct sutures and continuous suturing with 10.0 monofilament. Some suggestions are made as to the best method of keeping astigmatism to a minimum.

Astigmatism↗
PubMed1988

Changes in the axis of astigmatism: a longitudinal study.

Changes in the axis of astigmatism have been followed up in the same individuals over several decades. Only a proportion of subjects with direct astigmatism in their youth change to inverse astigmatism by way of oblique astigmatism.

Adolescent↗
PubMed1986

Corneal power and astigmatism.

A study investigating the corneal power and degree of astigmatism in 520 patients at a university optometry clinic in Benin-City, Nigeria was undertaken. The mean low corneal power and the mean high corneal power were 42.7 +/- 1.5 diopters and 43.3 +/- 1.5 diopters, respectively. The mean corneal astigmatism was 0.61 +/- 0.63 diopters. Although female corneas were significantly steeper than those of males, there was no significant difference between the corneal astigmatism with regard to sex. The data reported suggest that nutrition plays a less important role in corneal astigmatism than other authors have proposed.

Adolescent↗
PubMed1979

Calculation of the change in corneal astigmatism following cataract extraction.

Obtaining a minimal amount of postoperative astigmatism following cataract surgery is becoming increasingly important. One aspect of the patient's surgery which should not be overlooked is the preoperative keratometry which provides a basis for preoperative planning of surgical technique to be used and a point of reference for determining the amount of change in astigmatism produced by the surgery. Analysis of the surgically induced change in astigmatism using the calculations described in this paper will allow the surgeon to evaluate his own techniques and to maximize his potential for obtaining consistently good postoperative astigmatic results without the need for suture removal. The method presented is based upon concepts in common use in surgical ophthalmology and requires only simple mathematical procedures, familiar to all with a background in algebra and trigonometry.

Astigmatism↗
PubMed1979

Residual astigmatism and visual acuity with hydrogel contact lenses: a comparative study.

Residual astigmatism, visual acuity, and transferred corneal toricity were measured in a double masked fashion on 24 randomly selected patients fitted with Buasch and Lomb Soflens contact lenses, the Hydrocurve II contact lenses, and the AOSoftTM hydrophillic contact lenses. None of the subjects had any contraindications to hydrogel lens wear. All three lens types produced a small but similar reduction in refractive astigmatism. However, because of residual astigmatism, fewer eyes achieved 20/20 or better visual acuity with each of the hydrogel lens types than with the best spectacle correction. Corneal toricity was found to be transferred to the front surface of all three lens types. Our findings indicate that generally these three types of hydrogel lenses result in similar residual astigmatism, visual acuity and transferred corneal toricity. However, individual differences may occur. Therefore, the choice of lens type should be based on the individual patient's response to various lens types.

Adult↗
PubMed1983

[Severe astigmatism following transfixing keratoplasty: how to attempt to reduce it].

Surgical treatment of astigmatism has been practised since the nineteenth century. Ophthalmologists' attitude has to change with respect to the problem of astigmatism after penetrating keratoplasty. A high astigmatism must no longer be considered as a fatality, particularly in young patients, except in special circumstances to be considered case by case. Rather than waiting for corneal healing, and operating only some time after ablation of the edge-to-edge suture by practising for example a wedge resection, it appears logical to act sooner to benefit from the temporary flexibility of a recent scar. Initially, 5 or 6 very tight sutures should be inserted in the axis of the flatter meridian as a routine procedure. Overcorrection must be as high as the astigmatism to be corrected; the total correction achieved will be reduced by about 50% in the following weeks and will then become stable. The sutures have to be kept in position until the corneal scar is completely healed. Such a method has the drawback of remaining approximate, but this is also the case with other operations proposed at a later stage. It has the advantage of being simple and without risk of lasting overcorrection. This study was essentially a prospective and preliminary one, and analysis of results with more cases will determine whether this method is effective.

Adult↗
PubMed1984

Selective positioning of the donor cornea in penetrating keratoplasty for keratoconus: postoperative astigmatism.

The final "sutures-out" astigmatism in patients who had undergone penetrating keratoplasty for keratoconus was evaluated for two groups of patients. Group 1 consisted of patients operated upon using the Troutman surgical keratometer but without giving attention to the orientation of the donor button in the recipient bed. Patients in Group 2 were also operated upon utilizing the surgical keratometer, but the donor button was rotated in the recipient bed until a position of apparent sphericity was indicated by the keratometer before suturing the graft. The mean final astigmatism was 4.42 +/- 1.85 D for Group 1 and 5.13 +/- 3.17 D for Group 2. The difference was not statistically significant. The results indicate that selective positioning of the donor button in an attempt to minimize astigmatism, as determined with a qualitative surgical keratometer, does not lead to a reduction in the final astigmatic error in patients undergoing penetrating keratoplasty for keratoconus.

Adult↗
PubMedDate not supplied

Induction of astigmatism by straight transverse corneal incisions, 45 degrees long, at different clear zones in human cadaver eyes.

BACKGROUND: Two of the major factors affecting the amount of astigmatism correction are the length of the transverse incision and its distance from the center of the cornea. Many nomograms used in clinical practice have been created by varying the length or clear zone diameter of the incisions. A simplification of this situation has been suggested by Thornton, who has theorized that straight transverse incisions, subtending 45 degrees of arc, have equal astigmatic corrective effect at different clear zones. Our study tested Thornton's theory in human donor eyes. METHODS: Ten eyes were tested at four clear zones: 5.0, 6.0, 7.0, and 8.0 mm. Paired straight transverse incisions, subtending an arc of 45 degrees (2.1 to 3.3 mm long), were centered on the 90-degree meridian. Preoperative keratometric readings at the 180- and 90-degree meridians were compared to the postoperative readings; the difference was the total astigmatism induced. We also calculated the coupling ratio. RESULTS: Student's t-tests comparing clear zones 6.0 and 7.0 mm revealed a statistical difference (p = .0085) in total astigmatic induction, greater for the 6.0-millimeter zone. The coupling ratio decreased as the clear zone diameter increased, presumably as a result of diminished flattening effect along the incised meridian. One-way analysis of variance indicated that the groups were different (p = .0001), and that the theory noted above was incorrect. CONCLUSIONS: The effect of transverse incisions subtending the same angular length, drops off dramatically with clear zones larger than 6.0 mm, contrary to the theory of Thornton. This effect may be due to reduction in coupling as the clear zone diameter increases, suggesting that the greatest efficacy is achieved for transverse incisions placed between 5.0- and 6.0-millimeter zones.

Astigmatism↗
PubMedDate not supplied

[Postoperative astigmatism after extracapsular cataract extraction].

The authors analysed the occurrence and changes of postoperative astigmatism in three groups of patients after the performed extracapsular cataract extraction, regarding the type of the applied sutures: single, continuous double row and combined suture. One hundred and fifty-eight eyes were followed up over the period of 6 months. The quickest decreasing of astigmatism and its lowest values were recorded in the application of the combined suture. A statistically significant decrease of astigmatism values (p < 0.01) was already found after 1 month, and after 6 months 98.7% of the operated eyes had the postoperative astigmatism lower than 0.9 D.

Adult↗
PubMed1994

Radial suture stabilized by fibrin glue to correct preoperative against-the-rule astigmatism during cataract surgery.

We evaluated the efficacy of using a modified wound-closure technique in cataract surgery to reduce presurgical against-the-rule (ATR) astigmatism. Seventy-seven eyes received a radial 10-0 nylon suture in the axis of the preexisting ATR cylinder, combined with an application of fibrin glue to stabilize the wound. A control group of 76 patients with comparable preoperative ATR astigmatism was operated on in the same manner, but only fibrin glue and no suture was used for wound closure. The mean induced astigmatism in these two groups differed by 0.42 diopters, a significant difference (P < .05). In the cases with preoperative astigmatism greater than 1.00 D, the difference between the two groups, again a significant one, was 0.73 (P < .05).

Aged↗
PubMed1993

[Intraoperative control of corneal astigmatism during cataract extraction with PC IOL implantation].

The surgical keratoscope and Terry surgical keratometer were used in 29 (group a) and 34 (group b) eyes respectively during cataract extraction with PC IOL implantation to monitor the corneal astigmatism and to adjust the tension of sutures. Two weeks after the operation, the corneal astigmatism in group a was 3.50 +/- 1.70D, and that in group b was 2.56 +/- 1.60D. Two months after the operation, 55.2% of the eyes in group a and 38.2% of the eyes in group b had corneal astigmatism > 2.00D, differing significantly from the higher percentage in the controls. The authors opined that the intraoperative use of the surgical keratoscope and Terry surgical keratometer helped reduce the corneal astigmatism following the intraocular operation.

Aged↗
PubMed1994

[Natural history of corneal astigmatism following posterior chamber intraocular lens implantation].

The natural history of corneal astigmatism in 118 eyes following extracapsular cataract extraction and PC IOL implantation demonstrated that the average surgery induced with-the-rule astigmatism of 3.37D one week after the operation declined at a rate of 0.60, 0.63 and 0.39D during the 1st, 2nd and 3rd months respectively, indicating that the with-the-rule astigmatism of 2.00-3.00D would be corrected spontaneously to the normal or physiological status. The relationship between the changes in astigmatism and postoperative vision and the intraocular pressure was discussed.

Aged↗
PubMed1993

[Changes in corneal astigmatism with aging].

Change in physiologic corneal astigmatism due to aging was studied. A series of 868 cases (1,660 eyes) was evaluated. These eyes were divided into 6 groups by age; A) below 40 years, B) in the 40's, C) in the 50's, D) in the 60's, E) in the 70's, and F) over 80. Corneal astigmatism was examined with an autokeratometer. In Group A, 88.5% had with-the-rule astigmatism (WTR), whereas only 3.7% had against-the-rule astigmatism (ATR). The cylindrical diopter (CD) of WTR was 1.29 +/- 0.73 D, which was significantly the largest among the groups. In Group C, WTR decreased to 55.9% and ATR increased to 22.9%. The CD of WTR also decreased to 0.85 +/- 0.47 D. In Group E, WTR was 31.4% and ATR was 49.3%. The CD of ATR increased to 0.88 +/- 0.70 D. In Group F, WTR was 19.9%, whereas ATR was 65.9%. The CD of ATR was 1.48 +/- 0.88 D, which was the largest among the groups. As such, WTR was dominant at younger ages, and ATR increased with aging at older ages. The CD of WTR decreased, and ATR increased, with aging.

Adult↗
PubMed1993

[Size of incision and induced astigmatism in cataract surgery].

A study was carried out of postoperative astigmatism in three groups of 50 eyes which had had cataracts removed by phacoemulsification or by planned extracapsular removal through incisions of 3.5-4 mm, 7-7.5 mm, and 10-11 mm respectively. No statistically significant differences were observed in the average number of cases of astigmatism found 100 days after the operation in the patients in whom incisions of 10-11 mm (1.82 +/- 0.95 Dp) and 7-7.5 mm (1.78 +/- 0.90 Dp) were made. Appreciable differences were discovered when these two groups were compared with cases in which small incisions had been used and who presented a lower degree of astigmatism (1.02 +/- 0.59 Dp). To ensure less postoperative astigmatism after phacoemulsification, the size of the incision should be modified as little as possible during the insertion of the intraocular lens.

Adult↗
PubMedDate not supplied

The erodible mask in photorefractive keratectomy for myopia and astigmatism.

This paper reports a new approach for performing photorefractive keratectomy (PRK) that uses an erodible mask to control shape transfer processes. The advantages of this technique, when compared to conventional PRK performed with mechanical diaphragm, are 1) the possibility of transferring almost any shape onto corneal surface; 2) a smoother corneal surface following photoablation; 3) easier eye fixation; and 4) a controlled humidified environment over ablation zone. We report our experimental study on scanning electron microscopy of polymethylmethacrylate (PMMA) plates ablated using conventional technique versus erodible mask technique; the results showed a smoother surface in the PMMA plate ablated using the erodible mask. We also report our preliminary clinical results of four eyes treated for the correction of myopia combined with astigmatism. Myopia ranged from -2.00 to -10.00 D, and astigmatism ranged from -1.50 to -2.50 D. Three months after surgery, all four eyes were within +/- 1.00 D of myopic attempted correction, but astigmatism was completely corrected only in one eye. No complications or scarring have been reported. We believe the erodible mask could be effective in the correction of myopia and myopic astigmatism, but further improvements are necessary to allow easier alignment of the mask over the eye. All commonly available excimer laser devices produce photorefractive keratectomy as a concentric ablation of the corneal stroma, deeper in the center than in the peripheral part; this is produced by means of an iris or diaphragm which, depending on the type of laser, progressively opens or closes, allowing a greater laser beam delivery in the center.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1996

Wavefronts and their propagation in astigmatic optical systems.

The geometry of the astigmatic wavefront is derived from the symplectic nature of linear optics. It is shown to be paraboloidal. Equations are derived that govern the propagation of such wavefronts through astigmatic systems in general and through thin lenses and across refracting interfaces and homogeneous gaps in particular. The equations allow the generalization of the concept of wavefront curvature or vergence to astigmatic systems. In particular they show how the step-along method of calculating wavefront curvature is generalized. Not only are Keating's earlier conclusions on this topic confirmed but also they are shown to hold under more general circumstances. They hold even when the system contains gradient-index elements such as the natural lens of the eye. Some of the premises used in the earlier study are shown not to be necessary: they are a consequence of symplecticity. The analysis also provides a step-along procedure for calculating wave-front direction. A numerical example in the Appendix shows the application of the step-along method to a particular separated astigmatic system: the back-vertex power of the system is determined as is the equation of the emergent wavefront for a distant object point.

Astigmatism↗
PubMed1997

[The incision in the surgery of cataract and postoperative astigmatism].

There are presented effects of the incision in cataract surgery on postoperative astigmatism. Big changes of astigmatism can be eliminated by applying several basic principles of cataract incisions. Despite the rapid changes in incision technology, these concepts can be applied to all cataract surgery, whether a large or small incision is used, to achieve increased stability and decreased astigmatism. There are also reviewed possibilities of controlling postoperative astigmatism by varying the location and size of the cataract incision.

Aged↗
PubMed1997

Frequency of induced astigmatism following phacoemulsification with suturing versus without suturing.

BACKGROUND AND OBJECTIVES: To compare the postoperative astigmatism between sutured wounds and nonsutured wounds after cataract surgery with a 3.2-mm scleral tunnel incision. PATIENTS AND METHODS: One hundred ten eyes of 110 patients were studied. Eyes with cataracts were randomly assigned to either the sutured or the unsutured procedure. Identical surgical methods were used in every case except for wound closure technique. Data on uncorrected visual acuity and induced astigmatism were analyzed for 6 months after the surgery. RESULTS: Both groups displayed similar uncorrected visual acuity. Mean induced corneal astigmatism was "against-the-rule" with both techniques, and it remained stable during the study. No significant differences were found between the two groups (P > .1). CONCLUSION: This study has shown that the differences in surgically induced astigmatisms of sutured wounds and nonsutured wounds after cataract surgery were not statistically significant when a 3.2-mm self-sealing incision was used.

Aged↗