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PubMed2003

[Role of astigmatism in the creation of myopia].

PURPOSE: To determine, whether the presence of astigmatism has an influence on the creation of myopia. MATERIAL AND METHODS: A total of 167 people with myopia (117 women and 50 men) of the age between 12 and 51 were examined. The overall average age was 24. Routine ophthalmological examinations, keratometry as well as refractometry were carried out. The data was analysed using the coefficient of rang Spearman's correlation and the coefficient of linear Pearson's correlation. RESULTS: A negative correlation was found between the corneal astigmatism and myopia progress (P < 0.000001). A positive correlation was observed between total astigmatism and myopia (P < 0.000001). CONCLUSIONS: Corneal and total astigmatism predisposes the progress of myopia.

Adolescent↗
PubMed2004

[Astigmatism among students ranging from 6 to 18 years of age].

PURPOSE: To determine the prevalence of astigmatism among students ranging from 6 to 18 years of age. MATERIAL AND METHODS: 5023 students from elementary schools, junior high schools and high schools, aged 6-18 years were examined. Measurements of visual acuity as well as retinoscopy after cycloplegia have been carried out. The data was analyzed using chi-square test, and the coefficients of rang Spearman's correlation were calculated. RESULTS: It was found that 4% of the students, aged from 6 to 18 suffers from astigmatism. No influence of the students' age on the prevalence of astigmatism was observed. It was found that astigmatism occurs more frequently among boys rather than girls.

Astigmatism↗
PubMedDate not supplied

Cat keratoplasty wound healing and corneal astigmatism.

BACKGROUND: A major contributor to postkeratoplasty astigmatism may be donor/recipient disparity. Deficient or excess cornea at the wound is thought to influence the directions of the steep and flat meridians. Using an established model of penetrating keratoplasty in the cat, this study evaluated the morphometry of histopathologic wound features in the steep and flat meridians. METHODS: Thirteen cats had successful penetrating keratoplasties after intentionally misshapen donor corneas were misaligned in misshapen recipient beds. At 9.50 +/- 0.32 (mean +/- 1 SEM) months after keratoplasty, photokeratography was performed and analyzed, corneas were sectioned along the steep and flat meridians, and four histologic sections were processed. Features of the wounds were measured using a Zeiss Videoplan. The relationships between the morphometry of each feature and every other feature, between the morphometry of each feature and eccentricity, and between the steep and flat section morphometry of each feature were statistically evaluated. RESULTS: Epithelial thickness, area of lamellar alteration, length of Descemet's membrane produced postoperatively, and the depth that preoperative Descemet's membrane was embedded in the stroma were correlated with eccentricity (corneal astigmatism). Stromal thickness and the presence or absence of folded and fragmented Descemet's membrane were not correlated with eccentricity. Wound morphometry at the steep meridians was neither correlated with nor significantly different from wound morphometry at the flat meridians. CONCLUSIONS: Differences between healing at the steep and flat meridians were not likely contributors to astigmatism. Disproportionate availability of tissue in wound regions may have affected healing throughout the entire wound over time. The absence of Bowman's layer in cats restricts application of our results to understanding the etiology of corneal astigmatism after penetrating keratoplasty in humans.

Animals↗
PubMed1991

[Modified scleral pocket incision to control corneal astigmatism after intraocular lens implantation].

Modified scleral pocket incision was used on 37 cases (37 eyes) with senile cataract when extracapsular cataract extraction with posterior chamber intraocular lens implantation was performed. The peak value of postoperative corneal astigmatism was 3.60 dioptor (D), corneal astigmatism regression was 2.11 D. Modified scleral pocket incision could reduce significantly postoperative corneal astigmatism and promote to recover of visual acuity. The mechanism of modified scleral pocket to reduce postoperative corneal astigmatism is discussed.

Aged↗
PubMedDate not supplied

Use of keratoscopy, slit-lamp biomicroscopy, and retinoscopy in the management of astigmatism after penetrating keratoplasty.

Selective suture removal following corneal transplant surgery can facilitate the reduction of astigmatism. We present concepts concerning astigmatism analysis after keratoplasty related to suture compression by reviewing keratoscopy, slit-lamp biomicroscopy, and retinoscopy findings. Keratoscopy observations indicating tight sutures include peripheral indentation of the keratoscope rings, individual keratoscope ring images between tight sutures, and decentration of the corneal apex away from a tight suture. The utilization of the Van Loenen keratoscope at the slit-lamp in "dynamic keratoscopy" allows the surgeon to readily recognize these findings and also proves useful intraoperatively. Slit-lamp biomicroscope observations indicative of tight sutures include a doughnut of tissue compression, Kaye's epithelial white dots, and epithelial or endothelial stress lines. Retinoscopy observations demonstrate that tight sutures induce astigmatism with the narrowest side of the retinoscopy beam pointing directly toward the tightest suture. Astigmatism management plays a major role in the future success of ophthalmology and needs to be increasingly integrated into the practice of the general ophthalmologist.

Aged↗
PubMedDate not supplied

Management of corneal astigmatism after cataract surgery.

High degrees of surgically induced astigmatism following cataract surgery may limit the desired visual rehabilitation. The induced astigmatism is a reflection of the cataract incision, its closure, and subsequent wound healing. Excessively tight sutures induce central corneal steepening. Wound dehiscence and wound gap cause a flattening of the central cornea along this axis. Wound compression steepens the central curvature. The management of induced astigmatism is directed to the underlying problem. Suture cutting and removal will reduce suture compression of the wound. Repair of wound dehiscence and wound gap will reestablish wound integrity. Incisional keratotomy will compensate the corneal steepening induced by limbal wound compression. The reduction of astigmatism aids visual function by realizing the visual potential of the operated eye.

Astigmatism↗
PubMed1990

Astigmatism and visual impairment in pterygium: affected eyes in Jos, Nigeria.

One hundred and forty one pterygium-affected and 50 control eyes were examined. It was found that in most of the pterygium-affected and control eyes (85.7% and 79.4% respectively) astigmatism was with-the-rule. It was also found that overall the degree of astigmatism was higher in pterygium-affected eyes (Av. 1.56D) than in control eyes (Av. 0.92D). The degree of astigmatism was much higher in recurrent pterygium eyes when considered separately (Av. 1.81D). Visual impairment in both pterygium-affected and control eyes was in most cases due to co-existing organic diseases. In the remaining pterygium eyes without other organic diseases, the visual impairment could not be correlated with the degree of astigmatism (r = 0.547).

Adolescent↗
PubMed1990

[Surgical correction of corneal astigmatism].

Corneal astigmatism can be treated optically or surgically. First, we try to manage the astigmatism with glasses or contact-lenses. If it cannot be managed successfully with optical devices, a surgical approach may be indicated. Corneal wedge resections and relaxing incisions can be effective. The wedge resection is the more difficult procedure with reasonably predictable results. In recent years corneal relaxing incision has gained popularity because it is a simple technique with fairly rapid visual rehabilitation. However, the correction result is quite unpredictable. We try to evaluate the factor that created the astigmatism. The steep and flat corneal meridian are identified with keratoscopy, and the correction is performed at the end of the corneal meridian causing the astigmatism. The technique and results are discussed.

Astigmatism↗
PubMed1990

Refractive astigmatism and pterygium.

The refraction of 50 patients with pterygium and their age- and sex-matched controls was carried out. Patients with pterygium had surgery by the bare sclera method. A post-operative refraction was carried out at 12 weeks. A refraction was also done in both eyes of patients with unilateral pterygium. There was a statistically significant association between refractive astigmatism and the presence of pterygium (P less than 0.01). Astigmatism was the rule in most patients. Surgical removal caused a reduction in refractive astigmatism. The change in refractive astigmatism was as high as 1.50DC (diopter cylinder). The majority of the patients were in the presbyopic age group. Surgical removal of pterygium will significantly alter the refraction of patients.

Adult↗
PubMed1990

Limbal wedge resection at the time of intraocular lens surgery for reducing postkeratoplasty astigmatism.

Thirteen limbal wedge resections performed to reduce postkeratoplasty astigmatism in patients undergoing secondary intraocular lens placement were reviewed. Eleven of the 13 procedures reduced preoperative astigmatism 3.12 diopters (+/- 1.77 D; range, 0.50 D to 6.25 D). The average follow-up time was 17 months (range, 4 to 36 months). The average flat/steep ratio was 1.19 (+/- 0.96), indicating approximately equal degrees of corneal flattening and steepening. Average central corneal keratometric values steepened 0.47 D, with a range of 0.56 D of flattening to 2.41 D of steepening. Keratometric values were stable by 4 months in most patients. All patients except one with amblyopia had a corrected visual acuity of 20/60 or better. A dellen formation developed in one case, but it caused no permanent negative visual complications. As generally found in previous studies, each 0.1-mm wedge-width resected induced 1 D of astigmatic correction. Limbal wedge resection in conjunction with intraocular lens implantation can safely and effectively reduce astigmatism following penetrating keratoplasty.

Aged↗
PubMed1990

[Accommodation in ametropia and the effect of targets on astigmatism].

Measurements of accommodative responses in 28 astigmatic eyes (22 patients, 19-32 years of age) were made with an objective Auto Refkeratometer (Canon, RK-1). We constructed an actual target representative instrument with a star burst chart and a fine line chart, and attached this instrument to the Auto Refkeratometer. The fine line chart was turned around the sight line of the eye at a fixed distance. The amount of mean accommodative responses decreased in the following order; the fine line chart parallel to the first principal meridian of subjects, the star burst chart, the fine line chart parallel to the second principal one. This tendency was also shown in cases of subjects with astigmatism less than 1.25 diopters. The slopes of mean accommodative response curves reduced in the similar order as above, significantly in the cases of astigmatism over 1.25 diopters. These results suggest that target charts for accommodation and the degree of astigmatism have influence on the amount of accommodative response and the slope of its curve.

Accommodation, Ocular↗
PubMed1990

Prospective topographic analysis in peripheral arcuate keratotomy for astigmatism.

Delimited peripheral arcuate keratotomy was performed on five eyes of four patients with naturally-occurring astigmatism. Refraction, keratometry, and computer-assisted corneal topographic analysis were performed before and after the procedure. In some eyes, preoperative topographic analysis revealed steepening distributed symmetrically about the corneal apex; in three eyes the steepening was asymmetrically distributed about the corneal apex. In one eye, surgery in a single, steep hemi-meridian superior to the corneal apex flattened that steep hemi-meridian but did not appear to alter the topography of the inferior steep hemi-meridian. Refractive and keratometric astigmatism decreased in all eyes (mean reductions of 3.25 and 2.30 diopters, respectively), and all incisions healed without incident. Surgery extended beyond the zone of steepening in one eye, shifting the axis of astigmatism. A large, multicenter, randomized trial will be necessary to determine whether detailed preoperative topographic analysis can be used to improve the results of surgery for astigmatism.

Adult↗
PubMed1989

Masking of astigmatism with selected spherical soft contact lenses.

This observational study investigated the ability of three current brands of spherical soft contact lenses to correct or "mask" low amounts of refractive astigmatism. The lens brands were worn by 16 subjects having at least 0.50 D, but not more than 1.00 D, of refractive astigmatism. Spherocylindrical refraction over the soft lenses was used to determine the amount of astigmatism that was masked by the lenses. Results showed that the wearing of spherical soft contact lenses, such as those used in this study, cannot be expected to predictably mask astigmatism.

Astigmatism↗
PubMed1989

[Wedge resection, corrective treatment of giant corneal astigmatism].

This study divides major astigmatism into 2 groups for which the authors advocate a new type of wedge resection. Group I includes 18 patients with astigmatism occurring as a complication of penetrating keratoplasty. Group II includes 10 patients with astigmatism due to circumscribed peripheral limbal corneal dystrophy. Wedge resection over a 180 degrees corneal arc resulted in a significant reduction of preoperative astigmatism and an improvement of visual acuity. Use of a photokeratoanalysor could permit better prediction of the expected effect of wedge resection. This instrument provides measurements of all corneal parameters necessary for determining whether surgery should be performed and which technique to use.

Astigmatism↗
PubMed1989

[Experimental studies on the influence of astigmatism on eye accommodation].

We studied the influence of astigmatism on eye accommodation by means of a cathode ray tube (CRT) screen as a visual display terminal. Experiments using an infrared optometer and personal computer showed that artificial astigmatism over 1 diopter induced effects in the visual accommodation system of subjects in their twenties, decreasing the contraction velocity of accommodation, prolonging the settling time of accommodation and increasing the amplitude of accommodative fluctuation. Even if the visual acuity is fairly good with mild astigmatism, astigmatism need to be corrected for preservation of eye accommodation for VDT work in the young age group.

Accommodation, Ocular↗
PubMed1988

Modified relaxing incision technique for postkeratoplasty astigmatism.

A modified relaxing incision technique for postkeratoplasty astigmatism is described in this article. Following the initial, standard relaxing incision techniques, a planned spreading and recutting of the initial relaxing incision was performed at 1-3-week intervals following the initial surgery. The wound may be deepened and lengthened if more effect is needed. The number of spreading and recutting procedures is also dependent on the effect required. This additional procedure may be performed for late regression of the desired effect. The endpoint for the procedure is corneal astigmatism that will allow either spectacle or contact lens correction, depending on the patient's visual needs. Corrections of greater than 10 D of astigmatism are possible. The technique allows for evaluation of the corneal astigmatism with no sutures in place. No complications of the recutting and spreading procedure have been noted. There have been no microperforations or macroperforations requiring suturing, no infections, and no graft rejections following the procedures. Seven cases using the modified relaxing incision technique are described.

Astigmatism↗
PubMedDate not supplied

The theoretical effect of trephine tilt on postkeratoplasty astigmatism.

Most corneal surgeons use a free-hand technique to perform trephination. Of the factors thought to be associated with postkeratoplasty astigmatism, surgeons agree that the process of trephination has the greatest effect on astigmatism. We describe the use of a new trephine that, while affixed to the donor and/or recipient by suction, applanates the cornea to eliminate the oblique incision and undercutting that occur with currently available suction trephines. By mathematical analysis we demonstrate that a 5 degrees to 10 degrees tilt of the trephine can induce significant astigmatism. In theory, the use of the guided trephine system described here will eliminate this complication. This new instrument should be capable of producing identical incisions in the donor and recipient, thereby allowing easier wound coaptation with sutures. This new technology has the potential to eliminate trephination errors as a major cause of postkeratoplasty astigmatism.

Astigmatism↗
PubMed1986

Reduction of astigmatism following cataract surgery.

This study documents the induced corneal astigmatism following cataract surgery. All patients developed significant astigmatism with the rule which decreased with time and following division of sutures. Corneal incision induced a significantly higher degree of astigmatism than limbal incision, but this difference was negated by suture division. There were no cases of wound dehiscence following division of sutures. Suture division is therefore recommended as a method of reducing astigmatism following cataract surgery.

Astigmatism↗