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At least 1,099 records · Page 61Linked to original sources
PubMed1986

A form of variable astigmatism induced by pseudopterygium.

Pterygium and pseudopterygium have long been known to induce astigmatism and may do so without entering the visual axis. We present a case report of a 34-year-old man with a traumatic pseudopterygium which produced a "dynamic" astigmatism, varying in different fields of gaze. Due to the pseudopterygium's attachment to the lateral canthus, it produced a tethering effect with markedly decreased vision and wrinkling of Descemet's membrane when the eye was directed away from the anchoring point. This model may apply to other ocular diseases where perilimbal attachments and adnexal adhesions to the corneal surface may occur; such connections should be looked for in cases with unexplained low levels of visual acuity.

Adult↗
PubMed1986

Two simple calculating schemes for use in ophthalmic optics--I. Tracing oblique rays through systems including astigmatic surfaces.

A ray tracing scheme using paraxial approximations is described to allow oblique rays to be traced through lenses or optical systems in which some or all of the surfaces may be astigmatic, even at different axes. It is based on consideration of the prismatic effects introduced at each surface. A numerical example reveals some lesser known properties of the circle of least confusion of astigmatic pencils.

Astigmatism↗
PubMed1986

Changes in the orientation of the axis of astigmatism associated with age.

A new regression equation for the change in the axis of astigmatism with age, as deduced from cross-sectional studies, is presented. Possible artefacts arising from the methods used to obtain mean prescriptions are discussed; it is shown that these may result in over-estimation of the occurrence of oblique cylinders in middle-age and that a previously demonstrated gradual change of orientation of the axis of astigmatism may have no basis in reality. The need for further longitudinal studies is emphasized.

Adolescent↗
PubMed1979

A review of one thousand cases of intracapsular cataract extraction: II. Visual results and astigmatic analysis.

A review of 1,000 cases of intracapsular cataract extraction revealed that in eyes in which no factor predisposed to complication, the early visual results were equal to or better than 20/40 in 97% of the cases. Complications of surgery in this group accounted for decreased visual acuity in only 1.7% of the eyes. In the group of patients with high myopia, previous surgery, known corneal disease, or some other factor thought to predispose to a complication, the visual acuity was equal to or better than 20/40 in only 74% of the cases, most of the decrease being due to preexisting factors within the eye rather than complications themselves. In the first group, the total amount of astigmatism produced by all the suturing techniques reviewed was similar. With interrupted suturing techniques, the axis of the correcting cylinder was more often against the rule while continuous closures with monofilament nylon more frequently produced with the rule astigmatism.

Astigmatism↗
PubMed1986

Trapezoidal relaxing incision for post keratoplasty astigmatism.

Eleven patients with high astigmatism after penetrating keratoplasty underwent a new form of relaxing keratotomy, the trapezoidal relaxing keratotomy, originally described by Ruiz. The average preoperative astigmatism was 7.89 diopters (range 4.25 to 12.50 diopters) with an average reduction in cylinder of 5.00 diopters (range 0-9.5 diopters). No complications were experienced.

Astigmatism↗
PubMed1978

Astigmatism and acuity in two primate infants.

The development of grating acuity was followed in two astigmatic primate infants, one a human being and one a pigtail macaque monkey. Both infants showed variations of acuity with grating orientation, predictable from the orientation and type of astigmatism present. Optical correction of the human infant during testing virtually eliminated the variation of acuity with orientation, suggesting that a neurally based meridional amblyopia had not yet been established.

Age Factors↗
PubMed1978

[Postoperative astigmatism and visual acuity after cataract extraction with various operative methods (author's transl)].

UNLABELLED: The postoperative findings after cataract extraction with corneoscleral incision were compared with those after corneal incision in two groups consisting of 70 patients each. The criteria used were the degree and axis of postoperative astigmatism evaluated ophthalmometrically and the postoperative visual acuity. The preoperative values were taken into account. RESULTS: The mean values of astigmatism shortly after corneal incision were very much higher than those after corneoscleral incision, and they approached each other 6 months after cataract extraction. Patients who had an operation done with corneoscleral incision had a better visual acuity than those with corneal incision.

Astigmatism↗
PubMed1980

A pocket corneal astigmatism indicator.

A pocket-sized self-illuminated diagnostic instrument is described which projects a series of white dots upon the cornea from the center to the periphery radially disposed in a fashion similar to an astigmatic dial. The battery-operated instrument allows for a rapid qualitative estimate of corneal astigmatism and the meridians involved.

Astigmatism↗
PubMedDate not supplied

Photorefractive keratectomy for myopic astigmatism using the emphasis erodible mask. Spanish User Group.

Photorefractive keratectomy (PRK) using the Summit emphasis erodible mask was performed on 229 eyes with myopic astigmatism. To analyze the efficacy and safety of the method, we evaluated the following: spectacle corrected visual acuity and refractive error as parameters of efficacy; corneal clarity, decentration of the ablation zone and complications as parameters of safety. Despite the short follow up (the longest was 12 months) our results show that the emphasis erodible mask appears to be an effective surgical method for correcting myopic astigmatism. However, we found a great number of complications and subjective symptoms that worsened the visual outcome. We conclude that the emphasis erodible mask has satisfactory efficacy but unsatisfactory safety.

Astigmatism↗
PubMed1995

Astigmatism analysis after radial keratotomy.

Radial keratotomy without T-cutting was performed on 245 eyes of 124 patients with 6-8 months of post-operative follow-up. The results showed that post-operatively astigmatism was increased in 74 eyes (30.2%) with the increased range from +0.50 to +3.50DC, decreased in 27 eyes (11.0%) and not changed in 144 eyes (58.8%). The main causes of astigmatic change included microperforations, irregular incisions, incisions across the central optical zone and various depths of incisions, etc.

Adolescent↗
PubMed1995

[Calculation of surgically induced astigmatism].

We compared several mathematical methods for the calculation of surgically induced astigmatism, including Jaffe's horizontal component, Jaffe's vector, Cravy's axis-based cylinder, and Holladay's with-the-wound cylinder. Computer stimulation indicated that Jaffe's vector and Holladay's with-the-wound cylinder methods correctly calculate the surgically induced astigmatism regardless of the direction of wounds. The remaining two methods, however, were found to give erroneous values when the wound is constructed off the x-y axis. Holladay's parameter was least affected by the deviation of the surgical axis. When pre- and postsurgical data of eyes undergoing cataract surgery were analyzed (55 eyes were operated on with a 5.5 mm incision located superiorly, 35 eyes with a 5.5 mm incision located supratemporally, and 40 eyes with a superiorly located 3.2 mm incision), only the Holladay's with-the-wound cylinder method could calculate the actual amount of with-and/or against-the-wound changes.

Aged↗
PubMedDate not supplied

Comparison of astigmatic axis in the seated and supine positions.

BACKGROUND: Refractive error is assessed in the seated position while keratorefractive procedures are performed in the supine position. Since position-induced ocular torsion could yield suboptimal results from improper axis alignment, this study was undertaken to ascertain whether ocular cyclotorsion occurs when a subject moves from a seated to supine position. METHODS: Fifty eyes of 29 subjects with refractive cylinder greater than 0.50 diopters were enrolled. Refraction was done with a phoropter and the correction was placed in a trial frame using plus cylinder. Astigmatic axis was determined in the seated and supine positions for 32 eyes by utilizing the "rocking the cylinder" technique and for 32 eyes using the Jackson cross cylinder. Both techniques were used for 14 eyes. RESULTS: No statistically-significant difference for cylinder axis measured in the seated versus supine position was observed using the rocking the cylinder (4.3 degrees standard deviation [SD], 3.5 degrees, range 0 degrees to 13 degrees, p = NS) or the Jackson cross cylinder methods (2.3 degrees, SD, 1.9 degrees, range 0 degrees to 7 degrees, p = NS). Approximately 25% of eyes had a change in axis of 7 degrees to 16 degrees. CONCLUSIONS: These data suggest that the cylinder axis does not change significantly or predictably when most subjects move from the seated to supine position. The Jackson cross cylinder method seems more accurate and reproducible than the rocking the cylinder technique in determination of astigmatic axis under these circumstances.

Adult↗
PubMedDate not supplied

[The potentials of laser refractometry in selecting the eyeglass correction in astigmatism].

Based on the results of clinical trials of a new commercial laser analyzer LAR-2, the author developed a method for laser specification of astigmatic refraction with the use of this device. The method helps adequately solve the principal refraction problem, specify the optimal eyeglass correction for patients with astigmatism. A conclusion is made on diagnostic fitness of LAR-2 laser analyzer.

Adolescent↗
PubMed1993

Myopic astigmatism and simple myopia correction.

A new technique for the treatment of myopic astigmatism and simple myopia correction is described. The technique is based on bioengineering concepts previously studied by the authors that accurately and mathematically describe the transformation of an ellipsoidal surface (astigmatic eye) into a spheroidal one (nonastigmatic eye) by means of minimal cuts (keratotomies). The surgical procedure is described using selected cases to illustrate the alternatives the model can handle. The model itself is not presented because the calculations were done by computer.

Adolescent↗
PubMed1993

[Probability studies on the variations of anterior corneal astigmatism].

The probability method of analysis of astigmatism variations respects both astigmatism components, quantity and axis. The two random variable model that we introduce here analyses cylinder variations and axial variations. After describing the contingency table and the probability table. Expectation of each component and its confidence interval are calculated together with the variance and the standard deviation. Covariance and correlation are calculated. If we want to compare different groups we test cylinders with cylinders and axes with axes. This method does not distort reality and is applicable to the semi meridians from 0 degree to 360 degrees. Only large samples of patients can be studied by this method.

Astigmatism↗
PubMed1993

A longitudinal study of corneal astigmatism changes in Asian eyes.

This study investigated changes in corneal astigmatism with age of 494 Asian eyes in a retrospective study. The results are compared to previous studies of non-Asian eyes. The current study demonstrates a greater magnitude in the rate of change of corneal astigmatism.

Adolescent↗
PubMed1996

Corneal topographic changes and induced astigmatism resulting from superior and temporal scleral pocket incisions.

BACKGROUND AND OBJECTIVE: To determine the corneal topographic changes that are induced by superior and temporal 5-mm scleral pocket incisions. PATIENTS AND METHODS: The authors retrospectively reviewed the records of 43 patients who underwent phacoemulsification with posterior chamber lens implantation through unsutured 5-mm scleral pocket incisions, 24 superiorly and 19 temporally. Corneal curvature was measured using computerized videokeratography, and the induced astigmatism was calculated with the Holladay-Cravy-Koch formula. RESULTS: At 4 to 6 weeks, postoperatively there was mild flattening along with the meridian of the incision in both groups. The change was greater with the superior incisions, but the differences between the groups were not statistically significant. Surgically induced astigmatism was 0.7 D (+/-0.1 D) in the eyes that received superior incisions, and 0.3 D (+/-0.1 D) in the eyes that received temporal incisions; this difference was statistically significant (P < .03). CONCLUSIONS: At 4 to 6 weeks postoperatively, temporal 5.0-mm scleral pocket incisions provide more stable postoperative topography than do superior scleral pocket incisions.

Adult↗