Induced Higher-order aberrations after Laser In Situ Keratomileusis (LASIK) Performed with Wavefront-Guided IntraLase Femtosecond Laser in moderate to high Astigmatism.

BACKGROUND: Wavefront-guided Laser-assisted in situ keratomileusis (LASIK) is a widespread and effective surgical treatment for myopia and astigmatic correction but whether it induces higher-order aberrations remains controversial. The study was designed to evaluate the changes in higher-order aberrations after wavefront-guided ablation with IntraLase femtosecond laser in moderate to high astigmatism. METHODS: Twenty-three eyes of 15 patients with moderate to high astigmatism (mean cylinder, -3.22 ± 0.59 dioptres) aged between 19 and 35 years (mean age, 25.6 ± 4.9 years) were included in this prospective study. Subjects with cylinder ≥ 1.5 and ≤2.75 D were classified as moderate astigmatism while high astigmatism was ≥3.00 D. All patients underwent a femtosecond laser-enabled (150-kHz IntraLase iFS; Abbott Medical Optics Inc) wavefront-guided ablation. Uncorrected (UDVA), corrected (CDVA) distance visual acuity in logMAR, keratometry, central corneal thickness (CCT) and higher-order aberrations (HOAs) over a 6 mm pupil, were assessed before and 6 months, postoperatively. The relationship between postoperative change in HOA and preoperative mean spherical equivalent refraction, mean astigmatism, and postoperative CCT were tested. RESULTS: At the last follow-up, the mean UDVA was increased (P < 0.0001) but CDVA remained unchanged (P = 0.48) and no eyes lost ≥2 lines of CDVA. Mean spherical equivalent refraction was reduced (P < 0.0001) and was within ±0.50 D range in 61% of eyes. The average corneal curvature was flatter by 4 D and CCT was reduced by 83 µm (P < 0.0001, for all), postoperatively. Coma aberrations remained unchanged (P = 0.07) while the change in trefoil (P = 0.047) postoperatively, was not clinically significant. The 4th order HOAs (spherical aberration and secondary astigmatism) and the HOA root mean square (RMS) increased from -0.18 ± 0.07 µm, 0.04 ± 0.03 µm and 0.47 ± 0.11 µm, preoperatively, to 0.33 ± 0.19 µm (P = 0.004), 0.21 ± 0.09 µm (P < 0.0001) and 0.77 ± 0.27 µm (P < 0.0001), six months postoperatively. The change in spherical aberration after the procedure increased with an increase in the degree of preoperative myopia. CONCLUSIONS: Wavefront-guided IntraLASIK offers a safe and effective option for vision and visual function improvement in astigmatism. Although, reduction of HOA is possible in a few eyes, spherical-like aberrations are increased in majority of the treated eyes.

[Distribution and compensation mechanism of aberrations between anterior and posterior surface of the cornea in myopia and myopic astigmatism eyes].

Objective: To study the compensation mechanism of aberrations between anterior and posterior corneal surface, and to investigate the correlations between corneal aberrations and K values, intraocular pressure and central corneal thickness. Methods: One hundred and sixty-one subjects (300 eyes) with myopia and myopic astigmatism were recruited randomly. Corneal aberrations (anterior, posterior and total) in three different optical zones (2 mm, 4 mm, and 6 mm) centered on the corneal vertex were assessed with a corneal topographer (Sirius). We also calculated compensation factors (CFs) as a measure of the relative efficiency of the aberration compensation mechanism. Astigmatism was divided into corneal astigmatism and non-corneal astigmatism. Mann-Whitney U test was utilized for the comparison of different aberrations and CFs between the two astigmatism groups. Spearman correlation was applied to analyze the correlations between corneal aberrations and K values, intraocular pressure and central corneal thickness. Results: As the order of the aberrations elevated from the second to the seventh, the RMS values decreased significantly. The larger the optical zone, the greater the values of aberrations and the lower the percentage of the compensation mechanism among all the Zernike terms. At the same time, as the order of the aberrations increased, the predominance of the compensation mechanism was increasingly obvious. Slight compensation of spherical aberration (Z40) was observed in the peripheral. In the center of the analyzing zones (2 mm), compensation mechanism represented in coma (Z3±1), and it disappeared in the peripheral. We detected slight compensation of the corneal astigmatism (Z2±2) in the surrounding zone, although the compensation factors were closed to zero in diverse optical zones. Superposition was found in trefoil (Z3±3) straightly. Nevertheless, a tendency towards compensation was discovered with the enlargement of the optical zones. And the secondary spherical aberration (Z60) behaved compensation continuously. However, similar compensation was discovered between the right eye and left eye in different analyzing optical zones. There were significant correlations between the flattest K values and Z2±2, Z3±3and Z40 in the anterior, posterior and total cornea. It was similar with the steepest K values. When the optical zone expanded to 6 mm, Z3±1 and Z40 significantly decreased with intraocular pressure (rcoma=-0.188, P<0.05. rspherical=-0.147, P<0.05). No correlation was found between various aberrations and central corneal thickness (P>0.05). Conclusions: Compensation dominated in the corneal center, while the percentage decreased gradually as the optical zone extended. Slight compensation in astigmatism and spherical aberration between the anterior and posterior cornea may be benificial to the scotopic visual quality. Corneal aberrations were significantly related to K values and intraocular pressure. (Chin J Ophthalmol, 2016, 52: 840-849).

Prevalence of high astigmatism in children aged 3 to 6 years in Guangxi, China.

PURPOSE: To investigate the prevalence and type of high astigmatism among children aged 3 to 6 years in Guangxi, a relatively undeveloped province in western China, and to examine the correlation between astigmatism and visual acuity. METHODS: Children aged 3 to 6 years in Nanning, the capital of Guangxi Province, participated in a population-based survey using a cluster random sampling technique. Eye examinations included autorefraction, visual acuity measurements, and assessments of the external eye, anterior segment, media, and fundus. Data for the right eyes were analyzed. RESULTS: Among the 2304 children examined, the overall prevalence of high astigmatism (≥1.25 diopters by noncycloplegic SureSight autorefraction) was 12.7% (95% confidence interval, 11.3 to 14.0%). The age-specific prevalences of high astigmatism in 3-, 4-, 5-, and 6-year-old children were 13.8, 13.2, 12.9, and 8.1%, respectively. The prevalence of high astigmatism did not vary with age or gender (p > 0.05). The majority of cases of high astigmatism were with-the-rule astigmatism (82.9%), followed by against-the-rule (12.6%) and oblique (4.5%) astigmatism. A linear correlation was found between astigmatism magnitude and visual acuity (logMAR acuity = 0.068 + 0.055 × astigmatism) in all participants. Multiple linear regression analysis further showed that the correlation of astigmatism with visual acuity was magnitude dependent (ß = 0.240). When with-the-rule astigmatism was used as a reference group, against-the-rule astigmatism (ß = 0.137) and oblique astigmatism (ß = 0.154) were closely correlated with visual acuity. CONCLUSIONS: High astigmatism was moderately prevalent among children aged 3 to 6 years in Guangxi Province. With-the-rule astigmatism was the dominant form of astigmatism. Magnitude- and orientation-dependent correlations of astigmatism with visual acuity were confirmed.

How to convert the obliquely crossed to non-crossed astigmatism? A simple method using vector analysis.

The authors discussed about the problem of special form in astigmatism classification. This special type of astigmatism is the form of obliquely crossed astigmatism. In which the meridians, major and minor, are not right angles. In this astigmatism is not possible to prescribing for cylindrical (toric) spectacle lens. Authors describe the Thompson formula for oblique crossed cylinder and observe that this formula is to complicate for calculation new cylinder power. In this reason, the authors create the new formula and simple procedure for this calculation. This simple formula based on vector analysis and read: DM3 = DM2 x cos2 beta.

Prevalence of astigmatism in 6- to 72-month-old African American and Hispanic children: the Multi-ethnic Pediatric Eye Disease Study.

PURPOSE: To determine the age-, gender-, and ethnicity-specific prevalence of astigmatism in African American and Hispanic children aged 6 to 72 months. DESIGN: Population-based, cross-sectional study. PARTICIPANTS: The Multi-Ethnic Pediatric Eye Disease Study is a population-based evaluation of the prevalence of vision disorders in children ages 6 to 72 months in Los Angeles County, California. Seventy-seven percent of eligible children completed a comprehensive eye examination. This report provides the results from 2994 African American and 3030 Hispanic children. METHODS: Eligible children in 44 census tracts were identified during an in-home interview and scheduled for a comprehensive eye examination and in-clinic interview. Cycloplegic autorefraction was used to determine refractive error. MAIN OUTCOME MEASURES: The proportion of children with astigmatism defined as cylindrical refractive error ≥ 1.50 diopters (D) in the worse eye. The astigmatism type was defined as with-the-rule (WTR) (+ cylinder axis 90 ± 15 degrees) and against-the-rule (ATR) (+ cylinder axis 180 ± 15 degrees); all other orientations were considered oblique (OBL). The prevalence of astigmatism and its types were also determined for worse eye cylindrical refractive error ≥ 3.00 D. RESULTS: Prevalence of astigmatism ≥ 1.50 D was higher in Hispanic children compared with African American children (16.8% vs. 12.7%, respectively; P<0.0001). Hispanic children also showed a higher prevalence of astigmatism ≥ 3.00 D than African American children (2.9% vs. 1.0% respectively; P<0.0001). The prevalence of astigmatism ≥ 1.50 D showed a significant decreasing trend with age (P<0.0001). The prevalence of WTR, ATR, and OBL astigmatism ≥ 1.50 D was 13.9%, 0.6%, and 2.2%, respectively, in Hispanic children, and 7.8%, 2.2%, and 2.7%, respectively, in African American children. CONCLUSIONS: We observed ethnicity-related differences in astigmatism prevalence in preschool children. The age-related decrease in astigmatism prevalence in preschool children likely reflects emmetropization.

Comparison of corneal irregular astigmatism by the type of corneal regular astigmatism.

We investigated the relation between corneal regular and irregular astigmatism in normal human eyes. In 951 eyes of 951 patients, corneal irregular astigmatism, such as asymmetry and higher-order irregularity components, was calculated using the Fourier harmonic analysis of corneal topography data within the central 3-mm zone of the anterior corneal surface. The eyes were classified by the type of corneal regular astigmatism into four groups; minimum (< 0.75 diopters), with-the-rule (WTR), against-the-rule (ATR), and oblique astigmatism. The mean age was significantly different among the four groups (P < 0.001); patients with WTR astigmatism were the youngest, followed by those with minimum, oblique, and ATR astigmatism. Significant inter-group differences were found among the four groups in asymmetry (P = 0.005) and higher-order irregularity components (P < 0.001); the largest was in eyes with oblique astigmatism, followed by ATR, WTR, and minimum astigmatism. The stepwise multiple regression analysis revealed that corneal regular astigmatism pattern significantly influenced the amount of corneal irregular astigmatism after controlling for confounding factors (P < 0.001). Corneal irregular astigmatism, such as asymmetry and higher order irregularity components, was the largest in eyes with oblique astigmatism, followed by those with ATR, WTR, and minimum astigmatism, even after adjustment for age of subjects.

[Agreement measurement of ocular wavefront aberrations with three different aberrometers].

OBJECTIVE: To assess the repeatability and difference of ocular wavefront aberrations measured with ray-tracing, dynamic skiascopy, and Hartmann-Shack aberrometers. METHODS: It was an agreement study. Ocular aberrations data obtained by using iTrace (Tracey Technologies), OPD SCAN (Nidek) and WASCA (Zeiss) wavefront aberrometers were analyzed. Eighty six eyes of 45 patients were measured three times. The difference between the measurement and the mean of three consecutive measurements were analyzed to verify the reproducibility. The difference in sphere, cylinder, spherical equivalent (SEQ) and high order aberration (HOA) errors obtained from different aberrometers were evaluated. RESULTS: Repeatability errors of these three wavefront analyzer were found to be low. Comparisons on the same eye showed that there was a significant difference (P < 0.01) in sphere and cylinder between ray-tracing aberrometer and the others in high SEQ group (>or= -6.00 diopter). For HOA, all aberrometers obtained similar results in low SEQ group (< -6.00 diopter). In the high SEQ group, the ray-tracing aberrometer showed statistically higher data in HOA and coma (P < 0.01), and there was no significant difference between the skiascopy and the Hartmann-Shack aberrometer. The iTrace-OPD and iTrace-WASCA HOA difference correlated with spherical equivalent in the high SEQ group (r = -0.418, -0.399, P < 0.01). CONCLUSION: All devices produced similar results of reproducibility, but showed varying results in the ocular total wavefront reading.

[Methods of calculating surgically induced astigmatism]. / Metody obliczania niezbornosci indukowanej chirurgicznie.

Evaluation of surgically induced astigmatism is important, as it allows to thoroughly assess the influence of surgical incision on corneal refraction. This influence can be established by calculating surgically induced astigmatism according to an appropriate mathematical method. The purpose of the study was to describe various mathematical methods used in the current literature to calculate surgically induced astigmatism. When comparing results of calculation of surgically induced astigmatism among different studies, it is necessary to take into account values obtained with the use of the same method of calculation, as various methods evaluate astigmatism differently.

Can information on the purpose of spectacle use and age at first use predict refractive error type?

PURPOSE: To assess the sensitivity and specificity of predicting refractive error type using information from a four-item questionnaire on the purpose of spectacle use and age at first use. METHODS: The Sydney Myopia Study examined 1,740 year 1 (78.9% response) and 2,353 year 7 students (75.3% response) from a random cluster sample of 34 primary and 21 secondary schools across Sydney. Parents of participants completed a four-item questionnaire that sought data on parental spectacle use, age at first use, and purpose of use (for clear distant vision, close work, or both). Prescriptions were obtained for 720 of 3,209 (22%) parents (73% of those approached) for validation. A receiver operating characteristic (ROC) curve was used to determine the optimal cutoff age for spectacle use in myopia classification. RESULTS: Using the ROC curve, a cutoff age of 30 years at first spectacle use produced the highest accuracy in determining myopia. We combined information on the purpose for using spectacles (for distant and near vision) and age of first use at 30 years or younger to determine myopia, otherwise hyperopia. Validated against prescriptions, the sensitivity and specificity of these predictions were 0.89 and 0.83, respectively, for myopia. The specificity was 0.92 for hyperopia and 0.80 for astigmatism, though corresponding sensitivities were lower at 0.23 and 0.46, respectively. CONCLUSIONS: In a sample of the parents of Sydney Myopia Study participants, information on the purpose of spectacle use with an age-at-first-use criterion can identify myopic refractive error with reasonable sensitivity and specificity. This four-item questionnaire may assist future epidemiological studies of screening for myopia.

[Infant ametropias and their evolutions (myopia, hyperopia, astigmatism)]. / Ametropies de l'enfant et leurs évolutions (myopie, hypermétropie, astigmatisme).

Infant ametropias are defined as the whole optic caracteristics of the eyeball which do not allow a clear vision whithout functional disorder. As the sensorial maturity is only achieved at 4 to 5 years, the limits of ametropias are variable before that age. The majority of ametropias is constituted as early as 9 months and may be detected by a refractive examination under cycloplegia. This situation is especially true for hyperopia and astigmatism. The more important are initial ametropias the more unchanged they remain. At 9 months, 1 infant out of 5 present a non-physiological refraction. From 4 to 5 years, 1 child out of 4 needs a refractive correction. Significant myopias are uncommon in infants. They generally appear between 7 and 12 years.

Comparison of surgically induced astigmatism of temporal versus superior clear corneal incisions.

PURPOSE: Comparison of the astigmatism induced by the operation based on the 2.8 mm incisions in the clear cornea, performed by temporal approach and superior approach. MATERIAL AND METHODS: Retrospective analysis was performed on the group of 65 patients (41 women and 24 men), mean age 74.5 +/- 7.1 years old. We studied a series of 70 eyes (32 right eyes and 38 left eyes). All of the patients underwent cataract surgery by means of ultrasonic phacoemulsification conducted at the Department of Ophthalmology, Military Health Services Institute in Warsaw, Poland within 2004-2005. Follow-up examinations took place 6 months after operation. There were DBCVA. NBCVA, intraocular pressure, anterior segment of the eye and fundus examined. Curvature of the cornea was measured by means of Javal's ophthalmometry. The results were assumed as significant in view of corneal curvature stabilization. Vector analysis of astigmatism was performed on the basis of method described by Jaffe. There was preoperative astigmatism vector (K1) and post-operative astigmatism vector (K3) calculated, as well as surgically inducted astigmatism (SIA)--vector (K2). From the group of 70 eyes, 19 were excluded from the study, where vector K1 was > 1.0 D as well as four eyes, where the main opening site depended on the size and axis of K1 vector. The group of 47 eyes was divided according to the opening site into two subgroups--group I (temporal approach--2.8 mm)--25 eyes and group II (superior approach 2.8 mm)--22 eyes. Statistical analysis was performed based on Statistica package 6.0 PL., using U-Mann-Whitney's test, Chi square Yates' test, Kruskal-Wailis' variance analysis, logistic regression and W Shapiro-Wilk's test. RESULTS: Studied groups were homogeneous with respect to age structure, sex, number of operated eyes and pre-operative size of corneal astigmatism vector K1 (p > .05). The mean values of SIA in group I and II were respectively: 0.63 +/- 0.28 and 1.00 +/- 0.54 and were statistically significant (p < .05). The mean values of K3 post-operative vector measured 6 months following the operation was: 0.54 +/- 0.35 in the group I and 0.96 +/- 0.43 in the group II. Differences between two groups show statistical significance (p < .05). Size of SIA has crucial influence on generating post-operative astigmatism > 1.0 D (p = .03). CONCLUSIONS: Clear corneal temporal approach 2.8 mm is more beneficial method comparing to superior approach of the same width, because of the scale of SIA.

Topography-Guided Transepithelial Surface Ablation in the Treatment of Moderate to High Astigmatism.

PURPOSE: To analyze the outcomes of treatment of astigmatism of 2.00 diopters (D) or greater with topography-guided transepithelial surface ablation. METHODS: Retrospective analysis of a series of 206 eyes divided into two groups: myopic astigmatism (153 eyes) and mixed astigmatism (53 eyes). All cases were treated with topography-guided transepithelial surface ablation. Efficacy, safety, and predictability were evaluated, and vector analysis of cylindrical correction was performed. RESULTS: The median preoperative spherical equivalent was -2.63 and -0.63 D for the myopic and mixed astigmatism groups, respectively, with median cylinder of -2.50 D. Postoperative uncorrected distance visual acuity was 20/20 or better in 92% and 83% of eyes in the myopic and mixed astigmatism groups, respectively; the corresponding efficacy indices were 1.00 and 0.96 and residual astigmatism of 0.50 D or less was present in 82.4% and 56.7% of eyes in the myopic and mixed astigmatism groups, respectively. The arithmetic mean magnitude of the difference vector was 0.38 (myopic) and 0.65 (mixed) D. Difference vector magnitude was positively correlated with the magnitude of target induced astigmatism in both groups. The geometric mean coefficient of adjustment index was 1.04 and 1.19, representing undercorrection of 4% and 19% in the myopic and mixed astigmatism groups, respectively. CONCLUSIONS: Topography-guided transepithelial ablation is a safe, effective, and predictable treatment for moderate to high astigmatism. [J Refract Surg. 2016;32(6):418-425.].

The pattern of astigmatism in a Canadian preschool population.

PURPOSE: To measure magnitude, type, and central tendency of astigmatism found in a county-wide population of Canadian preschool children (mean age, 48.1 months). METHODS: Noncycloplegic autorefractive measures were taken in 1179 children attending a preschool health fair operated by their county board of health. Spherocylinder measures were transformed into three independent components. RESULTS: The equivalent sphere showed considerable variation between retinoscopy and autorefraction that was attributed to the variable overaccommodation induced by the autorefractor. Astigmatic components were not affected. Small discrepancies between the two techniques were similar to those in adults and were not of sufficient magnitude to affect validity. With-the-rule (WTR) astigmatism of at least 0.25 D was the most frequent form (45%) followed by against-the-rule (ATR; 40%) and oblique (15%). The 95th percentile for cylinder magnitude was found at 1.25 D. Astigmatisms beyond this value were predominately WTR. The mean (negative) cylinder magnitude was 0.08 Dx 015 degrees. CONCLUSIONS: When spherocylinder values are transformed into a mathematical continuum rather than WTR and ATR classifications, the true central tendency of the population is better defined and is close to zero. Astigmatisms of more than 1.25 D in the preschool child exceed the 95th percentile in this population and were more frequently WTR.

Detection and classification of mild irregular astigmatism in patients with good visual acuity.

Videokeratography has been available for a decade, and this test is essential for determining the presence and type of irregular corneal astigmatism. Three eyes diagnosed with myopic astigmatism and considered good candidates for refractive surgery with conventional examination were studied. Color-coded maps with videokeratography showed regular astigmatism in one eye and the existence of irregular astigmatism in two eyes. Videokeratography showed that one of these eyes had a keratoconus suspect pattern and the second showed a pattern consistent with pellucid marginal degeneration. Videokeratography can detect and classify irregular astigmatism in cases where routine examination shows no abnormal findings.

Developing entry criteria for studies of severe postkeratoplasty astigmatism.

Investigators who use keratometry or topography systems to plan operations for the correction of severe postkeratoplasty astigmatism assume the study group is homogeneous. To test this hypothesis, we established four entry criteria we believed were necessary to ensure a homogeneous group. The criteria were as follows: (1) best-corrected or pinhole visual acuity greater than or equal to 20/40; (2) graft well centered relative to the corneal light reflex; (3) corneal light reflex within 0.5 mm of the center of the entrance pupil; and (4) a minimum of ten central keratoscope rings of the Corneal Modeling System accurately digitized. A retrospective analysis of the keratoscope images of 20 consecutive patients (20 eyes) referred for correction of postkeratoplasty astigmatism was performed to determine the percentage of patients who met the proposed criteria. Only seven (35%) simultaneously met all four entry criteria. Investigators interested in comparing techniques to correct this problem are faced with a dilemma. Strict entry criteria will ensure a homogeneous study group but will exclude most patients. More lenient entry criteria will increase the number of eligible subjects but will introduce heterogeneity, which may confound results.

[Bioptic. A refractive surgery procedure for correction of high and extreme myopia]. / Bioptik Ein Verfahren der refraktiven Chirurgie zur Korrektur der hohen und extremen Myopie.

BACKGROUND: The complete correction of highly or extremely myopic eyes to emmetropia can only be achieved by very few procedures: The combination of implanting phacic intraocular lenses and the use of LASIK (laser in-situ keratomileusis) - Bioptic - makes it possible to achieve this goal to a great extent. PATIENTS AND METHODS: The Bioptic procedure was carried out on 17 eyes of 10 patients. Two weeks after corneal dissection with the Hansatom,an implantable phacic lens (STAAR) was introduced into the posterior chamber and 4 weeks later the residual myopia was treated with LASIK combined with the correction of astigmatic errors. The follow-up time was 10.2 (6.7) months. RESULTS: Preoperative average values of the manifest refraction were -16.22 sph (3.86) with 1.40 cyl (1.30) which changed to -3.85 sph (2.73) with -1.50 cyl (0.87) after implantation of an ICL trade mark into the posterior chamber. Visual acuity increased from uncorrected hand motion to 0.13 (0.10) and corrected from 0.53 (0.19) to 0.63 (0.19). The refraction of implanted ICLs trade mark was 14.6 dpt (1.1). Following the LASIK procedure the uncorrected visual acuity improved to 0.68 (0.16) and fully corrected to 0.79 (0.20). The final refraction measured +0.16 sph (0.67) with -0.48 cyl (0.25). The keratectomy depth was 80.63 -m (26.9) and the optical zone showed a horizontal distance of 6.28 mm (0.39). CONCLUSION: Bioptic is able to correct highly and extremely myopic eyes with the combination of phacic lenses and subsequent LASIK. A concomitant astigmatism can be corrected up to 2.5 dpt simultaneously. With the combination of both procedures,the optical zone can be enlarged. Keeping in mind that phacic lenses reveal a constant refraction after a few days and also that LASIK is refractively safe in low myopia of -4 dpt to -5 dpt, it can be expected that the refractive deviation following the Bioptic procedure is low.

How to calculate surgically induced astigmatism after cataract surgery?

Corneal astigmatism is a complex entity with a power and an axis. The purpose of this article is to give a summary of the most popular methods to calculate surgically induced astigmatism, and to discuss their differences. Various methods exist, but we will only discuss the most popular ones. The interested surgeon can use these methods on his patients to calculate and compare the surgically induced astigmatism of each of his surgical techniques. Doing so, he will be able to use the ideal technique in each individual case. Astigmatism-neutral as well as astigmatism-inducing techniques should be used. A correct pre- and postoperative keratometry is of course very important.

Refractive astigmatism and size of pterygium.

The study evaluates the relationship between varying sizes of pterygium and refractive astigmatism. All patients with pterygium seen at the eye clinic of the University College Hospital within a six months period were included. The length, width and area of pterygium were measured. Refractive astigmatism in the subjects were measured. The findings showed that the length of pterygium on the cornea has a statistically significant relationship with the amount of refractive astigmatism. The amount of astigmatism increases with increase in the length of pterygia. A linear regression analysis showed that 38% of the total variability in astigmatism could be explained by the length of pterygium. The width and area of pterygium on cornea had no significant association with amount of refractive astigmatism. Size of pterygia could be an important predictor of the amount of astigmatism in an eye. However, a larger study need to be done to find other possible factors associating refractive astigmatism in eyes with pterygium.

[A clinical report on mixed astigmatism].

OBJECTIVE: This study was designed to analyze the common cause of asthenopia, mixed astigmatism. METHODS: The types and characters of mixed astigmatism in 356 eyes (207 patients) were analyzed and their naked and corrected visual acuities were investigated. Some problems of mixed astigmatism were discussed. RESULTS: Most of the patients had evident visual defects, the average naked visual acuity being 0.3 (20/60). However, all the patients had better corrected visual acuities with an average of 0.6 (20/30). CONCLUSIONS: Due to the presence of accommodation during the examination, an incorrect lens may be prescribed. Three mistakes might occur, (1) A mixed astigmatism is not detected, and a simple myopic lens is prescribed; (2) An eye with mixed astigmatism is diagnosed as simple or compound myopic astigmatism; (3) A hyperopic astigmatism is diagnosed as mixed astigmatism. The visual defects caused by mixed astigmatism can be satisfactorily corrected by spectacles.

[Eight year results of excimer laser correction for irregular astigmatism by linear excimer laser photoablations of the cornea in cases of keratoconus]. / Osmioletnie wyniki korekcji astygmatyzmu nieregularnego metoda linijnych fotoablacji laserem excimerowym w przypadkach stozka rogówki.

PURPOSE: The purpose of this study was to evaluate changes of the corneal curvature as a result of linear incisions with excimer laser and also to evaluate durability of the achieved effect, including the changes in visual acuity, topographic maps of the corneal curvature and keratometric changes at the location of keratoconus 2, 4, 8, 16, 24 weeks postoperatively. MATERIAL AND METHODS: At the First Department and Clinic of Ophthalmology, Silesian Medical School in Katowice, 294 patients went through ophthalmological examinations. 164 patients (187 eyes) with the III degree of keratoconus according to the Amsler scale, including 69 women (77 eyes) and 95 men (110 eyes), were classified for the excimer laser surgery with the method of linear, corneal incisions with MEL-60 (Aesculap-Meditec). The eyes did not tolerate contact lenses at all or because of peripheral location of the keratoconus. The patients were from 16 to 60 years of age (the mean age was 27.9 years). RESULTS: According to the statistical results, there were no difference between the effects of treatment between men and women. Correlation between the results of the surgery and the patients age showed that the latter did not have any effect on the final result. Lack of correlation between the height of the absolute corneal curvature at the keratoconus and the achieved change after the surgery was reported, thus changes of the corneal curvature parameters do not depend on its parameters before the surgical procedure. Absolute visual acuity of patients was improving and reached maximally 0.252 of the unit. As a result of the single surgery, the maximum change of keratometric values was 4.949 D, and the minimum was 3.611 D. In the case of the secondary surgery, the maximum keratometric value at the axis of the incision was 8.55 D and the minimum one was 7.101 D. CONCLUSION: To sum up, we can say that the favourable effect of decreasing the irregular corneal astigmatism with the method of linear laser fotoablations was maintained throughout the whole observation period, which allowed to shift in time planned corneal transplantation.