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PubMed2003

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.

Adult↗
PubMed2007

Astigmatism in 12-year-old Australian children: comparisons with a 6-year-old population.

PURPOSE: To study the distributions of refractive (RA), corneal (CA), and internal astigmatism (IA) in 12-year-old Australian children and to explore differences from previous findings in 6-year-old children. METHODS: Eligible year 7 students (2353/3144 [75.3%], median age, 12 years) from a random cluster sample of 21 high schools in Sydney, Australia, were examined by keratometry, cycloplegic autorefraction, and review of questionnaire data. RESULTS: Prevalence rates of RA, CA, and IA > or =1.0 D in right eyes were 6.7% (95% confidence interval [CI], 5.0-8.4), 26.6% (CI, 22.1-31.1), and 26.5% (CI, 22.9-30.0), respectively. RA was predominantly with-the-rule (WTR; 40.4%, CI, 32.6 to 48.2) and against-the-rule (ATR; 43.6%, CI, 35.7-51.5), CA was WTR (88.8%, CI, 86.3-91.3), and IA was ATR (90.2%, CI, 87.8-92.6). The girls had significantly greater CA and IA prevalence, with greater ATR astigmatism and lower oblique IA than did the boys. The European white-Australian children had lower CA prevalence than did the East Asian-Australian children and higher IA prevalence than did the South Asian-Australian children. Ethnic differences in RA prevalence were not significant, when adjusted for confounders. RA was more frequently ATR in European white than in other ethnic groups. Compensation between CA and IA reduced the magnitude of RA. Comparison with the data on 6-year-old children revealed minimal differences for all astigmatic components. CONCLUSIONS: There was a relatively low prevalence of RA, due to compensation between CA and IA. The minimal differences in all components of astigmatism between the two age cohorts suggest that astigmatism is stable between ages 6 and 12 years, although this conclusion needs to be confirmed in longitudinal studies.

Adolescent↗
PubMedDate not supplied

Analysis of the pterygium size inducing marked refractive astigmatism.

PURPOSE: Astigmatic changes induced by the pterygium and their relation to its size and morphology were analysed to establish the critical size for surgery before significant astigmatism occurs. MATERIALS AND METHODS: We evaluated the refraction in 148 eyes of 108 adult patients with primary pterygia. We grouped the astigmatic values according to the keratometric results correlating with the maximal length, width and the approximate total area of the pterigium encroaching on the corneal surface. RESULTS: Pterygia with length or width > or = 3.00 mm were related to significantly higher astigmatism than other groups (p<0.01). The effect of the pterygium morphology on corneal astigmatism was not significant. CONCLUSIONS: Pterygia exceeding 3.00 mm of length or width should be considered within the limits of surgery.

Adult↗
PubMedDate not supplied

Excimer laser photorefractive keratectomy (PRK) in myopic astigmatism.

UNLABELLED: To assess the visual and refractive results of excimer laser photorefractive keratectomy (PRK) in myopic astigmatism. METHODS: Excimer laser PRK was performed using an Aesculap Meditec MEL 60 laser in 46 myopic astigmatic eyes. Preoperative corneal astigmatism was -1.50 D. (+/- 0.50) in 7 eyes (15.2%); -2.50 D. (+/- 0.50 in 14 eyes (30.5%); -3.50 D. (+/- 0.50) in 13 eyes (28.3%); -4.50 D. (+/- 0.50) in 8 eyes (17.4%); and -5.50 D. (+/- 0.50) in 4 eyes (8.6%). Mean preoperative cylinder was -3.50 D. (+/- 2.50). Mean preoperative sphere was -4.50 D. (+/- 2.25). Pre and post-operative visual acuity, refraction, keratometer readings, corneal topography, intraocular pressure, and slit lamp findings were recorded. RESULTS: By one year of follow-up, postoperative cylinder was between +0.50 and -0.50 D. in 31 eyes (67.4%); between -0.50 and -1.50 D. in 11 eyes (23.9%); between -1.50 and -2.50 D. in 4 eyes (8.7%). Mean post-operative cylinder was -1.21 D. (+/- 1.70). Mean postoperative sphere was -1.09 D. (+/- 1.25). Myopic and astigmatic improvement was achieved in each patient (100%). Topography analysis showed 69.4% were within 0.5 mm, 96.8% within 1 mm, 97.8% within 1.5 mm of centration; 55% of the patients achieved uncorrected visual acuity of 10/10 (Snellen). One patient (2.2%) lost one line of best corrected vision due to decentration and change of axis. CONCLUSION: These preliminary results of myopic astigmatic excimer laser PRK procedures compare favorably in efficiency and safety with reports of PRK for myopia.

Adult↗
PubMed1994

Lower-field myopia and astigmatism in amphibians and chickens.

In some afoveate vertebrates refractive state appears to vary over the eye to match the average viewing distances of different areas of the visual field. However, precise measurements are difficult to obtain even in anesthetized animals, because standard methods of refraction are not designed for off-axis measurements and because the presence of astigmatism may fog the results. Therefore we developed a new automated objective technique, automated infrared photoretinoscopy, and measured off-axis refractions in alert chickens and amphibians. We found, in agreement with previous studies, that chickens (Gallus domesticus) are myopic and also have some astigmatism in the lower visual field. Lower-field myopia was, however, variable. It did not match the distance to the ground precisely, but it declined with age (as increased head height would predict). With-the-rule astigmatism was noticed in early posthatching development; it was striking even along the optic axis. The astigmatism lessened with age, as it does in human infants. Frogs (Rana pipiens and Rana temporaria) displayed pronounced myopic astigmatism that was confined to the lower visual field. Salamanders (Salamandra salamandra) and toads (Bufo bufo) showed less variation in refractive state across the visual field, although toads also were myopic in the lower visual field.

Animals↗
PubMedDate not supplied

Measurement of irregular astigmatism using semimeridian data from videokeratographs.

BACKGROUND: Irregular astigmatism is one of the most troublesome side effects of corneal surgery. We attempted to quantify irregular astigmatism in a simple way, using semimeridian data from videokeratographs of corneas with different amounts of irregular astigmatism. METHODS: We studied the corneal topography of 30 normal corneas to be used as controls, 30 corneas from patients after radial keratotomy, 30 corneas from patients after nonfreeze myopic keratomileusis, and 30 corneas with clinically apparent keratoconus. We developed two diagnostic formulas, a refractive power symmetry index and an angle symmetry index, using the absolute-scale, color-coded map, and semimeridian data from the EyeSys Corneal Analysis System, and used them to compare the four groups of corneas. RESULTS: In the corneas with irregular astigmatism, values for the refractive power symmetry index and angle symmetry index were significantly higher than in the normal corneas. The refractive power symmetry index confidence interval set at 95% was 0.58 diopters (D) (range 0.00 D to 0.58 D) in the control group. Using these limits, most values in the radial keratotomy, keratomileusis, and keratoconus groups were abnormal. Spectacle-corrected visual acuity correlated negatively with the refractive power symmetry index (rs = -0.58, p < .001). The refractive power symmetry index sensitivity and specificity were respectively 97% and 66%. Spectacle-corrected visual acuity did not correlate with the angle symmetry index. CONCLUSIONS: Semimeridian data from videokeratographs can be used to quantify irregular astigmatism.

Adult↗
PubMedDate not supplied

Hot needle thermal keratoplasty to correct naturally occurring hyperopic astigmatism.

OBJECTIVE: To study the safety, effectiveness, predictability and stability of sectoral thermal keratoplasty in the treatment of naturally occurring hyperopic astigmatism. METHODS: Using Fyodorov's technique, sectoral controlled coagulations were applied on both sides of the flattest meridian in 12 eyes from eight patients with naturally occurring hyperopic astigmatism. Preoperative average refractive cylinder was +3.19 +/- 1.13 diopters (D), and the mean spherical component was +0.71 +/- 1.03 D. Mean follow-up time was 13.2 months. RESULTS: Immediately after surgery, we observed a significant overcorrection in the treated meridian in all patients. Then, a gradual decrease of the refractive effect was noticed, since the average refractive astigmatism was +0.25 +/- 1.23 D at 6 months and +1.15 +/- 0.86 at 12 months after surgery. At 1 month after surgery, the mean shift in the cylinder axis was 83.75 degrees +/- 8.82 degrees and 12.08 degrees +/- 12.33 degrees at the 1-year examination. Uncorrected visual acuity was 20/40 or better in all patients 1 year after surgery. We did not observe severe corneal complications, such as irregular astigmatism or delayed epithelial wound healing. CONCLUSION: Hot needle sectoral thermal keratoplasty appears to be safe and partially effective in reducing hyperopic astigmatism, but considerable postoperative regression may occur.

Adult↗
PubMedDate not supplied

Experimental circular keratotomy for correction of corneal astigmatism.

PURPOSE: To investigate the effect of circular keratotomy depth and diameter on corneal astigmatism. METHODS: High astigmatism was induced in 25 human donor eyes by an anterior radial 7-0 silk suture across the corneoscleral limbus. With a 6.0, 6.5, 7.0, or 7.5 mm trephine, a 0.3 mm deep circular incision was made in 20 donor eyes. In 5 donor eyes 5 circular incisions were made with a diamond knife set at 0.1, 0.2, 0.3, 0.4, and 0.5 mm depths. RESULTS: The reduction of astigmatism between the 4 groups in which different trephination diameters were used showed no statistically significant difference (P > .1). The relationship between incision depth and reduction of astigmatism was statistically significant (P < .001). CONCLUSION: Artificially induced corneal astigmatism was reduced by a circular keratotomy in this donor eye model. Deeper incisions showed a greater effect.

Astigmatism↗
PubMedDate not supplied

Toric laser in situ keratomileusis for myopic astigmatism using an ablatable mask.

BACKGROUND: To assess the results of toric laser in situ keratomileusis (LASIK) correction of myopic astigmatism. METHODS: A prospective study was performed over a 20 week period for consecutive patients treated for myopic astigmatism. Spectacle-corrected visual acuity, uncorrected visual acuity, spectacle refraction, videokeratography, and complications were recorded. Vector analysis was performed by the ASSORT program. RESULTS: Sixty-five eyes of 42 patients underwent toric LASIK with a Summit Technologies Apex Plus excimer laser. Mean preoperative spherical equivalent refraction at the spectacle plane was -6.24 +/- 2.42 D (range, -1.63 to -14.63 D) and mean pre-operative refractive cylinder magnitude was 1.99 +/- 1.35 D (range, 0.75 to 7.00 D); mean attempted refractive cylinder correction was 1.90 +/- 1.00 D. Six months after LASIK (43 eyes followed), mean spherical equivalent refraction at the spectacle plane was -0.40 +/- 0.55 D and 31 eyes (72.1%) were within +/- 0.50 D of emmetropia. At 6 months, mean refractive cylinder magnitude was 0.74 +/- 0.70 D, mean surgically induced astigmatism was 1.46 +/- 0.86 D, mean absolute angle of error was 10.33 degrees, mean astigmatic correction index was 0.93 +/- 0.36 D, and mean index of success was 0.46 +/- 0.39. Uncorrected visual acuity was 6/12 or better in 34 eyes (79.1%) and 6/6 in 15 eyes (35%); spectacle- corrected visual acuity was 6/9 or better in 41 eyes (95.35%). Six eyes (14.0%) lost 1 line of spectacle-corrected visual acuity at 6 months and one eye (2.3%) lost 2 lines. Ten eyes (23.3%) gained 1 line at 6 months. CONCLUSION: Toric LASIK with an ablatable mask using the Summit Apex Plus excimer laser is a safe and relatively accurate procedure for the correction of myopic astigmatism.

Adult↗
PubMedDate not supplied

Limbal relaxing incisions to correct astigmatism in clear corneal cataract surgery.

PURPOSE: To prevent surgically induced astigmatism following clear corneal cataract surgery. METHODS: Limbal relaxing incisions of 6- or 8-mm length and 0.55-microm depth were performed in 52 patients (52 eyes) with a spherical cornea (20 eyes) or mean with-the-rule astigmatism (32 eyes) of 0.80 +/- 0.30 D after temporal corneal cataract incision. A control group (47 eyes; 19 spherical and 28 with-the-rule astigmatism) underwent the same surgical procedure without limbal relaxing incisions. RESULTS: Six months after surgery, mean with-the-wound change using the Holladay analysis was -0.08 +/- 0.50 D in spherical eyes with limbal relaxing incisions and +0.50 +/- 0.70 D in control eyes. Patients with preoperative with-the-rule astigmatism showed a mean with-the-wound change of -0.09 +/- 0.50 D after limbal relaxing incisions; in corresponding control eyes, mean change was +0.39 +/- 0.70 D. CONCLUSION: Limbal relaxing incisions are a reliable and safe procedure to reduce postoperative astigmatism.

Astigmatism↗
PubMedDate not supplied

Bivariate polar value analysis of surgically induced astigmatism.

PURPOSE: To demonstrate the use of bivariate polar value analysis of surgically induced astigmatism following various cataract incisions. METHODS: In a prospective study, we investigated surgically induced astigmatism following cataract surgery through 9.0-mm, 5.5-mm, and 4.0-mm superior corneal incisions. Autokeratometry was performed preoperatively and during the first year. All net astigmatisms were converted to polar values with reference to the 90 degrees meridian. Univariate and bivariate polar value analyses were performed. RESULTS: After 1 year, univariate polar value analysis disclosed flattening averaging 1.02 D for 9.0-mm incisions, 0.71 D for 5.5-mm incisions, and 0.64 D for 4.0-mm incisions. The induced torque was 0.46 D counterclockwise for the 9-mm incision and close to zero for the 5.5 and 4-mm incisions. Bivariate polar value analysis disclosed a statistically significant (P < .05) difference in surgically induced astigmatism between the 9.0-mm incisions and the two smaller incisions at all follow-up points. CONCLUSION: Univariate polar value analysis demonstrated the surgically induced steepening and torque. Bivariate analysis demonstrated the joint variation in these entities and therefore always yielded the correct result. Univariate and bivariate polar values may be used for analysis of surgically induced astigmatism following cataract surgery in any meridian.

Adult↗
PubMedDate not supplied

Surgically induced astigmatism after laser in situ keratomileusis for spherical myopia.

PURPOSE: To study risk factors for surgically induced astigmatism (SIA) after laser in situ keratomileusis (LASIK). METHODS: In a retrospective case control study of 104 eyes (52 patients) that underwent LASIK for myopia (spherical ablation alone), two groups were studied: 42/104 eyes with SIA, and controls (62/104 eyes). The main variables studied were preoperative refraction, corneal thickness, preoperative keratometric power, amount of ablation, ablation zone diameter, flap thickness, flap size, and the presence of complications. The effect of SIA on visual performance was also evaluated. RESULTS: The mean myopia for which LASIK was undertaken was -4.50 +/- 2.04 D. Mean scalar astigmatism induced was 0.35 +/- 0.50 D at 1 month, 0.33 +/- 0.40 D at 3 months, and 0.16 +/- 0.60 D at 6 months. SIA based on refractive cylinder was 0.66 +/- 0.29 D at 1 month, 0.54 +/- 0.32 D at 3 months, and 0.49 +/- 0.34 D at 6 months. Mean axis of vector induced astigmatism was 82.5 degrees +/- 57 degrees at 1 month, 98.86 degrees +/- 52.4 degrees at 3 months, and 113.9 degrees +/- 62.6 degrees at 6 months. Risk factors associated with the occurrence of SIA were preoperative keratometric power of >44 D [OR (95% CI); 1.97 (0.62 to 6.26)], ablation zone diameter of <6 mm [OR (95 % CI) 2.76; (0.6 to 12.6)], and suction ring diameter of 8.5 mm [OR (95% CI) 12.46; (2.0 to 77.38)]. The occurrence of SIA had no significant effect on uncorrected Snellen high contrast visual acuity, contrast sensitivity, and glare in comparison with controls. CONCLUSION: Surgically induced astigmatism was more likely to occur with the use of smaller suction rings of 8.5 mm and in ablation zones less than 6 mm. Parameters for visual performance were not affected by the presence of surgically induced astigmatism.

Adult↗
PubMedDate not supplied

Photorefractive keratectomy using the meditec MEL 70 G-scan laser for hyperopia and hyperopic astigmatism.

PURPOSE: To evaluate the results of photorefractive keratectomy (PRK) using Gaussian flying spot technology in the treatment of hyperopia and hyperopic astigmatism. METHODS: Two hundred eyes were evaluated with 12-month follow-up. An Asclepion-Meditec MEL 70 G-scan flying spot ArF excimer laser with a Gaussian scanner was used (6.0-mm treatment zone and 9.0-mm transition zone). Eyes were divided into four groups: Group 1 (spherical hyperopia up to +3.50 D and astigmatism less than 1.00 D, n=62); Group 2 (hyperopia up to +3.50 D and astigmatism of 1.00 D or more, n=44); Group 3 (hyperopia greater than +3.50 D and astigmatism less than 1.00 D, n=56); and Group 4 (hyperopia greater than +3.50 D and astigmatism of 1.00 D or more, n=38). RESULTS: In Group 1, 82.2% (51/62 eyes) were within +/-0.50 D of target refraction; 88.7% (55/62 eyes) had 20/20 or better uncorrected visual acuity; 1.6% (1/62 eye) lost two or more lines, 3.2% (2/62 eyes) gained two or more lines of spectacle-corrected visual acuity. In Group 2, 68.1% (30/44 eyes) were within +/-0.50 D; 77.2% (34/44 eyes) had 20/20 or better uncorrected visual acuity; 9.1% (4/44 eyes) lost two or more lines of spectacle-corrected visual acuity. In Group 3, 76.8% (43/56 eyes) were within +/-0.50 D; 78.6% (44/56 eyes) had 20/20 or better uncorrected visual acuity; 5.4% (3/56 eyes) lost two or more lines of spectacle-corrected visual acuity. In Group 4, 42% (16/38 eyes) were within +/-0.50 D; 60.5% (23/38 eyes) had 20/20 or better uncorrected visual acuity; 15.8% (6/38 eyes) lost two or more Snellen lines. CONCLUSION: PRK with the flying spot Meditec MEL 70 G-scan was most safe and effective for low hyperopia.

Adult↗
PubMedDate not supplied

Laser in situ keratomileusis for correction of induced astigmatism from cataract surgery.

PURPOSE: To evaluate the efficacy, predictability, stability, and safety of laser in situ keratomileusis (LASIK) to correct residual astigmatism after cataract surgery. METHODS: LASIK was performed on 20 eyes of 20 patients with refractive myopic or mixed astigmatism (3.00 to 6.00 D) at least 1 year after extracapsular cataract extraction with posterior chamber intraocular lens implantation without complication. Each eye received bitoric LASIK with the Nidek EC-5000 excimer laser and the Automated Corneal Shaper microkeratome. RESULTS: At 6 months after LASIK, mean refractive cylinder decreased from 4.64+/-0.63 D to 0.44+/-0.24 D (P<.001). Mean percent reduction of astigmatism was 90.4+/-5.0% (range 80% to 100%). Mean spherical equivalent refraction decreased from -2.19+/-0.88 D (range -1.00 to -3.88 D) to -0.32+/-0.34 D (range -1.25 to +0.38 D) (P<.001). Vector analysis showed that the mean amount of axis deviation was 0.7+/-1.2 degrees (range 0 degrees to 4.3 degrees) and the mean percent correction of preoperative astigmatism was 92.1+/-5.9% (range 85.6% to 108%). Eighty-five percent of all eyes had a mean spherical equivalent refraction and mean cylinder within +/-0.50 D of emmetropia. Change in spherical equivalent refraction and cylinder from 2 weeks to 6 months was < or = 0.50 D in 90% (18 eyes) and 95% (19 eyes), respectively. Spectacle-corrected visual acuity was not reduced in any eye. Diffuse lamellar keratitis occurred in three eyes (15%) after LASIK, and were treated successfully with eyedrops. CONCLUSION: LASIK was an effective, predictable, stable, and safe procedure for correction of residual myopic or mixed astigmatism ranging from 3.00 to 6.00 D with a low spherical component after cataract surgery.

Aged↗
PubMedDate not supplied

Diode laser thermal keratoplasty for hyperopia and hyperopic astigmatism in patients younger than 40 years.

PURPOSE: We performed a prospective, nonrandomized investigation of contact continuous wave diode laser thermal keratoplasty (DTK) for correction of hyperopia and hyperopic astigmatism. The goal of surgery was not to achieve emmetropia but to investigate the refractive effect in patients younger than 40 years. METHODS: Twenty eyes with spherical hyperopia (Group A) and 15 eyes with hyperopic astigmatism (Group B) were treated with two rings; treatment zone diameter of the inner ring was 6 or 7 mm. Each ring consisted of eight spots for hyperopia correction; for astigmatism correction four additional pairs of spots were applied around the flat corneal meridian. RESULTS: Mean change in manifest spherical equivalent refraction 18 months postoperatively in Group A was 2.00 +/- 0.90 D (Group B, 15 mo, 1.80 +/- 0.60 D). Mean increase in keratometric power was 1.20 +/- 0.60 D (1.30 +/- 0.60 D). Mean refractive astigmatism reduction was 0.10 D (1.70 D). Mean paired differences per month for regression between spherical equivalent manifest refraction/keratometric power was 0.12/0.04 D (0.06/0.05 D) from 9 to 12 months, 0.01/0.04 D (0.06/0.06 D) from 12 to 15 mo, and -0.03/ +/- 0 D from 15 to 18 months. Mean uncorrected visual acuity improved from 20/100 to 20/32 (20/63 to 20/32). No eye lost more than 1 line of BSCVA. The amount of correction showed an age dependency. CONCLUSION: DTK is a minimally invasive, low-risk procedure, and was effective for correction of low hyperopia and low to moderate hyperopic astigmatism in patients less than 40 years.

Adult↗
PubMedDate not supplied

Strategic planning in topography-guided ablation of irregular astigmatism after laser refractive surgery.

PURPOSE: To identify an optimal customized ablation strategy in the treatment of eyes with secondary irregular astigmatism. METHODS: Corneal anterior surface elevation maps of 50 eyes with secondary irregular astigmatism after decentered laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) and 50 virgin eyes were used for customized ablation simulations. Two ablation simulations with targeted postoperative surfaces perpendicular to either the visual or corneal morphological axis were made for each eye. All ablations were programmed for correction of corneal irregularities, including corneal astigmatism. The manifest refractive error was not corrected. Optical diameter was 6.5 mm and total diameter was 7.5 mm. Maximum ablation depths and maximum transition zone gradients were registered and analyzed. RESULTS: In eyes with secondary irregular astigmatism, mean maximum ablation depth was 48.21 +/- 25.96 microm and 26.31+/- 14.08 microm, whereas mean maximum transition zone gradient was 29.07 +/- 25.15 microm and 9.88 +/- 6.41 microm in ablation simulations based on the visual and corneal morphological axes, respectively. The difference between the ablation strategies was highly statistically significant for both parameters (P < .001). In virgin eyes, only a minor difference was noted between the visual and corneal morphological axis ablation simulations (P = .15 for maximum ablation depths and P=.19 for maximum transition zone gradient). CONCLUSIONS: In secondary irregular astigmatism, ablation based on the corneal morphological axis appears to minimize corneal tissue consumption and allows a smoother transition zone.

Adult↗
PubMedDate not supplied

Fourier analysis of irregular astigmatism after trabeculectomy.

OBJECTIVE: To examine irregular astigmatism following trabeculectomy using Fourier analysis of videokeratography data. PATIENTS AND METHODS: Forty eyes of 40 glaucoma patients, undergoing primary trabeculectomy, underwent videokeratographic examinations preoperatively, and at 2 weeks and 1, 3, 6, and 12 months postoperatively. The dioptric data of the central cornea were decomposed into spherical, regular astigmatic, and irregular astigmatic (decentration and higher-order irregularity) components using Fourier analysis. RESULTS: The mean spherical equivalent did not change throughout the observation period. The regular astigmatic component from 2 weeks to 6 months post-operatively was greater than the preoperative diopter, but the increase was not significant. In contrast, the decentration component increased significantly after surgery, but returned to the preoperative level by 12 months. The higher-order irregularity component also presented a transient increase postoperatively. CONCLUSIONS: Irregular astigmatism, particularly decentration component, increases significantly after trabeculectomy, but returns to the preoperative level 12 months after surgery.

Adult↗
PubMed2001

Comparison of preschool vision screening methods in a population with a high prevalence of astigmatism.

PURPOSE: To compare the effectiveness of four methods of screening 3- to 5-year-old children for astigmatism high enough to require spectacle correction. METHODS: Lea Symbols Visual Acuity Screening (LSVAS), MTI Photoscreening (MTIPS), Nidek KM-500 Keratometry Screening (KERS), and Retinomax K-Plus Noncycloplegic Autorefraction Screening (NCARS) were attempted on 379 preschool children who are members of a Native American tribe having a high prevalence of astigmatism that is primarily corneal in origin. The need for spectacle correction was determined by cycloplegic refraction. Receiver Operating Characteristic (ROC) curves were fit, confidence intervals were determined, and area under the curves was compared. RESULTS: Astigmatism > or = 1.00 D was present in the right eye of 47.5% and in the left eye of 48.0% of children. Spectacles were prescribed for children < 48 months of age who had cylinder > or = 2.00 D and children > or = 48 months who had cylinder > or = 1.50 D, with the result that 33% of subjects required spectacles. Area under the ROC curve was 0.98 for NCARS, 0.92 for KERS, 0.78 for MTIPS, and 0.70 for LSVAS, and each of these values differed significantly from the other three (all P < 0.007). Testability was significantly higher for NCARS (99.5%) and KERS (99.7%) than for MTIPS (93.5%) and LSVAS (92.0%). CONCLUSIONS: In a population that included many children with astigmatism, objective, fully automated screening methods (NCARS and KERS) were superior to both visual acuity screening and photoscreening with subjective interpretation in identifying children who had astigmatism requiring spectacle correction.

Amblyopia↗