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At least 1,405 records · Page 78Linked to original sources
PubMed2006

A comparison of autorefraction and subjective refraction with and without cycloplegia in primary school children.

PURPOSE: To evaluate the accuracy of autorefraction using three autorefractors comparing to subjective refraction in diagnosing refractive error in children. DESIGN: A cross-sectional study. METHODS: setting: Community based study. study population: 117 children sampled from primary schools. procedures: All subjects underwent autorefraction using three auto refractors and subjective refraction with and without cycloplegia. main outcome measures: Spherical power, cylindrical power, and spherical equivalence (SE). RESULTS: Without cycloplegia, the mean SE were significantly different for Retinomax K plus 2 (-1.55 diopters, SD 2.37 diopters; 95% CI -1.98 to -1.12; P < .0001) and Canon RF10 (-1.11 diopters; SD 2.61 diopters; 95% CI -1.59 to -0.64; P = .0023) compared with monocular subjective refraction (-0.80 diopters; SD 2.25 diopters; 95% CI -1.21 to -0.35). Mean SE was significantly different for Grand Seiko WR5100K (-0.79 diopters; SD 2.40 diopters; 95% CI -1.23 to -0.35; P = .0002) compared with binocular subjective refraction (-0.62 diopters; SD 2.51 diopters; 95% CI -1.07 to -0.16). With cycloplegia, there was no significant difference in mean SE between refraction methods. Sensitivity and specificity results for the diagnosis of myopia: Without cycloplegia: Retinomax K plus 2 (sensitivity 1.0, specificity 0.51); Canon RF10 (sensitivity 0.92, specificity 0.81); and Grand Seiko WR5100K (sensitivity 0.91, specificity 0.98). With cycloplegia: Retinomax K plus 2 (sensitivity 0.97, specificity 0.99); Canon RF10 (sensitivity 0.97, specificity 0.96); and Grand Seiko WR5100K (sensitivity 1.0, specificity 0.97). CONCLUSIONS: Under noncycloplegic conditions, all three autorefractors have a tendency towards minus over correction in children resulting in over diagnosis of myopia. However autorefractors were accurate under cycloplegic conditions.

Child↗
PubMed2005

Changes in scleral MMP-2, TIMP-2 and TGFbeta-2 mRNA expression after imposed myopic and hyperopic defocus in chickens.

Induction of myopia leads to a decreased glycosaminoglycan synthesis and smaller collagen fibrillar diameters, increased levels of gelatinase-A (MMP-2) and decreased amounts of tissue inhibitor of matrix metalloproteinase-2 (TIMP-2) in the fibrous sclera of both chicks and tree shrews. Another factor found to be involved in altered eye growth is the transforming growth factor beta-2 (TGFbeta-2). The aim of the current study was to measure MMP-2, TIMP-2 and TGFbeta-2 mRNA expression changes separately in the two scleral layers of chicks, following myopic and hyperopic defocus. Chicks were treated unilaterally with positive and negative lenses for different time periods. All contralateral eyes wore plano lenses and additional controls, treated binocularly with plano lenses, were included. Real-time PCR was used to measure MMP-2, TIMP-2 and TGFbeta-2 mRNA levels. Few changes in MMP-2 and TIMP-2 mRNA levels were measured following treatment with plus and minus lenses for up to 3 days. The mRNA levels of MMP-2 and TIMP-2 were either unchanged or co-regulated in both eyes, even though only the eye with the powered lens actually displayed changes in growth. In contrast, TGFbeta-2 mRNA was significantly up-regulated in the cartilaginous layer following treatment with plus lenses after 24 hr, compared to all other groups. These changes were confined to the eyes that also displayed reduced growth, suggesting a role of TGFbeta-2 in the final steps of visual eye growth regulation.

Animals↗
PubMed2004

Refractive lensectomy and cross-cylinder laser in situ keratomileusis for the correction of extreme hyperopic astigmatism.

Refractive lensectomy followed by cross-cylinder laser in situ keratomileusis was performed in both eyes of a 46-year-old patient with extreme hyperopic astigmatism. Six months postoperatively, the uncorrected visual acuity was 20/25 with a manifest refraction of +0.25 -0.50 x 44 in the right eye and +0.25 -0.25 x 10 in the left eye. The best corrected visual acuity remained unchanged in both eyes at 20/25. Refractive lensectomy and cross-cylinder LASIK can be effective for treating extreme hyperopic astigmatism.

Astigmatism↗
PubMed2004

New formula for calculating intraocular lens power after laser in situ keratomileusis.

PURPOSE: To assess the validity and accuracy of a proposed formula for keratometry (K) readings after laser in situ keratomileusis (LASIK). SETTING: The Eye Center and the Eye Foundation for Research, Riyadh, Saudi Arabia. METHOD: This studied comprised 34 eyes that had LASIK surgery. Refraction and an automated K-reading (auto-K) were performed preoperatively. Refraction, auto-K, and K-reading assessment by the clinical history method and the proposed formula were performed 4 to 12 weeks postoperatively. The proposed formula is K(postop) = K(preop) - [(N(c) - 1) x (R(a-postop) - R(a-preop))/(R(a-postop) x R(a-preop))], where K(postop) is the K-reading after LASIK, K(preop) is the K-reading before LASIK, N(c) is the index of refraction of the cornea (1.376), R(a-postop) is the radius of curvature of the anterior corneal surface after LASIK, and R(a-preop) is the radius of curvature of the anterior corneal surface before LASIK. RESULTS: Twenty patients (10 men, 10 women) were included in the study. The mean age of the patients was 30.58 years +/- 17.68 (SD) (range 18 to 44 years). Preoperatively, the mean spherical equivalent (SE) was -4.99 +/- 2.82 diopters (D) (range -1.12 to -15.00 D), the mean R(a) was 7.76 +/- 0.32 mm (range 7.33 to 8.50 mm), and the mean auto-K reading was 43.45 +/- 1.73 D (range 39.62 to 46.00 D). Postoperatively, the mean SE was +0.02 +/- 0.63 D (range -2.75 to +1.00 D), the mean R(a) was 8.63 +/- 0.53 mm (range 7.80 to 9.92 mm), and the mean K-reading assessed by auto-K, clinical history method, and the proposed formula was 39.17 +/- 2.35 D (range 34.00 to 43.25 D), 38.79 +/- 2.52 D (range 33.1 to 42.78 D), and 38.69 +/- 2.51 D (range 33.1 to 43.0 D), respectively. The results obtained by the proposed formula were similar to those obtained by the clinical history method (P =.098). Auto-K readings significantly overestimated the K-values (P<.0001) when compared to the proposed formula and clinical history method. CONCLUSION: The proposed formula was simple, objective, not dependent on refraction, and as accurate as the clinical history method in determining K-readings after LASIK.

Adolescent↗
PubMed2004

Wavefront-optimized ablation profiles: theoretical background.

PURPOSE: To describe a method for calculating wavefront-optimized ablation profiles to precompensate for the spherical aberration and higher-order astigmatism induced by myopic, hyperopic, and astigmatic corneal laser corrections. SETTING: IROC-Institut für Refraktive und Ophthalmo-Chirurgie, and Institute for Biomedical Engineering, Swiss Federal Institute of Technology, Zürich, Switzerland. METHODS: The basic ablation profile for myopic, hyperopic, and astigmatic correction is derived from the 2nd-order Zernike representation of wavefront aberrations. Including 4th-order spherical aberration and higher-order astigmatism in the theoretical calculation of the ablation profile allows precompensation for the expected amount of higher-order aberrations (HOAs). The shapes of wavefront-optimized ablation profiles are compared with the shapes of "classic" ablation profiles for myopic and astigmatic corrections. RESULTS: The introduction of precompensating spherical aberration and higher-order astigmatism leads to a more aspheric ablation profile with a significant increase in ablation depth (up to 35%) in the midperiphery of the optical zone. The central ablation depth remains unchanged in the myopic correction but increases by 3% in cylinder correction. CONCLUSIONS: Wavefront-optimized ablation profiles provide a simple method to precompensate for the expected 4th-order spherical aberration and higher-order astigmatism in the average eye. Further clinical studies must be performed to prove the theoretical results; demonstrate the reduction in HOAs; and predict safety, predictability, and stability of wavefront-optimized ablation profiles.

Algorithms↗
PubMed2004

Laser in situ keratomileusis for treated anisometropic amblyopia in awake, autofixating pediatric and adolescent patients.

PURPOSE: To establish the safety and efficacy of laser in situ keratomileusis (LASIK) in pediatric and adolescent patients with anisometropic amblyopia who completed amblyopia therapy and had a visual acuity of 20/30 or better bilaterally. SETTING: Department of Ophthalmology and Visual Science, University of Texas-Houston Medical School, Houston, Texas, USA. METHODS: From August 2000 to March 2002, LASIK was performed in 21 eyes of 19 consecutive patients meeting eligibility requirements. The procedure was performed with the Summit Autonomous LADARVision 4000 excimer laser (Alcon Laboratories, Inc.) in the amblyopic eye for the correction of anisometropia or in both eyes. All patients were awake and autofixating during the procedure. RESULTS: The mean patient age was 13.14 years (range 8 to 19 years). Seventeen patients were treated in the amblyopic eye only to correct anisometropia; treatment was performed in both eyes of 2 patients who were older than 18 years. Patients were followed for a mean of 18.0 months (range 8.6 to 26.5 months). Anisometropia was greater than 2.00 diopters (D) in all cases (mean 4.43 D, range 13.25 to 2.25 D). The percentage deviation from the attempted correction in the myopic group was 4.0% +/- 4.0% (SD) (range 2.0% to 10.0%) and 38.0% +/- 13.0% (range 5.0% to 58.0%) in the hyperopic group. Anisometropia decreased uniformly to less than 2.00 D in all patients (mean 1.52 D). The percentage of patients with stereo acuity increased from 63.0% preoperatively to 84.0% postoperatively. CONCLUSIONS: Laser in situ keratomileusis safely and effectively reduced anisometropia in these patients. If stereo acuity is not possible preoperatively, it may be obtained postoperatively.

Adolescent↗
PubMed2004

Fourier analysis.

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Astigmatism↗
PubMed2004

Contact between 3 phakic intraocular lens models and the crystalline lens: an anterior chamber optical coherence tomography study.

Three phakic intraocular lens (IOL) models were implanted in 3 different patients. With the usual slitlamp examination, it was not possible to determine whether there was contact between the IOLs and the natural crystalline lens. Using the anterior chamber optical coherence tomography (AC OCT) scanner, direct contact between the natural crystalline lens and the 3 phakic IOLs was revealed. A dynamic study of the contact was performed during accommodation. These observations show that examination of the anterior segment with the AC OCT scanner provides new data about the status of the anterior segment after implantation of phakic IOLs.

Accommodation, Ocular↗
PubMed2005

Off-axis refraction and aberrations following conventional laser in situ keratomileusis.

PURPOSE: To investigate off-axis refraction and aberrations following conventional laser in situ keratomileusis (LASIK) for myopia and hypermetropia. SETTING: School of Optometry, Queensland University of Technology, Australia. METHODS: Using an autorefractor, off-axis refractions were analyzed along the horizontal visual field between 35 degrees nasally and 35 degrees temporally in 1 eye each of 15 emmetropic subjects (-0.50 to +0.50 diopters [D]), 6 myopic subjects (-2.25 to -6.50 D), 6 hyperopic subjects (+1.50 to +3.00 D), 6 myopic LASIK patients (presurgical refraction -2.75 to -9.00 D), and 6 hyperopic LASIK patients (presurgical refraction +0.75 to +2.00 D). Wavefront sensing measured off-axis higher-order aberrations in 2 myopic LASIK patients. RESULTS: In myopic LASIK, the mean spherical components of refraction M became highly myopic away from the center of the visual field; in emmetropic and untreated myopic eyes, there were relatively small myopic shifts and hyperopic shifts, respectively. Off-axis 90-degree to 180-degree astigmatisms J180 in myopic LASIK subjects were greater than in untreated subjects. In hyperopic LASIK, there were mainly hyperopic shifts in M, opposite the direction in emmetropic and untreated hyperopic subjects. Off-axis J180 was less than in emmetropic and untreated hyperopic subjects. Some hyperopic LASIK patients had greater off-axis 45-degree to 135-degree astigmatisms J45 than patients in the other groups. In 2 myopic LASIK patients, Zernike root-mean-square 4th-order aberrations were higher than in the near-emmetropia group because of higher levels of positive spherical aberration. CONCLUSIONS: Off-axis aberrations can be dramatically affected by conventional myopic and hyperopic LASIK. In myopic LASIK, the increased off-axis refractive errors may have adverse effects on peripheral visual tasks that are dependent on off-axis refractive errors. The relatively low off-axis refractive errors in hyperopic LASIK patients may improve peripheral visual tasks.

Adult↗
PubMed2005

Pigment dispersion and Artisan phakic intraocular lenses: crystalline lens rise as a safety criterion.

PURPOSE: To validate the theory that crystalline lens rise can be used as a safety criterion to prevent pigment dispersion in eyes with an Artisan phakic intraocular lens (IOL) (Ophtec BV). SETTING: Monticelli Clinic, Marseilles, France. METHOD: A comparative analysis of crystalline lens rise in 9 eyes with pigment dispersion and 78 eyes without dispersion was performed. All eyes had previous implantation of an Artisan IOL. Anterior segment imaging was done using an anterior chamber optical coherence tomography (AC OCT) prototype. Crystalline lens rise was defined by the distance between the anterior pole of the crystalline lens and the horizontal plane joining the opposite iridocorneal recesses. RESULTS: The study confirmed that crystalline lens rise can be considered a safety criterion for implantation of Artisan-type phakic IOLs. The higher the crystalline lens rise, the greater the risk for developing pigment dispersion in the area of the pupil. This complication occurred more frequently in hyperopic eyes than in myopic eyes. Results indicate there is little or no risk for pigment dispersion if the rise is less than 600 microm; 67% of eyes with a rise of 600 microm or more developed pupillary pigment dispersion. In some cases in which the IOL was loosely fixated, there was no traction on the iris root and dispersion was prevented or delayed. CONCLUSIONS: Crystalline lens rise should be considered a new safety criterion for Artisan phakic IOL implantation and should also be applied to other types of phakic IOLs. The distance remaining between the crystalline lens rise and a 600 microm theoretical safety level allows one to calculate how long the IOL can safely remain in the eye.

Adolescent↗
PubMed2005

Randomized prospective clinical study comparing induced aberrations with IntraLase and Hansatome flap creation in fellow eyes: potential impact on wavefront-guided laser in situ keratomileusis.

PURPOSE: To measure and compare the changes in objective wavefront aberration and subjective manifest refraction after laser in situ keratomileusis (LASIK) flap creation with a mechanical microkeratome and a femtosecond laser. SETTING: Private practice refractive surgery center, Irvine, California, USA. METHODS: This randomized prospective study comprised 9 patients (18 eyes) treated with a 2-step LASIK procedure: lamellar keratectomy with a Hansatome microkeratome (Bausch & Lomb) or the IntraLase femtosecond laser in fellow eyes followed by non-wavefront-guided (standard) excimer laser treatment with the Technolas 217A (Bausch & Lomb) excimer laser 10 weeks later. Fellow eyes were matched to within 0.75 diopter (D) sphere and 0.50 D cylinder. Patients were followed for 3 months after excimer laser treatment. Preoperative and post-flap creation wavefront aberrometry using a Hartmann-Shack aberrometer and manifest refraction were compared between the 2 groups. The same tests were performed 3 months after excimer laser ablation. RESULTS: Statistically significant changes were seen in defocus wavefront aberrations after Hansatome (P=.004) and IntraLase (P=.008) flap creation. A hyperopic shift in manifest refraction was noted in the Hansatome group after the creation of the corneal flap (P=.04); no statistically significant changes in manifest refraction were seen in the IntraLase group. Statistically significant changes in total higher-order aberrations (HOAs) (trefoil and quadrafoil Zernike terms) were seen after flap creation in the Hansatome group (P=.02). No significant changes in HOAs were noted after flap creation in the IntraLase group. After the flap was relifted and standard excimer laser ablation was performed, a statistically significant increase in coma occurred in the Hansatome group (P=.008). Standard refractive outcomes in the 2 groups were similar. CONCLUSIONS: The creation of the LASIK flap alone can modify the eye's optical characteristics in low-order aberrations and HOAs. A significant increase in HOAs was seen in the Hansatome group but not in the IntraLase group. This may have significant clinical implications in wavefront-guided LASIK treatments, which are based on measurements made before flap creation.

Adult↗
PubMed2005

Causes of spherical aberration induced by laser refractive surgery.

PURPOSE: To develop a corneal model to better explain how refractive surgery procedures induce spherical aberration. SETTING: Department of Ophthalmology and Center for Visual Science, University of Rochester, Rochester, New York, USA. METHODS: The preoperative cornea was modeled as a rotationally symmetric surface with various radii of curvature and asphericities. The postoperative cornea was defined as the difference between the preoperative cornea and an ablation thickness profile computed based on the Munnerlyn equation. A ray-tracing program and Zernike polynomial fitting were used to calculate the induced amount of spherical aberration assuming a fixed ablation depth per pulse or a variable ablation depth depending on the incidence angle of each pulse on the cornea. A biological eye model of the corneal surface change after laser refractive surgery was also developed to explain the induced spherical aberrations after myopic and hyperopic treatments. RESULTS: The clinical data showed that positive spherical aberration was induced after myopic correction and negative spherical aberration increased after hyperopic correction. In contrast, assuming a fixed ablation depth per pulse, the theoretical prediction was that negative spherical aberration with myopic treatment and positive spherical aberration with hyperopic treatment would increase. However, when assuming a variable ablation depth per pulse caused by non-normal incidence of laser spot on the cornea, the theoretically predicted induction of spherical aberration tends to fit better with the myopic and hyperopic clinical data. The effect of a variable ablation depth accounted for approximately half the clinically observed amount of spherical aberration. The biological model of the corneal surface change used to explain this remaining discrepancy showed the magnitude of the biological response in myopic correction is 3 times smaller than in hyperopic correction and that the direction of the biological response in hyperopic treatment is opposite that in myopic treatment. CONCLUSIONS: This nontoric eye model, which separates the effects of differences in ablation efficiency and biological corneal surface change quantitatively, explains how spherical aberration is induced after myopic and hyperopic laser refractive surgery. With the corneal topographic data, this model can be incorporated into the ablation algorithm to decrease induced spherical aberrations, improving the outcomes of conventional and customized treatments.

Computer Simulation↗
PubMed2005

Thin flap laser in situ keratomileusis: flap dimensions with the Moria LSK-One manual microkeratome using the 100-microm head.

PURPOSE: To determine the predictability and consistency of corneal flap thickness, flap diameter, and hinge length with the modern 100 microm head of the Moria LSK-One manual microkeratome. SETTING: Private clinic, office-based practice. METHODS: Forty-two consecutive eyes with no previous surgery having thin flap laser in situ keratomileusis with the Moria LSK-One manual microkeratome had a new 100 microm (predicted flap thickness) head used for flap creation. Flap thickness was measured intraoperatively by subtraction ultrasound pachymetry (difference between central corneal thickness before flap cutting and residual stromal bed thickness after flap lifting). Vertical flap diameter and nasal hinge length were measured with calipers. RESULTS: Mean flap thickness was 107 microm +/- 14 (SD) (range 82 to 137 microm). Standard deviation for mean vertical flap diameter was +/-0.24 mm. The cord length of the nasal hinge was variable with a mean of 4.26 +/- 0.63 mm (range 3.12 to 5.75 mm) in length. Postoperatively, there were no slipped flaps, flap striae, diffuse lamellar keratitis, or epithelial defects; there was 1 epithelial slide. At 1 day, the visual acuity was 20/20 or better in 76% of eyes. CONCLUSIONS: The 100 microm head of the Moria LSK-One manual microkeratome cut a very predictable flap thickness and diameter but with variable length hinges. This flap thickness predictability was superior to that in other series with thicker intended flaps cut with mechanical microkeratomes and is comparable to that reported with the IntraLase FS femtosecond laser. Visual recovery was rapid, epithelial risks minimal, efficiency superior, and cost nominal relative to femtosecond laser technology.

Adult↗
PubMed2005

Temporal hinge laser in situ keratomileusis: maximizing treatable stromal bed area.

PURPOSE: To compare the treatable stromal bed area created by a temporal versus superior hinge laser in situ keratomileusis (LASIK) flap. SETTING: Assil Sinskey Eye Institute, Santa Monica, California, USA. METHODS: A randomized retrospective case review was performed of 2 subgroups (each with 12 eyes) of a cohort having LASIK for the correction of hyperopic astigmatism between August 2001 and March 2002. In 1 group, superior hinge LASIK was performed using the standard surgical technique for the 9.5 mm Hansatome suction ring. In the other group, the keratome was rotated 90 degrees such that a temporal hinge LASIK was performed with the 9.5 mm Hansatome suction ring. Corneal curvature (central mean keratometric value), flap diameter (arc length), and treatable stromal bed area were measured in each eye, and mean values were compared between the 2 groups. A treatable stromal bed area was defined as the circle centered over the entrance pupil, tangent to the hinge (devoid of hinge interference). RESULTS: The mean keratometry and mean flap diameter in the superior and temporal hinge groups measured 42.3 diopters (D) and 9.68 mm and 42.2 D and 9.69 mm, respectively. These differences were not significant (P=.882 for average keratometry and P=.943 for flap diameter). The mean treatable stromal bed area in the superior versus temporal hinge group measured 44.14 mm(2) and 62.25 mm(2), respectively. The difference between the 2 groups was highly significant (P<.0001). CONCLUSIONS: A large diameter, temporal hinge LASIK flap yielded a significantly greater area of treatable corneal stromal bed than a superior hinge flap. There are several clinical and theoretical advantages of optimizing stromal bed exposure for any given flap diameter.

Astigmatism↗