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At least 721 records · Page 40Linked to original sources
PubMed1979

Contrast (modulation) sensitivity functions measured in patients with high refractive error with emphasis on aphakia: I. Theoretical considerations.

Recently, alterations in contrast (modulation) sensitivity functions of patients with high refractive errors have been noted. For example, this seems to be a common finding in aphakia. In some measure the observed alterations are due to the effect of the corrective lens and the optics of the eyes. These optical effects (in addition to blur) must be factored out in order to determine whether residual effects on the visual system remain. The argument is applicable to photographs of sine wave fringes as well as devices designed to produce interference patterns directly on the retina. A simple means for largely correcting these lens effects is discussed.

Aphakia↗
PubMed1991

Ellipsoidal confidence regions for mean refractive status.

Confidence regions for mean dioptric power can be represented by ellipsoids in a three-dimensional space called h-space. A convenient graphical representation is provided by stereo-pair drawings that, at a glance, show the estimated accuracy with which the mean power is known. As an example, a sample of autorefractor measurements made on one eye were used to construct a 95% confidence ellipsoid for the mean objective refractive status of that eye. Key dimensions of the ellipsoid are compared with those of another eye. The analysis is of fundamental importance for scientific studies of variation and change of refractive status. Its potential clinical importance is also discussed.

Adult↗
PubMed2006

[Fundus oculi changes in myopia].

I. SIMPLE MYOPIA: Simple refractive error, which is not associated with fundus changes; Optical correction/refractive surgery brings the patient to visual acuity=1. II. DEGENERATIVE MYOPIA: Refractive error which is associated with fundus changes (during the "fundus changes" progression, the visual acuity is getting worse); Myopic fundus changes-classification: A/ RETINA: Posterior staphyloma Chorioretinal atrophy. Optic disc changes = 1-3. Macula changes (Myopic maculopathy) = 1-7. Peripheral fundus changes = 1-6. B/ VITREOUS: Fundus examination should be performed on any myopic patient; Fundus fluorescein angiography allows the objective follow-up of the fundus lesions and also the evaluation of the treatment results; Optical correction/refractive surgery cannot bring the patient to visual acuity=1, due to fundus lesions; For some lesions--which can generate serious visual complications, it is necessary prophylactic treatment by ARGON laser photocoagulation or cryotherapy.

Fluorescein Angiography↗
PubMed1985

A schematic eye for the mouse, and comparisons with the rat.

The thicknesses and spheric and aspheric curvatures of the optic components were measured from cross-sections of frozen eyes of C57B1/6J mice. The equivalent refractive index of the crystalline lens was obtained from its back-vertex power in albumin. Refractive indices of the cornea, aqueous and vitreous humors were obtained by refractometry or interferometry at four wavelengths across the visible spectrum. The measurements parallel earlier ones on the hooded rat. The eyes of the mouse and rat differ mainly in size, by a linear scale factor of 1.9-2.0, and only slightly in refractive index. Thus refraction, chromatic aberration, and retinal illumination are easily compared in the two species. An analysis of the contribution of each optical surface to refraction may facilitate extrapolation to other strains of mice. Chromatic aberration is discussed with respect to depth of field and the retinoscopy artefact.

Animals↗
PubMedDate not supplied

Preoperative simulation of outcomes using adaptive optics.

Measurements of the wavefront of light reflected from the retina of the human eye can be used to determine optical aberrations of the human eye for large pupils. An instrument based on the Hartmann-Shack principle was developed. The wavefront is refracted by a microlens array and detected by a CCD camera. In first clinical studies human volunteer eyes and preoperative and postoperative refractive surgical patient eyes have been examined. An adaptive optical closed loop system has been devised for preoperative simulation of refractive outcomes of aberration free refractive surgical procedures.

Adaptation, Ocular↗
PubMed1986

Mass screening of children for strabismus or ametropia with two-flash photoskiascopy.

UNLABELLED: 169 non-selected 1-5 year-old children (338 eyes) were screened by two-flash photoskiascopy with an autofocus camera for strabismus, high anisometropia and high ametropias without cycloplegia. The photography was performed by nurses or technicians and the photographs were analyzed by an optician. The sensitivity of the method for the refractive errors was tested with an optical demonstration eye. FINDINGS: 5 esotropias, 1 exotropia, 1 straight-eyed hypermetropic anisometropia of 4 diopters; 1 false positive high hyperopia (of +2.5 diopters) of both eyes. The examination of the photographs showed slight refractive errors in 33 cases (66 eyes; 19.5%): two of them of symmetrical myopia of -1.0 and -1.75 diopters and 31 of symmetrical hyperopia of +0.25 to +4.25 diopters in retinoscopy. 128 cases (256 eyes; 76%) were normal on the photographs. Of these, 37 non-selected cases (74 eyes) were checked clinically and were symmetrical cases of -1.0 to +3.25 diopters on retinoscopy. No false negative cases appeared among these control cases. 2,4% of the photographs failed technically or because of noncooperation of the children. Two-flash photoskiascopy, performed by technicians or nurses provides a valuable tool for mass screening of infants for strabismus and/or ametropia causing amblyopia.

Child, Preschool↗
PubMed1994

Asthenopia and the dark focus of accommodation.

To study asthenopia, we compared the dark focus of accommodation of 54 symptomatic and 56 asymptomatic control subjects. The two groups were matched for age and cycloplegic refractive error. Symptomatic subjects were defined as those who complained of asthenopia daily even though their refractive error had been corrected. Subjects with other eye diseases that could produce asthenopia such as strabismus or aniseikonia were excluded. Using a Nidek Autorefractometer AR1600, we first measured non-cycloplegic refractive error (Non-Cyclo R) in a bright room, then the dark refractive state (Dark R) in complete darkness using the instrument with the optical target light extinguished and, finally, determined the cycloplegic refractive error (Cyclo R) after instilling cyclopentolate hydrochloride. The difference between Dark R and Cyclo R was defined as DFcus (Cyclo R) and that between Dark R and Non-Cyclo R as DFcus (Non-Cyclo R). We found both DFcus (Cyclo R) and DFcus (Non-Cyclo R) to be smaller in the symptomatic than in the asymptomatic subjects, indicating that asthenopia is associated with a low rather than a high level of tonic accommodation.

Accommodation, Ocular↗
PubMedDate not supplied

The theoretical effect of measured wavefront diameter on estimating peripheral wavefront data.

PURPOSE: To compare the difference between wavefront data measured in the periphery and that calculated from estimations using a smaller measured region. METHODS: A total of 32 eyes were measured using the Alcon LADARWave aberrometer (Alcon Laboratories Inc, Fort Worth, Tex). Aberrations were measured through a dilated pupil to the 6th order at a 6.5-mm diameter. Data were then "clipped" to 5.0, 5.5, and 6.0 mm, and each of these smaller diameter wavefronts was used to estimate the larger diameter wavefront coefficients. The measure of interest was the mean and range of error between the estimated and measured values, and how they varied for the different diameters of known data. RESULTS: The differences in both the mean and range of error were inversely correlated to the diameter of the region of known data. As this region grew smaller, the region estimated grew larger, with resultant larger mean errors. At 5 mm, the estimated zone was an annulus of 0.75-mm width; in this case the estimated higher order aberrations were 60% higher than those measured, with a range of 40% lower to 300% higher. At 5.5 mm and 6.0 mm, these differences were much smaller, but statistically significant. The differences were greatest when significant peripheral aberrations were measured, as can occur with post-laser in situ keratomileusis eyes. CONCLUSION: Basing a treatment on an estimation of the peripheral wavefront may lead to an inaccurate ablation profile. The inaccuracy increases as the size of the measured wavefront decreases relative to the planned ablation zone. The inaccuracy is also greatest when significant peripheral aberrations are present. Refractive surgery systems should only treat optical zones that are smaller than or equal to the diameter of the measured wavefront.

Corneal Topography↗
PubMed1991

[Reliability of the SRK formula].

The authors investigate the postoperative dioptric deviation from the calculated dioptric power of emetropic intraocular lenses by means of the SRK formula. The deviation varied in 82% of the operated eyes within the range of +/- 1.5 D. More accurate calculations were achieved in a group of eyes with a normal axial length of the eyeball (22.0 to 24.5 mm). The authors discuss also circumstances which influence the accuracy of calculation according to formula SRK (assessment, calculation) and factors participating in the final postoperative refraction (different surgical techniques).

Aged↗
PubMed2006

Diurnal variation in clinically significant diabetic macular edema measured by the Stratus OCT.

PURPOSE: To investigate diurnal variation in clinically significant macular edema (CSME) using the Stratus OCT (Carl Zeiss Meditec). METHODS: Fifteen eyes of 15 diabetic patients with CSME and 10 healthy subjects (controls) underwent four optical coherence tomography (OCT) measurements of macular thickness with the fast macular thickness mapping protocol of the Stratus OCT at 9 am, 12 pm, 3 pm, and 6 pm. Early Treatment Diabetic Retinopathy Study visual acuity and refraction data were also collected at each time. Retinal thickness measurements from each of the nine macular Early Treatment Diabetic Retinopathy Study areas of the retina map, visual acuity, and refraction were plotted over time. RESULTS: Mean retinal thickness remained unchanged in all retinal sectors over the course of the day for the controls and the 6 diabetic patients with a baseline foveal thickness of <300 mum, and it significantly decreased in 7 of the 9 retinal sectors for the 9 diabetic patients with a baseline foveal thickness of > or =300 microm (ANOVA model for repeated measures). In these patients, the mean initial foveal thickening +/- SD of 211 +/- 104 microm was reduced by an average of 6.1%, 15.2%, and 21.2% at 12 pm, 3 pm, and 6 pm, respectively. Two of these nine patients also had an increase in visual acuity without change in refraction. There were no changes in refractive errors over the course of the study in the two groups. A positive correlation between initial central thickening and decrease in thickness was found (r = 0.732; P = 0.002). CONCLUSION: This study suggests that macular thickening, as measured by the Stratus OCT, may spontaneously decrease in some patients with more severe CSME over the course of the day, and it confirms previous findings. However, in our study, the entity of this decline was relatively small and not relevant from a clinical standpoint.

Aged↗
PubMed2004

[Childhood refraction: epidemiology, progression, evaluation and a method for correcting ametropia].

Children's refraction and its progression are important because refractive errors can be precisely corrected. Some types of simple ametropia can generate reversible perturbations after optical correction and others are amblyogenic and strabogenic ametropia. Definition, epidemiology (frequency and risk factors), progression of refraction, evaluation and an optical correction method are described.

Child↗
PubMed1996

Constitutive laws for biomechanical modeling of refractive surgery.

Membrane inflation tests were performed on fresh, intact human corneas using a fiber optic displacement probe to measure the apical displacements. Finite element models of each test were used to identify the material properties for four different constitutive laws commonly used to model corneal refractive surgery. Finite element models of radial keratotomy using the different best-fit constitutive laws were then compared. The results suggest that the nonlinearity in the response of the cornea is material rather than geometric, and that material nonlinearity is important for modeling refractive surgery. It was also found that linear transverse isotropy is incapable of representing the anisotropy that has been experimentally measured by others, and that a hyperelastic law is not suitable for modeling the stiffening response of the cornea.

Cornea↗
PubMed2004

Oxasmaragdyrin-ferrocene and oxacorrole-ferrocene conjugates: synthesis, structure, and nonlinear optical properties.

Ferrocenyl macrocyclic conjugates involving 22 pi oxasmaragdyrins and 18 pi oxacorroles have been synthesized and characterized. The direct covalent linkage of the ferrocenyl moiety to the meso position of the macrocycle is achieved by simple oxidative coupling of appropriate precursors with trifluoroacetic acid as catalyst. The electronic coupling between the ferrocenyl moiety and the macrocyclic pi system is apparent from: a) the red shifts (293-718 cm(-1)) of the Soret and Q-bands in the electronic absorption spectra of ferrocenyl conjugates; b) the shift of oxidation potentials (50-130 mV) of both the ferrocene and the corrole rings to the positive potentials; and c) considerable shortening of the C-C bond which connects the ferrocene and the meso-carbon atom of the macrocycle. The single-crystal X-ray structure of oxasmaragdyrin-ferrocene conjugate 9 reveals the planarity of the 22 pi skeleton with very small deviations of the meso-carbon atoms. The meso-ferrocenyl substituent has a small dihedral angle of 38 degrees, making way for mixing of the molecular orbitals of the ferrocene and the macrocycle. However, the other two meso substituents are almost perpendicular to the mean plane, defined by the three meso carbon atoms. Classical C-H...O and nonclassical C-H...pi interactions lead to a two-dimensional supramolecular network. Ferrocene-smaragdyrin conjugate 9 bonds to a chloride ion in the protonated form and a rhodium(i) ion in the free base form. Nonlinear optical measurements reveal a larger nonlinear refractive index (-5.83 x 10(-8)cm(2)W(-1)) and figure of merit (2.28 x 10(-8)cm(3)W(-1)) for the rhodium smaragdyrin-ferrocene conjugate 19 than for the others, suggesting its possible application in optical devices.

Journal Article↗
PubMed2003

Intraocular lens calculations in patients with corneal scarring and irregular astigmatism.

PURPOSE: To compare various methods of estimating corneal power for intraocular lens (IOL) calculation in patients with irregular corneal astigmatism. SETTING: Pepose Vision Institute, St. Louis, Missouri, USA. Case reports and review of the medical literature. RESULTS: Two patients with irregular corneal astigmatism had an IOL exchange after a "surprise" post-cataract-surgery refraction. In the first case, the patient had a post-cataract-surgery refraction of +5.50 -0.75 x 69 and in the second case, a refraction of -7.00 -1.00 x 180. The central corneal power before IOL exchange was assessed using manual keratometry, various computerized videokeratography curvature and power maps, and contact lens overrefraction. The total axial power map (Orbscan(R), Bausch & Lomb), total optical power map (Orbscan), and contact lens overrefraction method provided the most accurate estimates of central corneal power in these 2 patients. CONCLUSION: Computerized scanning-slit videokeratography, which analyzes the anterior and posterior surfaces of the cornea, and the contact lens overrefraction method gave good estimations of corneal power in patients with irregular corneal astigmatism. This type of analysis may improve the accuracy of IOL calculation in patients with corneal pathology and irregular astigmatism.

Adult↗
PubMed1995

Spherocylindrical refractive errors and visual acuity.

BACKGROUND: Understanding the relation between refractive error and visual acuity is complicated if astigmatic blur is present. No models are in widespread use that allow the combination of spherical and astigmatic errors for the purpose of predicting visual performance. METHODS: Models for combining spherical and astigmatic errors are discussed, and predictions of these models using data from the literature are presented. RESULTS: Three models for combining astigmatic with spherical errors are shown to predict visual acuity performance in uncorrected myopic refractive errors. A dioptric vector addition model is shown to have advantages over other candidate models. CONCLUSIONS: It is possible to combine spherocylindrical refractive errors into a single value when the objective is to correlate these values with visual acuity performance.

Eyeglasses↗
PubMed2004

Linear and nonlinear optical properties of Ag-As-Se chalcogenide glasses for all-optical switching.

We prepared Ag(x)(As0.4Se0.6)(100-x) chalcogenide glasses by a melt-quenching method and measured their linear and nonlinear optical properties to evaluate their potential applications to all-optical ultrafast switching devices. Their nonlinear refraction and absorption were measured by the Z-scan method at 1.05 microm. The addition of Ag to As2Se3 glass led to an increase in the nonlinear refractive index without introducing an increase in the nonlinear absorption coefficient. The glass with a Ag content of x = 20 at. % revealed high nonlinearity ranging from 2000 to 27,000 times that of fused silica, depending on the incident optical intensity.

Journal Article↗