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At least 217 records · Page 12Linked to original sources
PubMed1997

[Mode of progression of visual field defects and risk factors in glaucoma patients].

A study of glaucoma was conducted at 17 institutions to clarify the mode of progression of visual field defects in specific types of glaucoma, including primary open angle glaucoma (POAG), primary angle closure glaucoma (PACG), and normal tension glaucoma (NTG). Staging of glaucoma was done by the Kosaki Classification or the Aulhorn Classification and the mode of progression was assessed by life-stable method. The progressive and non-progressive groups of patients in each glaucoma stage were compared with respect to age, intraocular pressure, refraction, and optic disc cupping. A total of 656 eyes were investigated in 656 patients (301 men and 355 women) with a mean age of 58.0 years. The average follow-up period was 5.8 years for the study using the Kosaki Classification and 4.0 years for that done with the Aulhorn Classification. The progression of visual field defects was rapid in the early stage but slow in the middle and late stages in the study by the Kosaki Classification, and it was slow in the late stages in the study by the Aulhorn Classification. The time for progression from stage Ia to stage VI was 43.3 years in the study by the Kosaki Classification and the time for progression from stage 0 to stage 6 was 47.2 years in the study by the Aulhorn Classification. The progressive and non-progressive groups differed significantly with respect to intraocular pressure at various stages.

Female↗
PubMed2004

[Individual postoperative refraction after cataract surgery -- a comparison of optical and acoustical biometry].

BACKGROUND: Optical biometry with the IOL-Master is an innovative technique that claims to improve the refractive results of cataract surgery compared to acoustical biometry. METHODS: In 140 consecutive non-selected eyes prior to cataract surgery firstly an optical biometry (IOL-Master, Zeiss, V.2.02) and secondly an ultrasound biometry (Sonomed) were carried out. Cataract surgery was performed using either a PMMA-IOL (n = 56) or an acrylic IOL (n = 84). The PMMA-IOL's were implanted in the capsular bag via a scleral tunnel. The acrylic-IOL's were implanted via a clear cornea incision in the capsular bag. The length of the globe was analysed and the deviations between the postoperative refraction after 3 month and the preoperative planned refraction were compared. RESULTS: The mean axial length difference between optical biometry and acoustical biometry was 0.19 mm in the PMMA-lens group and 0.16 mm in the acrylic-lens group. The deviation of postoperative refraction (spherical mean) from the planned refraction was 0.46 +/- 0.88 D in the PMMA-IOL group and 0.25 +/- 0.77 D in the acrylic IOL group when biometry was performed by ultrasonography. When optical biometry was performed the respective values were 1.15 +/- 0.83 D in the PMMA-IOL group and 0.84 +/- 0.75 D in the acrylic IOL group. The differences in mean postoperative refraction of optical and acoustical biometry can be compensated by adaptation of the A constants. The standard deviation of the difference between the postoperative refraction and the preoperatively planned refraction - that means the individual deviations between postoperative refraction and preoperatively planned refraction - were almost identical in optical and acoustical biometry. CONCLUSION: Optical biometry represents a significant simplification in the course of investigation prior to cataract surgery. The claim of optical biometry, however, to gain a higher precision and thus a significantly better prediction of individual postoperative refraction after cataract surgery is not yet fulfilled.

Acrylates↗
PubMed1999

A 2-year longitudinal study of myopia progression and optical component changes among Hong Kong schoolchildren.

This study investigated refractive error and optical component changes in a group of 142 Hong Kong schoolchildren from age 6 to 17 years over a 2-year period between 1991 and 1993. Subjects were refracted subjectively and corneal curvatures and ocular dimensions were measured. At the end of the 2-year study, the mean spherical equivalent refraction (SER) was -1.86 D (SD 1.99 D) and 62% of the schoolchildren were myopic. The annual incidence of myopia was 11.8%. Children aged 10 years and under had a greater change in SER toward myopia than older children. The annual rate of myopia progression for the myopic children was -0.46 D (SD 0.40 D) and the rate of progression was greatest between age 6 and 10 years old. Vitreous depth/axial length elongation was the main component contributing to the progression of myopia. Hong Kong schoolchildren develop myopia as early as 6 years old and myopia progresses at a greater rate compared with children of European extraction.

Adolescent↗
PubMed2003

[A comparison of visual field and optic disc appearance depending on the peak intraocular pressure in patients with normal-tension glaucoma].

PURPOSE: To investigate the clinical differences between the two groups depending on the peak intraocular pressure(IOP) in patients with normal-tension glaucoma(NTG). METHODS: We studied 96 eyes of 48 NTG patients who were hospitalized for diurnal IOP measurement. Then we selected the eye whose peak IOP was higher than the other, or the right eye if the peak IOP of both eyes was equal. We divided these eyes into a "high-teen" group (peak IOP > or = 16 mmHg) and a "low-teen" group(peak IOP < or = 15 mmHg). We compared these two groups by age, gender, refraction, IOP, visual field defect, optic disc appearance, and tomograph. We used a Humphrey C 30-2 program to estimate the visual field defect and classified the optic disc into four types according to Nicolela's criteria. 22 eyes were imaged with Heidelberg Retina Tomograph (HRT) to obtain topographic parameters of the optic disc. RESULTS: There were no significant differences in age, gender, refraction, optic disc appearance, or tomograph between two groups. The trough and variation range of diurnal IOP were significantly larger in the high-teen group(p < 0.01). The value of mean deviation(MD) given by STATPAC was statistically lower in the high-teen group(p < 0.01). CONCLUSIONS: In patients with NTG, the visual field damage tended to be greater in the high-teen group than in the low-teen group. We surmise that the IOP might influence the progression of visual field defect in NTG.

Adult↗
PubMed2006

Matrix approach to quantitative refractive index analysis by Fourier domain optical coherence tomography.

The rapid development in the field of optical coherence tomography has demanded increasingly sophisticated numerical models to enable the interpretation of image data and extract quantitative results. We use a matrix formulation of Fresnel's equations for multilayered media to extract layer-dependent thickness and refractive index directly from Fourier domain optical coherence tomography spectrograms. An eigenanalysis spectral decomposition approach is used to constrain the least squares fitting algorithm, avoiding the need for initial estimates of the parameter values. We demonstrate this novel quantitative analysis approach by using a multilayered phantom and show good agreement with the known layer parameter values. This approach introduces a powerful tool for the analysis of layer-dependent optical properties that could have an important role in the differentiation of healthy and diseased tissue.

Algorithms↗
PubMed2004

[Comparison of ultrasound and optic biometry with respect to ocular refraction after cataract surgery].

In the prospective study of 56 patients with cataract (67 eyes) the authors compared axial length biometry) regarding to postoperative refraction of the eyes. Dioptric power of the intraocular lens (IOL) was determined by SRK II. formula. The difference between predicted and actual postoperative refraction in the spherical equivalent were compared 3 months postoperatively. Axial length measured by ultrasound differed significantly from the axial length measured by optical biometry (p = 0.016). Dioptric power of IOL calculated according to the axial length measured by ultrasound was significantly different from the dioptric power of IOL calculated according to the axial length measured by optical biometry (p = 0.003). The difference between predicted and actual postoperative refraction was not statistically significant (p = 0.384) even if we considered both type of measurement. In conclusion, we found partial coherence interferometry was an accurate and reproducible method for measurement of axial length of the eye before cataract surgery. In the cases of advanced dense cataracts backup of ultrasonic biometry is still necessary.

Cataract↗
PubMed2006

Delay times and detector times for optical pulses traversing plasmas and negative refractive media.

We show that arrival times for electromagnetic pulses measured through the rate of absorption in an ideal impedance matched detector are equivalent to the arrival times using the average flow of optical energy as proposed by Peatross [Phys. Rev. Lett. 84, 2370 (2000)]. We then investigate the transport of optical pulses through dispersive media with negative dielectric permittivity and negative refractive index choosing the geometry such that no resonant effects come into play. For evanescent waves, the definitions of the group delay, and the reshaping delay get interchanged in comparison to propagating waves. The total delay times for the evanescent waves can be negative in an infinite plasma medium even for broadband pulses. The total delay time is, however, positive for broadband pulses in the presence of an interface when the radiation is detected outside the plasma. We find evidence of the Hartman effect for pulses when the distance traversed in the plasma is much smaller than the free space pulse length. We also show that for a negative refractive index medium (NRM) with epsilon(omega)=mu(omega) the reshaping delay for propagating waves is identically zero. The total delay time in NRM is otherwise dominated by the reshaping delay time, and for broadband pulses in NRM the total delay time is subluminal.

Journal Article↗
PubMed2005

Determination of polar stratospheric cloud particle refractive indices by use of in situ optical measurements and T-matrix calculations.

A new algorithm to infer structural parameters such as refractive index and asphericity of cloud particles has been developed by use of in situ observations taken by a laser backscattersonde and an optical particle counter during balloon stratospheric flights. All three main particles, liquid, ice, and a no-ice solid (NAT, nitric acid trihydrate) of polar stratospheric clouds, were observed during two winter flights performed from Kiruna, Sweden. The technique is based on use of the T-matrix code developed for aspherical particles to calculate the backscattering coefficient and particle depolarizing properties on the basis of size distribution and concentration measurements. The results of the calculations are compared with observations to estimated refractive indices and particle asphericity. The method has also been used in cases when the liquid and solid phases coexist with comparable influence on the optical behavior of the cloud to estimate refractive indices. The main results prove that the index of refraction for NAT particles is in the range of 1.37-1.45 at 532 nm. Such particles would be slightly prolate spheroids. The calculated refractive indices for liquid and ice particles are 1.51-1.55 and 1.31-1.33, respectively. The results for solid particles confirm previous measurements taken in Antarctica during 1992 and obtained by a comparison of lidar and optical particle counter data.

Algorithms↗
PubMed2004

Corneal and epithelial thickness changes after 4 weeks of overnight corneal refractive therapy lens wear, measured with optical coherence tomography.

PURPOSE: To investigate thickness changes of the total cornea and epithelium across the horizontal corneal meridian after 4 weeks of overnight corneal refractive therapy (CRT) rigid contact lens (Paragon Vision Sciences, Mesa, AZ) wear. METHODS: Thirty subjects were fitted with CRT contact lenses (Dk/t = 67), which were worn overnight for 4 weeks. Corneal thickness was measured at nine locations along the horizontal meridian by using optical coherence tomography (OCT) before lens insertion in the evening. Corneal thickness was measured the next morning immediately after lens removal and 1, 3, 7, and 14 hours later. This was repeated on days 4, 10, and 28 of the study and then 3 days after discontinuing lens wear. RESULTS: Twenty-three subjects completed the study. At lens removal on day 1, the central and paracentral cornea swelled by 4.9% and 6.2%, respectively (both P = 0.000). The central epithelium thinned by 7.3%, and the mid peripheral epithelium thickened by 13% (both P = 0.000). Corneal swelling recovered throughout the day, with most of the deswelling taking place within the first 3 hours after lens removal. Maximal central epithelial thinning reached 13.5% by day 4. Three days after the study completion, corneal and epithelial thickness had recovered to baseline values. CONCLUSIONS: This study shows that CRT lenses induce differential overnight swelling across the cornea, with rapid deswelling during the day. Central epithelial thinning and paracentral thickening occurs, with recovery 3 days after discontinuation of lens wear.

Adult↗
PubMedDate not supplied

Nomogram considerations with the Technolas 217A for treatment of myopia.

PURPOSE: To determine whether surgeon-specific nomogram adjustments are useful when using the Technolas 217A excimer laser for treating myopia and myopic astigmatism. METHODS: We conducted a prospective evaluation of 216 consecutive eyes with 6 months follow-up after treatment of myopia or myopic astigmatism with the Technolas 217A laser. Attempted vs. achieved change in refraction was analyzed with a statistical analysis software program. Factors such as age, corneal thickness (pachymetry), preoperative spherical equivalent refraction, preoperative cylinder, and optical zone were studied to evaluate their role in predicting refractive outcome at 6 months after LASIK. RESULTS: The mean value of attempted spherical equivalent refraction was -5.32 +/- 2.72 D. The mean achieved refractive correction at 6 months was -5.55 +/- 2.78 D, with a mean spherical equivalent of 0.13 +/- 0.54 D. The percent achieved effect at 1 month was 105%, and at 6 months, 103%. Preoperative spherical equivalent refraction and optical zone size were strong predictors of 6-month LASIK outcome. There was a 9% difference in the percent achieved effect between a 4 and 7-mm optical zone. There was no correlation between age, preoperative cylinder, or surgeon and 6-month outcome. CONCLUSIONS: Surgeons using the planoscan software on the Technolas 217A may experience a small initial overcorrection. There may be a benefit to reducing the treatment given with larger optical zones and smaller corrections.

Adult↗
PubMedDate not supplied

Older age as risk factor for deviation from emmetropia in pseudophakia.

PURPOSE: To find risk factors for deviation from emmetropia after cataract surgery in clinical practice. METHODS: We evaluated the refractive outcome in 106 patients who had underone phacoemulsification and in-the-bag IOL placement 115 +/- 10 days after surgery. Postoperative optical correction and refractive error (diopters of spherical equivalent--ED) were related to age and sex, pre-operative axial length and keratometric diopter power, and operative incision technique. RESULTS: Emmetropia was achieved in 15% of cases; 65% of eyes needed a myopic correction, averaging = 0.46 +/- 0.91 ED. The refractive error was 0.74 +/- 0.61 ED (< or = 1 ED in 77% of cases, < or = 2 ED in 97%). Both optical correction and refractive error were correlated to older age at the time of surgery (p=0.002 and p=0.001, respectively). Astigmatism appeared greater in clear-cornea incision than in limbar incision cases (p=0.05). CONCLUSIONS: The higher refractive error in patients aged over 73 years suggests that age may be a risk factor for deviation from emmetropia after cataract surgery.

Adult↗
PubMed2006

[Spectroscopic ellipsometry investigations of amorphous diamond films deposited with filtered arc].

In order to investigate thoroughly the optical properties of amorphous diamond (alpha-D) films deposited by the filtered vacuum arc technology, the optical constants of the films were measured by spectroscopic ellipsometry. Moreover, the dispersion relations of the optical constants, and the correlations among refractive index, extinction coefficient, optical gap and the substrate bias were also analyzed. It has been shown that the refractive index of alpha-D films is higher than that of diamond crystal, and the absorption edge corresponding to the interband transformation can be described with the parabolic line shape. With increasing the wavelength, the extinction coefficient gradually declines and approaches nearly to zero in the infrared band. In addition, the adjustable amplitudes of the optical constants owing to the changing bias also reduce strikingly with the extension of the wavelength. With raising the bias, the refractive index and the optical gap firstly augment, then minish, and there is a maximal value when the substrate bias is -80 V. However, the extinction coefficient firstly minishes, then augments, and there is a minimal value when the bias is -80 V.

English Abstract↗
PubMed2006

History and development of the apodized diffractive intraocular lens.

The ReSTOR intraocular lens presents a unique apodized diffractive design within a refractive foldable acrylic optic, which makes an unprecedented level of mulifocal optical performance available. We describe the history and principles of diffractive optics used in the development of this refractive-diffractive IOL.

Cataract Extraction↗
PubMed1993

Surface refractive index of the eye lens determined with an optic fiber sensor.

The use of a fiber-optic sensor for measurement of the refractive index on the surface of eye lenses is described. The technique makes use of the fact that the amount of light reflected at the interface of two media (Fresnel reflectance) depends on the refractive-index difference between them. The sample is probed with a single-mode fiber, and the refractive index is calculated from the proportion of light reflected at the probe-sample interface.

Animals↗
PubMed2001

Optical detection of small changes in refractive indices in water by single-beam scattering.

We studied forward-scattered laser light that is produced when the light strikes an abrupt interface (air bubble in water) and when it passes unimpeded through diffused water layers caused by temperature gradients. Measured intensities of the scattered light indicated patterns that are due to both geometrical and physical optics. Distribution of intensities within the scattered beam changed with the average vertical temperature gradient. Shifts in locations of intensities indicated small changes in the index of refraction in the diffused scattering case.

Journal Article↗
PubMed1996

Light intensity distributions in refracting structures placed between crossed polarizers.

A number of refracting structures each with different optical properties, were placed between crossed polarizers, illuminated with diffuse light and photographed. The images of the characteristic cross pattern (isogyres) seen in such structures, viewed under these conditions, were analysed to determine the relative distributions of light intensity within the patterns. The experimental findings show that intensity distributions are related to the optical properties of a refracting structure. Comparison of dimensional differences shows that in a larger sample the profile of light intensity distribution (in the quadrants between the isogyres) is more symmetrical and the peak is closer to the centre of the quadrant. Sharper peaks are seen in the intensity distribution profiles of gradient-index structures than in profiles of homogenous-index bodies of comparable dimensions. Some agreement was found between an experimental observation and a previously derived mathematical model for homogenous index, curved bodies.

Animals↗