A case of gonococcal kerato-conjunctivitis mimicking orbital cellulitis.
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Adult↗
Biomedical subjects
George Smith
Publications and source records attributed to George Smith.
Chromatic dispersions of the ocular media of human eyes.
Of the commonly used chromatic dispersion equations, only the Sellmeier and the Cauchy equations seem to be theoretically based. Cauchy's equation is derived from the Sellmeier equation, is simpler to implement, and was found to give an excellent fit to published refractive-index data of the human eye. We used Cauchy's equation to model the chromatic difference in refraction of the Gullstrand number 1 schematic eye with a gradient-index lens. To estimate the dispersion at different refractive-index levels within the lens, a single dispersion equation at one nominal refractive index was linearly scaled. This scaling was justified after exploring the effect of mean refractive index on dispersion by using Sellmeier's equation and finding that a dispersion equation for one wavelength is just a linearly scaled version of the dispersion equation at any other wavlength. Because Cauchy's equation is theoretically based and gives excellent fit to data in the visible spectrum, it can be used to extrapolate results into the near infrared with confidence.
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Tomographic method for measurement of the gradient refractive index of the crystalline lens. I. The spherical fish lens.
We present an iterative tomographic algorithm to reconstruct refractive-index profiles for meridional planes of the lens of the spherical fish eye from measurements of deflection angles of refracted rays. Numerical simulations show that the algorithm allows accuracy up to the fourth decimal place, provided that the refractive index can be regarded as an analytical function of the radial coordinate and the experimental errors are neglected. An experimental demonstration is given by applying the algorithm to retrieve the refractive-index profile of a spherical fish lens. The method is conceptually simple and does not require matching of the index of the surrounding medium to that of the surface of the lens, and the related iterative algorithm rapidly converges.
Animals↗
Auto-regeneration of anion-trap columns for improved determination of silica by ion chromatography.
The goal of this project was to develop an automated method to regenerate the ATC-3 trap columns that are used on the DX-800 on-line ion chromatography silica systems. The old method of regenerating the ATC-3 trap columns was to physically remove the trap columns from the silica system once every 2 weeks and manual regenerate them. A new automated regeneration method was developed by re-plumbing the silica system to allow 300 mM NaOH to run as the eluent. This regenerates the trap column automatically once every 24 h. The data have shown that regenerating the ATC-3 trap columns once per day improves the R.S.D. values for 250 ng/l silica analysis from 26.0 to 8.7%. The length of useful lifetime for the silica concentrator column was increased by an average of 9 months.
Anions↗
Review and proposed action of alpha-fetoprotein growth inhibitory peptides as estrogen and cytoskeleton-associated factors.
The (H) human growth-promoting factor, alpha-fetoprotein (AFP), has been reported to possess a growth inhibitory motif as an occult epitope in the compactly folded circulating form of the protein. Intermediate unfolded forms of the human HAFP molecule induced by stress, shock, and high ligand concentrations have revealed the presence of an encrypted growth-suppressive segment on the third domain of HAFP. A purified linear synthetic 34-mer segment termed the "growth inhibitory peptide" (GIP) exhibits various oligomeric forms with complex aggregation behaviors, in which dominant trimeric forms were found to be suppressive in assays of estrogen-induced growth. While several amino acid analogs of the cysteines of the GIP retained inhibitory activity, heavy metal binding and pre-incubation of the peptides with a variety of cations and hormone ligands were found to influence the outcomes of growth bioassays. Smaller segments of the original 34-mer were each found to display growth activities of their own, with the middle segment (P149b) also showing hydrophobic dye-binding properties. Studies of amino acid sequence identity further revealed that the GIP sequences displayed identity/similarity matches to both cytoplasmic and nucleus-cytoskeleton-associated proteins, and experimental evidence served to support these findings. That is, the peptide was capable of modulating tubulin polymerization, cell shape, and cell-surface aggregation phenomena reminiscent of a microtubule-associated protein. Immunofluorescence studies further pinpointed the localization of the GIP to cytoplasmic regions of high cytoskeletal density in the cell. Because of the involvement of the GIP in experimental models of the estrogen receptor/cytoskeleton, a mechanism of action is forwarded in which the linear GIP is proposed to be a G-coupled receptor binding ligand that is translocated across the plasma membrane via receptor-mediated endocytosis. Thus, it was predicted that the linear GIP and possibly its peptidic segments serve as decoy ligands to cell-surface receptors in order to gain access to the cytoplasmic compartment of the cell.
Amino Acid Motifs↗
Possible errors in determining axial length changes during accommodation with the IOLMaster.
PURPOSE: The Zeiss IOLMaster uses partial coherence interferometry to measure the optical path length within the eye. This is converted into the axial length. There are errors in measuring possible changes in axial length as a result of accommodation, because the instrument uses an average refractive index in the eye. We determined the likely extent of these errors. METHOD: Errors were estimated using Gullstrand's no. 1 schematic eyes. One set of these had the shell structure of the eyes, and another set had the gradient index structure specified by Gullstrand. RESULTS: Errors were 18 to 26 microm for an accommodation of 10.9 D. CONCLUSIONS: The worth of the IOLMaster would be increased if it used an equation for conversion from optical length to geometrical length that took into account variations in lens thickness and if it were able to be modified to provide component distances and the axial length using partial coherence tomography.
Accommodation, Ocular↗
The optical properties of the crystalline lens and their significance.
We do not yet have definitive data on the optical structure of the lens, including surface shapes and gradient refractive index distribution. Some data do exist but we need much more data to complete our knowledge of this structure. However, using current and sparse knowledge, we can use mathematical modelling to study the effects of surface shapes and gradient refractive index structure on the Gaussian and aberration properties of the lens. The equations extracted from this modelling show some interesting results, for example, the way the gradient index structure provides some of the refractive power and how this structure possibly predicts a negative spherical aberration of the lens, which is observed in real eyes. This modelling will provide a firm theoretical foundation for analysing more accurate and extensive lenticular shape and refractive index data as they become available.
Humans↗
Optical design and evaluation of a three-dimensional imaging and ranging system based on time-correlated single-photon counting.
The design and operation of a noncontact surface profilometry system based on the time-correlated single-photon-counting technique are described. This system has a robust optomechanical design and uses an eye-safe laser that makes it particularly suitable for operation in an uncontrolled industrial environment. The sensitivity of the photon-counting technique permits its use on a variety of target materials, and its mode of operation does not require the continual presence of an operator. The system described has been optimized for a 1-25-m standoff, has a distance repeatability of <30 microm, and has a transverse spatial resolution of approximately 60 microm at a 2-m standoff and approximately 400 microm at a 13-m standoff.
Journal Article↗
Designing lenses to correct peripheral refractive errors of the eye.
The purpose of this work was to design ophthalmic lenses that correct peripheral refractive errors of human eyes along a meridian. We designed lenses with the tangential section of one surface based on a figured spheroid but figured in the tangential section only. The curvature of the sagittal section of this surface was adjusted separately. A merit function was used to modify these surfaces until the lenses had power errors that corrected the eye. Examples are presented of lenses that correct a schematic eye. They do excellent jobs of correcting the peripheral power errors of the eye and are relatively insensitive to small changes in fitting distance. We conclude that it is theoretically feasible to design lenses to correct peripheral refractive errors.
Equipment Design↗
Refractive index of the crystalline lens in young and aged eyes.
BACKGROUND: When the ageing crystalline lens is modelled on the basis of a constant equivalent lens, the changes in ocular dimensions would lead to an increase in power of the order of two dioptres. A comparable increase in myopia is usually not evident with increasing age and this inconsistency has been referred to as the lens paradox. It has been proposed that this paradox can be resolved if the refractive index is modelled as a gradient refractive index. The purpose of this paper was to study differences in the equivalent, gradient and surface refractive index of the crystalline lens between a young and old age group. METHODS: Biometric data was collected for 96 subjects: 48 young adults with an age range 19 to 31 years (mean 22.10 +/- 2.93 years) and 48 old adults with an age range 49 to 61 years (mean 53.88 +/- 3.88 years). The equivalent refractive index was determined for each subject by paraxial ray tracing and a merit function based on refractive error and Purkinje image height. The refractive index gradient was determined by modelling the crystalline lens as a bi-elliptical iso-indicial structure in a three-surface Gullstrand-Emsley schematic eye and a merit function based on the surface power, the gradient refractive index power and the equivalent power of the lens. The central refractive index of the lens was assumed to be 1.406. RESULTS: The differences between the groups included a decrease in the mean equivalent refractive index from 1.427 +/- 0.007 to 1.418 +/- 0.006, an increase in surface refractive index from 1.386 +/- 0.007 to 1.394 +/- 0.006 with a concurrent change in the gradient refractive index profile. The refractive index changes maintained a constant mean lens power in each group. CONCLUSIONS: The so-called 'lens paradox' whereby an increase in the power of the crystalline lens does not lead to an increase in myopia is resolved by a decrease in the equivalent refractive index of the lens or when modelled as a gradient refractive index structure, by an increase in the surface refractive index and an associated change in gradient for an assumed central refractive index of 1.406.
Journal Article↗
Gas discharge headlights and visibility of coloured road signs.
BACKGROUND: Automotive headlamps mostly use the tungsten halogen bulb but several years ago a new type of headlamp, the gas discharge bulb, was introduced. Because of the different spectral output of this type of lamp, there has been a suggestion that it may affect the colour recognition and sign conspicuity under night-time conditions. In this study, the visibility of the road signs is used to examine the effect of the gas discharge lamp's spectrum compared with that of the conventional halogen headlamp. METHODS: The spectral output of the lamps and the spectral reflectance of common-coloured road signs were measured using a Spectra-Pritchard spectroradiometer. Using luminous reflectance data, chromaticity co-ordinates and the colorimetric shift of the road signs, when illuminated by gas discharge lamps, were plotted using CIE x,y co-ordinate system. Colour rendering indices of the lamp were calculated using Munsell samples and road signs as proscribed by the CIE Publication. In addition, the visibility index of the road signs was calculated using Adrian's 'Visibility of Target' model. RESULTS: The gas discharge headlamp has more energy in the blue region and less energy in the red region of the spectrum than the halogen headlamp. The general colour rendering index of the gas discharge lamp is higher than that of the halogen lamp. When compared with daylight, all coloured road signs used in this study have less colorimetric shift when illuminated by the gas discharge headlamp than by the halogen headlamp. CONCLUSION: The result indicates that the gas discharge lamp, while having a very different spectrum from daylight or tungsten halogen lamps, should not have a deleterious effect on sign detection or recognition, when compared to daylight or tungsten halogen lamps.
Journal Article↗