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At least 505 records · Page 28Linked to original sources
PubMed1992

Ophthalmic manifestations of head injury.

Head injuries are frequently associated with ophthalmic problems. The commonest problems seen in this series of 161 patients with head injury were problems with poor accommodation (16% of patients; 58% of these persisted), convergence (14% of patients; 35% of these persisted), pseudomyopia (19%; 55% persisted) and optic atrophy (26% of the patients; 78% of these were mild and easily missed on routine testing, and 22% were severe). Motility disorders were common, especially cranial nerve palsies. Other less frequent motility disturbances included apparent inferior oblique palsy, comitant esotropia, and exotropia which was often of the convergence insufficiency type.

Adolescent↗
PubMedDate not supplied

Toward a miniaturized fundus camera.

Retinopathy of prematurity (ROP) describes a pathological development of the retina in prematurely born children. In order to prevent severe permanent damage to the eye and enable timely treatment, the fundus of the eye in such children has to be examined according to established procedures. For these examinations, our miniaturized fundus camera is intended to allow the acquisition of wide-angle digital pictures of the fundus for on-line or off-line diagnosis and documentation. We designed two prototypes of a miniaturized fundus camera, one with graded refractive index (GRIN)-based optics, the other with conventional optics. Two different modes of illumination were compared: transscleral and transpupillary. In both systems, the size and weight of the camera were minimized. The prototypes were tested on young rabbits. The experiments led to the conclusion that the combination of conventional optics with transpupillary illumination yields the best results in terms of overall image quality.

Animals↗
PubMed1992

Controlled study of ocular morbidity in school children born preterm.

Two hundred children who were of very low birth weight (VLBW) (1500 g or less) and 193 controls who were of normal birth weight (NBW) were examined at approximately 9 years of age. Binocular visual acuity of 6/6 or better was noted in 178 (89.5%) VLBW children and 189 (97.9%) NBW children. Visual morbidity was significantly higher among VLBW children. Strabismus was present in 38 (19%), cicatricial retinopathy of prematurity in 13 (6.5%), and optic atrophy in six (3%) children in this group. Children who were VLBW were also more myopic than the NBW controls. Optic atrophy was frequently associated with cerebral dysfunction. Regular assessments to identify ocular abnormalities in children who were VLBW are recommended.

Eye Diseases↗
PubMed1995

Optic disc measurement: a comparison of indirect ophthalmoscopic methods.

AIMS: Two methods of indirect ophthalmoscopic estimation of optic disc size, the 78 dioptre lens and optic disc biometer were evaluated. METHODS: Twenty nine eyes of 29 patients were measured by both methods and compared with optic disc size calculated using the three planimetric corrections described by Bengtsson and Krakau. RESULTS: The closest agreement with the clinical measurements was found using correction 3. There was a significant difference between both the 78 D lens (p < 0.0001) and the biometer (p = 0.0027) and the planimetric results. There was also a significant difference between the two clinical methods (p < 0.0001). Both methods showed acceptable intraobserver variation (CoV 2.45% and 3.13% respectively). CONCLUSION: Overall, both methods give larger measurements than planimetry; the 78 D lens by 0.41 mm and the biometer by 0.15 mm. Neither method gives a satisfactory estimation of optic disc size when compared with planimetry.

Biometry↗
PubMed2004

The use of contact lenses to treat visually symptomatic congenital nystagmus.

It has been suggested that contact lens wear improves the visual function of patients with visual loss from congenital nystagmus. In this study, four patients with congenital nystagmus had two evaluations separated by at least one week (one with spectacles, one with contact lenses) including visual acuity, contrast sensitivity, oscillopsia scale, quality of life questionnaire (NEI VFQ-25), and eye movement recording with an infrared tracking system. All patients subjectively preferred contact lenses to spectacles. Their contrast sensitivity and VFQ-25 scores were improved with contact lenses compared with spectacles alone. Several parameters of nystagmus showed no change in two patients, worsening in one patient and improvement in one patient. This suggests that much of the clinical improvement observed in our patients may result from a better optical correction of their refractive error with contact lenses than with spectacles, rather than from a true damping effect of the nystagmus by contact lenses.

Adolescent↗
PubMedDate not supplied

Phase-contrast radiography.

For the past 100 years, the paradigm for radiography has been premised on absorption as the sole means of contrast formation and on ray optics as the basis for image interpretation. A new conceptual approach to radiography has been developed that includes phase (ie, refractive) contrast and requires wave optics for proper treatment. This new approach greatly increases the amount of information that can be obtained with radiographic techniques and is particularly well suited to the imaging of soft tissue and of very small features in biologic samples. A key feature of the present technique of phase-contrast radiography is the use of a microfocus x-ray source about an order of magnitude (< or = 20 microm) smaller than that used in conventional radiography. Phase-contrast radiography offers a number of improvements over conventional radiography in a clinical setting, especially in soft-tissue imaging. These improvements include increased contrast resulting in improved visualization of anatomic detail, reduced absorbed dose to the patient, inherent image magnification and high spatial resolution, use of harder x rays, and relative ease of implementation. More technologically advanced detectors are currently being developed and commercialized, which will help fully realize the considerable potential of phase-contrast imaging.

Animals↗
PubMed2006

A simple, cross-linked collagen tissue substitute for corneal implantation.

PURPOSE: To develop a simple corneal substitute from cross-linked collagen. METHODS: Porcine type I collagen (10%; pH 5), was mixed with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS). The final homogenous solution was molded to corneal dimensions, cured, and then implanted into rabbits and minipigs by lamellar keratoplasty. The implants were followed for up to 6 months after surgery. Clinical examinations of the cornea included detailed slit lamp biomicroscopy, in vivo confocal microscopy, topography and esthesiometry for nerve function. Histopathologic examinations were also performed on rabbit corneas harvested after 6 months. RESULTS: Cross-linked collagen (refractive index, 1.35) had optical clarity superior to human corneas. Implanted into rabbit and porcine corneas, only 1 of 24 of the surgical corneas showed a slight haze at 6 months after surgery. All other implants showed no adverse reactions and remained optically clear. Topography showed a smooth surface and a profile similar to that of the contralateral nonsurgical eye. The implanted matrices promoted regeneration of corneal cells, tear film, and nerves. Touch sensitivity was restored, indicating some restoration of function. The corneas with implants showed no significant loss of thickness and demonstrated stable host-graft integration. CONCLUSIONS: Collagen can be adequately stabilized, using water soluble carbodiimides as protein cross-linking reagents, in the fabrication of corneal matrix substitutes for implantation. The simple cross-linking methodology would allow for easy fabrication of matrices for transplantation in centers where there is a shortage of corneas, or where there is need for temporary patches to repair perforations in emergency situations.

Animals↗
PubMed2005

ABCD matrix for reflection and refraction of Gaussian beams at the surface of a parabola of revolution.

We report the formulation of an ABCD matrix for reflection and refraction of Gaussian light beams at the surface of a parabola of revolution that separate media of different refractive indices based on optical phase matching. The equations for the spot sizes and wave-front radii of the beams are also obtained by using theABCD matrix. With these matrices, we can more conveniently design and evaluate some special optical systems, including these kinds of elements.

Journal Article↗
PubMed1997

Optical density of the human lens.

Optic disk reflectance was measured from 27 normal observers with their physiological lenses (aged 21-74 yr) and from two pseudophakic observers (aged 69 and 70 yr) with use of a Utrecht fundus reflection densitometer. Psychophysical heterochromatic flicker photometric luminance matches (10 degrees field) were obtained on the same group of the observers. A four-parameter model incorporating lens density, hemoglobin absorption, optic disk reflectance, and superficial stray light was used to fit the reflectometric data. A model incorporating lens density and the Judd revised spectral luminous-efficiency function was used to fit the psychophysical data. The lens-density spectrum used the two-factor aging model of Pokorny, et al. [Appl. Opt. 26, 1437 (1987)]. The lens density for each normal observer was estimated through a least-squares fitting procedure yielding an estimated lens age. For the reflectometric data the observer's chronological age agreed with estimated lens age with a correlation coefficient of 0.92. The reflectometric regression line underestimated chronological age by approximately 5 yr. The mean reflectance of the optic disk was 0.047 with standard error of the mean of 0.0044. Data from the pseudophakic observers were well described when corneal density was used to replace lens density. The lens density was also estimated from the psychophysical data. The observer's chronological age agreed with psychophysically estimated lens age with a correlation coefficient of 0.92. It was concluded that the in vivo lens density can be estimated from the reflectance spectrum measured off the optic disk. The reflectance spectrum of the optic disk was inferred to be close to spectrally neutral.

Adult↗
PubMed2001

Photonic bandgap structures in planar waveguides.

If a one-dimensional (1D) or two-dimensional (2D) photonic bandgap (PBG) structure is incorporated into a planar optical waveguide, the refractive-index nonuniformity in the direction perpendicular to the waveguide plane responsible for waveguiding may affect its behavior detrimentally. Such influence is demonstrated in the paper by numerical modeling of a deeply etched first-order waveguide Bragg grating. On the basis of physical considerations, a simple condition for the design of 1D and 2D waveguide PBG structures free of this degradation is formulated; it is, in fact the separability condition for the wave equation. Its positive effect is verified by numerical modeling of a modified waveguide Bragg grating that fulfills the separability condition.

Journal Article↗
PubMed2003

Sommerfeld revisited: a new approach to the third-order Seidel aberrations.

In following a suggestion of Sommerfeld, who was able to derive the paraxial properties for points on the optic axis from the existence and continuity of wave fronts satisfying the eikonal equation, it will be shown how the whole set of the third-order Seidel aberrations of a centered optical system made of refracting surfaces of revolution can be obtained if the series expansion in the radial coordinates is continued up to the fourth order.

Journal Article↗
PubMed2004

Experimental demonstration of guiding and confining light in nanometer-size low-refractive-index material.

We experimentally demonstrate a novel silicon waveguide structure for guiding and confining light in nanometer-wide low-refractive-index material. The optical field in the low-index material is enhanced because of the discontinuity of the electric field at high-index-contrast interfaces. We measure a 30% reduction of the effective index of light propagating in the novel structure due to the presence of the nanometer-wide low-index region, evidencing the guiding and confinement of light in the low-index material. We fabricate ring resonators based on the structure and show that the structure can be implemented in highly integrated photonics.

Journal Article↗
PubMed2002

The effect of UV absorbing sunscreens on the reflectance and the consequent protection of skin.

The in vivo reflectance spectra of Caucasian skin, coated with preparations containing sunscreen vehicle, vehicle with olive oil and vehicle with the UVB and UVA absorbers 2-ethylhexyl-4-methoxycinnamate and 4-t-butyl-4'-methoxydibenzoylmethane were determined. All preparations reduced the reflectance of skin throughout the UVA spectral range (320 to 400 nm), with the sunscreen preparations containing the UVB and UVB plus UVA absorbers reducing the reflectance more than the sunscreen vehicle alone. This phenomenon, which facilitates the penetration of UV radiation to the lower epidermis and dermal layers of skin and therefore lessens sunscreen efficacy, is attributed to optical coupling mediated by refractive index matching of the sunscreen to the upper epidermis. The greater reduction in skin diffuse reflectance caused by sunscreens containing methoxycinnamate is associated with this compound's high refractive index. Also, by determining the excitation spectra of the autofluorescence originating from the dermal layer of skin, the transmission spectra of the various components of sunscreen on skin were established, and these were in good general agreement with previously published spectra.

Benzoates↗
PubMed2002

Measuring higher order optical aberrations of the human eye: techniques and applications.

In the present paper we discuss the development of "wave-front", an instrument for determining the lower and higher optical aberrations of the human eye. We also discuss the advantages that such instrumentation and techniques might bring to the ophthalmology professional of the 21st century. By shining a small light spot on the retina of subjects and observing the light that is reflected back from within the eye, we are able to quantitatively determine the amount of lower order aberrations (astigmatism, myopia, hyperopia) and higher order aberrations (coma, spherical aberration, etc.). We have measured artificial eyes with calibrated ametropia ranging from +5 to -5 D, with and without 2 D astigmatism with axis at 45 degrees and 90 degrees. We used a device known as the Hartmann-Shack (HS) sensor, originally developed for measuring the optical aberrations of optical instruments and general refracting surfaces in astronomical telescopes. The HS sensor sends information to a computer software for decomposition of wave-front aberrations into a set of Zernike polynomials. These polynomials have special mathematical properties and are more suitable in this case than the traditional Seidel polynomials. We have demonstrated that this technique is more precise than conventional autorefraction, with a root mean square error (RMSE) of less than 0.1 micro m for a 4-mm diameter pupil. In terms of dioptric power this represents an RMSE error of less than 0.04 D and 5 degrees for the axis. This precision is sufficient for customized corneal ablations, among other applications.

Corneal Topography↗