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At least 433 records · Page 24Linked to original sources
PubMed2006

[Effect of pirenzepine on form deprivation myopia in chicks and its possible mechanism].

OBJECTIVE: To observe the effect of M1-selective muscarinic antagonist, pirenzepine, on form deprivation myopia and investigate the expression of MMP-2 and its inhibitor TIMP-2 in the fibrous sclera in order to better understand the mechanism by which pirenzepine inhibits myopia. METHODS: 40 chicks after birth one day were divided into 4 groups randomly: I. Control group; II. Form deprivation group; III. Vehicle application group; IV. Pirenzepine injected group. Form deprivation myopia was established in right eyes of group II, III, IV by placement of a translucent occluder. The deprived eyes of group III and IV received daily subconjunctival administration of vehicle PBS and pirenzepine respectively. Optical measures such as refraction, axial length, equatorial diameter were made at the end of the experiment. Total RNA and protein were extracted from the posterior fibrous sclera chicks. The expression of MMP-2 and TIMP-2 mRNA and protein were investigated with RT-PCR and Western blot analysis respectively. RESULTS: Refraction status, axial length, equatorial diameter of the eyes in pirenzepine injected group were significantly lower when compared with form deprivation group (P < 0.01), but the parameters were higher when compared with normal control group therefore relatively myopic changes were detected. There were no significant difference between drug control and pirenzepine injected group when optical measures and the expression of MMP-2, TIMP-2 were concerned (P > 0.05). The expressions (mRNA and protein) of both MMP-2 and TIMP-2 were significantly different in form deprivation group when compared with normal control group (MMP-2 mRNA increased by 143.51%, P < 0.01; protein increased by 114.60%, P < 0.01; TIMP-2 mRNA decreased by 55.05%, P < 0.01; protein decreased by 53.73%, P < 0.01). In pirenzepine injected group the relative expression of MMP-2 mRNA and protein were decreased obviously by 41.95% (P < 0.01) and by 36.16% (P < 0.01), while TIMP-2 mRNA and protein expression was increased significantly by 72.46% (P < 0.01) and by 53.05% (P < 0.01) respectively compared with the form deprived group. CONCLUSION: Subconjunctivally administration of the M1 selective muscarinic antagonist, pirenzepine, partly prevents or restrains form deprivation induced myopia. It may exert its inhibitory effect by modulating the expression of MMP-2 and TIMP-2 in fibrous sclera.

Administration, Topical↗
PubMed2002

Hyperopic laser in situ keratomileusis for refractive accommodative esotropia.

PURPOSE: To assess the efficacy of hyperopic laser in situ keratomileusis (LASIK) in creating orthophoria without optical correction in adult patients with refractive accommodative esotropia (RAE). SETTING: Instituto Oftalmológico de Sabadell, Sabadell, Barcelona, Spain. METHODS: This prospective single-center clinical trial studied 9 eyes (18 patients) with RAE having hyperopic LASIK. The mean follow-up was 20 months (range 12 to 24 months). The mean preoperative refraction was +5.01 diopters (D) and the mean deviation angle without optical correction, 36 prism diopters. The intervention was hyperopic LASIK using the Automated Corneal Shaper microkeratome (Bausch & Lomb) and the Apollo broad-beam excimer laser using a 5.5 mm optical zone and an 8.0 mm transition zone; astigmatism was treated by steepening the flattest meridian. RESULTS: All patients achieved orthophoria or the preoperative microtropia without optical correction immediately after surgery. This was maintained throughout the follow-up. Fifty-six percent of all cases were within +/-0.5 D of emmetropia, and 89% were within +/-1.0 D. The uncorrected visual acuity improved significantly (P <.005), especially at near, and the mean best corrected visual acuity (BCVA) was maintained, although 4 eyes (22%) lost 1 line of BCVA. There were no significant complications. CONCLUSIONS: In adult patients with RAE, treatment of the refractive error using hyperopic LASIK was safe and effective and corrected the esodeviation. Further studies in younger patients will help determine the age at which this intervention may be indicated.

Accommodation, Ocular↗
PubMed2001

Rigid gas-permeable contact lens fitting in LASIK patients for the correction of multifocal corneas.

BACKGROUND: Laser in situ keratomileusis (LASIK) has recently become the most commonly performed refractive surgery procedure. Results are promising in correcting low to moderate myopia. Most complications occur during the surgeon's learning curve. One of the complications is a decentration of the ablated area that causes monocular diplopia and a nocturnal halo phenomenon due to a multifocality of the corneal surface overlying the entrance pupil. The corneal shape is significantly altered after LASIK. We evaluate the efficacy of rigid gas-permeable contact lens designs and fitting techniques used in eight eyes with multifocal LASIK ablations to correct haloes and impaired night vision complaints. METHODS: We used large-diameter tetra-curved rigid gas-permeable (RGP) contact lenses for visual recovery in eight eyes of seven LASIK patients. We used the power on the transition zone of the corneal topographic map, 0.2 mm outside the ablated refractive area, for selection of the back optic zone radius of the RGP contact lenses. Procedures for lens fitting are described. Visual acuity (high-contrast logarithm of the minimum angle of resolution, LogMAR) was measured before- and 6 months after contact lens fitting. RESULTS: Large-diameter tetra-curve RGP lenses with a mean diameter of 11.85 (SD 0.16) mm were successfully used in LASIK patients with multifocal corneas. Mean best spectacle-corrected visual acuity was +0.3 LogMAR (SD 0.19; in Snellen equivalent, 20/40) and improved significantly with the contact lenses to +0.08 LogMAR (SD 0.11; in Snellen equivalent, 20/25, P=<0.01). During the follow-up period of 16.7 months, the average daily wearing time of the lenses was 12.5 h. Contact lenses with a standard geometry were not useful due to excessive movement and inadequate centration. CONCLUSIONS: Contact lenses with large diameters, in combination with selection of the back optic zone radius 0.2 mm peripheral of the refractive ablation zone, facilitate contact lens fitting to restore best-corrected visual acuity in LASIK patients with multifocal corneas.

Adult↗
PubMed1988

Quantitative photorefraction using an off-center flash source.

When an eye is refracted by "eccentric photorefraction" with a flash source off-centered from a camera lens, a crescent of light is formed in the margin of the pupil. The size of the crescent varies directly with the eye's refractive error. This photographic method has been used in vision screening studies of young children where the appearance of a crescent indicated that the refractive error was above a certain threshold. Usually quantification of the refraction could not be achieved by the photorefractor but relied upon subsequent testing using retinoscopy. My research aimed to expand eccentric photorefraction so as to enable it to provide quantification of the eye's refractive error. This was achieved by varying the eccentricity of the flash source from the camera lens and then calibrating the instrument over a large range of refractive errors. The calibration modified a previously derived optical relation which defined the eye's refractive error in terms of the eccentricity of the source for a given pupil size. Eccentric photorefraction of 26 infants and children aged 7 to 48 months showed a good correlation with retinoscopy (r = 0.82). It is concluded that this method would be complementary to other photorefractive methods (e.g., isotropic) particularly as it is able to measure a large range of refractive errors once the astigmatic meridians of the eye are known.

Calibration↗
PubMed2004

Optical transmission of photonic crystal structures formed by dielectric cylinders: evidence for non-negative refraction.

By a rigorous numerical simulation based on the standard multiple scattering theory, we investigate optical transmission in photonic crystal structures, formed from dielectric cylinders embedded in parallel in a uniform medium. In contrast to previous conjectures, the results indicate that the imaging effect of a flat photonic crystal slab, which has been interpreted as a signature of negative refractive effects, is caused by a tunneling or self-guiding effect in the presence of partial band gaps.

Journal Article↗
PubMed1984

Refractive state, depth of focus and accommodation of the eye of the California ground squirrel (Spermophilus beecheyi).

Retinoscopy and electrophysiological refraction were performed on 55 and 24 far-accommodated eyes of California ground squirrels (Spermophilus beecheyi), respectively. These two indices were highly correlated, revealing the eye of this animal to be roughly emmetropic (-0.25 to -0.13 D). Depth of focus was assessed by measuring the effect which defocusing produced on the spatial resolving power of 32 optic nerve fibers. Depth of focus of the ground squirrel eye for a pupil diameter of 2.5 mm is estimated to be +/- 1.6 D, but will increase rapidly for smaller pupils. Accommodation in eleven ground squirrels ranged from 2 to 6 D, with a mean value of 3.9 D.

Accommodation, Ocular↗
PubMedDate not supplied

Visually evoked potentials: theory, techniques and clinical applications.

The visually evoked potential (VEP), the recording of which has recently been made possible by the development of computer averaging techniques, is a gross electrical signal generated by the occipital region of the cortex in response to visual stimulation. It is more specific than the electroencephalogram (EEG) and more sensitive to changes in the visual stimulus; thus, it can provide ophthalmologists and vision researchers with information about the human visual system that is unavailable by other methods. Clinically, the VEP is of special value in the areas of refraction, infant acuity, diseases of the optic nerve, color blindness, amblyopia and field defects. Theory, techniques and instrumentation are described, and applications of the VEP to clinical situations and to vision research are discussed.

Adult↗
PubMed2005

Optic disk ovality as an index of tilt and its relationship to myopia and perimetry.

PURPOSE: To examine the association of optic disk ovality with myopic refractive error, axial length, and the visual field. DESIGN: Prospective observational case series. METHODS: The study included 150 randomly recruited male subjects with myopia. In all cases, one eye was randomly selected, and subjective refraction, slit-lamp examination, applanation tonometry, gonioscopy, A-scan ultrasonography, funduscopy, and color optic disk stereo photography were performed. Disk ovality was assessed using the ratio of minimum to maximum disk diameter (index of tilt). A ratio of < or = 0.8 was considered as significant disk tilt. Visual fields were tested using static automated threshold perimetry with two methods of optical correction: trial lenses and contact lenses. RESULTS: Of the total sample, 137 subjects completed the study. Mean age was 21.2 +/- 1.1 year, and mean spherical equivalent was -6.36 +/- 3.56 diopters. Mean ovality ratio was 0.83 +/- 0.09; 55 subjects (40.2%) had significant tilted optic disks. Greater optic disk ovality (tilt) correlated with greater myopia (P = .009) and longer axial length (P = .009); 95.6% of subjects had normal visual fields with both methods of optical correction. Using multiple linear regression analysis, greater tilt was independently related to a higher mean defect on testing with trial lenses (P < .01). CONCLUSIONS: Increased optic disk tilt was associated with higher myopia and reduced sensitivity on field testing. These factors are important in the assessment of glaucoma in patients with myopia.

Adult↗
PubMed2004

Variation of corneal refractive index with hydration.

We report the effect of changes in the corneal hydration on the refractive index of the cornea. Using optical coherence tomography (OCT), the geometrical thickness and the group refractive index of the bovine cornea were derived simultaneously as the corneal hydration was varied. The corneal hydration was then calculated from the corneal thickness. The group refractive index of the cornea increased non-linearly as the cornea dehydrated. In addition, a simple mathematical model was developed, based on the assumption that changes in corneal hydration occur only in the interfibrilar space with constant water content within the collagen fibrils. Good agreement between the experimental results and the mathematical model supports the assumption. The results also demonstrate that the measurement of refractive index is a quantitative indicator of corneal hydration.

Animals↗
PubMed1991

Wavefront aberration of the eye: a review.

The concept of monochromatic wavefront aberration is discussed in relation to ray aberration, and methods for its measurement in the case of the eye are described. Examples are given of the measured aberration in individual eyes: in general the aberration falls within the Rayleigh quarter-wavelength criterion for pupil diameters less than 2 to 3 mm but significantly degrades image quality for larger pupils. The use of wavefront data to explore both the modulation and phase transfer functions of the eye as a function of pupil diameter and focus is described, together with typical results. Potential applications to clinical problems such as the effects of contact lenses, intraocular implants, refractive surgery, and pathology on the optical quality of the eye are outlined.

Eye↗
PubMedDate not supplied

Temperature-dependent optical properties of individual vascular wall components measured by optical coherence tomography.

Optical properties of tissues and tissue components are important parameters in biomedical optics. We report measurements of tissue refractive index n and the attenuation coefficient mu(t) using optical coherence tomography (OCT) of individual vascular wall layers and plaque components. Moreover, since the temperature dependence of optical properties is widely known, we compare measurements at room and body temperatures. A decrease of n and mu(t) is observed in all samples, with the most profound effect on samples with high lipid content. The sample temperature is of influence on the quantitative measurements within OCT images. For extrapolation of ex-vivo experimental results, especially for structures with high lipid content, this effect should be taken into account.

Body Temperature↗
PubMed1965

The effects of solvent environment on the optical rotatory dispersion parameters of polypeptides. II. Studies on poly-L-glutamic acid.

The Moffitt b(0) parameter of poly-L-glutamic acid in the presumed helical state varied with solvent composition, ranging in magnitude from less than 600 degrees in aqueous solution to 800 degrees in methanol. b(0) was also dependent on temperature throughout the excessable temperature range. The value in aqueous solution is at least 100 degrees smaller than the values for a number of polypeptides in organic solvents, when compared at the same refractive index. Therefore the optical rotatory dispersion data do not provide evidence that the molecule is completely helical in aqueous solution. Since other types of evidence for helical content are not sufficient to establish that PLGA is a complete helix, the helical content of proteins and polypeptides determined by rotatory dispersion measurements should be regarded as uncertain by about 20 per cent.

Chemical Phenomena↗
PubMed2002

Anisometropia and degree of optic nerve damage in chronic open-angle glaucoma.

PURPOSE: To address the question of whether the refractive error plays a role in the amount of optic nerve damage in glaucoma, we intraindividually compared inter-eye differences in refractive error with inter-eye differences in parameters indicating the degree of glaucomatous optic nerve damage, and we interindividually correlated refractive error with neuroretinal rim area and visual field loss. DESIGN: Comparative clinical observational study. METHODS: This comparative clinical observational study was conducted in a university eye hospital. The study included 1,444 eyes of 876 patients with primary or secondary chronic open-angle glaucoma. Patients with a highly myopic refractive error (> or = -8 diopters) were excluded, owing to differences in the anatomy of the optic nerve head. Color stereo optic disk photographs were taken and morphometrically evaluated. The main outcome measures were refractive error, neuroretinal rim area, horizontal and vertical cup/disk diameter ratios, and visual field loss. RESULTS: In an interindividual statistical analysis, area of neuroretinal rim, horizontal and vertical cup/disk diameter ratios, and mean visual field loss were not significantly (P >.10) correlated with refractive error. In an intraindividual comparison, inter-eye differences in refractive error were not significantly (P >.05) correlated with inter-eye differences in neuroretinal rim area and mean visual field defect. The eye with the more myopic refractive error and the contralateral eye with the less myopic refractive error did not vary significantly in neuroretinal rim area and mean visual field defect. CONCLUSIONS: For nonhighly myopic (< -8 diopters) patients with primary or secondary chronic open-angle glaucoma, the refractive error may not play a major role for the amount of glaucomatous optic neuropathy. For nonhighly myopic (< -8 diopters) patients with primary or secondary chronic open-angle glaucoma, myopia may not be an important risk factor for glaucoma.

Adolescent↗
PubMed2006

Optical properties of the poly(N-benzylaniline) thin film.

The optical properties of the poly(N-benzylaniline) thin film were investigated by optical characterization. The optical constants such as refractive index and dielectric constant were determined from the transmittance and reflectance spectra of the film. The refractive index dispersion was analyzed by the Wemple-DiDomenico model. The n(infinity) values changed from 6.37 to 5.71 and these values did not show any certain trend with annealing temperatures. The average oscillator parameter So value, which is the strength of the individual dipole oscillator, was found to be in the range of 1.15 x 10(13) to 1.03 x 10(13) m(-2). The optical band was determined from the direct optical transitions in K space. The optical band Eg of the film decreases from 2.089 to 2.046 eV with increasing annealing temperatures while the Urbach energy Eu called the width of localized states in the optical band gap increases from 0.544 to 0.598 eV. Consequently, the optical constants and optical band gap of the poly(N-benzylaniline) change with the annealing temperatures.

Journal Article↗
PubMed2004

Posterior retinal contour in adult human anisomyopia.

PURPOSE: It is well documented that myopia is associated with an increase in axial length or, more specifically, in vitreous chamber depth. Whether the transverse dimensions of the eye also increase in myopia is relevant to further understanding of its development. METHODS: The posterior retinal surface was localized in two-dimensional space in both eyes of young adult white and Taiwanese-Chinese iso- and anisomyopes (N = 56), from measured keratometry, A-scan ultrasonography, and central and peripheral refraction (+/-35 degrees) data, with the aid of a computer modeling program designed for this purpose. Anisomyopes had 2 D or more interocular difference in their refractive errors, with mean values in their more myopic eyes of -5.57 D and in their less myopic eyes of -3.25 D, similar to the means of the two isomyopic groups. The derived retinal contours for the more and less myopic eyes were compared by way of investigating ocular shape changes that accompany myopia, in the posterior region of the vitreous chamber. The presence and size of optic disc crescents were also investigated as an index of retinal stretching in myopia. RESULTS: Relative to the less myopic eyes of anisometropic subjects, the more myopic eyes were more elongated and also distorted into a more prolate shape in both the white and Chinese groups. However, the Chinese eyes showed a greater and more uniform relative expansion of the posterior retinal surface in their more myopic eyes, and this was associated with larger optic disc crescents. The changes in the eyes of whites displayed a nasal-temporal axial asymmetry, reflecting greater enlargement of the nasal retinal sector. CONCLUSIONS: Myopia is associated with increased axial length and a prolate shape. This prolate shape is consistent with the proposed idea that axial and transverse dimensions of the eye are regulated differently. The observations that ocular shape changes are larger but more symmetrical in Chinese eyes than in eyes of whites warrant further investigation.

Adolescent↗
PubMed2003

Continuous ambient lighting and lens compensation in infant monkeys.

PURPOSE: Protracted daily lighting cycles do not promote abnormal ocular enlargement in infant monkeys as they do in a variety of avian species. However, observations in humans suggest that ambient lighting at night may reduce the efficiency of the emmetropization process in primates. To test this idea, we investigated the ability of infant monkeys reared with continuous light to compensate for optically imposed changes in refractive error. METHODS: Beginning at about 3 weeks of age, a hyperopic or myopic anisometropia was imposed on 12 infant rhesus monkeys by securing either a -3 D or +3 D lenses in front of one eye and a zero-powered lens in front of the fellow eye. Six of these monkeys were reared with the normal vivarium lights on continuously, whereas the other six lens-reared monkeys were maintained on a 12-h-light/12-h-dark lighting cycle. The ocular effects of the lens-rearing procedures were assessed periodically during the treatment period by cycloplegic retinoscopy, keratometry, and A-scan ultrasonography. RESULTS: Five of six animals in each of the lighting groups demonstrated clear evidence for compensating anisometropic growth. In both lighting groups, eyes that experienced optically imposed hyperopic defocus (-3 D lenses) exhibited faster axial growth rates and became more myopic than their fellow eyes. In contrast, eyes treated with +3 D lenses showed relatively slower axial growth rates and developed more hyperopic refractive errors. The average amount of compensating anisometropia (continuous light, 1.6 +/- 0.5 D vs. control, 2.3 +/- 0.5 D), the structural basis for the refractive errors, and the ability to recover from the induced refractive errors were also not altered by continuous light exposure. CONCLUSION: Ambient lighting at night does not appear to overtly compromise the functional integrity of the vision-dependent mechanisms that regulate emmetropization in higher primates.

Animals↗
PubMed2004

Visibility of lamina cribrosa pores and open-angle glaucoma.

PURPOSE: To determine prevalence and associations of visible lamina cribrosa pores in an older population and assess whether this feature is associated with open-angle glaucoma (OAG). DESIGN: Case-control study nested within a large, population-based cross-sectional study. METHODS: The Blue Mountains Eye Study examined 3654 persons (82.4% of permanent residents of a defined area) aged over 48 years. Stereo optic disk photographs were taken and graded reliably in a masked fashion. RESULTS: Lamina pore visibility was associated with larger vertical cup-disk ratio and optic disk diameter, hyperopic refraction, and male gender. Pores were slightly less visible with increasing age. They were visible in 70.8% of subjects with open-angle glaucoma but in only 29.3% of normals. This strong association disappeared after adjusting for other variables. CONCLUSION: Lamina cribrosa pores are commonly visible in glaucoma subjects and less commonly in normals. This association, however, is almost entirely because of an increased visibility associated with larger vertical cup-disk ratio and optic disk size.

Aged↗