摘要:

Purpose.The aim of this article was to report the prevalence of refractive errors, mainly myopia, among 12- to 13-year-old children in a metropolitan setting in Mexico.Methods.A total of 1035 schoolchildren were examined in a field study in Monterrey, Mexico. The examination included best-corrected visual acuity and refraction during cycloplegia. A sample of the children was sent to a pediatric eye clinic and underwent cycloplegic refraction with an autorefractor.Results.We found a prevalence of myopia (≥−0.5 D SE) of 44%, whereas bilateral myopia was present in 37% of the children. In the total sample, high myopia (≥−5D) was found in 1.4%. The prevalence of myopia was significantly higher in girls. Only 20% of children with bilateral myopia used prescription glasses; 8% had prescribed glasses, but did not use them. Hyperopia (≥+1 D) was present in 6.0% of the total population, and astigmatism (≥−1.5 D) was present in 9.5%.Conclusions.The prevalence of myopia among 12- to 13-year-old children in Mexico is high. The majority of cases are low grade, and a large number of the myopic children do not have, or do not use, prescription glasses.

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

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.

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Purpose.Prior studies in humans measured time constants of biometric accommodative changes as a function of amplitude, and prior studies in monkeys used slit lamp videography to analyze dynamic lenticular accommodative movements. Neither of these studies related biometric changes to refractive changes. We wished to develop and test methodology to begin to test the hypothesis that ocular biometric changes are well correlated with accommodative refractive changes in rhesus monkeys.Methods.Methodology is described to dynamically measure biometric accommodative changes with A-scan ultrasonography. Lens thickness, anterior chamber depth, and anterior segment length (anterior chamber depth plus lens thickness) were measured dynamically during Edinger-Westphal-stimulated accommodation in two eyes of one rhesus monkey. In addition, dynamic accommodative refractive changes were measured with infrared photorefraction. Functions were fit to the accommodative and disaccommodative responses to obtain time constants. Derivatives of these functions allow peak velocities to be determined for each amplitude. Dynamic changes in lens thickness and anterior chamber depth measured with A-scan biometry were compared with dynamic measures of accommodation using infrared photorefraction.Results.Lens thickness and anterior segment length increase and anterior chamber depth decreases during accommodation. The biometric changes are well correlated with the accommodative optical changes. Peak velocities of accommodative changes in lens thickness and anterior chamber depth increase with amplitude and peak velocities for disaccommodation were higher than those for accommodation.Conclusions.Dynamic A-scan provides a method for dynamic analysis of the accommodative biometric changes during Edinger-Westphal-stimulated accommodation in monkeys, although the measurement resolution of this approach is limited.

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Stray light in spectacle lenses may affect the overall vision. It may also affect the measurement of ocular stray light, contrast sensitivity, or glare sensitivity. This article describes common stray light characteristics for glass and plastic spectacle lenses and compares this to the stray light characteristics of the eye, which are well known from the literature. Stray light is described by the skirts of the point-spread function (PSF), which were measured for angles from 4° to 30°. The PSF of spectacle lenses appears to follow the equation PSF = a10· (&thgr;/10)b, with a10and b representing fitting parameters and &thgr; representing the stray light angle. The slope b is on average −2, which similar to that of the eye. For clean spectacle lenses, the PSF is usually at least an order of magnitude lower than that of the eye, whereas “as worn” (uncleaned) spectacle lenses may approach the PSF of the eye. To reach the PSF of the eye, the spectacle lens needs to be contaminated by as much as one or two fingerprints. The article also shows that plastic spectacle lenses degrade much faster than glass spectacle lenses when looking at the amount of stray light.

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID

ISSN:1040-5488    

出版商:OVID    

年代:2003

数据来源: OVID