摘要:

AbstractOptical pachometry was used to monitor thickness increases in six human corneas exposed to an anoxic external environment. Corneal swelling was observed to occur to an extent consistent with an earlier study (5%/hr or 25μm/hr). Use of Darcy's law allows analysis of the “pump-leak” equilibrium, which leads to the conclusion that any direct interference by surface anoxia affecting corneal hydration must be at the endothelial side of the cornea.

ISSN:0093-7002    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

AbstractThis study describes an in vitro preparation of isolated corneal endothelium, in which silver is used to stain the endothelial cell outlines. This permits high-power light microscopy and accurate measurement of individual cell characteristics. The photographed cell areas were measured with a planimeter and mean areas and cell densities were calculated. A total of 40 individual cells were measured from each of 11 guinea-pig corneas to give a mean cell area of 293 μm2and a mean cell density of 3413 cells/mm2. These figures are similar to findings for young human subjects. The accuracy and repeatability of the method were examined and an analysis of variance was carried out to ascertain the effects of interaction between zones and eyes within individual guinea pigs. Differences between eyes were rarely significant and peripheral cells were not found to be significantly different in area from central cells.

ISSN:0093-7002    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

AbstractThe pressures induced in a tear film between a contact lens and the eye during the initial stages of a blink are estimated by means of a flexible slider-bearing model. Calculations are made of the pressure distributions as functions of two nondimensional parameters, one of which is purely geometrical and the other involves the sliding velocity, the viscosity of the tear film, and the flexibility of the lens. For the dimensions and velocities which apply to a typical blink, it is found that the effects of soft lens deformation in reducing pressure can be significant, especially for small tear film thicknesses.

ISSN:0093-7002    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

AbstractThe cyclofusional response to stimuli containing depth cues was studied. Eye positions were monitored by an objective, binocular, eye movement measuring technique while a psychophysical method was used to measure the stereoscopic responses. We found that the overall response contains both stereoscopic and cyclofusional components and that the cyclofusional response includes a large nonmotor, or sensory, contribution. The composition of the response was unaffected by changes in stimulus size. Increased stimulus complexity elicited larger cyclotorsional eye movements and diminished the amount of perceived inclination which was observed in the fused percept.

ISSN:0093-7002    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

AbstractThe average axial length for eyes grouped according to refractive error must vary as a function of refractive error. In fact, this change in the average axial length can account almost totally for the change in refractive error. This finding is incompatible with the usual interpretation of correlation ametropia. When the categorization of eyes is based on axial length rather than on refractive error, then a more statistically meaningful division of eyes into component and correlation categories is achieved.

ISSN:0093-7002    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

AbstractThe optical density for the noncataractous crystalline lens is written as a sum of two terms, each with a specific dependence on wavelength. The first term, proportional to 1/2, represents all light-scattering processes in the lens. The second term, assumed significant only for A ≤ 500 nm, accounts for absorption by lens pigments. By analyzing transmittance data on lenses of subjects aged 21 to 63 years, a spectrum for light absorption by lens pigment is derived and it is shown to be essentially the same for all of the lenses.

ISSN:0093-7002    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

AbstractPooled human tear samples were subjected to biochemical and surface chemical analyses. Gel filtration chromatography yielded four fractions. The second fraction was the most surface active, closely followed by the first. By ionic exchange chromatography, the first fraction obtained by gel filtration chromatography could be further separated into three subfractions. The second of these subtractions was found to be the most surface active, even surpassing the combined surface activity of all the tear components.Altogether eleven protein components were identified in human tears by gradient polyacrylamide gel electrophoresis with sodium dodecyl sulfate (SDS). Their molecular weights range from 16,000 to 400,000 daltons. Isoelectric focusing indicated that most of the tear proteins are negatively charged, whereas the rest are positively charged at physiological pH's.

ISSN:0093-7002    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

AbstractSome hypermetropes, when corrected with contact lenses, appear to have a much smaller AC/A ratio than when corrected with spectacle lenses. Ocular convergence measured with contact lenses is greater than that measured with spectacles. Studies were carried out to establish the cause of these effects. Theoretical considerations are compared with the experimental results obtained. This study emphasizes the importance of the different amounts of magnification induced by contact lenses as compared with spectacles.

ISSN:0093-7002    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

AbstractChromostereopsis is a perceived depth difference between coplanar objects of different color and can be used for highly accurate measurement of interocular separation (PD). A survey of PD measurement with Chromostereopsis and with the PD rule on 83 subjects shows that these methods on average result in the same PD, indicating that Chromostereopsis is a valid technique for PD measurement. Repeated PD measures by these 83 individuals on the authors, using the PD rule and Chromostereopsis, shows that the Chromostereopsis result is far more repeatable than the PD rule. Suggestions are made for the use of the Chromostereopsis technique in optometric practice.

ISSN:0093-7002    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

AbstractMany health professionals screen for the early detection of disease. Unfortunately, many of the tests and programs have poor validity or are applied to screening populations where the prevalence of disease precludes efficient screening operations. The epidemiological concepts of validity testing are presented to aid those designing or implementing screening programs.

ISSN:0093-7002    

出版商:OVID    

年代:1982

数据来源: OVID