ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

Current diabetes research is directed at preventing secondary complications such as diabetic retinopathy (DR) that can have devastating effects on vision. Diagnosis of DR is traditionally dependent on visible alterations of retinal vasculature. However, the detection offunctionaldisorders, likely occurring before observable changes in structure, may provide advanced warning of impending DR. We examined the neural function of the retina by electroretinograms (ERG's) and the macular-cortical pathways by visual evoked potentials (VEP's) in 30 insulin-controlled juvenile diabetics and an age-and sex-matched group of nondiabetics. The average duration of diabetes in the test group with normal retinal vasculature was S.6 ± 4.6 years. Results showed small but measurable differences in the amplitude and timing characteristics of retinal and cortical potentials for the test and control groups. The most surprising findings related to shorter response times for the “b” wave of the photopic ERG, larger amplitude oscillatory potentials, and larger steady-state VEP's. These may be the earliest signs of increased segmental blood flow by vascular autoregulatory mechanisms to compensate for generalized hypoxia. Longitudinal studies are required to determine the physiological significance of our findings and the prognostic value of evoked potentials in diabetes.

ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

Several methods which have been proposed to aid the identification of polarity in Farns-worth-Munsell (FM) 100-Hue test plots are described. The assumptions which underlie one type of method are discussed and problems identified. Two methods are taken as representative of the two types of analysis and their performance compared on plots from congenital and acquired color defectives. The key difference between the two methods and the types of method which they represent lies in the imposition of symmetry on the plot. From the performance of 200 diabetic subjects, the problems created by the presence of monopolar plots, plots with unequal magnitudes of errors in the two poles of bipolar plots, and plots in which the two poles are not diametrically opposite are highlighted. It is concluded that the simpler type of analysis is sufficient and retains more information.

ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

Conflicting reports on the adequacy of the visual performance provided by hydrogel contact lenses continue to appear in the literature. We conducted a study to determine the effect on visual performance, as assessed by contrast sensitivity measurements, of (1) lens wear of optimally fitting 38% water content lenses and (2) altered lens parameters, including fitting characteristics, of 38% and 67% water content lenses. During normal wear of lenses, neither the lenses themselves nor any contact lens-induced corneal changes produced measurable visual losses. The visual performance was also independent of lens fit or lens thickness over the ranges used here. The higher water content lenses provided marginally poorer visual performance.

ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

Three hydrogel contact lenses of measured oxygen transmissibility (Dk/L = 20, 12, and 6 x 10−9cm ml O2/s ml mm Hg, respectively) were used to induce central corneal swelling as measured by optical pachometry in five human subjects under open-eye conditions (8 h wear). Both contact lenses with higher Dk/L values induced mean central corneal swelling of about 1.5%. The lower Dk/L lens induced a mean central corneal swelling of 2.2%. However, statistical analysis of the differences in central corneal swelling between the lens-wearing and the control eyes indicates that swelling induced by the higher Dk/L lenses is not identical, and indicates that even a Dk/L of 20 x 10−9is insufficient to reduce corneal swelling to zero. This suggests that the “critical oxygen tension” (COT) could be in excess of 20 to 40 mm Hg, but not necessarily as high as 70 mm Hg.

ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

To examine whether certain aspects of the environment can have a significant effect upon the steady-state water content of hydrogel contact lenses during normal wear, nine volunteers monitored ambient temperature, ambient humidity, and the water content of their contact lenses over a 5-day period of daily lens wear. Three subjects wore Hydron zero-6 lenses (38% nominal water content), three wore Hydrocurve II lenses (55%), and three wore Permalens contact lenses (71%). The results indicate that a knowledge of ambient temperature and humidity is of little value in predicting the water content of hydrogel lenses under normal wearing conditions, at least with respect to the range of environmental conditions encountered in the course of this experiment

ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID

ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

Badal's optometer is used to change the vergence of the accommodative stimulus without changing retinal image size. It has been accepted that this can be accomplished by putting the optometer's secondary focal point at either the eye's anterior nodal or anterior focal point. I show that there can be only one solution because the simultaneous truth of both solutions would lead to a paradox. The most precise solution is slightly different for the accommodated and the unaccommodated eye, but the nodal point provides the best general solution. For the accommodating eye there is a residual increase in image size with accommodation due to the anterior displacement of the nodal points. For the unaccommodated eye, the correct reference point is its entrance pupil. Use of the nodal point results in accommodation creating an anomalous, but slight, change in retinal image size

ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

In the period of almost 100 years since Javal proposed an empirically determined rule for the prediction of refractive astigmatism on the basis of corneal astigmatism, many authors have made suggestions for the modification of “Javal's Rule.” These modifications, rather than being based on clinical data, have been based on concepts of mechanisms that can contribute to refractive astigmatism, but in most cases the modifications do nothing more than complicate the process of predicting refractive astigmatism, with the result that only Javal's original rule is widely used. In this paper, keratometric and refractive data for three groups of subjects are used to demonstrate that a simplified version of Javal's rule is more effective in predicting refractive astigmatism than is Javal's rule itself

ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

This study was designed to compare quality control between six aphakic contact lens brands. The methodology eliminates the sampling and experimental variables of previous studies. The lenses were all purchased new at +13.00 D power, with the same number of lenses and distribution of manufacturing batch/lots per brand. We measured or assessed 120 study lenses (20 per brand) for diameter, front sagittal height, power and image quality, center thickness, surface and edge quality, and edge design. The base curve radius was calculated accurately using lens cross-sectioning techniques. The reproducibility of measured lens parameters (precision) and conformance to label claims (accuracy) were tabulated separately and the lens brands were ranked and grouped statistically. The tabulated results are represented graphically in one spread sheet where selected American National Standards Institute (ANSI) tolerances were used as a standard to which all lens brands were compared. Lens brands coded as Brand A and Brand B rated the highest using our criterion for ranking overall quality control

ISSN:0093-7002    

出版商:OVID    

年代:1988

数据来源: OVID