ISSN:1040-5488    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

In order to determine the tear pump efficiencies associated with three plus-power rigid contact lens designs (single cut, lenticular, and minus-carrier), we measured corneal oxygen uptake rates on the right eyes of six human subjects under three conditions: (1) normal open eye, (2) after 5 min of static (without blinking) wear of the contact lens, and (3) after 5 min of dynamic (with blinking once every 5 s) wear of the same lens. The differences among the corneal oxygen uptake rates measured under static and dynamic conditions, relative to those measured for the normal open eye, served as an index of tear pump efficiency. Under both static and dynamic conditions, no significant differences were found among the corneal oxygen uptake rates associated with the three plus-power lens designs. In addition, no significant differences were found in the differences among the static and dynamic condition data, an indication of tear pump efficiency, associated with the three plus-power lens designs. This was true for both the population data and for the data from each subject. Nevertheless, there were significant differences among subjects in the static condition, dynamic condition, and difference data.

ISSN:1040-5488    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Diplomates in the Contact Lens Section of the American Academy of Optometry were surveyed to determine how they managed contact lens patients with pingueculae or pterygia. Responses indicated that many patients with these conditions can be successful contact lens wearers. Specific management techniques used by these practitioners are reported.

ISSN:1040-5488    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

The intraocular pressure (IOP) measurements for 30 myopic and 30 nonmyopic children between 6 and 9 years of age were extracted from eye examination records. The mean IOP of 30 myopic children was 13.69 mm Hg (SD 3.4) and that of 30 nonmyopic children was 11.55 mm Hg (SD 2.06). The difference between the two is significant. These results suggest that IOP may play a role in the determination of refractive error.

ISSN:1040-5488    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Previous studies have shown that S-cone pathway sensitivity is selectively decreased in the early stages of diabetic retinopathy. In the present study, rod system sensitivity was evaluated in a group of diabetic patients using psychophysical techniques. The course of dark adaptation was first determined, then absolute thresholds were measured in the horizontal and vertical meridians. For all patients, although the recovery of the initial portions of rod dark adaptation were normal, absolute thresholds were increased in both the horizontal and vertical meridians. The findings provide evidence that patients with early diabetic retinopathy show a generalized dysfunction of the rod system.

ISSN:1040-5488    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

We studied the influence of color and accommodation on the contrast sensitivity function (CSF). At the same time, we measured the effect of axial chromatic aberration (ACA) on the CSF. The CSF's of two observers were determined using red, green, blue, and white light, at 5- and 0.5-m viewing distances. At 5 m the CSF's were measured with natural vision and also with lenses which compensated the ACA. Results show that the effect of ACA on the CSF is to reduce the sensitivity to blue with respect to the red. The difference in sensitivity between these two colors is between 50 and 150% and varies with the frequency and the subject. When the ACA is compensated the influence of the color on the CSF is very small, in our experiment, and this result is discussed in relation to the compensating effects of chromatic adaptation of the color mechanisms. In near vision, the CSF's were measured with natural vision and also with the lenses required to give the same accommodative stimulus for all colors. We discuss the effect of accommodation on the CSF. For both far and near the results are compared with the CSF with white light.

ISSN:1040-5488    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

The technique of assessing tear stability using the fluorescein instillation technique has been widely used in the clinical diagnosis of “dry eye” and in the screening of potential contact lens wearers. Various inconsistencies in the application of the tear break-up time (TBUT) techniques and the results obtained were noted in the literature and this review summarizes the differences and the conclusions of various investigators. The reliability of this technique using two different methods of observation was examined and the mean TBUT of Hong Kong Chinese subjects (HK-Chinese) was determined. We conclude that the TBUT can be measured reliably using either the scanning or full beam method in most patients. The mean TBUT of HK-Chinese is approximately 8 s and about 70% of HK-Chinese have TBUT's less than 10 s.

ISSN:1040-5488    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Levels of impairment and disability determine eligibility for different welfare programs for visually handicapped persons. General eye care practitioners have to determine the level of impairment for administrative purposes, whereas the low-vision practitioner measures the level of impairment in order to plan the rehabilitation program. We compared the severity of visual impairment reported by the referring practitioners and the one reported by the low-vision specialists for the population of elderly low-vision patients receiving care from one of the largest rehabilitation centers for the visually handicapped in Quebec. Visual acuity ratings reported by general practitioners are lower than those reported by low-vision practitioners. The presence of visual handicap is generally well identified but the severity of visual impairment according to the World Health Organization (WHO)'s categories is not properly gauged by the general eye care practitioners as expressed by the sensitivity and the positive predictive value of the classification of the general practitioners in respect to the classification of the low-vision optometrists. The need to use existing standardized methods to measure visual acuity (VA) is emphasized. It may be hypothesized that this overestimation of the severity of the visual condition may have a negative impact on the process of rehabilitation of the elderly.

ISSN:1040-5488    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

We measured visual acuity in 10 young subjects, 10 times each over a period of approximately 3 weeks, using Bailey-Lovie charts. We used a consistent endpoint criterion and scored each letter read on the chart. We derived the mean and standard deviation of visual acuity measures for each subject, and for the group. The standard deviation for the group was about 3 times that of the individuals in the group. We calculated the criterion for reduction of visual acuity for the group, as group mean plus 1.96 group standard deviations; use of this criterion would consistently fail to detect patients with clinically significant reductions in visual acuity. We recommend that visual acuity be measured to threshold for every patient. Measuring visual acuity between three and five times provides an estimate of the patient's variability and allows a criterion for reduction of visual acuity to be established for the individual patient. Use of this criterion will enhance the sensitivity of visual acuity measurement as a diagnostic tool.

ISSN:1040-5488    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

We have applied research on the visual psychophysics of reading to low vision assessment. Research on different aspects of the reading process found that reading rate rather than reading comprehension is more sensitive to variations in a subject's visual functioning or the stimulus properties of print. The research identified four different visual factors that significantly affect reading rate: (1) acuity reserve [print size relative to acuity threshold], (2) contrast reserve [print contrast relative to contrast threshold], (3) field of view [number of letters visible], and (4) in cases of maculopathy, central scotoma size. Our research indicates that fluent reading rates can be attained with a restricted field of view, as little as four characters. However, attainment of fluent reading levels requires that print size and contrast should be several times threshold and the diameter of a central scotoma should be less than 22°. Although important clinical studies are lacking, we derived specific visual requirements for different reading rates from published experimental research to provide a starting point and to illustrate how visual requirements could be derived, even with poor correlations. Research has made significant progress toward the development of a comprehensive low vision assessment that will allow the practitioner to identify visual impediments to reading, other than reduced visual acuity. Having more fully characterized a visual impairment, the practitioner may tailor devices or interventions to the individual's needs and capabilities.

ISSN:1040-5488    

出版商:OVID    

年代:1993

数据来源: OVID