摘要:

We used the noninvasive tear break-up time (NITBUT) technique to measure the tear stability of 24 asymptomatic Hong Kong (HK)-Chinese before and after instillation of fluorescein. One eye was used as the test eye while the fellow eye served as control. We compared the NITBUT of the test eyes pre- and postinstillation of fluorescein, and compared the NITBUT of the test eyes measured postinstillation of fluorescein with the NITBUT of the control eyes. After instillation of fluorescein, both longer and shorter NITBUT were recorded in the test eyes; similar results were observed for the control eyes (no fluorescein instilled) between the first and second measurement. The median NITBUT of the test eye pre- and postf luorescein instillation were 13.3 and 13.0 s, respectively. Fluorescein did not cause any significant change in the NITBUT of HK-Chinese and the instillation of fluorescein in one eye does not affect the NITBUT of the fellow eye. Fluorescein did not appear to affect the locations of tear break up (tear defects) observed using the NITBUT test. Tear defects are most frequent near the inferior periphery of the cornea.

ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Background. Scratch-resistant (SR) and anti-reflective (AR) coatings are commonly applied to plastic ophthalmic lenses. Fracture resistance is greatly affected by surface characteristics, and coatings may have a weakening effect. Static load testing is an efficient, quantifiable alternative to the drop ball test and has been suggested as useful for comparing lenses of a given material. Methods. An Instron static load tester was used to test the fracture resistance of 140 CR-39 lenses divided into 4 groups: uncoated, prepared for AR coating but not actually coated, AR coated, and factory SR coated. Results. Compared to the control uncoated group, AR coating reduced the required fracture energy by 63% and SR coating by 57%. Preparation for AR coating had no significant effect. Conclusions. These results are at least qualitatively consistent with drop ball testing and have significant implications as new plastic materials are developed, made thinner, and variously coated

ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Twelve subjects were fitted with a high water content, nonionic contact lens (Pilkington Barnes-Hind “Precision UV”), which was either replaced every month for 3 months or worn for 3 consecutive months before replacement occurred. Visual quality, high and low contrast acuity, and comfort were unaltered with either replacement schedule, but overall satisfaction was significantly greater with the shorter replacement schedule (p=0.04). Front surface wettability revealed a large amount of intersubject variability and was reduced at the 3-month visit with the longer replacement period lenses (p=0.003). Visible deposits also increased with longer replacement times (p<0.05). Laboratory-based analytical results showed that both gross lipid and gross extractable protein significantly increased in the 3-month lenses compared with the 1-month lenses, with 44% less lipid accumulation and 60% less protein deposition occurring with the shorter replacement time. The results support the replacement of high water content lenses on a monthly ba

ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The purpose of this study was to provide optometrists with suggested base curves and powers for initial lens choice based on the infant's age. A retrospective chart review of 16 congenital cataract patients fitted at U.C. Davis Eye Clinic between July 1987 and May 1993 was performed. Patients with associated ocular pathologies were excluded. All patients were fitted with a Bausch & Lomb Silsoft lens, a Silicone Elastomer, set at a 3.00 D myopic posture, which was decreased with the child's increasing age and activity. This study provides a graphical approach to pediatric aphakic silicone elastomer contact lens fitting. Best-fit regression lines for both graphs have an r squared value better than 0.9. Optometrists will now be able to reference the Base Curve vs. Age and Power vs. Age graphs to determine the initial lens choice when keratometry is unachievable. Furthermore, the data suggest a need for an increased range of powers provided by the Silicone elastomer lens in order to approximate normal visual development.

ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Background. Lens adherence and a reduced postlens tear film circulation have been suggested as factors contributing to some adverse reactions in extended wear of hydrogel contact lenses. In this study, we determined lens fitting and postlens tear film characteristics during closed-eye wear. Methods. Twenty subjects wore hydrogel lenses for 3 h of eye closure, followed by 30 min of open-eye wear. Lens movement was measured with a video biomicroscope. Postlens tear film appearances in specular reflection were classified as either amorphous, or as one of four color intensity grades, where a colored appearance was taken as indicative of a depleted postlens tear film. Results. All subjects showed lens adherence (movement <0.1 mm) and postlens tear film depletion within 45 min of eye closure. These changes were sustained for the remainder of the closed-eye period, but were reversed within 15 min of eye opening. Lens adherence was associated with colored postlens tear film patterns of any intensity. Conclusion. Closed-eye wear was invariably associated with the onset of lens adherence and postlens tear film depletion. This finding emphasizes the need for adequate lens movement during the open-eye phase of extended wear

ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The effects of auditory biofeedback training on myopia, visual acuity (VA), and psychological distress were evaluated in a controlled prospective study involving 55 mildly myopic (≤-3.5 D) high school students. These myopes were divided into 2 groups, matched for age and dioptric defect: 33 were treated with visual training and 22 were not; 27 emmetropic subjects formed a further control group. Subjects were evaluated at the baseline (TO), at 10 weeks after the end of the treatment (T1), and after an interval of 12 months (T2) from the baseline for: (1) manifest and cycloplegic refraction, and the difference between them (cycloplegic tonus); (2) VA measured with a conventional optotype in all subjects, and also with a computer-generated optotype in the treated group; and (3) psychometric values and personality profile. At T2, myopia had significantly worsened both in the treated and in the control myopes; VA in the treated myopes appeared significantly improved when measured by the conventional optotype, but unchanged when measured by computer. Psychometric scores improved significantly in the treated myopes and in the emmetropic controls. Objectively the autorefractometer showed that 38% of the myopes had voluntary control of positive accommodation, i.e., the ability to increase spherical defect; no voluntary control of negative accommodation was observed. An increase in VA was associated with a significant increase in the foveation time (i.e., the period of time when the target is imaged on the fovea and the eye is motionless), and was partly attributable to a learning effect. In conclusion, biofeedback visual training had a positive effect on psychological distress and subjective VA improvement, but failed to reduce the existing myopia or delay its evolution.

ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

A new tool to measure changes in random dot stereoacuity development from 6 months to 5 years of age was developed and tested. Either a forced choice or operant preferential looking (PL) paradigm with a happy face target was successfully used to test 136 children. Results indicate that stereoacuity measurements continue to develop through the first years of life. Although children below 24 months of age can be expected to have stereo thresholds in the range of 300 sec arc, there is a transition at approximately 24 months of age after which stereoacuity approaches adult levels. The sensitivity of this test in detecting binocular vision problems was 80%. These results provide guidelines for the assessment of stereoacuity in young children and also provide a new tool for the early detection of binocular vision anomalies.

ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The Freiburg Visual Acuity test is an automated procedure for self-administered measurement of visual acuity. Landolt-Cs are presented on a monitor in one of eight orientations. The subject presses one of eight buttons, which are spatially arranged on a response box according to the eight possible positions of the Landolt-Cs' gap. To estimate the acuity threshold, a best PEST (best Parameter Estimation by Sequential Testing) procedure is used in which a psychometric function having a constant slope on a logarithmic acuity scale is assumed. Measurement terminates after a fixed number of trials. With computer monitors, pixel-discreteness artifacts limit the presentation of small stimuli. By using anti-aliasing, i.e., smoothing of contours by multiple gray levels, the spatial resolution was improved by a factor of four. Thus, even the shape of small Landolt-Cs with oblique gaps is adequate and visual acuities from 5/80 (0.06) up to 5/1.4 (3.6) can be tested at a distance of 5 m.

ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The variability of optic nerve parameters obtained with versions 3.4 and 3.5 of the Topcon IMAGEnet computer stereo analysis system was studied. The consistency of horizontal cup-to-disc ratio, vertical cup-to-disc ratio, cup volume, neuroretinal rim area, neuroretinal rim-to-disc area, and the percentage of poorly correlated conjugate points (bad points) on the stereo pair was compared. The updated computer program for stereo analysis provides a significantly more accurate means to assess both the cup volume and the neuroretinal rim area as evidenced by the smaller number of bad points.

ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Background. A new Arabic visual acuity chart has been designed using the various recommendations made by vision scientists for achieving a standardized acuity chart. Our goal was to design a standardized Arabic distance visual acuity chart. Method. The chart is based on the design principle devised by Bailey and Lovie. Twelve Arabic letters of nearly equal legibility values, which could be constructed on a 5 by 5 Snellen framework, were used. The LogMAR method of scaling visual acuity was used, hence the size of letters in the rows progresses in a uniform step of 0.1 logarithm unit. Result. The size of letters in the chart ranged from 58.2 to 4.6 mm, corresponding to visual acuity of 4/40 to 4/3 (6/60 to 6/4) (20/200 to 20/15). The chart is designed for use at 4 m; acuity values for a 6-m testing distance are, however, provided on the chart. Conclusion. The chart will be useful for examining Arabic speaking patients.

ISSN:1040-5488    

出版商:OVID    

年代:1996

数据来源: OVID