摘要:

To evaluate the effects of base curve radius, overall diameter, and axial edge lift on rigid contact lens tear pump efficiency, corneal oxygen uptake rates were measured on six eyes under three conditions: normal open eye, after 5 min of static (without blinking) wear, and after 5 min of dynamic (with blinking once every 5 s) wear. The three parameters were varied one at a time from a standard lens design. Differences in corneal oxygen demands between the static and dynamic rates provided quantitative measures of the tear pump efficiency for each lens design. Tear exchange was found to be most sensitively related to changes in base curve radius, followed by overall diameter changes (66.9% as effective) and axial edge lift changes (64.6% as effective). Design equivalencies (to produce identical tear exchange to a 0.05-mm flattening of base curve toward alignment) were 0.07-mm steepening of the base curve toward alignment, 0.35-mm decrease in overall diameter, or 0.037-mm increase in axial edge lift.

ISSN:1040-5488    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Thin lens equations accurate to third order are presented for the effective spherocylindrical parameters for oblique central refraction through spherocylindrical lenses that are tilted around an off-axis meridian. This situation occurs in either pantoscopic or faceform tilt for spectacle corrections for oblique astigmats. The thin lens equations appear to be good approximations for oblique central refraction through actual spectacle lenses.

ISSN:1040-5488    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

The application of vertical rod stimuli to obtain apparent frontoparallel plane (AFPP) settings is well-known. A geometrical relation based on observation distance, interpupillary distance, and retinal disparity determines the deviation of the setting from the objective frontoparallel plane. Further developments of this procedure have established that a similar relation exists for oblique presentations of parallel rod stimuli, the orientation of the rods being an additional variable. This extension of the AFPP procedure is referred to as the multimeridional AFPP or MAFPP. It permits the determination of aniseikonia in oblique as well as horizontal meridians. Although oblique disparities contain a vertical component, an induced effect is absent as long as parallel rod stimuli are used alone. If an induced effect were present, the MAFPP geometrical relations would be expected to break down. To test this hypothesis, random dot arrays and a row of dots of the same frequency as a control stimulus of parallel lines were presented alone and in combination with the line stimuli. Binocular disparities were induced by a meridional afocal magnifier placed at various axes before one eye. It was found that the dot arrays caused a breakdown of the geometrical relation when presented alone or in combination with the parallel lines. The amount of deterioration varied only slightly with the number and arrangement of dot stimuli but increased as the vertical component of the oblique magnification increased. In addition to proving the main hypothesis, the data provide information pertaining to the MAFPP theory as well as offering some insight into the induced effect. The most important practical implication of the results is that the MAFPP theory can be used to measure unknown retinal disparities only if continuous parallel lines are presented in isolation.

ISSN:1040-5488    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Fifty-four asymptomatic Hong Kong-Chinese subjects were recruited and their lacrimation was assessed using a modified cotton thread test (CTT). The CTT was performed once on each subject and, for seven subjects, the test was repeated seven times on different days over a period of 2 weeks to test the reliability of the CTT. The mean (±SD) CTT value (length of wetting of thread in millimeters for a 1-min testing period) of this group of subjects was 22.8 (±9.4) mm/min. Repeated measures analysis of variance revealed no significant difference in the CTT values made on different days. The CTT was found to be superior to the conventional Schirmer test in terms of comfort and consistency of results obtained. A brief review of some studies and results reported by previous investigators using the CTT is also presented for comparison.

ISSN:1040-5488    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Purpose. This study was designed to determine the extent of visual deficits in Alzheimer's disease (AD) patients relative to normal aging changes and to patients with other types of dementia.Methods. Four groups of subjects were tested: patients with probable AD (N = 10), patients with other dementias (N = 10), age-matched controls (N = 11), and young controls (N = 10). Color vision was assessed with the L'Anthony D-15 desaturated color test, contrast sensitivity with the Pelli-Robson chart, and stereoacuity with the RANDOT test.Results. Visual changes were found in AD patients that can be accounted for by age-related deficits (color vision), deficits found in other types of dementia (stereoacuity), and deficits specific to AD (low spatial frequency contrast sensitivity).Conclusion. We conclude that AD patients show a variety of visual deficits. With our tests, only deficits in contrast sensitivity were specific to AD.

ISSN:1040-5488    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

We compared the dark focus of accommodation in 33 healthy children, 19 eyes with good uncorrected visual acuity (1.0 or more) vs. 14 with poor uncorrected visual acuity (below 1.0). The two groups were matched for age and cycloplegic refractive error. Cycloplegic refractive error ranged from +0.15 to +1.75 D in the good visual acuity group and from +0.25 to +1.87 D in the poor visual acuity group. The dark focus was defined as the difference between the refractive error in the dark and the refractive error under cycloplegia. Initially, visual acuity was measured subjectively. Next, refractive error in the dark was measured using the Nidek Autorefractometer AR1600 with its optical target light off. Refractive error under cycloplegia was measured 40 min after the instillation of cyclopentolate hydrochloride using the same autorefractometer. There was a significant correlation between the dark focus and the cycloplegic refractive error (r = -0.53, p < 0.01). Despite an equal refractive error under cycloplegia the dark focus was significantly larger in the eyes with good uncorrected visual acuity than in those with poor uncorrected visual acuity (p < 0.01). Tonic accommodation may influence uncorrected visual acuity.

ISSN:1040-5488    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

A study was performed to evaluate the clinical usefulness of dapiprazole in a private clinical setting. This study was unmasked, but used one eye of each subject as a control. Thirty consecutive subjects were given dapiprazole as directed by the manufacturer. The administration of dapiprazole followed bilateral dilation for routine fundus examination. Subjects were dilated using one drop each of proparacaine 0.5%, tropicamide 1.0%, and phenylephrine 2.5%. Pupil diameter, amplitude of accommodation, and conjunctival injection were evaluated. Each of these three variables was measured (1) before instillation of the diagnostic agents, (2) before the instillation of dapiprazole, and (3) at 30, 60, 120, and 180 min after the final instillation of dapiprazole. The average pupillary recovery time for dapiprazole-treated eyes was similar to previously published data. Accommodation also showed significant recovery, with comfortable reading ability returning after approximately 30 min. The design of our study did not permit us to determine what portion of accommodation recovery was attributable toalphaciliary muscle effect and what portion resulted from the increased depth of field that was due to the pupillary constriction. All of our subjects exhibited conjunctival hyperemia after the administration of dapiprazole. This side effect persisted through the entire 180-min observation period that followed dapiprazole administration.

ISSN:1040-5488    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

The impact resistance of chemically and thermally hardened glass lenses of 2.2- and 3.0-mm thicknesses was evaluated using a ballistic test. Each lens was edged and mounted into a spectacle frame, which was placed on a standard headform. A 6.5-mm steel ball was fired from an air gun at the center of the lens at increasing speeds until the lens broke. The multiple impact data were used to plot cumulative breakage curves. We found that heat-treated photochromic glass and heat-treated crown glass fail at similar missile speeds and that chemical treating considerably improves the impact resistance of crown glass but not of photochromic glass. The poorer performance of photochromic lenses indicates that they should not be prescribed when optimal impact protection is required. Plastic lenses show superior performance.

ISSN:1040-5488    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

We investigated the effect of age and gender on the tear break-up time (TBUT) of 2 groups of normal, asymptomatic subjects [92 Hong Kong-Chinese (HK-Chinese) and 76 Singapore-Chinese (S-Chinese)] using the conventional fluorescein-instillation technique. The mean TBUT (±SD) is 6.5 (±4.0) s for the S-Chinese and 7.8 (±2.4) s for the HK-Chinese. The mode was 7.0 s for HK-Chinese and 5.0 s for S-Chinese. About 80% of the subjects of each group have TBUT less than 10 s. The TBUT of both groups of Chinese decreases with age. It was found that TBUT was significantly different between the two sexes in the S-Chinese but no equivalent effect was observed in the HK-Chinese.

ISSN:1040-5488    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

We investigated the benefits of a new test on the lacrimal system for Dry Eye. This additional test to facilitate the diagnosis of dry eye is described and compared with the Schirmer test and with the results of a patient questionnaire. This simple test uses materials available in all optometric practices. An assistant with brief training can administer the test for the optometrist. The patient's monocular distance visual acuity was measured. One drop of Celluvisc was instilled into each eye; a stop watch recorded the time necessary for the patient to regain the predropped visual acuity. Each patient received a standard Schirmer test and answered a questionnaire. Preliminary results from this new test suggest a correlation between a dry eye with patient symptoms and the length of time for return to normal visual acuity after the use of one drop of Celluvisc. Further investigations should be conducted with a larger population using a precise eye drop dispenser. With this new test, a practitioner would have another method to diagnose a dry eye.

ISSN:1040-5488    

出版商:OVID    

年代:1993

数据来源: OVID