摘要:

To determine the efficacy and stability of therapy, we reviewed the charts of 64 amblyopes with strabismus and/or anisometropia who had been treated by direct occlusion. For patients aged 7 years or less (N=39), 90% (35/39) showed some acuity gain, with 69% (27/ 39) achieving at least a doubling of acuity (0.3 log units). Fifty-four percent obtained 20/40 (6/12) or better after an average treatment period of 3.8 months. Some reduction in visual acuity (VA) subsequently occurred for 75% (24/32) of those patients followed. For patients aged 8 years or more (N=26), 77% (20/26) showed some acuity gain with 31% (8/26) improving at least 0.3 log units. Twenty-seven percent (7/26) obtained 20/40 (6/12) or better after an average treatment period of 4.2 months, although no patients older than 10 years (N=13) achieved 20/40 (6/12). Loss of some of the acuity gain subsequently occurred for 67% (12/18) of those followed. These findings indicate that VA can be improved by patching therapy in most patients older than 7 years, but the acuity improvement is somewhat less than in younger patients. At least 67% of all amblyopes followed for 1 year lost some of the acuity gain after cessation of therapy, regardless of the age when treated. As a reduction of the acuity gain is likely to occur within the first year after cessation of therapy, it is recommended that amblyopic patients of all ages be followed at regular intervals.

ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Hydrogel contact lens surfaces partially desiccate during extended interblink intervals, producing a microscopically rough and irregular surface that scatters light. Such light scattering could reduce retinal image contrast, elevating thresholds for target perception. To test this idea, we measured low (7%)-contrast visual acuity of subjects who wore: (1) hydrogel contact lenses, (2) rigid gas permeable (RGP) lenses, and (3) no contact lenses when the subjects blinked normally and when they suppressed blinking. Acuity thresholds were determined using computer-generated acuity stimuli and a staircase psychophysical procedure. Cessation of blinking resulted in small reductions in lowcontrast acuity for subjects wearing RGP lenses (mean loss: 0.1 line) or no lenses (mean loss: 0.3 lines). Subjects wearing hydrogel lenses, however, generally exhibited substantial reduction of acuity (mean loss: 4.1 lines) when blinking was suppressed.

ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Monovision (MV) contact lens correction of presbyopia induces substantial reductions in stereoacuity and small reductions in binocular visual acuity (VA). This study examined those effects in a group of successful and a group of unsuccessful MV patients. Compared to performance with a full binocular correction, the unsuccessful group demonstrated significant losses in both functions. These reductions were smaller in the successful group and of marginal statistical significance only for stereoacuity. Laterality of sighting dominance and laterality of distance/near correction had minimal effect on the results.

ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Common sense suggests that decreasing visual acuity will have a negative effect on basketball shooting performance. To test the hypothesis that basketball shooting performance monotonically decreases with decreasing acuity, 19 subjects attempted 25 set shots from a fixed location at each of 5 different acuity levels: 6/6 or better and vision blurred (by optical defocus) to visual acuities of 6/12,6/24,6/48, and 6/75. Our results revealed a small but statistically nonsignificant decrease in shooting performance between the 6/6+and 6/12 conditions. For visual acuities between 6/12 and 6/75, the number of baskets made remained constant. We conclude that decreases in visual acuity over the range of 6/6+to 6/75 resulting from defocus do not significantly reduce set shot shooting performance.

ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Equivalent viewing power (EVP), field of view, and working distance (WD) were calculated for 4 different magnifier equivalent powers, four magnifier-to-eye distances, and for uncorrected spherical ametropias varying from +20.00 to −20.00 D in 0.25 D steps. Results show that the various viewing conditions which arise (depending on whether or not the refractive correction is worn) can differ considerably. The uncorrected unaccommodating myope has a greater EVP than the equivalent power of the magnifier if he chooses a magnifier-to-eye distance shorter than the focal length of the magnifier. In this situation, field of view is also enhanced. The uncorrected unaccommodating hyperope using a magnifier-to-eye distance longer than the focal length of the magnifier achieves a stronger EVP than the equivalent power of the magnifier. However, field of view is then reduced. For the uncorrected unaccommodating spherical ametrope, the use of a magnifier-to-eye distance corresponding to the focal length of the magnifier seems to be a good compromise between EVP, field of view, and working distance.

ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

The four prism diopter base-out (4ΔBO) test is often recommended for use as an objective assessment of binocular visual function in patients with suspected microstrabismus or central suppression; however, many aspects of the test are unknown. In this series of investigations we evaluated: (1) inter-observer agreement between 2 examiners, using 15 subjects; (2) types of eye movements made and prevalence of the various response types demonstrated in 212 children and 116 adults with normal binocular vision, and 10 children and 4 adults with abnormal binocular vision; and (3) repeatability of test results for 22 subjects evaluated on two separate occasions. In addition, using an SRI Eyetracker, we documented the eye movements made while testing 2 subjects with small angle strabismus and 4 subjects with normal binocular vision. We found the following results: (1) inter-observer agreement is high; (2) both children and adults exhibit many atypical responses, whether or not they have normal binocular vision; (3) diplopia awareness does not differentiate between subjects with normal and abnormal binocular vision; and (4) 4ΔBO test results are not repeatable. Due to frequent atypical and variable responses in subjects with or without normal binocular vision, we suggest the examiner use caution when making a diagnosis based solely on the 4ΔBO test.

ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

A mathematical expression for the joint probability density function of sphere, cylinder, and axis is presented for the first time. It holds under certain circumstances. A relation is derived which may be useful in obtaining the joint probability function when that expression does not hold. The joint probability density function is of fundamental importance in all quantitative studies of dioptric power in the form sphere, cylinder, and axis. Some of its properties are described. It represents a hypersurface in a four-dimensional space with a maximum, a saddle point, and variety of ridges.

ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Measurements obtained in this study include facial and head dimensions. From our findings, it would appear that the Chinese population in Hong Kong have not become different in the two or three generations that separate them from those living in Guangdong province of China.

ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Although diffractive contact lenses have been well documented in theory, no definitive experimental data have been reported which confirm that the near image is in fact created by diffraction rather than by refraction. We have tested the diffraction hypothesis for one type of diffractive contact lens (the Hydron Echelon bifocal) experimentally by measuring its longitudinal chromatic aberration in isolation and when worn on the eye. The basis of this test is that, according to theory, diffractive lenses should have chromatic aberration which is opposite in sign to that measured for the eye. Objective measurements of chromatic aberration were made with a focimeter when the lens was in a wet cell. Subjective measurements were made with a Badal optometer when the lens was worn on the eye. Four control experiments were conducted to provide baseline measurements of the eye's chromatic aberration, against which we compared the results obtained for the diffractive contact lens. The data were also compared with conventional measurements of refractive error obtained by standard subjective techniques and by an automated infrared refractor. Our results showed that the longitudinal chromatic aberration of the diffraction image of the Echelon bifocal lens was about one-half that obtained under the four control conditions: for the naked eye, for the nondiffraction image of the Echelon lens, or for either image of a refractive bifocal contact lens (CIBA Bisoft). These results are consistent with the theoretical prediction that the negative chromatic aberration of a diffractive contact lens should partially cancel the positive chromatic aberration of the human eye. Conversely, it would be difficult to explain these results on the basis of any other known technique for achromatizing the human eye. We therefore conclude that diffraction is responsible for one of the images formed by the Echelon bifocal lens.

ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Although many investigations have examined the parameters of hydrogel lens hydration loss, the in vivo effect (in humans) on lens oxygen behavior has not been characterized previously. Human subjects wore 2 different lenses (a thin, 38% water polymacon lens and a thin, 55% water bufilcon lens) for 5-min periods under either fully hydrated (i.e., with saline regularly applied to the lens) or partially hydrated (i.e., with “normal” wear of 1 blink every 5 s) conditions. An equivalent oxygen percentage (EOP) technique and a gravimetric method were used to determine lens oxygen behavior and hydration, respectively. The hydration results demonstrate that significant lens dehydration occurs during the partially hydrated (normal blink rate) condition compared to thein situ, fully hydrated situation. A corresponding, statistically significant diminution in oxygen equivalency was also observed.

ISSN:1040-5488    

出版商:OVID    

年代:1992

数据来源: OVID