摘要:

Background.Accommodative spasm (AS) has been reported to be a rare cause of an acquired unilateral visual loss. We describe a unique case of acquired visual loss due to an apparent unilateral AS triggered by occlusion of the contralateral eye. Clinical examination and photorefraction techniques were performed during the acute phase of the disorder and in the follow-up evaluations.Case Report.An otherwise healthy 27-year-old woman presented with a 2-month decrease of vision in her left eye. Unaided visual acuity in the right eye was 20/20 and in the left eye was finger counting. Orthophoria existed at distance and near. The decrease in vision in the left eye was attributed to an apparent unilateral AS of 5 D, which occurred only when the right eye was occluded. Under the occluder, the right eye also manifested an AS. With the left eye occluded or with binocular viewing, the right eye and left eye accommodated normally. With a 5 D convex lens before the right eye, the visual acuity in the left eye was 20/20. Refractive error with cycloplegia revealed low hyperopia in each eye.Conclusion.AS can be the cause of acquired unilateral visual loss. To our knowledge, this is the first documented report of an apparent unilateral AS triggered by occlusion of the contralateral eye.

ISSN:1040-5488    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Introduction.The assessment of individuals’ near work by survey methods is challenging. The feasibility of the Experience Sampling Method to quantify daily visual tasks was evaluated.Methods.Twenty-one subjects were randomly paged five times per day for 6 days. When paged, the subjects dialed into a telephone survey to report the nature, duration, and working distance of their visual activity at the time of the page.Results.The overall response rate was 81.3% (512/630 pages). The individual response rates varied from 6.7% to 100% (median, 86.7%). Responses were grouped into 11 categories/activities for ease of analysis. Of 506 responses, the most common activity category was “distance tasks,” which included driving and walking (N = 92). Other common responses included computer use (N = 68), reading (N = 66), household tasks, e.g., cleaning, cooking, and showering (N = 64), and watching television (N = 61). Activities with a mean distance ≤26 inches (arm length) were combined as near-work responses and accounted for 54.3% (258/475) of all responses.Conclusion.A modification of the Experience Sampling Method can be used to obtain a “real-time” sampling of visual activities.

ISSN:1040-5488    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Purpose.The aim of this study was to characterize binocular through-focus function in white light and to investigate the effect of induced anisometropia on binocular depth of focus.Methods.The subjects viewed sine-wave gratings generated on a monitor through a modified Badal system that produced gradual changes in target vergence ranging from −4.00 to +2.00 D. Binocular through-focus contrast sensitivity curves were obtained at a spatial frequency of 11 cpd and for different levels of induced anisometropia. Subjective depths of focus were derived from the through-focus curves.Results.An induced anisometropia lower than 1.00 D led to a monomodal through-focus curve involving a single depth of focus, whereas with higher anisometropia, the curves became bimodal indicating a lack of performance at intermediate distance. Binocular thresholds predicted by the quadratic summation model from our monocular measurements were well correlated to our binocular measurements. Predictions allowed us to estimate optimum levels of induced anisometropia.

ISSN:1040-5488    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Purpose.Psychophysical studies indicate that many dyslexics have a motion-processing deficit. The purpose of this study was to determine whether elevated motion coherence thresholds correlate with the specific dyslexic subtypes as defined by the Boder classification scheme.Methods.Twenty-one dyslexics (seven dyseidetics, six dysphonetics, and eight dysphoneidetics) and 19 age- and gender-matched controls participated in the study. The dyslexics were identified by an exclusionary approach and then subtyped with the Adult Dyslexia Test or the Dyslexia Determination Test. Motion coherence thresholds were determined with random dot kinematograms composed of signal dots and noise dots. Signal dots moved either left or right on each trial, whereas noise dots moved in random directions. The percentage of dots that comprised the signal was varied randomly on each trial (0 to 21% in 3% increments). Subjects guessed the direction of signal dot motion on each trial (two-alternative forced-choice task). A 75% correct threshold was determined with a Weibull equation fit to the psychometric function.Results.All three dyslexic subtypes had elevated motion coherence thresholds (t-test; dyseidetics p = 0.01, dysphonetics p = 0.039, dysphoneidetics p = 0.048).Conclusion.Motion-coherence deficits are not correlated with a specific dyslexic subtype, but, rather, are common to all subtypes. However, some individuals in each of the dyslexic subtypes were found to have normal motion coherence thresholds, suggesting that other factors must be considered to predict the motion sensitivity deficits found in dyslexia.

ISSN:1040-5488    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Purpose.This study was designated to evaluate, through a static load test, the influence of lens base curve on the fracture resistance of three common plastic materials.Methods.A JJ Lloyd load cell machine was used to test the fracture resistance of −4.00 D spherical lenses. The samples had a nominal center thickness of 2.0 mm and a base curve distributed in one of five groups (+0.50, +2.50, +4.50, +6.50, and +8.50 D). The lenses were manufactured in CR39, polycarbonate, and TL16, a high refractive index plastic (n = 1.599).Results.The lens base curve influenced fracture resistance for all materials. For these materials, resistance increased as the base curve varied from +0.50 to +8.50 D. The resistance of CR39, TL16, and polycarbonate lenses was found to be linearly dependent on lens base curve. The effect is stronger for polycarbonate. Fracture resistance was higher for TL16 than for CR39, and polycarbonate was much more resistant to breakage than the two other materials.Conclusions.For a given power, the fracture resistance of an ophthalmic lens is reduced when its base curve has a low value. Consequently, the flattening of ophthalmic lenses for cosmetic purposes is not recommended as far as fracture resistance is concerned.

ISSN:1040-5488    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Background.Concern about the safety of laser pointers has increased as these devices have become readily available to the public, which includes children who may use them improperly. According to federal (Food and Drug Administration) standards, laser pointers are class 3a devices, and power output cannot exceed 5.0 mW.Methods.We tested a sample consisting of 29 red diode laser pointers obtained from various sources that were equipped with fresh batteries. Power output was measured with an optical power meter with the sensor 5.0 cm from the laser. The laser was turned on for 60 s and a reading was taken every 10 s. This procedure was repeated five times for every laser.Results.The power output of unaltered lasers ranged from 0.7 mW to a high of 3.9 mW. Alterations to some of the lasers increased the output slightly above 5.0 mW.Conclusions.When the laser pointers in our sample were used as packaged, they did not exceed the federal standards of 5.0 mW.

ISSN:1040-5488    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Background.Logarithm of the minimum angle of resolution (logMAR) charts come in a variety of alternative forced-choice (AFC) formats and can be used with a variety of different rules to determine when to stop a subject reading down a chart (termination rules).Methods.Exact calculation and Monte Carlo simulation techniques were used to compare logMAR scores for different termination rules and for infinite-, 26-, 10-, 8-, 4-, and 2-AFC logMAR chart formats. Slope-corrected standard deviation, an index of variability of the underlying ideal threshold, was used as a common metric for the different test conditions.Results.The mean and standard deviation of logMAR scores can be significantly affected by termination rules and AFC format. For different AFC formats, different termination criteria were found to give optimal slope-corrected standard deviations.Conclusion.A number of clinically suitable termination rules are proposed for different AFC format logMAR charts. For letter-by-letter scoring of Bailey-Lovie and EDTRS charts, it is recommended that researchers and practitioners use a termination rule of stopping after four or more mistakes on a line.

ISSN:1040-5488    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Prismatic imbalance produced in the reading area by an anisometropic spectacle correction can be offset by various methods. If a reading addition is present, one method is to provide differently shaped segments and allowing their optical centers to be separated vertically while the segment tops remain in horizontal alignment. Traditionally, to apply this method, the relative prismatic difference at the reading point is first determined by a thin lens application of Prentice’s rule. This rule is then applied a second time to determine the placement of the segments that will offset the prismatic difference produced by the major lenses. However, the conventional application of Prentice’s rule for determining the fusional demand in a particular area of the spectacle field often produces very large errors, which will affect the calculation of the placement of the segments. This article develops and demonstrates more accurate methods for applying the principle of compensating segments.

ISSN:1040-5488    

出版商:OVID    

年代:2001

数据来源: OVID

ISSN:1040-5488    

出版商:OVID    

年代:2001

数据来源: OVID