The effects of monocular refractive blur on gait parameters when negotiating a raised surface.

Falls in the elderly are a major cause of mortality and morbidity. Elderly people with visual impairment have been found to be at increased risk of falling, with poor visual acuity in one eye causing greater risk than poor binocular visual acuity. The present study investigated whether monocular refractive blur, at a level typically used for monovision correction, would significantly reduce stereoacuity and consequently affect gait parameters when negotiating a raised surface. Fourteen healthy subjects (25.8 +/- 5.6 years) walked up to and on to a raised surface, under four visual conditions; binocular, +2DS blur over their non-dominant eye, +2DS blur over their dominant eye and with their dominant eye occluded. Analysis focussed on foot positioning and toe clearance parameters. Monocular blur had no effect on binocular acuity, but caused a small decline in binocular contrast sensitivity and a large decline in stereoacuity (p < 0.01). Vertical toe clearance increased under monocular blur or occlusion (p < 0.01) with a significantly greater increase under blur of the dominant eye compared with blur of the non-dominant eye (p < 0.01). Increase in toe clearance was facilitated by increasing maximum toe elevation (p < 0.01). Findings indicate that monocular blur at a level typically used for monovision correction significantly reduced stereoacuity and consequently the ability to accurately perceive the height and position of a raised surface placed within the travel path. These findings may help explain why elderly individuals with poor visual acuity in one eye have been found to have an increased risk of falling.     

Potential vision testing – the relationship between visual acuity and Vernier acuity in the presence of simulated cataract

To evaluate the utility of a computer controlled two-bar Vernier acuity measurement as a predictor of visual function in the presence of cataract we measured logMAR visual acuity and Vernier acuity in a group of 40 young normal observers under various levels of dioptric blur (0-3 D in dioptre steps). The Vernier thresholds were resistant to dioptric blur up to 2 D, but performance degraded with blur of 3 D for non-optimised Vernier stimulus parameters. The stimulus parameters, bar length and bar separation, were further investigated in two subjects under conditions of blur. By extending the Vernier bar length and increasing the bar separation the effect of blur could be further reduced even under the most blurred condition. The relationship between visual acuity and Vernier acuity was determined. Vernier acuity was measured in the presence of Vistech cataract simulating lenses and a prediction of visual acuity was made for three observers, two with no ocular abnormality and one with age-related maculopathy. The cataract simulating lenses affected the measured visual acuity in all three subjects, but had less effect on Vernier acuity. Predicted visual acuities were all within six letters (0.12 log units) of the visual acuity without the simulated cataract. As expected, the subject sufferng from age-related maculopathy, whilst showing similar levels of Vernier acuity to the two ocularly healthy subjects at 1.5 degrees of retinal eccentricity, showed much poorer Vernier acuity for stimuli presented at fixation.     

The effect of monocularly and binocularly induced astigmatic blur on depth discrimination is orientation dependent.

PURPOSE: Naturally occurring astigmatism varies according to the age of the person. Although uncorrected astigmatism may be associated with meridional amblyopia, there is little information of its effect on stereopsis. The purpose of this study was to determine the effect of astigmatism on depth discrimination and whether this was dependent on the axis of the astigmatism. METHODS: Astigmatic blur was induced in four healthy subjects (mean age, 31.5 years; range, 22 to 42 years) using plain cylinders (-8.75 D to +11.5 D) for orientation control and Jackson cross-cylinders (0 to 12 D) for spherical neutrality. Horizontal, vertical, and oblique astigmatism was induced with five monocular and three binocular axis steps. Depth discrimination was recorded at near using Frisby, TNO, and Titmus stereoacuity tests and at distance (4 m) using the variable distance stereoacuity test. Visual acuity was recorded at 0.4 m and 4 m. RESULTS: Visual acuity and depth discrimination degraded with increasing astigmatic blur. The effect of monocular astigmatic blur on depth discrimination and visual acuity was not dependent on the axis of orientation. For binocular astigmatic blur, the reduction in depth discrimination was dependent on the axis of the induced astigmatism (p < 0.01). The maximum effect occurred with orthogonal-oblique orientations (x45 left; x135 right), followed by against-the-rule (ATR) astigmatism; with-the-rule (WTR) astigmatism had the least effect (p < 0.001). CONCLUSIONS: The lesser effect of WTR compared with ATR astigmatic blur on depth discrimination may reflect the contribution of horizontal compared with nonhorizontal disparity processing in stereopsis. The pronounced effect of oblique astigmatic blur may be because of the effects on horizontal and nonhorizontal disparity and interocular differential image blur.     

Measuring colour rivalry suppression in amblyopia

AIMS: To determine if the colour rivalry suppression is an index of the visual impairment in amblyopia and if the stereopsis and fusion evaluator (SAFE) instrument is a reliable indicator of the difference in visual input from the two eyes. METHODS: To test the accuracy of the SAFE instrument for measuring the visual input from the two eyes, colour rivalry suppression was measured in six normal subjects. A test neutral density filter (NDF) was placed before one eye to induce a temporary relative afferent defect and the subject selected the NDF before the fellow eye to neutralise the test NDF. In a non-paediatric private practice, 24 consecutive patients diagnosed with unilateral amblyopia were tested with the SAFE. Of the 24 amblyopes, 14 qualified for the study because they were able to fuse images and had no comorbid disease. The relation between depth of colour rivalry suppression, stereoacuity, and interocular difference in logMAR acuity was analysed. RESULTS: In normal subjects, the SAFE instrument reversed temporary defects of 0.3 to 1. 8 log units to within 0.6 log units. In amblyopes, the NDF to reverse colour rivalry suppression was positively related to interocular difference in logMAR acuity (beta=1.21, p<0.0001), and negatively related to stereoacuity (beta=-0.16, p=0.019). The interocular difference in logMAR acuity was negatively related to stereoacuity (beta=-0.13, p=0.009). CONCLUSIONS: Colour rivalry suppression as measured with the SAFE was found to agree closely with the degree of visual acuity impairment in non-paediatric patients with amblyopia.     

The effects of blur and size on monocular and stereoscopic localization

Monocular localization of non-abutting stimuli and stereoscopic localization of the same second-order targets are performed with the same precision (Wilcox, L.M. & Hess, R.F. (1996) Is the site of non-linear filtering in stereopsis before or after binocular combination? Vision Research, 36, 391-399). Further, both tasks show a similar dependence on the scale of the stimulus. Since prior studies used Gaussian-enveloped stimuli, modifications of stimulus scale produced concurrent changes in edge blur. The experiments reported here assess the relative contributions of size and blur to the observed dependence on envelope scale for both monocular localization and stereoacuity. Stereoacuity for first-order targets was found to be an order of magnitude better than stereoacuity for second-order targets and monocular acuity for both first- and second-order targets. Further, while first-order stereopsis was found to depend solely on blur, second-order stereoacuity and monocular acuity were affected by both size and blur. These results suggest that while stereoacuity for first-order stimuli may be determined by a correlative process limited by early additive noise, stereoacuity for second-order stimuli and monocular acuity for non-abutting targets are more likely limited by stimulus-dependent spatial subsampling.     

Stereopsis after Implantation of Intraocular Lens in Patients under 40 Years Old with Unilateral Cataract

 PURPOSE:To investigate the stereopsis after single focus intraocular lens (SIOL) implantation in patients aged <40 years with unilateral cataract. METHODS:In total, 36 patients (36 eyes) were divided into emmetropia and myopia groups. Twenty seven subjects with good uncorrected distance visual acuity (UCDVA) after surgery were enrolled in the emmetropia group. The myopia group consisted of 9 subjects whose one eye had mild myopia postoperatively and the other was emmetropic or myopic. Visual acuity, distance and near stereoacuity were measured post-operatively. RESULTS:In the emmetropia group, uncorrected near visual acuity (UCNVA) did not differ significantly between eyes (t=1.87, P>0.05). The LogMAR UCNVA of the operated and fellow eyes were (0.71±0.12) and (-0.05±0.07, t = 28.4, P<0.001) respectively. Distance stereoacuity was 60"; the near stereoacuity with uncorrected visual acuity and BCNVA in the operated eyes were 200" and 30" respectively (Z=－4.121, P<0.001). In the myopia group, the BCDVA did not differ significantly between the operated and fellow eyes (t =-0.636, P>0.05). The UCNVA of the operated eyes (0.18±0.12) was significantly better compared with that of the fellow eyes (-0.04±0.10, t = 4.2252, P<0.001). The distance stereoacuity with uncorrected visual acuity and BCDVA in the operated eyes were 200" and 60" respectively (Z =-2.371, P<0.05). The near stereoacuity with uncorrected visual acuity was 50". CONCLUSION:For patients with unilateral cataract aged <40 years, stereopsis is closely associated with refractive status after IOL implantation. Near stereoacuity in emmetropic eyes can be improved with refraction, and that in mildly myopic eyes can be enhanced by leaving myopia uncorrected.     

Stereoacuity testing in patients with retinal and optic nerve disorders

A study comparing the relative sensitivity for detecting abnormal stereoacuity in patients with retinal or optic nerve disease on clinically used stereoacuity tests is not available. It is also not apparent from the ophthalmic literature if optic nerve or retinal diseases are likely to have a greater impact on stereoacuity performance. We were also interested in determining a level of visual acuity loss that would likely result in an impairment of stereoacuity on these clinical tests. Forty-two patients with various retinal and optic nerve disorders and eighteen normal subjects were evaluated for stereoacuity using three tests: Titmus Stereoacuity Test (TST), Randot Stereoacuity Test (RST), and TNO Stereoacuity Test (TNO). The performance on these three stereoacuity tests was compared with the normal subjects. Additionally, TST scores from our patients were compared to predicted TST scores derived from a previously published nomogram. For patients with retinal and optic nerve disease, an abnormal score on one clinical test of stereoacuity was likely to predict an abnormality on the other tests. Performance on the TST relative to the predicted value derived from a nomogram was not significantly different for patients with retinal vs. optic nerve disease. With some exceptions, patients with visual acuities of 20/30 or worse in at least one eye were likely to show abnormal stereoacuity.This study was supported by a center grant from The Foundation Fighting Blindness, Baltimore, Maryland     

Factors influencing success and failure in monovision

This study compared the visual performance of 70 successful and 18 failed monovision (MV) wearers, measured before contact lens dispensing. Compared with successful MV wearers, the failed group showed greater levels of ghosting at distance and near, lost more stereoacuity at 6 m, and lost slightly more near visual acuity. The failed MV group was also older on average than the successful group. Both groups showed worse visual acuity at distance and near with MV than at spectacle baseline, as well as worse stereoacuity at 6 m and 40 cm. Discriminant analysis indicated that distance ghosting, distance stereoacuity, and age were predictive of both success and failure (78% sensitivity; 82% specificity). An investigation, before lens fitting, of other effects of monocular blur on binocular function, as well as an assessment of personal characteristics such as motivation and the nature of visual demands, may further improve the accuracy of prediction of patient success with MV found in this study.     

Stereoacuity and binocular visual acuity in prism-induced exodeviation.

BACKGROUND: Intermittent exotropia may be controlled by accommodative or motor convergence. Previous studies have reported that reduced binocular visual acuity in intermittent exotropia is due to the accommodation required to control the deviation. To test this hypothesis, we simulated convergence stress by inducing exodeviations in normal volunteers to investigate whether the transition from nonfused to fused is associated with a gradual or immediate transition in stereoacuity and binocular visual acuity. METHODS: Convergence stress was induced in 25 visually normal adults with 40(Delta) base-out prism and reduced stepwise in increments of 5(Delta) until 20(Delta), and 2(Delta) thereafter. Stereoacuity (Frisby Davis Distance [FD2] and the Distance Randot [DR]) and binocular visual acuity were measured at each step. For each subject, the recovery of fine stereoacuity (< or =60 arcsec) was categorized as immediate (nil to fine) or gradual (nil to moderate to fine). RESULTS: Twenty-four of 25 (96%) showed gradual recovery of fine stereoacuity on either FD2 or DR. Median binocular visual acuity at baseline, first level of fusion, and subsequent levels was 20/15. CONCLUSIONS: Under convergence stress, the transition from nonfused to fused is accompanied by a gradual recovery of fine stereoacuity in most individuals, consistent with some studies of patients with intermittent exotropia. Nevertheless, this degradation of stereoacuity was not associated with decreased binocular visual acuity, suggesting that accommodative convergence may not be recruited to restore and maintain binocularity under conditions of convergence stress.     

Comparison of suppression, stereoacuity, and interocular differences in visual acuity in monovision and acuvue bifocal contact lenses.

PURPOSE: The relationship between visual acuity and stereoacuity has been well documented: as binocular visual acuity increases, stereoacuity improves. We compared interocular differences in visual acuity and stereoacuity in two presbyopic soft contact lens modalities, monovision and a new soft bifocal contact lens, the Acuvue Bifocal. The Acuvue Bifocal is hypothesized to show a smaller interocular acuity difference, increased stereoacuity, and decreased suppression over monovision at distance and near. METHODS: Monovision patients wearing Acuvue or Surevue soft contact lenses were tested for visual acuity, stereoacuity, and suppression at distance and near. Stereoacuity was tested with the Randot Stereotest (near) and the BVAT (distance). Suppression was evaluated with the Acuity Suppression Vectogram (near) and the BVAT (distance). Patients were then fit with the Acuvue Bifocal in each eye. After wearing the lenses for 1 week, the same tests of visual acuity, stereoacuity, and suppression were performed. RESULTS: The mean interocular acuity difference (IAD) at distance with monovision was 0.712 logarithm of the minimum angle of resolution (logMAR) (SD = 0.275) and 0.188 logMAR (SD = 0.252) (p < 0.001) with the Acuvue Bifocal. At near, the mean IAD with monovision was 0.420 logMAR (SD = 0.183) and 0.137 logMAR (SD = 0.147) (p < 0.001) with the Acuvue Bifocal. Of the monovision subjects, 89% (17 of 19) demonstrated suppression at near while only 26% (5 of 19) did with the bifocal lenses (statistically significant at p < 0.001). Stereoacuity at near improved from a median of 200 sec arc with monovision to 50 sec arc with the bifocal lenses. CONCLUSIONS: In this study, correcting presbyopia with the Acuvue Bifocal versus monovision resulted in a statistically significant decrease in the interocular difference in visual acuity at distance and near. The decreased interocular difference in visual acuity improved certain aspects of binocularity as demonstrated by a decrease in suppression and an increase in stereoacuity.     

Stereoacuity in unilateral visual impairment detected at preschool screening: outcomes from a randomized controlled trial

PURPOSE: Reduced stereoacuity is commonly found in association with reduced visual acuity or strabismus and may significantly affect neuro-developmental performance. Treatment for reduced visual acuity due to refractive error or amblyopia is believed to result in improved stereoacuity. This study was undertaken to investigate the effect on stereoacuity of treatment for unilateral visual impairment detected at preschool vision screenings, in the setting of a randomized controlled trial. METHODS: Children identified through preschool vision screening were recruited and randomized to one of three groups (no treatment, glasses only, or full treatment with glasses and occlusion) for a period of 12 months, after which full treatment was given when indicated. Logarithm of the minimum angle of resolution (LogMAR) visual acuity and random-dot (Randot; Stereo Optical, Chicago, IL) stereoacuity were assessed at recruitment and at 12- and 18-month follow-ups by an orthoptist masked to group allocation. RESULTS: One hundred seventy-seven children were recruited and randomized, 59 to each group. Comparison of stereoacuities showed an immediate median improvement of 30 seconds of arc in each group from refractive correction. Age significantly affected stereoacuity performance at recruitment (mean age, 4 years) but not at follow-up (mean age, 5 years). Deferring treatment did not affect final stereoacuity. CONCLUSIONS: In this group, stereoacuity improved to a normal level as a result of refractive correction. Children in whom treatment was deferred for 12 months did not demonstrate significantly poorer stereoacuity than those in treatment.     

The effect of dioptric blur on reading performance

Little is known about the systematic impact of blur on reading performance. The purpose of this study was to quantify the effect of dioptric blur on reading performance in a group of normally sighted young adults. We measured monocular reading performance and visual acuity for 19 observers with normal vision, for five levels of optical blur (no-blur, 0.5, 1, 2, and 3D). Dioptric blur was induced using convex trial lenses placed in front of the testing eye, with the pupil dilated and in the presence of a 3 mm artificial pupil. Reading performance was assessed using eight versions of the MNREAD Acuity Chart. For each level of dioptric blur, observers read aloud sentences on one of these charts, from large to small print. Reading time for each sentence and the number of errors made were recorded and converted to reading speed in words per minute. Visual acuity was measured using 4-orientation Landolt C stimuli. For all levels of dioptric blur, reading speed increased with print size up to a certain print size and then remained constant at the maximum reading speed. By fitting nonlinear mixed-effects models, we found that the maximum reading speed was minimally affected by blur up to 2D, but was ∼23% slower for 3D of blur. When the amount of blur increased from 0 (no-blur) to 3D, the threshold print size (print size corresponded to 80% of the maximum reading speed) increased from 0.01 to 0.88 logMAR, reading acuity worsened from −0.16 to 0.58 logMAR, and visual acuity worsened from −0.19 to 0.64 logMAR. The similar rates of change with blur for threshold print size, reading acuity and visual acuity implicates that visual acuity is a good predictor of threshold print size and reading acuity. Like visual acuity, reading performance is susceptible to the degrading effect of optical blur. For increasing amount of blur, larger print sizes are required to attain the maximum reading speed.     

The influence of ocular dominance on monovision--the interaction between binocular visual functions and the state of dominant eye's correction

PURPOSE: To examine the interaction between binocular visual functions and the correction of the dominant eye, i.e., for far vs. near vision in monovision. SUBJECTS AND METHODS: Ten healthy subjects without any ophthalmological disease were examined. After cycloplegia, the eyes of the subjects were corrected by soft contact lenses (difference in lens power between the lenses: 2.5 D) with an artificial pupil(diameter: 3.0 mm). Visual acuity at various distances, contrast sensitivity, and near stereoacuity were measured while the dominant eye determined by the hole-in-card test (sighting dominance) was corrected for far and near vision. RESULTS: Binocular visual acuity was better than 1.0(20/20) at all distances. When the dominant eye was corrected for distance, the binocular visual acuity at 0.7 m was better than the monocular visual acuity; contrast sensitivity was better within the spatial frequency range of 0.5-4.0 cycles per degree, and near stereoacuity by Titmus stereo tests improved. CONCLUSION: These results suggest that dominant eyes should be corrected for far vision for better binocular summation at middle distances, and near stereoacuity.     

以眼底像模糊程度预测白内障术后视力的研究

目的研究免散瞳眼底照相白内障筛查法以眼底像的模糊程度反映白内障混浊程度的可行性,并以此预测白内障术后视力的效果。设计前瞻性病例系列。研究对象北京同仁医院眼科中心连续的白内障手术患者123例（171眼）。方法在暗室进行眼底照相,自然瞳孔〈4mm时需药物散瞳,并加照外眼视网膜反光像,以此鉴别晶状体或角膜混浊。眼底模糊度分5级：O级为眼底清晰;1级为视网膜小血管隐见;2级为视网膜大血管隐见;3级为视盘隐见;4级为眼底结构全不见。于术前及术后2周内查矫正视力。主要指标矫正视力、眼底像模糊度。结果术前眼底模糊程度为1、2、3、4级的眼,术后视力分别平均提高0．37±0．24．0．45±0．26,0．53±0．24和0．60±0.31。眼底像模糊度与术前视力负相关（r=-0．59,P=0．000）;眼底像模糊度与视力改善行数正相关（r=0．54,P=0．000）;白内障术后矫正视力〈0．5者（21眼）主要的眼底病变为视盘周萎缩环14眼（66．7％）、视神经萎缩3眼（14．3％）、黄斑病变4眼（19．0％）。结论免散瞳眼底照相的眼底像模糊程度可以反映白内障混浊程度,可能成为白内障手术前预测术后效果的评价指标之一。（眼科,2010,19：81-83）     

Effects of age and optical blur on real depth stereoacuity

Stereoscopic depth perception utilizes the disparity cues between the images that fall on the retinae of the two eyes. The purpose of this study was to determine what role aging and optical blur play in stereoscopic disparity sensitivity for real depth stimuli. Forty‐six volunteers were tested ranging in age from 15 to 60 years. Crossed and uncrossed disparity thresholds were measured using white light under conditions of best optical correction. The uncrossed disparity thresholds were also measured with optical blur (from +1.0D to +5.0D added to the best correction). Stereothresholds were measured using the Frisby Stereo Test, which utilizes a four‐alternative forced‐choice staircase procedure. The threshold disparities measured for young adults were frequently lower than 10 arcsec, a value considerably lower than the clinical estimates commonly obtained using Random Dot Stereograms (20 arcsec) or Titmus Fly Test (40 arcsec) tests. Contrary to previous reports, disparity thresholds increased between the ages of 31 and 45 years. This finding should be taken into account in clinical evaluation of visual function of older patients. Optical blur degrades visual acuity and stereoacuity similarly under white‐light conditions, indicating that both functions are affected proportionally by optical defocus.     

Effect of naturally occurring visual acuity differences between two eyes in stereoacuity

Stereoacuity was measured in 30 subjects with a naturally occurring visual acuity (VA) difference between the eyes. The stereoacuity was measured by a modified Howard's apparatus using the staircase method and VA was measured with log MAR charts. Stereoacuity was worse in subjects with a large VA difference between the two eyes; the correlation between stereoacuity and VA difference was significant ( r = 0.76, P < 0.001). Neither the VA of the worse eye nor of the better eye contributed to the reduction in stereoacuity. The deterioration was more obvious if VA difference between the two eyes was one line or more (correlation coefficient, r = 0.88, P < 0.001). This study also reinforces the use of a 70% stereo-threshold when attempt stereoacuity results to compare with other studies.     

Involvement of neural adaptation in the recovery of vision after laser refractive surgery

PURPOSE: To investigate whether the gradual improvement in unaided visual acuity commonly seen after laser refractive surgery is attributable, in part, to neural adaptation to blur. METHODS: Unaided logMAR visual acuity was measured at presentation (blur adapted) and immediately after refraction and removal of refractive correction (correction adapted) in 26 patients with low myopic residual refractive error after laser in situ keratomileusis (LASIK). The difference in unaided visual acuity (correction adapted--blur adapted) indicates a dominance of practice effect (if negative) or blur adaptation (if positive). A combination of blur adaptation and practice effect is possible. RESULTS: Overall, the mean unaided visual acuity at presentation (blur adapted) was 0.16+/-0.16 (mean+/-standard deviation) logMAR, and the mean unaided visual acuity immediately after refraction and removal of refractive correction (correction adapted) was 0.14+/-0.14 logMAR, giving a difference (correction adapted--blur adapted) of -0.02+/-0.06 logMAR. This difference was not significant (analysis of variance [ANOVA] F1,25=0.204, P>.05), suggesting neither blur adaptation nor practice effect. However, during the first 10 weeks after surgery, the difference in unaided visual acuity was -0.07+/-0.05 logMAR, suggesting a practice effect. After 10 weeks, the mean difference was +0.02+/-0.05 logMAR, suggesting any practice effect is offset by blur adaptation. These values were significantly different (ANOVA F1,25= 13.53, P<.01). CONCLUSIONS: These data suggest that patients do not adapt to surgically induced blur, on average, until 10 weeks after LASIK. The reason for this delay is uncertain; perhaps instability of blur hinders adaptation during the early postoperative period. Part of the gradual visual improvement after LASIK appears to be due to neural adaptation to blur.     

THE EFFECT OF OPTICAL BLUR ON VISUAL ACUITY FOR TARGETS OF DIFFERENT LUMINANCES

We studied the effect of 1.25 D of optical blur on visual acuity at luminances ranging from photopic to low mesopic levels. Optical blur reduces acuity at all luminances tested, this reduction being fourfold at a high photopic level (170 cd m-2) and twofold in low mesopia (0.017 cd m-2). The reduction of visual acuity with blur at low luminances is greater than might be expected from a spatial frequency analysis of vision.     

Pulfrich's phenomenon in unilateral cataract

AIMS—To determine whether unilateral cataract causes a pathological Pulfrich's phenomenon.
METHODS—29 subjects with unilateral cataract and contralateral pseudophakia were assessed on their ability to perceive the Pulfrich phenomenon. Using a computer generated pendulum image, and graded neutral density filters, a series of forced choice trials were performed in which the subject was required to describe the direction of any apparent pendulum rotation. A pathological Pulfrich effect was said to occur when apparent rotation was perceived in the presence of a zero strength neutral density filter. The size of any pathological Pulfrich effect which was present was quantified by neutralising the perceived pendulum rotation with neutral density filters of varying strength placed before the better seeing eye.
RESULTS—20 out of 29 subjects were able to perceive apparent pendulum rotation when uniocular filtering was performed. In the group (n=12) which was tested both before and after cataract extraction with intraocular lens implantation, a statistically significant pathological Pulfrich effect was demonstrated preoperatively, compared with a group of normal control subjects. This effect was abolished after cataract extraction (p=0.009). The median size of the effect was equivalent to a 0.25 log unit neutral density filter over the non-cataractous eye. The subjects who were unable to perceive the Pulfrich phenomenon at all had a significantly greater difference in the visual acuity of each eye (p=0.045) and significantly worse stereoacuity than those who were able to perceive the effect (p=0.002).
CONCLUSIONS—Unilateral cataract can cause a pathological Pulfrich phenomenon. This finding may explain why some patients with unilateral cataract complain of visual symptoms that are not easily accounted for in terms of visual acuity, contrast sensitivity, or stereoacuity.

     

左旋多巴改善屈光参差性弱视视功能的远期效果

目的：观察“思利巴”的有效成分左旋多巴改善屈光参差性弱视单字视力、拥挤视力、对比敏感度、立体视的远期效果。方法：61例5．5－15岁难治性屈光参差性弱视患者，被随机分成实验组和对照组，两组均用传统治疗，实验组加服思利巴3个月，观察两组实验前，实验第1个月、第2个月、第3个月、第6个月、第9个月末的单字视力、拥挤视力、对比敏感度变化及实验前和实验第9个月的立体视变化。结果：（1）服药组弱视眼：（1）单字视力：第1个月、第2个月逐渐提高且变化有显著性。（2）拥挤视力：第1个月提高有显著性。（3）对比敏感度：服药后1个月中低空间频率改善有显著性，高空间频率无变化。以上结果均保持到实验结果。（2）立体视变化无显著性。（3）服药组优势眼及对照组比较，各项指标无变化。结论：（1）服药2个月后，可改善难治性屈光参差性弱视眼的单字视力，服药1个月可改善拥挤视力。（2）思利巴可改善中低空间频率的对比敏感度。（3）服用思利巴3个月对立体视及优势眼无影响。