CONTRAST SENSITIVITY IN AMBLYOPIA

Contrast sensitivity function(CSF) for sinusoid gratings of varying spatial frequencies was determined for each eye of 21 cases with unilateral amblyopia. The CSF of all amblyopic eyes, except one, showed reduced sensitivity when compared with the non-amblyopic eye of the same person. The curve showed reduction more significantly at middle and high spatial frequencies. The cut-off frequency was shifted toward lower spatial frequencies. The relationship between CSF and various degree of amblyopia was als...     

Treated amblyopes remain deficient in spatial vision: a contrast sensitivity and external noise study

To evaluate residual spatial vision deficits in treated amblyopia, we recruited five clinically treated amblyopes (mean age=10.6 years). Contrast sensitivity functions (CSF) in both the previously amblyopic eyes (pAE; visual acuity=0.944+/-0.019 MAR) and fellow eyes (pFE; visual acuity=0.936+/-0.021 MAR) were measured using a standard psychophysical procedure for all the subjects. The results indicated that the treated amblyopes remained deficient in spatial vision, especially at high spatial frequencies, although their Snellen visual acuity had become normal in the pAEs. To identify the mechanisms underlying spatial vision deficits of treated amblyopes, threshold vs external noise contrast (TvC) functions--the signal contrast necessary for the subject to maintain a threshold performance level in varying amounts of external noise ("TV snow")--were measured in both eyes of four of the subjects in a sine-wave grating detection task at several spatial frequencies. Two mechanisms of amblyopia were identified: increased internal noise at low to medium spatial frequencies, and both increased internal noise and increased impact of external noise at high spatial frequencies. We suggest that, in addition to visual acuity, other tests of spatial vision (e.g., CSF, TvC) should be used to assess treatment outcomes of amblyopia therapies. Training in intermediate and high spatial frequencies may be necessary to fully recover spatial vision in amblyopia in addition to the occlusion therapy.     

弱视治疗前后对比敏感度的分析

目的：分析弱视患者治疗前后的对比敏感度的变化。方法随机选取40例（80眼）健康体检儿童（视力≥1.0）为正常对照组,47（79眼）例弱视儿童为病人组。利用美国 STEREO 公司生产的 OPTEC 6500视功能测试仪分别测量正常对照组和病人组治疗前、综合治疗5个月时5种空间频率[1.5、3、6、12和18周/度（cycles/degree, c/d）]的对比敏感度（contrast sensitivity , CS）。所有检查对象在正常光线下,采用自然瞳孔测试,病人组先检查患者视力较好的眼,后检查视力较差的眼,将测试结果存储,通过相应软件处理,自动生成资料,即时呈现出对比敏感度函数（contrast sensitivity function, CSF）曲线图。用 SPSS17.0统计软件对比正常组、弱视组治疗前后不同空间频率对比敏感度数值有无差异。结果（1）正常儿童的 CSF 曲线其峰值位于空间频率6 c/d 附近,在较低、较高空间频率,CSF均降低,曲线呈一倒“ U“字形。曲线向高空间频率端外推,得截止率为25c/d。（2）轻度弱视组：治疗前 CS 在高空间频率时,振幅比正常对照组降低明显,,两组差异有统计学意义（P ＜0.05）。治疗后 CS 较治疗前升高,治疗前后差异有统计学意义（P＜0.05）,治疗后 CS 与正常对照组差异无统计学意义。（3）中度弱视组：治疗前 CS 在中、高空间频率比正常对照组降低,和正常对照组之间差异有统计学意义（P ＜0.05）。治疗后 CS 较治疗前升高,差异有统计学意义（P＜0.05）,治疗后 CS 与正常对照组差异无统计学意义。（4）重度弱视组：治疗前 CS 在低、中、高空间频率均比正常对照组降低,在中、高空间频率和正常对照组之间差异有统计学意义,但在低空间频率差异无统计学意义。治疗后CS 较治疗前升高,差异无统计学意义,和正常对照组差异亦无统计学意义。（5）弱视程度与疗效：弱视越重,疗效     

客观对比敏感度检查在弱视患者中的应用研究

目的:本文通过利用稳态图形VEP,对正常人及弱视患者行对比敏感度检查,初步探讨客观对比敏感度检查的可行性、优越性。方法:所有检查对象,在正常光线下,采用自然瞳孔测试,按常规图形VEP检查方法贴放电极,先检查患者视力较好的眼,后检查视力较差的眼,每一对比度条件下,空间频率自0.5,1.0,2.0,4.0,6.0,8.0,12.0,24.0cpd自动翻转,每只眼依次按照对比度从低到高检查10次,采集,分析不同空间频率的对比度值,输入计算机后,得到空间频率和对比度之间的函数曲线。每一组病例分别计算不同空间频率对比敏感度阈值的样本均数,各组之间采用组间t检验。结果:(1)正常对照组:对比敏感度曲线为钟形,曲线最高点对比度为1.97±0.03,对应空间频率为2.0~4.0cpd。(2)轻度弱视组:在高空间频率与正常组比较差异有统计学意义(P<0.05)。(3)中、重度弱视组:在中、高空间频率,与正常组比较,差异有统计学意义(P<0.05)。(4)不同类型弱视组的对比敏感度曲线仅在中、高空间频率差异有统计学意义(P<0.05),三者之间对比敏感度阈值差异无统计学意义。结论:利用稳态图形VEP作对比敏感度检查是一个较为客观、简单、易行的方法,检查结果与对比敏感度仪检查结果有一致性。     

Contrast sensitivity in amblyopia. II. Changes during pleoptic treatment

Contrast sensitivity at spatial frequencies 1-19 c/deg was measured in 56 children (mean age 10 years), who had received pleoptic treatment. Measurements were done at the beginning and at the end of a pleoptic treatment period as well as at follow-up using vertical gratings. A deficiency was observed in contrast sensitivity of amblyopic eyes at all spatial frequencies, but it was most notable at high spatial frequencies. Both types of CSF presented by Hess & Howell (1977) were found in all groups of amblyopia. A statistically significant improvement in the mean value of contrast sensitivity of the amblyopic eyes was observed at all spatial frequencies during the pleoptic treatment, although in 12 cases fixation and vision did not improve. Correlation with the improvement in visual acuity was poor. In several cases a change was observed in only one of the two parameters in question. Regarding the better eye, there were some signs of 'hidden occlusion amblyopia': in a few cases contrast sensitivity of the dominant eye deteriorated during the treatment period without a changes in visual acuity only to risk back to the previous level at the follow-up.     

Contrast sensitivity in amblyopia due to stimulus deprivation.

Contrast sensitivity functions for sinusoidal gratings of varying spatial frequency and stimulus duration were determined for both eyes of 2 patients with amblyopia due to early occlusion and lid closure. The amblyopic eyes showed reduced contrast sensitivity over a wide range of spatial frequencies and stimulus durations, and the temporal integration time of the amblyopic eye was increased by comparison with the non-amblyopic eye at high spatial frequencies. When the gratings were flickered at 10 Hz the sensitivity for both flicker and pattern detection was reduced in the amblyopic eye over the entire spatial frequency range. Abnormal flicker perception by the amblyopic eyes was also evident in the reduced photopic luminosity functions of these patients.     

Spatial contrast sensitivity deficits in monkeys produced by optically induced anisometropia

An anisometropia was simulated in infant rhesus monkeys by securing a high-powered minus lens (-10 D) in front of one eye. The anisometropia rearing procedure was initiated at 30 days of age and was continued for durations of 30, 60, or 90 days. Behavioral measurements of spatial contrast sensitivity obtained when the animals were 9 months of age indicated that the monkeys treated for 30 days had equal or nearly equal contrast sensitivities and cut-off spatial frequencies in the two eyes. The 30-day monkeys also demonstrated normal binocular summation for threshold stimuli. In contrast, the monkeys treated for either 60 or 90 days showed a significant reduction in contrast sensitivity in the defocused eyes for spatial frequencies greater than 1.0 cycles/deg and failed to show an improvement in contrast sensitivity under binocular viewing conditions. The cut-off spatial frequencies obtained at moderate luminance levels for the defocused eyes of the 60- and 90-day monkeys were slightly more than 1.0 octave lower than the cut-offs for the nondeprived eyes and, like humans with anisometropic amblyopia, the deficits in the spatial resolving capacity of the defocused eyes were observed over a large range of background luminances. The results indicate that the lens-reared monkey is a promising model for anisometropic amblyopia in humans.     

Binocular contrast summation and inhibition in amblyopia

The monocular contrast sensitivity loss in amblyopia is well documented. We investigated the influence of interocular sensitivity difference on binocular contrast sensitivity in amblyopia. Monocular and binocular contrast sensitivity functions of six amblyopes (three strabismic and three anisometropic) were measured. The monocular contrast sensitivity loss depended on the type of amblyope. Anisometropic amblyopes generally showed high frequency losses. Strabismic amblyopes showed losses at both low and high spatial frequencies. Binocular performance was assessed in terms of binocular ratios (binocular/non-amblyopic). A binocular ratio greater than 1 indicates binocular summation (binocular > monocular) while a ratio less than 1 shows binocular inhibition (binocular < monocular). In all subjects, the binocular ratio depended on the difference between the amblyopic and the non-amblyopic eye. Minimal interocular difference produced binocular summation, the magnitude of which decreased as the difference between the two eyes increased. Further increases in the monocular difference produced binocular inhibition. Anisometropic amblyopes showed a greater degree of binocular summation at low spatial frequencies compared to strabismic amblyopes. Both types of amblyopes showed binocular inhibition at high spatial frequencies. Clinical implications of binocular summation and inhibition in amblyopia are discussed.     

弱视儿童与正常儿童对比敏感度差异

目的：探讨弱视儿童治疗前后对比敏感度（CS）改变及与正常儿童CS的差异。方法:回顾性病例对照研究。收集2019年6月至2020年12月在武汉大学附属爱尔眼科医院就诊的弱视患儿作为弱视组。根据弱视程度诊断标准将患儿弱视眼分为轻、中、重3组;对弱视组中的单眼弱视患儿再细分为弱视眼组和对侧眼组。选择同期就诊的视力正常儿童作为对照组。共纳入弱视组83例（137眼）,对照组26例（52眼）。双眼弱视54例（108眼）;单眼弱视共29例（29眼）,即弱视眼组29眼,对侧眼组29眼。轻、中、重度弱视组分别为45、69、23眼。检查单眼弱视对侧眼组及轻、中、重各组治疗前、治疗后1年及正常对照组的CS。采用配对t检验、LSD-t检验、Spearman相关性检验进行数据分析。结果:在各空间频率上,各组治疗前CS均明显低于正常组（均P<0.05）。同一组内,治疗后CS均比治疗前明显提高均（P<0.05）。在空间频率18.0 cpd下,对侧眼组和轻度弱视组治疗后CS与正常组差异均有统计学意义（P<0.05）;余空间频率下治疗后CS与正常组差异无统计学意义。在空间频率6.0、12.0、18.0 cpd上,中度弱视组治疗后CS与正常组仍有差别（P<0.05）,在空间频率3.0 cpd下,中度弱视组治疗后CS与正常组无差别。各空间频率下重度弱视组治疗后与正常组仍有差别（P<0.05）。弱视治疗前,在各空间频率下,弱视眼CS与弱视程度呈负相关（r=-0.52、-0.60、-0.55、-0.54,均P<0.001）。结论:不同严重程度的弱视患儿的CS均低于正常对照组;治疗后,CS会有一定程度提升,其中轻度弱视眼比中、重度弱视眼更容易恢复。     

Suprathreshold spatial frequency detection and binocular interaction in strabismic and anisometropic amblyopia.

We have investigated suprathreshold contrast sensitivity and binocular interactions in strabismic and anisometropic amblyopes using a reaction time paradigm. For every spatial frequency, reaction time increased as the grating contrast decreased. At all spatial frequencies and contrast values the reaction times using the amblyopic eye were prolonged compared to the nonamblyopic eye, but most markedly at high spatial frequencies. In the middle range of spatial frequencies, the contrast vs. reaction time function for the nonamblyopic eyes was biphasic, suggesting that two separate mechanisms detect gratings at high and low contrast levels. These functions in deep amblyopia were monotonic, and in shallow amblyopia the break in the functions was present but shifted to lower contrast levels. Binocular interaction experiments showed that binocular summation was absent at all contrast levels, but binocular occlusion was evident at high contrast levels for amblyopic observers.