The slope of the psychometric function and non-stationarity of thresholds in spatiotemporal contrast vision

The slope of the two-interval, forced-choice psychometric function (e.g. the Weibull parameter, β) provides valuable information about the relationship between contrast sensitivity and signal strength. However, little is known about how or whether β varies with stimulus parameters such as spatiotemporal frequency and stimulus size and shape. A second unresolved issue concerns the best way to estimate the slope of the psychometric function. For example, if an observer is non-stationary (e.g. their threshold drifts between experimental sessions), β will be underestimated if curve fitting is performed after collapsing the data across experimental sessions. We measured psychometric functions for 2 experienced observers for 14 different spatiotemporal configurations of pulsed or flickering grating patches and bars on each of 8 days. We found β ≈ 3 to be fairly constant across almost all conditions, consistent with a fixed nonlinear contrast transducer and/or a constant level of intrinsic stimulus uncertainty (e.g. a square law transducer and a low level of intrinsic uncertainty). Our analysis showed that estimating a single β from results averaged over several experimental sessions was slightly more accurate than averaging multiple estimates from several experimental sessions. However, the small levels of non-stationarity (SD ≈ 0.8 dB) meant that the difference between the estimates was, in practice, negligible.     

Identifying steep psychometric function slope quickly in clinical applications

Knowledge of an observer’s psychometric function slope is potentially useful in clinical visual psychophysics (for example, perimetry), however, the short test times necessary in a clinical setting typically prevent slope estimation. We explore, using computer simulation, the performance of several possible procedures for estimating psychometric function slope within limited presentations (aiming for approximately 30 or 140 trials). Procedures were based on either adaptive staircase or Bayesian techniques, and performance was compared to a Method of Constant Stimuli. An adaptation of the Ψ algorithm was best performing, being able to reliably identify steep from flat psychometric functions in less than 30 presentations, however reliable quantification of shallow psychometric functions was not possible.     

Variations in the slope of the psychometric acuity function with acuity threshold and scale

Psychometric measurement of visual acuity not only determines an acuity threshold, but also, by the slope of the psychometric function, reveals how the percentage of correct responses changes with increasing target size. In this study we determined how the slope of the psychometric function changed for different threshold acuities. Psychometric visual acuity functions were obtained using a clinical contour-interaction chart for 35 naive, normal subjects with best refractive correction and with 1.5 and 3.0 diopters of spherical blur. The slope of the psychometric acuity function remained essentially constant for different threshold acuities when acuity was scaled logarithmically (log MAR), but varied with the threshold when inverse Snellen (MAR) and Snell-Sterling scales were used. Our results lend support to the use of the log MAR scale for acuity but, because normal subjects' slopes range tenfold, the use of this parameter in making clinical distinctions may be problematic.     

The slope of the psychometric function for Bailey-Lovie letter charts: defocus effects and implications for modeling letter-by-letter scores.

BACKGROUND: Visual acuity measurement often results in an imprecise endpoint because subjects correctly identify some but not all of the letters on one or more size levels on a letter chart. The extent of this transition zone from seeing to nonseeing can be described by probit size, which is calculated by performing Probit Analysis on letter chart data. There has been no previous research into the effects of optical defocus on letter chart probit size. METHODS: We tested 18 young visually normal subjects monocularly during three different defocus conditions: best spectacle correction (zero defocus) and +1.00 D and +2.00 D additions. Stimuli were Bailey-Lovie-style logarithm of the minimum angle of resolution (log MAR) letter charts constructed with a 0.05 logMAR size progression between size levels. Frequency of seeing data from these charts were used to calculate probit size. RESULTS: There were statistically significant effects of optical defocus on mean probit size. After Monte Carlo correction for bias, we believe that true mean values for probit size are about 0.07 logMAR for well-corrected subjects and up to 0.12 logMAR with optical defocus. CONCLUSION: The smaller probit size for well-corrected subjects should correspond to a sharper logMAR visual acuity endpoint and less intrasubject variability in logMAR acuity than for subjects with a larger probit size (optical defocus). Our modeling shows that these different probit sizes can also significantly affect letter-by-letter visual acuity scoring.     

Bayesian adaptive estimation of psychometric slope and threshold.

We introduce a new Bayesian adaptive method for acquisition of both threshold and slope of the psychometric function. The method updates posterior probabilities in the two-dimensional parameter space of psychometric functions and makes predictions based on the expected mean threshold and slope values. On each trial it sets the stimulus intensity that maximizes the expected information to be gained by completion of that trial. The method was evaluated in computer simulations and in a psychophysical experiment using the two-alternative forced-choice (2AFC) paradigm. Threshold estimation within 2 dB (23%) precision requires less than 30 trials for a typical 2AFC detection task. To get the slope estimate with the same precision takes about 300 trials.     

Covert attention affects the psychometric function of contrast sensitivity

We examined the effect of transient covert attention on the psychometric function for contrast sensitivity in an orientation discrimination task when the target was presented alone in the absence of distracters and visual masks. Transient covert attention decreased both the threshold (consistent with a contrast gain mechanism) and, less consistently, the slope of the psychometric function. We assessed performance at 8 equidistant locations (4.5 degrees eccentricity) and found that threshold and slope depended on target location-both were higher on the vertical than the horizontal meridian, particularly directly above fixation. All effects were robust across a range of spatial frequencies, and the visual field asymmetries increased with spatial frequency. Notwithstanding the dependence of the psychometric function on target location, attention improved performance to a similar extent across the visual field.Given that, in this study, we excluded all sources of external noise, and that we showed experimentally that spatial uncertainty cannot explain the present results, we conclude that the observed attentional benefit is consistent with signal enhancement.     

The development of the Indian vision function questionnaire: field testing and psychometric evaluation

OBJECTIVE: To develop and evaluate the acceptability, reliability, validity, and responsiveness of the Indian vision function questionnaire (IND-VFQ). METHODS: Problem statements from previous qualitative studies were reduced to a 45 item interviewer administered questionnaire representing three a priori domains (general functioning, psychosocial impact, and visual symptoms) which was evaluated in patients with cataract (n = 420), glaucoma (n = 120), diabetic retinopathy, or age related macular degeneration (n = 120) and normal controls (n = 120). Standard methods were used for item reduction and to evaluate psychometric properties. RESULTS: Psychometric item reduction produced a 33 item questionnaire. Psychometric evaluation showed that two of the three scales (psychosocial impact and visual symptoms) had good acceptability, and that all three scales showed high internal consistency (alpha >0.80; item-total correlations 0.54-0.86) and test-retest reliability (>0.89). All three scales showed moderate evidence of convergent and discriminant validity. Responsiveness, assessed in cataract patients (n = 120) before and after surgery, was good for all three scales (effect sizes >1). CONCLUSIONS: The IND-VFQ33 is a psychometrically sound measure of vision function addressing a gap in patient defined measures of vision function developed in populations living in low income countries.     

Ocular fundus auto-fluorescence observations at different wavelengths in patients with age-related macular degeneration and diabetic retinopathy

Background Post-translational protein modification by lipid peroxidation products or glycation is a feature of aging as well as pathologic processes in postmitotic cells at the ocular fundus exposed to an oxidative environment. The accumulation of modified proteins such as those found in lipofuscin and advanced glycation end products (AGEs) contribute greatly to the fundus auto-fluorescence. The distinct fluorescence spectra of lipofuscin and AGE enable their differentiation in multispectral fundus fluorescence imaging. Method A dual-centre consecutive case series of 78 pseudo-phacic patients is reported. Digital colour fundus photographs as well as auto-fluorescence images were taken from 33 patients with age related macular degeneration (AMD), 13 patients with diabetic retinopathy (RD), or from 32 cases without pathologic findings (controls). Fluorescence was excited at 475–515 nm or 476–604 nm and recorded in the emission bands 530–675 nm or 675–715 nm, respectively. Fluorescence images excited at 475–515 nm were taken by a colour CCD-camera (colour-fluorescence imaging) enabling the separate recording of green and red fluorescence. The ratio of green versus red fluorescence was calculated within a representative region of each image. Results The 530–675 nm auto-fluorescence in AMD patients was dominated by the red emission (green vs. red ratio, g/r = 0.861). In comparison, the fluorescence of the diabetics was green-shifted (g/r = 0.946; controls: g/r = 0.869). Atrophic areas (geographic atrophy, laser scars) showed massive hypo-fluorescence in both emission bands. Hyper-fluorescent drusen and exudates, unobtrusive in the colour fundus images as well as in the fluorescence images with emission >667 nm, showed an impressive green-shift in the colour-fluorescence image. Conclusions Lipofuscin is the dominant fluorophore at long wavelengths (>675 nm or red channel of the colour fluorescence image). In the green spectral region, we found an additional emission of collagen and elastin (optic disc, sclera) as well as deposits in drusen and exudates. The green shift of the auto-fluorescence in RD may be a hint of increased AGE concentrations. None of the authors has any financial relationship. All primary data are under full control of the authors and may be reviewed upon request.     

不同波长有色光对豚鼠眼球生长发育的影响

目的:探讨不同波长的有色光线对眼球生长发育的影响,并进一步分析动物模型中RPE细胞在有色光信号传导中的作用。方法:选用出生2w、体重为100～150g的幼年健康有色豚鼠,将36只豚鼠随机分为4组,A组8只,为红光照射组;B组9只,为黄光照射组;C组10只,为蓝光照射组;D组9只,为正常对照组,置于各箱中饲养。4w后测定眼轴长度,每组中各随机选取3只动物,摘除双眼球做冷冻切片,进行原位杂交检测视网膜中TGF-β的mRNA表达。结果:红光照射组眼轴长度的变化与对照组相比差异有统计学 意义,双眼眼轴分别延长了(0.99±0.02)mm和(1.01±0.01)mm,P<0.05。豚鼠视网膜各层均表达TGF-β,红光照射组视网膜各层TGF-β的mRNA表达量较高,蓝光照射组视网膜各层TGF-β的mRNA表达量较低,黄光照射组的与正常对照组无明显差异。结论:眼球的生长发育是一个错综复杂的过程,可能受多种因素调控,RPE细胞在眼球生长发育中的作用机制尚不可知,但其接受不同波长的有色光信号后所产生的生长因子不同,有可能是其在眼球生长发育中产生作用的一个重要环节。     

Color perception with binocularly fused adapting fields of different wavelengths

By presenting to one eye a small test superimposed on a background field, and to the other eye only a similar background field of a different wavelength (arranged so that the fused percept is the test centered upon a single fused background), the color appearance of the perceived background can be changed while keeping constant the light stimulating the test eye. Measurements demonstrate that the contralateral field clearly influences the color of the test, even when the left- and right-eye backgrounds are very different in wavelength and illuminance. This change in color appearance cannot be explained (a) by simple contribution of a color signal from the contralateral eye, (b) by the perceived color of the fused background, or (c) by combining the effects of contralateral adaptation (alone) and monocular adaptation (alone). Instead, the central-mechanism response depends on the particular pair of wavelengths that are fused. The results suggest chromatic coding of neural signals arriving at the central locus.     

Repeatability of visual acuity testing using a psychometric function

Purpose

To evaluate the repeatability of a new method of measurement of visual acuity by use of a psychometric function.

Methods

The visual acuity of 15 healthy adults was measured by use of a psychometric function (PFVA) and by use of a conventional method using a decimal visual acuity chart (DeVA). We performed two tests. To evaluate intra-rater reliability, a tester measured the visual acuity three times for each subject, and the intraclass correlation coefficients, ICC (1,1), were calculated for PFVA and DeVA. Next, to evaluate inter-rater reliability, three testers measured the visual acuity for one subject, and the ICC (2,1) were calculated for PFVA and DeVA. The PFVA and DeVA of five subjects with ocular diseases were also measured.

Results

In the evaluation of intra-rater reliability, the ICC (1,1) of the DeVA was 0.83 and the ICC (1,1) of the PFVA was 0.95. In the evaluation of inter-rater reliability, the ICC (2,1) of the DeVA was 0.88 and the ICC (2,1) of the PFVA was 0.93. In both tests the standard deviations of the PFVA were significantly lower than those of the DeVA. For four of the five subjects with ocular diseases, the PFVA was significantly improved by treatment.

Conclusion

The repeatability of our method is better than that of the conventional method using a decimal visual acuity chart.     

Laser-induced chorioretinal venous anastomosis using combined lasers with different wavelengths

AIM: To evaluate the effectiveness of combined lasers with different wavelengths in creating chorioretinal venous anastomosis (CRVA) in nonischaemic central retinal vein occlusion (CRVO). METHODS: In this retrospective, noncomparative, consecutive case series, records of all patients with a diagnosis of nonischaemic CRVO who underwent combined laser treatment to induce CRVA and who were followed-up for 6 months or longer were reviewed. RESULTS: Records of 85 patients (85 eyes) were analysed. These patients were divided into two groups. In group 1 (24 cases, 24 eyes), combined lasers with two different wavelengths (argon blue-green laser combined with Nd-YAG laser were used. In group 2 (61 cases, 61 eyes), combined lasers with three different wavelengths (argon blue-green laser combined with krypton red laser and Nd-YAG laser) were used. Functional anastomosis formed in 13 out of 24 eyes (54%) in group 1 and 47 out of 61 eyes (77%) in group 2. In patients with successful anastomosis, visual acuity improved for two or more lines in 49 out of 60 eyes (82%), with the remaining eyes undergoing no change. There were no serious complications. CONCLUSION: The use of three laser wavelengths results in the creation of laser anastomosis and the success rate may be higher than when using two wavelengths alone.     

不同波长的蓝光对人视网膜色素上皮细胞的影响

目的：探讨不同波长的蓝光对人视网膜色素上皮细胞(RPE)的影响。

方法：将体外培养的ARPE-19细胞随机分为对照组、447nm蓝光组、456nm蓝光组、468nm蓝光组,对照组细胞于常规条件下培养,蓝光组细胞使用光强为200Lx的OLED蓝光背光源照射72h,利用细胞活/死染色实验、CCK-8实验、Real-time PCR等方法比较不同波长的蓝光对细胞形态、细胞活性、增殖能力及视循环功能指标和炎症指标mRNA表达的影响。

结果：蓝光照射后,ARPE-19细胞的形态发生变化,细胞融合减少。蓝光波长越短,对细胞增殖抑制作用越明显,细胞内增殖标志物Ki-67 mRNA表达越少,视循环功能指标卵磷脂视黄醇酰基转移酶(LRAT)、视黄醛结合蛋白(CRALBP)、视黄醛脱氢酶(RDH)、光受体视黄醇类结合蛋白(IRBP)mRNA表达下调越明显,细胞内炎症因子单核细胞趋化因子(MCP-1)、白介素-6(IL-6)mRNA表达水平上调越明显。

结论：不同波长蓝光对RPE细胞均有损害作用,且蓝光波长越短,其损害作用越大。     

不同手术年龄间歇性外斜视术后双眼视功能的临床观察

目的:探讨不同手术年龄的间歇性外斜视患者术后双眼视功能的恢复情况。方法:选取2016-01/2018-01在我科住院行斜视矫正术的间歇性外斜视患者172例,其中男95例,女77例,年龄3~32岁(平均11.4±1.5)岁。间歇性外斜视患者均为基本型。根据手术年龄分为两组:≤9岁组(90例)和>9岁组(82例)。术前和术后1、7d,1、3mo,采用同视机检查双眼视功能,Titmus检查近立体视。结果:≤9岁组患者的同时视功能、融合功能、融合范围、远立体视、近立体视随术后时间的增长恢复效果优于>9岁组患者(P<0.05)。结论:间歇性外斜视患者建议在9岁前手术治疗,尽早手术有利于术后双眼视功能更好地改善。     

Psychometric视力表对弱视儿童视力的评估作用

目的评价Psychometric视力表在弱视儿童诊治中的应用价值．拥挤现象对正常视力儿童和弱视儿童的影响是否相同。方法我院门诊5～15岁儿童113人，男65人，女48人，平均年龄（7.42±2．03）岁，用标准对数视力表和包含拥挤现象的Psychometric视力表分别检查左右眼的两种视力，比较正常眼和弱视眼两种视力的差别。结果正常视力儿童和弱视儿童的两种视力差异都有显著性（P〈0．05）。对数视力比P视力高。弱视儿童的两种视力差别比正常儿童大。不同弱视类型之间视力差别不大．不同弱视程度之间两种视力有差别。结论儿童都受拥挤现象的影响，但是弱视儿童的拥挤现象更明显。拥挤现象影响程度与弱视程度有关。与弱视类型关系不大。Psychometric视力表适合弱视患者的视力检查。     

羊膜保存方法及其对羊膜活性影响的研究

目的观察不同保存方法及保存时间对羊膜活性的影响.方法取健康剖宫产产妇胎盘,剥离其羊膜,分成2.5×2.5cm2小块,随机分成四组,每组8块,按四种不同方法保存.保存1、3个月后分别取羊膜行光镜、电镜、酶组织化学[乳酸脱氢酶(LDH)、琥珀酸脱氢酶(SDH)]及免疫组织化学[碱性成纤维细胞生长因子(bFGF)]观察,并与新鲜羊膜对比.结果①光镜下,甘油4℃保存1、3个月羊膜上皮层结构破坏明显;DMEM甘油-70℃保存1、3个月羊膜组织结构基本完整;简化二、一步深低温保存1、3个月的羊膜上皮形态完好.②电镜下,甘油4℃保存1、3个月上皮细胞破坏明显;DMEM甘油-70℃保存1、3个月羊膜上皮细胞线粒体肿胀,部分细胞核染色质边集;简化二、一步深低温保存1、3个月部分线粒体肿胀.细胞核变化不明显.③甘油4℃、DMEM甘油-70℃保存法保存1、3个月羊膜上皮细胞SDH、LDH活性与对照组相比差别有极显著性(P＜0.001),保存3个月与保存1个月之间差别有极显著性(P＜0.001);简化二、一步深低温保存1、3个月的两种酶活性与对照组相比差异无显著性(P＞0.05).④bFGF分布于羊膜上皮和基质层.甘油4℃和DMEM甘油-70℃保存1、3个月bFGF在上皮层的表达与对照组相比差别有极显著性(P＜0.001),保存3个月与保存1个月之间差别有极显著性(P＜0.001).简化二、一步深低温保存1、3个月其表达与在新鲜羊膜中的表达无显著性差异(P＞0.05),这两种方法之间也无显著性差异(P＞0.05). 结论甘油4℃和DMEM甘油-70℃保存的羊膜活性下降,并随保存时间的延长活性明显下降.简化二、一步深低温保存的羊膜能长期保持活性.简化一步深低温保存法方法简便,更适用于羊膜的保存.