Visual function thresholds in children

PURPOSE: The aim of the present study was to establish a range of values for individual visual function measurements in Primary 1 schoolchildren. METHODS: 93 visually normal children with a mean age of 5.4 +/- 0.3 years were recruited with parental consent. Measures of visual acuity obtained included 1) High Contrast (CAT) 2) Low Contrast (LC) 3) Single Letter (SLA) and 4) Repeat Letter Acuity (RRL). These measurements were randomised and obtained during the same visit. Hyperacuity thresholds were obtained at a separate visit, using both Vernier and oscillatory motion displacement stimuli (OMDT). Re-test data for all tests was collected from a random sample of 30 children after a period of at least two weeks. RESULTS: For all measures the distribution of scores was found to be normal. All visual acuity scores are in log units. Mean ( +/- SD) values for each test were as follows; CAT = 0.11 +/- 0.07; LC = 0.38 +/- 0.08; RRL = 0.04 +/- 0.07; SLA = -0.02 +/- 0.09; Vernier threshold = 69 +/- 21 arcsec; OMDT = 60 +/- 9 arc sec. The confidence limits of the test-retest discrepancies were as follows; CAT = +/- 0.05; LC = +/- 0.07; RRL = +/- 0.04; SLA = +/- 0.04; Vernier = +/- 17 arcsec; OMDT = +/- 6 arcsec. The confidence limits of the interocular discrepancies were as follows; CAT = +/- 0.08; LC = +/- 0.08; RRL = +/- 0.08; SLA = +/- 0.11; Vernier = +/- 14 arcsec; OMDT = +/- 11 arcsec. CONCLUSIONS: To fully describe an individual's visual capacity it is important that new tests of visual function are developed based on emerging knowledge of visual physiology. In this study confidence limits can be constructed for each visual function measure, test-retest and interocular discrepancies using the normal distributions found above. This will provide the clinician with further age-matched values and contribute to our understanding of functional visual development.     

学龄前儿童视觉发育的研究进展

了解学龄前儿童视觉发育特点及视功能检查方法，及时发现患儿视功能障碍，掌握最佳治疗时机。视功能检测大体可分为两类：一种为心理物理方法，另一种为客观检查法。①学龄前儿童视力检测分为定性和定量检查或电生理方法[如视觉诱发电位（visual evoked potential，VEP）]等。②对立体视的检查方法有Titmus偏振光立体图、颜少明立体视脸查图及随机点立体图、计算机立体觉检测和视差诱发电位（disparity evoked potentials，DEP）检测法等。③分析综述国内外常见眼病如斜视、弱视的最新动向和研究现状。学龄前儿童视觉发育具有规律性和特殊性，采用适合于各年龄段视觉功能检测手段进行筛查和检查，才能真正落实早期发现和早期干预，提高儿童眼病的防治水平。     

Visual function in low birthweight children

AIM: To determine the visual functions, at age 10-12 years, of a geographically based cohort of children of birth weight less than 1701 g. The results were compared to a group of children born at full term. METHODS: 572 low birthweight (LBW) "low birthweight cohort" children who had been examined in the neonatal period were invited for review at 10-12 years of age. 169 11 year old schoolchildren born at full term were also recruited, "school cohort." Visual acuity (at distance and near), contrast sensitivity, colour vision, and visual fields were measured. RESULTS: 293 of the original 572 participants consented to a further examination. Compared to the school cohort of children born at term the low birthweight cohort showed significantly lower near and distance acuities and contrast sensitivity (p<0.001 for all uniocular and binocular measures). Retinopathy of prematurity (ROP) was a very poor predictor of outcome and multivariate analysis did not identify any key neonatal factors as predictors of long term visual outcome. CONCLUSIONS: Low birthweight children have a small but statistically significant deficit in both visual acuity and contrast sensitivity. Low birth weight and ROP both impact on long term visual functions.     

Visual deficits in anisometropia

Amblyopia is usually associated with the presence of anisometropia, strabismus or both early in life. We set out to explore quantitative relationships between the degree of anisometropia and the loss of visual function, and to examine how the presence of strabismus affects visual function in observers with anisometropia. We measured optotype acuity, Pelli-Robson contrast sensitivity and stereoacuity in 84 persons with anisometropia and compared their results with those of 27 persons with high bilateral refractive error (isoametropia) and 101 persons with both strabismus and anisometropia. All subjects participated in a large-scale study of amblyopia (McKee et al., 2003). We found no consistent visual abnormalities in the strong eye, and therefore report only on vision in the weaker, defined as the eye with lower acuity. LogMAR acuity falls off markedly with increasing anisometropia in non-strabismic anisometropes, while contrast sensitivity is much less affected. Acuity degrades rapidly with increases in both hyperopic and myopic anisometropia, but the risk of amblyopia is about twice as great in hyperopic than myopic anisometropes of comparable refractive imbalance. For a given degree of refractive imbalance, strabismic anisometropes perform considerably worse than anisometropes without strabismus - visual acuity for strabismics was on average 2.5 times worse than for non-strabismics with similar anisometropia. For observers with equal refractive error in the two eyes there is very little change in acuity or sensitivity with increasing (bilateral) refractive error except for one extreme individual (bilaterally refractive error of -15 D). Most pure anisometropes with interocular differences less than 4 D retain some stereopsis, and the degree is correlated with the acuity of the weak eye. We conclude that even modest interocular differences in refractive error can influence visual function.     

Visual function and visual perception in cerebral palsied children

PURPOSE: To investigate visual function and perception in cerebral palsied (CP) children. METHODS: A total of 105 congenitally CP children (aged 6-15 years), without severe mental retardation, were classified into three groups: those with spastic quadriplegia, spastic diplegia and spastic hemiplegia. Data collected included patient history, IQ, refraction, far and near visual acuity, position of the eyes and eye movements, visual fields, colour perception, stereoacuity, slit lamp and fundoscopic examinations, and evaluation of visual perception. The results were compared with a control group from the general paediatric population. RESULTS: The IQ of the CP children ranged between 70 and 100. A total of 59% of them had best corrected distance visual acuity <6/6, with 25.5% <6/9. Near visual acuity was also reduced (70.1% scored <6/6 and 38.4% scored <6/9). Incidence of refractive errors was higher than in the control group (hypermetropia in 43.8% of the eyes, myopia 16.19% and astigmatism 40.9%) as was the incidence of strabismus (26.7% esotropic and 27.6% exotropic). In visual field testing, 80.95% of CP children were normal. A total of 94.28% had normal colour perception and 89.52% were free of ocular pathology. Stereopsis was abnormal or absent in 85.71% of the cases. Visual perception was markedly reduced: in 57.14% of the cases it was less than or equal to that of 6-year-old children; in 26.66% equal to that of 6- to 7.5-year-old children, and in 16.2% of the cases greater than or equal to that of 7.5-year-old children. CONCLUSIONS: In the absence of severe mental retardation, CP children have deficient visual skills. It is suggested that the poor visual skills of CP children are a separate, identifiable factor compounding the adverse effects of mental retardation.     

Visual deficits in pre-readers at familial risk for dyslexia

Visual processing deficits in dyslexic readers are argued to evolve as a consequence of reading failure. This study examines dorsal stream functioning of children before they commence formal reading instruction to determine whether visual deficits precede reading difficulties. Coherent motion and visual frequency doubling detection were measured in children at familial risk for dyslexia and in children unselected for family reading history. Here we show that children who are at family risk for dyslexia demonstrate dorsal stream deficits before they learn to read, whilst demonstrating no corresponding deficits in coherent form and static grating control tasks. Results indicate that the dorsal visual deficits observed in dyslexic readers are unlikely to be the result of reading failure.     

Visual function in hypermetropia

Dark-adapted retinal function was tested electroretinographically and psychophsysically in patients with severe hypermetropia. These patients were first tested in 1982 and were classified into three electroretinographic categories subnormal, normal and supernormal, according to the amplitudes and the b-wave to a-wave relationships of their dark-adapted electroretinographic responses. These patients were invited for a follow-up examination to examine whether the subnormal electroretinogram represented a stationary or a progressive syndrome, to correlate functional vision to the electroretinographic findings and to determine the changes in refraction and electroretinographic responses that might have occurred during an 8-year period. No significant changes were seen in the amplitudes and b-wave to a-wave relationships of the electroretinographic responses. These observations supported the initial electroretinographic classification of the hypermetropic patients and indicated that the patients belonging to the subnormal group were probably characterized by a stationary defect. The psychophysically determined thresholds at different retinal loci (from 30° nasal to 40° temporal) were within the normal range for all the patients regardless of their electroretinographic characteristics. Thus, the abnormal electroretinographic responses of hypermetropic patients probably did not reflect abnormal retinal function but may be accounted for by changes in the electrical resistances of extraretinal tissues relative to that of the retina itself.     

盲/低视力儿童视力康复和阅读功能研究

目的：观察盲校及低视力门诊的15周岁以下患者，用低视力助视器对其视力特别是阅读功能进行康复和评估。方法：总共有55位来自盲校和低视力门诊的儿童，其好眼的最佳远矫正视力都低于4．5，进行低视力助视器的验配和训练，然后进行望远镜助视器视觉评价、近用助视器视觉评价和在配戴近用助视器的基础上，对患儿的阅读功能进行评怙。结果：戴远用助视器前后盲童的脱盲率为33、3％，戴运用助视器前后低视力患儿的脱残率为87．1％。戴低视力助视器前后患儿阅读四号字的速度差异有显著性(t=5．238；P=0.001)；戴低视力助视器前后患儿阅读小五号字的速度差异有显著性(t=4．818；P=0．008)。结论：低视力助视器对盲／低视力患儿视觉康复有效，不仅可有效地改善视力，而且可提高阅读速度，对患儿进一步接受教育极其重要。     

Visual function in Vogt-Koyanagi-Harada patients

Background Vogt-Koyanagi-Harada (VKH) disease presents with anterior segment inflammation, choroiditis and exudative retinal detachment. Following resolution of the inflammation, VKH patients have been noted to complain of visual disturbances despite good visual acuity. We therefore investigated the visual function deficits of convalescent VKH patients.Methods A cross-sectional observational nonrandomized controlled study of convalescent VKH patients from the Uveitis Service of the Singapore National Eye Centre, and normal subjects was performed. The best-corrected visual acuities (BCVA) and multifocal electroretinograms (mfERGs) of VKH patients with and without peripapillary atrophy (PPA) were compared with those of the normal eyes. The mfERG results were subdivided into those obtained from the peripapillary area and those from the rest of the macular.Results Eleven VKH eyes with large PPA to disc ratios (PPA/D ratio >2), 15 VKH eyes with PPA/D ratios<1 and 6 normal eyes were included in the study. Five eyes (54.5%) of VKH patients with PPA/D>2 had a BCVA of less than 20/40. All the other eyes had 20/20 vision. Nine of the 11 VKH eyes with PPA/D>2 also had large areas of chorioretinal atrophy.The mfERG responses of VKH eyes with PPA/D ratio >2 were markedly reduced in amplitude (p<0.001) and delayed in implicit time (p<0.001) throughout the entire macular area. VKH patients with PPA/D ratio<1 had significantly reduced mfERG amplitudes throughout the entire macular area, as well as delayed implicit times at the peripapillary region (p=0.026). Sub-division of VKH eyes with PPA/D<1 into eyes with no PPA and eyes with a small PPA, showed that both groups had a similar reduction in response amplitude over the entire macular region. However, the implicit time was significantly delayed in eyes with small PPA when compared to those without PPA (p<0.03).Conclusions VKH patients with large PPA have clinically significant visual dysfunction. VKH patients without PPA also have subclinical retinal dysfunction. The mfERG may be a useful adjunct in the management of VKH by detecting early retinal damage.The authors have no financial relationship with the Singapore Eye Research Institute that has sponsored the research, and have full control of all primary data and agree to allow Graefes Archives for Clinical and Experimental Ophthalmology to review our data if requested.     

Visual function in retinitis pigmentosa

This report describes diagnostic findings in a classic case of retinitis pigmentosa. The status of central vision is considered in particular detail.     

Visual deficits in amblyopia constrain normal models of second-order motion processing

It is well established that amblyopes exhibit deficits in processing first-order (luminance-defined) patterns. This is readily manifest by measuring spatiotemporal sensitivity (i.e. the “window of visibility”) to moving luminance gratings. However the window of visibility to moving second-order (texture-defined) patterns has not been systematically studied in amblyopia. To address this issue monocular modulation sensitivity (1/threshold) to first-order motion and four different varieties of second-order motion (modulations of either the contrast, flicker, size or orientation of visual noise) was measured over a five-octave range of spatial and temporal frequencies. Compared to normals amblyopes are not only impaired in the processing of first-order motion, but overall they exhibit both higher thresholds and a much narrower window of visibility to second-order images. However amblyopia can differentially impair the perception of some types of second-order motion much more than others and crucially the precise pattern of deficits varies markedly between individuals (even for those with the same conventional visual acuity measures). For the most severely impaired amblyopes certain second-order (texture) cues to movement in the environment are effectively invisible. These results place important constraints on the possible architecture of models of second-order motion perception in human vision.     

Visual fixation development in children

Background The ability to keep steady fixation on a target is one of several aspects of good visual function. However, there are few reports on visual fixation during childhood in healthy children. Methods An infrared eye-tracking device (Orbit) was used to analyse binocular fixation behaviour in 135 non-clinical participants aged 4–15 years. The children wore goggles and their heads were restrained using a chin and forehead rest, while binocularly fixating a stationary target for 20 s. Results The density of fixations around the centre of gravity increased with increasing age (p < 0.01), and the time of fixation without intruding movements increased with increasing age (p = 0.02), while intruding saccades decreased with increasing age (p < 0.01). The number of blinks and drifts did not differ between 4 and 15 years, and there were no significant differences with regard to gender or laterality in any of the investigated variables. No nystagmus was observed. Conclusion This study establishes values for visual fixation behaviour in a non-clinical population aged 4–15 years, which can be used for identifying children with fixation abnormalities.     

Visual conversion reaction in children

Visual conversion reaction (VCR) is a psychosomatic illness that will occasionally be seen by optometrists and ophthalmologists. This paper discusses some of the possible aetiologies and manifestations of the condition. Investigation and management of children with suspected VCR is discussed. Four case histories are presented in which signs of VCR included amblyopia, reduced accommodation and a deterioration in handwriting. The visual field defects presented include a static quantitative anomaly. Such a defect has not previously been reported.