Scale-invariant superiority of foveal vision in perceptual categorization

The recognition of objects is exceedingly difficult in indirect view. This complication cannot be explained in terms of retino-cortical magnification, as size scaling fails to establish position invariance both for character recognition [Strasburger, H. & Rentschler, I. (1996) Eur. J. Neurosci., 8 1787-1791] and pattern classification [Jüttner, M. & Rentschler, I. (1996) Vision Res., 36, 1007-1021]. Thus we compared, for two tasks of discrimination learning and category learning with respect to a common set of grey-level patterns, how humans perform in foveal and extrafoveal vision. Observers learnt to discriminate (size-scaled) images equally well in foveal and extrafoveal view, whereas they displayed profound deficiencies in extrafoveal category learning for the same patterns. From the behavioural learning data, internal representations of the learning signals were reconstructed by means of computer simulations. For foveal view, these representations were found to be veridical to their physical counterparts for both learning tasks. For extrafoveal view, they were severely distorted for category learning but not for discrimination learning. A variance reduction of the pattern classes by a factor of 100 reduced the dissociation between extrafoveal categorization and discrimination but did not remove it. These observations suggest a scale-invariant superiority of foveal vision for learning object categories. This implies a high degree of space variance of visual cognition which is vastly underestimated by classical measures of visual performance, e.g. acuity, visual field and contrast sensitivity.     

Comparison of computer-photoscreening with non-cycloplegic retinoscopy for amblyopiogenic risk factors in children

Objective To determine the sensitivity and specificity of using a computer-photoscreene r and non-cycloplegic retinoscopy in the detection of amblyopiogenic factors in nine to fifty months old infants and children.
Methods Three hundred children, nine to fifty months old, were screened with the compute r-photoscreener and non-cycloplegic retinoscopy.With a blinded standardized clinical assessment as the standard, an overall comparison of the sensitivity of and specificity results obtained with the two techniques was made.Photoscree n images on the computer monitor screen were reviewed and analyzed immediately by two independent observers for indicators of amblyopiogenic risk factors.Simu ltaneously, the results were compared to the findings of a full ophthalmologic examination.
Results The computer-photoscreener revealed a sensitivity of 94.6% and specificity of 90.1%, and the non-cycloplegic retinocopy revealed a sensitivity of 85.7% and specificity of 81.0% for the detection of amblyopiogenic risk factors, includi ng hyperopia (+2.75 D or more), myopia (-1.50 D or more), astigmatism (1. 75 D or more), anisometropia (2.00 D or more), ocular misalignment (5 degrees o r more), and media opacity (1.5 mm or more).
Conclusions The computer-photoscreener offers an opportunity to identify problems that limi t vision, and could provide a feasible and sufficiently reliable screening techn ique in infants and preschool children to be screened successfully for amblyopio genic risk factors.      

Diagnosing protan heterozygosity using the Medmont C‐100 colour vision test

Background : A surprisingly high 15 per cent of women in Caucasian societies are carriers of the genes for abnormal colour vision but there is no clinical method to identify them. It has long been known that heterozygotes for the protan colour vision deficiencies can demonstrate a reduced luminous sensitivity to red light. This is known as Schmidt's sign, which is thought to arise from mosaicism (Lyonisation). The Medmont C‐100 colour vision test measures relative spectral sensitivity using flicker photometry to differentiate protans and deutans. It should be able to diagnose Schmidt's sign. Method : We tested six known protan heterozygotes (four whose sons have a protan colour vision deficiency and two whose fathers are protan) with the Medmont C‐100 test. Results : All six heterozygotes made average settings of ‐1.75 or more negative at the Medmont C‐100 test, settings which are at or beyond the boundary of the distribution of settings made by observers with normal colour vision. There have been two previous cases reported in the literature of protan heterozygotes, who made protan settings on the Medmont C‐100 or its predecessor test, the OSCAR. We also tested six daughters of the known heterozygotes, 50 per cent of whom are likely to be heterozygotes. Four of the six (66 per cent) made protan settings on the Medmont C‐100. The other two made normal 0.0 settings. Conclusion : We conclude that the Medmont C‐100 can be used clinically to diagnose carriers of protan colour vision deficiency.     

双眼白内障摘除术后双眼视觉的测定

目的：了解双眼行白内障人工晶状体植入术后患者的双眼视功能恢复情况并探讨影响其恢复的因素。方法：对80例(160只眼)老年性白内障患者双眼均采用Phaco或小切口ECCE后房型人工晶状体植入术。术后检查矫正视力、同时视觉、融合功能及远、近距离立体视功能以及视网膜对应情况。结果：术后患者双眼矫正视力均≥0．3，其中矫正视力均≥0．5者76例(95％)，矫正视力均≥0．9者60例(75％)。术后均有同时视功能及一定的融合功能。近距离立体视检查：中心凹立体视(40″～60″)32例(占40％)，黄斑部立体视(80″-200″)30例(占37．5％)，周边部立体视(400″～800″)15例(占18．8％)，无立体视者3例(占3．7％)。远距离立体视中：中心凹立体视者65例(81．3％)，黄斑部立体视者12例(占15％)，周边部立体视者3例(占3．7％)。术后视网膜对应均正常。结论：双眼白内障摘除人工晶状体植入手术且双眼矫正视力均≥0．5者，均可较快地恢复一定程度的双眼视功能。     

School vision screening, ages 5–16 years: the evidence-base for content, provision and efficacy

The optometric profession in the UK has a major role in the detection, assessment and management of ocular anomalies in children between 5 and 16 years of age. The role complements a variety of associated screening services provided across several health care sectors. The review examines the evidence-base for the content, provision and efficacy of these screening services in terms of the prevalence of anomalies such as refractive error, amblyopia, binocular vision and colour vision and considers the consequences of their curtailment. Vision screening must focus on pre-school children if the aim of the screening is to detect and treat conditions that may lead to amblyopia, whereas if the aim is to detect and correct significant refractive errors (not likely to lead to amblyopia) then it would be expedient for the optometric profession to act as the major provider of refractive (and colour vision) screening at 5-6 years of age. Myopia is the refractive error most likely to develop during primary school presenting typically between 8 and 12 years of age, thus screening at entry to secondary school is warranted. Given the inevitable restriction on resources for health care, establishing screening at 5 and 11 years of age, with exclusion of any subsequent screening, is the preferred option.     

HGS-Dreiding分子模型在天然药物化学教学中的应用

介绍了HGS-Dreiding分子模型盒中的组成部件 ,以及使用该分子模型在解决某些天然药物立体化学教学中的使用价值 ,并就使用该分子模型对天然药物化学教材中紫乌定和葡萄糖的结构进行了深入的阐述     

Assessment of optic nerve and optic tract alterations in patients with orbital space-occupying lesions using probabilistic diffusion tractography

AIM: To investigate the diffusion changes in both the optic nerve and optic tract in orbital space-occupying lesion patients with decreased visual acuity, and its clinical significance using probabilistic diffusion tractography (PDT). METHODS: Twenty patients with orbital space-occupying lesions and 25 age- and gender-matched healthy persons were included. All patients and controls underwent routine orbital magnetic resonance imaging and diffusion tensor imaging (DTI), using a 3.0T magnetic resonance scanner (Trio Tim Siemens). After the image data were preprocessed, each DTI parameters of the optic nerve and optic tract was obtained by PDT, including fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD) and radial diffusivity (RD). The asymmetry index (AI) of each parameter was calculated. Compared the parameters of the affected side optic nerve and ipsilateral optic tract with the contralateral side by paired sample t-test; compared AI of parameters of optic nerve and optic tract between the patient group and the control group by independent sample t-test. Patients were divided into three subgroups according to the low vision grade standard of WHO, compared the FA and AI of FA between the three subgroups by single factor variance analysis. RESULTS: The affected side optic nerve presented significantly decreased FA, increased MD, AD, and RD values compared to the unaffected side (P<0.05). The AI of FA, MD, AD, and RD of optic nerve in the patients was significantly higher than that of the controls (P<0.05). The comparison results of the optic tract showed that there was no significant difference between the patient group and control group in terms of the bilateral optic tracts in patients (P>0.05). The AIs of the FA value of the optic nerve in the eyesight <0.1 subgroup was significantly higher than that in the other groups (P<0.05). CONCLUSION: FA, MD, AD, and RD of the affected side optic nerve of the orbital space-occupying lesions have significantly changed, the FA value is the most sensitive. The PDT could be a useful tool to provide valid quantitative markers of optic nerve injuries and evaluate the severity of orbital diseases, which other examinations cannot be acquired.     

Clinical Practice Guidelines on the Internet

Abstract

Access to quality information on the Internet for health care situations can be problematic. Currently there is a tremendous wealth of practice guidelines available over the Internet. The Institute of Medicine defines practice guidelines as systematically developed statements to assist practitioner and patient decisions about appropriate health care for specific clinical circumstances. This article discusses the role of practice guidelines in health care decision making, and highlights some of the practice guidelines that are available over the Internet.