In layer 4 of cat visual cortex, the monocular, concentric receptive fields of thalamic neurons, which relay retinal input to the cortex, are transformed into 'simple' cortical receptive fields that are binocular and selective for the precise orientation, direction of motion, and size of the visual stimulus. These properties are thought to arise from the pattern of connections from thalamic neurons, although anatomical studies show that most excitatory inputs to layer 4 simple cells are from recurrently connected circuits of cortical neurons. We examined single fibre inputs to spiny stellate neurons. We examined single fibre inputs to spiny stellate neurons in slices of cat visual cortex, and conclude that thalamocortical synapses are powerful and the responses they evoke are unusually invariant for central synapses. However, the responses to intracortical inputs, although less invariant, are strong enough to provide most of the excitation to simple cells in vivo. Our results suggest that the recurrent excitatory circuits of cortex may amplify the initial feedforward thalamic signal, subserving dynamic modifications of the functional properties of cortical neurons.

A straightforward argument is presented to calculate the number of different major histocompatibility complex (MHIC) molecules in an individual that maximizs the probability of mounting immune responses against a large number of foreign peptides. It is assumed that increasing the number of MHC molecules per individual, n, has three differ-

Objective To determine the age- and race-specific prevalence of amblyopia in Asian and non-Hispanic white children aged 30 to 72 months and of strabismus in children aged 6 to 72 months. Design Cross-sectional survey. Participants A population-based, multiethnic sample of children aged 6 to 72 months was identified in Los Angeles and Riverside counties in California to evaluate the prevalence of ocular conditions. Methods A comprehensive eye examination and in-clinic interview were conducted with 80% of eligible children. The examination included evaluation of ocular alignment, refractive error, and ocular structures in children aged 6 to 72 months, as well as a determination of optotype visual acuity (VA) in children aged 30 to 72 months. Main Outcome Measures The proportion of 6- to 72-month-old participants with strabismus and 30- to 72-month-olds with optotype VA deficits and amblyopia risk factors consistent with study definitions of amblyopia. Results Strabismus was found in 3.55% (95% confidence interval [CI], 2.68–4.60) of Asian children and 3.24% (95% CI, 2.40–4.26) of non-Hispanic white children, with a higher prevalence with each subsequent older age category from 6 to 72 months in both racial/ethnic groups (P=0.0003 and 0.02, respectively). Amblyopia was detected in 1.81% (95% CI, 1.06–2.89) of Asian and non-Hispanic white children; the prevalence of amblyopia was higher for each subsequent older age category among non-Hispanic white children (P=0.01) but showed no significant trend among Asian children (P=0.30). Conclusions The prevalence of strabismus was similar in Asian and non-Hispanic white children and was found to be higher among older children from 6 to 72 months. The prevalence of amblyopia was the same in Asian and non-Hispanic white children; prevalence seemed to be higher among older non-Hispanic white children but was relatively stable by age in Asian children. These findings may help clinicians to better understand the patterns of strabismus and amblyopia and potentially inform planning for preschool vision screening programs.

Purpose To determine the age-, gender- and ethnicity-specific prevalence of myopia, hyperopia and astigmatism in Non-Hispanic White (NHW) and Asian preschool children. Design Population-based cross-sectional study. Participants A population based sample of 1501 NHW children and 1507 Asian children aged 6-72 months from Los Angeles County and Riverside County, California. Methods Eligible children underwent an in-home and in-clinic interview and a comprehensive eye examination including cycloplegic auto-refraction from 100 census tracts. Main outcome measures The proportion of children with myopia (spherical equivalent (SE) <=−1.00 diopter (D)), hyperopia (SE >=+2.00) D and cylindrical refractive error >=1.50 D in the worse eye. The astigmatism type was defined as with-the-rule (WTR) (+cylinder axis 90° ± 15°) and against-the-rule (ATR) (+ cylinder axis 180° ± 15°); all other orientations were considered oblique (OBL). Results The prevalence of myopia, hyperopia and astigmatism in NHW children was 1.20% (95% Confidence Interval (CI) = 0.76-1.89%), 25.65% (95% CI= 23.5-27.9%), and 6.33% (95% CI = 5.21-7.68%), respectively. The prevalence of WTR, ATR and OBL astigmatism in NHW children was 4.33%, 1.00% and 1.00% respectively. Prevalence was lower with older age groups for astigmatism (p=0.0002), but not for myopia or hyperopia (p=0.82 and p=0.31, respectively). In Asian children, the prevalence of myopia, hyperopia and astigmatism was 3.98% (95% CI = 3.11-5.09%), 13.47% (95% CI= 11.8-15.3%) and 8.29% (95% CI=7.01-9.80%), respectively. The prevalence of WTR, ATR and OBL astigmatism was 6.50%, 0.80% and 1.00% respectively. The prevalence of hyperopia was higher in girls than boys (p=0.0002), but no significant differences were found for myopia and astigmatism. Conclusion Hyperopia was the most common refractive error in both Asian and NHW children. However, compared to NHW children, myopia was relatively more prevalent, and hyperopia less prevalent, in Asian children. The prevalence of astigmatism was highest in infants, and WTR astigmatism predominated at all ages. Myopia showed relatively stable prevalence across age groups, while hyperopia prevalence decreased after infancy and then increased again in older age groups; however, longitudinal studies are needed to evaluate refractive changes over time in individual children.

Purpose To provide population-based normative data for monocular visual acuity (VA) and interocular differences in VA (IOD), in African-American and Hispanic children 30–72 months of age without visually significant refractive errors or ophthalmic abnormalities. Methods In a population-based cohort of children in the Multi-Ethnic Pediatric Eye Disease Study, monocular HOTV VA measurements using the Amblyopia Treatment Study protocol were analyzed using continuous and dichotomous outcomes for VA and IOD, after excluding subjects with ophthalmic abnormalities or refractive error. Results The analysis cohort consisted of 1722 African-American and Hispanic children aged 30 to 72 months. Mean logMAR VA improved with age (P<0.0001) and male gender (p=0.0008). The proportion of children achieving VA 20/40 or better was associated with age (p<0.0001), but not ethnicity or gender, and was 81%, 94%, 99% and virtually 100% in children aged 30–35, 36–47, 48–59, and 60–72 months of age, respectively. The most stringent VA threshold that excluded <5% of normal children was 20/63, 20/50, 20/32, and 20/32 for children aged 30–35, 36–47, 48–59, and 60–72 months, respectively. Children attending preschool or daycare achieved VA 20/32 more often than those not attending, after age adjustment (P=0.01), as did children from higher-income families (p=0.04). There was no association between mean absolute IOD and age (P=0.45), ethnicity (P=0.12), or gender (P=0.19). The proportion of children achieving an IOD of 0–1 lines was higher in males than females (P=0.02); it did not vary by age (P=0.06) or ethnicity (P=0.17). IOD of two or more lines occurred in 6% of normal children. Conclusions Visual acuity test performance in normal preschool children improves with age. We propose new age-specific thresholds for defining abnormal monocular VA using HOTV optotypes in children between 2 and 5 years of age, for use in screening, clinical practice and research.

Recordings were made from pairs of neurons in cat striate visual cortex in vitro to study the AMPA-channel-mediated components of intracortical excitatory synaptic connections between layer 4 spiny neurons and between layer 6 and layer 4 spiny neurons. Forty-six of the 72 cells recorded were identified morphologically. They consisted of spiny stellate and pyramidal cells in layer 4, and pyramidal cells in layer 6. Connections between layer 4 excitatory cells involve excitatory postsynaptic potentials (EPSPs) averaging 949 microV, with an average coefficient of variation of 0.21 (n = 30). The synapses operate at very high release probabilities (0.69-0.98). With repetitive stimulation these EPSPs show varying degrees of depression, largely mediated by presynaptic changes in release probability. Four pairs of layer 4 cells were reciprocally connected. The connections from layer 6 to layer 4 involve smaller, more variable EPSPs, with an average amplitude of 214 microV, and average coefficient of variation 0.72 (n = 7). These synapses operate at moderately high release probabilities (0.37-0.56). They show facilitation with repetitive stimulation, mediated largely by presynaptic changes in release probability. One excitatory connection from a layer 4 neuron to a layer 6 pyramidal cell was also detected. Thus, layer 4 spiny neurons receive effective excitation from two intracortical sources that have different synaptic dynamics and are likely to contribute significantly to the temporal properties of these cells in vivo.

Objective To investigate risk factors associated with esotropia or exotropia in infants and young children. Design Population-based cross-sectional prevalence study. Participants Population-based samples of 9970 children ages 6 to 72 months from California and Maryland. Methods Participants were preschool African-American, Hispanic, and non-Hispanic white children participating in the Multiethnic Pediatric Eye Disease Study and the Baltimore Eye Disease Study. Data were obtained by parental interview and ocular examination. Odd ratios and 95% confidence intervals were calculated to evaluate the association of demographic, behavioral, and clinical risk factors with esotropia and exotropia. Main Outcome Measures Odds ratios (ORs) for various risk factors associated with esotropia or exotropia diagnosis based on cover testing. Results In multivariate logistic regression analysis, esotropia was independently associated with prematurity, maternal smoking during pregnancy, older preschool age (48–72 months), anisometropia, and hyperopia. There was a severity-dependent association of hyperopia with the prevalence of esotropia, with ORs increasing from 6.4 for 2.00 Diopters (D) to <3.00 D of hyperopia, to 122.0 for ≥ 5.00 D. Exotropia was associated with prematurity, maternal smoking during pregnancy, family history of strabismus, female sex, astigmatism (OR 2.5 for 1.50 to <2.50 D, and 5.9 for ≥ 2.5 D of astigmatism), and aniso-astigmatism in the J0 component (OR ≥ 2 for J0 aniso-astigmatism ≥ 0.25 D). Conclusions Prematurity and maternal smoking during pregnancy are associated with a higher risk of having esotropia and exotropia. Refractive error is associated in a severity-dependent manner to the prevalence of esotropia and exotropia. Because refractive error is correctable, these risk associations should be considered when developing guidelines for the screening and management of refractive error in infants and young children children.

The objectives of the MEPEDS are to: (1) estimate age- and ethnicity-specific prevalence of strabismus, amblyopia, and refractive error; (2) evaluate the association of selected risk factors with these ocular disorders; and (3) evaluate the association of ocular conditions on limitations in health-related functional status in a population-based sample of 12,000 children aged 6-72 months from four ethnic groups--African-American, Asian-American, Hispanics/Latinos and non-Hispanic White. Each eligible child undergoes an eye examination, which includes an interview with his/her parent. The interview includes an assessment of demographic, behavioral, biological, and ocular risk factors and health-related functional status. The examination includes fixation preference testing, visual acuity, stereoacuity, axial length measurement, cycloplegic refraction, keratometry, eye alignment, and anterior and posterior segment examination.