Effect of onset age of strabismus on the binocular responses of neurons in the monkey visual cortex.

PURPOSE: By 6 weeks of age, neurons in the monkey's primary visual cortex acquire qualitatively adult-like binocular response properties and behaviorally stereopsis emerges. In this study, it was determined whether the onset of strabismus has a more severe impact on cortical binocularity before or after this critical developmental age. METHODS: Infant monkeys were fit with a light-weight helmet which held a total of 27 diopters of base-in prisms in front of their two eyes for a fixed period of two weeks. For one group of infant monkeys, prism-rearing began at 2 weeks of age and for a second group, the onset was at 6 weeks of age. Immediately after the rearing period, i.e., at 4 weeks and 8 weeks of age, respectively, extracellular single-unit recording methods were used to determine the nature and severity of alterations in the binocular response properties of V1 neurons. Dichoptic sinewave gratings were used as visual stimuli. RESULTS: In comparison to normal age-matched infants, V1 neurons in both strabismic groups exhibited reductions in sensitivity to interocular spatial phase disparities (disparity sensitivity) and a higher prevalence of binocular inhibitory interactions (binocular suppression). However, the reduction in disparity sensitivity and the magnitude of binocular suppression were much greater in the late (6-8 weeks) than the early (2- 4 weeks) onset group. CONCLUSIONS: Discordant binocular signals due to brief periods of early strabismus have more serious effects on the development of binocular properties of V1 neurons if they occur shortly after rather than before the emergence of stereopsis (i.e., when the binocular connections are relatively more mature but the visual cortex still shows a high degree of plasticity).

Nasotemporal directional bias of V1 neurons in young infant monkeys.

PURPOSE: Optokinetic nystagmus (OKN) in young infants typically shows a temporal-to-nasal asymmetry under monocular viewing conditions. The neural basis for this asymmetry has been a matter of debate. One idea is that the OKN asymmetry reflects a similar asymmetry in the directional sensitivity of primary visual cortical (V1) neurons. An alternative hypothesis is that the OKN asymmetry is due to an immaturity in the ability of cortical neurons to influence the activity of subcortical structures that directly control OKN. We addressed this issue by studying the directional sensitivity of V1 neurons in young infant monkeys. METHODS: The neuronal activity of V1 units was recorded from anesthetized and paralyzed rhesus monkeys ranging in age from 6 days to 8 weeks using standard extracellular single-unit recording methods. For comparison, V1 units from normal adult monkeys were also studied. Using drifting sinusoidal gratings of the optimal spatial frequency and a moderate contrast, we measured the responsiveness of individual units to 24 directions of stimulus movement. The preferred stimulus direction and the magnitude of the directional response bias were determined by a vector summation method. RESULTS: No clear signs of nasotemporal asymmetries in direction tuning were found in our cell population from infant monkeys. However, the overall directional sensitivity and the peak monocular response amplitudes of these units were significantly lower, and binocular suppression was greater during the first 4 weeks of life than in adults. CONCLUSIONS: The OKN asymmetry in young infants may be more closely associated with the lower overall directional sensitivity and the subnormal responsiveness of V1 neurons rather than with an obvious asymmetry in the directional properties of V1 neurons.

Cataract in atomic bomb survivors.

PURPOSE: Ophthalmologic examinations were conducted on atomic bomb (A-bomb) survivors 55 years after exposure. MATERIALS AND METHODS: A-bomb survivors who had been exposed before 13 years of age at the time of the bombings in 1945 or who had been examined in a previous study between 1978 and 1980. The examinations, conducted between June 2000 and September 2002, included slit-lamp examination, digital photography and a cataract grading system for three parts of the lens (nucleus, cortex and posterior subcapsule) as an outcome variable. Proportional odds logistic regression analysis was conducted using the lowest grading class as a reference and included explanatory variables such as age, sex, city, dose and various cataract-related risk factors. When the grades in an individual differed, the worst grade was used. RESULTS: Results indicate that odds ratios (ORs) at 1 Sv were 1.07 (95% confidence intervals [CI] 0.90, 1.27) in nuclear colour, 1.12 (95% CI 0.94, 1.30) in nuclear cataract, 1.29 (95% CI 1.12, 1.49) in cortical cataract and 1.41 (95% CI 1.21, 1.64) in posterior subcapsular cataract. The same was true after excluding 13 people whose posterior subcapsular cataracts had been previously detected. CONCLUSION: Significant radiation effects were observed in two types of cataracts in A-bomb survivors.

Histopathological study of microspherophakia in the Weill-Marchesani syndrome.

A surgically obtained lens from a 66-year-old man with the Weill-Marchesani syndrome was examined histopathologically by light microscopy, transmission electron microscopy and scanning electron microscopy. The lens was diffusely opaque and brown. It was microspherophakic in appearance, 6.0 mm in equatorial diameter and 4.8 mm in anteroposterior diameter. The lens fibers were well preserved, and ran circularly in the cortex and elliptically in the fetal nucleus. The lens fibers had undergone hyaloid degeneration in the area from the deep cortex to the superficial portion of the adult nucleus. Hyaloid degeneration also extended from the anterior to the posterior pole and was more marked in the equator. The distribution of lens fibers suggested that microspherophakia had developed postnatally. It is surmised that later changes in the shape of the lens affected the lens fibers, inducing hyaloid degeneration.

Expression of stress-response protein 60 in iritis associated with experimental autoimmune encephalomyelitis.

PURPOSE: To study the expression of stress-response proteins in the inflamed iris of rats with experimental autoimmune encephalomyelitis (EAE). METHODS: EAE was induced in Lewis rats by immunization with homogenized spinal cord of the guinea pig emulsified in complete Freund's adjuvant (CFA) (group EAE). Control rats included those immunized with only CFA (group CFA) and those that were untreated (group Normal). Immunohistochemical study for the localization of stress-response protein (srp) 27, srp 60, srp 72, ubiquitin, and alphaB-crystallin was performed. RESULTS: All rats in group EAE developed iritis, whereas none of the rats in group CFA and group Normal developed iritis. No expression of ubiquitin, alphaB-crystallin, srp 27, srp 60, or srp 72 was seen in the epithelium of the iris in group CFA rats. In the eyes of rats in group EAE, srp 60 was expressed in the epithelium of the iris in 20 of 22 (90.9%), ubiquitin in 4 of 22 (18.2%), and alphaB-crystallin in 3 of 22 (13.6%). In the group Normal rats, only ubiquitin was expressed in the epithelium of the iris in 1 of 6 (16.7%) eyes examined. CONCLUSIONS: These results suggest that srp 60 may be a potential uveitogenic antigen in the iris in EAE.

[Expression of the stress-response protein 60 in iritis in experimental autoimmune encephalomyelitis--an immunohistochemical study].

Uveitis of unknown etiology is known to occur in association with various systemic disorders. We did an immunohistochemical study on the expression of stress-response proteins (srp's) in iritis associated with experimental autoimmune encephalomyelitis (EAE), which is regarded as a model of multiple sclerosis. EAE was induced in Lewis rats by sensitization with homogenized spinal cord of guinea pig in complete Freund's adjuvant (CFA) (Group EAE). For controls, we used rats sensitized with CFA only (Group CFA) and untreated rats (normal controls). All rats developed iritis in Group EAE. In Group CFA, no rats developed iritis. No expression of ubiquitin, alpha B-crystallin, srp 27, srp 60, or srp 72 was seen in the epithelium of the iris of the rats in Group CFA. In the rats in Group EAE, srp 60 was expressed in the epithelium of the iris in 20/22 (90.9%) of the eyes examined, ubiquitin in 4/22 (18.2%), and alpha B-crystallin in 3/22 (13.6%). In the untreated rats, only ubiquitin was expressed in the epithelium of the iris in 1/6 (16.7%) of the eyes examined. These results suggest that srp 60, 60 kDa srp, plays an important role in the occurrence of iritis associated with EAE.