Biomedical subjects

Barbara M Junghans

Publications and source records attributed to Barbara M Junghans.

5 recordsLinked to original sources

PubMed2006

Ionic control of ocular growth and refractive change.

The physiological mechanisms underlying the abnormal vitreal and ocular growth and myopic refractive errors induced under conditions of visual form deprivation in many animal species, including humans, are unknown. This study demonstrates, using energy dispersive x-ray microanalysis, a systematic pattern of changes in the elemental distribution of K, Na, and Cl across the entire retina in experimental form deprivation myopia and in the 5 days required for refractive normalization after occluder removal. In our report we link the ionic environment associated with physiological activity of the retina under a translucent occluder to refractive change and describe large but reversible environmentally driven increases in potassium, sodium, and chloride abundances in the neural retina. Our results are consistent with the notion of ionically driven fluid movements as the vector underlying the myopic increase in ocular size. New treatments for myopia, which currently affects nearly half of the human population, may result.

Animals↗

PubMed2005

Little evidence for an epidemic of myopia in Australian primary school children over the last 30 years.

BACKGROUND: Recently reported prevalences of myopia in primary school children vary greatly in different regions of the world. This study aimed to estimate the prevalence of refractive errors in an unselected urban population of young primary school children in eastern Sydney, Australia, between 1998 and 2004, for comparison with our previously published data gathered using the same protocols and other Australian studies over the last 30 years. METHODS: Right eye refractive data from non-cycloplegic retinoscopy was analysed for 1,936 children aged 4 to 12 years who underwent a full eye examination whilst on a vision science excursion to the Vision Education Centre Clinic at the University of New South Wales. Myopia was defined as spherical equivalents equal to or less than -0.50 D, and hyperopia as spherical equivalents greater than +0.50 D. RESULTS: The mean spherical equivalent decreased significantly (p < 0.0001) with age from +0.73 +/- 0.1D (SE) at age 4 to +0.21 +/- 0.11D at age 12 years. The proportion of children across all ages with myopia of -0.50D or more was 8.4%, ranging from 2.3% of 4 year olds to 14.7% of 12 year olds. Hyperopia greater than +0.50D was present in 38.4%. A 3-way ANOVA for cohort, age and gender of both the current and our previous data showed a significant main effect for age (p < 0.0001) but not for cohort (p = 0.134) or gender (p = 0.61). CONCLUSIONS: Comparison of our new data with our early 1990s data and that from studies of over 8,000 Australian non-clinical rural and urban children in the 1970's and 1980's provided no evidence for the rapidly increasing prevalence of myopia described elsewhere in the world. In fact, the prevalence of myopia in Australian children continues to be significantly lower than that reported in Asia and North America despite changing demographics. This raises the issue of whether these results are a reflection of Australia's stable educational system and lifestyle over the last 30 years.

Child↗

PubMed2005

Changes in ocular accommodation when shifting between global and local attention.

BACKGROUND: The link between cognitive changes in attentional focus and the physiological parameters of the eye is not well understood. The aim of the current work was to examine the role of ocular accommodation, that is, the process of changing the shape of the crystalline lens in order to focus an image onto the retina, in active shifts of visual attention between global and local information. METHOD: Ten adult participants (aged 19 to 27) viewed sequences of complex global/local figures presented at the same location. They were asked to identify either a global or local red target letter and to look for either a global or local letter x (probe) in the sequence following. Target and probe items were separated by a temporal gap of approximately one second. Refraction was measured using a Canon Autorefractor R1 at the time of target appearance and again at the time of probe presentation. Particular interest was paid to trials where participants were required to shift attention either from a local to global level or in the reverse direction. The difference between the two measurements of refraction gave a 'change score' which provided an indication of the change of accommodation. RESULTS: No significant change in refraction was observed when shifting from the local to the global condition. A mean change in refraction of -0.128 dioptres was observed for the global to local condition. The 95 per cent confidence interval for this difference did not overlap zero, indicating a significant change in refraction, which was attributed to an increase in accommodation. DISCUSSION: The results suggest that while a change in accommodation occurs in shifting attention from the global to the local aspect of the complex figures, a similar change is not observed in the reverse direction. These results are consistent with the hypothesis that it is more difficult to restrict attentional focus than it is to widen it.

Accommodation, Ocular↗

PubMed2004

Structural and elemental evidence for edema in the retina, retinal pigment epithelium, and choroid during recovery from experimentally induced myopia.

PURPOSE: The purpose of this study was to monitor temporal changes in the retina, retinal pigment epithelium (RPE), and choroid of chick eyes using biometric, ultrastructural, and elemental microanalysis techniques as a means of visualizing more detailed signs of the physiological processes underlying choroidal expansion and refractive normalization during recovery from form deprivation. METHODS: Axial dimensions and refractions were measured on form-deprived and fellow eyes of 117 experimental chickens reared with monocular translucent occlusion from days 1 to 15 and given different lengths of visual experience (T = 0-144 hours) before death. Tissue was analyzed ultrastructurally by electron microscopy and relative sodium (Na) and chloride (Cl) ion abundances, by using x-ray microanalysis to determine changes in the presence of these indicators of tissue hydration. RESULTS: Refractive error decreased from more than 20 D of myopia almost linearly over the first 144 hours after occlusion. Concurrent changes in thickness in the retina, RPE, and choroid were seen as a series of thickness increases and edema, which returned to normal thickness, first in the retina, and did not reach maximum until 3 days after occluder removal in the choroid. In freeze-dried tissue, Na and Cl ion concentrations were greatest in the RPE photoreceptor outer segments and extravascular choroid at T = 0, decreasing toward fellow eye levels by T = 48 in the RPE and choroid. Na and Cl ion abundances in the frozen lymph of choroidal lymphatics were nearly at control levels (T = 0) and increased later as the vessels became more distended after the extravascular edema became significant. CONCLUSIONS: The results suggest that occluder removal induces edema across the retina and choroid and that this fluid may be the vector eliciting choroidal expansion during recovery from form deprivation possibly driven by the hyperosmolarity in the choroid, RPE, and photoreceptor outer segments that accompanies deprivation.

Animals↗

PubMed2003

Prevalence of myopia among primary school children in eastern Sydney.

BACKGROUND: Worldwide there is concern that the prevalence of myopia is increasing but the prevalence of myopia in Australian school children has not been analysed in detail. This study examines the prevalence of refractive errors in a large unselected population of primary school children in the eastern suburbs of Sydney. METHODS: Children visiting the Vision Education Centre at the School of Optometry and Vision Science, University of New South Wales, on a school excursion during the first half of the 1990s were refracted by non-cycloplegic retinoscopy. Spherical equivalents were computed and analysis of variance carried out. RESULTS: There were 1,459 boys and 1,076 girls in the study, a total of 2,535 children of whom approximately 40 per cent were born overseas or were first generation Australians. Overall, there was no significant difference in refractive error between girls and boys, although there were age/gender interactions with older girls exhibiting more hyperopia than boys. The refractive error ranged from -0.25 to +1.25 D spherical equivalent in 87.3 per cent of children. Mean spherical equivalent for the group was +0.50 +/- 0.82 D. There was a significant shift (p < 0.001) towards increasing myopia with age. The prevalence of myopia greater than -0.50 D rose from 1.0 per cent of four-year-olds to 8.3 per cent of 12-year-olds. CONCLUSIONS: The prevalence of myopia found in a large multi-ethnic group of non-clinical primary school children in eastern Sydney is lower than expected from other studies in the USA and Asia. Compared with Australian data from the 1970s and 1980s, only a weak increase in the prevalence of myopia is revealed.

Age Distribution↗