Optometry and Vision Sciences - Research Publications
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ItemShort-Term Stability in Refractive Status Despite Large Fluctuations in Glucose Levels in Diabetes Mellitus Type 1 and 2(PUBLIC LIBRARY SCIENCE, 2012-12-28)PURPOSE: This work investigates how short-term changes in blood glucose concentration affect the refractive components of the diabetic eye in patients with long-term Type 1 and Type 2 diabetes. METHODS: Blood glucose concentration, refractive error components (mean spherical equivalent MSE, J0, J45), central corneal thickness (CCT), anterior chamber depth (ACD), crystalline lens thickness (LT), axial length (AL) and ocular aberrations were monitored at two-hourly intervals over a 12-hour period in: 20 T1DM patients (mean age ± SD) 38±14 years, baseline HbA1c 8.6±1.9%; 21 T2DM patients (mean age ± SD) 56±11 years, HbA1c 7.5±1.8%; and in 20 control subjects (mean age ± SD) 49±23 years, HbA1c 5.5±0.5%. The refractive and biometric results were compared with the corresponding changes in blood glucose concentration. RESULTS: Blood glucose concentration at different times was found to vary significantly within (p<0.0005) and between groups (p<0.0005). However, the refractive error components and ocular aberrations were not found to alter significantly over the day in either the diabetic patients or the control subjects (p>0.05). Minor changes of marginal statistical or optical significance were observed in some biometric parameters. Similarly there were some marginally significant differences between the baseline biometric parameters of well-controlled and poorly-controlled diabetic subjects. CONCLUSION: This work suggests that normal, short-term fluctuations (of up to about 6 mM/l on a timescale of a few hours) in the blood glucose levels of diabetics are not usually associated with acute changes in refractive error or ocular wavefront aberrations. It is therefore possible that factors other than refractive error fluctuations are sometimes responsible for the transient visual problems often reported by diabetic patients.
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ItemIntrinsic physiological properties of rat retinal ganglion cells with a comparative analysis(AMER PHYSIOLOGICAL SOC, 2012-10-01)Mammalian retina contains 15-20 different retinal ganglion cell (RGC) types, each of which is responsible for encoding different aspects of the visual scene. The encoding is defined by a combination of RGC synaptic inputs, the neurotransmitter systems used, and their intrinsic physiological properties. Each cell's intrinsic properties are defined by its morphology and membrane characteristics, including the complement and localization of the ion channels expressed. In this study, we examined the hypothesis that the intrinsic properties of individual RGC types are conserved among mammalian species. To do so, we measured the intrinsic properties of 16 morphologically defined rat RGC types and compared these data with cat RGC types. Our data demonstrate that in the rat different morphologically defined RGC types have distinct patterns of intrinsic properties. Variation in these properties across cell types was comparable to that found for cat RGC types. When presumed morphological homologs in rat and cat retina were compared directly, some RGC types had very similar properties. The rat A2 cell exhibited patterns of intrinsic properties nearly identical to the cat alpha cell. In contrast, rat D2 cells (ON-OFF directionally selective) had a very different pattern of intrinsic properties than the cat iota cell. Our data suggest that the intrinsic properties of RGCs with similar morphology and suspected visual function may be subject to variation due to the behavioral needs of the species.
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ItemInvestigation of Ocular Hemodynamics in Sturge-Weber Syndrome(LIPPINCOTT WILLIAMS & WILKINS, 2012-06-01)PURPOSE: Sturge-Weber syndrome (SWS) is a condition often associated with facial cutaneous angioma, vascular malformations in the brain, and ocular anomalies such as glaucoma. Reduced cerebral blood flow and ischemia have been well documented. Less is known about ocular blood flow despite the frequent associations between altered hemodynamics and the mechanisms underlying glaucomatous optic neuropathy. The aim of this research was to investigate retrobulbar hemodynamics in patients diagnosed with SWS. METHODS: The sample comprised 16 patients diagnosed with SWS and 16 age- and gender-matched normal control subjects. Four patients were diagnosed with both SWS and primary open-angle glaucoma (mean age 34.3 years; SD 26.9 years), three patients with both SWS and closed-angle glaucoma (mean age 23.3 years; SD 18.0 years), and nine patients with SWS and no glaucoma (mean age 17.2 years; SD 9.1 years). Systemic blood pressure and intraocular pressure were measured to determine the mean arterial pressure and ocular perfusion pressure. All patients and subjects underwent ultrasonography of the ophthalmic artery, central retinal artery, and short posterior ciliary arteries. RESULTS: No significant difference between groups for mean arterial pressure or ocular perfusion pressure (p > 0.05) was recorded. Participants diagnosed with SWS and primary open-angle glaucoma showed significantly reduced end-diastolic velocity (mean 0.036 m/s; SD 0.005 m/s) in their central retinal artery (p = 0.016) when compared against their age-matched normal controls (mean 0.054 m/s; SD 0.010 m/s). Participants diagnosed with SWS and no glaucoma also showed significantly reduced end-diastolic velocity (mean 0.038 m/s; SD 0.015 m/s) in their central retinal artery (p = 0.046) when compared against their age-matched normal controls (mean 0.054 m/s; SD 0.014 m/s). CONCLUSIONS: Retrobulbar hemodynamics appear to be altered in participants diagnosed with SWS irrespective of their diagnosis of glaucoma. Further research is needed to ascertain whether there are any long-term consequences of such changes to ocular physiology.
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ItemH Barry Collin Research Medal awarded to Professor Anthony J Adams(TAYLOR & FRANCIS LTD, 2012-05-01)
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ItemUsing Imaging for Education and Clinical Excellence(LIPPINCOTT WILLIAMS & WILKINS, 2012-10-01)