Optometry and Vision Sciences - Research Publications
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ItemNo Preview AvailableClinical Applications of Wavefront Refraction(LIPPINCOTT WILLIAMS & WILKINS, 2014-10)PURPOSE: To determine normative reference ranges for higher-order wavefront error (HO-WFE), compare these values with those in common ocular pathologies, and evaluate treatments. METHODS: A review of 17 major studies on HO-WFE was made, involving data for a total of 31,605 subjects. The upper limit of the 95% confidence interval (CI) for HO-WFE was calculated from the most comprehensive of these studies using normal healthy patients aged 20 to 80 years. There were no studies identified using the natural pupil size for subjects, and for this reason, the HO-WFE was tabulated for pupil diameters of 3 to 7 mm. Effects of keratoconus, pterygium, cataract, and dry eye on HO-WFE were reviewed and treatment efficacy was considered. RESULTS: The calculated upper limit of the 95% CI for HO-WFE in a healthy normal 35-year-old patient with a mesopic pupil diameter of 6 mm would be 0.471 μm (471 nm) root-mean-square or less. Although the normal HO-WFE increases with age for a given pupil size, it is not yet completely clear how the concurrent influence of age-related pupillary miosis affects these findings. Abnormal ocular conditions such as keratoconus can induce a large HO-WFE, often in excess of 3.0 μm, particularly attributed to coma. For pterygium or cortical cataract, a combination of coma and trefoil was more commonly induced. Nuclear cataract can induce a negative spherical HO-WFE, usually in excess of 1.0 μm. CONCLUSIONS: The upper limit of the 95% CI for HO-WFE root-mean-square is about 0.5 μm with normal physiological pupil sizes. With ocular pathologies, HO-WFE can be in excess of 1.0 μm, although many devices and therapeutic and surgical treatments are reported to be highly effective at minimizing HO-WFE. More accurate normative reference ranges for HO-WFE will require future studies using the subjects' natural pupil size.
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ItemInterventions to improve cultural competency in healthcare: a systematic review of reviews(BMC, 2014-03-03)BACKGROUND: Cultural competency is a recognized and popular approach to improving the provision of health care to racial/ethnic minority groups in the community with the aim of reducing racial/ethnic health disparities. The aim of this systematic review of reviews is to gather and synthesize existing reviews of studies in the field to form a comprehensive understanding of the current evidence base that can guide future interventions and research in the area. METHODS: A systematic review of review articles published between January 2000 and June 2012 was conducted. Electronic databases (including Medline, Cinahl and PsycINFO), reference lists of articles, and key websites were searched. Reviews of cultural competency in health settings only were included. Each review was critically appraised by two authors using a study appraisal tool and were given a quality assessment rating of weak, moderate or strong. RESULTS: Nineteen published reviews were identified. Reviews consisted of between 5 and 38 studies, included a variety of health care settings/contexts and a range of study types. There were three main categories of study outcomes: patient-related outcomes, provider-related outcomes, and health service access and utilization outcomes. The majority of reviews found moderate evidence of improvement in provider outcomes and health care access and utilization outcomes but weaker evidence for improvements in patient/client outcomes. CONCLUSION: This review of reviews indicates that there is some evidence that interventions to improve cultural competency can improve patient/client health outcomes. However, a lack of methodological rigor is common amongst the studies included in reviews and many of the studies rely on self-report, which is subject to a range of biases, while objective evidence of intervention effectiveness was rare. Future research should measure both healthcare provider and patient/client health outcomes, consider organizational factors, and utilize more rigorous study designs.
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ItemOcellar structure and neural innervation in the honeybee(FRONTIERS MEDIA SA, 2014-02-19)Honeybees have a visual system composed of three ocelli (simple eyes) located on the top of the head, in addition to two large compound eyes. Although experiments have been conducted to investigate the role of the ocelli within the visual system, their optical characteristics, and function remain controversial. In this study, we created three-dimensional (3-D) reconstructions of the honeybee ocelli, conducted optical measurements and filled ocellar descending neurons to assist in determining the role of ocelli in honeybees. In both the median and lateral ocelli, the ocellar retinas can be divided into dorsal and ventral parts. Using the 3-D model we were able to assess the viewing angles of the retinas. The dorsal retinas view the horizon while the ventral retinas view the sky, suggesting quite different roles in attitude control. We used the hanging drop technique to assess the spatial resolution of the retinas. The lateral ocelli have significantly higher spatial resolution compared to the median ocellus. In addition, we established which ocellar retinas provide the input to five pairs of large ocellar descending neurons. We found that four of the neuron pairs have their dendritic fields in the dorsal retinas of the lateral ocelli, while the fifth has fine dendrites in the ventral retina. One of the neuron pairs also sends very fine dendrites into the border region between the dorsal and ventral retinas of the median ocellus.
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ItemDoes the Swedish Interactive Threshold Algorithm (SITA) accurately map visual field loss attributed to vigabatrin?(Springer Science and Business Media LLC, 2014-12-23)BACKGROUND: Vigabatrin (VGB) is an anti-epileptic medication which has been linked to peripheral constriction of the visual field. Documenting the natural history associated with continued VGB exposure is important when making decisions about the risk and benefits associated with the treatment. Due to its speed the Swedish Interactive Threshold Algorithm (SITA) has become the algorithm of choice when carrying out Full Threshold automated static perimetry. SITA uses prior distributions of normal and glaucomatous visual field behaviour to estimate threshold sensitivity. As the abnormal model is based on glaucomatous behaviour this algorithm has not been validated for VGB recipients. We aim to assess the clinical utility of the SITA algorithm for accurately mapping VGB attributed field loss. METHODS: The sample comprised one randomly selected eye of 16 patients diagnosed with epilepsy, exposed to VGB therapy. A clinical diagnosis of VGB attributed visual field loss was documented in 44% of the group. The mean age was 39.3 years ± 14.5 years and the mean deviation was -4.76 dB ±4.34 dB. Each patient was examined with the Full Threshold, SITA Standard and SITA Fast algorithm. RESULTS: SITA Standard was on average approximately twice as fast (7.6 minutes) and SITA Fast approximately 3 times as fast (4.7 minutes) as examinations completed using the Full Threshold algorithm (15.8 minutes). In the clinical environment, the visual field outcome with both SITA algorithms was equivalent to visual field examination using the Full Threshold algorithm in terms of visual inspection of the grey scale plots , defect area and defect severity. CONCLUSIONS: Our research shows that both SITA algorithms are able to accurately map visual field loss attributed to VGB. As patients diagnosed with epilepsy are often vulnerable to fatigue, the time saving offered by SITA Fast means that this algorithm has a significant advantage for use with VGB recipients.
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ItemA Role for Smoothened during Murine Lens and Cornea Development(PUBLIC LIBRARY SCIENCE, 2014-09-30)Various studies suggest that Hedgehog (Hh) signalling plays roles in human and zebrafish ocular development. Recent studies (Kerr et al., Invest Ophthalmol Vis Sci. 2012; 53, 3316-30) showed that conditionally activating Hh signals promotes murine lens epithelial cell proliferation and disrupts fibre differentiation. In this study we examined the expression of the Hh pathway and the requirement for the Smoothened gene in murine lens development. Expression of Hh pathway components in developing lens was examined by RT-PCR, immunofluorescence and in situ hybridisation. The requirement of Smo in lens development was determined by conditional loss-of-function mutations, using LeCre and MLR10 Cre transgenic mice. The phenotype of mutant mice was examined by immunofluorescence for various markers of cell cycle, lens and cornea differentiation. Hh pathway components (Ptch1, Smo, Gli2, Gli3) were detected in lens epithelium from E12.5. Gli2 was particularly localised to mitotic nuclei and, at E13.5, Gli3 exhibited a shift from cytosol to nucleus, suggesting distinct roles for these transcription factors. Conditional deletion of Smo, from ∼E12.5 (MLR10 Cre) did not affect ocular development, whereas deletion from ∼E9.5 (LeCre) resulted in lens and corneal defects from E14.5. Mutant lenses were smaller and showed normal expression of p57Kip2, c-Maf, E-cadherin and Pax6, reduced expression of FoxE3 and Ptch1 and decreased nuclear Hes1. There was normal G1-S phase but decreased G2-M phase transition at E16.5 and epithelial cell death from E14.5-E16.5. Mutant corneas were thicker due to aberrant migration of Nrp2+ cells from the extraocular mesenchyme, resulting in delayed corneal endothelial but normal epithelial differentiation. These results indicate the Hh pathway is required during a discrete period (E9.5-E12.5) in lens development to regulate lens epithelial cell proliferation, survival and FoxE3 expression. Defective corneal development occurs secondary to defects in lens and appears to be due to defective migration of peri-ocular Nrp2+ neural crest/mesenchymal cells.
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ItemThe Role of Histamine in the Retina: Studies on the Hdc Knockout Mouse(PUBLIC LIBRARY SCIENCE, 2014-12-29)The role of histamine in the retina is not well understood, despite it regulating a number of functions within the brain, including sleep, feeding, energy balance, and anxiety. In this study we characterized the structure and function of the retina in mice that lacked expression of the rate limiting enzyme in the formation of histamine, histidine decarboxylase (Hdc-/- mouse). Using laser capture microdissection, Hdc mRNA expression was assessed in the inner and outer nuclear layers of adult C57Bl6J wildtype (WT) and Hdc(-/-)-retinae. In adult WT and Hdc(-/-)-mice, retinal fundi were imaged, retinal structure was assessed using immunocytochemistry and function was probed by electroretinography. Blood flow velocity was assessed by quantifying temporal changes in the dynamic fluorescein angiography in arterioles and venules. In WT retinae, Hdc gene expression was detected in the outer nuclear layer, but not the inner nuclear layer, while the lack of Hdc expression was confirmed in the Hdc-/- retina. Preliminary examination of the fundus and retinal structure of the widely used Hdc-/- mouse strain revealed discrete lesions across the retina that corresponded to areas of photoreceptor abnormality reminiscent of the rd8 (Crb1) mutation. This was confirmed after genotyping and the strain designated Hdcrd8/rd8. In order to determine the effect of the lack of Hdc-alone on the retina, Hdc-/- mice free of the Crb1 mutation were bred. Retinal fundi appeared normal in these animals and there was no difference in retinal structure, macrogliosis, nor any change in microglial characteristics in Hdc-/- compared to wildtype retinae. In addition, retinal function and retinal blood flow dynamics showed no alterations in the Hdc-/- retina. Overall, these results suggest that histamine plays little role in modulating retinal structure and function.
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ItemStudying Age-Related Macular Degeneration Using Animal Models(LIPPINCOTT WILLIAMS & WILKINS, 2014-08)Over the recent years, there have been tremendous advances in our understanding of the genetic and environmental factors associated with the development of age-related macular degeneration (AMD). Examination of retinal changes in various animals has aided our understanding of the pathogenesis of the disease. Notably, mouse strains, carrying genetic anomalies similar to those affecting humans, have provided a foundation for understanding how various genetic risk factors affect retinal integrity. However, to date, no single mouse strain that develops all the features of AMD in a progressive age-related manner has been identified. In addition, a mutation present in some background strains has clouded the interpretation of retinal phenotypes in many mouse strains. The aim of this perspective was to describe how animals can be used to understand the significance of each sign of AMD, as well as key genetic risk factors.
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ItemTarget direction rather than position determines oculomotor expectation in repeating sequences(SPRINGER, 2014-07)Saccadic latencies to targets appearing to the left and right of fixation in a repeating sequence are significantly increased when a target is presented out of sequence. Is this because the target is in the wrong position, the wrong direction, or both? To find out, we arranged for targets in a horizontal plane occasionally to appear with an unexpected eccentricity, though in the correct direction. This had no significant effect on latency, unlike what is observed when targets appeared in the unexpected direction. That subjects learnt sequences of directions rather than simply positions was further confirmed in an experiment where saccade direction was a repeating sequence, but eccentricity was randomised. Latency was elevated when a target was episodically presented in an unexpected direction. Latencies were also elevated when targets appeared in the correct hemifield but at an unexpected direction (35° polar angular displacement from the horizontal, a displacement roughly equivalent in collicular spacing to our unexpected eccentricity), although this elevation was of a smaller magnitude than when targets appeared in an unexpected direction along the horizontal. Finally, we confirmed that not all changes in the stimulus cause disruption: an unexpected change in the orientation or colour of the target did not alter latency. Our results show that in a repeating sequence, the oculomotor system is primarily concerned with predicting the direction of an upcoming eye movement rather than its position. This is consistent with models of oculomotor control developed for randomly appearing targets in which the direction and amplitude of saccades are programmed separately.
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ItemImproving high resolution retinal image quality using speckle illumination HiLo imaging(OPTICAL SOC AMER, 2014-08-01)Retinal image quality from flood illumination adaptive optics (AO) ophthalmoscopes is adversely affected by out-of-focus light scatter due to the lack of confocality. This effect is more pronounced in small eyes, such as that of rodents, because the requisite high optical power confers a large dioptric thickness to the retina. A recently-developed structured illumination microscopy (SIM) technique called HiLo imaging has been shown to reduce the effect of out-of-focus light scatter in flood illumination microscopes and produce pseudo-confocal images with significantly improved image quality. In this work, we adopted the HiLo technique to a flood AO ophthalmoscope and performed AO imaging in both (physical) model and live rat eyes. The improvement in image quality from HiLo imaging is shown both qualitatively and quantitatively by using spatial spectral analysis.
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ItemNo Preview AvailableChronic Hypertension Increases Susceptibility to Acute IOP Challenge in Rats(ASSOC RESEARCH VISION OPHTHALMOLOGY INC, 2014-12)PURPOSE: To consider the effect of chronic arterial hypertension on the susceptibility of the retina to acute IOP challenge. METHODS: Anesthetized adult Long-Evans rats with normal (n = 5, receiving saline subcutaneously), chronic high blood pressure (BP) for 4 weeks (n = 15, Angiotensin II subcutaneously), and acute high BP for 1 hour (n = 10, Angiotensin II intravenously) underwent IOP elevation (10-120 mm Hg, 5 mm Hg steps each 3 minutes). During IOP elevation, retinal function and ocular blood flow were monitored with electroretinogram (ERG) and laser-Doppler flowmetry (LDF), respectively. Blood pressure was monitored via a femoral artery cannula. Electroretinogram and LDF responses are expressed as a percentage of baseline and compared between groups. The left ventricle and the aorta were dissected to assess the morphologic changes associated with chronic hypertension. RESULTS: Four weeks of hypertension (systolic BP 192 ± 4 mm Hg) produced cardiac hypertrophy and thickened aortic arterial walls compared with controls (systolic BP 112 ± 3 mm Hg). Retinal function was unaltered with chronic hypertension compared with normotensive animals. During acute IOP elevation, ERG and LDF were reduced in a dose-dependent manner in all BP groups. Both chronic and acute hypertension made the ERG and LDF less susceptible to IOP elevation. However, the degree of resistance to IOP elevation was greater in acute hypertension compared with chronic hypertension (P < 0.05). CONCLUSIONS: Acute BP elevation makes retinal function and blood flow less susceptible to IOP elevation. The reduced susceptibility afforded by improved ocular perfusion pressure is compromised after 4 weeks of chronic hypertension.