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Biomedical subjects

Robyn H Guymer

Publications and source records attributed to Robyn H Guymer.

At least 19 recordsLinked to original sources
PubMed2006

Modifiable risk factors for age-related macular degeneration.

Age-related macular degeneration (AMD) is the leading cause of irreversible blindness in Australia and other Western countries. As there is no cure for AMD, and treatments to stop its progression have met with limited success, there is an interest in identifying modifiable risk factors to prevent or slow disease progression. To date, smoking is the only proven modifiable risk factor for AMD. Other factors under study include (i) cardiovascular risk factors such as hypertension, body mass index, and atherosclerosis; and (ii) dietary risk factors including fat and antioxidant intake, but so far these studies have produced conflicting results. Dietary fat in relation to AMD has recently attracted media attention. Despite very limited work supporting an association between vegetable fat and AMD, widespread publicity advocating margarine as a cause of AMD and encouraging use of butter instead has caused confusion and anxiety among sufferers of AMD and the general public, as well as concern among health professionals. The antioxidant carotenoids--lutein and zeaxanthin--found in dark green or yellow vegetables exist in high concentrations in the macula and are hypothesised to play a protective role. Of nine controlled trials of supplementation with carotenoids and other antioxidants, three suggested that various combinations of antioxidants and carotenoids were protective. While a low-fat diet rich in dark green and yellow vegetables is advocated in general, any specific recommendations regarding certain fats or antioxidant supplementation and AMD are not based on consistent findings at this stage.

Adult↗
PubMed2006

Apolipoprotein (APOE) gene is associated with progression of age-related macular degeneration (AMD).

Progression of age-related macular degeneration (AMD), the leading cause of blindness in the elderly, was followed in a cohort of 238 individuals from a single center. Individuals with an epsilon (epsilon)2 genotype (c.526C>T of reference sequence NM_000041.2) of the apolipoprotein (APOE) gene were found to be strongly associated with disease with a significant 4.8-fold increased relative risk compared to individuals with an epsilon4 genotype (c.388T>C of reference sequence NM_000041.2) (odds ratio [OR], 4.8; 95% confidence interval [CI], 1.19-19.09) and a nearly significant three-fold increased relative risk compared to individuals with an epsilon3 genotype (reference sequence NM_000041.2) (OR, 2.8; 95% CI, 0.96-19.09). This finding was present only in females who progressed with AMD, which suggests that there may be a gender-specific role in progression of AMD in individuals with an epsilon2 allele. A gender-related factor is therefore implicated either directly or indirectly in the AMD disease process.

Age Distribution↗
PubMed2006

Prophylactic laser treatment hastens choroidal neovascularization in unilateral age-related maculopathy: final results of the drusen laser study.

PURPOSE: The Drusen Laser Study evaluated macular laser to prevent choroidal neovascularization (CNV) and vision loss in high-risk age-related maculopathy (ARM). DESIGN: Prospective, interventional, randomized, controlled clinical trial in five hospital centers. METHODS: Patients in the unilateral group had neovascular ARM and drusen in the study eye. Study eyes were randomized to laser-treated or no-laser groups. For patients in the bilateral drusen group, eyes were randomized to right eye, laser or no laser; and left eye, alternative. Laser treatment comprised 12 argon spots. Outcome was best-corrected visual acuity and CNV signs, which were monitored for 3 years. RESULTS: In the unilateral group, vision loss occurred in 21 (28.8%) of 73 patients in laser vs 13 (19.7%) of 66 no-laser patients (P=.214). Incidence of CNV was 27 (29.7%) of 91 in laser vs 15 (17.65%) of 85 no-laser patients (P=.061). CNV onset was approximately 6 months earlier in laser-treated compared with no-laser patients (P=.05). In the bilateral group, vision loss occurred in six (8.3%) of 72 laser-treated vs 10 (13.9%) of 72 fellow eyes (P=.3877). CNV incidence was 12 (11.6%) of 103 in laser-treated vs seven (6.8%) of 103 fellow eyes (P=.225). There was no difference in onset of CNV. CONCLUSIONS: Results do not support prophylactic laser of the fellow eye of patients with neovascular ARM. Its role in patients with bilateral drusen remains unclear.

Aged↗
PubMed2006

Blood storage at 4 degrees C-factors involved in DNA yield and quality.

BACKGROUND: Whole blood provides one of the most common sources of both high-quality DNA and high-quantity DNA for molecular biological purposes. Typically, blood storage at 4 degrees C is short term, which ranges from a few days to a few weeks. However, long-term storage usually involves blood being frozen, with a resultant loss in DNA yield. The authors examined the effects of long-term storage at 4 degrees C. METHODS: Duplicate blood samples were collected from 301 participants (aged 20-98 years) enrolled as part of ongoing studies. Samples were stored at 4 degrees C for between 11 days and 922 days, and DNA was subsequently extracted using a phenol/chloroform procedure. RESULTS: A negative correlation of the number of storage days existed at 4 degrees C with DNA yield. The main determinant on DNA yield was the age of the participant in the study, with older persons having a lower DNA yield. CONCLUSIONS: Long-term storage of blood at 4 degrees C does have a detrimental effect on DNA yield, but this effect seemed less significant than the age of a person. The impact of age of a person or storage time has a minimal impact on DNA quality. Therefore, storage of blood at 4 degrees C offers an acceptable alternative to frozen storage.

Adult↗
PubMed2006

Facts on fats.

Cardiovascular disease and age-related macular degeneration (AMD) may share common risk factors in their causal pathways. Decades of research from the cardiovascular sciences on fats have led investigators to focus on specific types of fats rather than total fat as a whole. They have established that saturated and trans-unsaturated fats (trans fats) are damaging to cardiovascular health while polyunsaturated fats, particularly the marine omega 3 fatty acids appear protective. This has led to a number of studies investigating the associations of fat and AMD. Though the causal relationship between fats and AMD remain unproven, some studies suggest that an association may be present. To be able to understand and interpret the study results and their implications, an understanding of the fats in the diet is important. This review aims to give an overview of fatty acids, particularly the trans-unsaturated fatty acids, and the relevant food groups.

Dietary Fats↗
PubMed2006

Concordant bilateral Duane's Retraction Syndrome (type 1) in female monozygotic twins.

We report a single case study of concordant bilateral Duane's Retraction Syndrome (DRS) (type 1) in female monozygotic (MZ) twins aged 47 years. The twin pair were recruited through the Australian Twin Registry as part of a twin study on myopia. This twin pair were full term and had a similar birth weight: 2.27 kg and 1.81 kg in twin 1 and twin 2, respectively. There was no report of any other childhood medical conditions in either twin. Both twins had an equal amount of restriction in right and left abduction. Narrowing of the palpebral fissures and globe retraction in right and left adduction was also observed in both twins. To our knowledge this is the first case to report concordant bilateral DRS (type 1) in female MZ twins. The concordance for the presence of DRS and associated clinical signs observed in this MZ twin pair supports a genetic origin to DRS.

Diseases in Twins↗
PubMed2006

Australian Angiogram Review Panel--monitoring the use of photodynamic therapy with verteporfin.

BACKGROUND: Photodynamic therapy with verteporfin for choroidal neovascularization (CNV) secondary to macular disease received an Australian government grant in 2002 to fund treatment for 3 years. Funding was restricted to subfoveal predominantly classic CNV where visual acuity was at least 6/60. Access to this funding was via review of angiograms by an expert panel, the Angiogram Review Panel (ARP), managed by the Royal Australian and New Zealand College of Ophthalmologists. METHODS: De-identified data from the ARP were obtained for the period June 2002 to April 2005 inclusive and the panel's outcomes were analysed. Health Insurance Commission and Department of Veteran Affairs data for photodynamic therapy for the same interval were also retrieved. RESULTS: A total of 7198 submissions to the ARP were received for 5867 individuals in this period. Overall 86.6% eyes submitted were accepted for initial funding (treatments 2-4). There was no change over time in the percentage rejected during this period. The first reviewer accepted 77.2%. And the second reviewer accepted a further 7.7%. An additional 1.6% were accepted on appeal. It was estimated that 29.2% of this initial cohort received five or more treatments. CONCLUSIONS: The ARP data indicate an incidence of subfoveal predominantly classic CNV secondary to macular disease in Australia of about 2000 eyes per annum. Only one quarter of patients received five or more treatments. The panel provided a unique opportunity to estimate the 'whole of nation' incidence of predominantly classic subfoveal CNV secondary to macular disease and thus provides a firm foundation upon which to plan public health spending as new treatments become available.

Australia↗
PubMed2006

Heritability of macular thickness determined by optical coherence tomography.

PURPOSE: To examine whether genetic factors significantly influence macular thickness in healthy older subjects. METHODS: A classic twin study was performed to compare the correlation of macular thickness between monozygotic (MZ) and dizygotic (DZ) twins in a sample of population-based volunteer twins. The study included 109 white twin pairs from 50 to 80 years of age without evidence of manifest eye disease and corrected visual acuity better than 6/7.5. Dilated macular optical coherence tomography (OCT), fundus photography, clinical examination, ocular biometry, a health-dietary questionnaire, and subjective autorefraction were performed on all subjects. RESULTS: Correlation of retinal thickness was significantly greater between MZ twin pairs than DZ pairs in all macular regions. The MZ-to-DZ correlation was 0.88:0.44 for the foveal region, 0.79:0.47 for the inner macular region, and 0.81:0.50 for the outer macular region. With adjustment for significant covariates and model fitting, final heritability estimates of 85%, 81%, and 81%, respectively, were obtained. A significant correlation between foveal thickness and gender was present, with the men having significantly thicker foveae. There was a significant negative correlation between outer macular thickness and axial length. CONCLUSIONS: This study confirms that macular thickness in older healthy subjects, as measured by OCT, may be affected by genetic factors. Factors such as axial length, gender and age, warrant further examination in larger population-based studies, as variables that may influence macular thickness. This finding suggests an inherited basis of macular thickness and may help in the understanding of the factors that govern macular structure and function.

Aged↗
PubMed2006

Heritability of refractive error and ocular biometrics: the Genes in Myopia (GEM) twin study.

PURPOSE: A classic twin study was undertaken to assess the contribution of genes and environment to the development of refractive errors and ocular biometrics in a twin population. METHODS: A total of 1224 twins (345 monozygotic [MZ] and 267 dizygotic [DZ] twin pairs) aged between 18 and 88 years were examined. All twins completed a questionnaire consisting of a medical history, education, and zygosity. Objective refraction was measured in all twins, and biometric measurements were obtained using partial coherence interferometry. RESULTS: Intrapair correlations for spherical equivalent and ocular biometrics were significantly higher in the MZ than in the DZ twin pairs (P < 0.05), when refraction was considered as a continuous variable. A significant gender difference in the variation of spherical equivalent and ocular biometrics was found (P < 0.05). A genetic model specifying an additive, dominant, and unique environmental factor that was sex limited was the best fit for all measured variables. Heritability of spherical equivalents of 88% and 75% were found in the men and women, respectively, whereas, that of axial length was 94% and 92%, respectively. Additive genetic effects accounted for a greater proportion of the variance in spherical equivalent, whereas the variance in ocular biometrics, particularly axial length was explained mostly by dominant genetic effects. CONCLUSIONS: Genetic factors, both additive and dominant, play a significant role in refractive error (myopia and hypermetropia) as well as in ocular biometrics, particularly axial length. The sex limitation ADE model (additive genetic, nonadditive genetic, and environmental components) provided the best-fit genetic model for all parameters.

Adolescent↗
PubMed2006

Refractive errors in twin studies.

It is estimated that 1.6 billion people worldwide have myopia, a refractive error, and this number is expected to increase to approximately 2.5 billion by the year 2020. It is now well established that both the environment and genetics play a role in the development of myopia. However, the exact contribution of each of these components to myopia development has yet to be completely determined. Twin studies (classical twin model) are commonly used to determine the weighting of genetic and environmental components in disease. Over the last century, twin studies have investigated the heritability of refractive errors in different sample populations and have collectively supported a genetic basis to refractive errors. However, different sample populations and methods of data collection have produced a wide range of heritability estimates ranging from .5 to .9. This article will review those twin studies that have investigated refractive error, particularly myopia, as well as biometric measures linked to refractive error, to compare heritability estimates and methodology designs.

Diseases in Twins↗
PubMed2006

A review of drug options in age-related macular degeneration therapy and potential new agents.

Age-related macular degeneration (AMD) is the leading cause of legal blindness in people > 50 years of age in the developed world. AMD is both a debilitating and costly disease for the individual and the community. Greater understanding of the mechanisms and pathways involved in causing the visual loss in AMD has resulted in the advent of several newer and more effective treatment options, making it an exciting time in the management of AMD. This paper will examine the principles behind the existing drug therapies available, as well as those being developed in the management or prophylaxis of AMD and its vision-threatening complications.

Angiogenesis Inhibitors↗
PubMed2005

Disclosing disease mechanisms with a spatio-temporal summation paradigm.

BACKGROUND: We develop the logic for a stimulus that can evaluate cone-dependent spatial summation and detail the modelling and interpretation of thresholds obtained with this stimulus. METHODS: Fifteen observers participated, including two young normals tested extensively in control experiments, and a clinical trial based on four observers with age-related macular degeneration (AMD), four age-similar controls and five young observers. Monocular spatial summation functions were measured with contrast-modulated Gabor targets that approximated the optimal visual contrast detector. Thresholds were returned from a yes/no adaptive psychophysical algorithm. By fine titration along the size domain it was demonstrated that the spatial summation of normal observers can be adequately described by a two-component model. A reduced set of variables are proposed for clinical applications and the model was applied to data derived using these variables in persons with AMD and age-similar controls. RESULTS: We do not find a significant age-related loss of contrast sensitivity in our normal group. On the other hand, persons with early AMD exhibited a 0.41 log unit loss of sensitivity (P=0.04) from age-similar controls, without any change in their maximum summation area (A(max)). CONCLUSIONS: The nature of the spatial summation is consistent with the interpretation that early AMD produces a decrease in cone input to post-receptoral mechanisms in the absence of neural remodelling.

Adult↗
PubMed2005

Treatment of age-related macular degeneration.

Age-related macular degeneration (AMD) is the greatest cause of legal blindness in the western world. Established treatments include argon laser photocoagulation of extrafoveal choroidal neovascularisation (CNV) and photodynamic therapy of selected sub-foveal CNV. Newer approaches are targeting the angiogenic pathway in CNV development. Currently, other treatment modalities, such as radiotherapy and transpupillary thermotherapy do not have a clear role to play. Surgical options are experimental and only available in some centres for selected patients. Prevention of AMD remains elusive. Dietary supplements may have a role, while statins and prophylactic laser photocoagulation of drusen remain experimental. This paper explains the principles behind these approaches.

Animals↗
PubMed2004

Cytoarchitecture of choroidal capillary endothelial cells.

PURPOSE: To describe the cytoarchitecture of the choroidal capillary endothelial cells, especially as it relates to cellular processes that protrude through the basal lamina into Bruch's membrane (BM). METHODS: Human donor eyes and monkey and hamster eyes were examined by transmission electron microscopy and freeze-fracture replication. The number of endothelial cell processes and the characteristics of the processes and surrounding structures were determined in the maculae of human eyes and correlated with age-related changes in neighboring structures. RESULTS: Endothelial cell processes were observed in eyes of all species examined and at all ages. They typically occurred at sites of focally thickened, nonfenestrated regions of the endothelial cells. The basal lamina adjacent to the processes was often hypertrophic and associated deposits of long-spacing collagen (LSC) were observed frequently. In humans, there was no correlation between the number of processes per 100 micro m of the BM with age, sex, cause of death, postmortem time, RPE autofluorescence, or RPE residual body content. There was a weak linear association with the thickness of the BM. CONCLUSIONS: The finding of cellular processes of choroidal capillary endothelial cells penetrating their basal laminae is normal. These processes may serve to stabilize choroidal endothelial cells physically and play an important structural role in the maintenance of patency of the choriocapillaris. It is also possible that they have additional functions, as suggested for similar processes in other tissues. They are not necessarily the harbinger of choroidal neovascularization, although growth of new vessels may result from distortion of this normal attribute.

Adolescent↗
PubMed2004

The epsilon2 and epsilon4 alleles of the apolipoprotein gene are associated with age-related macular degeneration.

PURPOSE: To date, of all the genes studied in relation to age-related macular degeneration (AMD), the alleles of the apolipoprotein (apoE) gene have been the most consistently associated with disease. However, not all apoE studies have found an association, and among these the associations differ. The current study was conducted to investigate further the association of this gene in AMD. METHODS: Three hundred twenty-two unrelated individuals with diagnosed AMD and 123 unrelated but ethnically matched control subjects were analyzed. All subjects completed a standard questionnaire and were given a fundus examination. A blood sample was collected for DNA extraction. The common allelic variants of apoE were screened through the use of polymerase chain reaction (PCR) and restriction enzyme digestion followed by statistical analysis. RESULTS: Individuals with the epsilon3 epsilon4 genotype of apoE had an approximate halving of disease risk for late (end-stage) AMD (odds ratio [OR] 0.58, 95% confidence interval [CI] 0.34-0.98) relative to the epsilon3 epsilon3 genotype at age of ascertainment. Stratification of late AMD into atrophic and neovascular disease revealed that the greatest protective effect for the epsilon3 epsilon4 genotype was in individuals with atrophic disease (OR 0.35, 95% CI 0.13-0.92). Men with the epsilon3 epsilon4 genotype also showed almost a threefold reduction in risk of disease in late AMD (OR 0.36, 95% CI 0.16-0.82). However, individuals with late AMD and the epsilon2 epsilon3 genotype had a significantly earlier mean age of diagnosis of disease (3.4 years, P = 0.015) compared with those with the epsilon3 epsilon3 genotype, and this was most evident in women (3.9 years, P = 0.011) and in individuals with neovascular disease (4.7 years, P = 0.003). CONCLUSIONS: The alleles of apoE appear to have a role in the etiology of AMD, with the epsilon4 allele being protective, or at the very least, delaying the age of diagnosis of disease, whereas the epsilon2 allele appears to have a modifier effect by bringing forward the mean age of disease diagnosis.

Aged↗
PubMed2004

Flicker perimetry losses in age-related macular degeneration.

PURPOSE: To compare static and flicker perimetry outcomes in patients with early age-related macular degeneration (AMD). METHODS: Perimetry was performed in the central visual field of one eye of each of 25 patients with good visual acuity (> 6/12) and early AMD using static and flickering targets. These results were compared with data obtained from a single eye of 34 age-matched control subjects, 33 of whom were retested at 1 to 3 months after their initial visits. RESULTS: In all cases, patients with early AMD had greater mean defects for flickering than static targets, returning a significantly larger group average in response to flicker (4.3 +/- 0.6 dB) than to static (1.8 +/- 0.6 dB; P < 0.005). Greater pattern defect losses were also present in AMD-affected eyes with flicker compared with static perimetry (P < 0.02). These give a higher diagnostic sensitivity for flicker (68% vs. 42%, P < 0.05) at 90% specificity. Sensitivity can be increased to 84% +/- 6% (specificity 92% +/- 4%) if the criterion for failure is a more than 10-dB loss in the foveal region (1 degrees -3 degrees ). CONCLUSIONS: Flickering targets expose foveal deficits in early AMD better than do static targets. Flicker perimetry is an easy, short procedure that may be useful for monitoring the progression of AMD.

Aged↗