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Biomedical subjects

Paul Mitchell

Publications and source records attributed to Paul Mitchell.

At least 109 records · Page 6Linked to original sources
PubMed2005

Distribution of ocular biometric parameters and refraction in a population-based study of Australian children.

PURPOSE: To study the distribution of spherical equivalent refraction and ocular biometric parameters in a young Australian population. METHODS: Noncontact methods were used to examine ocular dimensions and cycloplegic autorefraction in a stratified random cluster sample of year 1 Sydney school students (n = 1765), mean age 6.7 years (range, 5.5-8.4 years). Repeated measures of axial length, anterior chamber depth, and greatest and least corneal radius of curvature (CR1, CR2, respectively) were taken in each eye. Refraction was measured as the spherical equivalent. RESULTS: Mean spherical equivalent refraction in right eyes was +1.26 +/- 0.03 D (SEM; range, -4.88 to +8.58). The distribution was peaked (kurtosis 14.4) and slightly skewed to the right (skewness, 1.7). Prevalence of myopia, defined as spherical equivalent refraction < or = -0.5 D, was 1.43% (95% CI, 0.94-2.18) in the overall population. Axial length, anterior chamber depth, and corneal radii of curvature were normally distributed. The mean axial length in right eyes was 22.61 +/- 0.02 mm (SEM; range, 19.64-25.35). The mean anterior chamber depth was 3.34 +/- 0.01 mm (SEM; range, 2.14-4.06). Mean CR1 was 7.85 +/- 0.01 mm (SEM) and mean CR2 was 7.71 +/- 0.01 mm (SEM). The distribution of axial length/mean corneal radius ratio was peaked (leptokurtic) with a mean of 2.906. Mean axial length was longer, anterior chambers were deeper, and corneas were flatter in the boys. CONCLUSIONS: A peaked (leptokurtic) distribution of spherical equivalent refraction was present in this predominantly hyperopic 6-year-old population. The results also showed that ocular biometric measures were normally distributed, with statistically significant gender differences found in measurements.

Adolescent↗
PubMed2005

Effect of stature and other anthropometric parameters on eye size and refraction in a population-based study of Australian children.

PURPOSE: To determine the effect of anthropometric parameters on refraction and ocular biometry. METHODS: Noncontact methods were used to examine ocular dimensions and cycloplegic refraction in a stratified random cluster sample of year-1 Sydney school students (mean age, 6 years; n = 1765). Height, body weight, and waist circumference were measured according to a standardized protocol. Body mass index (BMI) was subsequently calculated. The percentage of body fat was measured with leg-leg bioelectrical impedance analysis. Associations between parameters were analyzed by multiple linear regression. RESULTS: After adjustment for age in weeks, height was found to be strongly associated with axial length and corneal radius. Children in the 1st quintile for height had axial length of 22.39 +/- 0.04 mm compared with 22.76 +/- 0.04 mm in children in the 5th quintile. Other anthropometric parameters were not associated with axial length or corneal radius. Height was not associated with anterior chamber depth after adjustment for weight. Increases in weight, BMI, and waist circumference were associated with a deeper anterior chamber after adjustment for height. No associations were found between the measured anthropometric parameters and refraction or axial length-corneal radius ratio. CONCLUSIONS: This study found a strong association between height and axial length and corneal radius, but not spherical equivalent refraction. The findings may demonstrate the effectiveness of emmetropization in the presence of normal physiological influences.

Anterior Chamber↗
PubMed2005

Risk markers for the graded severity of auditory processing abnormality in an older Australian population: the Blue Mountains Hearing Study.

A recent report from a population-based survey of hearing loss in 2015 older adults showed that the overall prevalence of central auditory processing (CAP) abnormality was high at 76.4% using abnormality on one or more of seven speech-based test outcomes as the criteria. The present study grouped these test outcomes to reflect increasing severity of CAP abnormality and examined the relationship between this graded dependent variable and 16 independent variables. Logistic regression modeling suggested that moderate and severe CAP abnormality increased with age and was associated with increased hearing handicap, and men were more likely than women to show severe abnormality. While 98.5% of the population passed a cognitive screening assessment, declining cognitive function was still associated with the increased likelihood of CAP abnormality.

Aged↗
PubMed2004

Retinal arteriolar narrowing is associated with 5-year incident severe hypertension: the Blue Mountains Eye Study.

We assessed whether retinal arteriolar narrowing and structural abnormalities independently predicted 5-year incident severe (grade 2 or 3) hypertension in an older population-based cohort. The Blue Mountains Eye Study baseline (1992 to 1994) examined 3654 residents aged 49 and older in 2 postal code areas, west of Sydney. Of the 2335 participants (75.1% of survivors) who returned at the 5-year examinations, 1319 were normotensive or had mild (grade 1) hypertension at baseline. Baseline retinal photographs were graded for focal retinal vessel wall signs and vessel diameters were measured. Participants were classified as having normal, high-normal blood pressure [BP] (systolic BP 121 to 139 mm Hg and/or diastolic BP 81 to 89 mm Hg), mild hypertension (systolic BP 140 to 159 mm Hg and/or diastolic BP 90 to 99 mm Hg), or severe hypertension if they had a previous diagnosis of hypertension and were receiving antihypertensive medications or had systolic BP > or =160 mm Hg and/or diastolic BP > or =100 mm Hg at examination. Incident severe hypertension was defined in persons who were free of severe hypertension at baseline but classified as having severe hypertension at the 5-year examinations. Of the 1319 baseline subjects at risk, 390 (29.6%) developed severe hypertension. After adjusting for age, sex, body mass index, smoking, glucose, and total cholesterol, generalized retinal arteriolar narrowing at baseline was associated with increased risk of incident severe hypertension (odds ratio 2.6; 95% confidence interval, 1.7 to 3.9) when comparing the narrowest versus widest quintile. This association remained significant after further adjustment for baseline mean arterial BP or BP status. Our findings support the hypothesis that small vessel structural changes may precede the development of severe hypertension.

Aged↗
PubMed2004

Absence of change in choroidal nevi across 5 years in an older population.

OBJECTIVE: To determine the proportion of choroidal nevi that were previously identified in a population cross section and that showed evidence of growth or progression during a 5-year period. METHODS: The Blue Mountains Eye Study was a cohort study of residents 49 years and older living in an area west of Sydney, Australia. Retinal photographs were used to identify choroidal nevi. Repeat photographs were obtained 5 years later and graded side-by-side to ascertain clinical growth or progression of all identified nevi. The greatest diameter and surface area of each nevus were measured. Nevus growth was defined as an increase in size of at least 33%. RESULTS: There were 160 choroidal nevi identified in the 128 subjects with nevi who participated in both eye examinations. Only 1 nevus (0.6%) exhibited clinical growth during the 5 years. No nevi developed other indicators of progression, such as subretinal fluid or orange pigment accumulation. CONCLUSIONS: Findings from this study indicate that benign nevi in older persons rarely progress. Regular eye examinations may be unnecessary for clearly defined small nonsuspicious choroidal nevi. This information could relieve patient anxiety and reduce costs associated with regular monitoring of nevi.

Aged↗
PubMed2004

Safety of an intravitreal injection of triamcinolone: results from a randomized clinical trial.

OBJECTIVE: To determine the safety of a single intravitreal injection of triamcinolone acetonide (4 mg) in patients with subfoveal choroidal neovascularization caused by age-related macular degeneration. METHODS: A double-masked, placebo-controlled, randomized clinical trial was conducted at a public tertiary referral eye hospital. Patients participating had age-related macular degeneration with evidence of choroidal neovascularization, any part of which was classic; age older than 59 years; and best-corrected visual acuity of 20/200 or better. Eyes were assigned to active study treatment or to placebo. Intraocular pressure and cataract grading were performed every 6 months for 3 years. Adverse events, from mild to vision-threatening or life-threatening, were recorded as procedure-related or corticosteroid-related. RESULTS: Seventy-five eyes were assigned to study treatment and 76 eyes to placebo. There were no moderate or severe adverse events related to the surgical procedure in either group. Triamcinolone-treated eyes had a significantly increased risk of developing mild or moderate elevation of the intraocular pressure. Topical glaucoma medication reduced intraocular pressure to acceptable levels in all patients. There was significant progression of cataract in the triamcinolone-treated eyes. CONCLUSION: Despite a significant adverse event profile, intravitreal triamcinolone is generally well tolerated by the human eye as long as patients are carefully followed up by their surgeon and treated appropriately, when necessary.

Aged↗
PubMed2004

Causes and prevalence of visual impairment among adults in the United States.

OBJECTIVES: To estimate the cause-specific prevalence and distribution of blindness and low vision in the United States by age, race/ethnicity, and gender, and to estimate the change in these prevalence figures over the next 20 years. METHODS: Summary prevalence estimates of blindness (both according to the US definition of < or =6/60 [< or =20/200] best-corrected visual acuity in the better-seeing eye and the World Health Organization standard of < 6/120 [< 20/400]) and low vision (< 6/12 [< 20/40] best-corrected vision in the better-seeing eye) were prepared separately for black, Hispanic, and white persons in 5-year age intervals starting at 40 years. The estimated prevalences were based on recent population-based studies in the United States, Australia, and Europe. These estimates were applied to 2000 US Census data, and to projected US population figures for 2020, to estimate the number of Americans with visual impairment. Cause-specific prevalences of blindness and low vision were also estimated for the different racial/ethnic groups. RESULTS: Based on demographics from the 2000 US Census, an estimated 937 000 (0.78%) Americans older than 40 years were blind (US definition). An additional 2.4 million Americans (1.98%) had low vision. The leading cause of blindness among white persons was age-related macular degeneration (54.4% of the cases), while among black persons, cataract and glaucoma accounted for more than 60% of blindness. Cataract was the leading cause of low vision, responsible for approximately 50% of bilateral vision worse than 6/12 (20/40) among white, black, and Hispanic persons. The number of blind persons in the US is projected to increase by 70% to 1.6 million by 2020, with a similar rise projected for low vision. CONCLUSIONS: Blindness or low vision affects approximately 1 in 28 Americans older than 40 years. The specific causes of visual impairment, and especially blindness, vary greatly by race/ethnicity. The prevalence of visual disabilities will increase markedly during the next 20 years, owing largely to the aging of the US population.

Adult↗
PubMed2004

The prevalence of refractive errors among adults in the United States, Western Europe, and Australia.

OBJECTIVE: To estimate the prevalence of refractive errors in persons 40 years and older. METHODS: Counts of persons with phakic eyes with and without spherical equivalent refractive error in the worse eye of +3 diopters (D) or greater, -1 D or less, and -5 D or less were obtained from population-based eye surveys in strata of gender, race/ethnicity, and 5-year age intervals. Pooled age-, gender-, and race/ethnicity-specific rates for each refractive error were applied to the corresponding stratum-specific US, Western European, and Australian populations (years 2000 and projected 2020). RESULTS: Six studies provided data from 29 281 persons. In the US, Western European, and Australian year 2000 populations 40 years or older, the estimated crude prevalence for hyperopia of +3 D or greater was 9.9%, 11.6%, and 5.8%, respectively (11.8 million, 21.6 million, and 0.47 million persons). For myopia of -1 D or less, the estimated crude prevalence was 25.4%, 26.6%, and 16.4% (30.4 million, 49.6 million, and 1.3 million persons), respectively, of whom 4.5%, 4.6%, and 2.8% (5.3 million, 8.5 million, and 0.23 million persons), respectively, had myopia of -5 D or less. Projected prevalence rates in 2020 were similar. CONCLUSIONS: Refractive errors affect approximately one third of persons 40 years or older in the United States and Western Europe, and one fifth of Australians in this age group.

Adult↗
PubMed2004

Prevalence of open-angle glaucoma among adults in the United States.

OBJECTIVE: To estimate the prevalence and distribution of open-angle glaucoma (OAG) in the United States by age, race/ethnicity, and gender. METHODS: Summary prevalence estimates of OAG were prepared separately for black, Hispanic, and white subjects in 5-year age intervals starting at 40 years. The estimated rates were based on a meta-analysis of recent population-based studies in the United States, Australia, and Europe. These rates were applied to 2000 US census data and to projected US population figures for 2020 to estimate the number of the US population with OAG. RESULTS: The overall prevalence of OAG in the US population 40 years and older is estimated to be 1.86% (95% confidence interval, 1.75%-1.96%), with 1.57 million white and 398 000 black persons affected. After applying race-, age-, and gender-specific rates to the US population as determined in the 2000 US census, we estimated that OAG affects 2.22 million US citizens. Owing to the rapidly aging population, the number with OAG will increase by 50% to 3.36 million in 2020. Black subjects had almost 3 times the age-adjusted prevalence of glaucoma than white subjects. CONCLUSIONS: Open-angle glaucoma affects more than 2 million individuals in the United States. Owing to the rapid aging of the US population, this number will increase to more than 3 million by 2020.

Adult↗
PubMed2004

Prevalence of age-related macular degeneration in the United States.

OBJECTIVE: To estimate the prevalence and distribution of age-related macular degeneration (AMD) in the United States by age, race/ethnicity, and gender. METHODS: Summary prevalence estimates of drusen 125 microm or larger, neovascular AMD, and geographic atrophy were prepared separately for black and white persons in 5-year age intervals starting at 40 years. The estimated rates were based on a meta-analysis of recent population-based studies in the United States, Australia, and Europe. These rates were applied to 2000 US Census data and to projected US population figures for 2020 to estimate the number of the US population with drusen and AMD. RESULTS: The overall prevalence of neovascular AMD and/or geographic atrophy in the US population 40 years and older is estimated to be 1.47% (95% confidence interval, 1.38%-1.55%), with 1.75 million citizens having AMD. The prevalence of AMD increased dramatically with age, with more than 15% of the white women older than 80 years having neovascular AMD and/or geographic atrophy. More than 7 million individuals had drusen measuring 125 microm or larger and were, therefore, at substantial risk of developing AMD. Owing to the rapidly aging population, the number of persons having AMD will increase by 50% to 2.95 million in 2020. Age-related macular degeneration was far more prevalent among white than among black persons. CONCLUSION: Age-related macular degeneration affects more than 1.75 million individuals in the United States. Owing to the rapid aging of the US population, this number will increase to almost 3 million by 2020.

Adult↗
PubMed2004

Intraocular pressure asymmetry and undiagnosed open-angle glaucoma in an older population.

PURPOSE: To quantify prevalence of asymmetric intraocular pressure (IOP) and assess associations with undiagnosed open-angle glaucoma. DESIGN: Population-based cross-sectional study. METHODS: Participants underwent applanation tonometry. Intraocular pressure asymmetry was defined for differences > or = 3 mm Hg; open-angle glaucoma was diagnosed if glaucomatous optic disk and field changes were congruous. Analyses excluded subjects using glaucoma medication, known glaucoma, pseudoexfoliation, and cataract surgery. RESULTS: Intraocular pressure asymmetry was present in 5.1% of subjects and was greater for patients older than 70 years (6.2%). Of subjects with maximum IOP > 21 mm Hg, IOP asymmetry was present in 41.1%. Undiagnosed open-angle glaucoma was more frequent among subjects with (4.8%) than without (1.2%) IOP asymmetry. This relationship remained significant for maximum IOP < or = 21 mm Hg. CONCLUSIONS: Intraocular pressure asymmetry may be a useful sign of undiagnosed glaucoma in subjects without elevated IOP.

Aged↗
PubMed2004

Does refractive error influence the association of blood pressure and retinal vessel diameters? The Blue Mountains Eye Study.

PURPOSE: To determine if refractive errors influence the association of blood pressure and retinal vessel diameters. DESIGN: Population-based, cross-sectional study. METHODS: Retinal photographs from the right eyes of participants (n = 3,654, aged 49+ years) in the Blue Mountains Eye Study taken during baseline examinations (1992 to 1994) were digitized. The diameter of all retinal vessels located half to one disk diameter from the disk margin was measured using a computer-assisted imaging program. These measurements were combined to provide the average diameters of retinal arterioles and venules of that eye, and the ratio of their diameters, the arteriole-to-venule ratio (AVR). The association of blood pressure and retinal vessel diameters was analyzed before and after correction for refraction using the Bengtsson formula. RESULTS: Before correction, each 10-mm Hg increase in mean arterial blood pressure was associated with a 3.7-microm (95% confidence interval [CI], 3.2-4.3) decrease in arteriolar diameter and a 0.9-microm (95% CI, 0.3-0.9) decrease in venular diameter. After correction for refraction, each 1-mm Hg increase in mean arterial blood pressure was associated with a 3.7-microm (95% CI, 3.2-4.2) decrease in arteriolar diameter and a 0.8-microm (95% CI, 0.3-0.9) decrease in venular diameter. Refraction was not associated with the AVR and had no effect on the association of blood pressure and AVR. CONCLUSION: Refraction had no appreciable effect on the association of blood pressure and retinal vessel diameters or on the AVR. Correction for refraction is important for quantifying absolute retinal vessel caliber, but may not be particularly important in epidemiologic studies investigating the association of generalized retinal arteriolar narrowing and hypertension.

Aged↗
PubMed2004

Visibility of lamina cribrosa pores and open-angle glaucoma.

PURPOSE: To determine prevalence and associations of visible lamina cribrosa pores in an older population and assess whether this feature is associated with open-angle glaucoma (OAG). DESIGN: Case-control study nested within a large, population-based cross-sectional study. METHODS: The Blue Mountains Eye Study examined 3654 persons (82.4% of permanent residents of a defined area) aged over 48 years. Stereo optic disk photographs were taken and graded reliably in a masked fashion. RESULTS: Lamina pore visibility was associated with larger vertical cup-disk ratio and optic disk diameter, hyperopic refraction, and male gender. Pores were slightly less visible with increasing age. They were visible in 70.8% of subjects with open-angle glaucoma but in only 29.3% of normals. This strong association disappeared after adjusting for other variables. CONCLUSION: Lamina cribrosa pores are commonly visible in glaucoma subjects and less commonly in normals. This association, however, is almost entirely because of an increased visibility associated with larger vertical cup-disk ratio and optic disk size.

Aged↗
PubMed2004

MELAS A3243G mitochondrial DNA mutation and age related maculopathy.

PURPOSE: To determine whether mitochondrial DNA mutations play a role in the development of age related maculopathy (ARM). DESIGN: Case report. METHODS: Hair follicles were collected from 3557 persons aged 49 years or older during the Blue Mountains Eye Study. General health measures were assessed and a detailed eye examination was performed, including stereo retinal photography of the macula, and other retinal fields. ARM was graded according to international classification. Polymerase chain reaction and restriction fragment length polymorphism analysis was performed to detect the MELAS A3243G mutation in 570 subjects identified to have signs of Early or Late ARM, as well as in age- and gender-matched controls. RESULTS: Only one participant with Early ARM, mild hearing loss, hypertension, ischemic heart disease, and asthma was found to have the MELAS A3243G mutation. CONCLUSIONS: The MELAS A3243G mutation appears to be a very rare cause of typical ARM in the general population.

DNA, Mitochondrial↗
PubMed2004

Does hormone replacement therapy influence retinal microvascular caliber?

Previous population-based data suggest that retinal arteriolar diameter is wider in women than in men. Estrogen exposures could account for this difference. To evaluate the effects of HRT on small blood vessels, we assessed the relationship between use of hormone replacement therapy (HRT) and retinal microvascular diameter in older women in the Blue Mountains Eye Study baseline population (n = 1993, age >/= 49 years). Information on HRT use was recorded by trained interviewers. A computer-assisted program measured retinal vessel diameters from digitized photographs. Average arteriolar diameter was calculated as the central retinal arteriolar equivalent (CRAE); the lowest quintile of CRAE was considered generalized arteriolar narrowing. Of the 1897 women with complete data, 79 (4%) were premenopausal and 315 (17%), 224 (12%), and 1279 (67%) were current, past, and never HRT users, respectively. Among women aged < 65 years, multivariate-adjusted mean CRAE for the four groups was 196, 198, 201, and 200 microm (P < 0.0001), respectively. Among postmenopausal women >/= 65 years, multivariate-adjusted mean CRAE was 187, 188, 191 microm (P < 0.0001), respectively, for current, past, and never users. Current HRT users were 40% more likely than never users to have generalized arteriolar narrowing (95% confidence interval 1.0-2.1). It appears that the use of HRT in older women may not have any long-term vasodilatory effects on retinal arterioles. These data do not support our hypothesis that exogenous estrogen exposures account for observed wider retinal arteriolar diameters in women.

Aged↗