PURPOSE\nTo measure macular choroidal thickness in normal eyes at different points using enhanced depth imaging (EDI) optical coherence tomography (OCT) and to evaluate the association of choroidal thickness and age.\n\n\nDESIGN\nRetrospective, observational case series.\n\n\nMETHODS\nEDI OCT images were obtained in patients without significant retinal or choroidal pathologic features. The images were obtained by positioning a spectral-domain OCT device close enough to the eye to acquire an inverted image. Seven sections were obtained within a 5 x 30-degree area centered at the fovea, with 100 scans averaged for each section. The choroid was measured from the outer border of the retinal pigment epithelium to the inner scleral border at 500-microm intervals of a horizontal section from 3 mm temporal to the fovea to 3 mm nasal to the fovea. Statistical analysis was performed to evaluate variations of choroidal thickness at each location and to correlate choroidal thickness and patient age.\n\n\nRESULTS\nThe mean age of the 30 patients (54 eyes) was 50.4 years (range, 19 to 85 years), and 14 patients (46.7%) were female. The choroid was thickest underneath the fovea (mean, 287 microm; standard deviation, +/- 76 microm). Choroidal thickness decreased rapidly in the nasal direction and averaged 145 microm (+/- 57 microm) at 3 mm nasal to the fovea. Increasing age was correlated significantly with decreasing choroidal thickness at all points measured. Regression analysis suggested that the subfoveal choroidal thickness decreased by 15.6 microm for each decade of life.\n\n\nCONCLUSIONS\nChoroidal thickness seems to vary topographically within the posterior pole. The thickness of the choroid showed a negative correlation with age. The decrease in the thickness of the choroid may play a role in the pathophysiologic features of various age-related ocular conditions.

Enhanced Depth Imaging Optical Coherence Tomography of the Choroid in Normal Eyes

OBJECTIVES: To assess whether open angle glaucoma (OAG) screening meets the UK National Screening Committee criteria, to compare screening strategies with case finding, to estimate test parameters, to model estimates of cost and cost-effectiveness, and to identify areas for future research. DATA SOURCES: Major electronic databases were searched up to December 2005. REVIEW METHODS: Screening strategies were developed by wide consultation. Markov submodels were developed to represent screening strategies. Parameter estimates were determined by systematic reviews of epidemiology, economic evaluations of screening, and effectiveness (test accuracy, screening and treatment). Tailored highly sensitive electronic searches were undertaken. RESULTS: Most potential screening tests reviewed had an estimated specificity of 85% or higher. No test was clearly most accurate, with only a few, heterogeneous studies for each test. No randomised controlled trials (RCTs) of screening were identified. Based on two treatment RCTs, early treatment reduces the risk of progression. Extrapolating from this, and assuming accelerated progression with advancing disease severity, without treatment the mean time to blindness in at least one eye was approximately 23 years, compared to 35 years with treatment. Prevalence would have to be about 3-4% in 40 year olds with a screening interval of 10 years to approach cost-effectiveness. It is predicted that screening might be cost-effective in a 50-year-old cohort at a prevalence of 4% with a 10-year screening interval. General population screening at any age, thus, appears not to be cost-effective. Selective screening of groups with higher prevalence (family history, black ethnicity) might be worthwhile, although this would only cover 6% of the population. Extension to include other at-risk cohorts (e.g. myopia and diabetes) would include 37% of the general population, but the prevalence is then too low for screening to be considered cost-effective. Screening using a test with initial automated classification followed by assessment by a specialised optometrist, for test positives, was more cost-effective than initial specialised optometric assessment. The cost-effectiveness of the screening programme was highly sensitive to the perspective on costs (NHS or societal). In the base-case model, the NHS costs of visual impairment were estimated as 669 pounds. If annual societal costs were 8800 pounds, then screening might be considered cost-effective for a 40-year-old cohort with 1% OAG prevalence assuming a willingness to pay of 30,000 pounds per quality-adjusted life-year. Of lesser importance were changes to estimates of attendance for sight tests, incidence of OAG, rate of progression and utility values for each stage of OAG severity. Cost-effectiveness was not particularly sensitive to the accuracy of screening tests within the ranges observed. However, a highly specific test is required to reduce large numbers of false-positive referrals. The findings that population screening is unlikely to be cost-effective are based on an economic model whose parameter estimates have considerable uncertainty. In particular, if rate of progression and/or costs of visual impairment are higher than estimated then screening could be cost-effective. CONCLUSIONS: While population screening is not cost-effective, the targeted screening of high-risk groups may be. Procedures for identifying those at risk, for quality assuring the programme, as well as adequate service provision for those screened positive would all be needed. Glaucoma detection can be improved by increasing attendance for eye examination, and improving the performance of current testing by either refining practice or adding in a technology-based first assessment, the latter being the more cost-effective option. This has implications for any future organisational changes in community eye-care services. Further research should aim to develop and provide quality data to populate the economic model, by conducting a feasibility study of interventions to improve detection, by obtaining further data on costs of blindness, risk of progression and health outcomes, and by conducting an RCT of interventions to improve the uptake of glaucoma testing.

The clinical effectiveness and cost-effectiveness of screening for open angle glaucoma: a systematic review and economic evaluation.

Optic disc (OD) detection is an important step in developing systems for automated diagnosis of various serious ophthalmic pathologies. This paper presents a new template-based methodology for segmenting the OD from digital retinal images. This methodology uses morphological and edge detection techniques followed by the Circular Hough Transform to obtain a circular OD boundary approximation. It requires a pixel located within the OD as initial information. For this purpose, a location methodology based on a voting-type algorithm is also proposed. The algorithms were evaluated on the 1200 images of the publicly available MESSIDOR database. The location procedure succeeded in 99% of cases, taking an average computational time of 1.67 s. with a standard deviation of 0.14 s. On the other hand, the segmentation algorithm rendered an average common area overlapping between automated segmentations and true OD regions of 86%. The average computational time was 5.69 s with a standard deviation of 0.54 s. Moreover, a discussion on advantages and disadvantages of the models more generally used for OD segmentation is also presented in this paper.

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Detecting the Optic Disc Boundary in Digital Fundus Images Using Morphological, Edge Detection, and Feature Extraction Techniques

PURPOSE. To quantify the variation in primary open-angle glaucoma (OAG) prevalence with age, gender, race, year of publication, and survey methodology. METHODS. Medline, EMBASE, and PubMed were searched for studies of OAG prevalence. Studies with defined population samplings were sought. Forty-six published observational studies of OAG prevalence (103,567 participants with 2509 cases of OAG) were identified for inclusion in the systematic review and meta-analysis. Data on the number of people and the number of cases of OAG by age, race, and gender were sought for each study. Additional information was obtained regarding whether the definition of glaucoma relied on raised intraocular pressure (IOP) and whether visual field examination was performed routinely on all individuals. Bayesian meta-analysis was used to model the associations between the log odds of OAG and age, race, gender, year of publication, method of visual field testing, and effect of reliance on IOP in the definition of OAG. RESULTS. Black populations had the highest OAG prevalence at all ages, but the proportional increase in prevalence of OAG with age was highest in white populations. The odds ratio per decade increase in age was 2.05 in white populations (95% credible interval, 1.91 to 2.18), 1.61 (95% credible interval, 1.53 to 1.70) in black populations, and 1.57 (95% credible interval, 1.46 to 1.68) in Asian populations. The average estimated prevalence in those older than 70 years of age was 6% in white populations, 16% in black populations, and 3% in Asian populations. After adjusting for age, race, year of publication, and survey methods, men were 1.37 (95% credible interval, 1.22 to 1.53) times more likely than women to have OAG. The prevalence of OAG was one third lower in studies in which routine visual fields were not assessed and that used an IOP criterion in the definition of glaucoma; this effect was reduced to the null after adjustment for age, racial group, and year of publication.

Variations in primary open-angle glaucoma prevalence by age, gender, and race: a Bayesian meta-analysis.

Computer-aided diagnosis of diabetic retinopathy: A review

The purpose is to develop an automatic computerized screening system to recognize automatically the main components of the retina, an important features of background diabetic retinopathy and classify the normal, abnormal and unknown retinal image. This paper has presented 4 main methods to succeed of retinal diagnosis. Firstly, the retinal images are preprocessed via adaptive, local, contrast enhancement Secondly, the main features of a retinal image were defined as the optic disc, and blood vessels. The optic discs were located by identifying the area with the highest variation in intensity of adjacent pixels. Blood vessels were identified by means of a multilayer perceptron neural network, for which the inputs were derived from a principal component analysis of the image and edge detection of the intensity. Next, the background diabetic retinopathy features are identified. Recursive region growing segmentation algorithms were applied to detect the hard exudates. The haemorrhages and microaneurysms were recognised by detecting all feature similar to the blood vessels and removed the vessels out. Finally, all information is accumulated and diagnosed for diabetic retinopathy or a normal retina. The diabetic retinopathy screening technique has been applied to the 484 normal retina images and 283 images with diabetic retinopathy. The sensitivity and specificity for the computerized screening program to classify the images were corrected 80.21% and 70.66% respectively. The computerized screening system has been developed to classify the normal and abnormalities of retinal images. The development of getting higher performance is in progress.

Automated screening system for diabetic retinopathy

OBJECTIVE: To compare corneal thickness and endothelial morphology in patients with diabetes mellitus and age-matched normal subjects, and to determine whether the duration of diabetes mellitus, severity of diabetic retinopathy, and glycemic control are correlated with these measurements. DESIGN: Single center, case-control study. PARTICIPANTS: Sixty eyes of thirty diabetic patients and sixty eyes of thirty healthy nondiabetic subjects were studied. INTERVENTION: Corneal thickness was measured by ultrasonic pachymeter. Corneal endothelial morphology was examined with a contact specular microscope. MAIN OUTCOME MEASURES: Corneal endothelial cell density, mean,cell area, coefficient of variation, percentages of hexagonal cells, and corneal thickness were measured. RESULTS: There was statistically significant increased corneal endothelial cell density and decreased mean endothelial cell area in the diabetic patients. The diabetic corneas had an increased coefficient of variation of endothelial cell area, a decreased percentage of hexagonal endothelial cell and an increased corneal thickness compared with the control subjects, but these differences were not statistically significant. The duration of diabetes mellitus was significantly correlated with pleomorphism, polymegathism and corneal thickness. Severity of diabetic retinopathy was correlated with endothelial cell density, but these correlations were low. The corneal changes were not correlated with glycemic control. CONCLUSIONS: The diabetic corneas tended to be thicker and had more pleomorphism and polymegathism, though this was not statistically significant. Duration of diabetes mellitus correlated significantly with these corneal changes. This suggests that corneal changes should be evaluated and confirmed before intraocular surgery in chronic diabetic patients.

Corneal abnormalities in diabetes.

Feasibility study on computer-aided screening for diabetic retinopathy.

BACKGROUND Potassium iodate (KIO3) is an iodized salt used for iodine supplementation in areas endemic for goiter. KIO3 overdose in humans is rare. The authors report unusual cases of retinal toxicity from KIO3 overdose that caused acute vision loss. METHODS The clinical manifestations, toxic dosage of iodate, and ocular changes in five patients who had taken a KIO3 overdose were analyzed. Electroretinography, visual evoked potential (VEP), and fundus fluorescein angiography (FA) were performed to study retinal function and changes. RESULTS Two men and three women (age 22-65 years) ingested KIO3 solution at a concentration between 187 and 470 mg/kg body weight. Visual acuity ranged from light perception with projection to counting fingers and decreased from 2 to 12 hours after ingestion. Fundus FA showed bilateral extensive areas of retinal pigment epithelial (RPE) window defects, and electroretinography and VEP showed marked impairment of retinal function. Visual acuity improved from counting fingers to 20/80 in 3 months. CONCLUSION Potassium iodate can produce retinal toxicity that damages RPE and photoreceptor cells. The recovery of retinal function depends on the amount of chemical absorption, the regeneration of RPE, and the recovery function of photoreceptor cells.

Potassium iodate toxic retinopathy: a report of five cases.

The purposes of this study were to evaluate the accuracy of glaucoma screening tests and to assess the prevalence of glaucoma in an elderly Thai population over 60 years of age. This was a cross-sectional study. 3706 subjects were recruited from 33 communities in the vicinity of Siriraj Hospital. All received an eye examination from ophthalmologists and general practitioners including visual acuity, Schiotz tonometry and optic disc evaluation in their residential communities. Subjects who were suspected of having glaucoma were re-examined at the Glaucoma Clinic, Siriraj Hospital. They were then classified as having definite glaucoma of a specific type or as not having glaucoma. The overall prevalence of glaucoma was 6.1 per cent (128/2092). The percentages of primary open angle glaucoma, primary angle closure glaucoma, normotension glaucoma and secondary glaucoma were 47.7 per cent, 41.4 per cent, 9.4 per cent, and 1.6 per cent respectively. The sensitivity and specificity of the screening tests performed by ophthalmologists were 100 per cent and 97.2 per cent and those performed by general practitioners were 21.7 per cent and 96.5 per cent.

Apichart Singalavanija

Papers

Automated screening system for diabetic retinopathy

Corneal abnormalities in diabetes.

Feasibility study on computer-aided screening for diabetic retinopathy.

Potassium iodate toxic retinopathy: a report of five cases.

Evaluation of screening tests and prevalence of glaucoma: integrated health research program for the Thai elderly.