PubMed Health⌕ Search

Biomedical subjects

Anthony J Adams

Publications and source records attributed to Anthony J Adams.

At least 19 recordsLinked to original sources
PubMed2006

A multifocal electroretinogram model predicting the development of diabetic retinopathy.

The prevalence of diabetes has been accelerating at an alarming rate in the last decade; some describe it as an epidemic. Diabetic eye complications are the leading cause of blindness in adults aged 25-74 in the United States. Early diagnosis and development of effective preventatives and treatments of diabetic retinopathy are essential to save sight. We describe efforts to establish functional indicators of retinal health and predictors of diabetic retinopathy. These indicators and predictors will be needed as markers of the efficacy of new therapies. Clinical trials aimed at either prevention or early treatments will rely heavily on the discovery of sensitive methods to identify patients and retinal locations at risk, as well as to evaluate treatment effects. We report on recent success in revealing local functional changes of the retina with the multifocal electroretinogram (mfERG). This objective measure allows the simultaneous recording of responses from over 100 small retinal patches across the central 45 degrees field. We describe the sensitivity of mfERG implicit time measurement for revealing functional alterations of the retina in diabetes, the local correspondence between functional (mfERG) and structural (vascular) abnormalities in eyes with early nonproliferative retinopathy, and longitudinal studies to formulate models to predict the retinal sites of future retinopathic signs. A multivariate model including mfERG implicit time delays and 'person' risk factors achieved 86% sensitivity and 84% specificity for prediction of new retinopathy development over one year at specific locations in eyes with some retinopathy at baseline. A preliminary test of the model yielded very positive results. This model appears to be the first to predict, quantitatively, the retinal locations of new nonproliferative diabetic retinopathy development over a one-year period. In a separate study, the predictive power of a model was assessed over one- and two-year follow-ups. This permitted successful prediction of new retinopathy development in eyes with and without retinopathy at baseline. Finally, we briefly describe our current research efforts to (a) locally predict future sight-threatening diabetic macular edema, (b) investigate local retinal function change in adolescent patients with diabetes, and (c) better understand the physiological bases of the mfERG delays. The ability to predict the retinal locations of future retinopathy based on mfERG implicit time provides clinicians a powerful tool to screen, follow-up, and even consider early prophylactic treatment of the retinal tissue in diabetic patients. It also aids identification of 'at risk' populations for clinical trials of candidate therapies, which may greatly reduce their cost by decreasing the size of the needed sample and the duration of the trial.

Diabetic Retinopathy↗
PubMed2006

The new visual optics.

Explore the source record for details and available documents.

Education, Medical, Continuing↗
PubMed2004

Multifocal electroretinogram and short-wavelength automated perimetry measures in diabetic eyes with little or no retinopathy.

OBJECTIVE: To compare severity and locations of abnormalities detected by the multifocal electroretinogram (mfERG) and short-wavelength automated perimetry (SWAP) in diabetic eyes with early or no retinopathy. METHODS: One eye from each of 22 patients with diabetes mellitus who had early retinopathy and 18 patients with diabetes mellitus who had no retinopathy were tested on mfERG and SWAP. The mfERG implicit times were interpolated based on SWAP stimulus locations and compared with normative values obtained from 30 age-similar control subjects. The SWAP total threshold deviations were analyzed using an age-based control data set from 255 healthy subjects. The z scores of both measures were derived to allow measurement comparisons. RESULTS: Most responses for the 2 measurements were subnormal in both groups with diabetes mellitus. The 2 measurements showed a similar number of significant abnormalities (z score >/=2), about 40% and 20% of responses for diabetic patients with retinopathy and diabetic patients with no retinopathy, respectively. Local mfERG and SWAP results showed some spatial agreement for subjects with retinopathy (r = -0.38, P<.001) but not for those with no retinopathy. CONCLUSIONS: Both mfERG and SWAP are sensitive measurements of diabetic dysfunction, even prior to retinopathy. The lack of spatial correspondence between mfERG and SWAP abnormalities in diabetic patients with no retinopathy reflects overlapping, but different, retinal anomalies in early diabetic eye disease.

Adult↗
PubMed2004

Comparison of mfERG waveform components and implicit time measurement techniques for detecting functional change in early diabetic eye disease.

This study first compares two methods for measuring first order multifocal electroretinogram (mfERG) implicit time abnormalities in eyes with early diabetic retinopathy. Two analysis methods are used: template stretching (multiplicative scaling) of an 80 msec response epoch and template sliding (cross-correlation or additive scaling) of portions of responses containing the major waveform features. The study also compares the relative sensitivities of N1, P1 and N2 implicit time assessed by cross-correlation. The nature of the change in the mfERG waveform associated with diabetes is also assessed. MfERGs were recorded from 15 eyes of 15 individuals with diabetes and early non-proliferative retinopathy and 20 eyes of 20 healthy control subjects of similar age. Implicit time determined by template stretching is more frequently abnormal in the eyes of the diabetic subjects than the implicit time of any of the components assessed by template sliding. This is attributable to the lower variability of the template stretching implicit time measure in normals. Of the components, P1 is most often abnormal in the eyes of individuals with diabetes. Responses recorded from retinal areas with retinopathic signs are more often abnormal than those from other areas. Later components of the response are not delayed more than earlier ones. We conclude that template stretching is a sensitive measurement technique, but that it does not fully capture the effect of diabetes on the first order mfERG well.

Adult↗
PubMed2004

Ian L Bailey.

Explore the source record for details and available documents.

Australia↗
PubMed2004

Retinal function in normal and diabetic eyes mapped with the slow flash multifocal electroretinogram.

PURPOSE: It has been suggested that late components of the standard multifocal electroretinogram (mfERG) are preferentially affected by diabetes mellitus. The slow-flash (sf-)mfERG stimulates with flashes separated by dark periods, facilitating interpretation of late first-order response components compared with standard multifocal stimulation. Retinal function and response component changes were examined using the sf-mfERG in diabetic subjects with and without diabetic retinopathy. METHODS: Eighteen control subjects, 12 diabetic patients without retinopathy and 17 diabetic patients with nonproliferative diabetic retinopathy (NPDR), were tested monocularly. A total of 103 areas of the central 45 degrees were stimulated by pseudorandom 100-cd/m2 flashes separated by at least 53.3 ms. Major components and the amplitude of the first-order sf-mfERGs were examined. Each subject's N1, P1, and N2 implicit times (ITs) and scalar product amplitudes (SPs) were measured at all 103 retinal locations and converted into z-scores based on the control values. Abnormalities were defined as z-scores greater than 2.33 (P < 0.01). RESULTS: Local functional abnormalities were found in both the diabetic patients with NPDR and in those without retinal disease. In both groups of diabetic patients, most abnormalities occurred more frequently in the inferior retina. Later components (P1 and N2) of the local sf-mfERGs were not preferentially affected by diabetes. The local SP and P1 IT measures distinguished the subject groups better than N1 IT and N2 IT. CONCLUSIONS: Local functional retinal abnormalities in diabetic persons with or without NPDR can be detected and mapped by the sf-mfERG. Diabetes and NPDR do not, however, preferentially affect the late P1 and N2 response components.

Diabetes Mellitus, Type 1↗
PubMed2004

Multifocal electroretinogram delays predict sites of subsequent diabetic retinopathy.

PURPOSE: To examine the potential of abnormal mfERGs to predict the development of diabetic retinopathy at corresponding retinal locations 1 year later. METHODS: One eye of 11 diabetic patients with nonproliferative diabetic retinopathy (NPDR) and 11 diabetic patients without retinopathy were retested 12 months after initial testing. At each time, mfERGs were recorded from 103 retinal locations, and fundus photographs were taken within 1 month of each recording. Local mfERG implicit times were measured and their z-scores were calculated based on results obtained from 20 age-matched control subjects. mfERG abnormalities were defined as z-scores of 2 or more for implicit time and z-scores of -2 or less for amplitude (P < or = 0.023). mfERG z-scores were mapped onto fundus photographs, and the relationship between baseline abnormal z-scores and new retinopathy at follow-up was examined. RESULTS: New retinopathy developed in 7 of the eyes with NPDR after 1 year. In these eyes, 70% of the mfERGs in areas of new retinopathy had abnormal implicit times at baseline. In contrast, only 24% of the responses in regions that remained retinopathy free were abnormal at baseline. Relative risk of development of new retinopathy over 1 year in the areas with abnormal baseline mfERG implicit times was approximately 21 times greater than that in the areas with normal baseline mfERGs (odds ratio = 31.4; P < 0.001). Eyes without initial retinopathy did not develop new retinopathy within the study period, although 4 of these 11 eyes had abnormal implicit times at baseline. mfERG implicit times tended to be more delayed at follow-up than at baseline in NPDR eyes, but not in eyes without retinopathy and control eyes. mfERG amplitudes had no predictive power. CONCLUSIONS: Localized functional abnormalities of the retina reflected by mfERG delays often precede the onset of new structural signs of diabetic retinopathy. Those functional abnormalities predict the local sites of new retinopathy observed 1 year later.

Adult↗
PubMed2004

Local multifocal oscillatory potential abnormalities in diabetes and early diabetic retinopathy.

PURPOSE: To study retinal dysfunction in diabetes and early nonproliferative diabetic retinopathy (NPDR) using a new method to analyze local multifocal electroretinogram oscillatory potentials (mfOPs). METHODS: One eye of each of 26 normal subjects, 16 diabetic subjects without retinopathy (NoR), and 16 diabetic subjects with early NPDR was examined. Slow-flash multifocal electroretinograms (sf-mfERGs) were recorded from the central 45 degrees, and stereo fundus photographs of the diabetic eyes were taken. The first-order (K1), induced first-order (K1i), and second-order (K2) response components were extracted from each retinal location, and K1i and K2 were added to create Ks2. Responses from 35 contiguous areas were digitally filtered 90 to 225 Hz to isolate the mfOPs. The signal-to-noise ratio (SNR) of the mfOPs was calculated, and abnormality was defined as SNR below the fifth percentile of the normal subjects. RESULTS: Combining the K1i and K2 components to form Ks2 before isolation of the mfOPs by digital filtering increased the SNR. Mean Ks2 and K1 mfOP SNRs were abnormal in 25% and 19% of the NoR eyes, respectively, and both were abnormal in 62% of the NPDR eyes. The retinal distributions of the local Ks2 and K1 mfOP abnormalities overlapped, but they differed. Furthermore, local Ks2 mfOP abnormalities were preferentially associated with retinal sites containing NPDR but K1 mfOP abnormalities were not. CONCLUSIONS: The cells that contribute to the generation of local mfOPs are affected by diabetes and, to a greater degree, by early NPDR. The results suggest that fast adaptive mechanisms influencing the mfOPs are most abnormal at retinal sites containing NPDR.

Adult↗
PubMed2004

Formulation and evaluation of a predictive model to identify the sites of future diabetic retinopathy.

PURPOSE: To formulate and test a model to predict the development of local patches of nonproliferative diabetic retinopathy (NPDR), based on multifocal electroretinogram (mfERG) implicit times and candidate diabetic risk factors. METHODS: mfERGs and fundus photographs were obtained from 28 eyes of 28 diabetic patients during an initial and 12-month follow-up examination. mfERG implicit times were derived at 103 locations using a template-stretching method, and a z-score was calculated in comparison with 20 age-matched normal subjects. Thirty-five nonoverlapping retinal zones were constructed by grouping two to three adjacent stimulated locations, and each zone was assigned the maximum z-score within it. Zones containing initial retinopathy were excluded from further analysis. The probability that new retinopathy would develop in the remaining zones by the follow-up examination was modeled based on the mfERG implicit time z-score for the zone and other candidate diabetic risk factors determined during the initial visit. Data collected from four previously untested diabetic subjects and the other eye of eight previous subjects during their second year follow-up were used to test the predictive model. RESULTS: After 1 year, new retinopathy developed in 11 of the 12 NPDR eyes and 1 of the 16 eyes without initial retinopathy. After accounting for the correlation among zones within each eye, a predictive model was formulated with the variables mfERG implicit time, duration of diabetes, presence of retinopathy (NPDR or no retinopathy), and blood glucose level at initial visit. The area under the receiver operating characteristic (ROC) curve of this multivariate model is 0.90 (P <0.001). The predictive model has an expected sensitivity of 86% and a specificity of 84%, which was verified by the test data. CONCLUSIONS: The development of diabetic retinopathy over a 1-year period can be well predicted by a multivariate model. The inclusion of local mfERG implicit times allowed the model to identify the specific sites of future retinopathy.

Adult↗