Biomedical subjects

David Garway-Heath

Publications and source records attributed to David Garway-Heath.

4 recordsLinked to original sources

PubMed2006

Evaluation of Goldmann applanation tonometry using a nonlinear finite element ocular model.

Goldmann applanation tonometry (GAT) is the internationally accepted standard for intra-ocular pressure (IOP) measurement, which is important for the diagnosis of glaucoma. The technique does not consider the effect of the natural variation in the corneal thickness, curvature and material properties. As these parameters affect the structural resistance of the cornea, their variation is expected to lead to inaccuracies in IOP determination. Numerical Analysis based on the finite element method has been used to simulate the loading conditions experienced in GAT and hence assess the effect of variation in corneal parameters on GAT IOP measurements. The analysis is highly nonlinear and considers the hyper-elastic J-shaped stress-strain properties of corneal tissue observed in laboratory tests. The results reveal a clear association between both the corneal thickness and material properties, and the measured IOP. Corneal curvature has a considerably lower effect. Similar trends have been found from analysis of clinical data involving 532 patients referred to the Glaucoma Unit at Moorfields Hospital, and from earlier mathematical analyses. Nonlinear modelling is shown to trace the behaviour of the cornea under both IOP and tonometric pressure, and to be able to provide additional, and potentially useful, information on the distribution of stress, strain, contact pressure and gap closure.

Biomedical Engineering↗

PubMed2006

Diagnosing glaucoma progression: current practice and promising technologies.

PURPOSE OF REVIEW: An update on recent work is provided that has broadened our understanding of the evaluation of visual function and structure, and their use in evaluating glaucoma progression. RECENT FINDINGS: The challenge of determining visual-field progression and the implications of long-term fluctuation are reviewed and data to support the magnitude of the fluctuation are cited. The use of confirmatory testing can limit the over diagnosis of glaucoma progression. Focusing visual-field testing on the locations of present scotomas or using frequency doubling technology may provide new approaches to assessing visual function. New standardized techniques to interpret visual fields, including neural networks, unsupervised machine learning and pointwise linear regression, may provide more quantitative means for visual-field interpretation. These techniques, along with structural evaluation of the optic nerve and nerve fiber layer, are essential in glaucoma management. Optic-nerve-head photography is still a mainstay in evaluating glaucoma progression, although many technologies including scanning laser tomography, scanning laser polarimetry and optical coherence tomography offer more quantitative means to follow structural change. These modalities, in different ways, show promise in providing additional information regarding the stability of glaucoma. SUMMARY: Identifying the functional visual component as well as structural changes is essential in evaluating glaucoma progression. New techniques of testing and evaluating visual fields, the optic-nerve head, and the retinal nerve fiber layer offer exciting opportunities to more accurately identify glaucoma progression, and are likely to become more central as imaging devices and software support develop further.

Diagnostic Techniques, Ophthalmological↗

PubMed2005

A spatio-temporal Bayesian network classifier for understanding visual field deterioration.

OBJECTIVE: Progressive loss of the field of vision is characteristic of a number of eye diseases such as glaucoma which is a leading cause of irreversible blindness in the world. Recently, there has been an explosion in the amount of data being stored on patients who suffer from visual deterioration including field test data, retinal image data and patient demographic data. However, there has been relatively little work in modelling the spatial and temporal relationships common to such data. In this paper we introduce a novel method for classifying visual field (VF) data that explicitly models these spatial and temporal relationships. METHODOLOGY: We carry out an analysis of our proposed spatio-temporal Bayesian classifier and compare it to a number of classifiers from the machine learning and statistical communities. These are all tested on two datasets of VF and clinical data. We investigate the receiver operating characteristics curves, the resulting network structures and also make use of existing anatomical knowledge of the eye in order to validate the discovered models. RESULTS: Results are very encouraging showing that our classifiers are comparable to existing statistical models whilst also facilitating the understanding of underlying spatial and temporal relationships within VF data. The results reveal the potential of using such models for knowledge discovery within ophthalmic databases, such as networks reflecting the 'nasal step', an early indicator of the onset of glaucoma. CONCLUSION: The results outlined in this paper pave the way for a substantial program of study involving many other spatial and temporal datasets, including retinal image and clinical data.

Algorithms↗

PubMed2003

Results of the betaxolol versus placebo treatment trial in ocular hypertension.

PURPOSE: To determine whether treatment with betaxolol can delay or prevent the conversion from ocular hypertension to early glaucoma on the basis of visual field criteria, by means of a prospective, randomised, placebo-controlled trial. METHODS: Three hundred and fifty-six ocular hypertensives were randomized to treatment with either betaxolol drops or placebo drops during the period 1992-1996. Each patient was followed prospectively with 4-monthly visits. Examination at each visit included visual field testing, intra-ocular pressure (IOP) measurement and optic disc imaging. Conversion to early glaucoma was defined on the basis of visual field change by AGIS criteria. An intent-to-treat analysis compared visual field conversion after 3 years in the treatment and placebo arms. Normal visual field survival analysis was also performed. The IOP characteristics of the two treatment groups were compared. RESULTS: Two hundred and fifty-five patients completed the study, which ended in 1998, with a range of follow-up of 2-6 years. Sixteen (13.2%) of 121 patients in the placebo group converted to glaucoma, compared with 12 (9.0%) of 134 patients in the betaxolol group. The intent-to-treat analysis demonstrated no evidence of any difference in conversion rates between the betaxolol and placebo groups after 3 years. Visual field survival analysis demonstrated no significant difference between the betaxolol and placebo groups. The betaxolol-treated group had significantly lower post-treatment IOP values. Converters had significantly higher pre- and post-treatment IOP values than non-converters. CONCLUSIONS: Betaxolol significantly lowered the IOP level compared with placebo. Conversion to glaucoma was found to be related to both the baseline and post-treatment IOP levels. However the intent-to-treat analysis did not demonstrate a statistically significant reduction in the conversion rate in the betaxolol-treated group.

Adrenergic beta-Antagonists↗