Overview
Glaucoma is the name for a group of conditions in which the cells in the light-sensitive layer of the eye (the retina) that make up the optic nerve die off. The optic nerve is the only route for information about vision to get from eye to brain. When these cells die, patches of reduced vision, develop slowly, sometimes unnoticed until quite late.
Testing of the field of vision remains an important part of detecting glaucoma, but there is only a weak relationship between how well people can spot the flashes of light used during the test and the number of optic nerve cells that are left. This makes it hard to detect glaucoma early on and hard to monitor how it develops.
The team has results that suggest that a particular type of alternative test could be better for giving a good estimate of remaining cells.
In this project, the team is investigating the potential of this type of test with people with glaucoma and normal vision. It could then be possible to design a patient-friendly test for use in the clinic to provide more accurate and repeatable measures of damage to the retina. In turn, this should lead to better treatment programmes and make it easier to evaluate new therapies.
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Publications
- Shah, N. et al. Visual acuity loss in patients with age-related macular degeneration measured using a novel high-pass letter chart. Br J Ophthalmol (2016).
- Shah, N., Dakin, S. C., Whitaker, H. L. & Anderson, R. S. Effect of scoring and termination rules on test-retest variability of a novel high-pass letter acuity chart. Invest. Ophthalmol. Vis. Sci. 55, 1386–1392 (2014).
- Shah, N., Dakin, S. C. & Anderson, R. S. Effect of optical defocus on detection and recognition of vanishing optotype letters in the fovea and periphery. Invest. Ophthalmol. Vis. Sci. 53, 7063–7070 (2012).
- Shah, N., Dakin, S. C., Redmond, T. & Anderson, R. S. Vanishing Optotype acuity: repeatability and effect of the number of alternatives. Ophthalmic and Physiological Optics 31, 17–22 (2011).
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Research update
In this project the team has discovered that their new test targets are viewed differently in the centre of the field of vision (which is affected in age-related macular degeneration or AMD) compared the peripheral vision, which is more affected in glaucoma.
They have developed a new test, based on their results, that is better than standard tests at picking up early AMD.
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Scientific summary
Non-invasive measurement of functional ganglion cell density in glaucoma using high-pass filtered letter targets
Measurements of grating resolution acuity are closely related to the density of retinal ganglion cells in peripheral vision and display a strong relationship to retinal structure in diseases like glaucoma. However, using gratings, the test turns out to be time-consuming, variable and poorly understood by clinical patients. In preliminary experiments using pseudo high-pass filtered (‘Vanishing Optotype’) letters, where the mean luminance of the target is the same as the background, the research team has found that peripheral (but not foveal) resolution may also be limited by the density of the retinal ganglion cells, depending on the targets chosen. The added advantage of these targets is that they are better understood by clinical patients and display better repeatability and would permit a faster test strategy with lower variability and a shorter testing time.
Professor Anderson and PhD student Nilpa Shah wish to further examine detection and resolution acuity for high-pass letters in central and peripheral vision in normal participants to determine which targets and locations display ganglion cell density-related resolution, and how optical quality affects detection and resolution performance (to potentially separate neural and optical losses of vision in different conditions). These experiments should result in a perimetry type test that is easy to perform, less variable and can make reliable non-invasive measurements of localised ganglion cell density in clinical patients.