Retinal Topography

retinal topographyHigh quality ophthalmic care depends on the accurate assessment of ocular disease. Conventional direct ophthalmoscopy is used widely and provides good two dimensional views of the retina. However, the true nature of retinal disease is apparent only in three dimensions. Scanning laser ophthalmoscopes offer a radically different view of eye disease since they provide three dimensional views of the retina. The three dimensional imaging of the retina has been facilitated by two technical developments. The first is the availability of cheap and powerful computers. The second is the production of affordable optoelectronics such as digital cameras and diode lasers. The devices use laser light rather than conventional white light to image the fundus. A low powered diode laser beam scans the retinal surface to build up an image of the retina line by line, analogous to the formation of images on a television screen.

Diagnosing and Monitoring Glaucoma Disease
The retinal tomographer is a confocal laser scanning system for acquisition and analysis of three-dimensional images of the posterior segment of the eye. The general application of the retina tomograph is the quantitative assessment of the retinal topography and the quantification of topographic changes. Examples are the description of the glaucomatous optic nerve head, the analysis of macular holes and macular edema, and the analysis of nerve fiber layer defects.

The following concentrates on the application of the retina tomograph in glaucoma management.

The goal of the topographic analysis of the optic nerve head is either a quantitative description of its current state with the goal of a classification - e.g. normal or not normal - or to compare more than one topography image in order to follow up topographic changes and to quantify progression of glaucoma.

Glaucoma is a loss of nerve fibers and subsequent loss of visual field. The nerve fiber layer carries visual signals from the retina, to the optic nerve and then on the brain. By accurately measuring the thickness of the retinal NFL thickness and comparing the results statistically to a set of known patients, matched in gender and age, to the patient, it is possible to predict which patient may be at risk to develop glaucoma. The earlier glaucoma is detected and effective and aggressive treatment is begun, the less likely the patient will be to suffer serious visual damage in the long term from glaucoma.

Perhaps the most dramatic development in glaucoma detection has been optical coherence tomography. Optical coherence tomography (OCT) is analogous to ultrasound. But rather than measuring sound, it measures the backreflection of infrared light, which is reflected differently by different tissues. OCT creates a viewable image in which interference patterns generated from the reflection of partially coherent laser light are used to construct an optical cross section of the retina.

retinal topographyThis technology also aids in detecting progressive disease in patients who have already had glaucoma diagnosed. The ability to detect structural change is an important advantage since these changes usually occur before the onset of clinically detectable visual deficits such as a reduction in visual acuity or loss of visual field. The delay between the structural and visual changes reflects the redundancy of neural components that is built into the visual system. Thus, in glaucoma, it has been estimated that up to 50% of the retinal ganglion cells at any particular location can be lost before a visual field defect is detectable using currently available clinical methods. Consequently, if we rely on tests of visual acuity or visual field, significant retinal damage may have already occurred by the time that disease is detected, leading to a poorer visual prognosis. Early detection also gives clinicians greater flexibility in managing patients. In glaucoma, quantification of the rate of optic disc cupping allows clinicians to estimate the onset of serious visual field loss, which can help when discussing the timing and possible outcomes of treatment. The other major advantage of these imaging technologies is that they require little patient interaction. This contrasts with commonly used clinical tests such as automated perimetry, which can be arduous for some elderly patients.

Cirrus™ HD-OCT – Immerse Yourself In the Image.

This new high-performance OCT instrument from Carl Zeiss Meditec offers a quantum leap forward in imaging. Featuring spectral domain technology, Cirrus HD-OCT delivers exquisite high-definition images of ocular structures, precise registration and intuitive, efficient operation.

AAO 2008 video presentations
Glaucoma Detection and Management
OCT Technology
Straight Talk on Spectral Domain OCT
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Cirrus HD-OCT Webinars

High-Definition
Murray Murray and GrovesCirrus HD-OCT realizes the superior capabilities of ZEISS optics and provides exquisite high definition images and analyses for enhanced clinical confidence.

Beautiful high definition OCT scans and LSO fundus images provide visualization of retinal structure. HD layer maps and thickness maps reveal the critical details of histology and pathology at a glance.

Efficiency
Murray Murray and GrovesAdvanced hardware and software facilitate automated alignment and high patient through-put. An elegant user interface and fast electronics mean chair time is shortened.