Combining traditional diagnostic aids such as visual field analysis and optic disc photography with newer imaging technologies allows both structural features and risk factors to be considered in the diagnostic and therapeutic decision process. It is currently recommended that methods for detecting abnormality and documenting optic nerve structure should be part of routine clinical management of glaucoma.
Figure: The Glaucoma Continuum View large
Visual field testing (perimetry) is used to test peripheral vision and is now typically an automated process. Reduction of peripheral vision is associated with onset of moderate to severe glaucoma.
In standard automated perimetry, patients are asked to press a button when they see a point of light appear. These points appear in an automated sequence within the analyzer. The responses are analyzed statistically and compared with a database of statistically normal responses, with any deviations from normal being marked as black squares.
Figure: Outputs of automated perimetry (normal eye, left; glaucomatous eye, right)
There are many different visual field analysis tools on the market, including:
Humphrey Visual Field Analyzer (Carl Zeiss Meditec)
Octopus Visual Field Analyzer (Cephalon A/S)
Shortwave Automated Perimetry (SWAP) is a version of automated perimetry and is also known as blue-yellow perimetry. It uses points of blue light on a yellow background to study one of three neural pathways by which messages are sent from the retina to the brain. Several studies have demonstrated that SWAP may have value in identifying glaucomatous visual field defects. The output of a SWAP analysis is very similar to that of a white-light automated perimeter.
Figure: Output from a SWAP analysis (statistically normal eye)
Frequency-Doubling Perimetry (FDT) tests the function of another of the neural pathways from retina to brain, the magnocellular (M-cell) pathway. FDT produces an output which can be seen below.
Figure: Output of a typical FDT (in this case, demonstrating a pronounced defect)
Tonometry is used for testing IOP. Several different types of tonometers are in common use, but all work by causing an indentation in the surface of the eye, which is measured to establish the IOP.
Gonioscopy is performed to check the drainage angle of the eye, and is very important in differentiating between the main types of glaucoma: Primary Open Angle Glaucoma and Angle Closure Glaucoma.
PHOTOGRAPHY
Fundus photographs are pictures of the optic disc. Eye care professionals use these to look for changes in cup/disc ratio developing over time. They are taken for future reference and comparison.