Tests for Glaucoma at the COS

1. Visual Field Assessment: The Humphrey Field Analyzer II-HFA II

The Humphrey Field Analyzer II-i series is a wheelchair accessible, computerized perimeter used to examine the patient's visual field. The Humphrey Visual Field Analyser has become an industry standard machine for the diagnosis and monitoring of glaucoma and other ocular and neurological diseases, and allows us to look for defects in the sensitivity of the eye. For example, the central vision of the eye may be good, but the periphery of the visual field may be severely damaged. It is important to detect change in the visual field in order to maintain the function of the eye. As a good eye is able to compensate for poor vision in the other eye, the effects of visual field damage are often unnoticed by the patient until there is significant damage to the vision. The Humphrey visual field test is designed to pick up the earliest changes to the function of the eye.

The test works by displaying flashes of light around a bowl with a fixed background light level. The machine aims to find the dimmest light that the eye is able to detect at various locations in the visual field. The machine tests the patient's response to a visual stimulus and may be set to run one of many optimised programs. This test is based on the patient’s responses. Some visual field tests can be unreliable and may need to be repeated.


2. Intra ocular Pressure Measurement: Goldman Applanation Tonometry

The pressure in the eye is measured using a probe which touches lightly on the front surface of the eye. Drops are placed in the eyes which cause them to become numb for several minutes while the consultant takes the readings.The pressure readings only take a couple of minutes each time.

There may be a particular time of day when the pressure increases; and so the consultant may take intraocular pressure readings throughout the day in order to identify any fluctuations.


3. Retinal Nerve Fibre Layer Thickness: The GDx Nerve Fiber Analyzer

The GDx is a sophisticated new machine used to build up a 3-dimensional image of the optic nerve fibres at the back of the eye. Glaucoma will cause damage to the nerve fibres and this method is a powerful tool for detecting health changes within them. It is estimated that up to 50% of fibres may be lost before a visual field defect is detectable.The computer can then analyse this information, providing us with detailed measurements of the amount of healthy nerve fibre at the back of the eye. The test is very easy to do as most of the work is done by the computer. The machine scans the eye with a bright red light for a couple of seconds. Several scans are taken, and the best ones are used for analysis. The test is objective, and usually takes less than 5 minutes. The equipment is fully wheelchair accessible.

The advantage of the GDx is that it may help consultants detect earlier and more sensitive, objective changes in individuals who may have glaucoma. Additionally, the GDx is able to determine if you have glaucoma prior to a person experiencing any vision loss. The pupil does not have to be dilated and the results can be obtained quickly. The test itself is non-invasive and painless.

The GDx exam offers another method by which glaucoma can be evaluated and followed. A very safe, invisible laser scans the back of the eye and acquires an image in less than one second. Screening for glaucoma offers valuable information on suspect patients.