Visual Field Testing
At Peel Vision, we use the latest generation Zeiss Humphrey Visual Field Analyzer, the 750i HFA-II Analyzer. Considered the gold standard in visual field measurement, it has multiple advanced features that allow for the most accurate diagnosis and management of glaucoma. In addition, we also have the state-of-the-art Forum Workplace software, which performs advanced analysis and collation of results between our Zeiss OCT scanner and Visual Field Analyser, allowing the simultaneous viewing of structural and functional changes in the optic nerve in glaucoma.
What is Visual Field testing? (VFT)
VFT is an examination that generally used to detect any significant loss of peripheral vision, which can occur in a variety of eye and brain diseases, including glaucoma, optic neuropathy, stroke and other neurological conditions.
Most patients are not aware of any peripheral vision loss until it is very advanced. It is also difficult to detect early visual field changes with clinical or manual examination alone. Our peripheral vision is very important for many activities of daily living and for safe mobilization around our environment. A certain level of peripheral vision is required to meet Australian driving standards.
The Humphrey Visual Field test is a specialized automated procedure used to perform Perimetry, in which the entire area of peripheral vision is mapped out whilst the eye is focused on a central target. During this test, lights of varying intensity appear in different parts of the visual field while the patient’s eye is focused on a central spot. The patient indicates whether they see the light by pushing a button. The accuracy of the patient’s perception of these lights is recorded and charted by a computer, which analyses and compares their results to a normative database of other patients of the same age and ethnicity, in order to determine if their results are normal or abnormal.
The Humphrey Visual Field Analyzer has a very high sensitivity and specificity for detecting abnormal visual fields, as well as monitoring early changes in the field over time. Advanced software is used to chart progression of changes over time in any given patient.
How is Visual Field testing performed?
VFT with the Humphrey Analyzer is a safe, fast and non-invasive test performed in our clinic, usually by our Ophthalmic Assistants. The results are then analysed and interpreted by Dr Then.
Patients are seated comfortably in front of the machine, which comprises a small concave lighted dome. Their chin is placed in the machine on an electronically-adjustable chin rest, and each eye is tested separately (the eye not being tested is covered). A corrective lens is placed in front of the tested eye to adjust for any short-sightedness or long-sightedness in the patient. The patient is asked to maintain their focus on a lighted target in the center of the dome. A hand-held remote control with a button is placed in their hands, with instructions to press the button when they perceive a light in their peripheral vision. A computer then projects lights on the inside of the dome in various patterns, and the patient proceeds with the test. The computer will then map and analyse the visual field results of each eye.
Each eye test usually takes about 8-10 mins to perform. The test can be initially quite challenging to perform as it requires constant focus and concentration. Our experienced Assistant will guide and assist each patient throughout the test, to ensure the most accurate results are obtained.
What is Visual Field testing used for?
Most commonly, VFT is used for:
Glaucoma is a chronic condition in which the optic nerve is progressively damaged by high eye pressures. If untreated, it can result in increasing loss of peripheral vision over time. VFT is therefore useful at the time of diagnosis to see if any peripheral vision has already been lost prior to commencing treatment. Even after glaucoma treatment has been commenced, visual fields are performed every 6-12 months to ensure that the peripheral vision is not deteriorating despite treatment. If so, then treatment needs to be changed or escalated.
Many diseases can affect the optic nerve, which is the vital structure that transmits visual signals from the retina at the back of the eye toward the visual center in the brain. Any disease that affects optic nerve function is called an optic neuropathy. Inflammation (optic neuritis) or ischemia (ischemic optic neuropathy) are common types of optic neuropathy, and can result in significant loss of central and peripheral vision. VFT is important in assessing the degree of peripheral vision loss caused by these diseases.
A wide variety of peripheral retinal diseases can result in loss of peripheral vision. In particular, hereditary retinal degenerative diseases like Retinitis Pigmentosa, can result in significant peripheral vision constriction, along with night-blindess and color vision abnormalities, all of which can impact on driving and career choices for younger patients.
Strokes (or Cerebrovascular events) are usually due to a sudden loss of circulation to vital areas of the brain. Strokes can generally be ischemic (blockage of circulation) or hemorrhagic (bleeding of circulation, but both result in significant damage to brain function. The visual pathway of the brain extends from the eye to the occipital cortex at the back of the brain, and stroke involving any part of this visual pathway can result in loss of specific areas of the peripheral visual field. Often specific patterns of field loss will help pinpoint where in the brain the stroke has occurred.
5.Toxic reactions from various medications
VFT is being increasingly used to help detect and monitor for side effects in the eye from various long-term medications. Plaquenil, often used for autoimmune conditions like rheumatoid arthritis and lupus, can affect the macula, resulting in central vision loss. Regular eye tests are recommended for any patient on Plaquenil. Testing the central 10 degrees of visual field with the Humphrey Analyzer is a very useful way of detecting early vision loss from Plaquenil toxicity.
When peripheral vision is reduced by certain diseases of the eye or brain, VFT can be used to assess if the patient meets safe driving standards. Certain specific criteria for central and peripheral vision need to be met for an unrestricted driving license to be maintained. The presence of peripheral vision deficits does not necessarily mean a patient cannot drive, but may require a conditional license.