Service Category: DIAGNOSTICS

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VISUAL FIELD ASSESSMENT

What is a visual field test?

We normally see a wide area of the space in front of us. Without moving our eyes, we see not only what is straight ahead, but some of what is above, below, and off to either side. Most people are familiar with this as “peripheral vision.” The entire area that we see is called the visual field.

Vision is usually best right in the middle of the visual field. That is why we turn our eyes toward objects that we want to see better. The farther away from the center of our vision an object is, the less clearly we can see it. When an object moves far enough to the side, it disappears from our vision completely.

A visual field test measures two things:

  • How far up, down, left and right the eye sees without moving.
  • How sensitive the vision is in different parts of the visual field.

Why do people need a visual field test?

The visual field test can help the doctor find early signs of diseases like glaucoma that damage vision gradually. Some people with glaucoma do not notice any problems with their vision, but the visual field test shows that peripheral vision is being lost.

A visual field test can also help the doctor find out more about the part of the nervous system that allows us to see. The visual part of the nervous system includes the retina (the “film” in the camera-like eye), the optic nerve (the “wire” that carries images from the retina to the brain), and the brain itself. Problems with any part of this system can change the visual field. There are well-known patterns in the test results that help doctors recognize certain types of injury or disease. By repeating more visual field tests at regular intervals, doctors can also tell whether the patient is getting better or worse.

What happens during a visual field test?

There are several types of visual field tests, but they all have one thing in common: the patient looks straight ahead at one point and signals when an object or a light is seen somewhere off to the side.

If the patient turns the eye to look directly at the object or the light, only the very center of the visual field will be tested. The tester will explain to the patient exactly where to look so that the test is accurate.

The two most basic types of visual field tests are very simple:

  • Amsler grid: The Amsler grid is a pattern of straight lines that make perfect squares. The patient looks at a large dot in the middle of the grid and describes any areas where the lines look blurry, wavy, or broken. The Amsler grid is a quick test that measures only the middle of the visual field and provides your doctor with only a small amount of information.
  • Confrontation visual field: The term “confrontation” in this test just means that the person giving the test sits facing the patient, about 3 or 4 feet away. The tester holds his or her arms straight out to the sides. The patient looks straight ahead, and the tester moves one hand or the other inward. The patient gives a signal as soon as the hand is seen.

The confrontation visual field test measures only the outer edge of the visual field, and it is not very exact.

What kind of test does the doctor order for more detailed information?

Computerized instruments are available to perform visual field tests and calculate results. These instruments give more reproducible and accurate results because:

The head is always in the same place during the test.

The instrument has a large central “target” for the patient to look at, so the center of the visual field can be kept steady.

The instrument uses tiny spots of light to test vision, and the brightness and color of the light can be changed to measure the sensitivity of vision at each location.

The tests have been given to thousands of healthy people, so the “normal” results are fairly well known. The instrument can compare each new test to these standards.

What do the results of the visual field test mean?

A “normal” visual field test means that the patient can see about as well as anyone else does in the center and around the edges of the visual field.

A test that shows visual field loss means that vision in some areas is not as sensitive as normal. It could be just a little vision loss in a small area or all vision lost in large areas.

The amount of vision loss and the areas affected are measured by the visual field test. These results are printed out by the instrument as patterns of dots or numbers. The patterns tell the doctor a lot about how the eye and the visual field system are working. This helps your doctor decide whether you have a health problem that needs additional testing to be diagnosed or if treatment is recommended.

Why do some people need to have visual field tests many times?

Sometimes the doctor will want to repeat the visual field test right away to make sure the results are accurate. If the patient is tired, for example, the test results can be unreliable.

Your doctor might also recommend that a visual field test is taken again in a few weeks, a few months, or a year. This might be necessary to make sure that no new problems are detected. When a condition like glaucoma is found, visual field tests are performed regularly to find out how well the treatment is working.

Visual field tests are especially important in the treatment of glaucoma. These tests will tell the doctor if vision is being lost even before the patient notices. That is just one of the reasons why people who have glaucoma need to keep all their appointments with their doctor.

FLUORESCEIN ANGIOGRAPHY

Fluorescein angiography is an eye test that is used to detect blood circulation problems in the retina and choroid, structures that are located in the back of your eyes. The test uses an injected dye and a special camera to take photos of blood vessels. It is used to diagnose certain eye conditions, including retinopathies and macular degeneration. Fluorescein angiography is a simple and short test that is performed in your doctor’s office. There is no radiation associated with this test.

Fluorescein Angiography Eye Test

Fluorescein angiography is the technique used to examine the retina using a dye to highlight the blood circulation within the eye. If you have been referred for this test it is because the ophthalmologist (specialist eye surgeon) requires further information to help decide about the condition of the retina in your eyes

There are several stages to the test:

  • Drops will be administered to dilate the pupils of your eyes. This is done as soon as you attend the clinic and requires approximately 25-30 minutes to work.
  • Photographs of your retina will then be taken using a special camera. Although this not at all painful the flash can sometimes be rather bright.
  • While sitting at the camera you will be given an injection into a vein in the back of your hand
  • A series of photographs are taken immediately after the injection. This is to see the dye as it circulates through the eye

After you have had a short rest you will be able to go home, however as your vision will be significantly blurry from the drops you should not drive when you come for the test.

Are there any side effects?

There are two main side effects from the injection:

  • Firstly your skin will be slightly brown or orange for approximately one day. This is an effect from the dye and it usually appears similar to a mild tan.
  • Secondly, the dye passes out of the body through the kidneys and as a result, urine will be brown or orange.

These side effects are completely normal and nothing to be afraid of, however, if you are diabetic then you should not rely on urine testing for a few days after the test.

What happens after the test?

After you have had the test the photographs will be processed and the doctor will see you in the clinic to discuss the results. When you leave the clinic please ensure that the receptionist has all your current contact details.

OCT SCANNING

An OCT scan is completely different from an eye photograph that is sometimes taken by doctors’ diabetic clinics or other opticians. The OCT scan is able to examine eye health below the eye’s surface, is very quick to perform and is completely painless and non-invasive. Results are available instantaneously and it is a great way for clients to gain a better understanding of their eye condition

Ocular Coherence Tomography (OCT) is an extremely advanced health check for people of all ages. It is quite different from digital eye photographs offered by your doctor (if you have diabetes) or by other opticians since this only images the surface of the back of the eye. This scan sees under the retina to parts that cannot be seen by ordinary examination.

Very similar to Ultrasound, the OCT uses light rather than sound waves to illustrate the different layers that make up the back of your eye. We also capture a digital photograph of the surface of your eye to cross-reference areas of concern. There is an additional charge for our OCT scan, but the benefits are clear. So enjoy the peace of mind that comes from knowing that your eyes are in great condition.

The Retina, which is the back of the eye, is sensitive to light and it transmits the signals of light received by the eye to the brain. The brain interprets these signals and converts them to what we know as vision. The most detail-sensitive part of the eye is at the centre of the retina and is called the macula.

The retina is a window to the vasculature (blood vessels) within the body and many undiagnosed systemic vascular diseases can be discovered with a thorough retinal examination. Recognizing these findings can potentially save vision and reduce the risk of morbidity from life-threatening diseases.

Normal testing room equipment or eye camera can only see the surface of the eye. Many diseases, including oxidative stress, begin their damage in the layers of the retina below the surface and the OCT can view all these layers in cross-section. Our state-of-the-art OCT equipment optically slices through the thickness of the retina and images what appears under the retina. It’s like slicing through a cake and seeing all the invisible layers below.

FUNDUS PHOTOGRAPHY

Fundus photography (also called fundography[1]) is the creation of a photograph of the interior surface of the eye, including the retina, optic disc, macula, and posterior pole (i.e. the fundus)

Fundus photography is used by optometrists, ophthalmologists, and trained medical professionals for monitoring progression of a disease, diagnosis of a disease (combined with retinal angiography), or in screening programs, where the photos can be analysed later.

Compared to ophthalmoscopy, fundus photography generally needs a considerably larger instrument, but has the advantage of availing the image to be examined by a specialist at another location and/or time, as well as providing photo documentation for future reference. Modern fundus photographs generally recreate considerably larger areas of the fundus than what can be seen at any one time with handheld ophthalmoscopes.

What is it?

This is an imaging technique used to take photographs of the retina. This is useful to monitor the progression of conditions such as diabetic retinopathy, macular degeneration and glaucoma.

How is it done?

You place your chin on the instrument chin rest and fixate a target light within the instrument lens. Several images are captured within a few minutes. You will see a bright flash of light as each image is taken which may dazzle your eyes for a few minutes. Occasionally dilating drops may need to be used prior to fundus photography especially for patients with small pupils.

Indications

Fundus photography is used to detect and evaluate symptoms of retinal detachment or eye diseases such as glaucoma. In patients with headaches, the finding of swollen optic discs, or papilledema, on fundus photography is a key sign, as this indicates raised intracranial pressure (ICP) which could be due to hydrocephalus, benign intracranial hypertension (aka pseudotumorcerebri) or brain tumor, amongst other conditions. Cupped optic discs are seen in glaucoma.

In patients with diabetes mellitus, regular fundus examinations (once every 6 months to 1 year) are important to screen for diabetic retinopathy as visual loss due to diabetes can be prevented by retinal laser treatment if retinopathy is spotted early. In arterial hypertension, hypertensive changes of the retina closely mimic those in the brain, and may predict cerebrovascular accidents (strokes).

  • Corneal diseases
  • Corneal abrasions
  • Corneal deformities
  • Irregular astigmatism following corneal transplants
  • Postoperative cataract extraction with acquired astigmatism

CORNEAL TOPOGRAPHY

Corneal topography is a computer-assisted diagnostic tool that creates a three-dimensional map of the surface curvature of the cornea. The cornea (the front window of the eye) is responsible for about 70 percent of the eye’s focusing power. An eye with normal vision has an evenly rounded cornea, but if the cornea is too flat, too steep, or unevenly curved, less than perfect vision results. The greatest advantage of corneal topography is its ability to detect irregular conditions invisible to most conventional testing.

Corneal topography produces a detailed, visual description of the shape and power of the cornea. This type of analysis provides your doctor with very fine details regarding the condition of the corneal surface. These details are used to diagnose, monitor, and treat various eye conditions. They are also used in fitting contact lenses and for planning surgery, including laser vision correction. For laser vision correction the corneal topography map is used in conjunction with other tests to determine exactly how much corneal tissue will be removed to correct vision and with what ablation pattern.

Computerized corneal topography can be beneficial in the evaluation of certain diseases and injuries of the cornea including:

  • Corneal diseases
  • Corneal abrasions
  • Corneal deformities
  • Irregular astigmatism following corneal transplants
  • Postoperative cataract extraction with acquired astigmatism

The corneal topography equipment consists of a computer linked to a lighted bowl that contains a pattern of rings. During a diagnostic test, the patient sits in front of the bowl with his or her head pressed against a bar while a series of data points are generated. Computer software digitizes these data points to produce a printout of the corneal shape, using different colors to identify different elevations, much like a topographic map of the earth displays changes in the land surface. The non-contact testing is painless and brief.

BIOMETRY

What is it?

This is a test to measure the shape and size of the eye. It is commonly used to calculate the power of intraocular lens (IOL) implants required for cataract and refractive surgery. Biometry can be performed using either optical coherence interferometry or ultrasound technology.

At the Lakefield Surgical Centre we use the state of the art Zeiss IOL Master 500 (optical coherence interferometry). This equipment is able to measure the length of the eyeball (axial length), curvature of the cornea (keratometry), anterior chamber depth and white to white (corneal width). It uses several different formulas to give the surgeon options as to IOL lens powers for each individual eye

How is it done?

This is a non-invasive test performed by placing your chin on the instrument chin rest and focussing on a target light. It takes only a few minutes to perform.

Ultrasound biometry is used for patients who have dense cataracts where measurements on the IOL Master are not possible. This test involves placing an ultrasound probe on the surface of the cornea to obtain measurements of axial length. These can then be used along with keratometry measurements to calculate IOL lens powers. A local anaesthetic eye drop is inserted into the eye before this test is performed.

Before your appointment:

Whether we use the IOL Master or the ultrasound biometer it is important to remove your contact lenses prior to the measurements being taken. Below is a guide as to how long prior to your appointment your contact lenses should be left out:

  • Soft daily disposable contact lenses……………………………24 hours
  • Soft two weekly and monthly contact lenses……………48 hours
  • Extended wear soft contact lenses…………………………………………1 week
  • Rigid gas permeable contact lenses……………………………………2 weeks