Perimetry, or visual field testing, is a critical component of your modern ophthalmic practice.
Unlike visual acuity testing, which focuses primarily on what patients can see directly ahead of them with a fixed gaze, perimetry allows eye care professionals to examine the entire field of vision. In other words, they are able to measure what patients see not just centrally but also on either side (i.e., peripherally).
Why is perimetry testing important?
If you think of a patient's field of vision as a flat map, perimetry testing helps to pinpoint those areas where patients cannot see. These "blind spots" in the visual field are often undetectable by the individual, which makes perimetry testing an important part of the standard eye exam.
Modern perimetry equipment can help ophthalmic professionals identify any deficiencies or dysfunctions in vision that may be linked to specific medical conditions. By homing in on these abnormalities in vision, doctors can more effectively track and manage the progression of various diseases that can affect healthy vision.
How do modern perimeters work?
Nowadays, doctors use an automated piece of equipment called a perimeter to accurately map out the visual field and locate any deficiencies.
Patients are positioned in front of the perimeter and directed to look at the screen within. While focusing their eyes on a target straight ahead, lights flash in different locations on the screen at varying levels of brightness. Whenever the patient sees a flash of light in their periphery, they press a button on a handheld remote.
A computer records the location and timing of each flash during the exam, as well as the patient’s corresponding response (or lack thereof). Once the perimetry test is complete, a printout expresses any problematic areas of vision loss—those places where the patient did not see a flash of light. These complications may be a result of several conditions, including:
- Brain tumor
- Pituitary disease
- Other neurological deficiencies
Additionally, perimetry testing can be used to help monitor the patient's vision after a diagnosis has been made to ensure the prescribed treatment is effective in preventing further vision loss.
A look at visual field testing throughout history
It may come as a surprise to know that scholars were aware of the existence of the visual field long before the rise of digital technology and the first modern perimeter.
In fact, the concept of testing the entire visual field dates back as far as the fifth century, when Hippocrates first described hemianopia, or blindness over half of the visual field. In 150 BC, it was Ptolemy who described our field of vision as circular—many years before Hans Goldmann developed the hemispherical bowl perimeter in 1945. But it was Franz Fankhauser and his peers who created the first automated perimeter in 1975, dubbed the OCTOPUS, which made way for the automated testing practices used in perimetry today.
Currently, two types of perimetry testing are used to measure a patient's scope of vision and detect any issues. They are:
- Confrontation/Kinetic Perimetry: This method of visual field testing brings an object into a patient’s view using steady, horizontal motion. The stimuli moves from a blind area in the patient’s field of vision (typically the back of the head) until the patient says they can see the object. The location at which the patient first sees the stimuli is recorded. Think of this as the moving test target method.
- Static Perimetry: With static perimetry, stimuli appear in different locations within the visual field. The patient signals each time they identify the stimuli within their field of vision. Think of this as the stationary test target method.
Do all patients need visual field testing?
According to the American Academy of Ophthalmology:
Visual field testing is an important part of regular eye care for people who are at risk for vision loss from disease and other problems. People with the following conditions should be monitored regularly by their ophthalmologist, who will determine how often visual field testing is needed:
- Multiple sclerosis
- Thyroid eye disease
- Pituitary gland disorders
- Central nervous system problems (such as a tumor that may be pressing on visual parts of the brain)
- Long-term use of certain medications (such as Plaquenil, or hydroxychloroquine, which requires yearly visual field checkups)
People with diabetes and high blood pressure have a greater risk of developing blocked blood vessels in the optic nerve and retina. They may need visual field testing to monitor any effects of these conditions on their vision.
Find quality, affordable perimetry equipment at Veatch.
With more than 30 years of experience serving ophthalmic professionals, Veatch Ophthalmic Instruments is a leading provider of high-quality perimeters from top-name brands. Whether you are launching a new practice or upgrading your equipment to better meet the needs of your patients, we can help you find the right perimeter at the right price. We also offer general maintenance and repair services to help you extend the life of your equipment.
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