A visual field test is an eye examination that can detect dysfunction in central and
peripheral vision which may be caused by various medical conditions such as glaucoma, stroke,
brain tumours or other neurological deficits. Visual field testing can be performed clinically
by keeping the subject's gaze fixed while presenting objects at various places within
their visual field. Simple manual equipment can be used such as in the tangent screen
test or the Amsler grid. When dedicated machinery is used it is called a perimeter.
The exam may be performed by a technician in one of several ways. The test may be performed
by a technician directly, with the assistance of a machine, or completely by an automated
machine. Machine based tests aid diagnostics by allowing a detailed printout of the patient's
visual field. Other names for this test may include perimetry,
Tangent screen exam, Automated perimetry exam, Goldmann visual field exam, or the Humphrey
field exam.
Exam methods Here is a list of techniques used to perform
this test: Confrontation visual field exam: The examiner
will ask the patient to cover one eye and stare at the examiner. Ideally, when the patient
covers their right eye, the examiner covers their left eye, and vice versa. The examiner
will then move his hand out of the patient's visual field and then bring it back in. Commonly
the examiner will use a slowly wagging finger or a hat pin for this. The patient signals
the examiner when his hand comes back into view. This is frequently done by an examiner
as a simple and preliminary test. Perimetry
Perimetry or campimetry is one way to systematically test the visual field. It is the systematic
measurement of differential light sensitivity in the visual field by the detection of the
presence of test targets on a defined background. Perimetry more carefully maps and quantifies
the visual field, especially at the extreme periphery of the visual field. The name comes
from the method of testing the perimeter of the visual field.
Automated perimeters are used widely, and applications include: diagnosing disease,
job selection, visual competence assessment, school or community screenings, military selection,
and disability classifications. Types of perimetry
Tangent screen. The simplest form of perimetry uses a white tangent screen. Vision is tested
by presenting different sized pins attached to a black wand, which may be moved, against
a black background. This test stimulus may be white or colored.
Goldmann perimeter. The Goldmann perimeter is a hollow white spherical bowl positioned
a set distance in front of the patient. An examiner presents a test light of variable
size and intensity. The light may move towards the center from the perimeter, or it may remain
in one location. The Goldmann method is able to test the entire range of peripheral vision,
and has been used for years to follow vision changes in glaucoma patients. However, now
automated perimetry is more commonly used. Automated perimetry. Automated perimetry uses
a mobile stimulus moved by a perimetry machine. The patient indicates whether he sees the
light by pushing a button. The use of a white background and lights of incremental brightness
is called "white-on-white" perimetry. This type of perimetry is the most commonly used
in clinical practice, and in research trials where loss of visual field must be measured.
However, the sensitivity of white-on-white perimetry is low, and the variability is relatively
high; as many as 25-50 percent of the photoreceptor cells may be lost before changes in visual
field acuity are detected.This method is commonly used for early detection of blind spots. The
patient sits in front of an small concave dome in a small machine with a target in the
center. The chin rests on the machine and the eye that is not being tested is covered.
A button is given to the patient to be used during the exam. The patient is set in front
of the dome and asked to focus on the target at the center. A computer then shines lights
on the inside dome and the patient clicks the button whenever a light is seen. The computer
then automatically maps and calculates the patient's visual field.
Microperimeter. The microperimeter assesses the macular function in a computerised way.
A 2012 observational study by Pacella et al. found a significant improvement in both visual
acuity and fixation treating age-related macular degeneration or macular myopic degeneration
with biofeedback treatment through MP-1 microperimeter. Methods of stimulus presentation
Static perimetry Static perimetry tests different locations
throughout the field one at a time. First, a dim light is presented at a particular location.
If the patient does not see the light, it is made gradually brighter until it is seen.
The minimum brightness required for the detection of a light stimulus is called the "threshold"
sensitivity level of that location. This procedure is then repeated at several other locations,
until the entire visual field is tested. Threshold static perimetry is generally done
using automated equipment. It is used for rapid screening and follow up of diseases
involving deficits such as scotomas, loss of peripheral vision and more subtle vision
loss. Perimetry testing is important in the screening, diagnosing, and monitoring of various
eye, retinal, optic nerve and brain disorders. Kinetic perimetry
Kinetic perimetry uses a mobile stimulus moved by an examiner such as in Goldmann kinetic
perimetry. First, a single test light of constant size and brightness is used. The test light
is moved towards the center of vision from the periphery until it is first detected by
the patient. This repeated by approaching the center of vision from different directions.
Repeating this enough will establish a boundary of vision for that target. The procedure is
repeated using different test lights that are larger or brighter than the original test
light. In this way, kinetic perimetry is useful for
mapping visual field sensitivity boundaries. It may be a good alternative for patients
that have difficulty with automated perimetry, either due to difficulty maintaining constant
gaze, or due to congnitive impairment. External links
"Amsler Grid" Test from Ossibus Software Free visual field test
References ^ "Visual Field". NIH, US National Library
of Medicine. Medline Plus. Retrieved 28 November 2012.
^ "1990 Perimetry Standards". First Codicil. Imaging and Perimetry Society. Retrieved 28
November 2012. ^ a b c d e f g h i Cunningham, Emmett T.;
Paul Riordan-Eva. "Chapter 2: Ophthalmologic Evaluation - Specialized Ophthalmologic Examinations".
Vaughan & Asbury's general ophthalmology.. New York: McGraw-Hill Medical. ISBN 978-0071634205.
^ a b McKendrick, Allison M. "Recent developments in perimetry: test stimuli and procedures".
Clinical and Experimental Optometry 88: 73–80. doi:10.1111/j.1444-0938.2005.tb06671.x. PMID 15807638.
^ "Visual Field Testing". January 2, 2013. ^ Siverstone, DE, Hirsch, J: Automated Visual
Field Testing. Appelton-Century Croft. Norwalk, CT. 1986.
^ Pacella, E; Pacella, F; Mazzeo, F; Turchetti, P; Carlesimo, SC; Cerutti, F; Lenzi, T; De
Paolis, G; Giorgi, D. "Effectiveness of vision rehabilitation treatment through MP-1 microperimeter
in patients with visual loss due to macular disease". Clin Ter 163: 163(6):e423–8. PMID 23306757.
^ "What is Perimetry?". Imaging and Perimetry Society. Retrieved 28 November 2012.
^ Ing, Edsel. "Neuro-Ophthalmic Examination". Web MD, LLC. Medscape. Retrieved 29 November
2012.