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Visual Field Testing Suzanne Hansen, M.Ed., COMT, OSC Why are these tests ordered? Visual field testing is ordered to help the physician diagnose and manage conditions caused by glaucoma, neurological disorders, and retinal diseases. These tests map the perimetry or boundary between the areas of seeing and non-seeing for each eye tested for the patient. 1 What exactly is tested? 2 A normal patient can see approximately 90 temporally, 60 nasally, 60 superiorly, and 70 inferiorly. The majority of visual field tests ordered only test the central portion of the field. Therefore, the area tested depends on the type of test performed. Methods of Visual Field Testing 2,3,4 GVF Goldmann Visual Field Manual kinetic method of estimating patient s visual field Manual examiner manually presents each target for the patient during the test Kinetic refers to the target because it is moved from an area of non-seeing to seeing These may be ordered by ophthalmologists for: evaluating glaucoma, neurological disorders, retinal disorders, low vision, strabismus (map the area where the patient sees double), oculoplastics (maps the superior field with eyelids tapped up and untapped to show extent of field loss due to blepharoptosis) Advantage of GVF: More peripheral portions of the field are able to be tested. Disadvantage of GVF: Requires skilled examiner to administer test. 1
HVF Humphrey Visual Field Automated static method of estimating patient s visual field, may also be referred to as standard automated perimetry (SAP) Automated computer presents each target for the patient during the test Static refers to the target because it is not moving These may be ordered by ophthalmologists for many of the same reasons listed above for GVF. What do the HVF numbers mean? 3 The first number refers to the degrees of field tested. For example a 10-2 means that the machine tests points 10 degrees around the center vision (fovea). A 24-2 tests points 24 degrees around the fovea. The second number refers to the testing protocol. The HVF has two main testing protocols, 1 and 2. Protocol 1 tests points directly on the horizontal and vertical axis. Protocol 2 tests points on either side of the horizontal and vertical axis. Typically, protocol 2 is used. Common tests ordered include: HVF 10-2 or 24-2 or 30-2. Following the numbers full-threshold, SITA-Standard (SS), or SITA-Fast (SF) may also appear. Full-threshold tests take the longest because more field points are tested and plotted. SS refers to SITA-Standard which takes half as long as a full-threshold test but yields reliable information. SF refers to SITA-Fast which allows for a faster testing program to be used and takes about 70% less time than the full-threshold test. A HVF 60-4 measures from 30 degrees to 60 degrees (therefore misses the central visual field of the tests mentioned above). Advantage of HVF: Disadvantage of HVF: Test is considered more sensitive since the target is stationary (not moving such as in the kinetic method). Also, likely to have more reproducible results if the patient is tested by another examiner. Computer program dictates the test rather than the examiner. 2
Tangent Screen Visual Field Manual kinetic method of estimating patient s visual field Manual examiner manually presents each target using a wand with a target on it for the patient during the test Kinetic refers to the target because it is moved from an area of non-seeing to seeing These may be ordered by ophthalmologists for: evaluating hysterical blindness, malingering, and oculoplastics (maps the superior field with eyelids tapped up and untapped to show extent of field loss due to blepharoptosis) Advantage of Tangent Screen: Very effective for comparing visual field at 1 M and 2 M testing distances to confirm expansion of field or malingering. Central portions of the field are tested. Disadvantage of Tangent Screen: Requires skilled examiner to administer test and adequate space for conducting the test. CVF Confrontation Visual Field Manual kinetic and/or static method of screening patient s visual field Manual examiner manually presents each target using his/her hand to the patient during the test Kinetic refers to the target because it is moved from an area of non-seeing to seeing Static refers to the target because it is not moving Chart documentation of CVF results may be sketched as shown or described in words in the basic eye exam work up notes. This visual field test is part of the basic eye examination work up and is not a separate ordered visual field test like the other methods included above. Advantage of CVF: Disadvantage of CVF: Efficient method for screening the four quadrants of visual field without using extra instrumentation. Peripheral and central portions of the field are tested using kinetic and/or static targets. CVF is not as effective at identifying relative scotomas nor used for detailed central or peripheral visual field testing. 3
Why is it possible to order different visual field tests? In many cases, there is more than one possible choice of visual field test that may be appropriate for the patient. Sometimes the choice is simply due to the physician s preference and possible comfort in interpreting one type of test versus another. 2 It is also possible to simply test one eye, such as the right (OD) or left (OS) rather than both eyes (OU). If only one eye is to be tested, this is documented in the patient s chart by the physician. Visual field defects Reviewing common visual field defects and their causes can be helpful for ensuring best quality testing results for your physician s review. Absolute scotoma is represented by dark shaded area(s) in the examples. Neurological visual field defects occur due to various lesions affecting the visual pathway. Below are some of the common neurological visual field defects. 5 Remember to closely monitor the vertical meridian (90 meridian) of the visual fields of both eyes. Total blindness OD Complete lesion of right optic nerve Bitemporal hemianopia Chiasmal lesion Right Incongrouous hemianopia Lesion in the left optic tract Right homonymous inferior quadrantanipia Lesion in upper optic radiation in left parietal lobe Right homonymous hemianopia with mancular sparing Lesion of left occipital cortex Left homonymous superior quadrantanopia Lesion of the inferior optic radiation in right temporal lobe Right congruous incomplete homonymous heminanopia Lesion of the left occipital cortex 4
Glaucomatous visual field defects occur due to damage to the nerve fiber layer in the retina. Below are some of the common glaucomatous visual field defects. Remember to closely monitor the horizontal meridian (180 meridian), also known as the horizontal raphe, of the visual field. Examples of early glaucoma field defects: Paracentral scotoma Examples of advanced glaucoma defects: Temporal central island Nasal step Seidel s scotoma Temporal wedge Enlargement of blind spot Arcuate scotoma Double arcuate scotma Visual field defects will also occur with common retinal disorders such as age-related macular degeneration, retinal detachment, and diabetic retinopathy. However, these visual field defects will be less predictable compared to neurological and glaucomatous visual field defects. Amsler grid testing is another efficient screening method to assess the central visual field for patients with retinal disorders that can be completed as part of the basic eye exam. Checklist for visual field testing Verify supplies for conducting the appropriate visual field test are present (clean eye patch, appropriate testing paper or plenty of paper in the machine, etc.) Provide detailed instruction to your patient on the appropriate visual field testing method prior to starting the test. (If conducting the manual test, demonstrate prior to covering an eye. If conducting a static test show an example, if possible, and have the patient practice the appropriate method to respond once the target is seen.) Set up the visual field and remember to select appropriate trial lens(es) based on patient s age and refractive need for the appropriate test distance. Review the patient s chart to verify the correct visual field test or protocol is selected or ready for the patient. During the visual field test, monitor the patient s gaze regularly throughout the test to ensure most reliable results. Remember to pause testing if the patient becomes tired and looses focus during the test. Always note on the visual field exam comments regarding the patient s participation and cooperation during the visual field test for the physician s review. (If the patient was tired or had a hard time keeping eye open during the test, note this information on the visual field test. If the patient was alert and cooperated well during the exam, note this information.) 5
References: 1 Heijl, A. and Patella, V. The Field Analyzer Primer: Essential Perimetry. Carl Zeiss Meditec, 3 rd edition, 2002. 2 Dersu, I. et al. Understanding Visual Fields, Part I; Goldmann Perimetry. Journal of Ophthalmic Medical Technology. Vol. 2, Nu. 2, June 2006. 3 Wiggins, M. and Dersu, I. Understanding Visual Fields, Part III; Which Field Should Be Performed? Journal of Ophthalmic Medical Technology. Vol. 3, Nu 1, February 2007. 4 Ledford, J. and Lens, A. Principles and Practice of Ophthalmic Assisting. Chapter 9: Basic Eye Exam (Kiss, A. and Hansen, S.), SLACK, 2017. 5 Vaughan, D., Asbury, T., and Riordan-Eva, P. General Ophthalmology. McGraw-Hill, 15 th ed., 1999. p. 207, 247. Images from: Cassin, B. Fundamentals for Ophthalmic Technical Personnel. W.B. Saunders Co., 1995. Jones Eye Institute Clinic Stein, H. et. al. The Ophthalmic Assistant: A Guide for Ophthalmic Medical Personnel. Mosby, Inc., 7th edition, 1994. Western Ophthalmics, http://www.west-op.com/tangentscreen.html. Kiss, A. Chapter 9: Basic Eye Exam, Principles and Practice of Ophthalmic Assisting. SLACK, 2017. Adobe Stock photos (adapted with permission) 6