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Assessing visual fields in young patients is challenging - OCT may be a good place to start.
This article was reviewed by Andrew G. Lee, MD
The biggest challenge in visual field testing is recognizing when a child may have a visual field defect. A number of symptoms may be clues, including difficulty finding words, difficulty reading as evidenced by missing words or hemifield slip, difficulty during tests as the result of skipping letters, not reading an entire line, or only seeing one number of the Ichihara test when there actually are two.
Mitchell Strominger, MD, pointed out that physicians should be aware that some children compensate for their visual field defects, with, for example, head turns related to visual field loss that are not related to strabismus.
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“They may have head turning or head thrusting toward the nonseeing field or use touch to help navigate around,” said Dr. Strominger, professor of ophthalmology and pediatrics, Renown Medical Center, University of Nevada Reno School of Medicine, Reno.
Some children can have associated motor or sensory deficits, for example, children with cerebral palsy may have a hemiparesis on the side of the visual field deficit.
Children with a known central nervous system abnormality that includes perinatal stroke, encephalomalacia, periventricular leukomalacia, craniopharyngioma, pituitary adenoma, or optic pathway glioma, or a known systemic or genetic abnormality, such as neurofibromatosis, should undergo visual field testing, Dr. Strominger pointed out.
Other indications for visual field testing are the presence of retinal abnormalities and anterior visual pathway congenital disorders.
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Options in visual field testing
Many options are available that can be used to evaluate the visual fields, each with limitations. Visual field testing generally is done binocularly and monocularly. However, Dr. Strominger noted, if a patient has a bitemporal defect, testing should be done monocularly because the defect may not be apparent when binocularly is done.
Confrontation visual field testing, in which the child is shown toys and the clinician monitors the responses, is the most basic procedure that has not changed markedly over the decades.
Using the saccadic technique, a confrontation test, the clinician moves objects in front of young children in order to observe the saccades; in older children, counting fingers or the red object test can be used.
Arc perimetry is an old time-tested technique during which babies can be tested with the use of a flashing light to test the child’s response to the light.
Goldmann perimetry is another testing method in which a light moves from the periphery to the center of a hemisphere. The child signals when he or she detects the light by tapping on a buzzer; this method works best with cooperative patients.
The Humphrey visual field analyzer, the latest technology, is another option, but its use is extremely difficult in small children, Dr. Strominger noted.
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Contribution of OCTOCT can provide valuable information about the nerve fiber layer. He advises doctors to also measure the ganglion cell layer.
“The ganglion cell layer provides a lot of information that might not be available if only the nerve fiber layer is assessed,” he said.
Specifically, in a patient with cafÃ© au lait spots and glioma, the visual field deteriorate was progressing. OCT performed in this patient showed that the glioma was progressing along with a decrease in the nerve fiber layer over time.
Monitoring ganglion cell loss is informative. In a child with a suspect visual field, in whom assessing the nerve fiber layer may not provide a great deal of information, the ganglion cell layer may shed some light on the retinal status.
Dr. Strominger described a patient with binasal ganglion cell loss secondary to a suprasellar lesion, who was diagnosed with bitemporal hemianopsia.
In another case, in which a change in vision in the right eye was found, the bilateral vision was 20/20. The right eye appeared to have a subtle change in the visual field. Analysis of the nerve fiber layer on OCT showed a good structural appearance; however, a small ganglion cell loss was apparent in the left eye.
“This defect is seen more and more often in patients with demyelinating disease,” Dr. Strominger said. “The visual acuity can be completely normal, the color vision may be good, but there is a decrease in the ganglion cells.”
In a case of left homonymous hemianopsia, OCT showed a corresponding loss of ganglion cells with a lesion in the occipital lobe.
“Patients are being identified with retrograde axonal degeneration that can be identified by evaluating the ganglion cell layer,” he said. “In cases in which a visual field examination cannot be performed and in which ganglion cell loss is found, physicians should be concerned about a posterior defect.”
In a similar case, the patient had a superior quadrantic defect; the nerve fiber layer was normal on examination but the ganglion cell layer was defective and corresponded to that defect. The patient was diagnosed with post-lateral geniculate disease.
In commenting on the importance of OCT, Dr. Strominger noted that the nerve fiber layer thickness should be affected in anterior visual pathway disorders except in some cases with demyelinating disease in which the ganglion cell layer only may be affected.
“Some ganglion cell loss can be seen in retrograde axonal degeneration. OCT can be easier to perform in children and the findings can correspond to visual field defects,” Dr. Strominger explained.
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Technologies on the horizon
Saccadic vector optokinetic perimetry uses fixation targets and an eye tracking device to monitor real-time eye movement responses to visual field stimuli. The system includes separate patient and examiner displays, the eye tracker, and a height-adjustable table.
A head-mounted eye tracking perimeter (Virtual-Eye, BioFormatix Inc.) device capable of vector analysis is under development.
While many options are available to assess the visual fields in young patients, Dr. Strominger generally starts with OCT because of the wealth of information that the technology provides. Performing Humphrey visual field testing can be useful in cooperative patients. Some newer technologies in the pipeline may soon add to the ophthalmologist’s armamentarium in this challenging patient population.
Read more by Lynda Charters
Mitchell Strominger, MD
Dr. Strominger has no financial relationships related to this report.