This article was reviewed by Mays A. El-Dairi, MD
This article was reviewed by Mays A. El-Dairi, MDOptical coherence tomography (OCT) is popular for use in pediatric neuro-ophthalmology. The fast, non-invasive technology uses optical waves and inferometry, provides in vivo high-resolution tomograms, and displays pathologies that might otherwise go undetected.
“It is the ‘perfect’ non-invasive technology in pediatric neuro-ophthalmology patients with clear media,” said Mays A. El-Dairi, MD, associate professor, Pediatric Ophthalmology and Strabismus, Neuro-Ophthalmology, Duke Eye Center, Durham, NC.
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In the pediatric population, OCT is used most frequently to obtain measurement of the retinal nerve fiber layer (RNFL). This is associated with a couple of drawbacks, she pointed out, one being that most machines do not have an integrated normative database.
In some cases, if there is one, the database is extrapolated and it is not highly accurate. The normative database needs to be perfected.
In her neuro-ophthalmology practice, Dr. El-Dairi puts the OCT instrument to use in many ways over and above just evaluating the RNFL. Many diseases can be diagnosed without OCT imaging, but the imaging provides information that might otherwise be impossible to obtain.
Viewing pediatric neuro-ophthalmic disease
In patients with optic nerve hypoplasia, while OCT is not necessarily needed to establish a diagnosis most of the time, OCT facilitates measurement of the opening of Bruch’s membrane, which in optic nerve hypoplasia, is very small (Ophthalmology. 2015;122:1330-1339).
Optic nerve coloboma also can be diagnosed without use of OCT in most cases. However, in some cases when a tilted nerve is seen, a coloboma cannot always be identified as part of the optic nerve. OCT shows a signal that indicates that the nerve is just tilted, she explained.
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In cases of optic nerve head pit, the end of Bruch’s membrane is not visible.
“OCT is not needed to see the pit, but sometimes the pit can be associated with an area where the ganglion cell area did not form, which can help predict a problem with visual function,” she said, describing a patient who had 20/200 vision and was undergoing treatment for amblyopia. In actuality, she was able to determine that the ganglion cells that facilitate central vision had never formed in this patient.
A myelinated nerve fiber layer seen on an OCT image has a bright, thick, hyperreflective signal that is readily visible. In some cases of subtle pseudopapilledema, visualization of this signal is helpful to the diagnosis.
In all congenital optic nerve anomalies, OCT allows clinicians to evaluate the central ganglion cell layer since it correlates with presence of a central scotoma when the patient is too young for a visual field evaluation, she said.
OCT is useful for examining Bruch’s membrane. When differentiating papilledema from pseudopapilledema, clinicians look for signs of high intracranial pressure and the position of Bruch’s membrane can provide clues.
“Upward bowing of the membrane can indicate the presence of a retrobulbar process, something that is pushing behind the optic nerve, or high intracranial pressure,” Dr. El-Dairi said. “This is not a very sensitive marker, but it is quite specific; I always look at it when a nerve is elevated.”
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The size of the Bruch’s membrane also can be evaluated using OCT. In patients with pseudopapilledema, the nerves tend to be smaller; the RNFL is under 120 Î¼m and Bruch’s membrane opening is less than 1,500 Î¼m. When compared with true papilledema, the pseudopapilledema nerves are larger; Bruch’s membrane opening exceeds 1,650 Î¼m and the RNFL is thicker than 135 Î¼m.
In optic neuritis, imaging shows RNFL thickening even when no edema is seen during funduscopy. When optic atrophy becomes apparent, RNFL thinning is seen that is correlated with the final visual outcome.
“Imaging of the RNFL is not useful for diagnosing optic neuritis, but new baseline images are useful to have six months after resolution to more readily identify a recurrence,” she advised.
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Dr. El-Dairi does, however, like to use OCT in children with optic neuritis because in some cases with a bright internal limiting membrane, early-stage neuroretinitis may not be apparent.
“A macular scan can show changes in the retina, such as subretinal fluid and disrupted photoreceptors,” she explained.
Atrophic nerves are seen as thinning on the RNFL scan and macular map. Cystic lesions also may be visible in the inner nuclear layer.
“It is important to remember that when there is atrophy on top of papilledema, it is hard to determine how much is atrophy and how much is papilledema,” Dr. El-Dairi noted.
In a case of hydrocephalus, in which the patient had 20/400 vision, the RNFL measured about 80-plus Î¼m and while the referring physician thought the patient was fine and had non-organic visual loss, the ganglion cell layer was actually absent.
Dr. El-Dairi relies on OCT to monitor the visual fields in young patients. In some cases, imaging will show changes at the macular level and homonymous thinning is seen that is correlated with visual field deficits.
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In infants with nystagmus, she performs hand-held OCT evaluations to establish the need for electroretinography or neuroimaging.
Examples include Stargardt’s disease, retinoschisis, Best’s disease, and cone dystrophy, which have pathognomonic findings on the retinal OCT.
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In an example of Leber congenital amaurosis, Dr. El-Dairi highlighted the normal ganglion cell layer and the significantly attenuated photoreceptor layer. She showed examples of different stages of retinitis pigmentosa that show only rod involvement initially that progresses to both rod and cone involvement.
Batten disease shows a very specific pattern on imaging-both the outer and inner retina are involved, there is severe attenuation of the ganglion cell layer, and the outer photoreceptors are significantly damaged.
“High-resolution OCT imaging tomograms of the retinal tissues can frequently reveal pathology that is difficult to detect with the naked eye,” Dr. El-Dairi concluded. “With extra anatomic finding, it can help determine the path for further workup.”
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Mays A. El-Dairi, MD
Dr. El-Dairi has no financial interest related to this topic.