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Identifying Live Nematodes in Diffuse Unilateral Subacute Neuroretinitis by Using the Scanning Laser Ophthalmoscope
Lúcio R. Moraes, MD;
Arnaldo P. Cialdini, MD;
Marcos P. Avila, MD, PhD;
Ann E. Elsner, PhD
Arch Ophthalmol. 2002;120:135-138.
ABSTRACT
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Objective To describe use of the scanning laser ophthalmoscope (SLO) to identify
live nematodes in patients with diffuse unilateral subacute neuroretinitis.
Methods Infrared, red, and blue illumination (780, 633, and 488 nm, respectively)
in an SLO were used to image and evaluate functional retinal status in patients
with late-stage diffuse unilateral subacute neuroretinitis. An examination
to identify live nematodes was performed in the affected eyes.
Results Using blue illumination, the ocular fundus appeared dark and provided
a high-contrast background for the white image of the worm. The red laser
was used to perform red-on-red perimetry. We also used perimetry stimulus
to stimulate the worm's movement and pinpoint its location. We precisely defined
the relation between the fixation point and the worm to plan accurate laser
treatment. The infrared laser is safe and comfortable for prolonged examination.
Using the SLO, several physicians simultaneously visualized the ocular fundus.
Video output from the SLO provided temporal information, excellent for enhancing
detection of worms, which was displayed dynamically on video.
Conclusions Although examination with a fundus contact lens by skilled ophthalmologists
is the method of choice, the SLO provides a new examination modality with
distinct advantages for identifying live worms in young patients with diffuse
unilateral subacute neuroretinitis.
INTRODUCTION
DIFFUSE UNILATERAL subacute neuroretinitis (DUSN) is a clinical syndrome
characterized in the early stage by visual loss, vitritis, papillitis, retinal
vasculitis, and recurrent crops of evanescent gray-white outer retinal lesions
and later by progressive visual loss, optic atrophy, retinal vessel narrowing,
and diffuse retinal pigment epithelium (RPE) degeneration occurring in one
eye of otherwise healthy patients.1-3
The first patient, to our knowledge, with documented bilateral nematodes was
described recently.4 During the early course
of the disease, visual acuity may be normal or minimally affected.1, 5 In many patients, particularly in young
children, the disease remains undetected until the visual acuity decrease
is found during a school vision examination.
Diffuse unilateral subacute neuroretinitis is caused by at least 2 unidentified
nematodes of different sizes that vary in length from 400 to 2000 µm.1-5
Cialdini et al6 recently reported the first
South American case of DUSN caused by the larger nematode. The nematode can
be found at any stage of the disease and should be sought in patients with
optic atrophy, narrowing of the retinal vessels, and advanced degenerative
RPE changes.5
A careful search using a fundus contact lens is required to locate smaller
worms, which are barely visible by indirect ophthalmoscopy using a 20-diopter
lens. Larger worms are relatively easy to detect using indirect ophthalmoscopy
and are most likely found near active, deep, white retinal exudative lesions,
which are probably caused by a toxic inflammatory reaction to material left
in the wake of the nematode moving in the subretinal space. The magnification
and wide field of view provided by a fundus contact lens and the fundus camera
are the preferred methods for visualizing these worms but may require prolonged
and repeated examinations that are troublesome mainly because of patients'
young age and poor fixation. Early diagnosis of the disease is important because
destruction of the worm with laser photocoagulation prevents further loss
of visual function and occasionally can be followed by improvement in vision.7
We used the scanning laser ophthalmoscope (SLO) to identify live nematodes
in patients with DUSN, and we describe several distinct advantages of the
SLO system over conventional photography.
MATERIALS AND METHODS
We used an SLO (Rodenstock, Ottobrunn-riemerling, Germany) with direct
imaging to identify live nematodes in 3 young patients with late-stage DUSN.
The blue wavelength was used because at this wavelength, the presence of unbleached
photopigment darkens the fundus, so the fovea is darker than the peripheral
retina. This produces a high-contrast background for the worm,8
which is white in the picture.
The red wavelength was used to perform red-on-red perimetry simultaneously
with infrared imaging so that we could correlate retinal function with the
anatomic alterations near the worm.9 The infrared
illumination penetrates deeply into the retina and provides information about
the retinal and subretinal structures.8 The
low power needed to image the retina is virtually invisible to the patient,
comfortable, and safe, thereby allowing prolonged examination.
A frame grabber (DT-2861; Data Translation, Inc, Marlboro, Mass) was
used to digitize images, display them on the computer monitor in the laser
suite, and print them using a digital printer (Kodak XLS 8600; Eastman Kodak
Co, Rochester, NY) for clinical documentation. After the purpose, procedures,
and consequences of the study were explained to the patients and their guardians,
written informed consent was obtained from all.
REPORT OF CASES
CASE 1
An 11-year-old girl with the presumed diagnosis of diffuse bilateral
subacute neuroretinitis was referred to Bom Jesus Hospital, Ceres, Brazil,
for a second opinion. She had previously undergone laser treatment in both
eyes without improvement in vision. Her visual acuity levels were 20/200 OD
and counting fingers OS. Biomicroscopy revealed a normal anterior segment
in both eyes. Signs of mild vitritis associated with a path of RPE degeneration
were seen in both eyes; degeneration was worse in the left eye, which also
had an extremely pale optic nerve. Multiple crops of evanescent gray-white
outer retinal lesions were seen temporal to the macula in the right eye, which
had marked RPE involvement. Diffuse bilateral subacute neuroretinitis was
suspected. Fundus ophthalmoscopy and careful contact lens biomicroscopy examination
did not identify a subretinal worm in either eye because of the poor cooperation
and photophobia of the patient. Testing using an SLO revealed a motile subretinal
nematode inferotemporal to the fovea in the right eye (Figure 1). No worm was seen in the left eye. We also used perimetry
stimulus over the worm to stimulate its movement and define precisely the
relation between the fixation point and the worm to plan more accurate laser
treatment, considering that the worm was in the macular area (Figure 2).
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Figure 1. Argon blue laser (488-nm) scanning
laser ophthalmoscopic fundus photograph (direct mode) shows a subretinal,
motile, circular nematode inferotemporal to the fovea (arrow) under high magnification
(20° field).
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Figure 2. A, Helium-neon laser (633-nm)
perimetry scanning laser ophthalmoscopic fundus photograph (direct mode) over
the worm shows a poorly defined preferred retinal locus for fixation inferior
to the worm (black cross). The black As indicate absolute scotomas, and the
white As indicate the stimulus points seen by the patient. B, Infrared laser
diode (780-nm) scanning laser ophthalmoscopic picture (direct mode) shows
the motile, subretinal, snakelike nematode (arrow) (20° field).
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Argon green laser treatment was applied inferotemporally to the fovea
in the right eye where the motile 450- to 600-µm nematode was found,
and the retina was mapped by the SLO examination. The results of laboratory
investigations were negative. A stool sample was free of ova and parasites.
There was no history of cutaneous larval migrans. One month after laser treatment,
the patient's visual acuity improved to 20/60 OD; visual acuity in the left
eye remained unchanged.
CASE 2
An 8-year-old boy was first seen in January 1999 with a history of vision
loss in the right eye resulting from a diagnosis of "retinal lesions" made
by his ophthalmologist 1 year previously. His visual acuity levels were 20/400
OD and 20/20 OS. There was no afferent pupillary defect in either eye. Bilateral
intraocular pressure was 13 mm Hg. Biomicroscopy showed a normal anterior
segment in both eyes and vitreous cells in the right eye. The right fundus
examination showed a pale optic nerve, narrowing of the retinal vessels, and
focal plus diffuse RPE degeneration. The left fundus was normal. Diffuse unilateral
subacute neuroretinitis was suspected in the right eye, but careful contact
lens examination did not identify a motile subretinal worm because of poor
patient cooperation. However, argon laser treatment was applied to the superior
temporal retina in 2 small areas where we suspected that a small worm might
be present. After 4 weeks of laser treatment, visual acuity was unchanged
(20/400 OD), and no worm was seen. In December 2000, the patient returned.
Visual acuity remained 20/400 OD. An SLO examination identified a motile 550-
to 650-µm nematode inferonasally in the right eye. The worm's movements
were easily seen on the SLO video monitor (Figure 3) and were recorded on videotape. The subretinal worm was
destroyed by using laser photocoagulation. The patient was lost to follow-up.
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Figure 3. Argon blue laser (488-nm) scanning
laser ophthalmoscopic composite fundus photographs (direct mode) of the right
eye show the various shapes of the subretinal motile nematode inferonasally
(arrows) and demonstrate its coiling and uncoiling movements.
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CASE 3
A 15-year-old girl had an 18-month history of progressive visual loss
in the left eye. An ophthalmologist who examined her initially diagnosed optic
nerve atrophy. There was no history of ocular inflammation or pain. The patient
complained of occasional headaches. Visual acuity levels were 20/20 OD and
hand motions OS. There was a relative afferent pupillary defect in the left
eye. Intraocular pressure measurements and anterior segment biomicroscopic
findings were normal in both eyes. A few cells were seen in the anterior vitreous
in the left eye. The left fundus had severe optic nerve atrophy, narrowing
of the retinal vessels, and marked RPE degeneration in the posterior pole.
The electroretinogram was severely reduced (B wave < A wave). Diffuse unilateral
subacute neuroretinitis was suspected in the left eye, and a motile 400- to
500-µm subretinal nematode was found inferotemporally during SLO examination
(Figure 4). The nematode was destroyed
using continuous argon green laser treatments (150-200 mW, 150-µm spot
size). The patient was lost to follow-up.
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Figure 4. Helium-neon laser (633-nm) scanning
laser ophthalmoscopic fundus photograph (direct mode) of the left eye shows
the subretinal motile nematode (arrow) inferotemporally (40° field).
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COMMENT
The SLO uses a novel optical principle to obtain high-quality images
of the human retina.10-11 The
instrument enables several physicians to view the ocular fundus simultaneously.
This is potentially beneficial for finding areas of special interest during
examination and for facilitating the training of young physicians in the techniques
needed to recognize the worm in patients with late-stage DUSN. The instant
feedback that the video provides allows the examiner to optimize laser power
and video gain settings and to examine areas of special interest using high
magnification.
The contrast of the features in the image can be improved by using the
confocal imaging system. We used direct-mode imaging with a circular aperture;
the smaller the aperture, the more the image is determined from directly reflected
or backscattered light from the plane of focus. Unique to scanning laser tomography,
crops of evanescent gray-white outer retinal lesions were seen at different
depths, as described with exudative features in RPE detachment.12-13
The SLO video output provides a retinal image that can be reviewed dynamically
and repeatedly on video, and thus, a vital frame is unlikely to be missed.
This extra temporal information allows clinicians to perceive events not visible
in standard static photographs. In clinical examination, the areas of retinal
edema obscure the worm and its movements, which are important for identification.
Patients with DUSN are frequently children or young adults with an affected
retina and photophobia, so it is difficult for them to cooperate during the
long examination necessary to locate a small worm. The SLO provides for safe
and comfortable examination and thus improves patient cooperation. In clinical
examination, a slitlamp is used, which provides only a partial view of the
retina. An SLO can display the entire posterior pole live on a video monitor.
The results of an SLO examination are available instantly, allowing
immediate laser treatment. This is important in patients with DUSN because
continuous movement of the worm across the eye causes further damage to the
neuroretina. Immediately after laser treatment, digitized SLO images allow
production of simple overlays to confirm that laser treatments completely
destroyed the worm. Early diagnosis of the location of the worm is fundamental
in the treatment of DUSN and occasionally provides a better visual prognosis,
as seen in case 1.
In summary, careful clinical examination by skilled ophthalmologists
still plays a key role in the diagnosis of DUSN. The SLO technique, a new
method for identifying live nematodes in DUSN, has several distinct advantages
over conventional photography and might allow better management of this disease
in young patients.
AUTHOR INFORMATION
Accepted for publication October 17, 2001.
This study was supported by Fundação de Amparo à
Pesquisa, Saõ Paulo (Dr Moraes).
Corresponding author and reprints: Lúcio R. Moraes, MD, Centro
Brasileiro de Cirurgia de Olhos, Av. T2 n° 401 Setor Bueno, Goiânia—Goiás
74210-010, Brazil (e-mail: moraesl{at}terra.com.br).
From the Retina Ophthalmology Unit, Department of Ophthalmology, Centro
Brasileiro de Cirurgia de Olhos and the Universidade Federal de Goiás,
Goiânia, Brazil (Drs Moraes, Cialdini, and Avila); the Universidade
Federal de São Paulo, São Paulo, Brazil (Dr Moraes); and the
Schepens Eye Research Institute, Harvard Medical School, Boston, Mass (Dr
Elsner). The authors have no commercial interest in the scanning laser ophthalmoscope,
any hardware associated with it, or the software developed for it.
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