Diffuse Unilateral Subacute Neuroretinitis Workup
- Author: Lakshmana M Kooragayala, MD; Chief Editor: Hampton Roy, Sr, MD more...
Serologic studies for parasites, analysis of stool for ova and parasites, and hematologic evaluation for eosinophilia are of limited value in establishing the diagnosis of DUSN.
Some serological tests may be indicated to exclude other diseases.
Fluorescein angiography is useful for monitoring the status of the inflammation.
In early stages, fluorescein angiography may show the following:
Leakage from the optic nerve head capillaries and some generalized paravenous leakage
Window defects indicating minimal changes in the RPE
Staining of the clinically apparent gray-white lesions during the later phases of the angiogram, which are nonfluorescent in the early phase
Cystoid macular edema in some patients
In late stages, fluorescein angiography may show the following:
Diffuse areas of focal hyperfluorescence secondary to RPE loss
Leakage from choroidal neovascularization
Scanning laser ophthalmoscope
Although an examination with a fundus contact lens by a skilled ophthalmologist is the method of choice, the scanning laser ophthalmoscope (SLO) provides a new examination modality with distinct advantages for identifying live worms in young patients with DUSN. The infrared laser is safe and comfortable for a prolonged examination.
Using blue illumination, the ocular fundus appears dark and provides a high-contrast background for the white image of the worm. The red perimetry laser stimulus can be used to stimulate the worm's movement and to pinpoint its location.
Spectral domain optical coherence tomography
In the early stage, when worms can be localized, spectral domain optical coherence tomography (SD-OCT) may display a hyper-reflective object of irregular shape that affects all layers of the retina. This is associated with thinning of the nerve fiber layer and inner retinal layers and with diffuse disruption of the outer retinal architecture.
In late stages, thinning of the nerve fiber layer and inner nuclear layers persists and does not change with treatment or even in patients with improved vision. Some patients may have progressive restoration of the inner segment/outer segment junction and outer retinal architecture following treatment.[16, 17, 18]
An electroretinogram (ERG) is used to objectively evaluate the functional status of the retina and to differentiate from other retinal conditions, as follows:
In the affected eye, the ERG usually is reduced in all stages of the disease.
It is often moderately or severely reduced in the later stages of the disease.
The b-wave is affected more than the a-wave.
Rarely, the ERG may be extinguished completely.
ERG findings are normal in the unaffected eye.
ERG performed before and after laser photocoagulation appears to be useful in monitoring the retinal findings. After laser photocoagulation, recovery of ERG findings may be documented.
Electro-oculography (EOG) findings are abnormal in approximately 50% of patients.
Visual field testing may show the following:
Paracentral and central visual field defects
Useful to monitor the visual field over a period of time and to differentiate from other conditions
The only histologic findings are from an enucleated eye presumed to have DUSN. Histopathology showed nongranulomatous vitritis, retinitis, and retinal and optic nerve perivasculitis. RPE and low-grade, patchy nongranulomatous choroiditis were observed. There was no evidence of a worm.
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