Diffuse Unilateral Subacute Neuroretinitis Clinical Presentation

Updated: Apr 17, 2018
  • Author: Lakshmana M Kooragayala, MD; Chief Editor: Andrew G Lee, MD  more...
  • Print
Presentation

History

Early-stage history may include the following:

  • Mild-to-moderate visual loss

  • Paracentral or central scotomas

  • Floaters

  • Ocular discomfort

  • Conjunctival injection of affected eye

Late-stage history may include the following:

  • Severe unilateral visual loss

  • Paracentral or central scotomas

In some patients, the disease may be asymptomatic with the characteristic changes found only on routine eye examination.

Next:

Physical

Patients should undergo a complete eye examination, including visual acuity, pupillary reactions, visual fields, slit lamp examination of the anterior and posterior segments, indirect ophthalmoscopy, and detailed examination of the retina using a fundus contact lens. [12, 13]

Early stage

Visual acuity - Range is from 20/30 to 20/200 or less.

Visual field - Paracentral or central scotoma may be detected.

Pupils - A relative afferent pupillary defect may be noted.

Anterior segment findings reveal normal conjunctiva or conjunctival injection, ciliary flush, anterior chamber cells and flare, fine keratic precipitates, and small hypopyon.

Posterior segment examination findings reveal mild-to-moderate vitritis, optic disc swelling, narrowing of the retinal arterioles, retinitis, and nematodes.

Retinitis is the most characteristic feature of this syndrome. Transient, multiple, focal, gray-white lesions of the deep retina or RPE vary in size from 0.25-1 disc diameter and tend to develop in clusters over wide areas of the retina at various time periods. The active evanescent gray-white lesions fade within a period of 7-10 days as the nematode moves elsewhere in the eye, only to recur in an adjacent area or distant site over the ensuing weeks. Lesions typically resolve without any ophthalmoscopic or angiographic evidence of damage.

Nematode: Identification of the subretinal worm is the pathognomonic finding in DUSN. To localize the worm, careful and repeated examination with a fundus contact lens is required. The worm can be present in all layers of the retina, but it most frequently is found in the subretinal or outer retinal layers. The motile worm is more likely to be observed in the neighborhood of the active grayish-white retinal lesions. The worms appear smooth in outline, tapered on both ends, and often assume an S-shaped, coiled, or figure "8" configuration. These organisms propel themselves by a coiling and uncoiling motion and sometimes move in a snakelike fashion in the subretinal space. They may be noted to move under direct observation in an apparent aversion to bright light, and a white glistening sheen may be noted over the region.

Other less frequently encountered clinical signs include the following: focal retinal and subretinal hemorrhages, perivenous exudates and vascular sheathing, localized serous detachments of the neurosensory retina, cystoid macular edema, retinal striae, and choroidal neovascularization.

Late stage

Visual acuity - This ranges from 20/20 to 20/400 or less.

Visual fields - Dense central or paracentral scotoma may be seen.

Pupils - Relative afferent pupillary defect possible

Posterior segment examination reveals the following findings:

  • Focal and diffuse loss or mottling of the RPE, most typically seen in the paramacular region, sparing the center of the macula in most patients

  • Generalized narrowing of the retinal arterioles

  • Marked optic disc pallor

  • Choroidal neovascularization and/or disciform scarring

  • Peripapillary arteriolar sheathing

Previous
Next:

Causes

Precise identification of the worm has not been accomplished, but two different types of worms have been recognized in endemic areas.

In the southeastern United States, Caribbean, and Latin America, a larval worm measuring about 400-700 µm has been recognized. It is presumed to be Ancylostoma canium, which is a known frequent cause of cutaneous larval migrans. [14, 15]

In the north midwestern United States, a larger worm measuring 1000-2000 µm has been observed. It is proposed by some authors to be Baylisascaris procyonis and is a rare cause of visceral and ocular larval migrans. [16]

Previous