Uveal Effusion Syndrome

There are several theories regarding the pathogenesis of UES such as: increased choroidal permeability, intrinsic choroidal alterations, vortex vein obstruction and decrease in scleral permeability.[4,5,6,7,8,9,10,11] Histopathologic studies support the theory of a primary abnormality of the sclera, with secondary effects on trans-scleral protein permeability and compression of the vortex veins.

In the human eye, proteins can diffuse across the sclera, though the osmotic gradient across the sclera is near to zero with no osmotic fluid retention.[12] In 1983 Don Gass proposed that the cause of UES is impaired diffusion of protein across the sclera which results in secondary fluid retention in the suprachoroidal space.[7]

Histological studies which support Gass hypothesis show disruption and disorganization of the collagen fibers, thickening of the sclera and amorphous material expanding the space between scleral collagen fibers.[8,10,13] Another support to Gass' hypothesis was obtained by Jackson et al.[10] who demonstrated low diffusion coefficients of high molecular weight dextrans across the sclera of UES patients.

An alternative to Gass' hypothesis on the pathogenesis of UES is compression of the vortex veins by abnormally thick sclera. Yue et al.[14] reported resolution of the effusion in a patient with UES following surgical decompression of the vortex veins.

Most likely, hydrostatic forces (vortex vein compression) and osmotic forces (reduced trans-scleral protein diffusion) both cause UES, with the relative contribution of each varying in each patient with UES.[6]

UES clinical features may vary from small peripheral elevation with preserved visual acuity to extensive detachments of choroid and ciliary body with vision loss due to involvement of the macula. Deep retinal or subretinal exudates may appear prior to the serous detachment, and optic nerve edema may be present (Figure 29.1).[4,6] UES is usually defined by a relapsing clinical course. There is usually an associated serous retinal detachment, with shifting subretinal fluid as the subretinal fluid is heavy and proteinaceous. Uveal, retinal, or vitreous inflammation is minor or absent. In chronic conditions the subretinal fluid may lead to changes in the retinal pigment epithelium (RPE) which can cause leopard-spot fundus. Nanophthalmic eyes may have associated findings, such as high hyperopia and a history of angle closure glaucoma.[2] Resolution of the fluids occurs in most patients but it may take months. or even years.[4]

UES is a clinical diagnosis and may often be misdiagnosed. The first step in UES diagnosis is ruling out other causes of exudative retinal detachment. Measurements of the patient refraction and axial length should be done although one must keep in mind that UES can occur in a non-nanophthalmic eyes.

Optical coherence tomography (OCT) demonstrates subretinal fluid and focal thickening of the RPE through the leopard spots. Enhanced-depth imaging (EDI)-OCT discloses an increase in choroidal thickness and the presence of large areas of hypo¬reflectivity that may correspond to engorged choroidal veins or expan¬sion of the suprachoroidal space.[16] In the acute setting, the leopard spots will appear as hyperfluorescent on fundus autofluo¬rescence (FAF), but over time this may change to a mix of hyper- and hypo¬autofluorescence on FAF.[4,11] Fluorescein angiography in UES typically shows areas of hypofluorescence corresponding to leopard-spot pigmentation. ICG can confirm the presence of dilated choroidal vessels.[17] Ocular ultrasound should be used to measure the scleral thickness and to rule out a choroidal mass (Figure 29.3) as well as to obtain an axial length.[18] Although posterior scleral thickness greater than 2 mm is abnormal (normal value is 1 mm) and may indicate UES, recent studies showed that UES may not always be associated with an increase in scleral thickness, with mean values only 20% greater than controls in one series.[19]

In cases where surgery is done the diagnosis can be confirmed by taking scleral biopsies to be reviewed under light microscopy and scanning electron microscopy. Staining the specimen with hematoxylin and eosin will demonstrate the disordered collagen arrangements and staining with alcian blue will identify acid mucins that are deposited in between the collagen fibers. Electron microscopy can demonstrate degenerate collagen fibrils.