Uveal Effusion Syndrome and Hypotony Maculopathy

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Chapter 73 Uveal Effusion Syndrome and Hypotony Maculopathy

The clinical observation of abnormal serous fluid accumulation in the outer layer of the ciliary body and choroid is called uveal effusion. This exudative detachment of the choroid and the ciliary body is also known as ciliochoroidal effusion, ciliochoroidal detachment, choroidal effusion, or choroidal detachment. These names are used interchangeably in this chapter. Uveal effusion does not refer to a specific entity, but this name is used as the common term to describe a pathoanatomic condition caused by several ocular and systemic disorders. Uveal effusion is frequently associated with nonrhegmatogenous retinal detachment, secondary to the chronic accumulation of protein-rich fluid in the choroid and the breakdown of the retinal pigment epithelial fluid barrier. The term “idiopathic uveal effusion syndrome” or “uveal effusion syndrome” in short refers to the presence of ciliochoroidal effusion in an eye with no other known associated ocular or systemic disorder. Uveal effusion syndrome typically occurs spontaneously in an otherwise healthy middle-aged man.

Hypotony maculopathy refers to the structural changes in the macular region and related visual dysfunction that may develop in an eye with low intraocular pressure. In addition to the changes in the macular region, hypotony may be associated with other posterior-segment abnormalities, including optic nerve swelling, vascular tortuosity, and chorioretinal folds. The vision loss may be profound in the setting of persistent ocular hypotony, but visual improvement is typical after intraocular pressure is restored.

Uveal effusion syndrome

Introduction

Spontaneous exudative detachment of the choroid and ciliary body was first reported by Schepens and Brockhurst in 1963 ¹; these authors used the term “uveal effusion” in their description of this disorder. Almost two decades later, Gass and Jallow in 1982 coined the term “idiopathic uveal effusion syndrome” to describe idiopathic serous detachment of the choroid, ciliary body, and retina.² Uveal effusion syndrome is a rare ocular disorder that typically manifests itself in an otherwise healthy middle-aged male. In their original report, Schepens and Brockhurst described 17 patients, only one of whom was female. The diagnosis of uveal effusion syndrome is based on characteristic clinical findings and exclusion of other known causes of uveal effusion. Bilateral involvement is common and unilateral cases tend to occur in older males. In addition to the accumulation of serous fluid in the ciliary body and choroid, nonrhegmatogenous retinal detachment with marked shifting of the subretinal fluid are commonly observed in patients with uveal effusion syndrome. Retinal detachment often begins inferiorly, as in other causes of exudative retinal detachment. Other ocular findings include dilation of the episcleral blood vessels, blood in Schlemm’s canal, normal intraocular pressure, mild vitreous cells, leopard-spot retinal pigment epithelial alterations, elevation of the subretinal fluid protein levels, and elevation of the cerebrospinal fluid protein. Without treatment, a protracted clinical course with remissions and exacerbations over many months to years may cause significant visual decline and morbidity. Unlike other causes of ciliochoridal effusion, patients with idiopathic uveal effusion syndrome respond poorly to nonsurgical treatment, including corticosteroids or antimetabolites. Similarly, surgical treatment of nonrhegmatogenous retinal detachment in uveal effusion syndrome using conventional techniques, including scleral buckling or pars plana vitrectomy, fails to reattach the neurosensory retina secondary to persistent serous exudation. In most cases, successful reattachment of the nonrhegmatogenous retinal detachment requires a scleral-thinning procedure, including quadrantic partial-thickness sclerectomies and sclerostomies.

Pathophysiology of ciliochoroidal effusions

General mechanisms

Since idiopathic uveal effusion syndrome represents only a small percentage of ciliochoroidal effusions, it is important to discuss the general mechanisms of serous accumulation in the ciliary body and choroid. Most cases of ciliochoroidal effusion can be classified into one of the following pathophysiologic categories: (1) hydrodynamic; (2) inflammatory; (3) neoplastic; or (4) associated with abnormal sclera.³ Under physiologic conditions, a normal eye has equilibrium between the transmural hydrostatic pressure gradient, defined as the difference between the intravascular blood pressure and intraocular pressure, and the colloid osmotic pressure gradient of the choriocapillaris (Fig. 73.1). Albumin is the most abundant protein in the choroidal capillaries and is the primary driver of the colloid osmotic pressure. This pressure gradient draws fluid into blood vessels and maintains relative dehydration of the suprachoroidal space due to a low extravascular colloid concentration.⁴ Fenestrated capillaries of the choroid allow albumin to escape into the extravascular space. To maintain the colloid osmotic gradient, albumin leaves the choroid across the sclera and this transscleral protein flow is facilitated by intraocular pressure.⁵^–⁷

Fig. 73.1 In normal choroidal capillaries, the transmural hydrostatic pressure gradient is in equilibrium with the colloid osmotic pressure gradient. Colloids escaping the fenestrated capillaries move across the sclera by bulk flow, driven by intraocular pressure (IOP). BP, blood pressure.

(Courtesy of Biomedical Communications, University of Michigan.)

The fluid equilibrium across the layers of the choroid may be disturbed by several factors affecting one or more components of this intricate system.³ Ocular hypotony decreases the driving force for transscleral protein flow and increases the transmural hydrostatic pressure gradient. These changes then facilitate the accumulation of protein and fluid in the suprachoroidal space. Elevated uveal venous pressure increases the transmural hydrostatic pressure gradient and leads to increased fluid movement into the extravascular space. Vascular competence may be compromised by inflammation, which then increases capillary protein permeability and accumulation of protein in the extravascular space. This reduces the colloid osmotic pressure gradient and the absorption of extravascular fluid into the capillaries. Abnormal scleral composition or thickness may increase resistance to transscleral protein outflow and accumulation of protein-rich fluid in the suprachoroidal space. These alterations are more likely to affect the choroidal fluid dynamics when two or more are present simultaneously. Indeed, the creation of ciliochoroidal effusion in animal models requires experimental alteration of two or more pathophysiologic factors.^8,⁹

Idiopathic and nanophthalmic uveal effusion

In patients with uveal effusion syndrome or the closely related condition of nanophthalmos, abnormal sclera, referred to here as scleropathy, is the most likely primary ocular anomaly affecting choroidal fluid dynamics. In nanophthalmos, scleropathy is congenital in origin and associated with other ocular abnormalities. Acquired scleropathy may be secondary to a systemic disorder, such as the accumulation of amyloid in systemic amyloidosis or mucopolysaccharide in Hunter syndrome.^10,¹¹ In uveal effusion syndrome, scleropathy appears to be secondary to the abnormal accumulation of glycosaminoglycan-like deposits and thickening of the sclera in the absence of any known systemic disorder.¹²^–¹⁴ Ward et al. reported that electron microscopy of excised sclera showed increased glycosaminoglycan-like deposits between the scleral fibers.¹⁴ In a following report, Forrester and colleagues performed histochemical studies on scleras excised from patients with uveal effusion syndrome and showed deposition of the glycosaminoglycan proteodermatan sulfate and a smaller amount of proteochondroitin sulfate, indicating a primary defect in scleral proteodermatan metabolism and representing a form of ocular mucopolysaccharidosis.¹² Histologic similarities between scleras isolated from eyes with uveal effusion syndrome and nanophthalmos were demonstrated by Uyama et al., who found disorganized scleral fibers and proteoglycan deposits in 6 nanophthalmic eyes and 11 nonnanophthalmic eyes with uveal effusion syndrome.¹³ As discussed above, abnormal scleral composition increases resistance to transscleral protein outflow, which in turn leads to the accumulation of protein in the extravascular space of the choroid and higher colloid osmotic pressure. This results in reduced movement of fluid from the suprachoroidal space into the choroidal capillaries and leads to serous ciliochoroidal effusion. In vitro experimental evidence is consistent with this model, as chondroitinase ABC digestion, which removes glycosaminoglycans, improves scleral transport in human cadaver eyes.¹⁵

Ciliochoroidal effusion and nonrhegmatogenous retinal detachment can be successfully treated in patients with uveal effusion syndrome by quadrantic partial-thickness sclerectomies.^16,¹⁷ The disappearance of serous fluid after partial-thickness sclerectomies is consistent with the hypothesis that abnormally thickened sclera prevents outflow of protein and suggests that the removal of excess extravascular protein may be improved by reducing scleral thickness and resistance. Under normal conditions, eyes with congenital or acquired scleropathies may have enough redundancy in choroidal protein transport mechanisms to achieve physiologic fluid equilibrium and dehydration of the suprachoroid. However, when choroidal fluid dynamics are further stressed by additional pathologic factors, such as compression of the vortex veins, these compensatory mechanisms may no longer be sufficient to overcome the effect of increased colloids in the suprachoroidal space, which may then lead to increased extravascular fluid retention and ciliochoroidal detachment.

Vortex vein compression was first suggested by Schaffer in 1975 as a possible mechanism of uveal effusion in nanophthalmic eyes following glaucoma filtration surgery.¹⁸ Relative obstruction of venous outflow secondary to compressed vortex veins may cause congestion of the choriocapillaris and alter the transmural hydrostatic pressure gradient, favoring increased retention of fluid in the suprachoroidal space. Brockhurst reported successful reattachment of the retina and resolution of ciliochoroidal effusion in nanophthalmic eyes after surgical decompression of the vortex veins.¹⁹ Additional evidence for the role of increased intravascular pressure secondary to reduced ocular venous drainage in uveal effusion was provided by Casswell and colleagues, who reported resolution of retinal detachment after vortex vein decompression in patients with uveal effusion syndrome.²⁰ As proposed by Gass, compression of the vortex veins by an abnormally thickened sclera may contribute to increased fluid retention and serous exudation in the choroid and ciliary body in uveal effusion syndrome.¹⁶

Clinical features

Ciliochoroidal detachments in uveal effusion syndrome are brown-orange, solid-appearing elevations with smooth, convex surfaces (Fig. 73.2). Transillumination of the globe confirms the serous nature of the exudation. Choroidal detachments do not undulate appreciably with ocular movements, and this helps to distinguish them from rhegmatogenous retinal detachments. In early or mild cases, the diagnosis is suggested when the ora serrata is visible without the use of scleral depression secondary to shallow elevation of the pars plana and peripheral choroid (Fig. 73.3). As the effusion progresses, annular or lobular choroidal detachment may be seen. The characteristic four-lobed configuration results from the attachment of the choroid to the sclera at the vortex vein ampullae. The fluid accumulation is always greater anteriorly, as the anterior connecting fibers attaching choroid to the sclera are long and tangentially oriented, unlike the posterior fibers that are short and run more directly from uvea to sclera.²¹

Fig. 73.2 Ciliochoroidal effusion demonstrating the characteristic solid-appearing choroidal elevation with a smooth, convex surface.

Fig. 73.3 Visible ora serrata without the use of scleral depression secondary to shallow elevation of the pars plana and peripheral choroid in an eye with ciliochoroidal effusion.

Long-standing uveal effusion causes decompensation of the retinal pigment epithelial fluid barrier, resulting in increased protein and fluid accumulation in the subretinal space and development of nonrhegmatogenous retinal detachment (Fig. 73.4). There is greater absorption of fluid from the subretinal space compared with protein outflow, which results in rising protein concentration and marked shifting of subretinal fluid with changes in head position. Progressive subretinal fluid accumulation may lead to total retinal detachment. Chronic serous effusion and subretinal fluid accumulation may result in diffuse depigmentation and multifocal hyperplasia of the retinal pigment epithelium, forming the characteristic clinical finding of leopard spots in the fundus (Figs 73.4 and 73.5).

Fig. 73.4 Nonrhegmatogenous retinal detachment in a patient with uveal effusion. Location of the subretinal fluid is dependent on gravity. Leopard-spot retinal pigmentation is apparent superiorly.

Fig. 73.5 Leopard-spot retinal pigmentation in uveal effusion syndrome.

Anterior-segment examination in a patient with uveal effusion syndrome may reveal dilation of the episcleral blood vessels. Blood may be present in the Schlemm’s canal on gonioscopy. The anterior chamber is free of any signs of inflammation and the presence of anterior-chamber cell should increase suspicion of another ocular disorder with secondary uveal effusion. Mild vitreous cells may be present. Intraocular pressure is normal in patients with uveal effusion syndrome and hypotony would indicate the presence of an alternative etiology. Elevation of subretinal fluid protein levels has been documented.^2,^22,²³ Although not commonly tested today, earlier studies of patients with uveal effusion syndrome demonstrated increased cerebrospinal fluid pressure and protein levels in some cases.^1,²

Diagnostic studies

In addition to the clinical examination, ancillary studies are important for the diagnosis of uveal effusion syndrome and, more importantly, for the exclusion of other more common etiologies of ciliochoroidal effusion.

Ophthalmic ultrasound

B-scan ultrasound examination typically shows a smooth, thick, dome-shaped membrane with little aftermovement.²⁴ Ciliochoroidal effusion may be distinguished from retinal detachment by extension of the detachment anterior to the ora serrata. Highly bullous ciliochoroidal detachments may extend posteriorly and insert near the edge of the optic nerve. A-scan evaluation demonstrates a thick, 100% spike at tissue sensitivity, which at low sensitivity can often be seen to be double-peaked.²⁴ In early presentations of uveal effusion syndrome, the only evidence for ciliochoroidal effusion may be subtle degrees of supraciliary effusion on high-frequency ultrasound biomicroscopy. Diffuse, high-reflective thickening of the posterior choroid may be seen (Fig. 73.6). Low-reflective choroidal thickening should raise the suspicion for an infiltrative process secondary to an inflammatory or neoplastic condition.²⁴

Fig. 73.6 B-scan ultrasound of an eye with uveal effusion syndrome shows choroidal thickening and inferior nonrhegmatogenous retinal detachment.

Angiography and optical coherence tomography

The diagnostic value of fluorescein and indocyanine green angiography and optical coherence tomography is limited in uveal effusion syndrome and serves mostly to exclude other etiologies. Angiography may demonstrate a leopard-skin appearance of hyperfluorescence and hypofluorescence (Fig. 73.7). The presence of focal fluorescein leaks and focal pigment epithelial detachments should increase the suspicion for idiopathic central serous chorioretinopathy as the underlying diagnosis. Multiple pinpoint leaks may indicate the presence of an inflammatory or neoplastic choroidal infiltration. Indocyanine green angiography shows diffuse granular choroidal hyperfluorescence in the early phase, indicating marked hyperpermeability of the choroidal vessels.¹³ This choroidal hyperfluorescence persists into the late-phase angiogram and becomes more diffuse, demonstrating increased accumulation of fluid in the choroid. Spectral-domain optical coherence tomography may show focal thickening of the retinal pigment epithelium layer corresponding to the areas of leopard spots.²⁵