2
Pathogenesis, Epidemiology,
and Natural Course of
Retinal Detachment
Retinal detachment does not result from a single, specific disease; rather, numerous disease processes can result in the presence of subretinal fluid.
TYPES OF RETINAL DETACHMENT
The three general categories of retinal detachments are termed rhegmatogenous, exudative, and tractional. Rhegmatogenous detachments are sometimes referred to as primary detachments, while both exudative and tractional detachments are called secondary or nonrhegmatogenous detachments.
The three types of retinal detachments are not mutually exclusive. For example, detachments associated with proliferative vitreoretinopathy or proliferative diabetic retinopathy may exhibit both rhegmatogenous and tractional features. However, excluding the section on differential diagnosis in Chapter 5, the scope of this book is limited to rhegmatogenous retinal detachments. Accordingly, throughout the book, the term retinal detachment refers to the rhegmatogenous type, unless another type is specifically mentioned.
RHEGMATOGENOUS RETINAL DETACHMENTS
Rhegmatogenous detachments (from the Greek rhegma, meaning rent, rupture, or fissure) are the most common form of retinal detachment. They are caused by a break in the retina through which fluid passes from the vitreous cavity into the subretinal space. The responsible break(s) can be identified preoperatively in more than 90% of cases, but occasionally the presence of a minute, unseen break must be assumed.
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10 I: Principles
EXUDATIVE RETINAL DETACHMENTS
Exudative detachments, also called serous detachments, are due to an associated problem that produces subretinal fluid without a retinal break. This underlying problem usually involves the choroid as a tumor or an inflammatory disorder.
TRACTIONAL RETINAL DETACHMENTS
Tractional detachments occur when pathologic vitreoretinal adhesions or membranes mechanically pull the retina away from the pigment epithelium without a retinal break. The most common causes include proliferative diabetic retinopathy, cicatricial retinopathy of prematurity, proliferative sickle retinopathy, and penetrating trauma. Retinal breaks may subsequently develop, resulting in a combined tractional and rhegmatogenous detachment.
ROLE OF THE VITREOUS IN PATHOGENESIS
OF RHEGMATOGENOUS RETINAL DETACHMENT
The essential requirements for a rhegmatogenous retinal detachment include a retinal break and low-viscosity vitreous liquids capable of passing through the break into the subretinal space. Vitreous changes usually precede development of important defects in the retina. The usual pathologic sequence causing retinal detachment is vitreous liquefaction followed by a posterior vitreous detachment (PVD) that causes traction at the site of significant vitreoretinal adhesion with a subsequent retinal tear. Fluids from the vitreous cavity then pass through the tear into the subretinal space (Figure 2–1), augmented by currents within the vitreous cavity caused by rotary eye movements. Although a total PVD is usually seen, many detachments occur with partial vitreous detachment, and evidence of posterior vitreous detachment may not be seen.
Any ocular condition associated with an increased prevalence of vitreous liquefaction, posterior vitreous detachment, or an increased number or extent of vitreoretinal adhesions and traction is likely to be associated with a higher incidence of retinal detachment. As will be discussed later, most eyes with retinal breaks do not develop retinal detachment because existing physiologic forces are sufficient to hold the retina in place.
VITREOUS LIQUEFACTION
In early life, the vitreous body is a homogeneous gel consisting of a network of collagen fibrils separated from one another by macromolecules of hyaluronic acid. The density of fibrils is relatively higher near the retina, called the vitreous cortex, but is highest at the vitreous base, the zone of firm anterior vitreoretinal attachment.
Aging of the human vitreous (synchisis senilis) is characterized by liquefaction of the gel and the development of progressively enlarging pools of fluid (lacunae) within the gel. These optically empty liquid spaces continue to coalesce with advancing age, and extensive liquefaction within the vitreous cavity leads
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Figure 2–1. Classic pathogenesis of rhegmatogenous retinal detachment. An acute posterior vitreous separation causes traction on a vitreoretinal adhesion (white arrow), and this results in a retinal tear. Liquids in the vitreous cavity then gain access to the subretinal space via the opening in the retina (black arrow).
to both a reduction in the shock-absorbing capabilities and the stability of the gel (Figure 2–2). Accelerated vitreous liquefaction is associated with significant myopia, surgical and nonsurgical trauma, intraocular inflammation, and a variety of additional congenital, inherited, or acquired ocular disorders.
Myopia
There is abundant evidence that the vitreous gel in myopic eyes has a substantially increased liquid component compared to emmetropic and hyperopic eyes. This is associated with reduced vitreous viscosity and stability.
Trauma
Significant blunt or penetrating trauma can damage the vitreous or retina and cause immediate or late changes that increase the odds of subsequent retinal detachment. Blunt trauma can cause accelerated vitreous liquefaction, as well as retinal tears, dialyses, or postnecrotic holes. In eyes with penetrating trauma, dense fibrocellular bands may develop within the vitreous gel and result in traction causing retinal breaks and detachment.
Surgical trauma may contribute to changes in the vitreous that increase the likelihood of retinal detachment. Because the posterior capsule is left intact in the majority of modern cataract operations, the vitreous remains relatively undamaged following uncomplicated surgery. However, subsequent posterior capsulotomy by Nd:YAG laser accelerates the loss of hyaluronic acid, increasing the incidence of vitreous liquefaction and detachment and subsequent retinal tears and detachment.
12 I: Principles
A B
Figure 2–2. Dark-field illumination of the human vitreous. Specimens were obtained by peeling off the sclera, choroids, and retina. (Courtesy of Jerry Sebag, MD.) (A) A clear central vitreous is demonstrated in a 33-week gestational age human embryo. This is due to the homogeneous distribution of collagen and hyaluronan, which minimizes light scattering. (B) The vitreous from an 88-year-old patient. There is an overall reduction in size and a collapse of the shape of the vitreous body. Within the vitreous, a dissociation of collagen from hyaluronan has occurred, resulting in pockets (“lacunae”) of liquid vitreous and thickened fibers of collagen.
Inflammation
Intraocular inflammation may predispose to retinal detachment by causing vitreous liquefaction and detachment or by the development of transvitreal membranes, particularly cyclitic membranes. In addition, retinitis can cause severe retinal thinning and associated vitreous liquefaction.
VITREOUS DETACHMENT
Vitreous detachment, usually termed posterior vitreous detachment (PVD), usually occurs as an acute event following significant liquefaction of the vitreous gel. The precipitating event is probably a break in the posterior cortical vitreous in the region of the macula, followed by the passage of intravitreal fluid into the space between the cortical vitreous and retina (Figure 2–3). Characteristically, this rapid movement of fluid and the associated collapse of the remaining structure of the gel result in extensive separation of the vitreous gel from the retina posterior to the vitreous base, especially in the superior quadrants.
As the vitreous detaches from around the disc, it may pull loose a glial annulus (Weiss’ ring), which the patient may see as a prominent floater near the visual axis. This is generally considered to be pathognomonic for posterior vitreous detachment (Figure 2–4). With collapse of the vitreous gel, the remaining formed vitreous assumes a position in the inferior aspect of the globe. Because the vitreous remains firmly attached anteriorly, the pull of the collapsed gel frequently creates a fine circumferential retinal fold or ridge near the ora at the posterior limit of the vitreous base.
As noted above, the incidence of vitreous detachment is age related. In one study, slit-lamp examination revealed that 65% of patients older than 65 had vitreous detachment. However, vitreous surgical experience has shown that PVD is frequently misdiagnosed, and in a large series of autopsy eyes, only 22% of eyes
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Figure 2–3. The rapid evolution of a posterior vitreous detachment usually occurs when pockets of liquid in the posterior vitreous gel break through the posterior cortex of the vitreous, separating it from the underlying retina (black arrows).
Figure 2–4. Clinical photograph of a midvitreal annular opacity (Weiss’ ring), which is due to the posterior cortical vitreous separating from the optic nerve.
had vitreous detachment by age 65. This number increased to 60% by age 75. Complete and incomplete PVD may cause vitreoretinal traction sufficient to create a retinal break.
The classic symptoms associated with a PVD are the sudden appearance of “floaters” and “flashes.” The former are due to shadows cast by the suddenly collapsed gel,
14 I: Principles
vitreous hemorrhage, or glial tissue. Flashes are termed photopsias and appear to be due to vitreoretinal traction. The chance of a retinal tear due to PVD in eyes with these sudden symptoms is approximately 15% to 25%, and there is a direct relationship between the amount of vitreous hemorrhage and the likelihood of a tear.
VITREORETINAL TRACTION
Following complete or partial PVD, gravitational traction forces are important and are probably responsible for the predominance of retinal tears in the superior quadrants. However, rotational eye movements, which exert strong forces on all vitreoretinal adhesions, are also important causes of vitreoretinal traction. When the eye rotates, the inertia of the detached vitreous gel causes it to lag behind the rotation of the eye wall and the retina. The retina at the site of a vitreoretinal adhesion exerts force on the vitreous gel, causing the adjacent vitreous to rotate (Figure 2–5). The vitreous gel, because of its inertia, exerts an equal and opposite force on the retina, and this can cause a retinal break or separate the retina further from the pigment epithelium if a break is already present. When the rotational eye movement stops, the vitreous gel continues its internal movement and exerts vitreoretinal traction in the opposite direction.
Figure 2–5. Rotational eye movements cause vitreoretinal traction. When the eye rotates (large arrow), the detached vitreous gel lags behind the rotation of the eye wall and the retina. The retina at the site of a vitreoretinal adhesion exerts force on the vitreous gel, causing the adjacent vitreous to rotate (arrow). The vitreous gel exerts an equal and opposite force on the retina, causing a retinal break or separating the retina further from the pigment epithelium if a break is already present. Liquid currents within the vitreous gel aggravate the movement of the gel, whereas those in the subretinal space promote extension of the subretinal fluid (arrows).