Retinal detachment does not result from a single, specific disease; rather, numerous disease processes can result in the presence of subretinal fluid. 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 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. 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 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. 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.