RETINAL DETACHMENT

RETINAL DETACHMENT

SIGNS AND SYMPTOMS
There are three forms of retinal detachment:

1. Rhegmatogenous retinal detachment (RRD), which results from a retinal break. The vast majority of rhegmatogenous detachments are symptomatic, with patients reporting photopsiae, floating spots, peripheral visual field loss, central blurring of vision or metamorphopsia.

2. Exudative or serous retinal detachment (ERD), which results from fluid accumulation under the sensory retina without a retinal break. Exudative detachments do not generally present with photopsiae but may be associated with moderate vision loss, metamorphopsia or a visual field deficit.

3. Tractional retinal detachment (TRD), which results from the pull of proliferative fibrovascular vitreal strands. Tractional detachments are typically asymptomatic unless central vision is threatened, in which case the patient can suffer severe and abrupt vision loss.

In cases of extensive unilateral retinal detachment, you may observe a relative afferent pupillary defect. Intraocular pressure may be reduced in eyes with acute retinal detachment.

Ophthalmoscopy in cases of RRD usually reveals a clumping of pigment cells within the anterior vitreous (Shaffer's sign). There may be an area of white or grayish elevated retina adjacent to the instigating retinal break. If a significant area of the retina is involved, you may note a milky, lackluster appearance with undulating retinal folds.

A rhegmatogenous detachment will not change position with changes in body posture, however it may shift and then return to its original orientation with quick eye movements. Associated findings may include posterior vitreous detachment and preretinal or vitreal hemorrhage. Retinal pigment epithelial hyperplasia may be noted in cases of long-standing retinal detachment (pigment demarcation line), and is a good prognostic feature.

ERD appears clinically as a focal, serous elevation of the retina, which shifts position with changes in posture and eye movement. The subretinal fluid obeys gravity, always affecting the lowest aspect of the eye. Ophthalmoscopy reveals a smooth, translucent, dome-shaped protrusion of the retina. There are usually no hemorrhages, except in cases of associated retinal vasculopathy.

TRD is always associated with vitreal strands and membranes. It appears as a concave, smooth-surfaced detachment with marginal fibrovascular bands emanating into the vitreous body. It is sometimes difficult to assess where the necrotic retina ends and the vitreal membranes begin. Very often, this area encircles an intact posterior pole, resulting in a retinal "pseudo-hole." TRDs are dense and immobile. This motility lends itself well to ancillary testing with ultrasonography.

PATHOPHYSIOLOGY
All retinal detachments involve the sensory retina dissecting from the underlying pigment epithelial layer by subretinal fluid. In rhegmatogenous detachments, this fluid is liquefied vitreous, which accesses the subretinal space via a retinal break. In exudative detachments, the fluid is derived from the choroid, passing through a defective Bruch's membrane. The origin of the subretinal fluid in tractional detachments is unknown. Both passive and active movement of subretinal fluid induce progression of retinal detachments, leading to partial or total loss of vision in some patients.

Retinal breaks are the predisposing factor in patients with rhegmatogenous detachment. These may result from preexisting conditions or ocular trauma. Some of the more common entities associated with RRD include lattice degeneration, flap tears, atrophic holes, operculated retinal breaks, and acquired retinoschisis with both inner and outer holes. As the retinal tissue loses its connection to the RPE, it becomes edematous and dysfunctional. Without surgical intervention, death of this tissue occurs within 48 to 72 hours.

Exudative detachments are relatively rare, occurring in association with subretinal disorders that damage the RPE layer. These may include choroidal neoplasms, Vogt-Koyanagi-Harada syndrome, posterior scleritis, congenital optic disc anomalies (optic pits, morning glory syndrome, etc.), Coat's disease and uveal effusion syndrome.

Transudation of fluid through the RPE defects causes detachment of the otherwise normal sensory retina. As the fluid shifts with eye and head movements, the involved portion of the retina changes. This explains why most patients with ERDs suffer significantly less devastating visual compromise than those with RRDs or TRDs.

Tractional detachments occur only in proliferative vitreoretinopathies. The most common of these is proliferative diabetic retinopathy, but many TRDs are associated with ischemic retinal vein occlusions, sickle cell retinopathy, retinopathy of prematurity, toxocariasis and trauma.

The etiology of TRD involves fibrotic scaffolding of the vitreous along proliferative vascular networks which induce strong anterior tractional forces through vitreal shrinkage. These forces induce the sensory retina to separate from the underlying RPE.

Unlike rhegmatogenous or exudative detachments which tend to be abrupt, TRDs are often slow and insidious, progressing at the same rate as the associated fibrovascular proliferation. Peripheral TRDs are therefore rarely if ever noticed by the patient. Macular TRDs, on the other hand, tend to be symptomatic, unless the underlying disease process has already compromised visual acuity.