36 I: Principles
Figure 2–28. Demarcation lines are due to changes in the retinal pigment epithelium at the borders of chronic retinal detachments that have not progressed rapidly. They can be pigmented, as demonstrated, or unpigmented.
macrocysts before the detachment becomes symptomatic. Conversely, macrocysts are relatively rare in retinal detachments caused by superior breaks. With surgical reattachment, the macrocysts regress rapidly (Figure 2–27B).
DEMARCATION LINES
If the boundary of a retinal detachment remains stable for a long time, pigment epithelial hyperplasia occurs at the junction between the detached and attached retina. It is generally accepted that a minimum of 3 months is required to generate a demarcation line. The to-and-fro undulations of the retina probably have an irritating effect on the retinal pigment epithelium at the boundary and induce a proliferative change, which subsequently evolves to fibrous metaplasia.
Most demarcation lines have prominent pigmentation (Figure 2–28), but occasionally the pigment granules are lost and nonpigmented demarcation lines result. In rare cases, calcification of the line occurs in long-standing detachments. Demarcation lines may create a permanent barrier to the further progression of the detachment, but often the detachment extends through the barrier and progresses posteriorly. Several concentric demarcation lines may appear, indicating intermittent extension and temporary stability in the course of detachment.
NATURAL HISTORY OF UNTREATED DETACHMENT
A limited retinal detachment left untreated may follow one of four outcomes:
1.Usually, most untreated clinical rhegmatogenous detachments progress to near total or total detachment and blindness.
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Figure 2–29. A spontaneous reattachment of an old chronic retinal detachment in the inferior temporal quadrant. This occurs when the retinal reattachment forces are stronger than the factors promoting extension of subretinal fluid.
2.Occasionally, a detachment remains indefinitely as a subtotal detachment with stable borders and the creation of demarcation lines. This is most apt to occur in detachments caused by inferior breaks, particularly small breaks or dialyses.
3.Rarely, subretinal fluid due to a superior retinal break settles inferiorly away from the break, and the site of the original break flattens.
4.Very rarely, spontaneous reattachment occurs, usually associated with a very small break and excellent presumed “pumping” of the retinal pigment epithelium or closure of the break by scar tissue (Figure 2–29).
Retinal detachment is usually associated with decreased intraocular pressure secondary to increased resorption of fluid from the subretinal space. Uveitis or traction on the ciliary body by proliferative vitreoretinopathy may also decrease the production of aqueous humor to the point of hypotony and eventual phthisis.
Occasionally, the low-grade uveitis that accompanies retinal detachment damages the trabecular meshwork enough to produce elevated intraocular pressure. Rubeosis iridis may also develop in long-standing detachment, resulting in neovascular glaucoma. When a long-standing detachment is repaired, glaucoma may replace relative hypotony due to damage to the trabecular meshwork.
Clinically, proliferative vitreoretinopathy is seen most often after surgery, but it is also observed as the end result of the natural history of unoperated retinal detachment. Cataract may also develop as a late effect of retinal detachment.
SUMMARY
Retinal detachments may be caused by traction or by exudation from a choroidal tumor or inflammation, but most detachments are caused by retinal tears
38 I: Principles
(rhegmatogenous detachments). Vitreous liquefaction and vitreous detachment can lead to traction on the retina with subsequent retinal tear formation. Liquid currents within the vitreous cavity along with persistent traction promote retinal detachment.
Horseshoe tears and retinal dialyses have a much higher likelihood of leading to retinal detachment than atrophic or operculated retinal breaks, and not all tears require prophylactic treatment. Retinal breaks are most common in superior and temporal quadrants and less likely in the inferior and nasal retinal periphery. The most common risk factors for development of retinal detachment are myopia, history of cataract surgery, lattice degeneration, ocular trauma, and a personal or family history of retinal detachment. Various other ocular, systemic, and genetic conditions can also lead to retinal detachment. Combinations of risk factors increase the likelihood of retinal detachment.
Retinoschisis is to be distinguished from and may occasionally lead to retinal detachment. Proliferative vitreoretinopathy, intraretinal macrocysts, and demarcation lines may accompany chronic retinal detachment. Untreated retinal detachment usually progresses, leading to retinal deterioration and eventual blindness.
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