Etiology

RD occurs by the following principle mechanisms: a hole, tear or break in the neuronal layer allowing fluid from the vitreous cavity to separate sensory and RPE layers (i.e. RRD); traction from inflammatory or vascular fibrous membranes on the surface of the retina, which tether to the vitreous; exudation of material into the subretinal space from retinal vessels (such as in hypertension, central retinal venous occlusion, vasculitis, papilledema). Retinal detachments may be associated with congenital malformations, metabolic disorders, trauma, previous ocular surgery, vascular disease, choroidal tumors, high myopia, vitreous disease or degeneration.
Liquefaction of the vitreous is a major pre-requisite in the development of RRD. It occurs naturally with aging. This process is known as vitreous syneresis or synchysis senilis. It can also be associated with variety of congenital, inherited or acquired eye diseases and accelerated by high myopia, surgical and non-surgical trauma, and intraocular inflammation. Synchysis senilis is characterized by development of progressively enlarging pools (lacunae) of fluid within the vitreous gel. Significant liquefaction of the vitreous gel may lead to vitreous detachment (usually termed posterior vitreous detachment or PVD), which often precipitates RRD by producing tractional forces necessary to generate retinal breaks.

Posterior vitreous detachment (PVD) is typically an acute event that consists of partial or total (in majority of cases) separation of the posterior vitreous from the retina as a result of vitreous degeneration and shrinkage. Most persons develop PVD at some point in their lives. Less than 10% of patients with PVD are younger than 60 years of age, 30% of patients are in the seventh decade of life and more than 60% of patients are in the eighth decade of life. Patients with high myopia usually develop PVD earlier in life.

The most common symptoms of PVD are floaters of various types that may persist for months to years when uncomplicated, flashing lights, occasional vitreous hemorrhage and pigmentary debris. PVD may also be asymptomatic. In majority of cases, PVD is a benign condition that is not sight-threatening, does not require treatment and has no long-term complications. However, in the acute phase of PVD as the vitreous shrinks and detaches from the retina, tractional forces may be sufficient to cause a full-thickness tear in the retina. Such tears allow fluid to gain entry to the subretinal space. Due to rotational eye movements, gravitational and inertial forces or contracture of intraocular fibroproliferative tissue, vitreous currents force fluid through the retinal breaks and progressively extend the retinal detachment. A significant proportion of patients with acute PVD develop an associated retinal tear that can lead to RD and, if left untreated, permanent vision loss.

Retinal breaks may develop spontaneously in areas of strong vitreoretinal adhesion, typically along retinal vessels, or in patients with certain predisposing conditions, such as lattice retinal degeneration. In some cases patients describe a recent history of ocular trauma or surgery. Usually, the retinal breaks are located between the equator and ora serrata, or near the equator of the globe. Only 15% of retinal breaks develop posterior to the equator. Retinal breaks occur in about 6% of the general population, but most of them are benign atrophic holes that do not lead to RD.

There are several types of retinal breaks:

• Flap tear (also known as “horseshoe” due to the U-shaped morphology) are usually located near the equator of the eye and are most common in middle age. They have an acute onset and frequently lead to detachment. As symptomatic flap tears are at high risk, they should be properly treated to prevent an RD (Fig. 3-4).
• Atrophic retinal holes have round shape and gradual onset, are often within patches of lattice degeneration and are not associated vitreoretinal traction. Usually, they have low risk and do not require prophylactic treatment.
• Ocular breaks are characterized by flap shape and acute onset. They consist of complete separation of a free-floating vitreous operculum from the underlying break. Ocular breaks tend to locate more posterior than the flap breaks. The risk of RD is intermediate. Decision for treatment should be taken case by case (Fig. 5).
• Dialysis is a traumatic (or in some cases congenital) circumferential retinal tear by the ora serrata that has linear shape, acute onset and most commonly occurs in young individuals. Unlike the other breaks, vitreoretinal traction is on the posterior margin of the dialysis. The risk of RD is moderate (Fig. 6).

Lattice degeneration is one of the most important vitreoretinal abnormalities associated with an increased likelihood of retinal tears and RD. Approximately 30% of patients with RD also have lattice degeneration. Lattice degeneration is atrophic disease of the peripheral retina characterized by sharply demarcated round, oval or linear patches of retinal thinning that are circumferentially oriented and associated with liquefaction of the overlying vitreous gel (vitreoretinal degeneration). The disease occurs in 6 to 10% of the general population and is bilateral in approximately 50% of cases. Lattice degeneration can occur early in life and is usually diagnosed in the second decade of life. Lattice lesions are more common among patients with high myopia. Usually, the lesions are non-progressive or very slowly progressive. Lattice degeneration is typically asymptomatic unless associated with symptomatic retinal breaks. Thinning of the retinal surface of lattice degeneration may lead to formation of atrophic holes that occur in 20-35% of cases. Occasionally, they may encompass the entire lattice lesion. In this case, the overlying liquefied vitreous can pass through the hole into the subretinal space and predispose to retinal tears and retinal detachments. Longitudinal studies suggest that a new tear or detachment occurs in approximately 1% of patients with lattice retinal degeneration. No evidence of a benefit of prophylactic laser has been proven.

Retinal detachments after cataract surgery (pseudophakic RD) are probably due to vitreous changes (e.g. liquefaction and collapse of the vitreous secondary to diffusion of hyaluronic acid during surgery), disruption of the posterior capsule and vitreous loss at the time of surgery or following the surgical operation. The most important change in the vitreous after cataract surgery is the occurrence of PVD. Patients with pseudophakic RD, like those with other forms of RRD, usually present with symptoms of flashes of light, floaters, decreased visual acuity, or visual field defects. Over 50% of pseudophakic RD occur during the first year after cataract surgery. At 10 years, the risk of RD is 5 times higher in patients who had undergone cataract surgery than in those who did not have this surgical procedure. The overall risk of RRD after cataract surgery is approximately 1%. Post-cataract RRD tends to be more advanced, with total detachment (often involving the macula), multiple tiny breaks, fixed folds, and a higher incidence of proliferative vitreoretinopathy. Several risk factors for development of RD after cataract surgery have been suggested, e.g. high myopia and younger age. The occurrence of RD in the fellow eye increases the risk of RD in the eye undergoing cataract surgery.

Patients with high myopia (spherical equivalent of –6.0 diopters or more or an axial length of at least 26 mm) have 5- to 6-fold increased risk for developing RD. These patients represent only 10% of the general population but comprise 42% of the patients with RRD.

Blunt trauma is the leading cause of RD in children and adolescents. The vast majority of these patients are male. Boxers are at particularly high risk. Kickboxing and karate may also be associated with an increased risk of retinal tear. At the moment of impact, rapid compression and decompression of the globe may generate sufficient vitreoretinal traction to produce retinal tears. This type of tear can be detected and treated before it develops into RD. Individuals with high level of myopia should be advised to avoid activities carrying a risk of shock to the head or eye. Recommendations to avoid activities that may increase the intraocular pressure, such as diving and skydiving, in order to decrease the risk of RD have little supporting evidence.

Patients with congenital glaucoma and open-angle glaucoma are considered at increased risk for RRD.

Retinoschisis (splitting of the neurosensory retina into two layers) is responsible for about 2.5% of RRD cases. Most retinoschisis do not progress and do not require treatment. When both inner and outer layer holes develop, retinoschisis may convert into RRD, which will require a prompt treatment.

A cystic retinal tuft is a congenital abnormality that is characterized by a small, discreet, round or oval vitreoretinal lesion composed primarily of glial tissue. The lesion appears elevated, sharply circumscribed and chalky white. Vitreous condensations are attached to its surface, and its base may have pigmentary changes. It is estimated that the risk of RD in a patient with a cystic retinal tuft is only 0.3%.

In zonular traction tufts, thickened zonules are displaced posteriorly and attached to the anterior retina. This results in an abnormal tuft of tissue drawn from the surrounding retinal surface toward the ciliary body. RD due to development of retinal breaks in association with the zonular traction tuft occurs rarely.

Another condition that may lead to RD is a giant retinal tear, defined as a retinal tear that extends 3 clock hours (90 degrees) or more around the circumference of the globe. Individuals with high myopia and patients with Stickler’s syndrome have elevated risk of bilateral giant retinal tears. These cases are usually associated with a worse prognosis compared to breaks of other etiologies.

RRD is a common feature in several genetic syndromes. Stickler’s syndrome is the most common cause of RRD in young children, with most cases leading to total blindness if not diagnosed early. RRD develops in about 20% of individuals with Wagner syndrome and with patients with familial exudative vitreoretinopathy. Marshall syndrome, Knobloch syndrome, Marfan syndrome, Ehlers-Danlos syndrome are also at risk of development of RD.