Sunday, September 7, 2008

Retinal Detachment

Retinal Detachment and Related Retinal Degenerations
Vaughan & Asbury's General Ophthalmology 17th Edition


Retinal detachment is the separation of the sensory retina, ie, the photoreceptors and inner tissue layers, from the underlying retinal pigment epithelium. There are three main types: rhegmatogenous, traction, and serous or hemorrhagic detachment.

Rhegmatogenous Retinal Detachment

The most common type of retinal detachment, rhegmatogenous retinal detachment is characterized by a full-thickness break (a "rhegma") in the sensory retina, variable degrees of vitreous traction, and passage of liquefied vitreous through the break into the subretinal space. A spontaneous rhegmatogenous retinal detachment is usually preceded or accompanied by a posterior vitreous detachment and is associated with myopia, aphakia, lattice degeneration, and ocular trauma. Binocular indirect ophthalmoscopy with scleral depression reveals elevation of the translucent detached sensory retina with one or more full-thickness sensory retinal breaks, such as a horseshoe tear, round atrophic hole, or anterior circumferential tear (retinal dialysis). The location of retinal breaks varies according to type; horseshoe tears are most common in the superotemporal quadrant, atrophic holes in the temporal quadrants, and retinal dialysis in the inferotemporal quadrant. When multiple retinal breaks are present, the defects are usually within 90 degrees of one another.


Figure 1. Retinal Detachment
Treatment

The principal aims of detachment surgery are to find and treat all the retinal breaks, cryotherapy or laser being applied to create an adhesion between the pigment epithelium and the sensory retina, thus preventing any further influx of fluid into the subretinal space, to drain subretinal fluid, internally or externally, and relieve vitreo-retinal traction. Various surgical techniques are employed.

In pneumatic retinopexy air or expandable gas is injected into the vitreous to maintain the retina in position, while the chorioretinal adhesion induced by laser or cryotherapy achieves permanent closure of the retinal break. It has a lower success rate than other methods and is used only when there is a small accessible single retinal break, minimal subretinal fluid, and no vitreo-retinal traction.

Scleral buckling maintains the retina in position, while the chorioretinal adhesion forms, by indenting the sclera with a sutured explant in the region of the retinal break. This also relieves vitreo-retinal traction and displaces subretinal fluid away from the retinal break. The success rate is 92–94% in suitably selected cases. Complications include change in refractive error, diplopia due to fibrosis or involvement of extraocular muscles in the explant, extrusion of the explant, and possibly increased risk of proliferative vitreoretinopathy.

Pars plana vitrectomy allows relief of vitreo-retinal traction, internal drainage of subretinal fluid, if necessary by injection of perfluorocarbons or heavy liquids, and injection of air or expandable gas to maintain the retina in position, or injection of oil if longer-term tamponade or the retina is required. It is used if there are superior, posterior, or multiple retinal breaks, when visualization of the retina is inhibited, such as by vitreous hemorrhage, and if there is significant proliferative vitreoretinopathy. Vitrectomy induces cataract formation and may be contraindicated in phakic eyes. Postoperative posturing may be required.

The visual results of surgery for rhegmatogenous retinal detachment primarily depend on the preoperative status of the macula. If the macula has been detached, recovery of central vision is usually incomplete. Thus, surgery should be performed urgently if the macula is still attached. Once the macula is detached, delay in surgery for up to 1 week does not adversely influence visual outcome.

Traction Retinal Detachment

Traction retinal detachment is most commonly due to proliferative diabetic retinopathy. It can also be associated with proliferative vitreoretinopathy, retinopathy of prematurity, or ocular trauma. In comparison to rhegmatogenous retinal detachment, traction retinal detachment has a more concave surface and is likely to be more localized, usually not extending to the ora serrata. The tractional forces actively pull the sensory retina away from the underlying pigment epithelium toward the vitreous base. Traction is due to formation of vitreal, epiretinal, or subretinal membranes consisting of fibroblasts and glial and retinal pigment epithelial cells. Initially the detachment may be localized along the vascular arcades, but progression may spread to involve the midperipheral retina and the macula. Focal traction from cellular membranes can produce a retinal tear and lead to combined traction-rhegmatogenous retinal detachment.

Proliferative vitreoretinopathy is a complication of rhegmatogenous retinal detachment and is the most common cause of failure of surgical repair in these eyes.


Figure 2. Retinal Detachment
Treatment

Pars plana vitrectomy allows removal of the tractional elements followed by removal of the fibrotic membranes. Retinotomy and/or injection of perfluorocarbons or heavy liquids may be required to flatten the retina. Gas tamponade, silicone oil, or scleral buckling may be used.

Serous & Hemorrhagic Retinal Detachment

Serous and hemorrhagic retinal detachment occurs in the absence of either retinal break or vitreoretinal traction. They form as a result of accumulation of fluid beneath the sensory retina and are caused primarily by diseases of the retinal pigment epithelium and choroid. Degenerative, inflammatory, and infectious diseases, including the multiple causes of subretinal neovascularization, may be associated with serous retinal detachment and are described in an earlier section of this textbook. This type of detachment may also be associated with systemic vascular and inflammatory disease, or intraocular tumors.

Lattice Degeneration

Lattice degeneration is the most common vitreoretinal degeneration. The estimated incidence in the general population is 6–10%, of which up to 50% have bilateral disease. It is more commonly found in myopic eyes with some familial tendency. It produces localized round, oval, or linear areas of retinal thinning, with pigmentation, branching white lines, and whitish-yellow flecks, and firm vitreoretinal adhesions at its margins. Lattice degeneration results in retinal detachment in only a small percentage of affected eyes, but 20–30% of eyes with retinal detachment have lattice degeneration. Strong family history of retinal detachment, retinal detachment in the fellow eye, high myopia, and aphakia require the patient to be informed of the risks of retinal detachment and the relevant symptoms but rarely warrant prophylactic treatment with cryosurgery or laser photocoagulation.

Peripheral Chorioretinal Atrophy

Peripheral chorioretinal atrophy (paving stone degeneration) is a common benign chorioretinal degeneration found in nearly one-third of adult eyes. It is thought to be due to choroidal vascular insufficiency and is associated with peripheral vascular disease. The lesions appear as isolated or grouped, small, discrete, yellow-white areas with prominent underlying choroidal vessels and pigmented borders.

Retinoschisis

Degenerative retinoschisis is a common acquired peripheral retinal disorder that is believed to develop from coalescence of preexisting peripheral cystoid degeneration. The cystic elevation is most commonly found in the inferotemporal quadrant, followed by the superotemporal quadrant. It develops into one of two forms, typical or reticular, although clinically the two are difficult to differentiate.

Typical degenerative retinoschisis forms a round or ovoid area of retinal splitting in the outer plexiform layer. Posterior extension and hole formation in the outer layer is uncommon and therefore poses low risk of progression to retinal detachment.

Reticular degenerative retinoschisis is characterized by round or oval areas of retinal splitting in the nerve fiber layer forming a bullous elevation of an extremely thin inner layer. Retinal holes occur in 23%, and posterior extension or progression to rhegmatogenous retinal detachment may occur and requires treatment.

Natural History

Degenerative retinoschisis is present in about 4% of the population and is bilateral in approximately 30% of affected individuals. Spontaneous regression occurs in up to 9% of cases. Progression to retinal detachment occurs in up to 2%, with increased risk for those with a family history of retinal detachment. Whether cataract extraction increases the risk of retinal detachment is uncertain. Retinal detachment occurs in one of two ways. A hole in the outer but not the inner retinal layer allows the cystic fluid through the defect. This type is usually not or is only slowly progressive, and therefore a demarcation line forms. It rarely requires treatment. In the second type, holes form in both the inner and the outer layers. This causes collapse of the schisis and full retinal detachment forms. Progression is quick, and treatment is required by pneumatic retinopexy, scleral buckle, or vitrectomy, depending on the size and position of the retinal holes and whether there is any proliferative vitreoretinopathy.

Differentiation from Retinal Detachment

Retinoschisis causes an absolute scotoma in the visual field, whereas retinal detachment causes a relative scotoma. The cystic elevation of retinoschisis is usually smooth with no associated vitreous pigment cells. The surface of retinal detachment is usually corrugated with pigment cells in the vitreous ("tobacco dust"). Longstanding retinal detachment produces atrophy of the underlying retinal pigment epithelium, resulting in a pigmented demarcation line. As the retinal pigment epithelium is healthy in retinoschisis, there is no demarcation line. If argon laser photocoagulation to the outer retinal layer, aimed through an inner layer break, creates an equal gray response as in an adjacent area of normal retina, this is thought to be diagnostic of retinoschisis.

1 comments:

Argon Laser said...

What is the wavelength of the argon laser used in the procedure?