Retinal detachment and PVR

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CHAPTER 60 Retinal detachment and PVR

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Epidemiologic considerations and terminology

In the majority of cases, the retinal detachment is due to fluid which gains access to the subretinal space via a retinal hole, so called rhegmatogenous retinal detachment (RRD) (Fig. 60.1). In non-rhegmatogenous detachment the separation arises from serous exudation, or for other reasons, and will not be considered further in this chapter.

RRD affects about one in 10 000 adults annually1, and has a higher incidence in myopes2, pseudophakes3, and following trauma4.

Anatomical considerations

The subretinal space is a potential one, normally kept dry by the pumping action of RPE cells. If the rate of fluid flow through a retinal hole is greater than the rate at which it can be pumped out, then RRD occurs. The balance between ingress and outflow of fluid can be affected by a number of different factors (Fig. 60.2). Dynamic traction from the vitreous, for example following a PVD, can rapidly accelerate the progression of retinal detachment. Similarly increased concavity in the case of a posterior staphyloma, combined with a presumed reduction in the quality of the RPE pump in high myopes, can produce retinal detachments from macular holes, which do not otherwise occur in macular hole patients.

Ideally, RRD should be treated before the macula becomes detached. Once subretinal fluid has spread to involve the macula (macula off retinal detachments), then permanent damage occurs resulting in reduced acuity and metamorphopsia in the majority of patients.

Retinal holes can be classified into three groups: (i) round holes; (ii) traction, or ‘U’ tears; and (iii) other breaks. Round holes are very common, but rarely lead to RRD5. They are usually associated with patches of lattice degeneration. In a small subset of young myopic patients, they can cause slowly progressive retinal detachment, accounting for approximately 5% of patients requiring treatment. The majority of RRDs are caused as a result of one or more traction, or ‘U’ tears secondary to a PVD. The most common location for such tears is the superior temporal quadrant.

Preoperative assessment

The aim of preoperative assessment is to confirm the diagnosis, identify the retinal holes, and plan the most appropriate surgical technique. Although the vast majority of patients presenting with retinal detachments have RRD, the possibility of an exudative retinal detachment must always be considered, particularly if a retinal hole is not seen. The presence of pigment cells in the anterior vitreous (’tobacco dust’) is strongly correlated with the presence of a retinal hole, though a similar sign can occur as a result of iris trauma during cataract surgery (Fig. 60.3). Examination of the anterior segment is important, as it may give clues to the etiology, but is also helpful in determining the quality of the view that the surgeon will get during surgery.

Detailed drawings of the fundus are now rarely performed, but it is very important for scleral buckling surgery to know in advance the number and location of the retinal holes. The fundal view during scleral buckling surgery may be worse perioperatively than preoperatively, in contradistinction to vitrectomy, where the peroperative visualization of the retina is usually better, particularly when wide-angle viewing systems are used. If a decision has been made to carry out vitrectomy, then further detailed examination for detection of retinal holes can safely be left until surgery.

An assessment of the degree of proliferative vitreoretinopathy (PVR) should also be made. The proximity of ‘star folds’ near retinal breaks may mean that vitrectomy is required (Fig. 60.4). Contraction of the vitreous base may be an indication for an encircling buckle.

Operation techniques

There are a number of operative techniques that may be employed by vitreoretinal surgeons in the repair of retinal detachment according to the clinical characteristics of the detachment, presence of PVR, and surgeon preferences.

Scleral buckling

Scleral buckling is a surgical procedure in which indentation of the scleral surface is achieved by suturing a silicone support to the sclera, thus sealing the retinal break, relieving vitreoretinal traction and reducing the flow of fluid into the subretinal space (Fig. 60.5). When combined with retinopexy, chorioretinal adhesion results maintaining retinal reattachment even when the indent subsequently fades.

Scleral buckling is often the procedure of choice in round hole detachments where no PVD is present, in retinal dialysis and rhegmatogenous retinal detachments where breaks are confined to one or two quadrants, and in some cases may also be used in the treatment of detachments with PVR. Relative contraindications include media opacities preventing localisation of all the retinal breaks, giant retinal tears, posterior tears, and the presence of a large number of retinal tears in different meridia.

When placing a scleral buckle, a conjunctival peritomy is performed, followed by scleral inspection to ensure sufficient scleral thickness for safe indentation and placement of scleral sutures. The rectus muscles are isolated and bridled to allow manipulation of the eye during the procedure. Breaks within detached retina are then localized and marked using diathermy to demonstrate their posterior and lateral extension. The position and distribution of retinal breaks dictate the size, position and sometimes the orientation of the scleral explant. Explants may be radial (perpendicular to the ora serrata) or circumferential (parallel to the ora serrata), and may be segmental or held in place with an encircling band. Encircling bands may be used when a permanent indent is required such as in the treatment of PVR or when there is difficulty in detecting breaks for example small anterior breaks found in pseudophakic patients. Once a scleral explant has been selected, retinal breaks are treated with cryopexy prior to suturing the explant to the scleral surface using non-absorbable suture material. Laser retinopexy may also be used, either following drainage of subretinal fluid and application of the buckle or as a secondary procedure once sealing of the break by the indent has allowed sufficient absorption of SRF to allow laser uptake.

During the procedure, drainage of subretinal fluid may be desirable, for example in bullous detachments where the sclera cannot be apposed to the retina, the presence of multiple breaks requiring a large buckle, and in glaucoma patients where significant rises in intraocular pressure are undesirable. Although there are a number of techniques that may be used to drain SRF, they all run the risk of choroidal hemorrhage, retinal incarceration, vitreous loss, and retinal perforation. Subretinal hemorrhage, if subfoveal, can cause permanent visual loss.

Injection of intraocular gas or air may be used to provide additional retinal support in the event of fish-mouthing of retinal breaks, i.e. a meridional retinal fold formed by redundant retina on the posterior slope of the scleral indent, or to reform the vitreous cavity if the eye becomes hypotonous following drainage of SRF.

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