Ординатура / Офтальмология / Английские материалы / Clinical Ophthalmology A Systematic Approach 7th Edition_Kanski, Bowling_2011

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It should be noted that the spread of SRF is governed by three factors:

1The position of the primary break. SRF will spread more quickly from a superior break.

2The size of the break; large breaks lead to more rapid accumulation of SRF than small ones.

3State of vitreous gel. If the vitreous gel is healthy and solid, even giant retinal tears may not lead to RD. However, if syneresis is advanced as in myopia, progression is usually rapid and the entire retina may become detached within 1 or 2 days.

It is therefore apparent that a patient with a fresh RD involving the superotemporal quadrant but with an intact macula (Fig. 16.48) should be operated on as soon as possible. In order to prevent SRF spreading to the macula, the patient should be positioned flat in bed with only one pillow and with the head turned so that the retinal break is in the most dependent position. For example, a patient with a right upper temporal RD should turn his head to the right. Preoperative bed rest is also desirable in eyes with bullous RDs because it may lessen the amount of SRF and facilitate surgery. Patients with dense fresh vitreous haemorrhage in whom visualization of the fundus is impossible should also be operated on as soon as possible if B-scan ultrasonography shows an underlying RD (see Fig. 17.1D).

Fig. 16.48 Superotemporal retinal detachment with intact macula requires urgent treatment

(Courtesy of P Saine)

Choice of technique

The aim of surgery is to successfully repair the detachment with minimal trauma and attendant risks. If the retinal break has accumulated too much SRF to be suitable for retinopexy then a surgical procedure will be required.

Pneumatic retinopexy

Pneumatic retinopexy is an outpatient procedure in which an intravitreal expanding gas bubble is used to seal a retinal break and reattach the retina without scleral buckling (Fig. 16.49). The most frequently used gases are sulphur hexafluoride (SF6) and the longer-acting perfluoropropane (C3F8). Pneumatic retinopexy has the advantage of being a relatively quick, minimally invasive, ‘office-based’ procedure. However, success rates are usually slightly less than those achievable with conventional scleral buckling surgery. The procedure is usually reserved for treatment of uncomplicated RD with a small retinal break or a cluster of breaks extending over an area of less than two clock hours situation in the upper two-thirds of the peripheral retina.

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Fig. 16.49 Pneumatic retinopexy. (A) Cryotherapy; (B) gas injection; (C) gas has sealed the retinal break and the retina is flat; (D) gas has absorbed

Principles of scleral buckling

Scleral buckling is a surgical procedure in which material sutured onto the sclera (explant) creates an inward indentation (buckle). Its purposes are to close retinal breaks by apposing the RPE to the sensory retina, and to reduce dynamic vitreoretinal traction at sites of local vitreoretinal adhesion.

1Explants are made from soft or hard silicone. In order to adequately seal a retinal break it is essential for the buckle to have adequate length, width and height. The entire break should ideally be surrounded by about 2 mm of buckle. It is also important for the buckle to involve the area of the vitreous base anterior to the tear in order to prevent the possibility of subsequent reopening of the tear and anterior leakage of SRF. The dimensions of the retinal break can be assessed by comparing it with the diameter of the optic disc (1.5 mm) or the end of a scleral indenter.

2Buckle configuration

aRadial explants are placed at right angles to the limbus (Fig. 16.50A). They are used to seal U-tears or posterior breaks, because of inability to support them on a circumferential buckle.

bSegmental circumferential explants are placed in parallel with the limbus to create a segmental buckle (Fig. 16.50B). They may be used to seal multiple breaks located in one or two quadrants and/or at varying distances from the ora serrata, as well as anterior breaks and dialyses.

cEncircling explants are placed around the entire circumference of the globe to create a 360° buckle and, if necessary, may be augmented by local explants (Fig. 16.50C and D). They are now less commonly used.

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Fig. 16.50 Configuration of scleral explants. (A) Radial sponge; (B) circumferential sponge; (C) encirclement augmented by a radial sponge; (D) encirclement augmented by a solid silicone tyre

Technique of scleral buckling

aA peritomy is performed appropriate to the extent of scleral exposure required and episcleral tissue is cleared (Fig. 16.51A).

bA squint hook is inserted under a rectus muscle and a reverse-mounted needle with a 4/0 black silk suture is passed under (not through) the muscle tendon (Fig. 16.51B) and the suture secured by twisting it around ‘mosquito’ forceps.

cBreaks are localized by indenting the sclera whilst viewing with the indirect ophthalmoscope and marking the site with a spot of surgical ink.

dCryotherapy is applied by indenting the sclera gently with the tip of the cryoprobe and freezing is continued until the break is surrounded by a 2 mm margin of ice (Fig. 16.51C).

eWith calipers, the distance separating the sutures is measured, the sclera marked and a mattress-type suture which will straddle the explant inserted (Fig. 16.51D). As a general rule, the separation of sutures should be about 1.5 × the diameter of a sponge explant.

f The explant is fed through the sutures which are then tied (Fig. 16.51E).

gThe position of the buckle is checked in relation to the break. If the break is closed or very nearly closed, the operation can be terminated without drainage of SRF. If the buckle is incorrectly positioned it should be removed and repositioned (Fig. 16.51F).

h‘Fish-mouthing’ is a tendency of certain retinal tears, typically large superior U-tears located at the equator in a bullous RD, to open widely following scleral buckling and drainage of SRF (Fig. 16.52A). Management of this problem involves insertion of an additional radial buckle and injection of air into the vitreous cavity (Fig. 16.52B).

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Fig. 16.51 Technique of scleral buckling. (A) Conjunctival incision; (B) insertion of bridle suture; (D) cryotherapy; mattress suture in place; (E) suture is tied over the sponge; (F) appearance of indentation – in this case the buckle is too anterior in relation to the tear and must be repositioned

Fig. 16.52 (A) ‘Fish-mouthing’ of a U-tear that is communicating with a radial fold; (B) flat retina following insertion of a radial buckle

Drainage of subretinal fluid

1Indications. Although a large proportion of RDs can be treated successfully with non-drainage techniques, drainage of SRF may be required under the following circumstances:

aDeep SRF beneath the retinal break. In such case the application of cryotherapy may be difficult or impossible and the RD should be repaired using a D-ACE (Drain-Air-Cryo-Explant) technique although such cases are now often repaired via a vitrectomy procedure.

•Drain the SRF to bring the break closer to the RPE.

•Air injection into the vitreous cavity to counteract the hypotony induced by

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drainage.

•Cryotherapy to the break.

•Explant insertion.

bLong-standing RDs tend to be associated with viscous SRF and may take a long time (many months) to absorb. Drainage may therefore be necessary to restore macular attachment quickly, even if the break itself can be closed without drainage.

2Technique

a‘Prang’

•Digital pressure is applied to the globe until the central retinal artery is occluded and complete blanching of the choroidal vasculature is achieved in order to prevent haemorrhage from the drainage site.

•A full-thickness perforation is made in a single, swift but controlled fashion with the tip of a 27-gauge hypodermic needle bent 2 mm from the tip.

•Following drainage of SRF, air is injected to restore intraocular pressure.

b‘Cut-down’ (Fig. 16.53)

•The sclerotomy site should be beneath the area of deepest SRF but avoiding the vortex veins.

•A radial sclerotomy is performed, about 4 mm long and of sufficient depth to allow herniation of a small dark knuckle of choroid.

•A mattress suture is placed across the lips of the sclerotomy (optional).

•The assistant holds apart the lips and the prolapsed knuckle is inspected with a +20 D lens for the presence of large choroidal vessels.

•If large choroidal vessels are absent, gentle low-heat cautery is applied to the choroidal knuckle to decrease the risk of bleeding.

•If this does not result in drainage of SRF the choroidal knuckle is perforated with a 25-guage hypodermic needle on a syringe.

3Complications

aFailure of drainage of SRF ('dry tap’) may be caused by one of the following:

•Failure to perforate the full thickness of the choroid.

•Attempted drainage in an area of flat retina: therefore always check the position of the SRF immediately prior to drainage.

•Incarceration of the retina in the sclerotomy (see below).

bHaemorrhage is usually caused by damage to a large choroidal vessel (Fig. 16.54A). Although small bleeds may be innocuous because the blood escapes with the SRF, large bleeds may give rise to postoperative maculopathy as the result of gravitation of blood in the subretinal space to the fovea, as well as causing vitreous haemorrhage and haemorrhagic choroidal detachment.

cRetinal incarceration into the sclerotomy (Fig. 16.54B) is usually due to excessively elevated intraocular pressure at the time of drainage using the ‘cut-down’ technique. As already mentioned it is one of the causes of a dry tap although occasionally, after an initial appearance of SRF, the flow will suddenly cease despite the fact that a large amount of SRF still remains in the eye.

Fig. 16.53 Cut-down technique of subretinal fluid drainage

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Fig. 16.54 Complications of subretinal fluid drainage. (A) Haemorrhage; (B) retinal incarceration into the drainage site

The following clinical examples will emphasize the most important aspects of management just discussed.

Fresh retinal detachment

1Preoperative considerations. Examination shows a localized right upper temporal RD due to a U-tear (Fig. 16.55A). The prognosis for central vision is good because the macula is uninvolved. The patient should be operated on as soon as possible because the SRF is likely to spread quickly.

2Surgical technique for cryotherapy and buckle

•Peritomy should extend from 8.30 to 12.30 o’clock to expose the lateral and superior recti.

•The tear should close on a 5 mm sponge explant. The sutures should be about 8 mm apart to impart adequate height to the buckle.

•The sponge should be placed radially (Fig. 16.55B) to prevent ‘fish-mouthing’. Accurate positioning of the explant is vital in this case.

•Failure to close the break may be due to an undersized buckle (Fig. 16.55C) or to malposition of the buckle (Fig. 16.55D).

•Alternatively a solid-type silicone explant can be used although it creates less of an indent and is associated with an increased requirement for SRF drainage to ensure closure of the break.

•Drainage of SRF is not otherwise required because the retina is mobile, the break can be apposed to RPE without difficulty and SRF is not viscous as the RD is fresh.

•It may also be possible to treat this case with pneumatic retinopexy.

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Fig. 16.55 Treatment of a fresh upper temporal retinal detachment and causes of failure. (A) Prior to surgery; (B) successful outcome; (C) tear is still open because the buckle is undersized; (D) tear is still open because the buckle is incorrectly positioned

Long-standing retinal detachment

1Preoperative considerations. Examination shows an extensive right RD with macular involvement associated with a U-tear in the upper temporal quadrant and two small holes in the lower temporal quadrant (Fig. 16.56A). A partially pigmented demarcation line is present at the junction of detached and flat retina, and a secondary intraretinal cyst is present inferiorly. This is therefore a longstanding RD. The prognosis for restoration of good visual acuity is very poor because the fovea has probably been detached for at least 12 months. There is therefore no urgency for surgery.

2Surgical technique

•Peritomy should extend from 5.30 to 12.30 o’clock to expose the superior, lateral and inferior recti.

•The breaks can be sealed with a long 4 mm-wide circumferential sponge explant extending from 7 to 10.30 o’clock or a circumferential solid-type explant (Fig. 16.56B).

•Drainage of SRF may be required because in long-standing cases SRF is viscous and may take a long time to absorb.

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Fig. 16.56 Treatment of a long-standing retinal detachment. (A) Retinal detachment with three breaks (one U-tear and two holes), a secondary intraretinal cyst and a high water mark; (B) successful outcome following circumferential buckling with disappearance of the cyst but not the high water mark

Causes of failure

1Missed breaks. At surgery, the surgeon should not be satisfied if only one break has been found until a thorough search has been made for the presence of other breaks and the configuration of the RD corresponds to the position of the primary break.

2Buckle failure may be the result of the following:

•Buckle of inadequate size – replace (see Fig. 16.55C).

•Buckle incorrectly positioned – reposition (see Fig. 16.55D).

•Buckle of inadequate height – drain SRF or consider intravitreal gas injection.

3Proliferative vitreoretinopathy is the most common cause of late failure. The tractional forces associated with PVR can occasionally open old breaks and create new ones. Presentation is typically between the 4th and 6th postoperative weeks. After an initial period of visual improvement following successful retinal reattachment the patient reports a sudden and progressive loss of vision, which may develop within a few hours.

4Reopening of a retinal break in the absence of PVR as a result of inadequate cryotherapy or scleral buckling. It may occur when buckle height decreases either with time or following surgical removal.

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Tractional retinal detachment

The main causes of tractional RD are (a) proliferative retinopathy such as diabetic and retinopathy of prematurity, and (b) penetrating posterior segment trauma (see Ch. 21).

Pathogenesis of diabetic tractional retinal detachment

1Pathogenesis of PVD. Tractional RD is caused by progressive contraction of fibrovascular membranes over large areas of vitreoretinal adhesion. In contrast to acute PVD in eyes with rhegmatogenous RD, PVD in diabetic eyes is gradual and frequently incomplete. It is thought to be caused by leakage of plasma constituents into the vitreous gel from a fibrovascular network adherent to the posterior vitreous surface. Owing to the strong adhesions of the cortical vitreous to areas of fibrovascular proliferation, PVD is usually incomplete. In the very rare event of a subsequent complete PVD, the new blood vessels are avulsed and RD does not develop.

2Static vitreoretinal traction of the following three types is recognized.

aTangential traction is caused by the contraction of epiretinal fibrovascular membranes with puckering of the retina and distortion of retinal blood vessels.

bAnteroposterior traction is caused by the contraction of fibrovascular membranes extending from the posterior retina, usually in association with the major arcades, to the vitreous base anteriorly (Fig. 16.57).

cBridging (trampoline) traction is the result of contraction of fibrovascular membranes which stretch from one part of the posterior retina to another or between the vascular arcades, tending to pull the two involved points together.

Fig. 16.57 Tractional retinal detachment associated with anteroposterior and bridging traction

(Courtesy of CL Schepens, ME Hartnett and T Hirose, from Schepens’ Retinal Detachment and Allied Diseases, Butterworth-Heinemann, 2000)

Diagnosis

1Symptoms. Photopsia and floaters are usually absent because vitreoretinal traction develops insidiously and is not associated with acute PVD. The visual field defect usually progresses slowly and may become stationary for months or even years.

2Signs (Fig. 16.58A).

•The RD has a concave configuration and breaks are absent.

•Retinal mobility is severely reduced and shifting fluid is absent.

•The SRF is shallower than in a rhegmatogenous RD and seldom extends to the ora serrata.

•The highest elevation of the retina occurs at sites of vitreoretinal traction.

•If a tractional RD develops a break it assumes the characteristics of a rhegmatogenous RD and progresses more quickly (combined tractional-rhegmatogenous RD).

3 B-scan ultrasonography shows posterior vitreous detachment and a relatively immobile retina (Fig. 16.58B).

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Fig. 16.58 (A) Tractional retinal detachment in severe proliferative diabetic retinopathy; (B) B-scan image of another patient shows posterior vitreous detachment and a shallow tractional retinal detachment

(Courtesy of P Saine – fig. A; RF Spaide, from Diseases of the Retina and Vitreous, WB Saunders, 1999 – fig. B)

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