ANATOMY AND EMBRYOLOGY OF THE VITREOUS

The vitreous cavity is the space bounded anteriorly by the lens and its zonular fibres and more posteriorly by the ciliary body, retina and optic disc. Its volume is about 4 ml, although this may be as much as 10 ml in highly myopic eyes. Normally the space is entirely occupied by vitreous gel a virtually acellular, viscous fluid with 99 per cent water content. Its low molecular and cellular content is essential for maintaining transparency. Major constituents of the vitreous gel are hyaluronic acid and type 2 collagen fibrils. The cortical part of the vitreous gel has more hyaluronic acid and collagen than the less dense central gel. In addition, the gel exhibits ‘condensations’ both within its substance and along its boundaries. Boundary condensations are the anterior and posterior hyaloid membranes. The gel is unimportant in maintaining the shape or structure of the eye; indeed, apart from its role in oculogenesis, the vitreous has no well substantiated function. An eye devoid of gel is not harmed apart from having an increased risk of nuclear cataract, (which is thought to be due to increased partial pressure of oxygen (po₂) in the posterior segment after vitrectomy). The vitreous gel is implicated, however, in the pathogenesis of a variety of sight-threatening conditions.

During early development the invaginated optic vesicle (optic cup) contains the primary vitreous, a vascularized tissue supplying the lens and retina, both of which are of ectodermal origin. During the third month of gestation the primary vitreous gradually loses its vascularity and is replaced by the secondary vitreous which is derived from the anterior retina and ciliary body. The principal remnants of the primary vitreous are Cloquet’s canal, a central tubular stucture that stretches sinuously between the lens and the optic disc and some epipapillary gliosis. In later life an exaggeration of the latter is seen as Bergmeister’s papilla and a Mittendorf’s dot is a primary vitreous remnant seen on the posterior lens capsule (see Ch. 17). The most common and severe developmental anomaly of the vitreous is persistent hyperplastic primary vitreous. This usually presents in infancy as a microphthalmic squinting eye with leukocoria. Pupil dilatation may demonstrate dragging of the ciliary processes towards a central plaque of fibrovascular tissue; this invades the lens posteriorly and ultimately causes complete cataract and secondary angle closure glaucoma (see Ch. 8).

Fig. 12.1 Light micrograph of a section through the eye of a 13-mm human fetus showing primary and secondary vitreous with artefactual re-establishment of optic vesicle (silver stain).

Fig. 12.2 The hyaloid artery may occasionally persist as a vascular channel between the central gel and optic disc (left), or as a glial plaque on the posterior lens capsule (centre). The B scan (right) demonstrates a persistent hyaloid artery.

VITREOUS ATTACHMENTS TO SURROUNDING STRUCTURES

The posterior hyaloid membrane adheres to the internal limiting membrane of the retina (the basement membrane of the Müller cells consisting of type 4 collagen) by the insertion of vitreous gel fibrils. The potential space between the internal limiting membrane and posterior hyaloid membrane is the plane at which the gel cleaves from the retina in posterior vitreous detachment.

The vitreous adheres to surrounding structures at various sites; these attachments are responsible for much vitreoretinal pathology. The vitreous base is an annular zone of adhesion 3–4 mm wide straddling the ora serrata. The anterior border is the insertion of the anterior hyaloid membrane. The posterior border forms the anterior limit at which the gel and retina can potentially separate and is surgically important being a common site for retinal tears. Adhesion of the vitreous base to the retina and pars plana is strong and difficult to break even with severe trauma. Weiger’s ligament is a circular zone of adhesion, 8–9 mm in diameter, between the gel and posterior lens capsule. It is the junction between the anterior hyaloid membrane and the expanded anterior opening of Cloquet’s canal. The posterior hyaloid membrane and the slightly expanded posterior limit of Cloquet’s canal meet around the margin of the optic disc to produce another ring of adhesion. During posterior vitreous detachment gliotic tissue is avulsed from the edge of the optic nerve head to produce Weiss’ ring, a sign of posterior vitreous detachment. A circle of relatively increased adhesion to the retina may be present parafoveally and is implicated in macular hole formation.

Vitreoretinal adhesions are exaggerated in areas of lattice degeneration. Oval or elongated areas of retina are thinned with sclerotic vessels and degenerate overlying vitreous. The lesions tend to be oriented circumferentially but may also be radial or directed along postequatorial retinal veins. Lattice degeneration is found in approximately 7 per cent of normal eyes and is frequently associated with retinal tears. Some eyes have abnormally strong vitreoretinal adhesions along retinal veins (paravascular adhesions) which may also result in retinal tears.

Fig. 12.3 Diagram of normal vitreoretinal anatomy showing the macroarchitectural features of the gel and the important sites of vitreoretinal attachment.

VITREOUS CHANGES

POSTERIOR VITREOUS DETACHMENT

Posterior vitreous detachment which occurs when the posterior hyaloid and internal limiting membranes separate is the commonest and most important pathological event affecting the vitreous. It occurs in about 50 per cent of individuals aged between 40 and 80 years and earlier in myopes. Most patients do not have pathological sequelae but acute symptoms of floaters and flashers are associated with a 10 per cent risk of developing a retinal tear, the cause of most retinal detachments. The great majority of tears are associated with visible retinal pigment epithelium (RPE) cells in the anterior vitreous having been released through the tear (Shafer’s sign). Tearing of retinal blood vessels or neovascular complexes causes haemorrhaging into the vitreous cavity. Posterior vitreous detachment is also implicated in the pathogenesis of epiretinal membranes and macular holes.

Fig. 12.4 With ageing vitreous degenerates to cause syneresis (condensation) and lacuna (cavity) formation and collapse. At slit-lamp examination the detached posterior hyaloid membrane looks like a wrinkled hanging curtain moving freely on eye movement. It separates from the retina up to the posterior border of the vitreous base (or the posterior aspect of any vitreoretinal adhesions).

Fig. 12.5 On posterior vitreous detachment epipapillary glial tissue can become avulsed from the disc margin and is seen ophthalmoscopically as a ring of tissue on the detached posterior hyaloid interface situated in front of the optic disc (Weiss’ ring). The patient sees a circular or oval floater (depending on how it tilts) or describes a ‘cobweb’ or ‘spider’ that moves with the eye. Aggregations of collagen fibrils can also produce symptomatic floaters. ‘Lightening flashes’ may be seen in the temporal periphery, each typically lasting for a few seconds and induced by eye movement, possibly because photoreceptors depolarize when the vitreous base tugs on the retina; these flashes are often more noticeable on the transition from light to dark.

VITREOUS HAEMORRHAGE

Vitreous haemorrhage can reduce vision profoundly. Haemorrhage may be in vitreous gel (intragel) or behind a detached gel (retrohyaloid); haemorrhage in both situations tends to be associated with posterior vitreous detachment. Spontaneous vitreous haemorrhage is principally caused by retinal tears, retinal vein occlusion or retinal neovascularization, for example secondary to diabetic retinopathy. Other common causes are posterior vitreous detachment without retinal tear formation or retinal macroaneurysm. Haemorrhage elsewhere in the eye often disperses into the vitreous cavity (e.g. suprachoroidal blood from trauma, subretinal blood secondary to choroidal neovascularization or blood under the internal limiting membrane in Terson’s syndrome).

The blood in the vitreous gel initially forms a localized clot but subsequently disperses throughout the gel following fibrinolysis. During haemolysis biconcave erythrocytes loose haemoglobin to become spheroidal erythroclasts. Biodegraded haemoglobin stains the gel ochre-yellow or orange. Erythroclast clogging of the vitreous cortex produces an ‘ochre membrane’ at the posterior hyaloid face. The mechanisms by which vitreous haemorrhage is spontaneously absorbed are not clear although phagocytosis by macrophages, outflow through the trabecular meshwork and syneretic disintegration of the gel play a part. Erythroclasts in the trabecular meshwork can reduce outflow to produce raised intraocular pressure and ‘erythroclastic glaucoma’ (see Ch. 8). Rarely, vitreous haemorrhage causes ‘synchysis scintillans’, a localized form of cholesterolosis bulbi characterized by cholesterol crystal accumulation in the vitreous cavity. The crystals sediment inferiorly but shower through the vitreous cavity with eye movement.

Fig. 12.6 A bulla of subhyaloid haemorrhage forces the posterior hyaloid face forwards into the vitreous cavity.

Fig. 12.7 B scans show a retrogel haemorrhage moving from side to side with right and left gaze. There is complete vitreous detachment from the optic disc.

VITRITIS

Inflammatory cell infiltration of the vitreous is a feature of posterior uveitis, bacterial, viral, yeast and fungal infections, and intraocular lymphoma (see Ch. 10). Vitreous biopsy or vitrectomy has an increasing role in the management of these patients to obtain specimens for cellular diagnosis, microbial culture, removal of the vitreous scaffold and delivery of therapeutic drugs.

Fig. 12.8 Candidaemia in patients taking broad-spectrum antibiotics or with indwelling intravenous catheters or in intravenous drug users (Candida can grow in the lemon juice that may be used to dissolve heroin), carries a significant risk of metastatic endophthalmitis which manifests as intravitreal white puff-balls. Candida endophthalmitis, although more slowly progressive than bacterial endophthalmitis, usually requires vitrectomy to remove the infected gel, to administer intravitreal medication and to restore vision. Vitreous puff-balls are seen in this intravenous drug user with Candida endophthalmitis.

ASTEROID HYALOSIS

Asteroid hyalosis is a specific form of gel degeneration in which globules of calcium soaps aggregate on vitreous fibrils and move with the gel on eye movement. When dense, asteroid bodies may preclude ophthalmoscopy of the retina although they rarely impair the patient’s vision. They are not associated with any systemic condition and their aetiology is unknown.

Fig. 12.9 Typical white glistening particles are seen in the anterior gel of this patient. B scanning shows the densely reflective echoes in a collapsed gel.

AMYLOIDOSIS

Amyloidosis of the vitreous is a very rare condition usually associated with the primary or familial (dominantly inherited) forms of amyloidosis. Proteinaceous material, probably derived from the retinal circulation, becomes deposited on the collagenous framework of the gel bilaterally to produce a ‘glass-wool’ opacification; associated cellular invasion is conspicuous by its absence.

Fig. 12.10 Slit-lamp photograph showing proteinaceous material coating the retrolental vitreous fibrils.

RHEGMATOGENOUS RETINAL DETACHMENT

Strictly speaking, ‘retinal detachment’ is a misnomer. Rather than the retina detaching from choroid the retinal neuroepithelium separates from the RPE to re-establish the original space between layers of the embryonic optic cup. ‘Rhegmatogenous’ retinal detachment is most commonly caused by a ‘break’ or full-thickness discontinuity in the neuroepithelium allowing fluid from the vitreous cavity to enter the subretinal space. Classically breaks are subdivided into ‘tears’ due to dynamic vitreoretinal traction and ‘holes’ secondary to localized retinal disintegration or atrophy.

Most retinal tears occur in association with posterior vitreous detachment from the forces generated by ‘dynamic vitreous traction’. This is the transmission of rotational energy generated by saccadic ocular movement to the vitreous. If the vitreous remains attached to the retina this energy is uniformly dispersed over the whole area of vitreoretinal contact. With posterior vitreous detachment these forces accelerate the posterior gel and cause excessive traction at focal points of vitreo-retinal adhesion. The vitreous base remains anchored anteriorly; such gel movement can result in U-shaped tears at the site of ‘abnormal’ vitreoretinal adhesions. The tongue of retina which produces the U has its base anteriorly and points posteriorly; vitreous first separates posteriorly, tears the retina at the point of adhesion then extends the tear anteriorly back towards the vitreous base. Vitreous adheres to the periphery of lattice lesions so that the traction tears along the posterior border of the lesion and then extends anteriorly around its edge. Multiple tiny flap breaks at the posterior border of the vitreous base are associated particularly with aphakia or pseudophakia. If the flap of the tear is avulsed completely from the retina the piece of avulsed neurosensory retina is seen attached to the posterior vitreous membrane as an operculum and a round tear is produced. Haemorrhage from rupture of a blood vessel that crosses a U tear may produce a floater or shower of floaters.

Rhegmatogenous retinal detachment may also arise from atrophic retinal holes without posterior vitreous detachment, often in young myopic patients, or by dialysis at the ora serrata. In both retinal detachment is of slow onset, often noticed only coincidentally at routine examination or when the condition becomes symptomatic with foveal detachment. Atrophic holes are often equatorial and associated with lattice degeneration. Retinal dialyses are ellipsoid separations of the retina at the ora serrata, usually inferotemporally. They differ from U tears because there is no posterior vitreous detachment and the gel is attached to the posterior rather than the anterior margin of the break.

FORMATION OF RETINAL BREAKS

Fig. 12.11 Diagram illustrating the concept of dynamic vitreoretinal traction after posterior vitreous detachment and how this generates a flap-tear or an operculated tear. In contrast with a dialysis the vitreous remains attached and there is no posterior vitreous detachment.

Fig. 12.12 Lattice degeneration containing round holes is seen in the equatorial retina.

Fig. 12.13 A U-shaped horse-shoe tear is seen surrounded by subretinal fluid.

Fig. 12.14 A peripheral retinal dialysis seen through the indirect ophthalmoscope.

Fig. 12.15 Atrophic round retinal breaks are seen with an attached vitreous gel. They are usually equatorial and often associated with lattice degeneration. Recruitment of fluid with round hole detachment probably occurs by connection of the hole to vitreous lacunae; this may cause a stepwise detachment with multiple demarcation lines in a chronic-looking retinal detachment (see Fig. 12.24). The vast majority will not cause retinal detachment and prophylactic therapy is generally regarded as unnecessary.

Fig. 12.16 Retinal breaks are seen in a patient with retinal vasculitis in whom the vitreous has separated avulsing small discs of retina that remain attached to the posterior vitreous surface as opercula. Round retinal tears result.

Fig. 12.17 Slit-beam photograph of the anterior gel after a retinal break showing RPE cells in the retrolental gel (the ‘tobacco dust’ or Shafer’s sign). Retinal tears are usually associated with release of RPE cells into the vitreous cavity and, when seen, suggest that a retinal break is present. This is of particular value when assessing a patient following an acute posterior vitreous detachment. These cells transform into fibroblast-like cells in proliferative vitreoretinopathy.

Fig. 12.18 Haemorrhage from a ruptured blood vessel crossing a U tear may produce a ‘tadpole’ floater or shower of floaters. Shown here is a U-shaped tear, with a bridging blood vessel, surrounded by laser scars. These breaks may still bleed despite the laser therapy.

SUBRETINAL FLUID ACCUMULATION

Separation of the neuroepithelium from the RPE occurs at first in the immediate vicinity of the break. Progressively more subretinal fluid is recruited from the vitreous cavity (from the retrohyaloid space or syneretic gel) increasing the area and elevation of retinal separation. If the globe is completely immobilized at an early stage the retina may reattach partially or even completely. This implies that the movement of the eye causes gel movement and dynamic vitreoretinal traction that extends the retinal detachment. Gel movement induces fluid currents in the retrohyaloid space which forcefully elevate the neurosensory retina and gravity encourages spread of the subretinal fluid.

Subretinal fluid accumulates more quickly when fluid is recruited from the retrohyaloid space (e.g. through a U tear after posterior vitreous detachment) than when the posterior vitreous is still attached (e.g. atrophic holes and dialyses). In the latter, recruitment of fluid from syneretic gel may be limited by the size of adjacent lacunae in the gel. As a retinal detachment progresses the patient notices an increasing field defect corresponding to the detached area; central vision becomes distorted and lost as the fovea detaches.

Fig. 12.19 Gravity causes subretinal fluid to spread in a pattern that can help the surgeon localize a retinal break. A tear between the 11 and 1 o’clock positions causes a retinal detachment which becomes total (a). Tears above the horizontal meridian (from 3 to 9 o’clock) produce subtotal detachments. Fluid recruitment progresses downwards on the same side as the tear, at first producing a concave edge to the detachment, and then upwards as a convex edge on the opposite side of the disc but to a level lower than that on the side of the tear (b,c). Inferior subretinal fluid from a superior tear tends to separate partially into two bullae leaving a cleft or ‘cleavage’ of less elevated retina in the 6 o’clock meridian (b,c). A break located below the horizontal meridian tends to accumulate fluid more slowly than superior breaks (d). The upper limits of the detachment form convex curved edges on each side, the higher edge indicating the side of the break. Bullae are not seen with inferior breaks. Occasionally a small anterior and superior tear leaks fluid down the post-oral retina, producing an inferior retinal detachment. Therefore, inferior retinal detachments can occur from both superior and inferior tears.

NATURAL HISTORY OF RHEGMATOGENOUS RETINAL DETACHMENT

If untreated most retinal detachments progress to total or near-total detachment. Visual loss is profound and potential recovery of vision after successful surgery reduces as the weeks go by. Initially the retina is thickened and becomes less transparent; if left detached for many months it becomes progressively atrophic. In a longstanding subtotal retinal detachment a ‘high-water mark’ or pigment demarcation line of retinal pigment hyperplasia may appear which sometimes stops the detachment from extending further. Multiple high-water marks indicate recurrent extension of the detachment and are seen more often in slowly evolving detachments with round holes or dialyses. Other signs of longstanding detachment include retinal cysts (secondary retinoschises) and peripheral neovascularization. The longer the retina remains detached the higher the risk of proliferative vitreoretinopathy.

Very rarely the retina reattaches spontaneously to leave pigmented chorioretinal changes; invariably, however, surgery is required to reattach the retina. After successful surgery the rods recover their function surprisingly well and any visual field defect disappears. When the fovea has been involved recovery of cone function is good if the detachment is treated quickly (within 1 week of onset) but central vision may be permanently impaired after prolonged foveal detachment.

Fig. 12.20 Characteristic wrinkling of the retina from outer retinal swelling (outer retinal shagreen) is seen after detachment.

Fig. 12.21 These two photographs demonstrate a bullous superior retinal detachment with movement of subretinal fluid that spares the fovea as the eye rapidly looks up and down; the retinal detachment is ‘macula on’ and freely mobile with no retinal fibrotic changes.

Fig. 12.22 The fovea has been elevated by subretinal fluid in this ‘macula off’ inferior retinal detachment.

Fig. 12.23 A comparison of the histological appearance of normal and detached retina demonstrates shedding and shortening of rod outer segments. Pigment-laden macrophages are seen in the subretinal space.

By courtesy of Professor J Marshall.

Fig. 12.24 The pigmented demarcation line along the superior edge with thin strands of subretinal fibrosis and a rather atrophic appearance suggests that this retinal detachment is chronic.

Fig. 12.25 Intraretinal cysts in this retinal detachment suggests that the retina has been elevated for at least a year.

Fig. 12.26 A B scan shows a posterior vitreous detachment and total retinal detachment with the retinal attachment to the optic disc visible. The degree of retinal fibrosis can be assessed by watching the retinal mobility on dynamic B scan. The more fibrotic the retina the less retinal movement on ocular movement.

Fig. 12.27 This patient has a spontaneously reattached retinal detachment temporal to the macula associated with a round hole in an area of lattice. Although the retina is flat it is atrophic and the patient had a corresponding nasal field defect.

PROLIFERATIVE VITREORETINOPATHY

Some retinal detachments, especially those present for weeks or months, are complicated by proliferative vitreoretinopathy (PVR), a cellular proliferation producing ‘epiretinal membranes’ that has important implications in determining surgical management and visual prognosis. PVR is variable: some eyes develop proliferation quickly whereas others with chronic detachment remain free from proliferation. Proliferative change appears to start with RPE cells being dispersed from retinal breaks into the vitreous particularly after retinopexy or failed surgery. Metaplasia to myofibroblasts occurs through the action of growth factors released during or after retinal detachment. Types 1 and 3 collagen are laid down and contract as a wound healing response. Whereas wound contraction on a planar surface usefully closes a wound, wound contraction on the inside surface of the spherical eye tends to drag the neurosensory retina centripetally to worsen the retinal detachment. Occasionally the proliferation is predominantly subretinal producing fibrous strands that elevate the retina like the guy ropes of a tent or even ‘purse-string’ the retina around the optic disc. The response can be classified as:

Grade A— clumping of RPE cells and stiffening of the vitreous

Grade B— partial-thickness folding of the inner retina

Grade C— full-thickness fixed folding of the retina, commencing as localized star folds and progressing to an open funnel detachment, then to a closed funnel in the final stages. Grade C proliferative vitreoretinopathy can be further classified according to where the folding occurs as either anterior (A) or posterior (P) to the equator, and by the number of clock-hours of retina involved (1–12).

Fig. 12.28 This tear is distorted by early proliferative vitreoretinopathy. The tear will be splinted open by the fibrosis unless this is removed during surgery.

Fig. 12.29 This retina is wrinkled by preretinal fibrosis from proliferative vitreoretinopathy and graded as CP2 (full-thickness folds posterior to the equator extending for 2 clock-hours).

Fig. 12.30 Fundus photographs from an eye with a total retinal detachment and massive preretinal proliferation. The immobilized central retina is drawn into an open funnel-shaped configuration while stretching of the peripheral retina distorts and immobilizes the original flap-tear.

Fig. 12.31 Histological appearance of a fixed retinal fold showing striation of the retinal surface and maintenance of full-thickness folding by surface proliferations bridging between the retinal leaves.

By courtesy of Professor J Marshall.

Fig. 12.32 (Left) B-scan ultrasonography showing a rigid, closed, posterior funnel retinal detachment attached to the optic disc indicating CP12 proliferative vitreoretinopathy. (Right) A macrophotograph shows the clinical correlation.

DIFFERENTIAL DIAGNOSIS OF RHEGMATOGENOUS RETINAL DETACHMENT

The majority of retinal detachments are rhegmatogenous, caused by a break in the retinal neuroepithelium. ‘Traction’ detachments reflect the effect of ‘static’ tractional forces from fibrotic tissue directed either along the posterior hyaloid membrane or on the retinal surface. A combined rhegmatogenous and traction detachment can occur in PVR when abnormal epiretinal proliferation and contraction complicate the initial rhegmatogenous retinal detachment. Alternatively, in other ‘combined’ detachments, tangential traction from epiretinal proliferation is the primary event with subsequent retinal break formation, as frequently happens in proliferative diabetic retinopathy. Two other broad groups of retinal detachment are recognized in the absence of retinal breaks: ‘solid’ detachments (for instance those due to choroidal malignant melanoma; see Ch. 9) and ‘serous’ detachments (uveal effusion syndrome, Harada’s disease, central serous retinopathy, polypoidal choroidal vasculopathy; see Chs 9, 10 and 16). Disturbances in other coats of the eye may mimic retinal detachment; these include scleral infolding (e.g. from hypotony), scleral swelling (e.g. from posterior scleritis), choroidal detachment, RPE detachment and retinoschisis.

RETINOSCHISIS

Retinoschisis is a splitting of the neuroretina into two layers. It is classically divided into ‘juvenile’ and ‘senile’ varieties. Juvenile retinoschisis is a rare X-linked recessive dystrophy affecting young males (see Ch. 16) and must be considered when a boy presents with an apparent retinal detachment. A common presentation is vitreous haemorrhage, and central vision may be impaired by associated foveal schisis. The retina is split between the nerve fibre layer and ganglion cell layer.

Degenerative or ‘senile’ retinoschisis is usually bilateral, tends to be located inferotemporally, and is frequently discovered during routine examination of the peripheral fundus. The retina is split in the outer plexiform layer. The outer leaf of the schisis often has a grey translucency with a mottled pattern; the inner leaf is diaphenous and is most easily identified by the blood vessels on its surface. Outer leaf breaks tend to be large with rolled edges, whereas inner leaf breaks are usually small and round. Progression of schisis itself is exceptionally uncommon but combined schisis and rhegmatogenous detachment may occur.

Fig. 12.33 A retinoschisis with large outer leaf breaks in the temporal peripheral retina. Outer leaf breaks tend to be large with rolled edges whereas inner leaf breaks are usually small and round and best seen in the thin diaphenous retina by an oblique view with indirect ophthalmoscopy, with a fundus lens or three-mirror lens.

UVEAL EFFUSION SYNDROME

The uveal effusion syndrome (see Ch. 9) is an unusual condition, often mistaken for either a rhegmatogenous detachment complicated by choroidal detachment or a ‘ring melanoma’ of the anterior choroid. It is characterized by choroidal detachment, mottling of the overlying RPE (leopard spots) and serous retinal detachment which exhibits marked ‘shifting fluid’ (movement of subretinal fluid with gravity). PVR is not seen as there is no retinal break. The aetiology appears to be an abnormality of trans-scleral fluid outflow from the vitreous through an abnormally thickened sclera in a normally sized eye or vortex vein compression in a nanophthalmic eye. Spontaneous resolution may occasionally occur over months; otherwise the effusion responds to scleral thinning and decompression procedures.

Fig. 12.34 This photograph shows the typical ‘leopard spot’ pigmentation seen with chronic uveal effusions. These spots mask the background fluorescence on angiography. A B scan is necessary to look for scleral thickening and an A scan to measure axial length. Similar changes can be seen.

SPECIAL TYPES OF RHEGMATOGENOUS RETINAL DETACHMENT

Certain rhegmatogenous detachments pose special management problems owing to the unusual size or location of their retinal breaks. While most breaks are located between the equator and the ora serrata, more posterior breaks are sometimes seen related, for example, to posterior paravascular vitreoretinal adhesions or to radially oriented postequatorial lattice degeneration. This is especially true of the dominantly inherited vitreoretinal anomaly, Stickler’s syndrome.

Fig. 12.35 Stickler’s syndrome is characterized by myopia, paravascular pigmentary changes, dragging of major vessels at the optic disc, ‘veils’ or condensations of cortical vitreous around large lacunae or dehiscences in the gel and multiple posterior vitreoretinal adhesions. Patients have a characteristic facies with a flattened nasal bridge, a short mandible and long philtrum; other associations are a high palate and arthralgia. The gene has been localized to COLIIA1.

RHEGMATOGENOUS MACULAR HOLE DETACHMENT

Fig. 12.36 Breaks in the macula of emmetropic eyes do not usually cause retinal detachment (e.g. age related macular holes). In highly myopic eyes posterior breaks especially at the macula or temporal to the optic disc, often associated with areas of chorioretinal atrophy and posterior staphylomas, can cause retinal detachment. A macular hole has caused the retina to detach in this myopic eye with the subretinal fluid accumulating at the posterior pole. The detachment usually remains localized at the posterior pole but occasionally extends anteriorly if peripheral breaks are also present.

GIANT TEARS

Fig. 12.37 Other breaks are noted for their size. Giant retinal breaks are defined as extending for over 90° of the retinal circumference with a freely mobile posterior flap. They are located immediately post-orally or, less frequently, equatorially. They are caused by vitreous traction (the gel being attached to the anterior margin of the break). The posterior flap moves independently of the gel, essentially by gravity, and breaks may extend radially and posteriorly, especially at their upper limit. Giant tears may extend from 90° to 360° and often have satellite U tears. Giant tears are commonly associated with congenital myopia, Stickler’s syndrome and trauma and have a high risk of developing PVR.

TRAUMATIC RETINAL DETACHMENT

Many types of retinal break are found in traumatized eyes; they may develop at the time of impact or penetration, subsequently from incarceration of the retina or vitreous and the development of traction or as a consequence of later induced posterior vitreous detachment.

Fig. 12.38 Composite fundus painting demonstrating some of the types of retinal break seen after trauma. With blunt trauma the commonest break is an inferotemporal dialysis which, because of the slow onset of detachment, remains asymptomatic for months or years after the trauma until the macula detaches. The free posterior edge of torn retina may also become detached. Severe blunt trauma can produce commotio retinae which rarely can develop into a large ragged degenerative break. Occasionally an avulsion of the vitreous base is seen which comprises of a strip of ciliary epithelium, ora serrata and immediately post-oral retina, into which the basal vitreous gel remains inserted; this ‘bucket handle’ is most often found in the supranasal quadrant and hangs down in the vitreous cavity. Penetrating trauma can tear the retina at the site of injury or incarcerate vitreous, retina and choroid which progressively scars to shorten the vitreous and retina and produce further tears either at the incarceration site or, due to transvitreal traction, elsewhere.

INTRAOCULAR FOREIGN BODIES

Penetration of the posterior segment by a high-energy foreign body can result in severe vitreoretinal complications. To diagnose a retained small foreign body, careful attention needs to be paid to the history of the details and circumstances of the injury. The eye is examined for evidence of penetration such as an entry site, damage to the iris (often most easily seen by retroillumination) or, after mydriasis, to the lens as well as hypotony and blood or pigment in the vitreous. Immediate posterior segment damage is generally restricted to where the foreign body ultimately impacts or through-and-through perforation occurs.

In most hammer and chisel accidents (probably the commonest cause of intraocular foreign body), high-velocity ferrous material penetrates the cornea or limbal sclera, lens and vitreous and impacts in the retina. Initially there may be local tissue coagulation from the hot foreign body and bleeding into the cortical gel around the site of impaction and along the ‘track’ of penetration through the gel. If the foreign body impacts chorioretinal scarring usually secures the retina around the foreign body but a retinal break leading to retinal detachment may develop if the foreign body ricochets off rather than impacts in the retina. Subsequent fibroblast proliferation may occur at the site of impaction (to encapsulate the foreign body or distort the underlying and adjacent retina) or along the haemorrhagic track (to form a transgel traction band). Visual loss depends on the site of impaction (macular, papillary or peripheral), media opacity (cataract or vitreous haemorrhage) and retinal detachment.

Surgical removal of the foreign body is indicated to avoid severe posterior segment complications such as vitritis and endophthalmitis (infectious or toxic, e.g. acute chalcosis). Siderosis results from the ocular absorption of retained toxic ferrous material. Glaucoma and cataract appear several months after the injury (see Ch. 8). Destruction of photoreceptors produces characteristic ERG changes that are useful in assessing the remaining visual potential.

Radio-opaque intraocular foreign bodies are best detected by orbit CT scans, although plain radiography is also useful for screening and, by taking views on up and down gaze, showing whether or not the foreign body is retained in the eye. Ultrasonography is useful for detecting radiolucent foreign bodies although its main value is for assessing their vitreoretinal complications. Foreign bodies give rise to high-amplitude echoes, provided they are appropriately oriented to the sound beam. It is less effective for detecting small metallic foreign bodies, especially when they are embedded in the ocular coats. Magnetic resonance imaging is absolutely contraindicated as ferromagnetic particles rotate or move in the magnetic field.

Fig. 12.39 This patient has evidence of an intraocular foreign body with a corneal laceration (repaired with suture) (top left), iris damage, cataract and a poor red reflex from vitreous haemorrhage (top right). In another patient the entry site lies over the sclera at the limbus (bottom left).

Fig. 12.40 Fundus photograph of another patient shows a foreign body impaction site with prepapillary haemorrhage in the cortical gel and along the track of the foreign body (left). A lacuna of syneretic gel is seen overlying a large reactive foreign body on the retinal surface, viewed some days after injury (right).

Fig. 12.41 Radiological detection and localization of a foreign body by an ‘eye mover’ lateral film (left) and by computed tomography (centre). In another eye B-mode ultrasongraphy shows a large intravitreal foreign body with surrounding haemorrhage or vitreous inflammatory reaction (right).

Fig. 12.42 Metallic foreign bodies in the posterior segment are best removed by vitrectomy. This shows the operative view at the time of surgical removal.

VITREORETINAL COMPLICATIONS OF CATARACT SURGERY

Cataract surgery is associated with retinal detachment, occurring at a rate of 0.1–1 per cent of cases. Major risk factors are the degree of myopia and capsular rupture or vitreoretinal complications at the time of surgery. The phrase ‘dropped nucleus’ has been used to describe dislocation of the lens nucleus (or part of the nucleus) of a cataract into the vitreous cavity during phaco-emulsification. The nucleus can be seen in the inferior vitreous accompanied by fluffy white soft lens material. Pars plana vitrectomy and removal of the nucleus material is usually required within 1 week to avoid the development of glaucoma, chronic uveitis or corneal decompensation.

Fig. 12.43 Extensive soft epinuclear lens material can be seen lying in the posterior pole at the time of its surgical removal. In another patient a dislocated silicone plate lens is seen on the inferior retina following laser capsulotomy.

EXTRARETINAL NEOVASCULARIZATION

Vascularized epiretinal membrane formation in response to retinal hypoxia and ischaemia may be complicated by vitreous haemorrhage, vitreoretinal traction and retinal detachment. Causes of extraretinal neovascularization include retinal vein occlusion, haemoglobin SC disease and retinal vasculitis but the most common is diabetic retinopathy. Ischaemic diabetic retinopathy characteristically affects the mid-peripheral retina outside the major temporal vascular arcades and nasal to the optic disc (see Ch. 15). Neovascularization generally develops near the junction of ischaemic and normal retina (frequently at the optic disc and along the major vascular arcades). Abnormal neovascular tissue arising from intraretinal venules grows out through the inner limiting membrane and proliferates on the retinal surface or within the most cortical part of the vitreous gel as a vascularized epiretinal membrane (flat new vessels). New vessels do not grow into the central gel except occasionally within Cloquet’s canal. The membranes incarcerate the gel on which they proliferate producing vitreoretinal adhesions.

Fibroblasts within the vascularized membranes contract to cause tangential traction that is consolidated by subsequent collagen synthesis. Tangential traction is exerted along the retinal surface. It initially causes folding of the inner retinal layers (internal limiting membrane and nerve fibre layer) and may then progress to full-thickness retinal folding and to traction retinal detachment. Anteroposterior traction is exerted along the incompletely detached hyaloid face between the vitreous base and the point of vitreoretinal attachment. Contraction of membranes combined with vitreous gel shrinkage pulls the retina at these points of adhesion towards the centre of the eye. Without a retinal hole, subretinal fluid does not accumulate and the detached retina has a concave configuration. The vitreous detachment is taut and stretches from vitreous base to the neovascular membrane and between membranes. Areas of retinal detachment are often multifocal and surround neovascular membranes on the retinal arcades. Eventually the macula detaches whilst the periphery remains flat. If a hole appears in the fragile ischaemic retina subretinal fluid will accumulate; the retinal detachment then becomes convex and may extend anteriorly in a bullous fashion.

The vascularized membranes tend to become drawn forwards from the retinal surface and proliferate on the detached posterior vitreous cortex. Bleeding into the vitreous from neovascularization usually occurs at the time of posterior vitreous detachment or from vitreous traction on neovascular complexes. Haemorrhage invades the gel or, more commonly, the retrohyaloid space, which is loculated by the vitreoretinal adhesions, often covering the macula posterior to the hyaloid face. Retrohyaloid haemorrhage tends to clear more quickly than intragel haemorrhage. With a long-standing intragel haemorrhage lysed erythroclastic red cells in the cortical gel tend to settle on the internal side of the detached vitreous producing an ‘ochre membrane’, clearly seen on B scanning.

Although vitreous haemorrhage may clear spontaneously after some months, pars plana vitrectomy is frequently required to remove the haemorrhage and rehabilitate the patient. Surgery is more urgent in young diabetics to prevent irreversible loss of vision. Concurrent panretinal photocoagulation is applied to prevent iris neovascularization as removing the gel facilitates the access of angiogenic factors to the anterior segment. Dissection of any of membranes is required if there is significant neo-vascularization or retinal detachment; membranes must be removed totally to prevent future reproliferation and detachment.

Fig. 12.44 B scans showing a fluid level from retrogel haemorrhage over the posterior pole (left) and an intragel ‘ochre membrane’ (centre). A traction retinal detachment is seen in (right).

Fig. 12.45 Light microscopy of a diabetic retina shows a fibrovascular epiretinal membrane producing outer retinal folding.

By courtesy of Professor J Marshall.

Fig. 12.46 Macrophotograph of a hemisected diabetic globe shows an incomplete posterior vitreous detachment adherent to the optic disc and temporal parapapillary retina.

Fig. 12.47 (Left) This diabetic shows gross neovascularization, fibrosis and vitreoretinal traction along the temporal vascular arcades with tractional retinal detachment of the posterior pole. (Right) Inactive fibrotic changes are seen along the temporal vascular arcades with some tractional retinal detachment temporal to the macula.

Fig. 12.48 This is the appearance of a diabetic traction detachment before and after operation following vitrectomy, membrane dissection and intravitreal injection of gas to flatten the retina. The acuity improved from HM to 20/80. A considerable amount of retinal ischaemia is evident in the posterior pole; this will require further laser photocoagulation.

MACULAR VITREORETINAL PATHOLOGY

AGE-RELATED MACULAR HOLE

Age-related macular holes are due to a dehiscence of the neuroretina at the fovea which occur in middle-aged or elderly patients, more commonly in women. They are bilateral in 10 per cent of patients, usually presenting within 18 months of each other. Patients present with blurred vision, distortion or a scotoma. A helpful diagnostic test is the Watzke–Allen sign which is the perception of a break in a narrow beam of light projected on the macula. The underlying pathology appears to be tangential vitreofoveal traction before a posterior vitreous detachment has occurred which either causes a split (dehiscence) in the retina or avulsion the neuroretina.

Optical coherence tomography (OCT) is invaluable in confirming the diagnosis and in planning treatment. Macular holes can be closed by vitrectomy with insertion of a gas bubble to tamponade the hole for approximately one week. During this time the patient has to position themself face downwards to allow the bubble to float upwards and tamponade the hole. Supplementary manoeuvres such as dissecting the internal limiting membrane off the retina or applying autologous platelets to the hole, have been tried to maximize the chance of closure. Successful closure arrests progression to a stage 4 hole. About 70 per cent of patients improve by two lines or more of vision; many patients develop nuclear cataractous changes 1–2 years after surgery.

Fig. 12.49 Classification of macular holes. Stage 1A is an intrafoveal cyst. A yellow spot is seen with no PVD on biomicroscopy although there may be perifoveal detachment on OCT. Sometimes the anterior lamellae may separate at the stage 1A creating a lamellar hole. Stage 1B is an intrafoveal cyst with a posterior lamellar split. A yellow ring is seen on biomicroscopy with perifoveal detachment on OCT. The patient is usually asymptomatic or may have some metamorphopsia. Stage 1A and 1B may resolve spontaneously with posterior hyaloid separation or may progress to a full thickness hole with visual symptoms in 50% of cases, initially as a small hole of less than 300μm with posterior hyaloid attached to the lip (stage 2), enlarging to a hole of more than 300μm diameter, the vitreous separated from the fovea but with the PVD still incomplete (stage 3) and finally to a hole with complete posterior vitreous detachment (stage 4) over a few months.

By courtesy of Mr G Duguid.

Fig. 12.50 This fundus photograph shows a stage 1B hole. OCT shows that the neuroretina has been elevated by vitreous traction. Many stage 1 holes resolve or remain static.

Fig. 12.51 A small grade 2 macular hole (left) and an OCT scan showing foveal dehiscence with separation of the posterior hyaloid membrane and a tiny operculum (right). Cystoid spaces are present in the edge of the hole.

Fig. 12.52 A larger grade 3 macular hole. The visual falls to about 20/200 or CF. Typically the retina surrounding the hole is thickened and small yellowish excrescences can be seen on the exposed RPE. Fluoroscein angiography will show mild hyperfluorescence corresponding to the hole. OCT shows a partial vitreous separation from the fovea, an operculum and a large hole with rolled everted edges, adjacent cystoid intraretinal spaces and a shallow rim of subretinal fluid.

Fig. 12.53 Histology of a stage 4 hole. Note the retinal pigment epithelium is intact.

MACULAR EPIRETINAL MEMBRANE (PUCKER)

Idiopathic epiretinal membrane formation at the macula occurs with posterior vitreous detachment producing the clinical entities of macular pucker or cellophane maculopathy. In this situation RPE and glial cells from the retina, migrating through breaks in the internal limiting membrane, proliferate on the retinal surface to produce traction on the retinal surface. Epiretinal membranes can also occur without posterior vitreous detachment secondary conditions such as retinal vein occlusion, retinal vasculitis, cryotherapy or laser photocoagulation. The membrane can be seen as a reflective sheet (cellophane maculopathy) with minimal visual symptoms or as a thick opaque membrane drawing the retinal vascular arcades together and sometimes giving the appearance of a macular hole. The patient notices a reduction of vision coming on over some weeks accompanied by distortion of images and macropsia (increased image size) as the membrane pulls the retina into the glial focus, often preceded by symptoms of posterior vitreous detachment. After presentation, symptoms and signs remain static in the great majority of patients. The distorted vascular anatomy in the posterior pole gives the clue to the diagnosis.

Fig. 12.54 The OCT shows an epiretinal membrane distorting the inner retinal surface.

Fig. 12.55 (Left) A fine epiretinal membrane is seen over this macula with vascular distortion and an appearance of a pseudo-macular hole. Note the crinkly macular sheen from the epiretinal membrane giving the appearance of a pseudo-macular hole. Although the patient had metamorphopsia the acuity remained good. On the right an epiretinal membrane can be seen distorting the blood vessels in the posterior pole.

Fig. 12.56 In this eye, retinal folds originate from an area of epiretinal membrane temporal to the macula.

Fig. 12.57 A gross epiretinal membrane can be seen in the left eye of this patient (right), distorting the retinal vasculature when compared to the the normal eye (left).

PRINCIPLES OF VITREORETINAL SURGERY FOR RHEGMATOGENOUS RETINAL DETACHMENT

A variety of surgical techniques are used to treat vitreoretinal disorders; the choice of method depends on the condition needing correction and on the individual surgeon’s preferences. Certain principles need to be followed, however.

RETINOPEXY

If a patient presents with a retinal break that is at high risk of producing a retinal detachment (fresh U tear, paravascular tear, operculated tear or dialysis) but has no subretinal fluid then retinopexy is applied to seal the tear and prevent fluid from accumulating underneath the neurosensory retina. Laser therapy around the break (usually in two rows around the circumference of the break) or trans-scleral cryotherapy is used. Both methods damage the neurosensory retina, RPE and perhaps Bruch’s membrane and choroid causing scarring that results in adhesion within approximately 7 days sealing the retinal layers together, preventing fluid accumulation and detachment. However, once subretinal fluid is present, additional measures are needed to relieve vitroretinal traction and produce contact between the neural retina and RPE before retinopexy will work.

Fig. 12.58 Two rows of fresh argon laser burns seal this operculated peripheral round hole; within days they will start to become pigmented and atrophic producing a permanent chorioretinal adhesion.

Fig. 12.59 The histological appearance of a chorioretinal scar induced by laser photocoagulation shows damage at the level of the RPE and outer retina. Reparative glial tissue from the outer retina establishes a direct connection to Bruch’s membrane. RPE cells have migrated forwards in clumps.

By courtesy of Professor J Marshall.

REATTACHING THE RETINA, RELIEVING TRACTION AND TAMPONADE

Identifying and closing the retinal break or breaks is the prime aim of surgery and is acheived either by an external approach or by vitrectomy, depending on the case. Attaching a silastic explant (a plomb) to the sclera indents the eye wall underneath the break to relieve traction on the break and bring the retina and RPE into contact allowing the retina to reattach. Alternatively, the vitreous traction can be removed by pars plana vitrectomy and a long-acting gas bubble, such as sulfahexafluoride (SF₆—lasts for 2 weeks and expands 2-fold) or carbon tetrafluoride (C₃F₈—lasts for 2 months and expands 4-fold) inserted into the vitreous cavity. The gas bubble contacts the rim of the break (gas tamponade) to prevent fluid re-entry through the break. Thereafter subretinal fluid is reabsorbed and the retina flattens. Retinopexy is always needed because the gas bubble is only temporary and indentation from an explant gradually lessens with time. Fibrosis and shortening of the retina from proliferative vitreoretinopathy can prevent successful retinal reattachment; hence the fibrous membranes need to be removed surgically and in some cases the retina needs to be cut to relieve traction and allow it to refit the inside of the eye (retinectomy). Perfluorocarbon liquids (‘heavy’ liquids) can be used during surgery, for example to aid dissection of membranes, or to roll out folded retina and giant tears or to elevate intraviteal foreign bodies. When long-term tamponade is required silicone oil can be injected into the vitreous cavity to keep the reattached retina in place and allow time for the proliferative vitreoretinopathy process to become quiescent. Long-term use of silicone oil in the vitreous cavity is, however, associated with a number of complications such as cataract, glaucoma, refractive changes and low-grade retinal toxicity.

Fig. 12.60 A large variety of shapes and sizes of episcleral implants are available. This figure shows an encircling band, a circumferentially placed tyre and a radial plomb.

Fig. 12.61 Fundus painting of total retinal detachment with multiple breaks in lattice degeneration shows how explants can be used and the postoperative appearance after cryotherapy.

Fig. 12.62 Heightened light reflections are seen on the retinal surface following intraocular silicone oil tamponade indicating adequate oil filling.

Fig. 12.63 Perfluorocarbon liquids (‘heavy’ liquids) have been erroneously left in an eye after surgery and can be seen in the anterior chamber resting on the inferior angle with a long-term risk of glaucoma or corneal decompensation.