Introduction
Anatomy of the peripheral retina
Pars plana
The ciliary body starts 1 mm from the limbus and extends posteriorly for about 6 mm. The anterior 2 mm consist of the pars plicata, the remaining 4 mm the flattened pars plana. In order not to endanger either the lens or retina, the optimal location for a pars plana surgical incision or intravitreal injection is 4 mm and 3.5 mm posterior to the limbus in phakic and pseudophakic eyes respectively. An incision through the mid-pars plana will usually be located anterior to the vitreous base (see below).
Ora serrata
The ora serrata ( Fig. 16.1 ) is the junction between the retina and ciliary body. In retinal detachment (RD), fusion of the sensory retina with the retinal pigment epithelium (RPE) and choroid limits forward extension of subretinal fluid (SRF) at the ora. However, there is no equivalent adhesion between the choroid and sclera, and choroidal detachments may progress anteriorly to involve the ciliary body (ciliochoroidal detachment).
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Dentate processes are tapering extensions of retina onto the pars plana; they are more marked nasally than temporally and display marked variation in contour.
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Oral bays are scalloped edges of pars plana epithelium between dentate processes.
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Meridional folds ( Fig. 16.2A ) are small radial folds of thickened retinal tissue in line with dentate processes, most commonly in the superonasal quadrant. A fold may occasionally exhibit a small retinal hole at its apex. A meridional complex is a configuration in which a dentate process, usually with an associated meridional fold, is aligned with a ciliary process.
Fig. 16.2
Normal variants of the ora serrata. (A) Meridional fold with a small retinal hole at its base; (B) enclosed oral bay
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Enclosed oral bays ( Fig. 16.2B ) are small islands of pars plana surrounded by retina as a result of meeting of two adjacent dentate processes. They should not be mistaken for retinal holes.
Vitreous base
The vitreous base ( Fig. 16.3 ) is a 3–4 mm wide zone straddling the ora serrata, throughout which the cortical vitreous is strongly attached. Following posterior vitreous detachment (PVD), the posterior hyaloid face remains attached at the vitreous base. Pre-existing retinal holes within the attached vitreous base do not lead to RD. Blunt trauma may cause an avulsion of the vitreous base, with tearing of the non-pigmented epithelium of the pars plana along the base’s anterior border and of the retina along the base’s posterior border.
Innocuous peripheral retinal degenerations
Peripheral retinal degenerations and other lesions carrying the potential to lead to RD are described separately.
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Microcystoid (peripheral cystoid) degeneration consists of tiny vesicles with indistinct boundaries on a greyish-white background, making the retina appear thickened and less transparent ( Figs 16.4A and B ). The degeneration starts adjacent to the ora serrata and extends circumferentially and posteriorly with a smooth undulating posterior border. Microcystoid degeneration is present in essentially all adult eyes, increasing in extent with age. It is not in itself causally related to RD, though it may give rise to typical degenerative retinoschisis.
Fig. 16.4
Innocuous peripheral retinal degenerations. (A) Microcystoid seen on scleral indentation; (B) paving stone with adjacent microcystoid; (C) and (D) honeycomb (reticular); (E) and (F) peripheral drusen; (G) pars plana cyst
(Courtesy of U Rutnin, CL Schepens, from American Journal of Ophthalmology , 1967;64:1042 – fig. A; S Chen – figs B, C, E and G)
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Paving stone degeneration is characterized by discrete yellow–white patches of focal chorioretinal atrophy that may have pigmented margins ( Fig. 16.4B ). It is typically found between the equator and the ora, and is more common in the inferior fundus. It is present to some extent in at least 25% of normal eyes.
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Reticular (honeycomb) degeneration is an age-related change consisting of a fine network of perivascular pigmentation that sometimes extends posterior to the equator ( Figs 16.4C and D ).
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Peripheral drusen. Clustered or scattered small pale discrete lesions ( Fig. 16.4E ) that may have hyperpigmented borders ( Fig. 16.4F ); they are similar to drusen at the posterior pole and usually occur in the eyes of older individuals.
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Pars plana cyst. Clear-walled cysts ( Fig. 16.4G ), usually small, are derived from non-pigmented ciliary epithelium. They are present in 5–10% of eyes, and are more common temporally. They do not predispose to RD.
Sites of vitreous adhesion
Physiological
The peripheral cortical vitreous is loosely attached to the internal limiting membrane (ILM) of the sensory retina. Sites of stronger adhesion in the normal eye include:
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Vitreous base; very strong.
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Optic disc margins; fairly strong.
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Perifoveal; fairly weak.
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Peripheral blood vessels; usually weak.
Pathological
Abnormal adhesions may lead to retinal tear formation following PVD, or to vitreomacular interface disease; most are discussed in detail later in this chapter.
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Lattice degeneration.
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Retinal pigment clumps.
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Cystic retinal tufts.
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Vitreous base anomalies, such as extensions and posterior islands.
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‘White with pressure’ and ‘white without pressure’.
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Zonular traction tufts.
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Vitreomacular traction (see Ch. 14 ).
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Preretinal new vessels, e.g. proliferative diabetic retinopathy.
Definitions
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Retinal detachment (RD). RD refers to separation of the neurosensory retina (NSR) from the RPE. This results in the accumulation of SRF in the potential space between the NSR and RPE.
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Rhegmatogenous (Greek rhegma – break) RD requires a full-thickness defect in the sensory retina, which permits fluid derived from synchytic (liquefied) vitreous to gain access to the subretinal space. RRD, as opposed to the presence merely of a cuff of SRF surrounding a retinal break, is said to be present when fluid extends further than one optic disc diameter from the edge of the break.
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Tractional RD. The NSR is pulled away from the RPE by contracting vitreoretinal membranes in the absence of a retinal break.
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Exudative (serous, secondary) RD . SRF is derived from the vessels of the NSR and/or choroid.
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Combined tractional–rhegmatogenous RD results when a retinal break is caused by traction from an adjacent area of fibrovascular proliferation.
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Subclinical RD is generally used to refer to an asymptomatic break surrounded by a relatively small amount of SRF, by definition extending further than one disc diameter away from the edge of the break but less than two disc diameters posterior to the equator. It does not usually give rise to a subjective visual field defect. The term is sometimes also used to describe an asymptomatic RD of any extent.
Clinical examination
Head-mounted binocular indirect ophthalmoscopy
The term binocular indirect ophthalmoscopy (BIO) is by convention used to refer to the head-mounted technique, though strictly it also applies to slit lamp indirect ophthalmoscopy. BIO allows retinal visualization through a greater degree of media opacity than slit lamp biomicroscopy, and readily facilitates scleral indentation. Light is transmitted from the headset to the fundus through a condensing lens held at the focal point of the eye, providing an inverted and laterally reversed image that is observed through a stereoscopic viewing system ( Fig. 16.5A ).
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Lenses of various powers and diameters are available for BIO ( Fig. 16.5B ); a lens of lower power confers increased magnification but a smaller field of view. Yellow filters may improve patient comfort.
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20 D (magnifies ×3; field about 45°) is the most commonly used for general examination of the fundus.
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28 D (magnification with the head-mounted set of ×2.27, and a field of 53°) has a shorter working distance and is useful when examining patients with small pupils.
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40 D (magnification ×1.5, field 65°) is used mainly to examine small children; a broad fundus scan can be acquired rapidly; it can also be used at the slit lamp to provide very high magnification.
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Panretinal 2.2 combines magnification similar to the 20 D lens with a field of view similar to that of the 28 D, and can be used with small pupils.
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Ultra-high magnification lenses for macular and optic disc examination (e.g. Macula Plus® 5.5) are available.
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Technique. The patient should be supine on a bed or reclining chair rather than sitting upright. The pupils should be dilated. Reducing the ambient illumination is often helpful in improving contrast and allowing a lower incident light intensity to be used. The eyepieces are set at the correct interpupillary distance and the beam aligned so that it is located in the centre of the viewing frame. The patient is instructed to keep both eyes open at all times; if necessary, the patient’s eyelids are gently separated with the fingers. The lens is taken into one hand with the flat surface facing the patient. The peripheral fundus should be examined first in order to allow the patient to adapt to the light. The patient is asked to move the eyes into optimal positions for examination, e.g. looking away from the examiner to facilitate examination of the retinal periphery. For the examination of small children (e.g. retinopathy of prematurity – see also Ch. 13 ) a speculum may be utilized to keep the eyelids apart, with an implement such as a squint hook employed to direct the position of the eye.
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Scleral indentation. The main function of scleral indentation (depression) is the enhancement of visualization of the retina anterior to the equator; it also permits kinetic evaluation ( Fig. 16.6 ). Indentation should be attempted only after the basic technique of BIO has been mastered; it requires practised coordination between the relative position of the indenter and the viewing apparatus, as well as care to prevent patient discomfort. For example, to view the ora serrata at 12 o’clock, the patient is asked to look down and the scleral indenter (a cotton-tipped applicator is preferred by some practitioners) is applied to the outside of the upper eyelid at the margin of the tarsal plate ( Fig. 16.7A ). With the indenter in place, the patient is asked to look up; at the same time the indenter is advanced into the anterior orbit parallel with the globe, and the examiner’s eyes are aligned with the condensing lens and indenter ( Fig. 16.7B ). Gentle pressure is exerted so that a mound is created; after adequate viewing, the indenter is gently moved to an adjacent part of the fundus. The indenter should be kept tangential to the globe at all times, as perpendicular indentation will cause pain and even risk perforation if the sclera is very thin. For viewing the 3 and 9 o’clock positions, indentation directly on the sclera is sometimes necessary, facilitated by topical anaesthesia. Indentation can also be performed at the slit lamp using some fundus contact lenses.
Fig. 16.6
Appearance of retinal breaks in detached retina. (A) Without scleral indentation; (B) with indentation
Fig. 16.7
Technique of scleral indentation. (A) Insertion of indenter; (B) indentation
Slit lamp fundus examination
A range of diagnostic contact and non-contact lenses are available for use with the slit lamp. Contact lenses should not be used if a penetrating injury is suspected or in the presence of corneal trauma, hyphaema or corneal infection.
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Non-contact lenses
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60 D. High-magnification lens optimized for viewing the posterior pole. High working distance (13 mm).
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90 D. Wider-field lens with lower magnification and shorter (7 mm) working distance. Can be used with smaller pupils.
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78 D. Intermediate properties; ideal for general-purpose examination.
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Miscellaneous. Numerous other lenses are available, offering qualities such as a very wide field of view and extremely small pupil capability.
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Three-mirror contact lens ( Fig. 16.8A ). A central lens gives a 30° upright view of the posterior pole. An equatorial mirror (the largest) enables visualization from 30° to the equator, a peripheral mirror (intermediate) views the fundus between the equator and the ora serrata, and a gonioscopy mirror (smallest and dome-shaped) may be used for gonioscopy or for visualization of the extreme retinal periphery and sometimes the pars plana. A viscous coupling substance is required to bridge a gap between the cornea and the apposed lens. To visualize the entire fundus the lens is rotated for 360° using first the equatorial mirror and then the peripheral mirrors.
Fig. 16.8
Diagnostic contact lenses. (A) Three-mirror lens; (B) Goldmann 904® lens with indentation attachment
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Scleral indentation at the slit lamp can be accomplished using a three-mirror lens with a special attachment (Eisner funnel) or a purpose-made ora serrata contact lens that combines a mirror angled similarly to a gonioscopy lens with an incorporated attachment to facilitate scleral depression (e.g. Goldmann 904® – Fig. 16.8B ).
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Miscellaneous contact lenses are divided principally into those conferring high magnification for an optimal posterior pole view, and those offering a wide field of view, allowing visualization extending to the ora serrata under optimal conditions. Small pupil capability is available, and a flange is offered on many lenses with the aim of improving stability of retention and of lens position on the eye.
Fundus drawing
When available, wide-field photographic imaging can be an excellent aid in recording the features of a retinal detachment, but documentation generally takes the form of a manually drawn illustration that optimally is colour-coded ( Fig. 16.9 ). RD boundaries are drawn by starting at the optic nerve and then extending to the periphery; detached retina is shaded in blue and flat retina in red. The course of retinal vessels (usually veins) is indicated with blue. Retinal breaks are drawn in red with blue outlines; the flap of a retinal tear is also drawn in blue. Thin retina may be represented by red hatching outlined in blue and lattice degeneration by blue hatching outlined in blue. Retinal pigment is indicated in black, retinal exudates in yellow and vitreous opacities in green.
Ultrasonography
Introduction
Ultrasonography (US) utilizes high frequency sound waves that produce echoes as they strike the interface between acoustically distinct structures. B-scan (two-dimensional) US is a key tool in the diagnosis of RD in eyes with opaque media, particularly severe vitreous haemorrhage ( Fig. 16.10 ).
Technique
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The patient should be supine; anaesthetic drops are instilled.
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The examiner typically sits behind the patient’s head and holds the US probe with the dominant hand.
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Methylcellulose or an ophthalmic gel is placed on the tip of the probe to act as a coupling agent.
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The B-scan probe incorporates a marker for orientation that correlates with a point on the display screen, usually to the left.
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Vertical scanning is performed with the marker on the probe orientated superiorly ( Fig. 16.11A ).
Fig. 16.11
Technique of ultrasound scanning of the globe. (A) Vertical scanning with the marker pointing towards the brow; (B) horizontal scanning with the marker pointing towards the nose
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Horizontal scanning is performed with the marker orientated towards the nose ( Fig. 16.11B ).
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The eye is then examined with the patient looking straight ahead, up, down, left and right. For each position a vertical and horizontal scan can be performed.
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The examiner then moves the probe in the opposite direction to the movement of the eye. For example, when examining the right eye the patient looks to the left and probe is moved to the patient’s right, the nasal fundus anterior to the equator is scanned and vice versa. Dynamic scanning is performed by asking the patient to move the eye, whilst the probe position is maintained.
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Gain adjusts the amplification of the echo signal, similar to volume control of a radio. Higher gain increases the sensitivity of the instrument in displaying weak echoes such as vitreous opacities. Lower gain only allows display of strong echoes such as the retina and sclera, though improves resolution because it narrows the beam.
Peripheral Lesions Predisposing to Retinal Detachment
Patients with any predisposing lesion, or indeed any high risk features for RD, should be educated about the nature of symptoms of PVD and RD and the need to seek review urgently if these occur.
Lattice degeneration
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Prevalence. Lattice degeneration is present in about 8% of the population. It probably develops early in life, with a peak incidence during the second and third decades. It is found more commonly in moderate myopes and is the most important degeneration directly related to RD. Lattice is present in about 40% of eyes with RD.
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Pathology. There is discontinuity of the internal limiting membrane with variable atrophy of the underlying NSR. The vitreous overlying an area of lattice is synchytic but the vitreous attachments around the margins are exaggerated ( Fig. 16.12 ).
Fig. 16.12
Vitreous changes associated with lattice degeneration
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Signs. Lattice is most commonly bilateral, temporal and superior.
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Spindle-shaped areas of retinal thinning, commonly located between the equator and the posterior border of the vitreous base ( Fig. 16.13A ).
Fig. 16.13
Wide-field images of lattice degeneration. (A) Multiple lesions with small holes; (B) sclerosed vessels forming a characteristic white network; a vortex vein is seen superonasally; (C) retinal detachment with lattice on the flap of the tear
(Courtesy of S Chen)
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Sclerosed vessels forming an arborizing network of white lines is characteristic ( Fig. 16.13B ).
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Some lesions may be associated with ‘snowflakes’, remnants of degenerate Müller cells.
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Associated hyperplasia of the RPE is common.
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Small holes are common (see Fig. 16.13A ).
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Complications do not occur in most eyes with lattice.
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Tears may develop consequent to a posterior vitreous detachment (PVD), when lattice is sometimes visible on the flap of the tear ( Fig. 16.13C ).
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Atrophic holes may rarely (2%) lead to RD; the risk is higher in young myopes. In these patients the RD may not be preceded by acute symptoms of PVD (see below) and SRF usually spreads slowly so that diagnosis may be delayed.
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Management. Asymptomatic areas of lattice are generally not treated prophylactically, even if retinal breaks are seen, unless particular risk factors are present, perhaps including RD in the fellow eye; treatment of the fellow eye when extensive lattice (more than 6 clock hours) is present, or there is high myopia, may actually be associated with a higher risk of detachment. However, the patient should be advised of the symptoms of RD, optimally including the provision of written information. Many practitioners advise routine annual review of eyes with lattice, with or without asymptomatic round holes, particularly in young myopes. An associated asymptomatic U-tear should be managed as discussed later in the chapter.
Snailtrack degeneration
Snailtrack degeneration is characterized by sharply demarcated bands of tightly packed ‘snowflakes’ that give the peripheral retina a white frost-like appearance ( Figs 16.14A and B ). It is viewed by some as a precursor to lattice degeneration. Marked vitreous traction is seldom present so that U-tears rarely occur, although round holes are relatively common. Prophylactic treatment ( Fig. 16.14C ) is usually unnecessary, though review every 1–2 years may be prudent as RD occurs in a minority.
Cystic retinal tuft
A cystic retinal tuft (CRT), also known as a granular patch or retinal rosette, is a congenital abnormality consisting of a small, round or oval, discrete elevated whitish lesion, typically in the equatorial or peripheral retina, more commonly temporally ( Fig. 16.15A ); there may be associated pigmentation at its base. It is comprised principally of glial tissue; strong vitreoretinal adhesion is commonly present and both small round holes ( Fig. 16.15B ) and horseshoe tears can occur. It is likely to be an under-recognized lesion, though this may change with the adoption of wide-field imaging; CRT are present in up to 5% of the population (bilateral in 20%) and may be the causative lesion in 5–10% of eyes with RD, though the risk of RD in a given eye with CRT is probably well under 1%.
Degenerative retinoschisis
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Prevalence. Degenerative retinoschisis (RS) is present in about 5% of the population over the age of 20 years and is particularly prevalent in hypermetropia.
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Pathology. RS is believed to develop from microcystoid degeneration by a process of gradual coalescence of degenerative cavities ( Fig. 16.16A ), resulting in separation or splitting of the NSR into inner and outer layers ( Figs 16.16B and C ), with severing of neurones and complete loss of visual function in the affected area. In typical retinoschisis the split occurs in the outer plexiform layer, and in the less common reticular retinoschisis at the level of the nerve fibre layer.
Fig. 16.16
Development of retinoschisis. (A) Histology showing intraretinal cavities bridged by Müller cells; (B) OCT appearance showing separation principally in the outer plexiform layer; (C) OCT of retinal detachment for comparison; (D) circumferential microcystoid degeneration with progression to retinoschisis supero- and inferotemporally
(Courtesy of J Harry and G Misson, from Clinical Ophthalmic Pathology , Butterworth-Heinemann 2001 – fig. A; S Chen – figs B and C)
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Symptoms
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Photopsia and floaters are absent because there is no vitreoretinal traction.
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It is rare for the patient to notice a visual field defect, even with spread posterior to the equator.
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Occasionally symptoms result from vitreous haemorrhage or a progressive RD.
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Signs. RS is bilateral in up to 80%. Distinction between the typical and reticular types is difficult clinically, though the inner layer is thinner and tends to be more elevated in the latter; differentiation is based principally on behaviour, with complications much more common in the reticular form.
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Early retinoschisis usually involves the extreme inferotemporal periphery of both fundi, appearing as an exaggeration of microcystoid degeneration with a smooth immobile dome-shaped elevation of the retina ( Fig. 16.16D ).
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The elevation is convex, smooth, thin and relatively immobile ( Fig. 16.17 ), unlike the opaque and corrugated appearance of a rhegmatogenous RD.
Fig. 16.17
(A) Retinoschisis; (B) composite image of the same lesion showing merging microcystoid degeneration
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The thin inner leaf of the schisis cavity may be mistaken, on cursory examination, for an atrophic long-standing rhegmatogenous RD but demarcation lines and secondary cysts in the inner leaf are absent.
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The lesion may progress circumferentially until it has involved the entire periphery. The typical form usually remains anterior to the equator; the reticular type is more likely to spread posteriorly.
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The presence of a pigmented demarcation line is likely to indicate the presence of associated RD.
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The surface of the inner layer may show ‘snowflakes’ (whitish remnants of Müller cell footplates – see Figs 16.17 and 16.18 ) as well as sclerosis of blood vessels, and the schisis cavity may be bridged by grey–white tissue strands.
Fig. 16.18
Retinoschisis. (A) Inner and outer layer breaks; (B) large outer layer break; retinal vessels in the inner layer can be seen traversing the rolled edge undiverted
(Courtesy of S Chen – fig. B)
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Breaks may be present in one or both layers. Inner layer breaks are small and round ( Fig. 16.18A ), whilst the less common outer layer breaks are usually larger, with rolled edges ( Figs 16.18A and B ) and located behind the equator.
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Microaneurysms and small telangiectases are common, particularly in the reticular type.
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If a visual field defect is detectable it is absolute, rather than relative as in RD.
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Complications are uncommon, and are thought to be much more likely in the reticular form.
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RD is rare; even in an eye with breaks in both layers the incidence is only around 1%. The detachment is almost always asymptomatic, infrequently progressive and rarely requires surgery.
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Posterior extension of RS to involve the fovea is very rare but can occur; progression is generally very slow.
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Vitreous haemorrhage is rare.
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Management. Though RD is rare, discussion of the symptoms is prudent in all patients, especially those with double layer breaks.
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A small peripheral RS discovered on incidental examination, especially if breaks are not present in both layers, probably does not require routine review, though a routine community optometric examination every 1–2 years may be prudent.
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A large RS should be observed periodically, particularly if breaks are present in both layers or it extends posterior to the equator; the review interval is individualized. Photography and visual field testing are useful, with optical coherence tomography (OCT) imaging when posterior extension is present. OCT is also useful for distinguishing between RS and RD (see Figs 16.16B and C ).
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Retinopexy or surgical repair may be indicated for relentless progression towards the fovea, when complication by retinal detachment should be excluded. Some authorities also advocate prophylactic retinopexy of the posterior border of a large bullous RS with substantial breaks to prevent progression to symptomatic RD.
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Recurrent vitreous haemorrhage may necessitate vitrectomy.
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Progressive symptomatic RD should be addressed promptly. More than one procedure may be necessary; scleral buckling may be adequate for smaller RD with small outer layer breaks, but vitrectomy is generally indicated for more complex RD.
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Zonular traction tuft
This refers to a common (15%) phenomenon caused by an aberrant zonular fibre extending posteriorly to be attached to the retina near the ora serrata, and exerts traction on the retina at its base. It is typically located nasally. The risk of retinal tear formation is around 2%, and periodic long-term review is generally recommended.
White with pressure and white without pressure
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‘White with pressure’ (WWP) refers to retinal areas in which a translucent white–grey appearance can be induced by scleral indentation ( Fig. 16.19A ). Each area has a fixed configuration that does not change when indentation is moved to an adjacent area. It may also be observed along the posterior border of islands of lattice degeneration, snailtrack degeneration and the outer layer of acquired retinoschisis. It is frequently seen in normal eyes and may be associated with abnormally strong attachment of the vitreous gel, though may not indicate a higher risk of retinal break formation.
Fig. 16.19
(A) White with pressure; (B) white without pressure; (C) strong attachment of condensed vitreous gel to an area of ‘white without pressure’
(Courtesy of NE Byer, from The Peripheral Retina in Profile, A Stereoscopic Atlas , Criterion Press, Torrance, CA 1982 – fig. A; S Chen – fig. B; CL Schepens, ME Hartnett and T Hirose, from Schepens’ Retinal Detachment and Allied Diseases , Butterworth-Heinemann 2000 – fig. C)
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‘White without pressure’ (WWOP) has the same appearance as WWP but is present without scleral indentation ( Fig. 16.19B ). WWOP corresponds to an area of fairly strong adhesion of condensed vitreous ( Fig. 16.19C ). On cursory examination a normal area of retina surrounded by white without pressure may be mistaken for a flat retinal hole ( Fig. 16.20A ). However, retinal breaks, including giant tears, occasionally develop along the posterior border of white without pressure ( Fig. 16.20B ). For this reason, if white without pressure is found in the fellow eye of a patient with a spontaneous giant retinal tear, prophylactic therapy should be considered. Regular review should be considered for treated and untreated eyes, though evidence for the benefit of this is limited.
