Age-related macular degeneration
Introduction
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Definition: degeneration affecting the macula; characterized by drusen and RPE changes, and sometimes CNV.
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Classification: non-exudative (‘dry’)—most common, and exudative (‘wet’); the latter is associated with more rapid progression to advanced sight loss.
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Importance: most common cause of irreversible visual loss in industrialized countries; advanced age-related macular degeneration (AMD) in one eye confers a 50% chance of advanced AMD in the fellow eye within 5 years.
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Risk factors: (a) age, (b) race (higher in Caucasians), (c) family history (several genes implicated), (d) smoking (doubles risk), (e) dietary factors (e.g. high fat intake), and (f) others (cataract surgery, blue iris colour, sunlight).
Drusen
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Pathogenesis: extracellular deposits at the interface between the RPE and Bruch membrane, derived from immune-mediated and metabolic processes in the RPE.
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‘Hard’ drusen: well-defined and small (less than half a retinal vein width; Fig. 14.1 ); their presence in isolation carries little risk of visual loss.
Fig 14.1
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‘Soft’ drusen: less distinct and larger than hard drusen; numerous large soft drusen ( Fig. 14.2 ) are associated with a high risk of visual loss, including progression to CNV.
Fig 14.2
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‘Drusenoid RPE detachment’: caused by coalesce of soft drusen resulting in a localized elevation of the RPE, a ‘drusenoid RPE detachment’ ( Fig. 14.3 ).
Fig 14.3
Prophylactic antioxidant supplementation in AMD
The Age-Related Eye Disease Study (AREDS) established that taking high-dose antioxidant vitamins and minerals on a regular basis can decrease the risk of AMD progression.
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Indications: those aged older than 55 years with one or more of the following high-risk characteristics (extensive intermediate-sized drusen, at least one druse over 125 µm, geographic atrophy, advanced AMD in one eye); treatment confers a reduction in risk of up to 25% at 5 years.
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AREDS regimen: vitamins C and E, beta-carotene, zinc, and copper; possible adverse effects include an increased risk of lung cancer in smokers.
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Other measures: (a) macular xanthophylls (lutein and zeaxanthin) and omega-3 fatty acids, (b) adequate leafy green vegetable intake; (c) cessation of smoking and avoidance of excessive sunlight should also be considered.
Non-exudative AMD
Diagnosis
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Presentation: gradual impairment of central vision over months or years in one or both eyes.
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Signs: (a) numerous intermediate–large soft drusen, (b) focal RPE changes, and (c) areas of chorioretinal atrophy ( Fig. 14.4 ).
Fig 14.4
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Course: enlargement of atrophic areas to give ‘geographical atrophy’ ( Fig. 14.5 ) with disappearance of pre-existing drusen.
Fig 14.5
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FA: window defect if the choriocapillaris is still intact; exposed sclera may exhibit late staining.
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Treatment: prophylactic antioxidant supplementation; experimental surgical options (e.g. intraocular telescope implantation, retinal translocation, implantable photosensitive chip).
Retinal pigment epithelial detachment
Pathogenesis: separation of the RPE from Bruch’s membrane caused by disruption of the physiological forces maintaining adhesion.
Diagnosis
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Serous retinal pigment epithelial detaclment (PED): orange dome-shaped elevation with sharply delineated edges ( Fig. 14.6a ); subretinal blood or lipid and irregularly distributed fluid are suggestive of underlying CNV.
Fig 14.6
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Imaging of serous PED: (a) FA shows a well-demarcated oval area of hyperfluorescence increasing in intensity but not area—‘pooling’—in which a notch may indicate CNV ( Fig. 14.6b ), (b) ICGA shows an oval area of hypofluorescence and a faint ring of surrounding hyperfluorescence ( Fig. 14.6c ), and (c) OCT shows separation of the RPE from Bruch’s membrane by an optically empty area ( Fig. 14.6d ).
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Course of serous PED: (a) gradually increasing atrophy and an eventual VA of 6/60 or less; (b) spontaneous resolution can occur, sometimes with visual improvement but often leaving geographic atrophy; and (c) rapid visual loss is typical of associated CNV (over 30%) or RPE tear formation (see below).
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Fibrovascular PED: (a) a form of ‘occult’ CNV, much more irregular in outline and elevation than serous PED; (b) FA shows markedly irregular granular or ‘stippled’ hyperfluorescence, with uneven filling of the PED, leakage, and late staining; (c) OCT shows an optically denser lesion than serous PED.
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‘Drusenoid’ PED: (a) shallowly elevated pale area with irregular scalloped edges; (b) FA shows diffuse hyperfluorescence, and (c) OCT shows homogeneous hyperreflectivity.
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Haemorrhagic PED: virtually all eyes have underlying CNV or polypoidal choroidal vasculopathy (see below); (a) presentation is with sudden impairment of central vision, and prognosis is poor, (b) a dark red dome-shaped lesion is seen on examination, and (c) FA shows dense masking but with overlying vessels visible.
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Treatment
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Serous PED: observation may be appropriate in eyes without CNV, especially in younger patients. Options for CNV are (a) intravitreal anti-VEGF agents, (b) PDT, and (c) intravitreal triamcinolone, often in combination.
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Fibrovascular PED: as for serous PED with CNV.
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Drusenoid PED: observation in most cases.
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Haemorrhagic PED: see below for management of polypoidal choroidal vasculopathy (PCV) and small CNV.
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Retinal pigment epithelial tear
Pathogenesis: tearing at the junction of attached and detached RPE, either spontaneously or after interventions such as laser or intravitreal injection.
Diagnosis
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Presentation: sudden central visual loss.
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Signs: crescent-shaped pale area of RPE dehiscence, next to a darker area corresponding to the retracted and folded flap ( Fig. 14.7a ).
Fig 14.7
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FA: late phase shows hypofluorescence over the flap due to the thickened folded RPE, with a linear border and adjacent hyperfluorescence where the RPE is absent ( Fig. 14.7b ).
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OCT: hyperreflectivity adjacent to the folded RPE ( Fig. 14.7c ).
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Prognosis: poor in subfoveal tears.
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Treatment: unproven modalities such as RPE translocation.
Exudative AMD
Pathogenesis: abnormal vessel complexes originating from the choriocapillaris (CNV) grow through Bruch’s membrane; it is thought that an age-related lowering of the integrity of Bruch’s membrane is a key aetiological factor.
Diagnosis
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Presentation: in 6th to 8th decades with blurring and/or metamorphopsia.
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Signs: (a) localized subretinal fluid, (b) hard exudate ( Fig. 14.8 ), and (c) blood ( Fig. 14.9 ) (subretinal, preretinal); (d) CNV itself is sometimes identifiable as a grey-green or pinkish-yellow subretinal lesion; later, retinal and subretinal fibrosis ( Fig. 14.10 ) ensues in an evolved or treated lesion.
Fig 14.8
Fig 14.9
Fig 14.10
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Prognosis of untreated CNV: often very poor, leading to ‘hand movements’ vision ( Figs. 14.11–14.13 ).
Fig 14.11
Fig 14.12
Fig 14.13
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FA: (a) ‘classic’ CNV is a well-defined membrane that fills with dye in a ‘lacy’ pattern early, with later leakage and staining ( Fig. 14.14 ): (b) ‘occult’ CNV is much less well-defined ( Fig. 14.15 ) and often denotes a fibrovascular PED.
Fig 14.14
Fig 14.15
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ICGA: a focal hyperfluorescent ‘hot spot’ or ‘plaque’ ( Fig. 14.16 ) can be a more sensitive adjunct to FA for the detection of CNV, for distinguishing other entities such as PCV, and for identification of vascular feeder complexes in some situations.
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