Anatomy
The macula is the part of the retina that lies inside the temporal vascular arcades and has a diameter of between 5 and 6 mm. Histologically, the macula has more than one layer of ganglion cells. It subserves the central 15–20° of the visual field and is responsible for detailed vision. The fovea is a depression in the retinal surface at the centre of the macula with a diameter of 1.5 mm. The foveal avascular zone is the central area containing no blood vessels ( Fig. 14.1 ).
Age-related macular degeneration (AMD)
Introduction
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Definition : degeneration affecting the macula; characterized by drusen and RPE changes, and sometimes choroidal neovascularization (CNV).
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Classification : non-exudative form (‘dry’) and exudative form (‘wet’). Non-exudative AMD is more common than exudative AMD; the latter is more likely to progress rapidly 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 whites), (c) family history (three times greater in first degree relatives), (d) genetic factors, particularly variations in the complement factor H gene CFH on chromosome 1 and the ARMS 2 / HTRA genes on chromosome 10, (d) smoking (doubles risk), (e) dietary factors (e.g. high fat intake), (f) other factors include hypertension and blue iris colour.
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. 14.2A ). Their presence in isolation carries little risk of visual loss.
Fig. 14.2
Drusen: (A) hard, (B) soft, (C) drusenoid detachment of the RPE, (D) FA late phase of (C) showing hyperfluorescence due to staining.
( Figure 14.2A,B courtesy of S. Chen.)
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‘Soft’ drusen : less distinct and larger than hard drusen. Numerous large soft drusen ( Fig. 14.2B ) are associated with a high risk of visual loss, including progression to CNV.
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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. 14.2C and D ).
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: (a) extensive intermediate-sized drusen, (b) at least one druse over 125 μm, (c) geographic atrophy, (d) 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.
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, (c) areas of chorioretinal atrophy ( Fig. 14.3A ).
Fig. 14.3
‘Dry’ macular degeneration: (A) geographic atrophy and pigmentary abnormality, (B) geographic atrophy.
( Figure 14.3A courtesy of S. Chen.)
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Course : enlargement of atrophic areas to give ‘geographical atrophy’ ( Fig. 14.3B ) with disappearance of pre-existing drusen.
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FA : window defect if the choriocapillaris is still intact; exposed sclera may exhibit late staining.
Treatment
prophylactic antioxidant supplementation.
Retinal pigment epithelial detachment
Pathogenesis
separation of the RPE from Bruch membrane caused by disruption of the physiological forces maintaining adhesion.
Diagnosis
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Serous retinal pigment epithelial detachment (PED) : orange dome-shaped elevation with sharply delineated edges ( Fig. 14.4A ). Subretinal blood or lipid and irregularly distributed fluid are suggestive of underlying CNV.
Fig. 14.4
Detachment of the RPE: (A) clinical appearance, (B) FA at 10 minutes showing hyperfluorescence, (C) diagrammatic representation, (D) OCT showing separation of the RPE from Bruch membrane and material under the sensory retina.
(From Salmon JF, Kanski’s Clinical Ophthalmology: A Systematic Approach , 9th edition. Oxford, UK: Elsevier; 2020.)
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Imaging of serous PED : (a) FA shows a well-demarcated oval area of hyperfluorescence ( Fig. 14.4B ), increasing in intensity but not area – ‘pooling’ – in which a notch may indicate CNV, (b) ICGA shows an oval area of hypofluorescence and a faint ring of surrounding hyperfluorescence, (c) diagrammatical representation ( Fig. 14.4C ) and OCT show separation of the RPE from Bruch membrane by an optically empty area ( Fig. 14.4D ).
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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, (c) rapid visual loss is typical of associated CNV (over 30%) or the development of an RPE tear (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, (c) OCT shows homogeneous hyperreflectivity.
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Haemorrhagic PED : virtually all eyes have underlying CNV or polypoidal choroidal vasculopathy and the prognosis is poor. (a) Presentation is with sudden impairment of central vision, (b) a dark red dome-shaped lesion is seen on examination, (c) FA shows dense masking but with overlying vessels visible.
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, (c) intravitreal triamcinolone, often in combination. There is a 5–20% risk of RPE tear with treatment (see below).
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Fibrovascular PED : as for serous PED with CNV.
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Drusenoid PED : observation in most cases. Long-term stability is common, but 75% progress to develop geographic atrophy and 25% to CNV by 10 years.
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Haemorrhagic PED : see below for management of polypoidal choroidal vasculopathy (PCV) and small CNV.
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. 14.5A ).
Fig. 14.5
RPE tear: (A) clinical appearance, (B) FA late phase showing relative hypofluorescence of the folded flap with adjacent hyperfluorescence where the RPE is missing, (C) OCT showing multilobed PED with subretinal fluid prior to tear, (D) OCT after tear (arrow) showing corrugation of the elevated RPE.
( Figures 14.5C and D courtesy of A. Ambresin.)
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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. 14.5B ).
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OCT : hyperreflectivity adjacent to the folded RPE ( Fig. 14.5C and D ).
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Prognosis : poor in subfoveal tears.
Treatment
no recognized treatment.
Exudative AMD
Pathogenesis
abnormal vessel complexes originating from the choriocapillaris (CNV) grow through Bruch membrane. Aetiological factors at cellular level include: (a) age-related compromise of Bruch membrane, (b) promotion of blood vessel growth by vascular endothelial growth factor (VEGF), (c) influence of inhibitory mediators (complement factor H and pigment epithelium-derived factor).
Diagnosis
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Presentation : in 6th to 8th decades with blurring and/or metamorphopsia.
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Signs : (a) CNV itself is sometimes identifiable as a grey-green or pinkish-yellow subretinal lesion; localized subretinal fluid ( Fig. 14.6A ), (b) hard exudate ( Fig. 14.6B ), (c) blood ( Fig. 14.6C ) (subretinal, preretinal), (d) later, retinal and subretinal fibrosis ( Fig. 14.6D ) ensues in an evolved or treated lesion.
Fig. 14.6
Choroidal neovascularization (CNV): (A) CNV visible as a grey-green sub-macular area (arrow) with surrounding exudation, (B) extensive lipid deposition, (C) intra- and subretinal haemorrhage, (D) ‘disciform’ scar.
(From Salmon JF, Kanski’s Clinical Ophthalmology: A Systematic Approach , 9th edition. Oxford, UK: Elsevier; 2020.)
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Prognosis of untreated CNV : often very poor, leading to ‘hand movements’ vision.
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OCT used to confirm diagnosis and monitor response to treatment.
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FA : (a) ‘occult’ CNV (type 1) is poorly defined ( Fig. 14.7A ) and often denotes a fibrovascular PED; 80% of total, (b) ‘classic’ CNV (type 2) is a well-defined membrane that fills with dye in a ‘lacy’ pattern early, with later leakage and staining; 20% of total ( Fig. 14.7B ).
Fig. 14.7
Angiography: (A) FA of occult membrane showing hyperfluorescence with poorly defined membrane limits, (B) FA of classic membrane showing ‘lacy’ hyperfluorescence and an area of hypofluorescence secondary to a haemorrhage, (C) typical CNV membrane with (D) corresponding OCT angiographic appearance.
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