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Macula and fovea anatomy
Anatomy & Optics
Key Points
- •Macula lutea ~5.5 mm diameter, defined by GCL >1 cell thick; fovea ~1.5 mm (central pit, inner layers displaced); foveola ~0.35 mm (floor of pit, ONLY cones, no rods, no inner retinal layers, thinnest retina ~130 µm); umbo (central point, foveal light reflex); FAZ ~400-500 µm (capillary-free zone, foveola nourished by choriocapillaris)
- •Henle fibre layer: obliquely oriented photoreceptor axons radiating from the fovea to the parafovea (~40-45° angle); exudates tracking along these fibres create the macular star pattern - classic in neuroretinitis (Bartonella), hypertensive retinopathy (grade 4), papilloedema; also concentrates xanthophyll pigments (lutein + zeaxanthin)
- •Xanthophyll pigments (lutein, zeaxanthin, meso-zeaxanthin): carotenoids in the Henle fibre layer + IPL; absorb blue light (400-500 nm) + antioxidant → macular photoprotection; low MPOD = risk factor for AMD; AREDS2: lutein + zeaxanthin supplementation reduced AMD progression
- •Foveal specialisation for high acuity: (1) no inner retinal layers at the foveola → minimal light scatter, (2) only cones (densely packed, ~199,000/mm² - thinnest/longest cones in the retina), (3) 1:1 cone:ganglion cell ratio (private line to brain), (4) FAZ ensures no vascular shadowing; the parafovea has the thickest retina (~340-370 µm) with 6-8 layers of ganglion cells
- •Foveal hypoplasia: failure of foveal pit formation → inner retinal layers persist over the foveola on OCT → reduced VA + nystagmus; causes: albinism (most common - also foveal hypopigmentation + chiasmal misrouting), aniridia (PAX6), achromatopsia, prematurity; foveal maturation is not complete until age 4-5 years
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13 more sections are included with the Clinical plan.
- Definition
- Epidemiology
- Aetiology and causes
- Pathogenesis
- Classification
- Clinical features