macula lutea

**Anatomy/Histology** - Located at the posterior pole of the retina, ~3 mm temporal to the optic disc, along the visual axis. - Yellow color comes from xanthophyll carotenoid pigments (lutein and zeaxanthin). These absorb blue light and protect against photo-oxidative damage. - Subregions: parafovea and perifovea surround the fovea centralis (central depression, ~1.5 mm diameter). The foveola is the thinnest central part. - Fovea: contains only cones, with no rods. The inner retinal layers are displaced laterally, so light reaches the photoreceptors directly. It has a 1:1 cone-to-bipolar-to-ganglion cell ratio, which gives the highest acuity. It is avascular and gets its oxygen and nutrients from the choriocapillaris. - Rods predominate in the peripheral retina and mediate night (scotopic) vision. Cones mediate color and photopic vision. - Blood supply: the central retinal artery supplies the inner retina. The choroid supplies the outer retina and fovea (via posterior ciliary arteries).

**Clinical correlations** - **Age-related macular degeneration (AMD):** leading cause of irreversible central vision loss in people >50. - Dry (atrophic, ~90%): drusen (extracellular deposits between the RPE and Bruch membrane) and RPE atrophy. Treat with AREDS2 supplements (vitamins C and E, zinc, copper, lutein, zeaxanthin). - Wet (neovascular, ~10%): choroidal neovascularization driven by VEGF. It causes rapid vision loss, metamorphopsia (distorted straight lines), and central scotoma. Treat with intravitreal anti-VEGF (bevacizumab, ranibizumab, aflibercept). - Peripheral vision is preserved. - **Cherry-red spot on the macula:** the fovea has no ganglion cell layer, so the thin retina lets the intact choroid show through against a pale, opacified surrounding retina. - Central retinal artery occlusion (CRAO): sudden painless monocular vision loss. - Lysosomal storage diseases with ganglioside or sphingomyelin accumulation in ganglion cells: Tay-Sachs (hexosaminidase A deficiency), Niemann-Pick (sphingomyelinase deficiency). Also seen in Sandhoff disease. - **Diabetic retinopathy:** macular edema is the main cause of vision loss in diabetes. Treat with anti-VEGF and laser photocoagulation. - **Macular edema, central serous chorioretinopathy, macular hole, epiretinal membrane:** these cause central vision distortion or loss. - **Stargardt disease:** juvenile macular dystrophy (ABCA4 mutation, autosomal recessive). - **Hydroxychloroquine toxicity:** "bull's-eye maculopathy" with a cumulative dose. Screen with OCT and visual fields. - **Vitamin A deficiency / retinitis pigmentosa:** these affect rods first, causing night blindness and tunnel vision. Macular (central) vision is typically spared until late.

**Exam pearls** - Central scotoma + metamorphopsia → macular disease (AMD). - Amsler grid is used to detect macular disease. - Optic nerve lesions cause central scotoma with a relative afferent pupillary defect (RAPD). Optic neuritis in MS is the classic example. - The macula is responsible for the highest visual acuity, and the fovea has the highest cone density. - Macular sparing: occipital cortex (PCA) strokes spare the macula because of dual blood supply (MCA collateral) to the occipital pole.