Retina

 👁️ What Is the Retina?

The retina is the innermost layer of the eyeball, lining the interior surface of the posterior segment. It contains the photoreceptor cells that detect light and several layers of neurons that process visual information.

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📚 Layers of the Retina (From Outer to Inner)

There are 10 distinct layers, listed from closest to the choroid (outer) to the vitreous (inner) side:

#	Layer	Description
1	Retinal pigment epithelium (RPE)	Absorbs stray light, supports photoreceptors, forms blood-retina barrier
2	Photoreceptor layer	Contains rods (dim light) and cones (color, detail)
3	External limiting membrane	Tight junctions between photoreceptors and Müller cells
4	Outer nuclear layer	Cell bodies of rods and cones
5	Outer plexiform layer	Synapses between photoreceptors, bipolar, and horizontal cells
6	Inner nuclear layer	Cell bodies of bipolar, horizontal, amacrine, and Müller cells
7	Inner plexiform layer	Synapses between bipolar, amacrine, and ganglion cells
8	Ganglion cell layer	Cell bodies of ganglion cells
9	Nerve fiber layer	Axons of ganglion cells, converge to form optic nerve
10	Internal limiting membrane	Innermost layer, formed by footplates of Müller cells

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🔆 Photoreceptors:

1. Rods

• ~120 million

• Highly sensitive to dim light

• Found mostly in the peripheral retina

• No color vision

2. Cones

• ~6 million

• Function in bright light

• Responsible for color vision and fine detail

• Densest in the fovea centralis (center of macula)

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📍 Regions of the Retina:

🌟 Macula lutea

• Central yellowish zone

• High cone density

• Responsible for central, sharp vision

🎯 Fovea centralis

• Central depression in macula

• Contains only cones

• Region of maximum visual acuity

🧿 Optic disc (Blind spot)

• Where optic nerve exits

• No photoreceptors

• Entry/exit point for central retinal artery and vein

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🧠 Neural Pathway (Basic Flow):

Photoreceptors (rods/cones) → Bipolar cells → Ganglion cells → Optic nerve → Visual cortex (occipital lobe)