visual pathway. and macula

 Describe the blood supply of the visual pathway.

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✅ Answer:

The visual pathway includes:

1. Retina

2. Optic nerve

3. Optic chiasma

4. Optic tract

5. Lateral geniculate body (LGB)

6. Optic radiation

7. Visual cortex

🔹 1. Retina:

• Supplied by central retinal artery (branch of ophthalmic artery).

• Outer retina also receives blood from the choriocapillaris, via posterior ciliary arteries.

🔹 2. Optic Nerve:

Divided into 4 parts:

1. Intraocular (optic disc):

   • Supplied by short posterior ciliary arteries (via circle of Zinn-Haller).

2. Intraorbital part:

   • Pial plexus from branches of:

     • Ophthalmic artery

     • Central retinal artery

     • Short posterior ciliary arteries

3. Intracanalicular part (in optic canal):

   • Branches from the ophthalmic artery

4. Intracranial part:

   • Small branches from the internal carotid artery, anterior cerebral, and anterior communicating arteries

🔹 3. Optic Chiasma:

• Supplied by:

  • Anterior cerebral artery

  • Anterior communicating artery

  • Internal carotid artery

🔹 4. Optic Tract:

• Supplied by:

  • Anterior choroidal artery

  • Posterior communicating artery

🔹 5. Lateral Geniculate Body (LGB):

• Supplied by:

  • Anterior choroidal artery

  • Posterior choroidal arteries (branches of posterior cerebral artery)

🔹 6. Optic Radiations:

• Supplied by:

  • Middle cerebral artery (especially temporal and parietal lobes)

  • Posterior cerebral artery

🔹 7. Visual Cortex (occipital lobe):

• Supplied mainly by:

  • Posterior cerebral artery

• Sometimes by:

• Middle cerebral artery (especially macular area)

🟦 2. Give an account on the anatomy of the macula.

✅ Answer:

🔹 Definition:

The macula lutea is a small, yellow-pigmented, oval area located temporal to the optic disc in the posterior pole of the retina. It is the area of maximum visual acuity.

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🔹 Dimensions:

• Diameter: ~5.5 mm

• Located about 3 mm lateral (temporal) to the center of the optic disc

• Occupies the posterior pole of the eyeball

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🔹 Divisions of the macula:

1. Fovea centralis (central depression of macula)

   • Diameter: 1.5 mm

   • Area of sharpest vision

   • Contains only cones

   • No blood vessels (called foveal avascular zone)

2. Foveola

   • Central part of the fovea

   • Diameter: ~0.35 mm

   • Contains densely packed cones only

   • Inner retinal layers are displaced to allow direct light access to photoreceptors

3. Parafoveal area

   • Around the fovea

   • Rich in cones and ganglion cells

   • Thickest retinal area (~7–9 layers of ganglion cells)

4. Perifoveal area

   • Surrounds parafovea

   • Transition zone between macula and peripheral retina

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🔹 Histological Features:

• Composed primarily of cone photoreceptors

• Inner layers of retina are displaced laterally at fovea

• Yellow pigment (lutein & zeaxanthin) gives yellow color (filters blue light)

• No rods at center (foveola)

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🔹 Blood supply:

• Outer retina (photoreceptors): by choriocapillaris (via short posterior ciliary arteries)

• Inner retina: by branches of the central retinal artery

• Foveal avascular zone (FAZ): maintained by diffusion from choroid

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🔹 Clinical relevance:

• Site affected in:

  • Age-related macular degeneration (AMD)

  • Central serous retinopathy

  • Macular holes

• Visual acuity depends on the integrity of foveola