Inner coat / Retina

 Retina:

• This is thin, delicate inner layer of the eyeball.
• It is continuous posteriorly with the optic nerve.
• The outer surface of the retina formed by pigment cells is attached to the choroid.
• The inner surface is in contact with vitreous.
• Opposite the entrance of the entrance of the optic nerve, inferomedial to posterior pole, there is a circular area known as optic disc.
• It is 1.5mm in diameter

The retina:

• It diminishes in thickness from behind forwards.
• It is divided into optic, ciliary and iridium parts.

The optic part:

• It contains nervous tissue and is sensitive to light.
• It extends from the optic disc to the posterior end of ciliary body.
• The anterior margin of optic part of the retina forms a wavy line called Ora serrata

Ciliary & Iridial parts

• Beyond the ora serrata, the retina  is continued forwards as thin, non-nervous insensitive layer, which covers the ciliary body and iris. 
• This forms the ciliary and iridial parts of the retina.
• These parts are made up of two layers of epithelial cells

• The depressed area of the optic disc is called the physiological cup.
• It contains no rods or cones, therefore insensitive to light - physiological blind spot.

Macula:

• At the posterior pole of the eye, 3mm lateral to the optic disc, there is another depression of similar size called the macula.
• It is avascular and yellow in colour.
• The centre of the macula is further depressed to form fovea centralis.
• The fovea is the thinnest part of the retina.
• The fovea contains cones only and is the site of maximum acuity of vision

The rods: 

• These are light receptors of the eye.
• Rods contain a pigment called visual purple.
• They respond to dim light - scotopic vision
• The periphery of the retina contains only rods
• Fovea has no rods.

The cones:

• They respond to bright light - photopic vision
• They are sensitive to colours
• The fovea centralis contains only cones.
• Their number diminishes towards the periphery of the retina

The retina is composed of ten layers

1. Outer pigmented layer
2. Layer of rods and cones
3. External limiting membrane
4. Outer nuclear layer
5. Outer plexiform layer
6. Inner nuclear layer - bipolar cells
7. Inner plexiform layer
8. Ganglion cell layer 
9. Nerve fibre layer
10. Internal limiting membrane

• The retina is supplied by Central artery 
• This is an end artery
• In the optic disc, it divides into upper & lower branches.
• Each gives of nasal and temporal branches
• The artery supplies the deeper part of retina up to the bipolar cells.
• The rods and cones are supplied by diffusion from the capillaries of the choroid.
• The retinal veins run with arteries.

Clinical anatomy

• Retinal detachment occurs between outer single pigmented layer an inner nine nervous layers.
• It is an inter retinal detachment
• Silicone sponge is put over detached retina, which keeps the retina in place 

Watch lectures on YouTube:

Inner Tunic of Eyeball - The Retina |Parts |Optic Disc |Macula Lutea |Layers of retina |Blood supply