Retina Anatomy 1

Retina

The innermost layer of the eye

Neural layer

Located between the choroid and vitreous

Thin and Transparent

Thickest in the macular region and thins out as the retina goes further out in the periphery

Extends from the optic disc in both directions to the ora serrata

Reddish color of retina

combination of the retinal pigment epithelium, choroid, and choroidal vasculature

phototransduction

Photoreceptor cells (Rods/Cones) transform photons of light into a neural signal

This signal is than sent to optic nerve and finally the brain

photoreceptor cells turn photons into neural signals → bipolar cells → ganglion cells → optic nerve → brain

Zones in the Retina

Posterior Pole: central zone of the retina

Mid-Periphery: Extends from the posterior pole to the posterior edge of the vortex veins

Equator: Located right at the posterior edge of the ampulla of a vortex vein

Far Periphery: Extends from the anterior edge of the ampulla of the vortex vein to the ora serrata

Posterior Pole (Central Retina)

Takes up very little area - optic nerve, macula, vascular arcades, and arcuate retinal nerve fibers

Majority of the cones and ganglion cells are found here

Designed for VA, detail, and color (photopic vision)

The edge of the temporal optic disc is 3.7 (3.4?) mm away from the fovea (center of macula)

Peripheral Retina

Takes up most of the area - equator, mid-periphery, and far periphery

Majority of the rods are found here

Designed for gross form and motion, less clear but more sensitive to motion (scotopic vision)

Key Structures Found In The Peripheral Retina

Short Ciliary Nerves

Long Ciliary Nerves

Short Ciliary Arteries

Long Ciliary Arteries

Vortex Veins

Short Ciliary Nerves (peripheral retina)

About 8-10 short ciliary nerves present per eye

Seen between 10 to 2 o’clock and 4 to 8 o’clock (nasal and temporal half)

arises from ciliary ganglion

Sensory (CN V1), sympathetic, and parasympathetic (CN III & CN VII) information transmitted to Sphincter muscle in iris, ciliary body, cornea

Long Ciliary Nerves (peripheral retina)

2 long ciliary nerves are present per eye

Found at 3 and 9 o’clock (superior and inferior half)

Sensory (Nasocilliary branch of CN V1) and sympathetic information to Dilator muscle in iris, ciliary body, cornea, conjunctiva

Short Ciliary Arteries (peripheral retina)

from the ophthalmic artery and divides into 10-20 branches

entwine with the short ciliary nerves

Long Ciliary Arteries (peripheral retina)

from the ophthalmic artery and divides into 2 branches

entwine with the long ciliary nerves

Vortex Veins (peripheral retina)

• Composed of tributary veins that come together at an ampulla

• Drains the vascular supply of the choroid

• About 4-8 vortex veins are present per eye (About 70% of eyes have more than 4 vortex veins)

• Are typically found in the oblique regions of the retina (IN, IT, ST, SN)

Ora Serrata

Made of dentate processes (Retina) and Bays (Pars Plana).

Serrated junction (Most serrated nasally) between the retina and ciliary body

equator region

posterior edge of the ampulla, about 2 disc diameters posterior to the vortex veins

vitreous base

Site of the strongest attachment of the vitreous to the retina

straddles the ora serrata

Anterior border: 1.5 mm anterior into the pars plana (ciliary body)

Posterior border: 2-3 mm posterior to ora serrata (2 mm temporal, 3 mm nasal)

Overall, about a 3-6mm wide zone

Right Vs. Left Eye

Optic nerve is closest to the nose

disc diameter (DD)

A disc diameter (DD) is equivalent to the size of the optic disc

• 1 Disc Diameter (DD) = 1,500 microns

• 100 microns = 0.1mm

• 1 degree = 300 microns

Describe The Location Of The White Without Pressure

Left eye

Superior Temporal

Zone: Far periphery

In relation to optic nerve, more anterior

In relation to ora serrata, more posterior

How Would You Describe The Choroidal Nevus Seen In The Retinal Photo?

1.55 DD H X 1.5 DD V (1.5 DD round)

choroidal nevus is noted about 1.75 DD superior nasal to optic nerve in the left eye

Anterior to the optic nerve head

Posterior to the equator

Fluorescein Angiography (FA)

Highlights the optic nerve, retinal, and choroidal circulation

Useful in detection of subclinical retinal/choroidal/optic nerve changes secondary to vascular conditions

Application:

• Diagnosis of retinal, choroidal, and optic nerve head vascular disorders

• Aids in treatment decisions

• Guides retinal laser therapy

Pathway: internal carotid → ophthalmic artery → choroid via short posterior ciliary arteries , retina via central retinal artery and cilioretinal artery

OCT (Optical Coherence Tomography)

helps visualize pathologies in each layer of the retina

OCT-A (Optical Coherence Tomography Angiography)

visualize vessels of the retina and choroid non-invasively

Vessels are able to be visualized based on active blood flow

What is wrong with this OCT-A picture?

The outer retina should have no blood vessels

Wet macular degeneration

FAF (Fundus Autofluorescence)

Reflects Lipofuscin at the level of the RPE

When photoreceptors shed their outer segments, the RPE ingests these outer segments through phagocytosis.

These molecules are stored in liposomes and form lipofuscin

RPE cells are made up of 25% lipofuscin. Reason why central retina normally has a slight glow on FAF

Plaquenil maculopathy on Fundus Aurofluorescence

Increased AF = excess lipofuscin accumulation

Decreased AF = loss/death of RPE cells

Bright: increase in lipofuscin (increase in break down of rods/cones) → Over time, becomes dark because photoreceptors are dead (irreversible)

Geographic Atrophy: FA vs FAF

Fluorescein Angiography (FA): blood vessels bright

Fundus Autofluorescence (FAF): blood vessels dark

B-scan Ocular UltraSound

uses high-frequency sound waves to localize and define the shape and extension of a lesion through the eyelid

10 main layers of the retina from inner (Closest to vitreous) to outer (Closest to choroid)

• Internal limiting membrane (ILM)

• Retinal Nerve fiber layer (NFL)

• Ganglion cell layer (GCL)

• Inner plexiform layer (IPL)

• Inner nuclear layer (INL)

• Outer plexiform layer (OPL)

• Outer nuclear layer (ONL)

• External limiting membrane (ELM)

• Photoreceptor layer (Ellipsoid Zone)

• Retinal pigment epithelium (RPE)

In New Generation It Is Only Optometrists Examining Patient’s Retina

Retinal Pigment Epithelium (RPE)

The outermost layer of the retina

Lies between Bruch’s membrane and the photoreceptor layer

Single-cell thick, heavily pigmented hexagonal cells (cube-like when viewed as a cross section) , highly metabolic

Heavily pigmented by melanin (melanosomes and lipofuscin), densest at the macula then equator

Pigmentation may increase with age (increase in pigmented bodies, lipofuscin, and breakdown of phagocytic material)

granular appearance of macula

Within individual cells, there is unequal distribution of pigment (Most apparent at the macula since RPE cells are most dense in the macula region)

Junctions in the RPE cells

Interlocked by zonulae occludens (tight junctions) and zonulae adherens (anchoring junctions - connects actin filaments) to form an outer blood-retina barrier

Desmosomes (anchoring junctions - connects intermediate filaments) and gap junctions create a channel for ions, metabolites, and nutrients from the choroid

Appearance And Number Of Retinal Pigment Epithelium (RPE)

Longer, narrower at macula

Flatter, wider near ora serrata (periphery)

Most dense at the macula (Specifically at the fovea) and decrease in density further out in the periphery

Tight Junction of RPE

Zonulae occludens: Prevent passage of material in between cells. Tight seal!! Based on neural signaling, can sometimes allow ions, water soluble materials, etc to pass through

Anchoring Junction of RPE

• Zonulae Adherens: Prevents cells from sliding out of position (Specifically connects actin filaments which is more dynamic and allows for coordination of cell movement).

• Desmosomes: Provides structural support between RPE cells (Specifically connects intermediate filaments with strong adhesion).

• Hemidesmosomes: Provides structural support between an RPE cell and basement membrane (Specifically connects intermediate filaments with strong adhesion)

Gap Junction of RPE

Gap Junction: Channel proteins that permit electrical and chemical communication between RPE cells

3 Main Parts To A RPE Cell

Basal Component of RPE cell

majority of the mitochondria

contains infoldings to increase SA for better absorption of nutrients

very strong adhesion to Bruch’s membrane via: infoldings, extracellular matrix proteins (fibronectin, vitronectin, laminin, collagen IV)Location of the large oval nucleus, and hemidesmosomes

Central Component of RPE cell

Location of the large oval nucleus

Apical Component of RPE cell

closest to the photoreceptors

Microvilli, which are located at the apical portion of the RPE, extend to outer segment tips of the photoreceptors

Majority of melanin granules are found here as well which are instrumental in absorbing scattered light and stabilizing free radicals

RPE-Photoreceptor Interface

potential space in between the RPE and Photoreceptors: subretinal space

potential space is absent along the peripapillary ring around the optic disc and the ora serrata which means that the neurosensory retina is strongly attached in these areas

5 Reasons For RPE-Photoreceptor Attachment

1. IOP

2. Osmotic pressure (Higher than normal)

3. Vitreous

4. Apical Microvilli of the RPE

5. Interphotoreceptor matrix (IPM)

IOP And RPE-Photoreceptor Attachment

Low IOP - risk of retinal detachment

Function Of The RPE

1. Absorption of scattered light (Decreases photo-oxidative stress to the retina)

2. Control of fluid, nutrients, and waste products

3. Visual pigment (Such as rhodopsin) regeneration and synthesis

4. Key for the visual cycle

5. Synthesis of signaling molecules

PDGF: Controls cell growth and healing

PEDF: Neuroprotectant

VEGF: Stimulates normal vascular growth and neovascularization

TGF: Controls inflammation

6. Phagocytosis of photoreceptor waste

7. Involved in regeneration and repair if there is retinal damage

8. Stores Vitamin A

9. Synthesizes IPM

10. Acts as the outer-blood retina barrier especially due to the tight junctions found in the RPE

Interdigitation Zone (IDZ)

apices of the RPE cells encase part of the cone outer segments as well as the rod outer segments

Typically only visible in the posterior pole

Part of the subretinal space

Verhoeff Membrane

Surrounds the apical portion of RPE

Composed of tight junctions between RPE cells

Found in the interdigitation zone