Surgical anatomy of the retina

Surgical Anatomy Of

The Retina

BY

Mohamed Abdel-Aziz (MSc,ICO,Egyption Board)

Eye from outside

The conjunctiva

-Is adherent to the sclera at the limbus,

- So the radial incisions to enter the subconjunctival plane have to

be made just behind the limbus.

Tenon’s capsule

-Is a layer of fascia that envelops the globe from the limbus to the optic nerve . -It is pierced by the extraocular muscles.-A glove-like sleeve of fascia extends anteriorly (to the rectus insertions) and posteriorly (for several mm) along the muscles from the points at which they pierce Tenon’s capsule.

-Between the rectus muscles anteriorly these sleeves are joined by a layer of fascia.

-Care must be taken when stripping fascia off the rectus

muscles because ligaments from the recti to the wall of the

orbit are functionally important in the actions of the muscle.

(a) Conjunctiva and (b) anterior Tenon’s have been dissected to revealthe (c) “posterior Tenon’s” glove-like extensions of tenons capsule alongthe recti and the associated intermuscular septum. (d) Bare sclera liesunder this.

The sclera

-The thickness of the sclera varies. It is thickest around the optic

nerve (1.2 mm) and thinnest under the recti behind their insertions

-So attempts to pass scleral sutures under the muscles are

particularly hazardous.Where scleral mattress sutures are more

typically passed, at the equator, it is approximately 1 mm thick.

Extra ocular muscles

-The recti are adherent to the sclera at the spiral of Tillaux. The location of

this ring corresponds approximately to that of the ora serrata .

-Circumferential scleral tires are therefore often placed as anteriorly as the

rectus muscle insertions will allow. In this position they support the retina asfar anteriorly as the ora serrata (“break ora occlusive buckling”).

-The superior oblique muscle runs laterally from the trochlea to its insertion

under the superior rectus.

-Passage of a superior rectus muscle hook from the temporal side of themuscle reduces the risk of inadvertently “hooking” the superior oblique as

well as does keeping the sweep of the hook pre-equatorial.

The ora serrata and the spiral of Tillaux (rectus insertions).The sclera has been rendered transparent to reveal the relationship between the ora serrata and the muscle insertions. Buckling anteriorly as far as the rectus insertions prevents anterior leakage.

Choroidal vasculature

-The long posterior arteries (as well as their correspondingnerves) run anteriorly from the equator at 3 and 9 o’clock .

-They may be damaged by subretinal fluid drainage in these

meridia .

-The anatomy of the vortex veins is somewhat variable but one

tends to leave the globe either side of the vertical recti just behind

the equator.

-They may be inadvertently hooked along with a vertical rectus

muscle if the muscle hook is passed behind the equator.

-Injury to the vortex veins may result in interruption to the venous

drainage from the choroid and choroidal detachment.

vortex veins (v), optic nerve (on), muscular tendon of inferior oblique (io), tendon of superior oblique (so), short posterior ciliary arteries (arrows), short posterior ciliary nerves (n), and long posterior ciliary artery and nerve (arrowhead).

-When operating near the vertical recti the vortex veins

should be identified to prevent injury.

- Because the vortex veins tend to be located near the vertical

recti subretinal fluid drainage is carried out closer to the

horizontal than to the vertical recti whenever possible.

-The anterior ciliary arteries are useful indicators of the meridia

of the rectus muscle insertions .

-As they supply the arterial circles of the iris surgical trauma

(including diathermy) should be minimized.

A, anterior ciliary artery; B, long posterior ciliary artery; C, vortex ampulla;D, vortex vein; E, greater arterial circle of the iris

Innervation

-Sensory nerves from the globe and bulbar conjunctiva pass

through the ciliary ganglion.

- Local anesthesia in this region, for example, sub-Tenon’sanesthesia, will therefore anesthetize the globe effectively.

-The innervation of the lids and palpebral conjunctiva is by the

lacrimal, frontal and infraorbital nerves, which do not pass

through the muscle cone.

-Blockage of the ciliary ganglion alone does not therefore

reliably provide adequate analgesia for buckling surgery.

The macula

the macula to the inferior oblique muscle was 1.35±0.42 mm.

Relationships among the optic nerve, superior oblique muscle (SO), inferior oblique muscle (IO), and macula (M). Right eye.

Eye from inside

-The vitreous can be considered as a three-dimensional matrix of

collagen fibers and hyaluronic acid gel .

-In the normal state, the outer surface of the vitreous is in contact

with the retina, pars plana, and ciliary body.

The vitreous

The vitreous is a three-dimensional matrix of collagen fibers and hyaluronic acid gel.

-Area centralis

-It measures 5.5 to 6 mm in diameter(outermost circle) and its subdivisions(inner circles).

-The central area of the macular regionis represented by the fovea centralis(2),approximately 1.85 mm in diameter,which has a central pit, the foveola(1),0.35 mm in diameter.

- The anatomically retinal belts thatsurround the fovea centralis are theparafovea (3), 0.5 mm wide, andperifovea (4), 1.5 mm wide.

Peripheral Retina

Pars plana

Ora serrata

-The ciliary body starts 1 mm from the limbus and extends posteriorly

for about 6 mm.

-The first 2 mm consist of the pars plicata and the remaining 4 mm comprises the flattened pars plana

Pars plana

The inner aspect of the ciliary body showing the pars plicata (a) and the pars plana (b). The ora-serrata is at (c), and posterior to it the retina shows cystoid degeneration (d).

ORA SERRATA

It is the last region where the retinaends and ciliary body starts.

consist of tooth like projection .

Retina is attached both to the vitreous& retinal pigmented epithelium.

Normal VariantS of Ora Serrata

-Meridoneal fold

-Enclosed oral bay

- Granulation tissue

Choroidal vasculature and nerves from

inside

Inferior short posterior ciliary nerve

(arrow) adjacent to vortex vein complex

Temporal long posterior ciliary nerve

-The long posterior

ciliary arteries (as well

as their corresponding

nerves) run anteriorly

from the equator at 3

and 9 o’clock .

-They may be damaged

by heavy

photocoagulation or

subretinal fluid

drainage in these

meridia .