Manual of

Rhegrnatogenous

retinal

detachments

are

caused

by

retinal

breaks,

which

in most

cases

result

from vit-

reorerinal

traction.

Fluid accumulates

between

the

sensory

retina and

the retinal

pigment

epithelium

(RPE).

Closing

(or sealing)

the retinal

break

is syn-

onymous

with

repairing

(or preventing)

a rheg-

m.uogenous

retinal detachment,

assuming

that

the

v itre oret inu! traction

has been relieved.

Under-

standing

the anatomic

and

physiologic

principles of

the posterior

segment

is essential

to

formulating

appropriate

treatment for

retinal

breaks

and

retinal

detachments.

Retinal

Anatomy

The retina

is a thin,

transparent

tissue

that lines

the

posterior two-thirds

of

the globe. The

retina varies

in thickness

from

0.13

mm

(in

the

center

of

the

fovea)

to 0.55 mm (at

the margin

of

the anatomic

fovea).

It extends

from

the optic

nerve

posteriorly

tothe

ora

serrate

anteriorly

(which

approximates

the line

of recti

muscle

insertion). Photoreceptors

(rods

and

cones)

are connected

to neuronal

path-

ways

terminating

in

nonmyelinated

fibers that

form

the

optic nerve. The

inner

two-thirds

of

the

retina

are

nourished

by the

retinal

circulation;

the

outer

one-third

of

the

retina

is

nourished

by

the

choroidal

circulation,

a

high

flow

circulation

that also

serves

as

the

cooling

system

for

the

eye

(Figure

1- I).

The

vortex

veins,

which are

readily

visible

through

the

retina,

are

important

landmarks

because

they

exit

through

the

sclera,

approxi-

mately

3 mm

posterior

to

the equator.

There are

usually

four to six vortex

veins,

and they

are fre-

quently

found

near

the 1,5,7,

and

II

o'clock

meridians

(Figure

1-2).

Ciliary

nerves

also

serve

as landmarks.

The anatomic

macula

is defined

as the

posterior

portion

of

the

retina

containing

two or more

lay-

ers of ganglion

cells.

It measures

from 5.5-7.5 mm

in diameter

and

is centered

approximately

4

mrn

temporal

to

and

0.8 mm inferior

to the

center

of

the optic

disc.

Clinically,

this

region

is

often

referred to

as

the

posterior pole,

The anatomic

fovea

is a depression

in

the inner

retinal surface in

the center

of the

macula

measur-

ing 1.5 mm in

diameter. The

anatomic

fovea

is

commonly referred

to clinically

as the macula.

On

the external

surface

of

the

globe,

it is centered

I

mm medial

to and

I mm

above

the posterior

border

of the inferior oblique insertion.

The RPE,

a single

layer

of

pigmented epithe-

lium,

is

located

external

to

the

sensory

retina,

and

the choroid

is

located

external

to the RPE. The

choriocapillaris

(the capillary

bed

of the choroid)

is

located adjacent

to the RPE,

allowing

access

to the

outer retina,

which

it nourishes

(Figure

1-1). The

retina, the

RPE,

and the choroid

are mechanically

supported

by

the

sclera,

which

varies

in

thickness

from

0.3

mm

(just

posterior

to the insertions

of the