88 MANUAL OF RETINAL

SURGERY

Peripheral

Membrane

Removal.

Peripheral

vit-

reoretinal membranes

are

found most commonly in

proliferative

vitreoretinopathy

or

following ocular

trauma. but

are sometimes

found

associated with

proliferative

vascular

retinopathies.

Most peripheral

membranes

are associated

with the vitreous

base

area. The most severe

forms

of

anterior

prolifera-

tive vitreoretinopathy

are found

following

previous

vitreous

surgery.

There

are two

major forms

of ante-

rior PYR: circumferential

contraction

caused

by

contraction

of membranes

formed

on the

peripheral

retina. usually at

the posterior

edge

of

the

vitreous

base; and

anterior

retinal

displacement,

once called

"anterior

loop contraction."

This latter

form

of PYR

is caused

by

fibrous proliferation

on the

surface of

the vitreous

base with contraction

that

leads

to trac-

tion retinal

detachment

and

anterior

displacement

of the peripheral

retina.

Figure

8-23A

shows an eye

with proliferative

vitreoretinopathy

with

prolifera-

tion of cells

on remaining

peripheral

vitreous

fol-

lowing vitrectomy.

Following

contraction

of

the

vitreous base,

the

anterior

retina

is pulled

forward

toward the

pars plana (Figure

8-23B),

the ciliary

body. or

even

the

posterior

iris surface.

Anterior

fibrovascular

proliferation

can be found

following

diabetic

vitrectorny

with either

fibrous

proliferation

and contraction

from

a sclerotomy

site

or severe

t'ibrovascular

proliferation

from the

peripheral

retina called

"anterior hyaloidal fibrovascular

pro-

liferation."

While

anterior

proliferative

membranes

in diabetic

retinopathy

tend to be more

vascular,

the

appearance

of the peripheral

retina

is similar

to that

found

in

anterior

retinal displacement.

Surgical Technique

Surgical

dissection

in the vitreous

base

area

neces-

sitates

removal

of the lens. It is recommended

that

the lens

capsule,

which may

become

involved

in

anterior

fibrous

proliferation,

be completely

removed

(as mentioned

above). Scleral

depression

is used

to

allow

visualization

of the

vitreous

base.

Wide iris dilatation

is helpful.

Iris retractors

may

be

useful

if the pupil is miotic.

Coaxial

illumination

is

used for the anterior

portion

of the

dissection.

While

depressing

the

anterior

vitreous into

view,

the

vir-

rectomy

instrument

is used to remove

any

remain-

ing formed

vitreous

(Figure 8-2'+).

Circumferential

contraction

becomes

apparent

as

membranes

are peeled from posteriorly to anteri-

orly. There

are

usually diffuse membranes

and

vit-

reous

is

often

adherent

to

these

membranes,

especially

throughout

the inferior

180 degrees

of

the retina.

The

vitreous

and

the membranes

should

be stripped

anteriorly

to the vitreous

base. Once

the

membranes

have

been

stripped

anteriorly

and

removed

if possible,

the vitreous

is excised

to

the

retinal surface

at the vitreous

base

with the

vitreous

cutter

utilizing

scleral

depression.

Anterior retinal displacement

may only be apparent

by a gray membrane

that covers

the tightly

contracted

vitreous

basco The

anterior

retina

is often

pulled

for-

ward but m~IYbe obscured. There

are two components

to the anterior

retinal displacement

and each must be

deal! with. Circumferential

sectioning

of a membrane

that covers the vitreous

base

is necessary

to relieve an

anterior-posterior (AP)

component

that pulls the retina

anteriorly. A circumferential

component of contraction

that pulls

the retina

centrally

and

causes

radial folds

that extend posteriorly.

must

also be relieved.

The tight capsule-like

membrane

that overlies

the

vitreous

base is incised

with

the

tip of a sharp

blade

such as the MVR

blade. After

an opening

is created in

this membrane,

vertically

cutting

scissors, such

as tile

membrane peeler-cutter

(MPC)

scissors

(Alcon Lab-

oratories, Fort

Worth) , are

used

to section

tile

mem-

brane anterior

to tile anterior

extent

of tile retina

in a

circumferential

direction

(Figure

8-25). A bimanual

technique

is often

useful

and

a fiberoptic

illuminated

pick or spatula can be used to retract the fibrous

mem-

brane away from

the

vitreous

base

as it is cut. The

anterior retinal displacement

is usually

most promi-

nent in the inferior

180 degrees

but

can

extend

360

degrees. There

may

be

a "trough"

created

by

the

membrane between

the anterior

and

posterior edges

of the membrane

(see

Figure

8-25).

Formed vitreous

Posterior Segment Vitrectorny

89

of tile vitreous

base

may be uncovered

in the

trough

after the membrane

is opened

and should

be cut to the

surface

of the peripheral

retina

and

pars

plana

usi-ng

the vitreous

cutting

instrument.

The circumferential

component

of

anterior reti-

nal displacement

is released

by

either

excising the

membrane

on the surface

of the

vitreous

base

using

bimanual dissection

or making

multiple

radial

cuts

in the membrane.

When

using coaxial

illumination,

it is possible

to

use

both

forceps

and

scissors

in a

bimanual dissection

technique.

For endoillurnina-

tion during bimanual

dissection,

the fibcroptic

illu- .

minared

pick

or

spatula is

useful.

Fiberoptic

illuminated forceps

and scissors

have

been intro-

duced,

but

have

not been

universally

adopted

because

of

their

expense

and

limited

availability.

These

illuminated

instruments

are helpful

during

bimanual dissection

of the vitreous

base.

Treatment

of Retinal

Breaks

and Retinal

Detachment

Retinal

breaks may

be

present

prior

to vitreous

surgery

or

may

occur

as

a

result of

membrane

Perfluorocarbon

Liquids

If a posterior break

is not available

and

it is necessary

to reattach

the retina

completely,

we now rarely create

a posterior

retinotomy.

In most

instances,

if a poste-

rior break

is not

present

for

drainage

of

subretinal

fluid. perfluorocarbon

liquid

(PFCL)

is used

to reat-

tach the retina,

PFCL is a synthetic

liquid that

is heav-

ier

than water'

or

saline and

will

displace

subretinal

fluid anteriorly

and

reattach

the retina from posteri-

orly

to anteriorly.

Perfluorocarbon

liquid

can

be

injected over the

posterior

pole

after

posterior

mem-

branes have been

removed

10 flatten

and stabilize

the

posterior

retina. The

heavy

liquid flattening

of

the

posterior retina

makes

midperipheral

and

far

periph-

eral

membrane

peeling

easier

by reducing

the

mobil-

Posterior Segment

Vitrectomy

91

ity of the

retina

during membrane

peeling

(Figure

8-28A).

As the retina

is reattached

with

PFCL, fluid

will egress through anterior retinal breaks

into the vit-

reous cavity and allow

near complete

reattachment

of

the retina

if the vitreous

cavity

is

filled

with PFCL

(Figure

8-28B). The PFCL should

never

be directed

toward

a retinal

break during

injection

because the

PFCL stream

will go into the subretinal

space

through

the break. IfPFCL

is to be used,

it is important

that all

traction

be released

before

the level

of PFCL is

extended

over a retinal

break,

otherwise

the PFCL,

which

has

a low

interfacial surface

tension,

will go

through

the break

into the subretinal

space. However,

once traction

is relieved

from

the retina,

it is safe to

extend

the PFCL

level anterior

to a retinal

break (Fig-

ure 8-28C). Once

the retina is attached,

the PFCL

can

92

MANUAL

OF RETINAL

SURGERY

be removed

by a PFCL-air

exchange. The

PFCL is

aspirated

with

a silicone-tip

suction

needle

as

the

eye is simultaneously

filled

with

air. If anterior

subretinal fluid

remains

before

PFCL-air

exchange,

it is desirable

to aspirate

subretinal

fluid duting

the

early

portion

of the exchange

through

an

anterior

retinal break

so

no subretinal

fluid

is forced

poste-

riorly into the

posterior

pole

by

the

air.

While

perfluoro-n-octane,

the

most commonly

used

PFCL

has

a high

vapor

pressure

and

will evaporate

in air at body

temperature.

other

commonly

used

PFCLs

do

not evaporate.

Therefore,

it is necessary

to place

a small

amount

of

BSS

over the

posterior

pole following

PFCL-air

exchange