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Ophthalmic Viscosurgical
Devices and Anterior Segment Surgery:
Surgical Applications and Complications |
| Suresh K. Pandey M.D., Jaya
Thakur M.D., Liliana Werner MD Ph.D., David J. Apple M.D. |
Background
Viscoelastic substances are solutions with dual properties; they
act as viscous liquids as well as elastic solids or gels. The
ideal viscoelastic substance in ophthalmology should be viscous
enough to prevent collapse of the anterior chamber at rest, yet
liquid enough to be injected precisely through a small cannula.
It should be elastic or shock absorbing and should enhance
coating yet has minimal surface activity. It should be cohesive
enough to be removed easily from the anterior chamber but not so
cohesive that it is aspirated during irrigation and aspiration,
which would provide no protection to endothelial cells during
surgical manipulations. It should be eliminated from the eye in
the postoperative periodwithout any effect on intraocular
pressure. Viscosurgery was a term coined by Balazs to describe
the use of these solutions that had viscous, elastic and pseudo
plastic properties during and after surgical procedures. During
viscosurgery, viscoelastic substances are used as a fluid or a
soft surgical instrument. |
The viscoelastic sodium
hyaluronate was first used in ophthalmic surgery in 1972,when it
was introduced as are placement for vitreous and aqueous humor.
Since then ophthalmic surgical procedures had undergone
considerable advancement.
The use of viscoelastic materials has become commonplace in
anterior and posterior segment surgeries.These agents facilitate
delicate and often difficult intraocular manipulations during
various ophthalmicsurgical procedures |
Use of OVDs in Cataract
Surgery
OVDs are helpful in each step of modern cataract surgery using
phacoemulsification with IOL implantation.Some of these details
are shown in the schematic photograph (Figures 1, 2).
Capsulorhexis
In order to perform an intact and successful capsulorhexis, the
contents of the anterior chamber have an
important role. Till date balanced salt solution (BSS®), air and
OVDs have been used. Out of these three the best is viscoelastic
as it is considered the easiest, safest, and the most
reproducible method in both routine and difficult cases (Figures
2A, 2B). To perform a good capsulorhexis, the viscoelastic to be
used should have the four basic features-
1- High molecular weight and high viscosity at zero shear rate,
which maintains the anterior chamber.
2- Excellent visibility provided by high transparency.
3- Make surgical maneuvers easy, due to high elasticity and
pseudoplasticity.
4- It should give a good capsular flap control, providing the
soft and permanent spatula effect.
Cleavage of lens structure
It is best performed with the use of OVDs. The ideal
viscoelastic material keeps the anterior chamber shape unchanged
during BSS® injection and also avoids increase in pressure,
which can be produced with excessive amount of BSS® known as
capsular blockade.
Nuclear emulsification
During phacoemulsification, the viscoelastic is likely to remain
in the anterior chamber instead of leaking
out of the eye (Figure2C). OVDs help in preserving the space and
also because of their low cohesiveness, they remain in the
anterior chamber despite high irrigation flow. Moreover OVDs
adhere to the corneal endothelium, thus protecting the corneal
endothelial cells. Healon® and Healon- GV® does not trap the air
bubble and provide excellent endothelial protection (Figure 2D).
This is because of-
1- Scavenger effect- This effect captures the free radicals
released during phaco with consequent inactivation.
2- Binding sites- There are chemical receptors for viscoelastic
materials on the corneal endothelium.
A molecular bond seems to occur between the viscoelastic
solution and the corneal endothelium.
3- High Elasticity- This also smoothes the possible impacts of
the lens material against the endothelium.
The phaco tip being in a closed system, its vibrations are
transmitted to the internal structures of the eye but
viscoelastic provides a smothering shield against them.
Irrigation and aspiration
The role of viscoelastic during this procedure is the protection
of the endothelium.
This is possible due to high adhesiveness. It remains where it
is placed, without mixing with the cortex
because of its low cohesiveness thus helping in easy removal of
cortex.
Fig.1A: Injection of the
viscoadaptive OV in the anterior chamber through a 25 G cannula.
Fig.1B: Capsulorhexis is in
progress.
Fig.1C: Phacoemulsification
in progress.
Fig.1 D: Viscoadaptive OVD
is transparent and easy to see during removal (left). Note the
presence
of the air bubbles within the anterior chamber after use of
dispersive viscoelastic solution
(right).
Fig.1 E: Implantation of a
posterior chamber intraocular lens in
the capsular bag.
Fig.1 F: Removal of the
viscoadaptive OVD using irrigation-aspiration
tip.
Fig. 2: Beside posterior
chamber IOL fixation in the capsular bag, OVDs can also be used
for implantation of the various phakic and aphakic IOL designs
in the anterior chamber, ciliary sulcus etc.Use of the OVD
facilitated the implantation of the Artisan® IOL as shown in
this photograph. (Courtesy: Camil Budo, M.D.).
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Capsular bag
filling and
IOL implantation
During IOL implantation,it is necessary to expand the
capsular bag with a viscoelastic.It allows the surgeon
to keep the bag well
opened and formed thus allowing
the easy IOL implantation.
OVD is also helpful
in correct positioning, centering
and allowing for possible
IOL rotation maneuvers
(Figs. 1E, 1F). Beside
posterior chamber IOL implantation,
OVD has also
been used for implantation
of other IOL designs (e.g.
anterior chamber, iris fixated,
artisan lenses, etc.) (Fig.
2).
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Cataract
Surgery in Pediatric
Cases
Pediatric cataract surgery like the adult surgery has undergone
major changes in recent years with the evolution of techniques
including small incision and the development of modern IOLs
(Wilson ME, Pandey SK,Werner L, Apple DJ. Pediatric cataract
surgery: Past, present and future, Third Prize for “Special
Interest”,Annual Video Festival, XXth Congress of the European
Society of Cataract and Refractive
Surgeons, Nice, France, September 2002). The main principle lies
in the control of the very elastic nature of ocular tissues. It
is difficult to perform a good capsulorhexis in the presence of
high capsular elasticity. Moreover there is low scleral
rigidity, greater intravitreal pressure that makes the
capsulorhexis even more difficult, as the pressure tends to
curve the capsulorhexis. But with the use of viscoelastic, e.g.
Healon-GV® the effective push is in the opposite direction and
hence completion of capsulorhexis can be done. In pediatric
cases, the capsulorhexis must be started in the central portion
and not towards the equator, in order to prevent radial
extension. The high density viscoelastic agents stabilize the
posterior chamber and push back the vitreous face
during the posterior capsulorhexis. During IOL implantation,the
capsular bag is kept open and the anterior chamber is well
formed thus ensuring easy and safe implantation of the IOL in
the bag. These agents also help to dilate the pupil thus
maintaining a good intraoperative mydriasis. OVDs like Healon-GV®
can easily be removed at the end of the surgery including the
position which is behind the IOL due to its high cohesiveness
thus preventing capsular blockade.
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Use of the OVDs in Glaucoma
Surgery
Viscocanalostomy
Viscocanalostomy is a
new surgical procedure for
glaucoma therapy. Viscoelastics
play an important
role in this procedure. Figure
3 illustrates the surgical steps of viscocanalosotomy.
Viscocanalostomy literally
means “opening of the canal
by means of viscoelastic substance”.
This procedure is a
non penetrating and independent
from external filtration.
The advantages are
decreased risk of infection,
and decreased incidence of
cataract, hypotony and flat
anterior chamber as the anterior
chamber is not opened,
and moreover, with the
absence of external filtration
the bleb formation is prevented and also the related
discomfort with it. It minimizes he risk of late infections
and is independent
from conjuntival and episcleral
scarring.
Viscocanalostomy allows
the aqueous to leave the eye,
through Schlemn’s canal
and episcleral veins thus restoring
the natural outflow
pathway. This procedure
creates a bypass by which
aqueous humor reaches
Schlemn’s canal, skipping
the trabecular meshwork. A
chamber is produced inside
the sclera, which is in direct
communication with the
Schlemn’s canal. There is
also a communication through
the Descemet’s membrane
with the anterior
chamber.The OVDs should have
high pseudoplasticity to allow
injection into Schlemn’s
canal through a small needle
and should have high viscosity
at shear rate of zero
to maintain the spaces as
long as possible. Healon-
GV® and Healon-5® are
viscoelastics of choice for
this procedure. |
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Fig 3A Fig 3B
Fig 3C
Fig.3.A: Deep block construction incision.
Fig.3.B: Cutting the deep block in a single plane with a spoon
blade.Fig.3.C: Proximal to Schlemm’s canal
there is a subtle change in the scleral fibers,from a crossing
pattern to a tangentialpattern, with an increased opacity
Fig 3D
Fig 3E
Fig 3F
Fig.3.D: Descemet’s window. Fig.3.E:
Cannulating Schlemm’s canal
with three puffs of viscoelastic directed at the osteum.
Fig.3.F: Tight closure suture of the flap
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OVDs for Intraocular Delivery of Dyes or Anesthetic Agents
Researchers and vision scientists have been using OVDs as a
vehicle to deliver
capsular dyes for use during cataract surgery. Mixing these
substances with the
viscoelastic agent was attempted to prolong their effect and to
limit the adverse
effect on ocular tissues. Ciba Vision Corp. (Duluth, GA, USA),
has recently proposed mixing an OVD with lidocaine.This was
termed “viscoa-nesthesia” and was intendedto prolong the
anesthetic effect of intracameral lidocaine, as a complement to
topical anesthesia. Also, the steps of intracameral injectionof
OVDs and of intracameral injection of lidocaine, as a complement
to topical anesthesia, would be combined in only one step |
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Removal of the
OVDs
Several techniques have been reported in the literature for
removal of the OVDs. These include: Rock and roll technique,
twocompartment technique and bimanual irrigation/aspiration
technique. We would like to emphasize that a careful and
thorough removal of the OVDs from the capsular bag and the
anterior chamber of the eye is must after the end of the
surgery. This is important to avoid complications such as rise
in intraocular pressure, crystallization of the IOL surface.
Studies
have shown that complete removal of viscoelastic material from
the capsular bag can be more difficult when some hydrophobic
acrylic lenses are used because of the IOL’s tacky
surfaces(Apple DJ, Auffarth GU,Pandey SK. Miyake posterior view
video analysis of dispersive and cohesive viscoelastics, video
presented at the Symposium on Cataract, IOL, and Refractive
Surgery, Seattle, WA, April 1999). |
Complications of OVDs:
OVDs have many positive attributes but their drawbacks and
complications must be given careful considerations. Some of the
important complications areas follows-
1. Increase in intraocular pressure Increase in
intraocularpressure is the mos important
postoperative complicationof OVDs. It was first noted with
Healonâ . The increase in pressure can be severe and prolonged,
if the material is not thoroughly removed at the end of the
surgery. The rise in pressure occurs in the first 6 to 24 hours
and resolves spontaneously within 72 hours postoperatively. The
rise in pressure is due to the mechanical resistance of the
trabecular meshwork to the large molecules of the viscoelastic
material, which decreases the outflow facility. Hence to
decrease the incidence of this complication many have advocated
removing and aspirating the viscoelastic material from the eyes
at the end of the surgery.
2. Capsular block syndrome or capsular bag distension syndrome
Capsular block syndrome (CBS), is a newly described complication
of cataract-IOL surgery. It is characterized by accumulation of
a liquefied substance within a closed chamber inside the
capsular bag, formed because the lens nucleus or the posterior
chamber IOL optic
occluded the anterior capsular opening created by the
capsulorhexis. Depending on the time of onset, CBS is classified
as intraoperative (CBS seen at the time of lens luxation
following hydrodissection), early postoperative(originally
described CBS), and late postoperative (CBS with liquefied
aftercataract or lacteocrumenasia). Recently use of high-density
viscoelastic agents, such as Healon-GV®, has been found to be
associated with complication of late CBS. Main ingredient of the
transparent liquid in capsular bags is sodium hyaluronate and
that the distention is caused by aqueous humor being drawn into
the capsular bag by an osmotic gradient across the capsule when
the capsulorhexis diameter is smaller than that of the PC IOL
and by viscoelastic material retained and trapped in the bag
intraoperatively.
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Suggested Reading:
1. Arshinoff SA, Opalinski YAV,Ma J. The pharmacology of
lens surgery: ophthalmic viscoelastic agents. In: Yanoff M,Ducker JS, eds, Ophthalmology.St Louis, Mosby-Yearbook,1998; 4:20.1-21.6
2. Pandey SK, Thakur J, Werner
L, Sharma V, Izak AM, Apple
DJ. Ophthalmic viscosurgical
devices: An update. In: Garg
A, Pandey SK, Sharma V,
Apple DJ, eds., Advances in
Ophthalmology. Jaypee Brothers, New Delhi, India 2003, .
3. Liesegang TJ. Viscoelastics.
Surv Ophthalmol 1990; 34:268-
293
4. Pandey SK, Werner L, Apple
DJ, et al. Dye-enhanced pediatric
cataract surgery. J Pediatr
Ophthalmol Strabismus 2003 )
5. Ram J, Pandey SK. Anesthesia
for cataract surgery. In:
Dutta LC. Modern Ophthalmology.
Jaypee Brothers, New
Delhi, India, 2000, PP 325-330.
437-440, 378-384.
6. Saini JS, Pandey SK. Advance
in techniques of penetrating
keratoplasty. In: Nema HV,
Nema N, eds., Recent Advances
in Ophthalmology, Volume IV,
Jaypee Brothers, New Delhi,
india, 1998, pp 37-51
7. Pandey SK, Thakur J, Werner
L, Izak AM, Apple DJ. Classification,
clinical applications
and complications of ophthalmic
viscosurgical devices:
An update. In: Garg A, Pandey
SK, eds., Textbook of Ocular
Therapeutics. Jaypee Brothers,
New Delhi, India 2002, PP:
392-407
8. Pandey SK, Wilson ME, Apple
DJ, Werner L, Ram J. Childhood
cataract surgical technique,
complications and
management. In: Garg A,
Pandey SK, eds. Textbook of
Ocular Therapeutics. Jaypee
Brothers, New Delhi, India 2002, PP 457-486 |
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