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ANIMAL EYE CLINIC INFORMATION SERIES!
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Vitreoretinal Surgery
Anatomy of the eye
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WHAT NORMALLY KEEPS THE RETINA IN PLACE?
As stated previously, the retina lies
against the back wall of the eye. The
back of the eye (vitreous cavity in
diagram) is filled with a transparent gel
which stabilizes the intraocular structures- much like styrofoam peanuts in a
box of fine glassware. When the head
moves rapidly, as when a dog shakes a
toy in his or her mouth, the vitreous
reduces the amount of turbulence inside the globe. The retina is fused to
the inside wall of the eye over 360 degrees in the area marked pars plana in
the diagram, as well as at the optic
nerve. Everywhere else, the retina is
held against the wall by a suction pump
that pumps fluid out of the space between the retina and the wall- the retina is essentially suctioned onto the
wall.
WHAT CAUSES RETINAL
DETACHMENT?
The retina can detach for a few reasons- the suction pump can fail, allowing fluid to build up between the
retina and the wall; fluid can be
forced out of the wall faster than
the pump can remove it; or a hole
can develop in the retina. In this
last example, the pump still works,
but fluid simply flows in through
the hole into the space between the
retina and the wall, resulting in detachment. This type of detachment
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is called a rhegmatogenous retinal detachment. While other types of retinal detachment
are often treatable with medications, a rhegmatogenous detachment requires surgery if it is
to get better.
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HOW DO HOLES FORM IN THE RETINA?
In animal patients, we are mostly concerned
with two scenarios. The first would be a dog
who has inherited defective vitreous. This is
called vitreal dysplasia- rather than a nice
firm molded gel, the vitreous is watery with
rope-like strands running through it. As the
head and eyes move, the strands are swinging
back and forth in the swirling liquid, pulling
on the retina. This can lead to tearing of the
retina, with subsequent fluid flow into the
hole and separation from the wall. This type
of inherited detachment is seen most commonly in certain breeds including the ShihTzu, Italian Greyhound, Parson Russell Terrier, Chinese Crested, as well as many mixed-breed
dogs.
The other scenario is in dogs who have developed cataracts +/- had cataract surgery. Cataract developmentespecially if very rapid in onset, can lead to inflammation. This inflammation in turn can lead to areas of adhesion between the retina and vitreous, with subsequent tearing.
HOW CAN I TELL IF MY DOG HAS A RETINAL DETACHMENT?
Most owners won’t recognize a problem in one eye. When the retina detaches the patient
will lose some or all of the vision in the affected eye. You might notice an increased glow in
the pupil as light reflects more brightly off of the bare wall in the back when the retina falls
away. Sometimes a torn retina will bleed, leading to a red appearance behind the pupil or in
the front of the eye. In the case of an inherited detachment most people don’t notice until
the second side detaches and the patient is suddenly acting blind. In the cataractpage 3
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associated type a detachment may be found before surgery (pre-operative ultrasound is performed to look for detachments when the cataract prevents us from directly viewing the
retina), or it is seen during routine post-operative rechecks if it develops later.
HOW CAN SURGERY HELP?
There are different surgical options depending upon the situation and the treatment goals.
1. Complete retinal detachment or giant retinal tear:
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This is the situation with the inherited type, as well as some of the post cataract
types. Basically there is a large tear in the retina, and as a result the majority of it has separated from the wall. In this case we would perform a vitrectomy. In this procedure three
holes are made into the back
of the eye. Fluid flows into
the eye through one, a light
is inserted into the second to
illuminate the area, and the
third is used to introduce
different surgical instruments. First the vitreous is
completely removed. Next a
heavy fluid is introduced
into the space- this flattens
the retina back against the
wall of the eye. A laser is
then used to seal any holes
or tears so the body’s own
suction pump will once again
be effective at keeping the
retina in place by removing
fluid. The heavy fluid will
cause problems if left in
place, so it is then removed
and replaced with silicone
oil- the new vitreous. This
procedure is approximately
85% successful in reattaching
the retina, but the amount of vision that returns is variable. Success depends upon how
long the retina has been separated, whether the retina has scarred while detached, and
other intrinsic factors. Surgery can be unsuccessful- problems can occur during or after-
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ward leading to failure. These include severe hemorrhage inside the eye while transferring
fluids (expulsive choroidal hemorrhage)- the most common intraoperative complication.
Post operative complications include: infection, glaucoma (increased pressure in the eye),
cataract formation (often this can be removed via cataract surgery), recurrence of the retinal detachment, and leakage of silicone oil into the front of the eye or into the tissues surrounding the eye. Some of these complications can be addressed with medications or additional surgery, but not all. In the worst case scenario, an eye might even require removal to
restore comfort if painful.
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Post operative care:
your dog would be discharged the same day. The
eyelids are often partially
closed with a temporary
stitch as they may not blink
fully for the first few days
after surgery. This stitch is
removed at the first recheckusually 3-5 days later. There
would be some eyedrops for
a few weeks, and oral medications to reduce inflammation, maintain comfort, and
prevent infection. An Elizabethan collar is kept on at all times for 2-3 weeks. Vision recovers slowly, and the amount of vision that returns varies between patients. It
can take as much as 6 weeks to see any improvement, although most will show
evidence of returning vision earlier. Some may not recover vision at all (uncommon), others appear to function normally. The most common successful outcome is a return of functional, but not normal vision. These dogs do better in
brightly lit surroundings. They seem to have better distance vision than close vision. They can avoid objects, find doorways, navigate well and confidently. If a
toy is tossed they will see that it was thrown, but not be able to pinpoint the spot
from where they sit.
2. Small tear with partial detachment:
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Sometimes in this situation we can use
a laser to “wall off ” the detached area in
hopes of preventing further spread of fluid
between the retina and wall. This is called a
barrier retinopexy. The chances of success
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depend upon the specific situation- your doctor would discuss more fully during the appointment.
3. Inherited vitreal dysplasia with retinal detachment in one eye, but currently no tears in the
second:
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In this case, the eye without any detachment
has a significant risk of detaching later. We do not
know how great this risk is as studies have not been
performed, and we don’t know how many dogs have
detached one side without their owner’s knowledge.
In human patients, the recommendation is to laser
the periphery of the retina in order to lower the risk
of tears leading to detachment later- prophylactic
retinopexy. This likely reduces future risk, but,
again, no studies have been done in dogs. It is painless post-operatively, so very low-impact
for the patient. There is a small risk that the inflammation in the immediate post operative
period can actually lead to detachment- especially in a very active patient. For this reason it
is best to keep your dog quiet for 7-10 days afterward. Otherwise there are no other complications associated with this procedure, but it may not work- i.e. tears and detachment
can still happen, although they are presumably less likely to occur.
WHAT IF I DECIDE NOT TO DO SURGERY?
There aren’t any right or wrong decisions. Long term, the presence of a retinal detachment
in an eye can lead to glaucoma. This is increased pressure inside the eye. It can lead to vision loss, although most eyes with retinal detachment will already be without vision. The
concern would be comfort as increased pressure can cause a headache sensation. Affected
dogs rarely squint or rub at the eye, rather they sleep more and play less. If the pressure increases, the eye might become more cloudy, or it may bulge and slowly enlarge. If any of
these changes occur, see your ophthalmologist right away. Otherwise it would be a good
idea to monitor pressure over time to watch for any increase. If both eyes are detached and
your dog has lost vision completely, he or she can still have an excellent quality of life. It is
important to keep in mind that most blind dogs have an excellent quality of life as long as
comfort is maintained. Not only are they in a protected and loving environment, dogs use
vision very differently than humans with their other senses far more developed than ours.
Sudden vision loss will take a longer period of adjustment than a gradual decline, but in either case most owners report that their pets adapt remarkably well.
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