25a. Surgical Management of Venous Occlusive Disease
Mark Humayun (Los Angeles)
Introduction
Retinal Venous Occlusive disease (RVO) is the second most common vascular cause of visual
loss. Incidence ranges from 0.7 % in people less than 60 years old to 4.6 % in people older
than 80 years of age. At any given time, 0.1 % of people aged 43 to 84 years old are affected
with central retinal vein occlusion (CRVO). Although most patients are older than 50, CRVO can
be seen in patients 20 years of age or younger. No definite cause has been found for the disease
but patients with hypertension and diabetes are at increased risk. In ischemic CRVO,
severe outflow obstruction results in substantial retinal damage which, in most cases, is associated
with permanent, marked visual loss. On the other hand, in non-ischemic CRVO, the
blockage is mild and the moderate visual loss improves in a significant number of patients with
time. Initially, 75 – 80 % of CRVO cases are non-ischemic but, within 3 years, about 34 % convert to the ischemic type.
Histopathological studies indicate that in most cases thrombosis occurs at or behind the lamina cribrosa. Inherent narrowing
of the vein at this area is thought to make it susceptible to thrombus formation1.
Existing therapies
Currently, there is no definite treatment for CRVO. Pan Retinal Photocoagulation (PRP) has been used to treat neovasculariztion,
which is a common and devastating complication of the ischemic type. PRP, however, has not been effective in treating
macular edema, which is an important secondary complication and a significant cause of visual loss – especially in nonischemic
CRVO. External optic nerve sheathotomy and radial optic neurotomy aim at releasing the pressure around the optic
nerve head2-6. Results using these techniques have been mixed. Intravitreal injection of triamcinolone7 and bevacizumab8, 9
are effective in reducing the macular edema and improving the vision but the effects are temporary, requiring repeated injections
which increases the risk of endophthalmitis. In addition, intravitreal triamcinolone is associated with complications such as
cataract and glaucoma. Treatments aiming to restore the blood flow have shown some success but have been associated with
serious complications. These treatments include: laser chorioretinal anastomosis10-13, susrgical chorioretinal anastomosis13,
intravitreal injection of tPA14, 15, intravenous injection of streptokinase16, 17, and injection of tPA into the retinal vein18. Macular
laser19-21 and retinal vein sheathotomy22, 23 are treatments specifically used to treat branch retinal vein occlusion (BRVO).
New concepts in surgical treatment of BRVO
Limited sheath manipulation (LSM):
This technique involves stretching the common arteriovenous advential sheath without performing vitrectomy. 25-gauge
Nitinol Flexible-Extendable blunt pick is used to lift the artery up proximal and distal to the crossing and then at crossing,
without severing the common advential sheath. During the manipulation, the vein is observed for reperfusion.
We performed a retrospective study on 16 eyes of 15 patients who underwent LSM. The study included BRVO cases complicated
by macular hemorrhage, macular edema recalcitrant to grid laser, and macular ischemia. The mean follow up period
was 43.4 +/-20.5 weeks, ranging from 18 to 78 weeks. Four eyes (25 %) underwent concomitant intravitreal steroid injection
after reperfusion visualization.
The results are as follows:
– Intra-operative reperfusion was observed in all patients.
– Mean preoperative LogMAR visual acuity of 1.0 +/- 0.3 (20/200) improved to 0.5 +/- 0.3 (20/60) postoperatively
(P<0.0001).
– In 15 eyes (94 %) there was an improvement in visual acuity
– One eye had stable VA (20/200)
– Eight eyes (50 %) had final visual acuity of 20/50 or better
– Mean preoperative macular thickness of 419.6 +/- 95.2 μm improved to 180.1 +/- 42.4 μm postoperatively (P<0.0001).
– There was no statistically significant difference between pre- and post-operative intraocular pressure
– There was no statistically significant difference between pre- and post-operative lens status
Conclusion:
– Vitrectomyless LSM is safe and efficacious
– It is reserved for BRVO complicated by macular hemorrhage, macular edema recalcitrant to grid laser, and macular
ischemia
New concepts in surgical treatment of CRVO
A) creating retinochoroidal anastomosis at disc:
This approach is perhaps most beneficial for those patients who are not suitable for retinal vein cannulation or do not
respond to that treatment. The aim is to bypass the obstruction by diverting the blood flow to choroidal vessels. The idea is
to inject or implant vascular growth factor coated devices in the optic nerve head, which can induce formation of a vessel
(or vessels) that connects the blocked retinal vein to the choroidal vasculature. Surgical and laser chorioretinal anastomosis
have been tried in the past, with partial success in creating an anastomosis but with a high rate of serious complications.
We speculate that creating an anastomosis at the optic disc reduces the risk of complications and that the use of vascular
growth factors expedites the process, giving more chance to the retina to recover before any irreversible damage can occur.
B) Retinal vein cannulation:
In this approach, a small, flexible cannula is used to penetrate one of the major retinal veins
close to the optic disc. Thereafter, a fibrinolytic agent is injected into the retinal vein in order to dissolve the blood clot24.
Although vein cannulation has been used by other investigators for the same purpose, our method is different in two main
aspects:
a) the cannula is composed of flexible and rigid parts. While the rigid part at the tip allows penetration of the vein, the flexible
part makes it possible to leave the cannula inside the vein for as long as required to infuse the drug. This is a significant
advantage over rigid cannulas which can rupture the retinal vein and cause retinal detachment. Also, with rigid cannulas,
the drug has to be delivered in a short time while the surgeon holds the cannula.
b) cannulation does not require a mechanical manipulator. Hence, the surgery can be performed by most vitreoretinal
surgeons with only minimal training.
Possible future Peri- and intra-operative diagnostics
A) Oxygen camera
B) Intraouclar Doppler ultrasound:
An intraocular Doppler probe which may be inserted through a 20g sclerotomy can measure the blood flow in the retinal
vessels during the surgery. By measuring the blood flow before and after the surgical procedure, the surgeon can confirm
the establishment of the retinal blood flow in the affected vein or in central retinal vein.
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