OCULAR ISCHAEMIC SYNDROME
Ocular ischemic syndrome refers to the development of ischemia, or a restriction in blood supply, to retinal cells due to cardiovascular disease. The most serious consequence of ocular ischemic syndrome is the growth of abnormal choroidal neovascular membranes which can lead to neovascular glaucoma. Treatment for ocular ischemic syndrome involves inhibiting the proliferation of these abnormal blood vessels.
Ocular ischemic syndrome is mainly caused by the occlusion, of blockage, of carotid arteries that supply the eyes and head with blood. When large or small carotid arteries become blocked by cardiovascular disease such as atherosclerosis, blood stops circulating within the eye. This condition, called ischemia, deprives retinal cells of nutrients while also preventing them from disposing of toxic waste products. As a result, retinal cells begin to die, stimulating the growth of abnormal choroidal neovascular membranes on the retina and/or the iris. Although these blood vessels are meant to stop retinal cell death, they are incredibly fragile and tend to break and bleed. The development of these blood vessels typically leads to vitreous hemorrhage and worsens the ischemia of retinal cells.
The most dangerous consequence of ocular ischemic syndrome, however, is the development of neovascular glaucoma due to abnormal choroidal neovascular membrane growth on the iris. When these abnormal membranes grow over and block the trabecular meshwork, the fluid drainage site situated near the iris, it prevents the outflow of fluid from the anterior chamber of the eye. Consequently, without a proper way to drain, the build up of fluid within the anterior chamber of the eye causes increased intraocular pressure, which in turn leads to the development of glaucoma.
Preventing ocular ischemic syndrome is limited to finding the major carotid artery occlusions within the patient. This is done using a technique called the Carotid Doppler which uses ultrasound waves to depict the blood flow patterns of major blood vessels. Finding a carotid artery occlusion indicates that the patient needs treatment for cardiovascular disease and that they are at a high risk of developing ocular ischemic syndrome. By managing the underlying cause of cardiovascular disease, such as hypertension, diabetes, or high cholesterol levels, a patient can effectively reduce their risk of developing ocular ischemic syndrome.
Management for carotid occlusions may be conservative, and includes the use of blood thinning agents up to surgical intervention, depending on the severity of the carotid occlusion, underlying risk factors, and the complications associated with surgical intervention.
CARDIOVASCULAR RISK REDUCTION
In patients who have ocular ischemic syndrome, there may be no underlying occlusion of the carotid artery identified on the Carotid Doppler.
The overall management of cardiovascular risk factors can be helpful in trying to reduce the risk of progression of disease and the possible development of disease in the second eye. Cardiovascular risk protection includes the management of underlying hypertension, diabetes, and cholesterol management.
While these represent the majority of cardiovascular risk management techniques, other, more advanced, management techniques of cardiovascular risk can be discussed with your doctor or general medical internist who is involved in your care. OCC Eyecare supports the involvement of other medical practitioners in the care of its patients when team management best suits patient outcome.
With the development of intra-retinal hemorrhages and neovascularization of the retina in patients with ocular ischemic syndrome, the development of vitreous hemorrhage can follow. Accordingly, the risk of further deterioration of sight is quite high in patients who develop ocular ischemic syndrome unless the underlying ischemia can be modified by surgical intervention or the use of anticoagulation medication.
Vitreous hemorrhage is a common complication of neovascularization of the retina in many diseases. The development of vitreous hemorrhage in patients with ocular ischemic syndrome heralds the onset of neovascularization of the retina. This requires PAN retinal photocoagulation and possible surgical intervention to remove the vitreous hemorrhage. As long as the vitreous hemorrhage is persistent, it is impossible to perform PAN retinal photocoagulation. Accordingly, early vitrectomy may be warranted depending on the underlying carotid disease or small vessel disease which caused blood to leak into the eye.
In a variety of retinal diseases, the development of neovascular glaucoma signals the onset of the more severe stage of retinal ischemia. When this happens, unfortunately, the risk of permanent and irreversible blindness is quite high unless aggressive retina laser treatments or surgical interventions are undertaken to relieve the ischemia. There may be indications for surgical large vessel disease in patients who develop neovascular glaucoma, depending on the status of their carotid occlusive disease. Left untreated, neovascular glaucoma will lead to blindness and ultimately severe pain, with a high chance of eventual removal of the eye.
Treating ocular ischemic syndrome primarily involves stopping the abnormal choroidal neovascular membranes from proliferating over the retina and iris. This can be done using laser treatment, cryotherapy treatment, or intraocular anti-vegf (vascular endothelial growth factor) drugs.
In cases where there is no visibility of the retina due to vitreous hemorrhage, vitrectomy surgery must be done to clear the vitreous fluid before other treatments can be performed. Patients who have already developed neovascular glaucoma, however, require surgical techniques such as trabeculectomy or the insertion of a Baerveldt Pars Plana Valve to reduce intraocular pressure and prevent the onset of blindness through glaucoma.
In patients with ocular ischemic syndrome who develop neovascularization of their anterior or posterior segment, PAN retinal photocoagulation or laser treatments are indicated. Laser treatments destroy the ischemic retina, or retina cells which are not functioning adequately because of poor blood supply, and by so doing, reduce the neovascular stimulus that is promoting new blood vessel formation. Retina laser treatments require extensive PAN retinal photocoagulation to try to reduce the neovascular stimulus.
The use of retinal cryotherapy is generally for those patients who have aggressive neoovascularization for which surgical intervention with lasers is impossible. This is commonly seen in patients who have medial opacity, including cataract formation or vitreous hemorrhage, or in those patients who have extensive neovascularization of their anterior segment that has led to corneal edema limiting the view of their retina. Retinal cryo treatments, while not the preferred method of treatment, remains one of the potent weapons used in the management of this disease.
A trabeculectomy is a surgical technique that involves making an incision in the sclera to allow excess fluid in the anterior chamber of the eye to drain out of the eye and into the blood vessels and lymph vein. By surgically creating a pathway for the escape of excess fluid, a trabeculectomy can drastically decrease intraocular pressure, thus preventing glaucoma.
Glaucoma surgery is a surgical technique that is performed to reduce intraocular pressure in patients who are suffering from elevated intraocular pressure.
Glaucoma surgery is only used for those patients who have failed other therapeutic options, such as topical ocular medications or the use of glaucoma surgery lasers. Glaucoma surgery has numerous complications associated with it, much like any surgical procedure. Accordingly, it is deferred until more conservative medical management is no longer effective.
Glaucoma surgical techniques used on patients with ocular ischemic syndrome are modified, especially when there is neovascularization of the anterior segment. Should there be severe neovascularization of the anterior segment, glaucoma surgical techniques and vitrectomy surgeries are often used in combination (i.e. Baerveldt pars plana valve implantation).
However, in those patients who do not have extensive neovascularization of the anterior segment, limited glaucoma surgical procedures, such as trabeculectomies, may be performed to reduce the intraocular pressure. OCC Eyecare’s surgical team includes an advanced glaucoma surgical management group that is well-versed in techniques to reduce complications and to maximize benefits from surgical intervention. The vitreoretinal team at OCC Eyecare remains one of the first facilities in Canada to perform combined vitreoretinal, cataract, and glaucoma integrated surgeries.
BAERVELDT PARS PLANA VALVE INSERTION
In those patients who develop neovascular glaucoma, or who are at high risk for developing neovascular glaucoma with anterior segment neovascularization, surgical intervention is warranted. OCC’s research arm, The Canadian Centre for Eye Therapeutics (CCAET) , has pioneered a complex combination of surgical treatments that include cataract extraction with vitrectomy surgery and endolaser combined with the Baerveldt pars plana valve. The Baerveldt pars plana valve is a device that is surgically inserted to allow the drainage of excess fluid into a space called the bleb.This extraocular surgical technique reduces intraocular pressure in those patients who have excessively high intraocular pressure.