Ischemic vein occlusions with neovascularization require panretinal photocoagulation to prevent severe vision loss. Clinicians once used prophylactic laser treatment to prevent neovascularization. Recent research, however, indicates you should monitor for neovascularization, and only then refer for treatment. 24.
The best way to assess ischemia in retinal vein occlusions is fluorescein angiography. However, wait several weeks after the occlusion appears to allow the hemorrhages to clear. Visual acuity and pupil testing can lend insight. If there’s an APD and vision worse than 20/200, the occlusion is likely ischemic. 25.
Visual acuity reduction of 20/200 or worse may be due to macular edema and hemorrhage. Otherwise, the most likely cause is macular infarction and destruction of the perifoveal capillary network. Angiography will show an enlarged foveal avascular zone and hypofluorescence beyond the macular region. Visual loss in these cases is irreversible.
Patients with retinal vein occlusions have a higher incidence of systemic disease, particularly vascular conditions. Refer to a primary care physician for evaluation. 26–28.
Retinal Artery Occlusion
Retinal artery occlusions manifest in two forms: central (CRAO) and branch (BRAO). In both, an embolism dislodges from an ulcerated, thrombosed carotid artery or from the heart. The embolus may then migrate to the eye and lodge in either the central or a branch retinal artery. Profound ischemia results. 29 Up to 10 percent of CRAO cases occur because inflammatory cells in giant cell arteritis infiltrate the vessel wall. Two–thirds of these cases progress to bilateral involvement within hours to days. 30, 31 Patients over 60 require a sed rate.
CRAO causes a sudden, painless loss of vision, typically finger counting or barely light perception. You’ll also note an APD. The inner retina will appear edematous and milky–white, as the underlying choroidal blood flow is obscured. You’ll see a “Cherry–red spot” in the macula as some choroidal blood does show through. The retinal edema and opaque appearance disappear over time, leaving a normal looking retina, attenuated retinal arterioles and an atrophic and pale optic nerve. 15, 16.
In BRAO you may see an embolus on ophthalmoscopy. Patients remain asymptomatic if the macula is not affected. Usually, though, they experience a severe reduction of visual acuity and/or field.
There’s little we can do to improve visual outcomes in CRAO or BRAO. In CRAO some doctors have had success dislodging the embolus by anterior chamber paracentisis, compressing the globe or increasing blood CO2 levels–thereby restoring blood flow and function to the retina. Yet, research shows that these measures have no greater effect than no treatment at all.
Retinal artery occlusion carries profound systemic implications, most commonly arteriosclerosis. Others include myocardial infarction, hypertension, carotid artery disease, diabetes, cardiac valve abnormalities and giant cell arteritis. 32, 33 Refer these patients to a cardiologist.